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Ram pressure stripping is perhaps the most efficient mechanism for removing gas and quenching galaxies in dense environments, as they move through the intergalactic medium. Extreme examples of on-going ram pressure stripping are known as jellyfish galaxies, characterized by a tail of stripped material that can be directly observed in multiple wavelengths. Using the largest homogeneous broad-band optical jellyfish candidate sample in local clusters known to date, we measure the angle between the direction of the tails visible in the galaxies, and the direction towards the host cluster centre. We find that 33 per cent of the galaxy tails point away from the cluster centre, 18  per cent point towards the cluster centre, and 49  per cent point elsewhere. Moreover, we find stronger signatures of ram pressure stripping happening on galaxies with a tail pointing away and towards the cluster centre, and larger velocity dispersion profiles for galaxies with tails pointing away. These results are consistent with a scenario where ram pressure stripping has a stronger effect for galaxies following radial orbits on first infall. The results also suggest that in many cases, radially infalling galaxies are able to retain their tails after pericenter and continue to experience significant on-going ram pressure stripping. We further constrain the lifespan of the optical tails from the moment they first appear to the moment they disappear, by comparing the observed tail directions with matched N -body simulations through Bayesian parameter estimation. We obtain that galaxy tails appear for the first time at |$\sim 1.16$| R |$_{200}$| and disappear |$\sim 660$| Myr after pericenter. [ABSTRACT FROM AUTHOR]

Recent observations have shown that the environmental quenching of galaxies at z ∼ 1 is qualitatively different to that in the local Universe. However, the physical origin of these differences has not yet been elucidated. In addition, while low-redshift comparisons between observed environmental trends and the predictions of cosmological hydrodynamical simulations are now routine, there have been relatively few comparisons at higher redshifts to date. Here we confront three state-of-the-art suites of simulations (BAHAMAS+MACSIS, EAGLE+Hydrangea, IllustrisTNG) with state-of-the-art observations of the field and cluster environments from the COSMOS/UltraVISTA and GOGREEN surveys, respectively, at z ∼ 1 to assess the realism of the simulations and gain insight into the evolution of environmental quenching. We show that while the simulations generally reproduce the stellar content and the stellar mass functions of quiescent and star-forming galaxies in the field, all the simulations struggle to capture the observed quenching of satellites in the cluster environment, in that they are overly efficient at quenching low-mass satellites. Furthermore, two of the suites do not sufficiently quench the highest mass galaxies in clusters, perhaps a result of insufficient feedback from AGN. The origin of the discrepancy at low stellar masses (⁠|$M_* \lesssim 10^{10}$| M⊙), which is present in all the simulations in spite of large differences in resolution, feedback implementations, and hydrodynamical solvers, is unclear. The next generation of simulations, which will push to significantly higher resolution and also include explicit modelling of the cold interstellar medium, may help us to shed light on the low-mass tension. [ABSTRACT FROM AUTHOR]

We use photometric redshifts and statistical background subtraction to measure stellar mass functions in galaxy group-mass (4.5−8 × 1013 M⊙) haloes at 1 < z < 1.5. Groups are selected from COSMOS and SXDF, based on X-ray imaging and sparse spectroscopy. Stellar mass (M stellar) functions are computed for quiescent and star-forming galaxies separately, based on their rest-frame UVJ colours. From these we compute the quiescent fraction and quiescent fraction excess (QFE) relative to the field as a function of M stellar. QFE increases with M stellar, similar to more massive clusters at 1 < z < 1.5. This contrasts with the apparent separability of M stellar and environmental factors on galaxy quiescent fractions at z ∼ 0. We then compare our results with higher mass clusters at 1 < z < 1.5 and lower redshifts. We find a strong QFE dependence on halo mass at fixed M stellar; well fit by a logarithmic slope of d(QFE)/dlog (M halo) ∼ 0.24 ± 0.04 for all M stellar and redshift bins. This dependence is in remarkably good qualitative agreement with the hydrodynamic simulation bahamas , but contradicts the observed dependence of QFE on M stellar. We interpret the results using two toy models: one where a time delay until rapid (instantaneous) quenching begins upon accretion to the main progenitor ('no pre-processing') and one where it starts upon first becoming a satellite ('pre-processing'). Delay times appear to be halo mass-dependent, with a significantly stronger dependence required without pre-processing. We conclude that our results support models in which environmental quenching begins in low-mass (<1014M⊙) haloes at z > 1. [ABSTRACT FROM AUTHOR]

We present the first public data release of the GOGREEN (Gemini Observations of Galaxies in Rich Early Environments) and GCLASS (Gemini CLuster Astrophysics Spectroscopic Survey) surveys of galaxies in dense environments, spanning a redshift range 0.8 < z < 1.5. The surveys consist of deep, multiwavelength photometry and extensive Gemini GMOS spectroscopy of galaxies in 26 overdense systems ranging in halo mass from small groups to the most massive clusters. The objective of both projects was primarily to understand how the evolution of galaxies is affected by their environment, and to determine the physical processes that lead to the quenching of star formation. There was an emphasis on obtaining unbiased spectroscopy over a wide stellar mass range (M ≳ 2 × 1010 M⊙), throughout and beyond the cluster virialized regions. The final spectroscopic sample includes 2771 unique objects, of which 2257 have reliable spectroscopic redshifts. Of these, 1704 have redshifts in the range 0.8 < z < 1.5, and nearly 800 are confirmed cluster members. Imaging spans the full optical and near-infrared wavelength range, at depths comparable to the UltraVISTA survey, and includes Hubble Space Telescope /Wide Field Camera 3 F160W (GOGREEN) and F140W (GCLASS). This data release includes fully reduced images and spectra, with catalogues of advanced data products including redshifts, line strengths, star formation rates, stellar masses, and rest-frame colours. Here, we present an overview of the data, including an analysis of the spectroscopic completeness and redshift quality. [ABSTRACT FROM AUTHOR]

We present results on the environmental dependence of the star-forming galaxy main sequence in 11 galaxy cluster fields at 1.0 < z < 1.5 from the Gemini Observations of Galaxies in Rich Early Environments Survey (GOGREEN) survey. We use a homogeneously selected sample of field and cluster galaxies whose membership is derived from dynamical analysis. Using [ |$\rm{O{\small II}}$| ]-derived star formation rates (SFRs), we find that cluster galaxies have suppressed SFRs at fixed stellar mass in comparison to their field counterparts by a factor of 1.4 ± 0.1 (∼3.3σ) across the stellar mass range: 9.0 < log (M */M⊙) < 11.2. We also find that this modest suppression in the cluster galaxy star-forming main sequence is mass and redshift dependent: the difference between cluster and field increases towards lower stellar masses and lower redshift. When comparing the distribution of cluster and field galaxy SFRs to the star-forming main sequence, we find an overall shift towards lower SFRs in the cluster population, and note the absence of a tail of high SFR galaxies as seen in the field. Given this observed suppression in the cluster galaxy star-forming main sequence, we explore the implications for several scenarios such as formation time differences between cluster and field galaxies, and environmentally induced star formation quenching and associated time-scales. [ABSTRACT FROM AUTHOR]

We present the first results of a new spectroscopic survey of the cluster Abell 85 targeting 1466 candidate cluster members within the central ~1 deg² of the cluster and having magnitudes mr < 20.5 using the VIsible MultiObject Spectrograph on the VLT and the Hydra spectrograh on WIYN. A total of 520 galaxies are confirmed as either relaxed cluster members or part of an infalling population. A significant fraction are low mass; the median stellar mass of the sample is 109.6.6⊙, and 25 per cent have stellar masses below 109⊙ (i.e. 133 dwarf galaxies). We also identify seven active galactic nuclei (AGN), four of which reside in dwarf host galaxies. We probe the evolution of star formation rates, based on Ha emission and continuum modelling, as a function of both mass and environment. We find that more starforming galaxies are observed at larger clustercentric distances, while infalling galaxies show evidence for recently enhanced star-forming activity. Main-sequence galaxies, defined by their continuum star formation rates, show different evolutionary behaviour based on their mass. At the low-mass end, the galaxies have had their star formation recently quenched, while more massive galaxies show no significant change. The time-scales probed here favour fast quenching mechanisms, such as ram-pressure stripping. Galaxies within the green valley, defined similarly, do not show evidence of quenching. Instead, the low-mass galaxies maintain their levels of star-forming activity, while the more massive galaxies have experienced a recent burst. [ABSTRACT FROM AUTHOR]

Context. There is some disagreement about the abundance of faint galaxies in high-redshift clusters, with contradictory results in the literature arising from studies of the optical galaxy luminosity function (GLF) for small cluster samples. Aims. We compute GLFs for one of the largest medium-to-high-redshift (0.4 ≤ z < 0.9) cluster samples to date in order to probe the abundance of faint galaxies in clusters. We also study how the GLF depends on cluster redshift, mass, and substructure and compare the GLFs of clusters with those of the field. We separately investigate the GLFs of blue and red-sequence (RS) galaxies to understand the evolution of different cluster populations. Methods. We calculated the GLFs for 31 clusters taken from the DAFT/FADA survey in the B,V,R, and I rest-frame bands. We used photometric redshifts computed from BVRIZJ images to constrain galaxy cluster membership. We carried out a detailed estimate of the completeness of our data. We distinguished the red-sequence and blue galaxies using a V - I versus I colour-magnitude diagram. We studied the evolution of these two populations with redshift. We fitted Schechter functions to our stacked GLFs to determine average cluster characteristics. Results. We find that the shapes of our GLFs are similar for the B,V,R, and I bands with a drop at the red GLF faint ends that is more pronounced at high redshift: αred ~ -0.5 at 0.40 ≤ z < 0.65 and αred > 0.1 at 0.65 ≤ z < 0.90. The blue GLFs have a steeper faint end (αblue ~ -1.6) than the red GLFs, which appears to be independent of redshift. For the full cluster sample, blue and red GLFs meet at MV = -20, MR = -20.5, and MI = -20.3. A study of how galaxy types evolve with redshift shows that late-type galaxies appear to become early types between z ~ 0.9 and today. Finally, the faint ends of the red GLFs of more massive clusters appear to be richer than less massive clusters, which is more typical of the lower redshift behaviour. Conclusions. Our results indicate that these clusters form at redshifts higher than z = 0.9 from galaxy structures that already have an established red sequence. Late-type galaxies then appear to evolve into early types, enriching the red sequence between this redshift and today. This effect is consistent with the evolution of the faint-end slope of the red sequence and the galaxy type evolution that we find. Finally, faint galaxies accreted from the field environment at all redshifts might have replaced the blue late-type galaxies that converted into early types, explaining the lack of evolution in the faint-end slopes of the blue GLFs. [ABSTRACT FROM AUTHOR]

Focuses on the Galaxy Evolution in Groups and Clusters workshop held from September 5-7, 2002 in Europe. Aim of the workshop; Sources of financial support; Names of participants.

We discuss the properties of the galaxies in about 60 rich, nearby clusters, using kinematic data from the ESO Nearby Abell Cluster Survey, combined with new imaging data. The images were used to classify the galaxies, and to recalibrate the galaxy types derived from the ENACS spectra; this yields galaxy-type estimates for about 4800 galaxies. For about 1200 galaxies, a bulge/disk decomposition could be made, which yields sizes and luminosities of bulges and disks. From the projected radial distances and relative l.o.s.-velocities we derived the galaxy ensembles with significantly different phase-space distributions. We find that galaxies in and outside substructure must be distinguished. The morphological composition of the substructures appears to vary with projected radius. Outside substructures, 4 galaxy ensembles must be defined: viz. the brighest Es, the other early-type galaxies, the early spirals (Sa-Sb), and the late spirals (including the emission-line galaxies). We also study the morphology-density relation, and we find that the segregation of the late spirals is driven mostly by global factors, while the segregation of Es, S0s and early spirals is driven mostly by local density. The properties of early spirals and S0s support the picture in which early spirals transform into S0s, while the properties of the late spirals do not support such a relation. [ABSTRACT FROM AUTHOR]