The Relation between Galaxy Activity and the Dynamics of Compact Groups of Galaxies

Peer reviewe

Infrared Surface Brightness Analysis of Galaxies in Compact Groups

Images of 7 Compact groups of galaxies (CG) were obtained using the 2.1m telescope in San Pedro Martir (B.C. Mexico) equipped with the NIR camera CAMILA. The NIR images trace the mass of the galaxies, through the oldest and more evolved stellar populations. The goal of this project is to search for evidence of morphological perturbations correlated with the level of activity (AGN or star formation) of the galaxies. We find that the level of perturbation is well correlated with activity observed in optical spectrocopy (Coziol et al. 2004). Evidence for perturbations decreases from more active groups to less active groups, confirming the classification. Our analysis suggests that galaxies in more active groups are undergoing important transformations due to interaction and merging and that the whole groups is on a merger path. Galaxies in less active CG have gone through similar processes in the recent past and are either in a final merging phase or in equilibrium due to a more massive halo of dark matter.Comment: 2 pages, 1 figure, Proc. ESO Workshop "Groups of galaxies in the nearby Universe", Santiago, Chile, 5-9 Dec. 2005, ESO Astrophysics Symposia, eds. I. Saviane, V. Ivanov & J. Borissova, Springer-Verla

Environmental effects on galaxy evolution. II: quantifying the tidal features in NIR-images of the cluster Abell 85

This work is part of a series of papers devoted to investigate the evolution of cluster galaxies during their infall. In the present article we imaged in NIR a selected sample of galaxies through- out the massive cluster Abell 85 (z = 0.055). We obtained (JHK) photometry for 68 objects, reaching 1 mag/arcsec^2 deeper than 2MASS. We use these images to unveil asymmetries in the outskirts of a sample of bright galaxies and develop a new asymmetry index, alpha_An, which allows to quantify the degree of disruption by the relative area occupied by the tidal features on the plane of the sky. We measure the asymmetries for a subsample of 41 large area objects finding clear asymmetries in ten galaxies, most of them being in groups and pairs projected at different clustercentric distances, some of them located beyond R500 . Combining information on the Hi-gas content of blue galaxies and the distribution of sub-structures across Abell 85, with the present NIR asymmetry analysis, we obtain a very powerful tool to confirm that tidal mechanisms are indeed present and are currently affecting a fraction of galaxies in Abell 85. However, when comparing our deep NIR images with UV-blue images of two very disrupted (jellyfish) galaxies in this cluster, we discard the presence of tidal 1 interactions down to our detection limit. Our results suggest that ram-pressure stripping is at the origin of such spectacular disruptions. We conclude that across a complex cluster like Abell 85, environment mechanisms, both gravitational and hydrodynamical, are playing an active role in driving galaxy evolution.Comment: 30 pages, 13 figures, Accepted for Publication in A

Highly perturbed molecular gas in infalling cluster galaxies : the case of CGCG97-079

Date of Acceptance: 14/07/2015We report on CO (J = 2 → 1) mapping with the IRAM 30-m HEtrodyne Receiver Array (HERA) of CGCG 97-079, an irregular galaxy in the merging galaxy cluster Abell 1367 (z = 0.022). We find that ˜80 per cent of the detected CO (J = 2 → 1) is projected within a 16 arcsec2 (6.5 kpc2) region to the north and west of the optical/NIR centre, with the intensity maximum offset ˜10 arcsec (4 kpc) NW of the optical/NIR centre and ˜7 arcsec (3 kpc) south-east of the H I intensity maximum. Evolutionary synthesis models indicate CGCG 97-079 experienced a burst of star formation ˜108 yr ago, most likely triggered by a tidal interaction with CGCG 97-073. For CGCG 97-079 we deduce an infall velocity to the cluster of ˜1000 km s-1 and moderate ram pressure (Pram ≈ 10-11 dyne cm-2). The observed offset in CGCG 97-079 of the highest density H I and CO (J = 2 → 1) from the stellar components has not previously been observed in galaxies currently undergoing ram pressure stripping, although previous detailed studies of gas morphology and kinematics during ram pressure stripping were restricted to significantly more massive galaxies with deeper gravitational potential wells. We conclude the observed cold gas density maxima offsets are most likely the result of ram pressure and/or the high-speed tidal interaction with CGCG 97-073. However ram pressure stripping is likely to be playing a major role in the perturbation of lower density gas.Peer reviewe

The HI distribution of spiral galaxies in the cluster A 262

We present results of an HI survey of the cluster of galaxies Abell 262, using the Westerbork Synthesis Radio Telescope (WSRT). Eleven galaxies were detected in five fields. In a few cases the gas in these galaxies shows an asymmetrical distribution; the most likely explanation is the interaction between the cluster medium and the gaseous disks. Only two of the detected galaxies are slightly HI-deficient. At 40" to the West of CGCG 160 - 049 we tentatively detect what may be an associated HI cloud. The total mass of this cloud is 2.5 10(8) M., and no optical counterpart has yet been found

The strong transformation of spiral galaxies infalling into massive clusters at z~0.2

We describe two peculiar galaxies falling into the massive galaxy clusters Abell 1689 (z~0.18) and 2667 (z~0.23) respectively. Hubble Space Telescope images show extraordinary trails composed of bright blue knots (-16.5<M<-11.5 mag) and stellar streams associated with each of these systems. Combining optical, near and mid-infrared and radio observations we prove that while both galaxies show similar extended trails of star-forming knots, their recent star formation histories are different. One (~L*) is experiencing a strong burst of star formation, appearing as a rare example of a luminous infrared cluster galaxy. In comparison, the other (~ 0.1 L*) has recently ceased its star formation activity. Our model suggests that the morphologies and star formation in these galaxies have been influenced by the combined action of tidal interaction (likely with the cluster potential) and of ram pressure with the intracluster medium. These results can be used to gain more insights to the origin of S0s, dwarf and ultra-compact dwarf (UCD) cluster galaxies