The rôle of the environment on galaxy évolution is still not fully understood.

In order to quantify and set limits on the rôle of nurture one must identify and study a sample of isolated galaxies. The AMIGA project " Analysis of the Interstellar Medium of Isolated GAlaxies" is doing a multi-wavelength study of a large sample of isolated galaxies in order to examine their inter stellar medium and star formation activity.

We processed 950 galaxies from the Catalogue of Isolated Galaxies (Karachentseva 1973) and evaluated their isolation using an automated star-galaxy classifi cation procedure (down to Mb ~17.5) on large digitised POSS-I fields surrounding each isolated galaxy. We defined, compared and discussed various criteria to quantify the degree of isolation for these galaxies: e.g. Karachentseva's revised criterion, local surface density computations, estimation of the external tidal force affecting each isolated galaxy. We find galaxies violating Karachentseva's original criterion, and we define various subsamples of galaxies according to their degree of isolation. Additionally, we sought for the redshifts of the primary and companion galaxies to access the radial di mension and hâve an accurate three dimensional picture of the surroundings. grueso de la materia visible en optico. Interpretamos las diferentes barras y morfologfas Ha observadas en términos de evolucion secular experimentada por las galaxias aisladas. La frecuencia observada de patrones particulares impone condiciones sobre los tiempos de vida de las barras, y las escalas de tiempo asociada a su destrucion. Usando simulaciones numéricas, cuando intentamos ajustar las distribuciones de morfologfa Ha obtenemos restricciones en la ley de formacion estelar, la cual probablemente difiere de una simple ley de Schmidt. tique. Nous interprétons les diverses barres et morphologies Ha observées en termes d'évolution séculaire subie par les galaxies isolées. La fréquence observée des modèles morphologiques particuliers apporte des contraintes sur la durée de vie des barres, et les temps de destruction associés. En utilisant des simulations numériques, l'essai d'adapter les distributions Ha apporte des contraintes sur la loi de formation d'étoiles, qui est susceptible de différer d'une simple loi de Schmidt. The kth local density and the tidal forces estimations are in Logarithmic scale (Logio). This note indicates that the criterion only included the similar size companions (factor of 4 with respect to the CIG diameter). CIG Kara. Pairs kthdensity Proj. dens. (0.5 Mpc) Proj. dens.! (0.5 Mpc) T. F.

Finally, we applied our pipeline to triplets, compact groups and clusters and interpret the isolated galaxy population in light of these control samples.

The star formation is known to be affected by the local environment of the galaxies, but the star formation rate also highly dépends on the intrinsic interstellar medium features. Disentangling these two effects is still a challenging subject.

To address this issue, we observed and gathered photometric data (Ha narrow-& r Gunn broad-band filters) for 200 spiral galaxies from the Catalogue of Isolated Galaxies which are, by définition, in low-density régions. We subsequently studied the Ha morphological aspect of the 45 biggest and less inclined galaxies. Using Fast Fourier Transform techniques, we focus on the modes of the spiral arms, quantify the strength of the bars, and we give the torques between the newly formed stars and the bulk of the optical matter. We interpret the various bar and Ha morpholo gies observed in terms of the secular évolution experienced by galaxies in isolation. The observed frequency of particular patterns bring constraints 1 on the lifetime of bars, and their fading time-scales. Through numerical simulations, trying to fit the Ho; distributions yields constraints on the star formation law, which is likely to differ from a simple Schmidt law.

Resumen

El papel del entorno en la evoluciôn galâctica aün no se comprende totalmente. Para cuantificar y poner limites al papel del proceso de évolution se debe identificar y estudiar una muestra de galaxias aisladas. El proyecto AMIGA "Anâlisis del Medio Interestelar de Galaxias Aisladas" esta 11evando a cabo un estudio multifrecuencia de una gran muestra de galaxias aisladas con el fin de estudiar su medio interestelar y la actividad de formaciôn estelar.

Hemos procesado los datos de 950 galaxias del Catâlogo de Galaxias

Aisladas [START_REF] Karachentseva | Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Observatorii[END_REF]) y evaluado su criterio de aislamiento usando un procedimiento automâtico de clasificaciôn entre estrellas y galaxias (hasta Mb ~17.5) en campos digitalizados del POSS-I alrededor de cada galaxia aislada. Definimos, comparamos y discutimos varios criterios para cuantificar el grado de aislamiento de estas galaxias: criterio revisado de Karachentseva, câlculo de la densidad superficial local y estimation de la fuerza de marea externa que afecta a cada galaxia. Encontramos galaxias que violan el criterio original de Karachentseva y definimos varias submuestras segün su grado de aislamiento. Adicionalmente buscamos el corrimiento al rojo de la galaxia primaria y sus vecinas para accéder a la dimension ra dial y obtener una vision tridimensional de los alrededores. Finalmente aplicamos nuestro procedimiento automâtico a tripletes, grupos compactos y cümulos de galaxias e interpretamos la poblaciôn de galaxias aisladas a la luz de estas muestras de control.

Es conocido que la formaciôn estelar se ve afectada por el entorno de las galaxias pero la tasa de formaciôn estelar también dépende de las propiedades intrmsecas del medio interestelar. Separar estos dos efectos aün es una tarea dificultosa. Para llevarla a cabo obtuvimos datos fotométricos (filtro Ha estrecho y r Gunn ancho) de 200 galaxias del Catâlogo de Galaxias Aisladas que, por definiciôn, se encuentran en regiones de baja densidad de galax ias. Estudiamos la morfologia en Ha de las 45 galaxias mayores y menos inclinadas. Usando técnicas de TYansformada Râpida de Fourier nos cen trâmes en los modos de los brazos espirales, cuantificando la fuerza de éstos.

Obtuvimos los momentos angulares entre las estrellas recién formadas y el

Résumé

Le rôle de l'environnement sur l'évolution des galaxies n'est pas encore entièrement connu. Pour quantifier et mettre des limites aux rôles joués par les processus externes, on doit identifier un échantillon de galaxies isolées.

Le projet AMIGA "Analyse du Milieu interstellaire des galaxies isolées" fait une étude multi-longueur d'ondes d'un grand échantillon de galaxies isolées pour examiner leur milieu interstellaire et l'activité de formation d'étoiles.

Nous avons étudié 950 galaxies en provenance du Catalogue de Galax ies isolées [START_REF] Karachentseva | Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Observatorii[END_REF]) et évalué leur isolation au moyen d'une procédure de classification automatique de séparation étoile/galaxie (jusqu'à Mb = 17.5) sur de larges champs digitalisés POSS-I autour de chaque galaxie isolée. Nous avons défini, comparé et discuté différents critères pour quantifier le degré d'isolation de ces galaxies, comme la révision du critère de Karachentseva, la densité de surface locale, l'estimation des forces de marées externes affectant chaque galaxie isolée. Nous trouvons des galax ies n'obéissant pas au critère de base de Karachentseva et nous définissons différents sous-échantillons de galaxies selon leurs degrés d'isolation. De plus nous avons cherché les redshifts des galaxies centrales ainsi que ceux de leurs compagnons pour avoir accès à la dimension radiale et ainsi une im age en trois dimensions de l'environnement. Enfin, nous avons appliqué nos procédures aux triplets, groupes compacts et amas de galaxies et interprété la population de galaxies isolées à la lumière de ces échantillons de contrôle.

La formation d'étoiles est connue pour être affectée par l'environnement local des galaxies mais le taux de formation d'étoiles dépend aussi grande ment des caractéristiques intrinsèques du milieu interstellaire. Séparer ces deux effets reste un problème difficile. Pour solutionner, nous avons observé et compilé des données photométriques pour 200 galaxies spirales issues du Catalogue des Galaxies Isolées qui sont par définition dans des régions de faible densité. Ensuite, nous avons étudié l'aspect de la morphologie en Ho; des 45 galaxies les plus grandes et les moins inclinées. En utilisant les techniques de Transformation de Fourier Rapide, nous nous focalisons sur les modes des bras spiraux. Nous quantifions la force des barres et nous donnons les couples entre les étoiles nouvellement formées et la matière op-

Introduction

The rôle of the environment on galaxy évolution is still not fully understood.

In order to quantify and set limits on the rôle of nurture one must identify and study an isolated sample of galaxies. The AMIGA project "Analysis of the Interstellar Medium of Isolated GAlaxies" is doing a multi-wavelength study of a large sample of isolated galaxies in order to examine their inter stellar medium and star formation activity.

The thesis presented here is focused on two aspects of this project: in the first part we hâve quantified the degree of isolation of our sample, and then we hâve concentrated on an Ha study of a selected subsample of 45 spiral galaxies.

We processed 950 galaxies from the Catalogue of Isolated Galaxies [START_REF] Karachentseva | Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Observatorii[END_REF]) and evaluate their isolation using an automated star-galaxy classifi cation procedure (down to Mb ~17.5) on large digitised POSS-I fields surrounding each isolated galaxy. We define, compare and discuss various criteria to quantify the degree of isolation for these galaxies: e.g. Karachentseva's revised criterion, local surface density computations, estimation of the external tidal force affecting each isolated galaxy. Additionally, we seek for the redshifts of the primary and companion galaxies to access the radial di mension and hâve a three dimensional picture of the surroundings. Finally, we apply our pipeline to triplets, compact groups and clusters which serve as control samples.

The star formation is known to be affected by the local environment of the galaxies, but the star formation rate also highly dépends on the intrinsic interstellar medium features. Disentangling these two effects is still a challenging subject. To address this issue, we observe and gather photometric data (Ha narrow-& r Gunn broad-band filters) for more than 200 spiral galaxies from the Catalogue of Isolated Galaxies which are, by définition, in low-density régions. So we can subsequently study the Ha morphological aspect of the biggest and less inclined galaxies (the fourth part of the Ha sample). Using Fast Fourier Transform techniques, we focussed on the modes of the spiral arms and also on the strength of the bars, looking at the torques between the newly formed stars and the bulk of the optical matter.

More specifically, the dissertation is articulated as follow:

The first chapter [1] présents an overview on the galaxy topic: an historical introduction on the discovery followed by the main features of galaxies, then the distribution of matter in the Uni verse is summarised and how this latter distribution could possibly affect the formation and évolution of galax ies.

The second chapter [2] introduces the AMIGA project, framework of the présent thesis. First, the refmements done on the original catalogue of isolated galaxies are presented. Second, the ISM multi-wavelength study is

evoked.

An exhaustive study [3] of the isolation présents the method used to identify the galaxies around the primary CIG ones, the révision of the Karachentseva's criterion and the new statistical isolation criteria applied to the CIGs:

local density and tidal force estimation.

Comparison samples, including triplets, compact groups and clusters of galaxies are used to see how the CIG sample is situated respecting to these higher density samples [4].

Finally, the next chapter [5] uses the redshift information available in the literature, to discuss the validity of our statistical study.

The sixth chapter [6] opens the Ha analysis. It présents the issue of the SFR dependency on environment and our sample of isolated spiral galaxies, which aimed to be taken as a reference to interpret SFR in denser environments.

We observed and gathered Ha data [7] for more than 200 CIG galaxies.

A typical réduction procedure is shown for one galaxy.

The last Ha chapter [8] focuses on the 45 biggest and less inclined galax ies observed for which we developed a study to estimate the torques between the newly formed stars and the bulk of the optical matter. At the end of the XIXth century, the extension of the Universe was generally assimilated to the one of our galaxy, the Milky Way, for which the astronomers could calculate the shape and the dimensions. At the same time, some of them were wondering about the nature of the nebulae visible in the sky. Already, in 1781, some 100 of these nebulae had been gathered in a catalogue by Messier. In particular, some observations had suggested that these nebulae could be other gathering of stars, similar to our galaxy, "island-universes" as imagined by the philosopher Emmanuel Kant at the same epoch.

The appendices gather various tables

The debate began accentuated about the nature and distance of these objects. From 1898, Keeler photographied some of the already catalogued nebulae and discovered many thousands of new ones. He also made the surprising discovery that more than half of ail the nebulae were spiral in form. Since 1911, at the Lowell observatory, the astronomer Slipher conducted spectrographic investigations of spiral nebulae and showed that they were animated by high velocities (Slipher 1911a(Slipher ,b, 1917)); these observations strengthened the theory that spiral nebulae were stellar Systems (like the Milky Way itself) seen at great distances. Edwin Hubble confirmed this view in the twenties, showing that the brightest of these spiral nebulae, Andromeda, was very outside our own galaxy. Hubble (1929) also found a linear relation between distance and apparent radial velocity among Extra-Galactic Nebulae (see Fig. 1.1). Hence, astronomers understood that the Universe was vaster than the Milky Way, and was inhabited by unnumbered other galaxies.

Actually, a galaxy is a gravitationally-bound collection of stars, with dust and gas. A typical spiral galaxy such as the Milky Way lias a mass of about 1011 solar masses. Ail the stars in our galaxy are not identical. Some are old, not very massive and not very bright. Mainly cold and red, they are distributed in our galaxy in a halo more or less spherical. On the other hand, young and blue stars are distributed within a thin disk where they draw spiral arms. The diameter of the disk is 30 kpc with a width of the order of 1 kpc.

The interstellar gas only represents a weak fraction of the total mass of the galaxies, the amount is about 10% in spiral galaxies. Nevertheless, it plays a major rôle in the formation and évolution of galaxies: the stars form from this gas. This gas is essentially constituted by Hydrogen, in the atomic, molecular or ionised state, mixed with Hélium (25% in mass) and traces of other éléments.

In the galaxies, the loci of stars and gas draw characteristic features: the galaxies were classified for the first time in various types following criteria

1.2

The morphologies of galaxies Hubble (193G), in the Realm of the Nebulae, classifies galaxies following their optical morphology (see Fig. 1.2). There are 3 fundamental categories: spirals amount ~70% of galaxies, ellipticals about 10% and lenticulars represent ~20%, although these proportions can widely be sensitive to the environment.

Spiral galaxies are essentially made up by two major components: a fiat, large disk gathering billions of bright stars, where one can sometimes see spiral arms (and often other structures as bars or rings) and in the centre, an ellipsoidal bulge. The disk also contains a lot of gas from which new stars are forming, while the bulge concentrâtes an older stellar population without interstellar matter. Spirals are rotating around their disk axis: stars within the disk are orbiting the galactic centre in nearly circular orbits.

Elliptical galaxies are named after their appearance in projection on the sky, but hâve a three-dimensional structure (i.e. an ellipsoid, with three axes of symmetry). They contain very little dust and gas and, as a conséquence, only old stars dispatching up into the ellipsoid. Their dynamics also differ from the spirals: they do not rotate as a whole, the stars hâve velocities randomly distributed. Intermediate types are classified by the degrees of ellipticity observed in the galaxy. Along the Hubble sequence, the link between these categories is still unclear but there are general trends within the Hubble sequence, from Sd to E: increasing bulge-to-disk luminosity ratio, increasing stellar âge, decreasing fractional gas content, decreasing ongoing star formation. For a review describing the dependency of the fundamental properties of the galaxies along the Hubble sequence, please see Roberts Sz Haynes (1994). Did the E hâve a SF in an early phase of their évolution? Are spirals and ellipticals generated in different conditions? Or do the latter resuit from the évolution of the former? At least in some cases, the merging of two spirals lead to the CHAPTER 1. OVERVIEW formation of a giant elliptical. Is it a general feature?

1.3

The distribution of matter in the Universe

The Andromeda galaxy was the first neighbour of the Milky Way discovered.

Our neighbourhood gathers, under the name of Local Group, a small group of galaxies: our galaxy (the Milky Way), Andromeda and about 15 smaller galaxies.

Nowadays, large surveys reveal that galaxies are not randomly distributed but gathered in groups and clusters. The Local Group is the nearest exam ple. Beyond, the Virgo cluster, located at about 10 Mpc, is richer, although quite poor compared to the average of the clusters. Lots of clusters exist beyond. The nearest ones hâve been catalogued by Abell (1958).

Matter, in the nearest tens of megaparsecs, draws a larger structure, the Local Supercluster. Also known as the Virgo supercluster, it contains eleven clusters along with groups and isolated galaxies. Its shape is fiat, about 1 Mpc thick. The distribution of galaxies or clusters is not regular: at large scales, superclusters are the rule. More or less lengthened and flattened, as ours, with a typical scale of about 20 megaparsecs, they seemed linked by immense bridges of matter.

If clusters and superclusters appear as condensations of matter at very large scales, reciprocally, huge zones deprived of matter also exist. An im mense void has been detected in the Boôtes constellation, at about 150 Mpc from us, with a size of about 30 Mpc (Kirshner et al. 1981). Such voids seem common, at these or smaller scales. Hoyle & Vogeley (2004) presented an analysis of voids in the 2dF Galaxy Redshift Survey: they detected 289 voids with radii larger than 10 h~l Mpc1. These voids filled 40% of the total volume of the survey and contain 5% of ail galaxies in the sample (see Fig. 1.4); these results are consistent with similar studies done on voids in the SDSS (Rojas et al. 2004(Rojas et al. , 2005)).

Influence of the environment

Décades ago, a debate about the influence of the environment on the forma tion and évolution of galaxies began: Oemler (1974), in a pioneering work, studied the properties of clusters of galaxies, identifying three main classes. The first class is spiral-rich, the second one consists of spiral-poor clusters dominated by S0 galaxies,

and clusters prevailed by central supergiant galaxies (cD) with a complété absence of spirals in their cores constitute the third class. The -rich, spiral- A few years later, Dressler (1980) found a strong relationship between the density and the morphological type of ~6000 galaxies distributed among 55 rich clusters in the Local Universe (z<0.06). Figure 1.5 shows the fraction of elliptical, S0 and spiral+irregular galaxies as a function of the log of the projected density, in galaxies Mpc-2. On the very left-hand, the location of the field galaxies (combination of isolated galaxies and loose groups) is

*• V T A-» .V. » .'•'jT V* * J. A •-. . yr -I . •• »..»• jfN v > •*' 1hîî?v- . VA .• . 'A/ V- 'X'VîîV-Hf v •>«;•/ -^VA-V5 v** * "a^: A -A J V à*» J* ' 1 ^.
shown. Dressler (1980) also find a trend of increasing luminosity of the spheroidal component with increasing local density. Dressler et al. (1997) confirmed the validity of the morphology-density relation at intermediate redshifts (z~0.5), though with a lower fraction of lenticular galaxies, suggesting that a fraction of spiral galaxies could hâve been converted into S0 at a recent epoch. Postman Sz Geller (1984) extended the morphology-density relation to groups. Rojas et al. (2004) identified void galaxies in the SDSS and found that they are bluer than wall galaxies of the saine intrinsic brightness: they demonstrated that the différence in colour could not be explained by the morphology-density relation.

Hence, the situation is still not fully understood, especially for the galax ies in low density environments. In this thesis, we will identify a well defined sample of strongly isolated galaxies (based on the Catalogue of isolated galaxies). In a second part, we will characterise the Ha: properties of some of the most isolated galaxies, focussing on the different cycles experienced by the bars of these galaxies.

Introduction

The evolutionary history of galaxies is thought to be strongly conditioned by the environment. Evidence has emerged for interaction-induced émission enhancements (e.g. Sulentic 1976;Larson & Tinsley 1978;Joseph & Wright 1985;Bushouse 1987;Xu & Sulentic 1991) and interaction-driven secular evolutionary effects (e.g. Moore et al. 1996;Verdes-Montenegro et al. 2001b).

This includes properties like stellar and gaseous content, kinematics, mass distribution or star formation activity. The observational evidence is sometimes weak or unclear.

For instance, there is a large incertitude concerning the efficacy of in teractions in the triggering of star formation and, still, no law is really well established, which could link the local density of gas, or its velocity dis persion, to the star formation rate (SFR). Globally in a given galaxy, one of the best relation seems to be the Schmidt law (Kennicutt 1998), linking the available quantity of gas (essentially the HI reserve) to the rate of stars newly formed, but lots of exceptions are observed to this relation, showing that others parameters hâve to be taken into account.

Part of the difficulty lies in the confusion between the rôles of one-on-one interactions vs. more general corrélations with average galaxy environmental density. Many of the uncertainties, both of the amplitude of enhancements and the connection between environment and parameters, reflect a lack of suitable control samples to which interacting sample properties can be compared. Ideally this would involve samples of isolated galaxies.

The most common reference or control samples found in the literature can be described as either "field" or "normal". The former can refer to the most isolated galaxies while the latter refer to galaxies which show none of the generally accepted signs of interaction-induced activity. A field sample (e.g. Kennicutt & Kent 1983) might include any galaxy not belonging to a cluster, so galaxies in pairs, triplets and loose/compact groups would not necessarily be excluded. Normal galaxy samples would be defined in terms of spécifie parameters such as HI content (Boselli et al. 2001) or a specified level of nuclear activity. Study of a selected quantity as a function of the environment is then one way to quantify the level of environmentally induced activity.

The alternative approach involves sample sélection using an isolation criterion. Studies of isolated galaxies usually involve from 10s to 100-200 objects (e.g. Huchra & Tlman 1977;Vettolani et al. 1986;Marquez & Moles 1999;Marquez et al. 2000;Colbert et al. 2001;Pisano et al. 2002;Varela et al 2004). The largest samples of isolated galaxies in the literature involve, in most cases, monochromatic observations of subsamples from the Cata logue of Isolated Galaxies CIG: [START_REF] Karachentseva | Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Observatorii[END_REF]) (Adams et al. 1980;Haynes & Giovanelli 1980;Sulentic 1989;Young et al. 1986;Xu &;Sulentic 1991;Perea et al. 1997;Toledo et al. 1999;Sauty et al. 2003).

Previous work suggests that small samples of isolated galaxies hâve limited statistical value. Ideally we seek a sample large enough to isolate a significant population of the most isolated galaxies.

This motivated us to use the CIG as the basis for a large, well-defined and statistically significant multiwavelength database that can serve as a comparison template for the study of galaxies in denser environments. CIG galaxies were selected to be free of equal mass perturbers but hierarchical pairs and groups could not be removed without reducing the sample to negligible size. A large sample like CIG can be refined and quantified in terms of degrees of isolation. It can then be correlated with multiwavelength interstellar medium (ISM) properties. The resuit can be a sample large enough to characterize the low density tail of the two-point corrélation function.

This constitutes the AMIGA Analysis of the Interstellar Medium of Isolated GAlaxies -AMIGA- (Verdes-Monténégro et al. 2001â, 2002[START_REF] Combes | IAU Symposium[END_REF], 2005). In particular, we are building a multi-wavelength database to com pare and discuss the properties of different phases of the ISM (cf. sec tion 2.4). Our catalogue of galaxies is based on the Catalogue of Isolated Galaxies [START_REF] Karachentseva | Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Observatorii[END_REF]) and the refmements we hâve done so far are presented in section 2.2.

2.2

The Catalogue of Isolated Galaxies [START_REF] Karachentseva | Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Observatorii[END_REF] compiled the Catalogue of Isolated Galaxies (CIG, hereafter) which includes 1051 objects. Ail of the CIG objects are found in the Catalogue of Galaxies and Clusters of Galaxies (Zwicky et al. 19G8) with mpg < 15.7 and <5 > -3°, ~3% of the CGCG).

The catalogue, built in 1973, could now be improved due to the better material available, including the digitized sky surveys (POSS-I and POSS-II). The sample is large with 1050 galaxies (one object, CIG 0781, was a globular cluster). This means that after refinement we will still be left with a statistically useful sample of several hundred galaxies. We refine the pioneering CIG on several aspects, the better accuracy on the positions is presented in the subsection 2.2.1, the collection of recession velocities in subsection 2.2.2 and the morphological identification in subsection 2.2.3.

The révision of the isolation will be detailed in Chapters Leon &; Verdes-Montenegro (2003) revised the positions for ail the CIG galaxies comparing CIG positions in the SIMBAD database and the Updated Zwicky Catalogue (UZC, Falco et al. 1999). They found différences of up to several tens of arcsec for some galaxies, large enough to make accurate telescope pointings or cross corrélations with on-line databases difîicult.

This motivated them to systematically revise ail of the CIG positions using SExtractor on the images of the digitized sky surveys. The différences found between old and new positions reached 38", with a mean différence of about 2.5" (see Fig. 2.1). They provided new positions with uncertainty of the order of 1" using SExtractor (Bertin & Arnouts 1996) on DSS images, checking visually the results (see Fig. 2.2).

Redshifts and distances

This part is inainly carried out. by

Lourdes Verdes-Montenegro L José Sabater Montes on behalf of the AMIGA project.

Publications to date report distances for 476 galaxies (Xu h Sulentic 1991). We retrieved distances for 574 additional galaxies, after compilation from 41 references, as well as from our own observations (Verdes-Montenegro et al.

2005

). Figure 2.3 shows the distribution of the recession velocities of 988 CIG galaxies (there are still missing the redshifts for 62 CIGs). The mean recession velocity is 6624 km s-1 (z~0.022): the catalogue samples the Local Universe.

The CIG redshift distribution re-enforces the evidence for a bimodal structure seen earlier in smaller samples. The peaks at redshift near 1500 and 6000 km s-1 correspond respectively to galaxies in the local superclus ter and those in more distant large-scale components (particularly Perseus-Pisces). The two peaks in the redshift distribution are superimposed on 50%

or more of the sample that is distributed in a much more homogeneous way.

The CIG probably represents the most homogeneous local field example that has ever been compiled.

Redshift distances were derived for ail galaxies with V > 1000 km s-1 and are expressed as D = V^k/Ho where V^k is the velocity after the 3K correction and assuming Ho = 75 km s-1 Mpc-1. 3K corrected velocities are computed in the reference frame defined by the 3K cosmological background radiation. They are corrected for local velocity inhomogeneities due to the Local Group and Virgo Cluster. The velocity conversion is made with the standard correction as defined in (Courteau & van den Bergh 1999). The velocity and apex directions of the Sun relative to the comoving frame hâve been derived from an analysis of the FIRAS data (Fixsen et al. 1996) with Vapex = 371 km s-1 and (lapexi Kpex) - (264.14, 48.26 independent distance estimâtes and references are provided for galaxies with V < 1000 km s-1.

Morphologies

This part is mainly carried out, by Jack Sulentic & Gilles Bergond on behalf of the AMIGA project.

Morphological classification available for AMIGA galaxies from the literature are not uniform, and even contradictory for the most part. So we downloaded POSS-II images for 80% of the sample for which spatial résolu tion was sufficient to achieve a new classification. We obtained CCD images for the remaining 20% with the 1.5m telescope at the Sierra Nevada Obser-

vatory. An analysis shows that many of the galaxies classified as early-type display a spiral structure with a prédominance of Sc galaxies (Sulentic et al. 2005). This most isolated sample of galaxies in the local Universe is dominated by two populations: 1) 82% spirals (Sa-Sd) with the bulk being luminous Systems with small bulges (63% between types Sb-Sc) and 2) a significant population of early-type E-S0 galaxies (14%). The derived types will be used in order to optically characterise the CIG sample (see sect. 2.3).

|

Figure 2.4: Left: OSN rGunn 12 min., Right: POSS II red.

Isolation

The révision of the isolation for 950 CIGs is presented in chapters 3, 4 & 5.

Optical characterisation of the sample

This part is mainly carried out by

Lourdes Verdes-Montenegro on behalf of the AMIGA project.

The optical émission (L#, in the blue band) traces the stellar content of a galaxy, hence we first performed an optical characterization of our sample. Verdes-Monténégro et al. (2005) inferred Lb for each galaxy with known re cession velocity, compiling optical magnitudes while applying required cor rections. This magnitude was supposed to be used only as a parameter in the multi-wavelength corrélations, but we found of interest to dérivé the optical luminosity function of the sample. Using the V/Vm Schmidt test, [START_REF] Verdes-Montenegro | IAU Sym posium[END_REF] find the CIG to be 80-95% complété down to mzw = 15.0 (see also Xu & Sulentic 1991). Its 2D distribution is reasonably homogeneous; in the redshift distribution, we again find evidence that 50% or more of the sample shows a quasi-homogeneous redshift distribution.

The CIG samples a large enough volume of space to allow us to sam ple the majority of the optical luminosity function (OLF). Galaxies with a recession velocity less than 1,000 km s-1 include the most isolated nearby dwarfs. Significant sampling at and beyond 10,000 km s-1 allows us to also sample the extreme bright end of the OLF. We hâve calculated the OLF which we compare with other recent estimâtes of the OLF for a variety of environments. Our dérivation of the CIG OLF is consistent with other studies of the OLF for lower density environments, re-enforcing the idea that CIG OLF is représentative of the lower density parts of the galaxy environment. This comparison via the Schechter parameter formalization INTRODUCTION TO THE AMIGA PROJECT

shows that: 1) M* increases with galaxy surface density on the sky and 2) a

shows a weaker tendency to do the same. Care must be taken with the local supercluster contribution to the CIG because it samples the OLF to much lower luminosities than the rest of the sample. In the Schechter formalism, M* represents the absolute magnitude of the galaxies which suppose a turnoff in the distribution and a is the slope of the faint-end distribution.

ISM multi-wavelength study

There are numerous works that study the effect of interactions on the ISM.

Most of them hâve not used strictly isolated galaxies as reference samples, and when it happened they were concentrated on few (usually no more than 2) components of the ISM. In the following sub-sections we sum up their main results.

Ha

A study of the Ha émission of a subsample of CIG galaxies is presented in Chapters 6, 7 & 8.

Far infrared

This part is mainly carried out by Ute Lisenfeld k Lourdes Verdes-Montenegro on behalf of the AMIGA project.

U FIR is the thermal émission re-radiated by dust grains, previously warmed up by UV radiation from young stars. Most of the studies about FIR émission of interacting galaxies are skewed towards bright galaxies, although it is unanimously recognised that they présent an higher infrared émission (Young & Scoville 1991;Braine & Combes 1993;Young et al. 1996;Solomon et al. 1997). Xu & Sulentic (1991) studied 528 pairs from the Catalogue of isolated pairs of galaxies [START_REF] Karachentsev | Soobshcheniya Spetsial'noj Astrofizicheskoj Observatorii[END_REF][START_REF] Karachentsev | [END_REF] covering a large luminosity range, and 295 galaxies from the CIG as a reference sample, and find out that late type galaxies in pairs show a higher infrared émission compared with the isolated galaxies and that the pairs made with two spirals hâve a higher Lfir/Lb ratio. Nevertheless, this study carries the problem, as

shown by the authors, that the pairs sample is deeper than the isolated one, which clearly shows that the excess could be due to the brightest galaxies. Believed to be principally synchrotron radiation produced by relativistically accelerated électrons by supernovae explosions (Lequeux 1971), the radio-continuum émission is directly proportional to the supernovae forma tion rate (Xu et al. 1994). This idea is reinforced by the narrow corrélation between radio luminosity and FIR for spiral galaxies, indicating that both are produced by the same stars (Lisenfeld et al. 1996a). This relation is quite robust and also valid for galaxies spanning a wide range in luminosity, including starburst galaxies (Lisenfeld et al. 1996b).

The effect of the environment on the radio-FIR corrélation is still not fully understood. Some studies indicate that there exist a small excess of radio émission for galaxies in clusters (Menou 1991;Niklas et al. 1995) although other works suggest that there is no due that the interaction influ ence the corrélation (Niklas 1997). However, the corrélation between nuclear activity and environment is not fully clarified. Dultzin-Hacyan et al. (1999) INTRODUCTION TO THE AMIGA PROJECT found that the interactions with a companion would produce the central activity, but the environment is likely to play a more complex rôle for the production of the central activity (Schmitt 2001). Thus, the study of radio galaxies with the IRAM-30m [START_REF] Leon | QSO Hosts and Their Environments[END_REF] would suggest that minor mergers are more important to feed the central black hole.

Atomic gas

Th is part is mainly carricd ont by Daniel Espada on behalf of the AMIGA project.

The atomic gas is a light component of the ISM dominating the gas in late type galaxies, and extending to the double of the optical disk (Cayatte et al. 1994). It makes the HI a very sensible tracer for the interaction. Haynes & Giovanelli (1984) characterise the HI content of a sample of 324 CIG galaxies as a function of the morphological type and the luminosity or the optical diameter, sample which will serve as a reference for further studies of the HI content in different environments. Spiral galaxies in clusters présent a deficiency in HI, especially the ones very near the centre of the cluster,

where the hot intra-cluster medium emitting X rays dominâtes [START_REF] Van Gorkom | The Minnesota Lectures on Extragalactie Neutral Hydrogen[END_REF]. As well, compact groups show a level of deficiency as high as 90%, although lots of them are within the error bars of the relations found by (Haynes & Giovanelli 1984) reaching 0.5 mag (Verdes-Montenegro et al. 2001b).

On the other hand, Zasov & Sulentic (1994) studied 50 E+S pairs and the comparison with the CIG sample does not show any déviation from the normality in the spiral of the pairs, though an increase of the star formation.

The shape of the HI profiles is a powerful tool to characterise the HI distribution in a given galaxy, and the level of perturbation (Espada et al. 2005). It was used by Sulentic & Arp (1983) as a diagnostic in a sample of pair galaxies, groups, also CIG, or by Richter & Sancisi (1994) connecting the prédominance of a spiral arm (lopsidedness) with asymmetries in the profile of the 21cm line.

Molecular gas

This part is mainly carried ont by The lines emitted by simple molécules, excited by collisions and going back to their fundamental State correspond to weak energy transitions. The CO molécule was first observed in 1970. It is quite abundant and its prés ence is linked to that of H2: collisions between H2 and CO molécules excite the latter to an excited State which corresponds to 2.6 mm. The H2 molécule is more abundant but hard to observe in radio spectroscopy: the spectrum of symmetric molécules is far poorer than the one of asymmetric molécules.

It was claimed that interactions could enhance the molecular content of the galaxies, but this is skewed towards the brightest galaxies in FIR (Braiiie & Combes 1993;[START_REF] Combes | [END_REF], and on the ratio M(H-2)/Lb which augment with Lg so gets higher values for the brightest galaxies.

When this effect is removed (Perea et al. 1997;Verdes-Monténégro et al. 1998;Leon et al. 1998), the molecular gas content of the samples seems indistinguishable from the isolated one.

Database

This part is mainly carried out by Emilio Garcia on behalf of the AMIGA project.

Ail the refinements done by the AMIGA project on the CIG are available at this web site: www.amiga.iaa.es/AMIGA.html/. As well, the ISM multiwavelength data will become public by means of the web database (based on MySQL) via a simple and efficient interface.

To access the AMIGA catalogue, two approaches are possible: using a web browser or directly from a terminal using scripts. Queries could be made entering the number of the CIG or any other identifiant (CGCG, NGC, UGC, ...) or entering parameters. The parameters could be applied separately (coordinates, velocities, morphologies, ...) or tangled one with another. The tool "Conesearch" allows to choose an ascension, a déclination and a search radius. The user has also the possibility to specify the output options. Finally, XML files containing compatible VO tables will also be produced.

Part I

Isolation

Chapter 3

The isolation study It is now generally recognised that the environment experienced by the galaxies during their whole lifetime plays a rôle perhaps as important as the initial conditions of their formation: the evolutionary history of galax ies is thought to be strongly conditioned by the environment. But the rôle and the influence of the environment on galaxy évolution are still not fully understood. In order to quantify and set limits on the rôle of nurture one must identify and study a sample of isolated galaxies. Systematic work on isolated galaxies is needed to separate the influence of the environment and of the initial conditions at formation. The purpose of the coming Chapters is to provide a sample of isolated galaxies, with a well characterised isolation définition.

A debate on the nature of the spatial distribution of galaxies took place in the 1970s: using the covariance function of the distribution of galaxies, Peebles (1974a,b) found no evidence of an initially homogeneous component of the galaxy population and, on the contrary, indorsed the view of hierarchical sériés of densities. However, studying galaxies brighter than 14</i magnitude, Turner & Gott (1975) found two distinct populations, one strongly clustered and a population of "single" galaxies (32%) distributed homogeneously on scales < 20 Mpc. But Soneira & Peebles (1977) showed that the previous sample did not constitute a true field population because of artifacts and if such a population exists, it amounted to substantially less than 18% in a catalogue selected by apparent magnitude. Huchra & Thuan (1977) revised the Turner & Gott sample down to a fainter magnitude (15.7 mag.) and found that isolated galaxies could only represent 3.6% of ail the galaxies. As well, Vettolani et al. (1986) emphasised that isolated galaxies did not exist in an absolute sense because clustering on large scale dominâtes in ali régions of space (for small z at least).

Studies comparing redshifts of isolated galaxies with redshifts of groups confirmed that isolated galaxies generally belong to groups, but at such large distances from their centres (~4 Mpc) that they hâve certainly not undergone any physical influence from these groups (Balkowski & Chainaraux 1981). Haynes &;Giovanelli (1983) likewise showed that most of the isolated galaxies are outer components of groups or clusters.

Hence, it seems difficult to find a truly isolated population of galax

ies, but instead one can hâve access to régions of very low galaxy density, where the galaxies found reflect properties characterising their formation.

For 30 years, a variety of widely different criteria has been used (mag nitude limited samples, redshift information used or not, distance to the nearest galaxies different from one définition to the other, etc.), as shown by the abundant literature: Turner & Gott (1975); Balkowski & Chamaraux (1981); Vettolani et al. (1986); Zaritsky et al. (1993); [START_REF] Aars | [END_REF]; Colbert et al. (2001); Pisano et al. (2002); Prada et al. (2003); Marquez & Moles (1996, 1999); Marquez et al. (2002Marquez et al. ( , 2003)); Varela et al. (2004). Most of these studies only sample ten to few hundreds of galaxies, which is not sufficient for further statistical significance.

We are constructing a control sample of the most isolated galaxies of the northern sky which will serve as a template in the study of star forma tion and galaxy évolution in denser environments (Verdes-Montenegro et al. 2001a, 2002[START_REF] Combes | IAU Symposium[END_REF], 2005;[START_REF] Leon | [END_REF]. The Catalogue of Isolated Galaxies compiled by [START_REF] Karachentseva | Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Observatorii[END_REF] has a well defined criterion of isolation and compiles a reasonably large, homogeneous sample (~103 galaxies) to allow us statistical significance (even for the properties of morphological subtypes).

In this chapter, we study and quantify the environment of the most isolated galaxies of the northern hemisphere, in the local Universe. In sec tion 3.2, we will présent the principal features of the CIG and also several révisions and improvements done so far. In section 3.3, we describe in detail our automated pipeline which allows us to infer various parameters (sec tion 3.4) to quantify the surroundings of the isolated galaxies.

3.2

The Catalogue of Isolated Galaxies

Définition

The catalogue is a compilation of information on 1051 objects with apparent magnitude brighter than 15.7 and north déclination > -3°. Karachentseva visually inspected the Palomar Sky Survey prints, trying to identify those galaxies in the Catalogue of Galaxies and Clusters of Galaxies (CGCG, [START_REF] Zwicky | Catalogue of galaxies and of clusters of galaxies[END_REF]) which hâve no near neighbours. Primary galaxies with angular major-axis diameter Dp are considered isolated if any neighbours with diameters Di, Dp/4 < Di < 4Dp hâve an apparent angular séparation Rip, from the primary galaxy under considération, greater than 20Df.

Rip > 20 x Di Dp < Di < 4 x Dp [START_REF] Karachentseva | [END_REF] discussed her isolation criterion and found that 24 galaxies (with known radial velocities) passed the isolation criterion and belong to pairs, groups, or clusters. Other authors (Stocke 1978;Haynes Sz Giovanelli 1984;Xu & Sulentic 1991) reported that soine CIG galaxies are, in fact, members of interacting Systems: CIGs 0006,0007,0080,0197,0247,0278,0324,0347,0349,0444,0469,0559,0663,0781,0802,0809,0819,0850,0851,0853,0938,0940,0946,1027,1028. Adams et al. (1980) and Karachentseva (1986 ), refined the original iso lation criterion by assigning codes:

• Code 0: Isolated according to Karachentseva (902 galaxies);

• Code 1: Marginally isolated (85 galaxies);

• Code 2: Member of a group or cluster (64 galaxies).

Nevertheless, the CIG remains a good starting point to analyse a large sample of isolated galaxies. For instance, for a CIG galaxy with Dp -3', no neighbour with Di = 12' may lie within 240' and no companion with Di = 0.75' may lie within 15'. If one assumes an average Dp = 25 kpc for a CIG galaxy and a typical "field" velocity V = 150 km s-1 then an approximately equal mass perturber would require 3xl09 years to traverse a distance of 20Di. Ail possible effects of a past interaction, on the morphological or dynamical properties or those concerning the enhancement of star formation processes, hâve been erased at the présent time (Marquez & Moles 1996). Because this is a lower limit on the time since the last galaxy-galaxy interaction for a typical-size galaxy in the CIG, these galaxies hâve apparently been isolated for much, if not ail, of their existence (Stocke 1978). This is a quite conservative criterion but it is clear that dwarf companions are not excluded.

Galaxies isolated in space do not necessarily appear isolated in the sky:

the CIG is not complété due to the projection effects, but ensures that ail the galaxies that hâve passed through are really isolated. Nevertheless, the sample is still reasonably complété, according to the Schmidt (1968) luminosity volume test which gives <V/Vm> = 0.42 (Huchra & Thuan 1977;Xu & Sulentic 1991;Toledo et al. 1999;[START_REF] Verdes-Montenegro | IAU Sym posium[END_REF].

Is the Milky Way isolated?

The Milky Way is a common spiral galaxy (its mass is about 1011 M0), with a disk of about 30 kpc in diameter. Hence, ail the galaxies which would possibly violate the Karachentseva criterion would hâve diameters comprised between ~7.5 kpc for the smallest and 120 kpc will be the upper ^npublished documentation supplied with the catalogue by the Centre de Données Astronomiques, Strasbourg.

limit. As the companion galaxies can lie 20 times their diameter away, we would hâve to check for ail the members within 2.4 Mpc. Among the nearby groups of galaxies, only the Sculptor group (1.8 Mpc away) lie inside this Also belonging to the local Group but farther away, the Andromeda Galaxy (M31) has an apparent angular major diameter of 190 arcmin., corresponding to about 40 kpc. Its influence would affect the galaxies as far as 800 kpc from it. Hence, since the distance separating the Milky Way from the Andromeda galaxy is about 725 kpc, this latter would also violate the Karachentseva criterion (see Fig. 3.2). On the other hand, the Triangulum galaxy (M33) is about 795 kpc away, and due to its relatively small diam eter (~16.2 kpc) would not exert any influence on the Milky Way. This would be true if the System Milky Way-M33 would hâve been seen in the best case (the line of sight perpendicular to the plane constituted by the two galaxies). If the System is seen from other points of view, the appar ent distance separating the two galaxies will become smaller and reach a point where the Milky Way would not any longer appear isolated respectively to M33. This implies that ail the galaxies in the CIG catalogue really are isolated but that the catalogue is not 100% complété due to this very strong définition of isolation, depending on apparent 2-dimensions distances.

The AMIGA révision

Despite the various révisions done by the authors above-cited, we choose to improve the Karachentseva sample in several ways: (1) check in an automated, homogeneous way the isolation of the galaxies (this section), (2)

give continuous parameters describing the degree of isolation for the isolated galaxy candidates (next section).

The sample used and revised fields

The radial velocities of the nearest galaxies in the CIG cannot be totally interpreted by the Hubble flow, because of the importance of the local dis persion velocity where galaxies can overcome the expansion on small scales.

Also, as pointed out by Stocke (1978) and Haynes & Giovanelli (1984), the area searched for potential companions of the nearby CIG galaxies is spread over a large surface on the sky, which makes the search overwhelmed. To avoid these cases, we removed ail the galaxies with radial velocities less than 1500 km s-1, which resuit of being 101 objects, thus our final sample contains 950 galaxies.

We chose to evaluate the isolation degree in a minimum physical radius of 0.5 Mpc (see Figure 3.3), centred on each CIG galaxy. If we assume a typical "field" velocity of 150 km s-1, it will require about 3 x 109 years for a companion to cross this distance.

Data analysis

We developed an original method to check the isolation of the CIG galaxies.

This work was motivated by the fact that images brighter than B ae 17 are miss-classified at a high rate in présent on-line réductions of the all-sky Schmidt surveys. In the following, we describe a method used to reliably identify bright (i.e. B < 17.5) galaxies around our CIG fields of interest.

Size of the fields

We performed star/galaxy séparation in 55 x 55 square arcminutes fields centred on each galaxy in the CIG. In order to recover the bright galaxies at high success rate, we reduced bright image classification in our CIG fields using Palomar Observatory Sky Survey (POSS-I E, central wavelength = 6510 Â) images obtained with DSS. We hâve assembled a software pipeline for producing star-galaxy catalogues in the area around each CIG field. The digital images hâve a pixel size of 25 microns (1.7 arcsec. per pixel).

We searched the companion galaxies within a minimum physical radius of 0.5 Mpc, centred on each CIG. Due to pipeline capacity and server limits, we could not handle fields larger than 55' x 55'. To reach the physical radius of 0.5 Mpc, the fields larger than 55' x 55' are composed by various 55' x 55' fields, with small strip overlapping between two adjacent fields. We developed a tool to keep only one source when an object was detected more than once on various fields. Below, we gathered CIG galaxies by the number of fields employed:

• 767 galaxies with 55' x 55';

• 134 galaxies with multi-fields 2x2;

• 49 galaxies with multi-fields 3x3.

The 55 x 55 square minutes fields concerned galaxies with an observed recession velocity greater than 4,687 km s-1 (including the 62 galaxies with no velocity data, see Table 3.2); the 2x2 multi-fields correspond to galaxies between 2,343 and 4,687 km s-1; the 3x3 multi-fields to recession velocities lower than 2,343 km s-1.

At high latitude (déclination > 37 degrees), an issue arises: the coordinate System drastically converges in RA towards the pôle. The composition of contiguous fields became very problematic: two fields with the centres shifted by ~55 arcmin. were not overlapping properly anymore. We tried to get images directly from the DSS DVDs but the compression level used highly deteriorate the quality of the images and any further star/galaxy sép aration. As we found no way to get around this matter, we decided to manually pull down the fields, adapting the offsets to obtain the proper overlaps.

The DSS scans corne from 6.5 square degrees plates. When our fields reached the edges of the scans, we downloaded bands from the adjacent DSS scans to complété our 55 x 55 fields.

Détection of the sources

We used SExtractor (Bertin & Arnouts 1996) to detect the sources in the images, with the following parameters: a threshold 3 times higher than the root mean square (RMS) of the background estimation. Before the détec tion of pixels above the threshold, there was the option of applying a filter.

This filter essentially smooths the image, we used a Gaussian convolution with a FWHM of 2 pixels and a typical size of 5 x 5 pixels. Then, ail the objects larger than 4 pixels had been detected.

Star/galaxy séparation

The images are reduced using AIMTOOL in LMORPHO (Odewahn 1995;Odewahn et al. 1996Odewahn et al. , 2002)), and GUI-driven star/galaxy séparation proce dure was used to classify detected sources as: STAR, Galaxy or UNKNOWN (for the faint, small extended sources). We performed a star/galaxy sépara tion by using the method of log(star/galaxy area) vs. star/galaxy magnitude -which is shown to work well down to the 17.5 magnitude, as displayed in Fig. 3.4. The galaxies hâve a lower surface brightness than the stars and in the log(area) vs. magnitude plane, the two classes of objects follow different loci. The stellar locus in logAREA vs. MAG-ISO space was manually located using an interactive GUI approach because the shape and location of this locus changes significantly on different POSS-I Schmidt plates. A typ ical star/galaxy séparation parameter space from a POSS-I E image (CIG 0714). Ail the points that lie above the curve defined by the BLUE points were classified as Galaxy. The points below this curve (which is described with a cubic spline) were classed as STAR. Points that lie outside the spline range (brighter or fainter in MAG-ISO than the extent of the red points)

were classified as UNKNOWN. As a final step, we archived our catalogues in the form of simple ASCII files; a CIG database manager (CIGWORK) has been developed under LMORPHO to manage and evaluate these catalogues.

First visual check

As a visual check, the GUI allowed the user to view the image catalogue in the form of coloured-ellipse markers over-plotted on the DSS in a ds9

window (see Fig. 14,000 at low galactic latitude!).

Second visual check

Finally, we also used POSS-II red plates of ail our Galaxy objects to per forai a final check of our final catalogues of Galaxy companions (55,154 stamps, visually checked by L. V.-M.). The choice of POSS-II instead of POSS-I for this second check removed the detected plate defects in the POSS-I survey that could hâve passed through our first révision and provided a better spatial resolution to distinguish compact galaxies from stars.

We sum up the results of this second visual inspection of the Galaxy ob jects: 98% really were Galaxy (~54,000 objects), almost 2% were plate defects (1,119 sources), 0.04% were Star (23 objects).

Catalogues of galaxies

The parameters that we keep for each Galaxy were stored in the form of ASCII catalogues; the first fines of the catalogues associated with CIG 0001

and CIG 0002 are shown Table 3.3. The parameters used during the SExtraction make the diameters of the detected objects being about two times smaller than the expected estima tion of the T>25. In each field, we calculated the scale factor between the known £>25 (from NED) and the SExtracted value of the CIG diameter. We reported this scale factor on the diameters of the companions in order to hâve an estimated value of their D25. When the scale factor was outside 2 o from the mean factor (equal to 2) calculated with the CIGs, we decided to replace it by the mean value. Hence, in these fields, the SExtracted factors of the companions were multiplied by 2 to infer the values of the £>25. An independent check of these values with the £>25 listed in the LEDA database validate our method.

Quantification of the isolation

As we hâve a total of more than 54,000 companions over the 950 fields, we can use a statistical approach to quantify the environment of the CIG galaxies.

Statistical criteria

We defined, compared and discussed various criteria to quantify the degree of isolation for these galaxies. They were calculated with the information available over the entire fields (except where specifically indicated a physical distance of 0.5 Mpc):

1. Karachentseva criterion In the coming paragraphs, we detail these criteria.

Révision of the Karachentseva's criterion

Although the criteria used in our study are not équivalent to the Karachent seva's sélection, they hâve allowed us to find some of the CIGs that failed her criterion. According to Karachentseva, a perturbative companion can be 4 times bigger and 20Di away from the CIG galaxy (this is a huge distance:

20T^= 20 x 4Dp = 80Dp\). We could only cover this area for 67 fields:

among them, we can attest that 54 CIGs are isolated following Karachent seva's criterion.

For the remaining fields, we hâve found 284 CIG galaxies violating Karachentseva's isolation définition (although we were not able to check on the whole 80 x Dp). Hence, still 666 CIG galaxies remain isolated accordingly to Karachentseva, taking into account that we cannot assert that some of these latter galaxies will not move from the "isolated" to the "not isolated" sample, with a more exhaustive study. Figure 3.6 shows these two populations; the axes are defined with two criteria defined hereafter (local density vs. tidal forces estimations).

Figure 3.6: Green: still isolated galaxies; Red: galaxies that are violating Karachentseva's criterion (Logarithmic scales on both axes).

Pair candidates

Table 3.4 lists ail the pair candidates defined as a CIG galaxy with at least one companion (factor 2 in size with respect to Dp) within 5 x Dp. The fields of the 10 pair candidates detected (over the whole CIG sample of 950 primary galaxies) are shown in page 50. CIG 0019 has 2 companions nearby, one without known velocity and one with a recession velocity very similar to the one of the CIG: this constitutes a physical pair. Among the Figure 3.9: CIG 0074.

Figure 3.10: CIG 0178. Figure 3.11: CIG 0233. Figure 3.12: CIG 0315.

Figure 3.16: CIG 0934.

Local density estimation

An estimation of the local density can be found by considering the dis tance to the kth nearest neighbour. An unbiased estimator can be obtained if neither the central galaxy nor the kth neighbour are counted, see Casertano & H ut (1985). For this parameter, only the companions with similar size (0.25 to 4 Dp) were taken into account. k is equal to 5, or less if there were not enough companions in the field:

k-1

Pk oc with V(rk) = 47rr|/3, where rk is the distance to the kth nearest neighbour.

We saved these values using a Logarithmic (Logio) scale, after applying an arbitrary scaling constant to shift the range of values near the unity.

Forty CIG galaxies do not hâve at least two companions in the field considered: we did not estimate the local density in these cases.

Projected surface density estimation

A variation of the previous A:-density estimation can be calculated by counting directly ail the companions over a fixed surface. We hâve the redshift for 888 CIGs (over 950), so we can dérivé isolation parameters associated with physical radius. Hence, we chose to count ail the companions within a physical projected distance of 0.5 Mpc around each CIG.

A refinement was to remove the background and foreground companions:

we used the Karachentseva's argument and only consider the companions having a size similar to the CIGs (a factor of 4).

These two criteria were not calculated for the 62 CIG galaxies which do not possess redshift information, as we could not dérivé the physical 0.5 Mpc associated.

Tidal forces estimation

To estimate the tidal forces (T. F.) affecting the primary galaxies, we used a formalism developed by Daliari (1984): the tidal force per unit mass produced by a companion is proportional to where Mi is the mass of the companion, and R{p is its distance from the centre of the primary.

However, no information on either Mi or on the absolute Rip is available in most cases. The dependence of Mi on size is uncertain, we adopted 7 = 1.5 (Daliari 1984). Since we are not using redshift information, the diameters of the primary galaxies are used as scaling factors, i. where S{v is the projected RiP distance. Q, defined by this équation, is a dimensionless estimation of the gravitational interaction strength. Again, these values were saved using a Logarithmic scale, after applying an arbitrary scaling constant to shift the range of values near the unity.

In spite of the lack of the redshift information, Q is expected to give a reasonable estimate of the tidal interaction strength in a statistical sense as can be seen from the following argument. If the candidate companion galaxy is in reality a background object we hâve underestimated the true distance but also underestimated the true size and mass. Both effects partly cancel out. Only in the case of the candidate companion being a foreground object Q is overestimated. Foreground objects are however rarer than background objects because of the smaller volume spanned.

Like for the previous criteria, we used two kind of criteria: one including ail the companions, another including only the similar size ones.

For the 888 CIGs with redshifts, we also derived the same tidal forces cri teria including the companions within 0.5 Mpc, to palliate biases that could rise from the different surfaces of our POSS-I digitised plates (see Fig 3 .3). The CIG is complemented by catalogues of galaxy pairs (Karacheiitsev 1972), triplets (Karaclientseva et al. 1979) and compact groups (Hickson 1982). Ail of these interacting comparison samples were visually compiled using also an isolation criterion. Ail avoid the pitfalls associated with com puter compilation from a magnitude-limited catalogue (i.e. selecting the brightest galaxy or galaxies in a cluster).

Table of the isolation criteria

To estimate the isolation degree of the CIG galaxies and to place it in a more general context of space galaxy distribution, we apply some of the isolation criteria defined in the previous Chapter on triplets, compact groups and clusters of galaxies. We followed the method described in the previous Chapter (POSS-I digitised fields, first and second visual checks, ...) to avoid to be biased by technical différences during the discussion and interprétation of this comparative study. . [START_REF] Karachentseva | Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Ob servatorii[END_REF] showed that triple Systems constitute 0.8% of northern galaxies brighter than 15.7 mag, 64% of the triplets are "completely isolated", and 24% of the triplet members are elliptical and lenticular galaxies, while 76% are spirals and irregulars.

Karachentseva Triplets of Galaxies

From the 84 triplets, we selected ail of them with the 3 galaxies having V > 4,687 km s"1 (to use one single 55 x 55 square arcminutes field, see previous Chapter). We applied the isolation parameters on the "A" galaxy (primary galaxy which will play the rôle of the CIG galaxy). The resuit is that 41 triplets were selected (see Table 4.1). The coordinates, major axis and velocity are those of the galaxy on which the isolation parameters are applied.

Figure 4.1 shows the triplet of galaxies 04 as an example.

The results of this study are summarised Figure 4.4. The value of ail the isolation parameters are higher than the ones of the CIG galaxies (see Figure 4.4).

Abell clusters

Only in the northern hemisphere, the Abell Clusters of Galaxies catalogue (ACO, Abell 1958;Abell et al. 1989) lists more than 2,700 clusters in six richness classes (with only one cluster in the richest class!). We selected ail the clusters with available recession velocities between 4,687 and 15,000 km s-1. The ACO is a deeper sample than the CIG, KTG and HCG: the higher eut (15,000 km s-1) is used in order to sample a volume of space roughly équivalent to the one spanned by the CIG and avoid possible biases. Among these, 15 clusters hâve a known diameter less than 55 arcminutes. Ta ble 4.3 summarises the main properties of the clusters selected (left) along with information on the primary galaxies (right) on which the isolation cri teria hâve been applied (central cD galaxy, or central brightest galaxy). The first striking feature is that, along the x axis (tidal forces estima tion), the CIG, KTG and HCG samples are classified following the expected order. The CIG is normally only constituted by isolated galaxies, the KTG by 3 galaxies and the HCG mainly by 4 galaxies. The tidal forces estimation is sensitive enough to disentangle these samples.

Along the y axis, reflecting the kth local density estimation, these three samples are more confounded. This reflects the fact that the KTG and the HCG are samples constructed also with the help of isolation requirements:

these are isolated triplets and isolated groups. Nevertheless, by définition, two of the triplet galaxies and at least three of the group galaxies are very close to the primary galaxy. This is why the 5th neighbour is, in average, doser to the triplet or the group than the 5th neighbour of an isolated galaxy.

The value of the kth local density estimation is the resuit of a compromise between the two effects cited above. The CIG, KTG and HCG samples are also in a logical order along the y axis, but less separated than along the x axis. The tidal forces and the kth local density estimations are complementary criteria and it is important to use both in order to hâve an accurate picture of the répartition of galaxies surrounding a primary galaxy.

The ACO entities are physically very different from the CIG, KTG or HCG as they can involve several thousand of galaxies. The average value of tidal forces applied on the primary ACO galaxies is in between the KTG and HCG ones. This is mainly because our ACO sample is biased towards We used more than a dozen databases and surveys for two reasons: 1) con firai the types of our objects when they were matched, 2) make use of the redshifts when they were available to try to identify a background population among the CIG companions. We sent batch for ail the 54,000 companions to each database, matching the coordinates within a tolérance of 6 arcseconds.

Redshift catalogues and surveys

NED

The NK database gathers 8.1 million objects over the whole sky. The red shifts are available for 972 thousand objects . Over the 54,000 companions, we obtained 35,811 matching including 8,024 with redshift.

HyperLEDA

At présent the IyperLEDA database contains about 3 million objects, out of them 1.5 million are certainly galaxies (with a high level of confidence) .

This database covers the whole sky. We obtained 28564 détections including 11608 with redshift.

SDSS -DR3

The SDSS -DI is a major, recent survey. We used the spectrophotometric

2dF

The IF Galaxy Redshift Survey (2dFGRS) is also a major spectroscopic survey. The 2dFGRS obtained spectra for 245591 objects, mainly galaxies, brighter than a nominal extinction-corrected magnitude limit of bJ=19.45.

Reliable (quality>=3) redshifts were obtained for 221414 galaxies. The galaxies cover an area of approximately 1500 square degrees, mainly in the Southern hemisphere. We obtained 3018 détections with redshift.

CfA

The FA Redshift Survey gathers various surveys in one. We obtained 9103 détections including 8864 with redshift (velocity.dat catalogue). 106 and 866 objects with redshift were matched in two smaller catalogues (CfAl and CfA2, respectively).

UZC

In the catalogues (Falco et al. 1999), respectively 1461 and 1445 dé tections with redshift were obtained in the catalogues UZC and UZC2000, respectively.

Nearby Optical Galaxies

The Nearby Optical Galaxy sample (NOG, Giuricin et al. 2000) is a com plété, distance-limited (cz < 6000 km s-1) and magnitude-limited (B < 14) sample of ~7000 optical galaxies. We obtained 67 identifications with red shift.

SSRS2

The Southern Sky Redshift Survey (SSRS, da Costa et al. 1998) reports red shifts, magnitudes and morphological classifications for 5369 galaxies with ms < 15.5 and 57 galaxies fainter than this limit, in two régions covering a total of 1.70 steradians in the Southern celestial hemisphere. The galaxy catalogue is drawn primarily from the list of non-stellar objects identified in the Guide Star Catalogue. We matched 50 objects with redshift.

ington.

Type of the companions

First, we used the databases to confirm the star/galaxy séparation done in section 3.3. NED, HyperLEDA, SDSS, CfA give types for the objects in their databases (Table 5.1). The CIG companions are classified as Galaxy in more than 99.90% of the cases.

Redshift analysis

We gathered ail the data coming from the various databases above cited.

We treat the widely different formats in order to end with one single, homogeneous (J2000 coordinates, heliocentric velocities, ...) final catalogue. A total of 16126 (29.9%) objects hâve redshift listed in at least one database.

The typical error on the velocities is about ~40 km s-1. For some galaxies, the redshifts were listed several times. The agreement is generally very good between the different databases. Only one redshift per companion was kept for the following study. To hâve the most homogeneous final database, we chose to keep preferentially the data in provenance from the larger surveys. The SDSS gave 12166 objects (75% of the redshift sample)

and besides this it gave the smallest error and confident data. Next, in or der, we used: the 2dF, the CfA (velocity), NED, LEDA, UZC. Because of the redundancy, the UZCJ2000, CfAl, NOG4 and SSRS2 were not used. (~6624 km s-1), we saw that the redshifts available concerned a deeper sample of galaxies. Hence, most of the companion galaxies are background galaxies.

We are missing the redshifts for 70% of the companions in our sample. A total of 89 fields are at least 80% complété (see Figure 5.2). We hâve made use of these data in order to perform a reliability test of our method.

We hâve used these 89 fields in order to estimate the isolation criteria defined in Chapter 3 including only the companions that can be considered physically associated to the CIGs, based on their redshift différence with re spect to CIG galaxy. Two different values of the différence in velocity (AV)

between the companions and the main galaxy hâve been considered: AV = 500 km s-1 and AV = 1000 km s-1. The high general level of isolation of the CIG sample is confirmée! by the low number of companions identified in these fields at the CIG redshift (typically, about 4 companions!). Furthermore, respectively 35/27 fields could not be used in our test since only 1 or even zéro companions were found within 500/1000 km s""1 from the CIG.

Hence our tests hâve been performed using respectively the 54/62 galaxies of this list for which at least 2 companions hâve been found. First we hâve checked Karachentseva criterion (see section 3.4.2) and we find that 44/51 galaxies were fond isolated by Karachentseva and are still isolated when redshift data are available. On the other hand 10/11 were not considered isolated while now 7/7 of them are reclassified as isolated. This supports that Karachentseva's sélection was very restrictive.

In Figure 5.3, we compare the tidal force estimations within 0.5 Mpc (see section 3.4.6), for ail companions (X axis) and for those with a velocity within 500 and 1000 km s-1, respectively, from the CIG (each point in Similar conclusions can be reached with the other isolation parameters defined in Chapter 3. In Figure 5.4, we show similar plots for the kth local density estimation, as well as the corresponding fits.

The similarity of the results obtained with AV < 500 km s-1 with those increasing the considered velocity différence to AV < 1000 km s-1 supports the robustness of our statistical study of the isolation.

The dispersion of the fits reflects on one hand the low (< 20%) but still existing incompleteness in the redshift coverage of the fields, and the errors in the isolation parameters produced by the inclusion of background or foreground companions. The projected physical density shows that once redshifts are taken into account the number of physical companions decreases dramatically, more frequently due to the presence of background companions than to foreground ones, indicating that our method is very sensible to fainter and/or farther galaxies.

Conclusions

The 30% of the companions having redshift information does not represent any particular subsample among the whole sample of companions. The red shifts are not available only for the nearest galaxies and missing for the faintest galaxies or the ones which would hâve recession velocities of several tens of km s-1. Indeed, Figure 5.1 shows that the companions do hâve recession velocities of about 30,000 km s-1. Principally, the redshifts are missing for zones in the sky where no surveys were ever undertaken, and for which the only available data corne from particular projects.

The similarity of the samples with and without known recession ve locities can be seen, for instance, by looking at the distributions of their magnitudes: Figure 5.5 shows that the missing velocities are randomly distributed (in magnitude) among the companions. Hence, we can infer that the study done above for the fields with a redshift completeness smaller than 80%, would provide similar results if the redshifts were known for most of the companions. With this argument, we can confirm the validity of the statistical study done in Chapter 3.

Ail these results support the use of the data derived in Chapter 3 for the CIG companions, without taking into account redshift information. This will allow us to study a sample of 950 CIG galaxies, instead of the order of 60. Therefore, we give the final results of the isolation study using the data without using the redshift information. This has the advantage of giving homogeneous estimation of the isolation parameters for the 950 CIG galaxies. Table 5.2 sums up the main results of this study.

We hâve revised the isolation of 950 CIG galaxies, discussed Karachentseva's criterion, but also refined this complété sample in a homogeneous way, by giving continuous parameters of isolation, based on local density and tidal forces estimations. From now, the AMIGA project is using a re vised sample based on the CIG, from which the galaxies not really isolated were removed (pairs, galaxies highly affected by tidal forces).

Introduction

The triggering of star formation at large scale in a galaxy can corne from several dynamical phenomenons, interactions between galaxies and density waves such as bars are among the main. Already, Larson & Tinsley (1978) interpreted the big dispersion in colours U-B/B-V of galaxies in interaction due to bursts in star formation, intense but brief.

The interactions between galaxies can also produce enhancements in far infrared (Joseph & Wright 1985;Surace et al. 1993), in radio-continuum (Stocke 1978), in Ha émission (Kennicutt et al. 1987), and also in CO émis sion (Braine & Combes 1993;[START_REF] Combes | [END_REF].

There are, nevertheless, lots of uncertainty concerning the efficacy of interactions in the triggering of star formation and, still, no law is really well established, which could linked the local density of gas, or its velocity dispersion, to the star formation rate (SFR). Globally in a given galaxy, one of the best relation seems to be the Schmidt law (Kennicutt 1998), linking the available quantity of gas (essentially the HI reserve) to the rate of stars newly formed, but lots of exceptions are observed to this relation, showing that others parameters hâve to be taken into account.

One purpose of studying an Ha sample of galaxies is to disentangle the interconnections between interactions, starbursts, nuclear activity, by analysing isolated galaxies. This would also provide information about the following issue: do high star formation rates indicate a better efficiency in the mechanisms that form stars or that there is a larger quantity of fuel (molecular gas, HI+H2)?

Influence of environment on star formation

The star formation rate derived from Ha, in the absence of nuclear activity, dominated by young (t < 20Myr), massive (M > 1OM0) stars is about 2.5 times higher in interacting than in isolated galaxies (Bushouse 1987). Kennicutt (1989) showed that this rate, averaged over the disk, has a better corrélation with the superficial density of HI than H2 in normal galaxies, which is a surprising resuit because of the différences in the distributions of HI and Ha. Similar conclusions were derived from studies based on global averages (Boselli 1994;Casoli et al. 1996). This was attributed to variations in the conversion factor CO/H2, suggested by a better corrélation between H2 and the star formation rate for luminous galaxies (Kennicutt 1998) although arguing that the global superficial HI + H2 gas density shows a better corrélation (Kennicutt 1989(Kennicutt , 1998)).

The Ha émission line as a tracer of star formation

If a young star is hot enough (T > 10,000 K), its UV photons can ionise the surrounding medium (circumstellar medium), forming an HII région. The free électrons and nuclei created this way can recombinate and émit new photons, or warm up the gas by collisions with other atoms. This way, the radiation emitted by the star is transmitted to the surrounding medium and making this latter also to emitt radiation. The radiation field diminishes as we are farther from the central star. Due to géométrie dilution, the farther from the star, the less the number of ionising photons by volume unit. Besides, during the recombination of the électrons and ions, the new emitted photons can be cast in any direction, scattering and diluting the original radiation field from the star. Also, the energy radiated during the recom bination process can be emitted by photons with energies minor than the original ionising photon. Ail these processes diminish the ionising capacity of the radiation field and put limits to the extension of the ionised région.

The shape of the HII région dépends on the initial distribution of the gas around the central star and its size dépends on the total quantity of energy radiated by the star. If the radiation field is intense enough, when reaching the limits of the cloud, the radiation escapes: the HII région is defined as limited by density.

6.2

The Ha sample of isolated spiral galaxies

For the AMIGA CO and the Ha: studies, the observations of the whole catalogue would hâve been too time-consuming. So we decided to focus on a smaller sample. To avoid well known biases due to flux-or magnitudelimited samples and to end with a complété and homogeneous sample, we kept ail the galaxies in a volume-limited sample, i.e. with observed recession velocities V: 1500/cras 1 < V < 5000kms 1.

It represents about one fourth (251 galaxies) of the whole CIG. Among them, 27 were early-type galaxies according to our new morphological clas sification (Sulentic et al. 2005) The sample consists of 224 galaxies across ail Hubble types from SOa to Im (see Figure 6.2).

The major axes of the galaxies are shown in Figure 6.3 (bin = 0.33 arcmin., only CIG 0080 with D = 7.2 arcmin. is not shown).

Figure 6.4 shows an histogram of the recession velocities of the galaxies in the sample (bin = 150 km s-1).

Finally, Figure 6.5 shows the distribution of the blue luminosities (bin = 0.1 mag.).

6.3

The observations

Report on the obtained data

Next, we indicate the so far obtained data:

Observed galaxies Appendix A Table A.l

Among the 224 galaxies from the Ha sample presented in subsec tion 6.2, 200 hâve been observed. The Ha Galaxy Survey (James et al. 2004(James et al. , 2005)), kindly gave us 19 reduced galaxies that were in common in our two programs. Galaxies still to be observed Table A.2 24 galaxies of our sample remain to be observed because we include recently the galaxies with Karachentseva's 1986 isolation code 0 and 1 that we first discarded.

Galaxies with V < 1500 km s 1 Table A .3 Data in the literature for CIGs with V < 1500 km s-1:

• fia: Galaxy Survey: 22 galaxies (James et al. 2004(James et al. , 2005) ) • GHASP: 16 galaxies (Garrido et al. 2002(Garrido et al. , 2003(Garrido et al. , 2004(Garrido et al. , 2005) ) • lhaBAR: 7 galaxies (Hernandez et al. 2005) 6.3.2

The télescopes

The galaxies of our sample sweep ail the northern sky, and we used 5 different (1-2 métré class) télescopes to collect our data:

four in Spain, one in Mexico (see Table 6.1, hereafter).

Number of nights Introduction

The galaxies composing the sample described in section 6.2 were observed in 1-2 métré class télescopes as a compromise between our large number of objects (more than two hundreds) and the needed resolution and quality of the data. A significant amount of time was spent writing applications in order to obtain observing time as well as preparing the observations (specificities of the telescope, sélection of the more adéquate targets for each telescope, observing strategy, etc.), which hâve been mostly carried out in situ. We observed ail over the year as our objects range the entire right ascension domain.

We specifically asked for dark nights because of the magnitudes of our objects and the use of narrow-band filters. In order to dérivé the Ha luminosity function, we needed also photometric data for our galaxies: we ob served spectrophotometric standard stars (about 3 different stars per night, 3 times each star). When a night occurred not to be fully photometric, we still took data for the galaxies without observing the stars. In order to be able to calibrate these images we repeated one Ha exposure during the next photometric night, together with exposures of standard stars. This method allowed us to calibrate the whole set of images previously obtained.

The spectrophotometric standard stars were chosen from the N G catalogue.

Hereafter, we detail the filters used in the observations:

1. Ha (narrow-band filter, typically 50 Â) -The Ha filter traces the régions ionised by newly born stars. For every galaxy, we selected the more appropriate redshifted Ha filter based on its observed recession velocity.

2. r Gunn (broad-band filter, typically 870 Â) -The r Gunn filter gives the bulk of the optical émission in a galaxy. As it includes wavelengths containing the Ha line, it is also used to subtract the continuum con tribution affecting the narrow-band filter.

The télescopes we used are equipped with recent Charge-Coupled Device (CCD) instruments. The CCD is constituted by a solid surface sensitive to the light, and contains an integrated circuit to read and store electronically the images projected on it.

Instrumental signature

The technical aspects and scripts that automated the réduction are given in Appendix B so as to render these sections more legible. We automated and adapted scripts to reduce our data in an homogeneous way and get high quality final images .

The CCD raw images suffer various limitations but the final quality of the images can be significantly improved following a basic treatment. In the most frequent cases, the raw images contain at least three artifacts: the dark current, the variations in sensitivity on the detector surface and the noise from different origins (mainly the read out noise).

To remove the instrumental signature from our data, we employed one of the most extensively used software in Astrophysics: the Image Réduction and Analysis Facility (IRAF). As an example of the typical réduction process we hâve followed, we show ail the steps for the April 2005 campaign done at the OSN (see Table 6.2). The galaxy that we consider is CIG 0744.

Bias

For details, please see B. 1.1.

The bias frames resuit from a current injected in the chip which defines the level zéro of the electronics, so its contribution has to be removed from each of the images, including the fiat fields. During the observation nights, we took a long sequence of bias at the beginning and end of the night, and also controlled the bias level various times (typically 5 times) distributed ail along the night to check for systematic changes. For example, in this particular campaign (one single night), we took 25 biases:

cl> imstat @bias.lis* 2

After checking the stability of the bias frames during the night, we decided to keep the 25 of them to produce the super-bias. We used the médian for the combination, less sensitive to discrepant values than the average: cl> imcombine @bias.lis superBias. fit combine-median reject=avsigclip

Fiat fields

For details, please see 3.1.2.

We always used sky fiat fields to remove the différences in sensitivity (quantum efficiency, dust, ...) to the light from pixel to pixel in the CCDs, because they give more accurate results (evenly illuminated) in the estima tion than dôme flats, more dépendent on the illumination conditions under which they are taken (illumination différences, ...). We used both sunset and sunrise exposures to improve the statistics and hâve a reduced noise in xThis réduction process greatly benefited from the help of Jorge Iglesias-Pâramo.

2Ail the command lines will be typed in this manner: showing the IRAF Command Language prompt "cl>", followed by the command line in red.

our final super-flat fields.

We first subtracted the super-bias to each fiat field:

cl> cl < fîat-b.cl
Then, we compared the fiat fields among themselves, dividing one by another, to check if there were peculiar ones:

cl> cl < flat-coinp.cl
We created a super-flat field for each filter (r Gunn and Ha). We did not compute the statistics over the whole chip but on slightly smaller régions to avoid edge effects (due to the placement of the filters in the wheel for instance):

cl> imcombine @superFlatH.lis superFlatH.fit. combine=median reject=avsigclip scale-mean statsec= [300:1750,300:1750] cl> imcombine @superFlatR.lis superFlatR.fit combine=median reject=avsigclip scale=mean statsec= [300:1750,300:1750] We had to normalise to 1 the level of these fiat fields in order to further keep the real counts from the galaxies: cl> cl < superFlatN.cl

Science images

For details, please see B.2.

At this point we can proceed to remove the additive and multiplicative errors estimated in the previous section from the images of the galaxies.

For our images of galaxies, we needed to build up signal to noise using long exposures, especially using narrow-band filters. Unfortunately there are some obstacles to make extremely long exposures, including imperfect tracking, accumulation of cosmic rays, ... The way to get around this is to take several exposures and combine them.

We systematically took 3 to 5 images in each filter (but up to 72 when the presence of nearby bright star prevented long time exposures!). We used auto-guiding pointing on relatively bright stars near the galaxy observed.

It took more than a couple of hours to complété the observations of a galaxy. The typical exposure times were 300 seconds for the r Gunn filter and 1200 seconds in Ha. We applied small shifts between two successive exposures to be able to treat bad pixels or bad lines on the chip and punctual events (cosmic rays, passage of space satellites, ...). We divided each image by its exposure time to hâve the flux of the galaxy per second: cl> cl < cig0744-bfst.cl

Centring

For details, please see B.2.6.

We needed to align the multiple images before the stacking. We centred ail the images (both filters), taking as a reference the first image in Ha. The coordinates (précisé to the tenth of a pixel, after applying a Gaussian fit) of at least five stars shared in common by ail the images were used:

cl> cl < cig0744-bfstc.cl 7.3.7 Point Spread Function
For details, please see B. 2.7.

In order to combine the images they need to hâve the same Point Spread Function (PSF). We degraded the seeing of the best images to reach the PSF of the image possessing the worst seeing:

cl> display TMP/c0744_002H6607-bfstc.fit 1 fi+ cl> rimcursor > starsPsf0744.1is cl> cl < cig0744-bfstcp.cl Sometimes, when the seeings of the images were very close and the matched images degraded too much or added parasite features to our science images, we did not use this option. We simply used the original centred im ages for the remaining steps. This is not critical because in these cases, ail the images of a given galaxy were taken on the same instrument, the same night, within a couple of hours.

Combining

For details, please see B. 2.8.

In each filter, the final image was obtained, using an algorithm to keep the médian value of each pixel. The rejection algorithm removed quite effectively the few cosmic rays in the r Gunn images:

cl> imcombine @c0744rG.lis Im/cig0744rG.fit combine^médian reject=avsigclip cl> imcombine @c0744Ha.lis Im/cig0744Ha.fit combine=median reject=avsigclip 7.3.9 Continuum subtraction

For details, please see B. 2.9.

The removal of the continuum contribution to the flux in the images taken through the narrow-band Ha filter is the most délicate task. James et al ( 2004) tested various methods: numerical intégration to find the ratio of the filter profile intégrais, photometry of standard spectrophotometric stars through the pair of filters to find the scaling factor, use of foreground stars in the narrow-band and continuum images of each galaxy. The two last meth ods gave the most consistent and accurate results. The latter method has two advantages: it takes into account any changes in the sky transparency between the two images and the possibility to use several stars improves the statistics and lead to the most accurate removal. Hence, we used this last method to find the scaling factor to be applied to the images used for continuum subtraction. To estimate the fluxes, we use the task qphot with the following parameters (Massey et al. 1989;Stetson 1990):

Final images

For details, please see B.2.10.

Stamps of 512 x 512 pixels

To hâve the very final images, we need to eut the images around the galaxy. We defined the centre as the maximum of the luminosity of the bulge. We eut 512 pixels per edge because these images will be involved in an Fast Fourier Transform treatment more effective with power of 2 sized images (see section 8.3). The centres in r and Ha continuum subtracted generally agreed perfectly. When there was no central émission in Ha, we used the centre defined in the r Gunn image. This is important because as we will dérivé the torques between the two components (see section 8.3.3), we do not want to add any artificial torque resulting from artifacts. But as the images were previously aligned to the tenth of a pixel, we are very confident, and this could be checked on the positions of more external Ha bursts.

For CIG 0744, the centre was: 1081.34 876.00. The presence of a bar in a spiral galaxy is a striking feature and, as such, is one of the fundamental éléments of the first morphological classification done by Hubble, which gives the aspect of a "tuning fork". The bar frequency that can be determined in galaxies dépends on the wavelength of the images but is always higher than 65%. Some estimations based on NIR However, Bournaud et al. (2005) hâve just shown, using fully self-consistent simulations, that with gas parameters typical for normal spirals, the mass concentration is not sufficient to fully dissolve the bar, as was also claimed by Slien & Sellwood (2004).

The second mechanism is due to the bar torques themselves. From the equality between action and reaction, the gas exerts a positive torque on the bar, which then gains angular momentum. Since the bar is a néga tive angular momentum wave, this gain will weaken and destroy it. The angular momentum lost by the gas is gained by the bar, which dissolves progressively. For typical Sb-Sc galaxies, the bar is destroyed in about 2

Gyr (Bournaud & Combes 2002). The observation of a high bar frequency from z ~0 to z ~0.7 (Eskridge et al. 2002) cannot thus be interpreted to support the existence of robust, long-lived bars. Instead, this supports the frequent renewal of bars. Berentzen et al. (2004) hâve shown that interac tions can only form bars in gas-poor galaxies, which is not the case for most spiral galaxies.

Bar renewal can occur when the disk of spiral galaxies are replenished in cold gas through external accretion, able to increase significantly the disk to bulge ratio. [START_REF] Block | [END_REF] suggests that external accretion of gas in the disk of spirals plays a fundamental rôle in explaining the high fraction of barred spirals and the observed torque distribution. Models of isolated, non accreting galaxies are very unlikely.

To better understand the frequency of bars and their origin, measurements of the gravitational torques and bar forces in field galaxies hâve been done [START_REF] Block | [END_REF]Laiirikainen et al. 2004a,b;Buta et al. 2004), but this is not the case for isolated galaxies.

We therefore présent such a study in the following chapter: we analyse through Fourier analysis of gravitational potential and density, the intensity of m = 1, m = 2, .. perturbations in an isolated sample of 45 galaxies. From the Ha maps, we dérivé the gravitational torques exerted by the stellar bar on the gas component (phase shift measured). We can thus deduce the life time of the bar, when there is one, and check whether the time spent in various bar strength categories correspond to the frequency observed.

We also classify the different spatial distributions of star forming régions (Ha) in barred galaxies. The most frequent distribution does not coincide with that of the gas. This implies that the classical Schmidt law for star formation, only function of density, is too simple, and that a dependency as a function of velocity should be taken into account.

The Ha subsample

We studied the morphology of some isolated spiral galaxies in more details.

We focused on a subsample drawn from the Ha sample defined in Chapter 6

(subsection 6.2).

From the sample of 200 spiral galaxies, with recession velocities 1500 < V < 5000 km s'1, we selected the galaxies with available data, respecting the following requirements:

Sufficient spatial resolution In the case of our observations, this trans lates into galaxies having major axis greater or equal to 1 arcmin;

Low-inclination In order to obtain a sufïiciently accurate deprojection, the inclination lias to be minor or equal to 50°.

With these criteria, we get 45 galaxies (almost one quarter of the whole Ha sample). The required data hâve been reduced following the method described in Chapter 7. The r Gunn broad-band images trace the stellar component of the galaxy, and the Ha images show the young stars born from the gas (HII régions). • We used the raw r band image (not scaled to Ho;) and the Ho; con tinuum subtracted image. We defined the centre as the maximum in luminosity near the geometrical centre. The centre is the same on the r and Ho image to avoid artificial torques between the two components.

We eut 512 x 512 pixels2 stamps.

• We removed the stars to avoid a contamination in the density and potential derived from the luminosity of the pixels.

• We deprojected the galaxy to hâve the gravitational potential in the disk plane.

• We determined the bar/arm force at each radius.

• We made use of the method developed a dozen years ago by F. C.'s team to compute the gravitational potential, applying it to our red images, supposing a constant M/L ratio. A Fourier-component anal ysis of the potential was performed, with a spécial interest on the m = 2 component to identify the bar(s) [START_REF] Block | [END_REF], and m = 0 to get the axisymmetric tangential and radial forces, depending on the radius. Their quotient provided us a measurement of the bar/arm force.

• We estimated the average torque depending on the radius: using the gravitational forces and the young stars born from the gas (Ha), we obtained the phase shift between gaseous arms and the potential well which créâtes the torques.

• We estimated the angular momentum transfer and therefore the évo lution time for bars in isolated galaxies.

• Gas déplétion time and possible requirement for an external source of gas.

• Comparison to galaxies in higher density environments, and with numerical models of évolution [START_REF] Block | [END_REF]Bournaud et al. 2005).

Potential

To get the stellar disk potential, we hâve to know how the mass is distributed in a typical spiral galaxy: we use a model to infer the third dimension. Spiral galaxies are composed by a bulge (spheroidal component in the centre) and a disk, very flat, extending far from the centre. The luminosity profile of 36 spiral galaxies (including S0) was studied by Freeman (1970) and can be

Surface density

The (disk) surface density is decomposed as: 0) = /i0(r) + ^2 am{r) cos(m0 -0m(r))

TU where the normalised strength of the Fourier component m is Am(r) =

The density is more local and raw, more noisy also. It's complementary

to the potential which is more model dépendent (spherical dark matter) the information is diluted.

Torques

The maximal torque at a given radius is defined by: Generally, the gas inflows towards the centre (négative torque) from the corotation radius to the inner Linblad résonance (ILR) and flows outwards (positive torque) when outside the corotation radius, until the outer Lindblad résonance (OLR).

Qt(R) = F™ax(R) F0(R) 1 _ r y do j d^o(R)
The next page shows a template summarising the information we présent for each of the 45 galaxies. For the graphies of the potential and the density, the legend is the following:

-dashed line represents m = 1 [0:27t];

-full line represents the m = 2 component (and the sum also for the ampli tude of the potential as it is always above and cannot be confused with the others);

-dot-dash-dot-dash represents m = 3;

-dotted line represents m = 4.

: ' i 1 1 1 -©• O î. ./ - - CM , -" 1 r : i 1 i 0 2 4 6 Radius (kpc) CM i i 1 1 - J r-' " e-o ï.'. : r'i ï îi ! •V ,v-rH y ! i j V i U .,1 i CM 1 _ V l . 1 '«y 1 i - 0 2 4 6
Radius (kpc)

Figure 8.10: CIG 0096.

Statistical study

Our sample is 94% complété (we are only missing data for 3 galaxies over 48). Hence, we can dérivé statistically significant characteristics for a sample of isolated galaxies. The barred galaxies represent 60% of our sample (the bar can be seen in r Gunn or Ha). As we are treating optical images, this resuit is consistent with the studies presented in the introduction. The unbarred galaxies rep resent 33% of the sample. Three galaxies hâve an intermediate stage bar, similar to the "SAB" kind, they represent 7% of the total. We can conclude that the isolated galaxies span the whole range of bar morphology, in quantifies similar to the galaxies in denser environments. Isolated galaxies are not preferentially barred or unbarred galaxies. This resuit is marginally in contradiction with the recent study by Varela et al. (2004), who estimate that bars are twice more frequent in perturbed galaxies compared to isolated galaxies, especially for early-types. Also Ehnegreen et al. (1990) find more bars in a sample of binary galaxies, and also more early-types.

b) Phase shift between gas and stellar components As some characteristics are frequently found among the galaxies of our sam ple, we chose to group the galaxies presenting the same features. In decreas-ing frequency order, we defined the three main groups:

Group E 19 galaxies -CIGs 0030, 0053, 0066, The principal features of this group are the following: a strong central peak in the Ho: émission; no Ha émission in the bar (for the barred galaxies in the r Gunn image); bright Ha knots at the end of the bar/beginning of the spiral arms; Ha émission along the spiral arms, generally clumpy.

Group F 9 galaxies -CIGs 0050, 0059, 0084, 0188, 0267, 0661, 0808, 0924, 0935.

This group is constituted by galaxies with less gas, having a smoother morphology. The galaxies do not présent any central émission spot in Ha.

Group G 8 galaxies -CIGs 0116, 0250, 0645, 0700, 0712, 0754, 0854, 1004.

This group gathers galaxies presenting Ha émission in the bar. CIG 0700 présents a very faint émission, but a bar can be distinguished.

Some of the galaxies of our sample did not fit in any of the main groups above. Some others presented characteristics mixing features from two of the above groups. Nevertheless, we could class them as follow:

Group H 3 galaxies -CIGs 0068, 0359, 0875.

This group is mostly constituted by early types galaxies, with very few émission in Ha and when it occurs, only in the centre.

Group EG 3 galaxies -CIGs 0512, 0652, 0744.

This group is a transition between the E and G groups presented above: fragments of bars. The central émission of CIG 0744 is very clumpy but seems to follow the shape of a bar, this is why we included it in this group.

Group EF 1 galaxy -CIG 0750.

CIG 0750 does not hâve a clear central peak in Ha but présents ail the other features of the galaxies in the group E: clumpy Ha émission along the spiral arms. We call this group EF as a resuit of the mixed features presented by CIG 0750.

Group Irr. 2 galaxies -CIGs 0085, 0575.

This last group gathers very irregular galaxies which do not fit particularly in any of the previous groups defined above.

b) Interprétation

We can try to estimate the lifetime of bars in galaxies if we consider the different features as different stages of an évolutive sequence. We see three main steps: by gravitational instability, a galaxy accretes gas from the intergalactic medium which makes it unstable for bar formation. The bar créâtes a torque which drives the gas inflow towards the centre. This phase corre sponds to our identified (G phase).

The second step is a transition between the G and E phases: the gas inflows towards the center while a ring is slowly forming at the résonance (pseudo-ring due to the winding of the spiral arms).

In a third step, the gas is progressively depopulated from the bar, and accumulâtes first in the very center of the galaxy (or a very small nuclear ring, at ILR), and also at the UHR résonance, near the corotation. The gas there is quite stable, with almost zéro velocity with respect to the bar pattern, and therefore the star formation is quite efficient. This corresponds to our identified more frequent phase, the E phase.

Since the gas infall destroys the bar, the latter becomes progressively weaker and weaker: the F phase is reached. The stars in the centre become an old population, contributing to increase the bulge mass. Without more gas fueling, the Ha spot in the centre is fading away in 108 years (OB stars).

The frequency of the F phase means that a bar is typically destroyed in a few 108 years.

The efficiency of the star formation as a function of the gas density is still a challenging issue. We made simulations (see Appendix C) to confront our observations to the theory. Initially, the galaxy is launched axisymmetric and the bar forms spontaneously by gravitational instability. The gas subject to the bar torques inflows towards the centre. We used the Schmidt law (SFR oc Pg-2, where pg is the gas volumic density) to détermine the star formation rate. In our simulations, the predicted frequency of the G Ha distribution is higher than the E phase. This is not in agreement with our observations where the E phase is about twice more frequent than the G phase. During the simulations, we can see the formation of rings at the Ultra Harmonie Résonance (UHR). But comparing with the galaxies from the group E, the ring gas density is relatively weaker than the gas density along the bar. To remove this discrepancy, it would be necessary to change the expression of the star formation rate: it should not only dépend on pg but should take into account the velocity of the gas too. In particular, the relative velocity of the gas with respect to the bar pattern is relevant. This work is in progress.

The question of star formation versus gas density means that the Ha émission is not a faithful tracer of gas density, but more of star formation (which should a good ersatz, in case of a simple Schmidt law). We can try to compare the quality of this tracer with that of CO émission.

We do not hâve galaxies in common with the BIMA Survey Of Nearby Galaxies (BIMA SONG, Helfer et al. 2002). But already, the BIMA SONG brings us some dues about the gas density. The E phase, although also présent there, is less frequent, relative to the G phase, as we could expect.

There is more CO émission in the bars of their galaxy sample (NGC 2903, 3627, 4535, 5457; see also Maffei2 by A. Weiss) compared to our Ha sample.

Therefore the Ha émission is indeed a more efficient tracer of star formation than of the total amount of gas available.

Some isolated galaxies in our sample (16%) présent signs of nuclear activ- confirm the types). Four galaxies (CIGs 0116, 0250, 0712, 1004) were listed in the group G, which is not really surprising because a bar is expected to enhance the gas flow towards the centre of galaxies and may provide a mechanism for triggering starbursts and fueling an AGN (e.g., Contini et al. 1998;[START_REF] Combes | IAU Symposium[END_REF]).

Conclusion

One key problem in astrophysics is to understand the rôle played by the environment in the formation and évolution of galaxies. To address this issue, we characterised a sample of reference in which the influence from the environment is minimal and hence which évolution is totally determined by its intrinsic properties.

This thesis takes place in the AMIGA project "Analysis of the Interstellar Medium of Isolated Galaxies" which is doing a multi-wavelength study of a large sample of isolated galaxies in order to examine their star formation activity and interstellar medium.

We begun with 950 galaxies from the Catalogue of Isolated Galaxies (Kfirachentseva 1973) and reevaluate isolation using an automated stargalaxy classification procedure (to = 17.5) on large digitised POSS-I fields surrounding each isolated galaxy. We defined, compared and discussed various criteria to quantify the degree of isolation for these galaxies:

Karachentseva's revised criterion, local surface density computations, esti mation of the external tidal force affecting each isolated galaxy. We also applied our pipeline to triplets, compact groups and clusters which serve as control samples. The advantages of our isolation révision are:

(1) computer processing: We do not only use eye-search companions, we run computer programs in order to detect and classify sources;

(2) magnitude: We revised the CIG catalogue up to a magnitude B = 17.5 while the previous catalogue was limited to B = 15.7;

(3) isolation degree: We systematically defined general isolation degrees consistent for the whole sample;

(4) redshift: We used the largest spectroscopic galaxy databases to con firai the type of the companions identified: they do are galaxies. We used 3 dimensional information, when available, to better quantify the environment. With this material, we could confirai the validity of the statistical study done for the whole sample of 950 galaxies. In order to understand the observed Ho; distributions, and the different phases identified, we performed N-body simulations with stars and gas, including star formation. Since we want to explore many physical parameters, we chose to carry out 2D simulations, which should capture the essential of the bar évolution, and location of star formation in thèse isolatcd galaxies.

The 3D components, bulge and dark matter halo, are therefore considered as rigid and spherical potentials, in which the disk component evolves. Selfgravity is only included for the disk (gas + stars). 2D N-body simulations were carried out using the FFT algorithm to solve the Poisson équation, with a cartesian grid, varying from 256x256 to 512x512 (useful grid, free of periodic images). Two spatial resolutions were selected, to appreciate its influence on the star formation physics. The cell size is then from 62.5 to 125pc, and the total size of the grid is 32kpc. The softening length of the gravity has the characteristic scale of the cell (62 to 125pc). More details on the numerical techniques can be found in Combes et al. (1990).

The stellar component is represented by 100k or 400k particles, and the gas component by 40k and 160k for the low and high resolutions adopted respectively.

The bulge is modelled as rigid spherical potential with Plummer shape: ®b(r) = -GMb \A2 + '6

for Mb and rb the mass and characteristic radius of the bulge.

The stellar disk is initially a Kuzmin-Toomre disk of surface density S(r) = Eo(l+r2/^)-3/2 truncated at 15kpc, with a mass M^. It is initially quite cold, with a Toomre Q parameter of 1. The halo is also a Plummer sphere, with mass M/j and characteristic radius r^. The time step is 0.5 and 1 Myr. The initial condi tions of the runs described here are given in Table C.l. The gas is treated as a self-gravitating component in the N-body simu lation, and its dissipation is treated by a sticky particle code, as in Combes &: Gerin (1985). The initial gas-to-total mass ratio (Fffas) in the disk ranges between 6 and 14%, since the star formation in the simulation is capable of reducing Fgas to a final lower value. The mass of one gas particle therefore varied between 8 104 and 3 105 M0.

The initial distribution of gas in the model is an exponential disk, truncated at 15kpc, and with a characteristic radial scale of 6kpc. Initially, its velocity dispersion corresponds to a Toomre Q-parameter of 1. The gas clouds are subject to inelastic collisions, with a collision cell size between 60 and 120pc (région where particles are selected to possibly collide). This corresponds to a lower limit for the average mean free path of clouds be tween two collisions. The collisions are considered every 5 to 10 Myr. In a collision, the sign of the relative cloud velocities is reversed and the absolute values are reduced: relative velocities after the collision are only fei times their original value, the elasticity factor fei being between 0.65 and 0.85, as indicated in Table C.l. The dissipation rate is controlled by this factor. Ail gas particles hâve the same mass.

Star formation is taken into account following a generalised Schmidt law:

the star formation rate is proportional to the volume density to the power n=1.2, provided that the density is larger than 1 H-atom cm-3, i.e. the rate of gas mass transformed into stars is dm = dtC*p1-2. To compute this rate, the same mass as each gas particle, about 3 times smaller than any old stellar particle. This simple scheme corresponds to an instantaneous recycling of matter, since the continuous mass-loss from recently formed stars is not followed. The rate of star formation is normalised so that in unperturbed runs (without galaxy interaction, galaxies are quiescently and regularly forming stars), the timescale for consumption of half of the gas mass is of the order of 2 Gyr (SFR ~1-2 M0/yr). At each star formation event, the neighbouring gas particles are given a small extra velocity dispersion of order ~10 km/s.

C.l Gaseous component

The second run used a less dissipative gaseous component.

C.l.l First run C.l.

Stars

Gas 1.9Gyr

Stars Gas 2.4Gyr

Figure 1 . 1 :

 11 Figure 1.1: Hubble's velocity-distance relation.

Figure

  Figure 1.2: Hubble's morphological classification (kindly from the University of Manitoba).

  poor sequence could be interpreted as a progression in dynamical évolution, ^ubble's constant can be parametrised as Ho -100 A km s 1 Mpc b

  Figure 1.4: Distribution of wall galaxies (circles) and the centres of voids (triangles) in thin (1°) slices of the North and South Galactic Pôles (from Hoyle & Vogeley 2004).

Figure 1 . 5 :

 15 Figure 1.5: Morphology -density relation.

  Figure 2.1: a) Différences between the measured positions and those retrieved from SIMBAD for the CIG galaxies, b) Histogram of the différence between the new positions and the SIMBAD positions for the a (dotted line), ô (dashed line) coordinates and the total distance (solid line) in arcsec. The plotted range is restricted to 10" for clarity of the plot.

Figure 2

 2 Figure 2.2: DSS images of the a) CIG 0402 field, where a bright star is superposed on the galaxy, and b) CIG 0828 field. The stars indicate the newly calculated positions, whereas the triangles correspond to the UZC positions.

  Figure 3.2: Local group [kindly from Wikipedia].

  Figure 3.4: Star/galaxy séparation parameter space.

Figure 3 . 5 :

 35 Figure 3.5: The distribution of galaxies around CIG 0714 (the bottom-right galaxy).

  c-density estimator (similar size companions) (Log) 4. Projected density within 0.5 Mpc 5. Projected density within 0.5 Mpc (similar size companions) 6. Tidal forces (Log) 7. Tidal forces (similar size companions) (Log) 8. Tidal forces within 0.5 Mpc (Log) 9. Tidal forces within 0.5 Mpc (similar size companions) (Log)

  e., 77 oc Di/Dp, and RiP oc Sip/Dp. Accordingly,

  Karaclientseva et al. (1979) listed 84 northern isolated galaxy triplets (KTG) compiled in a manner similar as the one used to compile the CIG. The ap parent magnitudes are brighter than 15.7 and the Catalogue was built up on the basis of a complété examination of Palomar Sky Survey prints (POSS-I)

Figure 4 .

 4 Figure 4.2 shows the compact group 33 as an example.

Figure 4 .

 4 Figure 4.3 shows the Abell cluster 2666 as an example.

  Figure 4.4 gathers the results obtained in this Chapter. We can compare the isolation level of the CIG with the kth local density and tidal forces estima tions on galaxies from the KTG, HCG and ACO. The scale is logarithmic (Logio) on both axes.

  the poorest clusters. The 15 clusters selected are not représentative of the mean characteristics of the ACO sample for various reasons: among the nearest ones, belonging to the 2 poorest richness classes, having a diameter minor than 55 arcminutes. The effects in ACO are mostly the cumulation of smaller interactions. Nevertheless one may expect that resuit as the HCGs are the densest concentration of galaxies in the Universe. The ACO sample possess the highest kth local density estimation, as expected because ail the 5 neighbours are included in the cluster: there is no effect due to an isolation requirement. A relevant value to characterise the ACO sample is the ratio kth local density over tidal forces estimation: they hâve the lowest value compared to the other samples. This is due to the combination in a single parameter, of the two effects just cited.

Figure

  Figure 4.3: Abell cluster 2666.

Figure 5 . 1 :

 51 Figure 5.1: SDSS redshifts of the companions.

Figure 5 .

 5 Figure 5.1 présents the distribution of the velocities available in the Sloan. The mean is z = 0.097 (about 30,000 km s-1). Compared with the histogram of the CIG recession velocities Figure 2.3 with a mean z = 0.022

  520 fîelds are strictly less than 10% complété, 641 fields less than < 20% complété. Nevertheless, some of our fields are rather complété (see Fig ure 5.2). Even fîve of them are 100% complété: CIG 0213 (25 objects), CIG 0359 (18), CIG 0492 (27), CIG 0655 (8), CIG 0892 (23).

Figure 5 . 2 :

 52 Figure 5.2: Redshift completeness.

  Figure 5.3: Left: AV < 500 km s Right: AV < 1000 km s 1 (Logarithmic scales on both axes).

Figure 5 . 5 :

 55 Figure 5.5: Magnitude distributions.

  Figure 6.1: Hydrogen sériés.

Figure

  Figure 6.2: Morphologies.

FigureFigure 6

 6 Figure 6.3: Major axes.

Figure 6 . 5 :

 65 Figure 6.5: Blue luminosities.

  high energy particles which pass through the CCD detector and deposit large amounts of energy. They show up in the images as pixels significantly brighter than their surroundings.Because of the long intégration time of the Ho; exposures, the number of cosmic rays reaching the chip meanwhile became very significant. On the other hand, the r Gunn images are only slightly affected by the presence of cosmic rays which will be well removed during the final combination of the exposures. Hence, we first removed the cosmic rays from the Ha images: cl> cl < cig0744-cr., the pedestal level of the super-bias obtained as explained in subsection T.2.1 was subtracted from ail the images (images of galaxies by the normalised super-fiat fields (obtained subsection 7.2.2) corresponding to each filter: was estimated from a région surrounding the galaxy (again to avoid edge effects where the level of the sky is generally smaller due to small vignetting by the filter stiles) and then, subtracted from the images: cl> cl < cig0744-bfs.cl 7

  photometric aperture: 1.5-2 x the seeing

Figure 7 . 1 :

 71 Figure 7.1: Raw r Gunn image.Figure7.2: Raw Ha image.

Figure 7 . 3 :

 73 Figure 7.3: Scale factor.

Figure 7

 7 Figure 7.4: Ha -continuum.

Figure 7

 7 Figure 7.5: r Gunn with stars.Figure7.6: r Gunn without stars.

  images, not affected by extinction and tracing mainly the old population, reveal that as high as 90% hâve bars.Numerical simulations hâve established that bars in gas-rich spiral galax ies are short-lived structures. There are at least two mechanisms able to weaken the bars. The first one is the building of a large central mass con centration, due to the gas inflow to the centre through the négative torques exerted on the gas by the bar. The torques are proportional to the phase shift between the gas and the stellar bar. It is well known that the gas is concentrated on the leading side of the bar (e.g.,de Vaucouleurs & de Vaucouleurs 1963). The gravitational torque of the bar makes the gas lose angular momentum, driving it towards the centre and creating a central mass concen tration. The latter is able to perturb the elongated orbits supporting the stellar bar, deflecting the stars passing close to the centre. This weakens the bar(Pfenniger & Norman 1990).

  the brightness extrapolated in the centre and ro the characteristic radius. The potential is decomposed as: $(r, 0) = $0(r) + ^2 ®m(r) cos(mQ -0m) m where the strength of the m-Fourier component is Qm(r) = m$m/r|Fo(r)|, and its global strength over the disk: maxr (Qm(r)) (e.g., Combes & Sanders 1981).

  represents the maximum amplitude of the tangential force at radius R, and Fq(R) is the mean axisymmetric radial force inferred from the m-0 component of the gravitational potential.

Figure

  Figure 8.20: CIG 0376. V = 3365 km s-1 Optical diameter: 1.5 arcmin. Blue luminosity: 9.73 Morphology: SB(rs)bc Group: E

  Figures 8.46 to 8.50 présent the tidal forces estimation in the x-axis and, along the y-axis, estimations of the maximal amplitudes of the m = 1 or m= 2 Fourier components. Three galaxies (CIGs 0080, 0085, 1001) possess an estimation of the tidal forces greater than 3. It is interesting to note that the m = 1 component dominâtes in the outer parts of CIG 0080, which possess a small companion nearby. CIG 0085 is a very irregular galaxy and seems to présent features due to strong interactions. Last, CIG 1001 is classified as peculiar by NED. These remarks comfort the validity of the isolation study done in the first part of the thesis which affected strong values of the isolation parameters to these three galaxies.

Frequently

  , we see bright Ha knots at the end of the bars, even when there is no émission in the bar. It is sometimes difficult to define where exactly the arms begin because the Ha could be very clumpy, but we can use the star formation spots at the end of the bars, to define the starting point of the spiral arms. The Ha émission is always leading with respect to the bar in the r Gunn image. The most évident cases of bar shifts between the r Gunn and the Ha images are listed hereafter (in parenthèses: an estimation of the shift angle in degrees): 0030 (20°); 0053 (10°); 0066 (5°); 0096 (10°); 0176 (10°); 0376 (30°); 0512 (10°); 0840 (15°); 1004 (5°).

  167

  at regular intervals of dt= 5-10 Myr, the gas density is averaged in each cell, and the probability of the gas particles being transformed into stars is computed by P = dm/Mceii for ail particles in this cell, of mass Mceu. Each new star formed has exactly

  Mpc; ...). The Sculptor group (1.8 Mpc away) is constituted by six members, NGC 0253 (diameter of 14.4 kpc), the brightest galaxy of the group would not violate the isolation criterion.Hence, the question of isolation of the Milky Way would involve galaxies of the Local Group (see Fig.3.1). The table 3.1, data taken from Galactic Astronomy[START_REF] Binney | Galactic astronomy (Galactic astronomy / James Binney and Michael Merrifield[END_REF], shows the Local Group members.

	limit, the others are ail father than 3 Mpc, hence not concerned (M81: 3.1
	Mpc; Centaurus: 3.5 Mpc; M101: 7.7 Mpc; M66 + M96: 9.4 Mpc; NGC
	1023: 9.5

Our galaxy's brightest satellite Systems are the Magellanic Clouds: the LMC is 49 kpc away and hâve a diameter of ~9.3 kpc: this companion violâtes the Karachentseva's criterion! The Small Magellanic Cloud has a diameter of about 5.4 kpc and would not be taken into account by the Karachentseva criterion: we see here a limitation of the criterion, already evoked in the previous section.

Table 3 .

 3 1: Local Group members.

	Name	Type	Distance(kpc)0
	M31	Sb
	Milky Way	Sbc
	M33	Sc
	LMC	Irr
	IC 10	Irr
	NGC 6822	Irr
	M32	dE2
	NGC 205	dE5
	SMC	Irr
	NGC 3109	Irr
	NGC 185	dE3
	IC 1613	Irr
	NGC 147	dE4
	Sextans A	Irr
	Sextans B	Irr
	WLM	Irr
	Sagittarius	dSph/E7
	Fornax	dSph/E3
	Pegasus	Irr
	Léo I	dSph/E3
	Léo A	Irr
	And II	dSph/E3
	And I	dSph/EO
	SagDIG	Irr
	Antlia	dSph/E3
	Sculptor	dSph/E3
	And III	dSph/E6
	Léo II	dSph/EO
	Sextans	dSph/E4
	Phoenix	Irr
	LGS 3	Irr
	Tucana	dSph/E5
	Carina	dSph/E4
	Ursa Minor	dSph/E5

Draco dSph/E3 Figure 3.1: Local group [drawing from this web site].

Table 3

 3

			.2: 62 unknown CIG rcdshifts.
	CIG	CIG	CIG	CIG	CIG	CIG	CIG
	0003	0272	0479	0629	0717	0814	0899
	0017	0297	0535	0632	0729	0821	0908
	0026	0311	0558	0664	0730	0822	0964
	0035	0320	0583	0673	0737	0842	0968
	0046	0360	0587	0681	0765	0846	0977
	0048	0369	0594	0687	0774	0869	0995
	0070	0394	0597	0704	0787	0878	0996
	0254	0414	0607	0707	0790	0885	1049
	0263	0459	0628	0713	0804	0887

Table 3 .

 3 3: Companions of the CIG galaxies.

	CIG	Comp.	RA	Dec.	LogAREA	Mag.	Dist.	Diameter
	0001	0	0.34147	-2.361358	1.77	15.626	2237.1	22.6
	0001	1	0.393433	-2.356566	1.568	17.378	2098.6	16.4
	0001	2	1.034508	-2.35613	1.518	17.38	1849.5	16.1
	0001	3	1.024575	-2.346702	1.602	17.123	1802.2	17.5
	0001	4	0.781704	-2.312119	1.698	17.03	1434.1	19.3
	0002	0	1.112587	29.343813	1.826	16.384	1850.9	17.4
	0002	1	0.62712	29.414143	1.77	16.42	1525.4	16.1
	0002	2	0.467379	29.498917	1.662	16.904	1573.5	15.0
	0002	3	0.467854	29.50506	1.505	16.957	1557.4	15.3
	0002	4	1.149291	29.516792	1.826	16.435	1410.9	18.4

Table 3

 3

			.4: Pair candidates.
	Galaxy	RA	Dec.	Distance	Diameter	Velocity
		(degrees)	(degrees)	(arcsec.)	(arcsec.)	(km s-1)
	CIG 0019	6.067841	14.237	2.0	54.0	5390
	Comp. 20	6.074004	14.272449	129.3	32.7	5396
	Comp. 22	6.130088	14.260384	234.6	39.1	No data
	CIG 0036	12.861758	40.725868	1.4	60.0	5855
	Comp. 8	12.952467	40.762981	282.3	36.5	No data
	CIG 0074	29.330297	28.590328	1.2	36.0	10188
	Comp. 62	29.314213	28.614264	100.0	29.1	10300
	CIG 0178	107.163582	61.305061	1.8	18.0	7610
	Comp. 17	107.11628	61.299938	82.8	10.9	No data
	CIG 0233	122.907974	27.538559	1.7	24.0	11225
	Comp. 21	122.879021	27.524349	104.2	12.1	No data
	CIG 0315	137.892471	-3.536764	2.3	54.0	5088
	Comp. 26	137.853882	-3.599669	265.2	33.3	No data
	CIG 0488	173.924164	73.452034	1.8	84.0	12501
	Comp. 35	174.137344	73.470009	229.6	56.9	12425
	CIG 0533	187.935638	-1.010247	1.6	24.0	21663
	Comp. 93	187.933319	-1.005513	18.8	13.5	21585
	CIG 0683	232.688354	-0.369905	1.1	36.0	11362
	Comp. 53	232.679489	-0.383188	57.1	20.0	21285
	CIG 0934	328.329865	-2.225402	2.2	42.0	5378
	Comp. 33	328.308563	-2.192905	138.8	25.0	No data

Table gathers

 gathers For instance, a companion very close to a CIG would be counted as one regular object by the kth local density estimation but will drastically increase the value of the tidal forces affecting the CIG (see for instance the CIG in the very right part Fig.3.6).Table3.5: The first Unes showing the values of the isolation criteria defined in the previous sections.

		Introduction
	0004	0.000	0.000	0.987	99.000	2.000	1.950	0.264	1.941	0.203	3 . 4 . Q U A N T I F I C A T I O N O F T H E I S O L A T I O N
	0005	1.000	0.000	1.588	12.000	12.000	1.067	1.067	1.038	1.038
	0006	0.000	0.000	1.373	7.000	7.000	0.769	0.751	0.467	0.467
	0007	0.000 Introduction 0.000	0.843	2.000	2.000	0.575	0.573	0.471	0.471
	0008 4.2	Karachentseva Triplets of Galaxies
	4.3	Hickson Compact Groups
	4.4	Abell clusters
	4.5	Discussion
											ai
											co
				55

ail the isolation values obtained for each CIG. There is a good concordance between the different criteria as shown in Fig.

3

.6 (Karachentseva révision, kth local density, tidal forces). Of course each criterion has its own specifîcities and is complementary with respect to the others.

Table 4 .

 4 1: Karachentseva Triplets of Galaxies sample. Our sélection process is fully consistent with the KTG one: we selected the groups in the northern hemisphere (because the POSS-I digitised plates are only available in the northern hemisphere and we wanted to mimic the study done for the CIG). We kept only the true physical groups following the work bySulentic (1997). To fit in our 55 x 55 square arcminutes fields, the recession velocities had to be greater than 4,687 km s-1. It remained 34 Hickson Compact Groups. The coordinates, major axis and velocity are those of the galaxy on which the isolation criteria are applied are shown Table4.2.

	KTG	RA	Dec	Major axis	Velocities
	number	(degrees)	(degrees)	(arcmin.)	(km s-1)
		14.412716	43.800764	1.4	5539
		19.018667	46.730500	0.8	5602
		20.627667	39.199278	0.6	8084
		21.090833	32.224167	1.0	5214
		48.980138	37.154116	0.6	6168
		105.614000	86.579556	0.9	5000
		101.516492	43.845451	0.4	6379
		106.753208	44.849694	1.0	15339
		116.618958	58.962556	1.4	6684
		156.854215	1.241640	0.3	9148
		160.434293	21.185364	0.8	7461
		161.774101	7.237705	0.4	6395
		164.880292	75.191278	1.2	7392
		167.232042	26.610278	1.3	6559
		170.194057	0.470549	0.5	7151
		171.946667	7.987778	1.5	6251
		181.180579	31.177281	0.9	7454
		185.258643	39.899982	0.55	6914
		188.779417	63.960000	0.6	10890
		199.494339	4.403461	1.7	6192
		204.618779	0.510336	0.8	6612
		205.917250	3.896389	1.4	6810
		206.555250	-3.384694	0.7	6728
		209.305000	12.021250	0.8	6309
		210.519975	-1.357981	1.2	7400
		215.667333	6.166833	1.1	6650
		216.825963	4.802831	2.2	8353
		220.878375	11.202694	1.0	8438
		228.899750	69.315806	0.85	6959
		230.075884	3.518260	0.6	11216
		230.732387	-1.356472	0.2	8427
		235.874542	4.794444	1.3	8217
		254.361458	40.735628	0.85	8770
		315.020105	9.582957	1.4	9495
		328.931614	5.807938	0.7	8952
		341.040706	9.989141	0.6	7632
		342.169400	27.611700	1.3	9918
		347.662250	9.188778	0.5	11850
		348.764185	18.973441	1.1	5093
		350.389583	27.118056	0.9	6134
		0.158083	28.384556	1.1	9084

Table 4 .

 4 2: Hickson Compact Groups sample.

	HCG	RA	Dec	Major axis	Velocity
	number	(degrees)	(degrees)	(arcmin.)	(km s-1)
	1	6.529708	25.725194	1.25	10237
	8	12.392292	23.578250	0.9	16077
		21.590750	34.703028	3.0	5189
		31.971167	2.167611	1.1	6967
		33.52135	13.31104	0.36	18228
		41.050292	26.099389	0.48	14477
		50.178917	-1.108583	1.3	6285
		77.698375	18.019667	0.37	7464
		131.338480	44.520873	0.3	15919
		142.365458	-1.345722	0.35	21119
		156.442792	13.716861	1.0	9692
		164.173375	67.184750	0.48	9937
		169.276667	54.917139	0.20	> 30000
		170.609792	24.299139	1.33	7626
		173.029000	70.815472	0.44	16070
		173.194333	52.940861	1.23	8245
		175.546208	10.277750	1.4	6138
		204.659500	57.312361	0.45	20688
		208.874000	25.073667	1.58	8856
		211.041851	33.337530	1.2	8238
		221.972459	19.076982	0.5	12506
		229.853042	20.896278	0.82	12255
		230.376625	21.190639	0.73	12538
		232.948250	7.308222	0.7	10088
		239.829500	65.232722	0.85	8975
		247.093217	32.849311	0.9	11177
		248.901286	6.265361	0.26	15560
		251.095095	77.838748	0.59	16654
		282.576860	73.351452	0.53	11155
		348.816699	18.961797	1.4	5072
		349.306500	18.708167	1.0	12045
	95	349.875208	9.508222	0.88	11879
		0.158083	28.384556	1.1	8705
	100	0.333208	13.111250	1.0	5366

to Table

4

.3: ACO clusters (left) and primary galaxies selected (right).

Table 5 .

 5 1: The vast majority of the companions are Galaxy.

	Database	Number of	Number of	Percentage of
	or survey	redshifts	matched objects	Galaxy
	NED	8024	35317	99.97%
	hyperLEDA	11608	25614	99.99%
	SDSS	12166	12166	99.79%
	CfA (velocity)	8864	9103	99.86%
	2dF	3018	3018	-
	UZC	1461	1488	-
	UZC J2000	1445	1485	-
	CfA2	866	866	100%
	CfAl	106	106	100%
	NOG2	67	67	-
	NOG4	66	66	-
	SSRS2	50	50	-

Table 5 .

 5 2: Classification of the isolation.

		Very isol.	Isol.	Quite isol.	Poorly isol.	Interacting
	Tidal forces	0	1	2	3
	Num. of CIGs	28	333	446	117	26

  , hence left apart. We finally ended up with 224 late-type galaxies or lenticulars (SOa included). It is still a rather big

	lonization occurs
	t t	?
	sample allowing statistical studies of the properties of isolated spiral galaxies
	in the local Universe.
	The observations are not complété since we only recently slightly change
	our initial strategy: we incorporate the CIGs with Karachentseva's isolation
	codes 1 & 2. The list of the 24 galaxies which are still to be observed are
	given in the Appendix A, Table A.2.

Table 8

 8

	.1 reports information about the main characteristics of the se
	lected galaxies, along with some technical indications. The PA, inclination
	and rotation direction listed are those used to run the programs (24 counter-
	clockwise, 19 clockwise).
	Spécial notes on individual galaxies:

  ity, from central HII régions: CIGs 0116, 0250, 1039 and Starburst Nucléus Galaxy (SBNG): CIG 0575 to LINER, Seyfert 2 or Seyfert 3: CIGs 0359, 0712, 1004. There is a very good correspondance between our observations and the HII activities listed in NED (which use the spectra of the AGN to

  : 1081.34 876.00 cl> imcopy Im/dg0744rG.fit[826:1337,621:1132] Im/cig0744rG512.fit cl> imcopy Im/cig0744Ha-rG.fit[826:1337,621:1132] Im/cig0744Ha-rG512.fit

	A.3 a typical file of coordinates "ali0744-2H.coo", the first two columns are the Ha galaxies with V < 1500 km s 1 ap> display Im/cig0744rG.fit 1 The simulations were conducted by
	x and y coordinates of the reference stars always ap> qphot Im/cig0744rG.fit	Françoise Combes.
	ap> txdump cig0744Ha.fit.mag,l flux > c0744Ha.flu
	CIG ap> txdump cig0744rG.fit.mag.l flux > c0744rG.flu UGC or NGC name Velocity
	0105 178.0 paste c0744rG.flu c0744Ha.flu > c0744flux.gnu UGC 01913 254.3 314.2 399.9	553
	0112 481.0 gnuplot> f(x) = a*x + b 557.4 770.9 857.0	UGC 02082	696
	0121 1417.4 gnuplot> fit f(x) "c0744flux.gnu" via a, b UGC 02455 1493.6 889.7 975.5 1592.8 1577.7 1516.4 1663.5 gnuplot> plot "c0744flux.gnu", f(x)	375
				0180	UGC 03734	974
	1761.2	234.1	1684.6	320.1
				0235	UGC 04274	431
	0239 = 0.04724 0265 cl> cl < cig0744-bfstc.cl # a # b = -0.1075	UGC 04305 +/-0.0004183 142 UGC 04499 691 +/-0.5568	(0.8855%) (517.9%)
	0428 imcopy TMP/c0744_001H6607-bfst.fit TMP/c0744_001H6607-bfstc.fit UGC 05789 739 ap> imarith Iin/cig0744rG.fit * 0.047 Im/cig0744rG-scaled.fit
	0434 0656 geomap ali0744-2H coo ali0744-2H UGC 05829 UGC 09649 data 1 2048 1 2048 629 447 ap> imarith Im/dg0744Ha.fit -Im/cig0744rG-scaled.fit Im/cig0744Ha-rG.fit > ali0744-2H.log
	0699 geomap ali0744-3H coo ali0744-3H UGC 09992 data 1 2048 1 2048 427	> ali0744-3H.log
	B.2.10	Final images
	0748 geomap ali0744-lR coo ali0744-lR UGC 10445 data 1 2048 1 2048 963	> ali0744-lR.log
	0813 geomap ali0744-2R coo ali0744-2R UGC 10897 data 1 2048 1 2048 1313 Stamps of 512 x 512 pixels	> ali0744-2R.log
	0850 geomap ali0744-3R coo ali0744-3R UGC 11218 data 1 2048 1 2048 1484	> ali0744-3R.log
				0855	UGC 11300	467
				0947	UGC 11914	952
	0105 geotran TMP/c0744_002H6607-bfst.fit TMP/c0744_002H6607-bfstc.fit ali0744-2H.data ali0744-2H.c NGC 0925 553
	0197 geotran TMP/c0744_003H6607-bfst.fit TMP/c0744_003H6607-bfstc.fit ali0744-3H.data ali0744-3H.c NGC 2403 131 Cleaning
	0347 geotran TMP/c0744_001rGunn-bfst.fit TMP/c0744_001rGmm-bfstc.fit ali0744-lR.data ali0744-lR.c NGC 2903 556 cl> imedit Im/cig0744rG512.fit Im/cig0744rG512cl.fit
	0442 geotran TMP/c0744_002rGunn-bfst.fit TMP/c0744_002rGunn-bfstc.fit ali0744-2R.data ali0744-2R.c NGC 3359 1014 cl> imcopy Im/cig0744Ha-rG512.fit Im/dg0744Ha-rG512d.fit # already
	0523 geotran TMP/c0744_003rGunn-bfst.fit TMP/c0744_003rGunn-bfstc.fit ali0744-3R.data ali0744-3R.c NGC 4236 clean
				0610	NGC 5457	241
	Final Images	0691	NGC 5964	1447
	0109 Point Spread Function UGC 01983 # flip around the X-axis B.2.7	611
	0121 0139 0175 cl> imcopy Im/cig0744rG512cl.fit[*,-*] Im/c0744R.fit UGC 02455 381 UGC 02947 856 1201 UGC 03580 TMP/c0744_001H6607-bfstc.fit 11.05 TMP/c0744_002H6607-bfstc.fit 12.75 <-reference image cl> imcopy Im/cig0744Ha-rG512cl.fit[*,-*] Im/c0744H.fit
	0180 TMP /c0744_003H6607-bfstc.fit 11.60 UGC 03734	974
	0224 TMP/c0744_001rGunn-bfstc.fit 9.80 UGC 04165	516
	0235 TMP /c0744_002rGunn-bfstc.fit 11.35 UGC 04274	447
	0265 TMP /c0744_003rGunn-bfstc.fit 11.35 UGC 04499	692
	0300 cl> display TMP/c0744_002H6607-bfstc.fit 1 fi+ UGC 04781	1442
	0388 cl> rimcursor > starsPsf0744.1is UGC 05373	301
	0434 cl> cl < cig0744-bfstcp.cl	UGC 05829	629
				0549	UGC 07901	805
	0624 psfmatch.psfdata="starsPsf0744.lis" UGC 09179	305
	0656 psfmatch.reference="TMP/c0744_002H6607-bfstc.fit" UGC 09649 447
				0682	UGC 09866	435
	imcopy TMP/c0744_002H6607-bfstc.fit Im/c0744_002H6607-bfstcp.fit
				0691	UGC 09935	1450
	Continuée! on next page psfmatch TMP/c0744_001H6607-bfstc.fit output="Im/c0744_001H6607-bfstcp.fit

centre

Table C .

 C l: Initial conditions parameters.

	Run		Mb		Md	r h	Mh	F r gas	fel
		kpc	M©	kpc	M©	kpc	M©	%
	Run 0	1.1	2.5el0	4.4	8.0el0	16.	7.2el0	14	0.65
	Run 1	1.1	6.8el0	4.4	8.0el0	16.	11.8el0	14	0.65
	Run 2	1.1	6.8el0	4.4	8.0el0	16.	11.8el0	14	0.85

2The full table will be available in electronic form at the AMIGA web site.

other pair candidates having velocity information, 3 CIGs are physically associated with their companions (CIGs 0074, 0488, 0533) while this is not the case for CIG 0683 (velocity différence of ~10,000 km s-1).Unfortunately, no velocities are available for the companions of the

remaining pairs(CIGs 0036, 0178, 0233, 0315, 0934). But, as 4 over 5 pair candidates appeared to be real pairs when the velocity is known, we can expect that, again, about 80% of the 5 pair candidates would be physically bounded.

Radius (kpc)

Ha 1.9GyrHa 2.4Gyr

Ha 1.4GyrHa 1.6Gyr

C.l. Stars Gas 0.3Gyr Stars Gas 0.7Gyr

Ha: There is a quite well defined ring which was not seen in the r Gunn.

There is also a strong central émission, but no émission at ail along the bar. The torques are noisy because of the very clumpy aspect of the galaxy. I give here the details of the scripts to reduce a whole campaign quite automatically, and some tips that might be usefull.