The effect of the environment on the gas kinematics and the structure of distant galaxies

With the aim of distinguishing between possible physical mechanisms acting on galaxies when they fall into clusters, we study the properties of the gas and the stars in a sample of 422 emission-line galaxies from the European Southern Observatory Distant Cluster Survey in different environments up to z∼ 1. We identify galaxies with kinematical disturbances (from emission lines in their 2D spectra) and find that they are more frequent in clusters than in the field. The fraction of kinematically disturbed galaxies increases with cluster velocity dispersion and decreases with distance from the cluster centre, but remains constant with projected galaxy density. We also studied morphological disturbances in the stellar light from Hubble Space Telescope/F814W images, finding that the fraction of morphologically disturbed galaxies is similar in clusters, groups and the field. Moreover, there is little correlation between the presence of kinematically disturbed gas and morphological distortions. For the kinematically undisturbed galaxies, we find that the cluster and field Tully-Fisher relations are remarkably similar. In addition, we find that the kinematically disturbed galaxies show a suppressed specific star formation rate. There is also evidence indicating that the gas discs in cluster galaxies have been truncated, and therefore their star formation is more concentrated than in low-density environments. If spirals are the progenitors of cluster S0s, our findings imply that the physical mechanism transforming cluster galaxies efficiently disturbs the star-forming gas and reduces their specific star formation rate. Moreover, this star-forming gas is either removed more efficiently from the outskirts of the galaxies or is driven towards the centre (or both). In any case, this makes any remaining star formation more centrally concentrated, helping to build the bulges of S0s. These results, in addition to the finding that the transformation mechanism does not seem to induce strong morphological disturbances on the galaxies, suggest that the physical processes involved are related to the intracluster medium, with galaxy-galaxy interactions playing only a limited role in clusters.