ALBERT

Description: By exploiting the data base of early-type galaxy (ETG) members of the WINGS survey of nearby clusters, we address here the long debated question of the origin and shape of the Fundamental Plane (FP). Our data suggest that different physical mechanisms concur in shaping and ‘tilting’ the FP with respect to the virial plane (VP) expectation. In particular, a ‘hybrid solution’ in which the structure of galaxies and their stellar population are the main contributors to the FP tilt seems to be favoured. We find that the bulk of the tilt should be attributed to structural non-homology, while stellar population effects play an important but less crucial role. In addition, our data indicate that the differential FP tilt between the V and K band is due to a sort of entanglement between structural and stellar population effects, for which the inward steepening of colour profiles ( V  –  K ) tends to increase at increasing the stellar mass of ETGs. The same kind of analysis applied to the ATLAS 3 D and Sloan Digital Sky Survey (SDSS) data in common with WINGS ( WSDSS throughout the paper) confirms our results, the only remarkable difference being the less important role that our data attribute to the stellar mass-to-light-ratio (stellar populations) in determining the FP tilt . The ATLAS 3 D data also suggest that the FP tilt depends as well on the dark matter (DM) fraction and on the rotational contribution to the kinetic energy ( V rot /), thus again pointing towards the above-mentioned ‘hybrid solution’. We show that the global properties of the FP, i.e. its tilt and tightness, can be understood in terms of the underlying correlation among mass, structure and stellar population of ETGs, for which, at increasing the stellar mass, ETGs become (on average) ‘older’ and more centrally concentrated. Finally, we show that a Malmquist-like selection effect may mimic a differential evolution of the mass-to-light ratio for galaxies of different masses. This should be taken into account in the studies investigating the amount of the so-called ‘downsizing’ phenomenon.

Description: We analyse the star formation history (SFH) of galaxies as a function of present-day environment, galaxy stellar mass and morphology. The SFH is derived by means of a non-parametric spectrophotometric model applied to individual galaxies at z  ~ 0.04–0.1 in the WIde-field Nearby Galaxy-cluster Survey (WINGS) clusters and the Padova Millennium Galaxy and Group Catalogue (PM2GC) field. The field reconstructed evolution of the star formation rate density (SFRD) follows the values observed at each redshift, except at z  〉 2, where our estimate is ~1.7 higher than the high- z observed value. The slope of the SFRD decline with time gets progressively steeper going from low-mass to high-mass haloes. The decrease of the SFRD since z  = 2 is due to (1) quenching – 50 per cent of the SFRD in the field and 75 per cent in clusters at z  〉 2 originated in galaxies that are passive today – and (2) the fact that the average SFR of today's star-forming galaxies has decreased with time. We quantify the contribution to the SFRD( z ) of galaxies of today's different masses and morphologies. The current morphology correlates with the current star formation activity but is irrelevant for the past stellar history. The average SFH depends on galaxy mass, but galaxies of a given mass have different histories depending on their environment. We conclude that the variation of the SFRD( z ) with environment is not driven by different distributions of galaxy masses and morphologies in clusters and field, and must be due to an accelerated formation in high-mass haloes compared to low-mass ones even for galaxies that will end up having the same galaxy mass today.

Description: In a hierarchical Universe clusters grow via the accretion of galaxies from the field, groups and even other clusters. As this happens, galaxies can lose and/or consume their gas reservoirs via different mechanisms, eventually quenching their star formation. We explore the diverse environmental histories of galaxies through a multiwavelength study of the combined effect of ram-pressure stripping and group ‘processing’ in Abell 963, a massive growing cluster at z = 0.2 from the Blind Ultra Deep H i Environmental Survey (BUDHIES). We incorporate hundreds of new optical redshifts (giving a total of 566 cluster members), as well as Subaru and XMM–Newton data from LoCuSS, to identify substructures and evaluate galaxy morphology, star formation activity, and H i content (via H i deficiencies and stacking) out to 3 x R 200 . We find that Abell 963 is being fed by at least seven groups, that contribute to the large number of passive galaxies outside the cluster core. More massive groups have a higher fraction of passive and H i -poor galaxies, while low-mass groups host younger (often interacting) galaxies. For cluster galaxies not associated with groups we corroborate our previous finding that H i gas (if any) is significantly stripped via ram-pressure during their first passage through the intracluster medium, and find mild evidence for a starburst associated with this event. In addition, we find an overabundance of morphologically peculiar and/or star-forming galaxies near the cluster core. We speculate that these arise from the effect of groups passing through the cluster (post-processing). Our study highlights the importance of environmental quenching and the complexity added by evolving environments.

Description: The growth of brightest cluster galaxies (BCGs) is closely related to the properties of their host cluster. We present evidence for dry mergers as the dominant source of BCG mass growth at z 1 in the XXL 100 brightest cluster sample. We use the global red sequence, Hα emission and mean star formation history to show that BCGs in the sample possess star formation levels comparable to field ellipticals of similar stellar mass and redshift. XXL 100 brightest clusters are less massive on average than those in other X-ray selected samples such as LoCuSS or HIFLUGCS. Few clusters in the sample display high central gas concentration, rendering inefficient the growth of BCGs via star formation resulting from the accretion of cool gas. Using measures of the relaxation state of their host clusters, we show that BCGs grow as relaxation proceeds. We find that the BCG stellar mass corresponds to a relatively constant fraction 1 per cent of the total cluster mass in relaxed systems. We also show that, following a cluster scale merger event, the BCG stellar mass lags behind the expected value from the M cluster –M BCG relation but subsequently accretes stellar mass via dry mergers as the BCG and cluster evolve towards a relaxed state.

Description: An understanding of the mass build-up in galaxies over time necessitates tracing the evolution of cold gas (molecular and atomic) in galaxies. To that end, we have conducted a pilot study called CO Observations with the LMT of the Blind Ultra-Deep H  i Environment Survey (COOL BUDHIES). We have observed 23 galaxies in and around the two clusters Abell 2192 ( z = 0.188) and Abell 963 ( z = 0.206), where 12 are cluster members and 11 are slightly in the foreground or background, using about 28 total hours on the Redshift Search Receiver on the Large Millimeter Telescope (LMT) to measure the 12 CO J = 1 -〉 0 emission line and obtain molecular gas masses. These new observations provide a unique opportunity to probe both the molecular and atomic components of galaxies as a function of environment beyond the local Universe. For our sample of 23 galaxies, nine have reliable detections (S/N ≥ 3.6) of the 12 CO line, and another six have marginal detections (2.0 〈 S/N 〈 3.6). For the remaining eight targets we can place upper limits on molecular gas masses roughly between 10 9 and 10 10 M . Comparing our results to other studies of molecular gas, we find that our sample is significantly more abundant in molecular gas overall, when compared to the stellar and the atomic gas component, and our median molecular gas fraction lies about 1 above the upper limits of proposed redshift evolution in earlier studies. We discuss possible reasons for this discrepancy, with the most likely conclusion being target selection and Eddington bias.

Description: We present the morphology–density and morphology–radius relations ( T – and T – R , respectively) obtained from the WIde-field Nearby Galaxy-cluster Survey (WINGS) data base of galaxies in nearby clusters. Aiming to achieve the best statistics, we exploit the whole sample of galaxies brighter than M V = –19.5 (5504 objects), stacking up the 76 clusters of the WINGS survey altogether. Using this global cluster sample, we find that the T – relation holds only in the inner cluster regions ( R  〈 1/3 R 200 ), while the T – R relation keeps almost unchanged over the whole range of local density. A couple of tests and two sets of numerical simulations support the robustness of these results against the effects of the limited cluster area coverage of the WINGS imaging. The above mentioned results hold for all cluster masses (X-ray luminosity and velocity dispersion) and all galaxy stellar masses ( M * ). The strength of the T – relation (where present) increases with increasing M * , while this effect is not found for the T – R relation. Noticeably, the absence/presence of subclustering determines the presence/absence of the T – relation outside the inner cluster regions, leading us to the general conclusion that the link between morphology and local density is preserved just in dynamically evolved regions. We hypothesize that some mechanism of morphological broadening/redistribution operates in the intermediate/outer regions of substructured (‘non-relaxed’) clusters, producing a strong weakening of the T – relation.

Description: In order to assess whether the environment has a significant effect on galaxy sizes, we compare the mass–size relations of cluster and field galaxies in the 0.4 〈  z  〈 0.8 redshift range from the ESO Distant Cluster Survey (EDisCS) using Hubble Space Telescope images. We analyse two mass-selected samples, one defined using photometric redshifts (10.2 ≤ log M * /M  ≤ 12.0), and a smaller more robust subsample using spectroscopic redshifts (10.6 ≤ log M * /M  ≤ 11.8). We find no significant difference in the size distributions of cluster and field galaxies of a given morphology. Similarly, we find no significant difference in the size distributions of cluster and field galaxies of similar rest-frame B  –  V colours. We rule out average size differences larger than 10–20 per cent in both cases. Consistent conclusions are found with the spectroscopic and photometric samples. These results have important consequences for the physical process(es) responsible for the size evolution of galaxies, and in particular the effect of the environment. The remarkable growth in galaxy size observed from z  ~ 2.5 has been reported to depend on the environment at higher redshifts ( z  〉 1), with early-type/passive galaxies in higher density environments growing earlier. Such dependence disappears at lower redshifts. Therefore, if the reported difference at higher- z is real, the growth of field galaxies has caught up with that of cluster galaxies by z  ~ 1. Any putative mechanism responsible for galaxy growth has to account for the existence of environmental differences at high redshift and their absence (or weakening) at lower redshifts.

Description: Using data from the Sloan Digital Sky Survey (SDSS)-DR7, including structural measurements from 2D surface brightness fits with gim2d , we show how the fraction of quiescent galaxies depends on galaxy stellar mass M * , effective radius R e , fraction of r -band light in the bulge, B / T , and their status as a central or satellite galaxy at 0.01 〈  z  〈 0.2. For central galaxies we confirm that the quiescent fraction depends not only on stellar mass, but also on R e . The dependence is particularly strong as a function of $M_*/R_{\rm e}^\alpha$ , with α ~ 1.5. This appears to be driven by a simple dependence on B / T over the mass range 9 〈 log ( M * /M ) 〈 11.5, and is qualitatively similar even if galaxies with B / T  〉 0.3 are excluded. For satellite galaxies, the quiescent fraction is always larger than that of central galaxies, for any combination of M * , R e and B / T . The quenching efficiency is not constant, but reaches a maximum of ~0.7 for galaxies with 9 〈 log ( M * /M ) 〈 9.5 and R e  〈 1 kpc. This is the same region of parameter space in which the satellite fraction itself reaches its maximum value, suggesting that the transformation from an active central galaxy to a quiescent satellite is associated with a reduction in R e due to an increase in dominance of a bulge component.

Description: We analyse the extended, ionized-gas emission of 24 early-type galaxies (ETGs) at 0 〈  z  〈 1 from the ESO Distant Cluster Survey (EDisCS). We discuss different possible sources of ionization and favour star formation as the main cause of the observed emission. 10 galaxies have disturbed gas kinematics, while 14 have rotating gas discs. In addition, 15 galaxies are in the field, while 9 are in the infall regions of clusters. This implies that, if the gas has an internal origin, this is likely stripped as the galaxies get closer to the cluster centre. If the gas instead comes from an external source, then our results suggest that this is more likely acquired outside the cluster environment, where galaxy–galaxy interactions more commonly take place. We analyse the Tully–Fisher relation of the ETGs with gas discs, and compare them to EDisCS spirals. Taking a matched range of redshifts, M B  〈 –20, and excluding galaxies with large velocity uncertainties, we find that, at fixed rotational velocity, ETGs are 1.7 mag fainter in M B than spirals. At fixed stellar mass, we also find that ETGs have systematically lower specific star formation rates than spirals. This study constitutes an important step forward towards the understanding of the evolution of the complex ISM in ETGs by significantly extending the look-back-time baseline explored so far.

Description: We present the optical spectroscopy for the Blind Ultra Deep H i Environmental Survey (BUDHIES). With the Westerbork Synthesis Radio Telescope, BUDHIES has detected H i in over 150 galaxies in and around two Abell clusters at z ~= 0.2. With the aim of characterizing the environments of the H i -detected galaxies, we obtained multifibre spectroscopy with the William Herschel Telescope. In this paper, we describe the spectroscopic observations, report redshifts and EW[O ii ] measurements for ~600 galaxies, and perform an environmental analysis. In particular, we present cluster velocity dispersion measurements for five clusters and groups in the BUDHIES volume, as well as a detailed substructure analysis.