We have surveyed the core regions of the z=1.46 cluster XCS J2215.9-1738 withthe Atacama Large Millimeter Array (ALMA). We obtained high spatial resolutionobservations with ALMA of the 1.2 mm dust continuum and molecular gas emissionin the central regions of the cluster. These observations detect 14 significantmillimetre sources in a region with a projected diameter of just ~500 kpc(~1'). For six of these galaxies we also obtain 12CO(2-1) and 12CO(5-4) linedetections confirming them as cluster members and a further two millimetregalaxies have archival spectroscopic redshifts which also place them in thecluster. An additional ~4 millimetre galaxies have photometric redshiftsconsistent with cluster membership, suggesting that the bulk (>12/14,~85%) ofthe submillimetre sources in the field are in fact luminous infrared galaxieslying within this young cluster. We then use our sensitive new observations toconstrain the dust-obscured star formation activity and cold molecular gaswithin this well-studied example of a z~1.5 cluster. We find evidence that thecooler dust and gas components of these galaxies may have been influenced bytheir environment reducing the gas reservoir for their subsequent starformation. We conclude that these actively star-forming galaxies have thedynamical masses and stellar population ages expected for the progenitors ofmassive, early-type galaxies in local clusters.

We present ALMA CO (2-1) detections in 11 gas-rich cluster galaxies at z~1.6,constituting the largest sample of molecular gas measurements in z>1.5 clustersto date. The observations span three galaxy clusters, derived from the SpitzerAdaptation of the Red-sequence Cluster Survey. We augment the >5sigmadetections of the CO (2-1) fluxes with multi-band photometry, yielding stellarmasses and infrared-derived star formation rates, to place some of the firstconstraints on molecular gas properties in z~1.6 cluster environments. Wemeasure sizable gas reservoirs of 0.5-2x10^11 solar masses in these objects,with high gas fractions and long depletion timescales, averaging 62% and 1.4Gyr, respectively. We compare our cluster galaxies to the scaling relations ofthe coeval field, in the context of how gas fractions and depletion timescalesvary with respect to the star-forming main sequence. We find that our clustergalaxies lie systematically off the field scaling relations at z=1.6 towardenhanced gas fractions, at a level of ~4sigma, but have consistent depletiontimescales. Exploiting CO detections in lower-redshift clusters from theliterature, we investigate the evolution of the gas fraction in clustergalaxies, finding it to mimic the strong rise with redshift in the field. Weemphasize the utility of detecting abundant gas-rich galaxies in high-redshiftclusters, deeming them as crucial laboratories for future statistical studies.

With the aim of understanding the effect of the environment on the starformation history and morphological transformation of galaxies, we present adetailed analysis of the colour, morphology and internal structure of clusterand field galaxies at $0.4 \le z \le 0.8$. We use {\em HST} data for over 500galaxies from the ESO Distant Cluster Survey (EDisCS) to quantify how thegalaxies' light distribution deviate from symmetric smooth profiles. Wevisually inspect the galaxies' images to identify the likely causes for suchdeviations. We find that the residual flux fraction ($RFF$), which measures thefractional contribution to the galaxy light of the residuals left aftersubtracting a symmetric and smooth model, is very sensitive to the degree ofstructural disturbance but not the causes of such disturbance. On the otherhand, the asymmetry of these residuals ($A_{\rm res}$) is more sensitive to thecauses of the disturbance, with merging galaxies having the highest values of$A_{\rm res}$. Using these quantitative parameters we find that, at a fixedmorphology, cluster and field galaxies show statistically similar degrees ofdisturbance. However, there is a higher fraction of symmetric and passivespirals in the cluster than in the field. These galaxies have smoother lightdistributions than their star-forming counterparts. We also find that whilealmost all field and cluster S0s appear undisturbed, there is a relativelysmall population of star-forming S0s in clusters but not in the field. Thesefindings are consistent with relatively gentle environmental processes actingon galaxies infalling onto clusters.

The dense environment of galaxy clusters strongly influences the nature ofgalaxies. Here, we study the cause of the size distribution of a sample of 560spectroscopic members spanning a wide dynamical range down to 10^8.5 M_sol(log(M)-2) in the massive CLASH cluster MACSJ 1206.2-0847 at z~0.44. We useSubaru SuprimeCam imaging covering the highest-density core out to the infallregions (3 virial radii) to look for cluster-specific effects. We also compareour measurements to a compatible large field study in order to span extremeenvironmental densities. This paper presents the trends we identified forcluster galaxies divided by their colors into star-forming and quiescentgalaxies and into distinct morphological types (using S\'ersic index andbulge/disk decompositions). We observed larger sizes for early type and smallersizes for massive late type galaxies in clusters in comparison to the field. Weattribute this to longer quenching timescales of more massive galaxies in thecluster. Our analysis further revealed an increasing importance of recentlyquenched transition objects ("red disks"). This is a virialized populationfound at higher cluster-centric radii with sizes similar to the quiescent,spheroid-dominated population of the cluster center, but with disks stillin-tact. The mass-size relation of cluster galaxies may therefore be understoodas the consequence of a mix of progenitors formed at different quenchingepochs. We also find that galaxy sizes smoothly decreasing as a function ofbulge fraction. At same bulge-to-total ratio and same stellar mass, quiescentgalaxies are smaller than star-forming galaxies. This is likely because of afading of the outskirts of the disk, which we saw in comparing sizes of theirdisk-components. Ram-pressure stripping of the cold gas and other forms of moregradual gas starvation are likely responsible for this observation.