FEATURED RESULTS:

These are some selected works which members of GaLSSev have conducted or contributed to. Major national and international collaborations related to GaLSSev and associated with the works featured below are highlighted in color, correspondingly. The information on this page may be updated with some delay. Please check regularly.

▲    ALMA CO (2-1) observations of the molecular gas in z~1.6 cluster galaxies from the SpARCS survey allowed the gas kinematic to be resolved. The resulting kinematic maps were analyzed to determine their degree of asymmetry. Two quantities are calculated to characterize this. On one hand, A_vel provides a measure of the amount of asymmetry in the rotation curve with respect to the minor axis. On the other hand, Δ χ²_reduced quantifies the difference in goodness of fit when two parabolas are fit to the receding and approaching sides of the galaxy, respectively, and then the same fit is compared with the oposite side of the galaxy. See Cramer et al. (2023) for more details on how these quantities are calculated. The results for the cluster galaxies in our sample (green solid circles) are compared with estimates for simulated field galaxies (orange symbols). While a linear relationship is observed between A_vel and Δ χ²_reduced, cluster galaxies are on average more kinematically asymmetric than field galaxies. This suggests the influence of dense environments on the evolution of galaxy properties being already at play at high redshifts. Figure taken from Cramer et al. (2023). Work in collaboration with SpARCS/GCLASS.



▲    The quenching effect of the cluster environment at z~1 on galaxies as shown by state-of-the-art, cosmological hydrodynamical simulations. The simulations considered are MACSIS/BAHAMAS, EAGLE/Hydrangea, and TNG300. Environmental quenching is quantified in terms of the quenched fraction excess (QFE), a measure of the amount of quenching in clusters relative to the field. The QFE from simulations is compared with that from real data at z~1 coming from the GOGREEN survey (clusters) and COSMOS/UltraVISTA (field). The simulations struggle to reproduce the observed variation of the QFE as a function of stellar mass, producing a significantly larger fraction of quenched, low-mass satellites. Some of the simulations also fail at sufficiently quenching cluster galaxies at the high-mass end, perhaps due to insufficient AGN feedback. The origin of the discrepancy shown at low stellar masses is not clearly understood, something to be studied in more depth with the next generation of simulations. See Egidijus et al. (2023) for details. Figure taken from Egidijus et al. (2023). Work in collaboration with GOGREEN and SpARCS/GCLASS.



▲    The satellite quenching time-scale in massive galaxy clusters at z≳1 as modeled by combining data from the GOGREEN and GCLASS surveys with the IllustrisTNG simulation. The fiducial model, parameterized by the satellite quenching time-scale, τ_quench, successfully reproduces previous observations from GOGREEN and GCLASS data, namely the observed satellite quenched fraction as a function of stellar mass, projected cluster-centric radius, and redshift. It is also consistent with the observed field and cluster stellar mass functions at z ~ 1. The resulting τ_quench is mass dependent, decreasing with increasing stellar mass at least in the M_* > 10¹⁰ M_⊙ mass range, being roughly consisten with the total cold gas depletion time-scales at intermediate redshifts (top panel). This suggests that starvation may dominate the environmental quenching of galaxies at z<2. Moreover, while the environment is relatively efficient at quenching massive satellites, the additional action of pre-processing makes τ_quench values less dependent on satellite stellar mass and more consistent with the estimated cold gas depletion time-scale at z~1-2 (bottom panel). See Baxter et al. (2022) for details. Figure adapted from Baxter et al. (2022). Work in collaboration with GOGREEN and SpARCS/GCLASS.



▲    Physical properties (stellar mass, SFR, sSFR, virial mass) of brightest cluster galaxies (BCGs) at 0.05 < z < 0.42 as a function of cooling time and spectroscopic redshift. This study was conducted using SDSS (optical) and WISE (IR) data. The strong, weak and none cool core regimes are indicated by the vertical lines: left of the red line, between the lines, and right of the blue line, respectively. The results indicate that the fraction of star-forming BCG galaxies is higher at higher redshifts with SFRs being higher at higher redshifts than at lower redshifts. The fraction of star-forming BCGs varies from 30% to 80% in the above redshift interval. However, only a 13% of them is located on the field Main Sequence at the same redshift. Correlations with virial mass, stellar mass and cooling time suggest the star formation in BCGs is mainly related to the cooling of the ICM, although AGN heating of the ICM is also present. Comparison with empirical models for the SFR evolution with redshift shows that a transition merger- to cooling-dominated star formation may happen at z<0.6. Figure taken from Orellana-González et al. (2022).



▲    ALMA ACA 1.3 mm maps (gray scale) of 16 sources with a >3σ central emission detection closer than 3.5 arcsec from a IR counterpart (see Messias et al. for details). Each panel is 1 arcmin a side. The ACA observations targetted 36 radio AGN candidates at 0.2 < z < 4.2 within 3.9 square degrees in the ELAIS-S1 field. This work presents the survey and preliminary results. Sixteen of the targets show a detection in the mm regime. In 8 of these, the emission has a non-thermal origin. ACA can be used as a survey machine of the gas and continuum properties of the most luminous high-redhisft radio galaxies. The detection of negative continuum features near 4 of the ACA maps (see Messias et al. for details) may be due to either calibration systematics or the kinematic SZE of gas clouds moving away from the observer. Whereas the former is unlikely for this survey, the latter requires extreme gas conditions. Further observations are needed to obtain a better understanding of the reality of these features. Figure taken from Messias et al. (2021).



▲    The redshift evolution of the spatial extent of the current star formation in comparison with the spatial extent of the integrated star formation history (stellar continuum), R[Hα/C], of galaxies as a function of environment (see Matharu et al. for details). Different symbols correspond to different measurements from the literature as indicated in the figure. The results from this work are obtained from HST/WFC3 grism data of GCLASS clusters at z~1. The WFC3 data are used to produce the first spatilly resolved Hα maps of star-forming galaxies in clusters at that redshift (see www.gclasshst.com for the data release). The measurements indicate that R is smaller in clusters by 6±9%, statistically consistent with the field within 1σ. This negligible difference is at odds with the high quenched galaxy fraction in clusters with respect to that in the field. This can be reconciled if environmental quenching is a fast process. When carrying out this analysis on recently quenchend cluster galaxies, also known as post-starburst galaxies (PSB), the R value is about 80% smaller in PSB than that in star-forming galaxies in the field at similar redshift. This result suggests that the star formation is truncated in a outside-in manner in clusters at z~1, likely due to ram-pressure stripping, in a way that is more rapid or efficient than that in cluster at z~0.5 or lower. The effects on R would thus become observable shortly after the galaxy is quenchend in the cluster. Taken from Matharu et al. (2021). Work in collaboration with SpARCS/GCLASS.



▲    Projected phase space diagram showing the distribution of member galaxies in Abell S1063 from CLASH-VLT observations. The distributions in clustercentric distance and velocity are also shown. Different colored symbols and curves correspond to different galaxy types classified according to their spectral features, namely the equivalent widths of [OII], [OIII] and Hα in emission, and Hδ in absorption (see Mercurio et al. for details). Also, different cluster regions of interest, such as virialized, backsplash, and infall are also shown (see Mercurio et al. for details). The detailed analyses of the data in hand indicate that low-mass quiescent galaxies are incorporated into the cluster earlier than high-mass galaxies, suggesting that the observed passive galaxies are low-mass galaxies that were accreted early as blue galaxies. The results also indicate that red galaxies move on more radial orbits, which can be explained if infalling galaxies remain blue by moving on tangential orbits, having time to quench their star formation within the cluster. Figure taken from Mercurio et al. (2021). Work in collaboration with CLASH-VLT.



▲    The mass dependence of the fraction of star-forming galaxies in the field that need to be quenched to reproduce the observed stellar mass function of quescent galaxies in GOGREEN. Eleven GOGREEN clusters with masses ~2 × 10 ¹⁴ M_☉ and in the range 1 < z < 1.4 are used in this study (see McNab et al. 2021 for details). Although uncertainties are lage, the oservations are consistent with an escenario where the most massive passive galaxies in the clusters are quenched before cluster accretion, via pre-processing in group or protocluster environments. When considering low-mass galaxies, on the other hand, about 20-30% of star-forming cluster galaxies are quenched every 1 Gyr, in excess of field expectations. A rapid (<1 Gyr) quenching process can explain most of the low-mass excess of passive galaxies in the clusters. Figure taken from McNab et al. (2021). Work in collaboration with GOGREEN and SpARCS/GCLASS.



▲    The number fraction distribution of quiescent galaxies in GOGREEN clusters and in the field as a function of the observed axis ratio, q, for different stellar mass intervals. Quiescent galaxies are selected according to their location in the rest-frame UVJ color-color space. A set of models is constructed to find the triaxial galaxy population that best-reproduces the observed distribution of q values. The model population assumes Gaussian ellipticity and triaxiality distributions, and three scenarios with different ssumptions are considered (as indicated by the curves; see Chan et al. for details). The median value of q of both star-forming and quiescent galaxies in clusters increases with stellar mass, in a similar manner to field galaxies. By using oblate and triaxial components, the modelling shows that there is an excess of quiescent galaxies with flattened oblate morphology relative to the field. The results from this work suggests that environmental quenching produces a cluster popultion with a different morphological mix than that resulting from quenching in the field. Figure taken from Chan et al. (2021). Work in collaboration with GOGREEN and SpARCS/GCLASS.



▲    Difference in average formation time between groups and clusters in GOGREEN and the field for quiescent galaxies. See Reeves et al. (2021) for technical details. Data estimates are compared with model predictions, with and without pre-processing (see also Webb et al. 2020). The simple model without pre-processing appears to be ruled out by the younger age of quiescent galaxies in groups than in clusters. Note that the stellar mass dependence of the formation time in the models is weak, but becomes stronger on halo mass for the no pre-processing model. This work supports models in which environmental quenching becomes important for group-size halos at z>1. Figure taken from Reeves et al. (2021). Work in collaboration with GOGREEN and SpARCS/GCLASS.



▲    Morpho-kinematical analysis of two AGN in the cluster of galaxies RXJ0152-137 at z=0.84. The figure shows the angular distribution of the Halpha and [NII] emission of AGN ID=557 in flux, velocity, velocity dispersion and signal-to-noise ratio (from left to right). The data were obtained with KMOS at the ESO VLT whose footprint is also shown (first column). This AGN is located in the central region of the cluster, possibly interacting with a nearby galaxy, whereas the other AGN (ID=300) is found in the outskirts of the cluster. The observed differences between both AGN suggest that the cluster environment may be a significant contributor to the processes that established the properties of both cluster member galaxies. Figure taken from Paillalef et al. (2021).


▲    Velocity anisotropy profiles for diffetent subsamples of galaxies in the GOGREEN clusters of galaxies at z~1.2. See Biviano et al. (2021) for technical details and definition of the samples. Although cluster mass does not seem to affect the kinematical anisotropy distribution of the overall cluster galaxy population, some trends can be seen with respect to redshift, stellar mass, and star formation activity of galaxies. The analisys of the galaxy velocity anisotropy distribution indicates that the internal dynamic of clusters in GOGREEN is similar to tha of clusters at lower redshifts. This is also in agreement with anisotropy predictions from simulations. All in all, GOGREEN clusters have reached an advanced stage of relaxation by the observed epoch. See Biviano et al. (2021). Work in collaboration with GOGREEN and SpARCS/GCLASS.



▲    The first public data release of the GOGREEN and GCLASS surveys of cluster galaxies at 0.8 < z < 1.5. The data come from both photometric (full optical and NIR wavelength coverage) and spectroscopic (optical) observations with major telescope from the ground and space of 26 overdense structures ranging in halo mass from groups to clusters of galaxies. The final spectroscopic catalog includes 2,771 redshifts, of which 2,257 are reliable. A total of 1,704 objects have redshifts within the above interval, with about 800 of them being confirmed as cluster members. This data release includes fully reduced images and GMOS spectra with catalogs of advanced data products. See Balogh et al. (2021) for more details. Taken from Balogh et al. (2021). Work in collaboration with GOGREEN and SpARCS/GCLASS.



▲    Cluster galaxies in Coma identified by a phylogenetic analysis to be part of a population with a similar abundance pattern. The spectrum of each galaxy is used to measure line indices to determine element abundances. Pairs of galaxies are compared and a chemical distance between them is determined to construct a phylogenetic tree. Tree structures composed of galaxies with short chemical distances among themselves in comparison with other galaxies in the sample are named branches. Each branch represents an individual population of galaxies with chemical similarities. The galaxies shown in the figure correspon to a population of early-type galaxies in the red sequence of the Color-Magnitude diagram of Coma. The numbers indicate the "chemical length" between the nodes of the branch. The results from this work show that a phylogenetic approach can be a powerful complementary, yet independent tool to more traditional photometric analyses to study the evolution of galaxies. The color stamps in the figure were taken from the SDSS SkyServer DR15. The numbers indicate the "chemical distance" of galaxies to nodes in the branch. Figure taken from Monserrat Martinez's M.S. thesis, Univ. de Concepción (2020). See Martínez-Marín et al. 2020. Work in collaboration with UdeC's astroinformatic group.



▲    Median star formation rate vs stellar mass distribution of field and cluster galaxies at z~1.6 from the SpARCS/GCLASS survey compared with similar measurements from the literature. Star formation rates are derived from H-α measurements in MOSFIRE spectra obtained for galaxies in three clusters, and for galaxies identified serendipitously in the field at similar redshifts. The distributions of star formation rates in cluster and field galaxies at z~1.6 show no significat difference from each other, and are also consistent with other works at similar redshifts, suggesting that cluster galaxies may have been accreted only recently as to show any significant environment quenching. Other possibility is that at those redshifts, cluster environments are too young, dynamically speaking, as to be able to produce significant environmental quenching effects on their galaxy populations relative to the field. Taken from Nantais et al. (2020). Work in collaboration with SpARCS/GCLASS.



▲    Stellar masses and mass-weighted ages for cluster (in red) and field (in blue) galaxies in the GOGREEN survey. Galaxies are grouped in bins according to their stellar mass (see Webb et al. 2020 for details). The age distributions shown indicate that although there are field galaxies as old as the oldest cluster galaxies, and cluster galaxies as young as the youngest field galaxies, field galaxies exhibit, on average, more extended star formation histories to get the same final stellar mass. The difference in mass-waited ages between cluster and field galaxies at those redshifts (0.8 < z < 1.5) is about 0.3 Gyr, consisten with zero within the errors. Simple quenching models using environmental quenching without pre-processing or different formation times cannot reproduce simultanously that average age difference and the measured quenchend fraction of galaxies. This is distinctively different from what is observed in local clusters, which suggests that galaxy quenching at high redshifts is driven by processes different from those in the local universe. Taken from Webb et al. (2020). Work in collaboration with GOGREEN.



▲    Stellar mass functions (SMFs) of quiescent and star-forming galaxies in cluster and field environemnts are determined from the extensive spectroscopic and photometric observations of the GOGREEN survey at 1.0 < z< 1.4. More than 500 hours of spectroscopic and imaging observations were invested to study the SMFs down to a stellar mass limit of 10^{9.5 - 9.7} M_☉. While the cluster environment is observed to have a significant quenching efficiency at those redshift, with stellar mass-dependent values as low as 30%, the shapes of the SMFs of star-forming and quescent galaxies across environments, however, are the same to a high statistical precision. Nevertheless, the total SMF shows a deficit of low-mass galaxies in clusters relative to the co-eval field. These results are different from findings in the local universe, indicating that a different quenching mode operates at high redshift. Taken from van der Burg et al. (2020). Work in collaboration with GOGREEN.



▲    The stellar mass-size relation for cluster galaxies in the GCLASS survey. In the main panel to the left, colors indicate galaxy morphology as encoded in the Sérsic index, n. Spectroscopically confirmed post-starburst galaxies (PSBs) are shown as large squares. Low-confidence spectroscopically confirmed PSBs are indicated with large diamonds. All other cluster members are indicated as small circular points. Objects below the stellar mass completeness limits are shown as open symbols. Solid black lines correspond to the expected field relations at z~1 obtained from the 3D-HST field sample relations for star-forming and quiescent galaxies. Cluster PSBs at z~1 follow a stellar mass-size relation that is in between the star-forming and quiescent field relations. This suggests that changes in the mass-to-light ratio gradient in galaxies are at play. A combination of "outside-in" fading from star-forming galaxies and a size growth of quiescent galaxies both from quenching and dry minor mergers may explain the observations. Taken from Matharu et al. (2020). Work in collaboration with SpARCS/GCLASS.



▲    Projected cumulative mass (left) and mass density (right) profiles obtained from weak lensing analyses of CLASH clusters using extensive CLASH-VLT spectroscopy. The profiles are rescaled by M₂₀₀ and R₂₀₀, and the vertical lines mark the distance of spectroscopically confirmed families of images from the cluster centers. The rescaled projected total mass and mass density profiles have very similar shapes, and the mean projected mass values measured within 10% of R₂₀₀ present a small scatter of 5%. The large number of high redshift galaxies and the precise magnification maps obtained represent a valuable addition to the sample of high-quality gravitational telescopes available to explore the distant universe. Taken from Caminha et al. (2019). Work in collaboration with CLASH-VLT.



▲    Galaxy images from the CLASH survey observed in different filters and the corresponding morphological (S: spheroid; D: disk; I: irregular; PS: point source; U: unclassifiable) probabilities as determined by a convolutional neural network model. This model has been trained using CANDELS observations in the same filters and morphologies determined visually by human classifiers. This method, as opposed to training directly over the CLASH data, showed to be more efficient and achieved a better performance. This approach is useful to minimize visual classification efforts when classifying unlabeled massive datasets from new surveys such as the LSST. Taken from Pérez-Carrasco et al. (2019). Work in collaboration with UdeC's astroinformatic group.



▲    Evolution of the cumulative fraction of quenched galaxies in the 10 most massive (C-1 through C-10) galaxy clusters from the EAGLE simulation. The time scale is shown with respect to the time of infall, t_infall, at which galaxies cross the cluster's R₂₀₀. The color bar indicates the total mass of the cluster at z=0. Between 20% and 60% of galaxies arrive already quenched to the cluster which highlights the role of pre-processing. This fraction depends on final cluster mass, being larger for more massive clusters. Also, the steeper slope at t=t_infall indicates the more rapid increase of the quenched population at infall more than at any other epoch. Taken from Pallero et al. (2019). Work in collaboration with GaTOS.



▲    The redshift evolution of the faint-to-luminous ratio, N_faint/N_lumin, of red-sequence galaxies in clusters belonging to the GOGREEN Survey. The ratio is derived from the red-sequence Luminosity Function down to M^*_H + (2.0-3.0). A consisten analysis was also carried out for UltraVISTA field galaxies. The faint-to-luminous ratio in clusters decreases with increasing redshift and becomes consistent with field values at z~1.15. The results indicate that the buildup of faint red-sequence galaxies occurs gradually and suggest that faint cluster galaxies already experience environmental quenching at z~1.15. Taken from Chan et al. (2019). Work in collaboration with GOGREEN.



▲    The cluster versus field stellar mass-size relation and the size growth of passive cluster galaxies as a function of redshift since z~1. The cluster galaxy sample has been drawn from the SpARCS/GCLASS survey. Redshift, stellar masses and sizes have been derived from Gemini/GMOS and HST/WFC3 spectroscopy, and HST/WFC3 imaging. The analyses show evidence that the cluster environment inhibits size growth between z~1.5 and z~1.0, and that subsequent size evolution of quiescent cluster galaxies is in part driven by minor mergers, together with other cluster-specific processes. Taken from Matharu et al. (2019). Work in collaboration with SpARCS/GCLASS.



▲    Offset from the Main Sequence as a function of gas fraction for galaxies in z~1.6 clusters resolved in CO(2-1) with ALMA. The scaling relation for field galaxies (Genzel et al. 2015), normalized to z=1.6 and at several stellar masses covering the mass range of the cluster sample, is also shown (dashed blue lines). See Noble et al. (2017, 2019 [this work]) for details. Cluster galaxies show typical main-sequence star formation rates and massive molecular gas reservoirs situated in rotating disks, similar to infalling field galaxies. However, they also present elevated gas fractions, slightly smaller CO disks, and asymmetric gas tails, suggesting tentative evidence for gas stripping in z~1.6 clusters. Taken from Noble et al. (2019). Work in collaboration with SpARCS/GCLASS.



▲    The Spitzer Planck Herschel Infrared Cluster (SPHerIC) survey of galaxy overdensities with red IRAC colors in the range [3.6]-[4.5] > -0.1. This color cut was intended to select high-redshift protoclusters of galaxies. The surface density distribution of IRAC red sources in SPHerIC is indicated by the red histogram in the left panel. The photometric redshift distribution of SPHerIC protocluster candidates obtained from the IRAC color selection is shown in the right panel. The hatched bars indicate the redshift interval where the color-redshift relation utilized (see Martinache et al. [2018] for details) is no longer effective. Taken from Martinache et al. (2018).



▲    Quenching timescale evolution with redshift for groups and clusters of galaxies. The results from this work, indicated by the red stars, were obtained from a sample of clusters at z~1 and z~1.6. They suggest, together with results from the literature, that kinematical quenching processes (e.g. ram-pressure stripping) may dominate in the evolution of high redshift cluster galaxies with stellar masses larger than log(M_*/M_☉)=10.5, although gas-depletion scenarios cannot be ruled out. See Foltz et al. (2018) for details. Taken from Foltz et al. (2018). Work in collaboration with SpARCS/GCLASS.



▲    Environmental quenching efficiency in two CLASH-VLT clusters, MACSJ0416-2406 and MACSJ1206-0847, and their substructures at z=0.4. The quenching efficiency, ε_q, of substructures in the outskirts (r>r_200,cl) of clusters becomes comparable to that of clusters. This suggests the existence of pre-processing in groups associated with massive clusters of galaxies. Taken from Olave-Rojas et al. (2018). Work in collaboration with CLASH-VLT.



▲    Oxygen abundance (top) and radial velocity (bottom) maps of two star-forming dwarf galaxies, UM 461 (left) and Mrk 600 (right), observed with VLT/VIMOS-IFU. The two galaxies show signs of morphological distortions, such as a cometary-like structure. The properties of the spatially resolved ISM in both systems are consistent with these galaxies being at different evolutionary stages. In particular, UM 461's O/H distribution shows indication of a recent infall of low-mass, metal-poor material into the galaxy, consistent with the picture through which galaxies form and grow via accretion of matter from the surrounding environment. Taken from Lagos et al. (2018).

See also this astrobite article on this publication.



▲    Background-corrected morphological fractions of red-sequence cluster members as a function of absolute magnitude (left) and stellar mass (right). The different panels correspond to different cluster surveys depending on redshift, as indicated in the figure. The vertical dotted lines at log (M_*/M_☉)=10.95 and and 11.5 indicate the stellar mass limit of the Hawk-I Cluster Survey (HCS) morphological sample and the maximum stellar mass of red-sequence galaxies in the HCS, respectively. Elliptical galaxies dominate in HCS clusters at all stellar masses while the red sequence of local clusters is dominated by ellipticals at log (M_*/M_☉)>11.3 and by S0s at log (M_*/M_☉)<11.3 (right). Disc-dominated galaxies make up to 40% of red-sequence galaxies in the intermediate redshift sample (left). Elliptical and S0 galaxies seem to follow different evolutionary histories, with intermediate-luminosity S0s likely resulting from the morphological transformation of quiescent spirals. Taken from Cerulo et al. (2017). Work in collaboration with HCS.



▲    The evolution in cosmic time of the fraction of gas in cluster galaxies that are on the main sequence of star formation. The field scaling relation for main-sequence galaxies is shown by the black line and gray region. In general, the gas fraction both in the field and in clusters increases with redshift. Nevertheless, z>1 main-sequence cluster galaxies have, on average, higher gas fraction than the coeval field. This difference also tends to be larger than that in the low-redshift universe. Taken from Noble et al. (2017). Work in collaboration with SpARCS/GCLASS.



▲   An unusual case of an early-type "jellyfish" galaxy in the galaxy cluster Abell 2670 (z=0.076). Observations with the MUSE instrument on the ESO VLT made it possible to obtain an unprecedented view of the ionized gas associated with the galaxy that is being affected by ram-pressure stripping. Most likely, this galaxy, classified as elliptical, acquired its gaseous component through a wet merger with other galaxy. The figure shows the MUSE Hα (a) flux map and (b) velocity offset map of the whole field of view. The zoom-in areas for detected Hα blobs are indicated with boxes (5(a) and (b)) in the Hα map. Taken from Sheen et al. (2017).

Press releases associated with this work include: AAS Nova, Phys.org, I4U News, The Science Times, CEA, KASI, and YTN Science (YouTube).


▲   Environmental quenching efficiencies as a function of redshift for clusters and groups of galaxies. The red symbol shows results from this study. Dash-dot lines connect related studies and solid lines connect results from the same study. Slight offsets between studies at the same redshift with overlapping error bars have been added for clarity. Quenching efficiencies appear to vary mostly by halo mass category (groups, clusters). Within each halo-mass category, there are signs of a decrease in environmental quenching efficiency with increasing redshift. Halo mass growth together the time spent by a galaxy in a cluster environment may lead to the observed trends at z>1. Taken from Nantais et al. (2016). Work in collaboration with SpARCS/GCLASS.



▲   Comparison between the red sequence number counts in clusters and in the field. Black filled circles represent the number counts of the entire Hawk-I Cluster Survey (HCS) red sequence sample, while red diamonds are the red sequence number counts in the WINGS red sequence sample. The number counts of the HCS and WINGS composite samples were obtained as in Garilli et al. (1999). Blue crosses are the red sequence number counts of passive red sequence galaxies in the COSMOS/UltraVISTA field at 0.8 < z_phot < 1.5. The number counts in the WINGS and UltraVISTA samples are normalized to match the value of the HCS number counts at approximately the Schechter turn-over magnitude M*_V. Solid lines are the best-fitting Schechter curves obtained for each sample. While no deficit of galaxies is observed in HCS with respect to WINGS, the UltraVISTA number counts decrease towards faint luminosities. This result suggests that the build-up of the red sequence is accelerated in clusters at low stellar masses. Taken from Cerulo et al. (2016). Work in collaboration with HCS.