• The BUFFALO HST Survey

      Steinhardt, Charles L.; Jauzac, Mathilde; Acebron, Ana; Atek, Hakim; Capak, Peter; Davidzon, Iary; Eckert, Dominique; Harvey, David; Koekemoer, Anton M.; Lagos, Claudia D. P.; et al. (IOP PUBLISHING LTD, 2020-04-03)
      The Beyond Ultra-deep Frontier Fields and Legacy Observations (BUFFALO) is a 101 orbit + 101 parallel Cycle 25 Hubble Space Telescope (HST) Treasury program taking data from 2018 to 2020. BUFFALO will expand existing coverage of the Hubble Frontier Fields (HFF) in Wide Field Camera 3/IR F105W, F125W, and F160W and Advanced Camera for Surveys/WFC F606W and F814W around each of the six HFF clusters and flanking fields. This additional area has not been observed by HST but is already covered by deep multiwavelength data sets, including Spitzer and Chandra. As with the original HFF program, BUFFALO is designed to take advantage of gravitational lensing from massive clusters to simultaneously find high-redshift galaxies that would otherwise lie below HST detection limits and model foreground clusters to study the properties of dark matter and galaxy assembly. The expanded area will provide the first opportunity to study both cosmic variance at high redshift and galaxy assembly in the outskirts of the large HFF clusters. Five additional orbits are reserved for transient follow-up. BUFFALO data including mosaics, value-added catalogs, and cluster mass distribution models will be released via MAST on a regular basis as the observations and analysis are completed for the six individual clusters.
    • Determining the Halo Mass Scale Where Galaxies Lose Their Gas

      Rudnick, Gregory; Jablonka, Pascale; Moustakas, John; Aragón-Salamanca, Alfonso; Zaritsky, Dennis; Jaffé, Yara L.; Lucia, Gabriella De; Desai, Vandana; Halliday, Claire; Just, Dennis; et al. (IOP PUBLISHING LTD, 2017-11-30)
      A major question in galaxy formation is how the gas supply that fuels activity in galaxies is modulated by their environment. We use spectroscopy of a set of well-characterized clusters and groups at 0.4 < z < 0.8 from the ESO Distant Cluster Survey and compare it to identically selected field galaxies. Our spectroscopy allows us to isolate galaxies that are dominated by old stellar populations. Here we study a stellar-mass-limited sample (log(M*/M-circle dot) > 10.4) of these old galaxies with weak [O II] emission. We use line ratios and compare to studies of local early-type galaxies to conclude that this gas is likely excited by post-AGB stars and hence represents a diffuse gas component in the galaxies. For cluster and group galaxies the fraction with EW([O II]) > 5 angstrom is f([O II]) = 0.08(-0.03)(+0.02) and f([O II]) = 0.06(-0.04)(+0.07), respectively. For field galaxies we find f([O II]) = 0.2 (+0.07)(-0.06), representing a 2.8 sigma difference between the [O II] fractions for old galaxies between the different environments. We conclude that a population of old galaxies in all environments has ionized gas that likely stems from stellar mass loss. In the field galaxies also experience gas accretion from the cosmic web, and in groups and clusters these galaxies have had their gas accretion shut off by their environment. Additionally, galaxies with emission preferentially avoid the virialized region of the cluster in position-velocity space. We discuss the implications of our results, among which is that gas accretion shutoff is likely effective at group halo masses (log M/M-circle dot > 12.8) and that there are likely multiple gas removal processes happening in dense environments.
    • Disc colours in field and cluster spiral galaxies at 0.5 ≲ z ≲ 0.8

      Cantale, Nicolas; Jablonka, Pascale; Courbin, Frédéric; Rudnick, Gregory; Zaritsky, Dennis; Meylan, Georges; Desai, Vandana; De Lucia, Gabriella; Aragón-Salamanca, Alfonso; Poggianti, Bianca M.; et al. (EDP SCIENCES S A, 2016-04-18)
      We present a detailed study of the colours of late-type galaxy discs for ten of the EDisCS galaxy clusters with 0.5 less than or similar to z less than or similar to 0.8. Our cluster sample contains 172 spiral galaxies, and our control sample is composed of 96 field disc galaxies. We deconvolved their ground-based V and I images obtained with FORS2 at the VLT with initial spatial resolutions between 0.4 and 0.8 arcsec to achieve a final resolution of 0.1 arcsec with 0.05 arcsec pixels, which is close to the resolution of the ACS at the HST. After removing the central region of each galaxy to avoid pollution by the bulges, we measured the V - I colours of the discs. We find that 50% of cluster spiral galaxies have disc V - I colours redder by more than 1 sigma of the mean colours of their field counterparts. This is well above the 16% expected for a normal distribution centred on the field disc properties. The prominence of galaxies with red discs depends neither on the mass of their parent cluster nor on the distance of the galaxies to the cluster cores. Passive spiral galaxies constitute 20% of our sample. These systems are not abnormally dusty. They are are made of old stars and are located on the cluster red sequences. Another 24% of our sample is composed of galaxies that are still active and star forming, but less so than galaxies with similar morphologies in the field. These galaxies are naturally located in the blue sequence of their parent cluster colour-magnitude diagrams. The reddest of the discs in clusters must have stopped forming stars more than similar to 5 Gyr ago. Some of them are found among infalling galaxies, suggesting preprocessing. Our results confirm that galaxies are able to continue forming stars for some significant period of time after being accreted into clusters, and suggest that star formation can decline on seemingly long (1 to 5 Gyr) timescales.
    • The GOGREEN Survey: A deep stellar mass function of cluster galaxies at 1.0 < z < 1.4 and the complex nature of satellite quenching

      van der Burg, Remco F. J.; Rudnick, Gregory; Balogh, Michael L.; Muzzin, Adam; Lidman, Chris; Old, Lyndsay J.; Shipley, Heath; Gilbank, David; McGee, Sean; Biviano, Andrea; et al. (EDP SCIENCES S A, 2020-06-23)
      We study the stellar mass functions (SMFs) of star-forming and quiescent galaxies in 11 galaxy clusters at 1.0<z<1.4 drawn from the Gemini Observations of Galaxies in Rich Early ENvironments (GOGREEN) survey. Based on more than 500 h of Gemini/GMOS spectroscopy and deep multi-band photometry taken with a range of observatories, we probe the SMFs down to a stellar mass limit of 10(9.7) M-circle dot (10(9.5) M-circle dot for star-forming galaxies). At this early epoch, the fraction of quiescent galaxies is already highly elevated in the clusters compared to the field at the same redshift. The quenched fraction excess (QFE) represents the fraction of galaxies that would be star-forming in the field but are quenched due to their environment. The QFE is strongly mass dependent, and increases from similar to 30% at M-star=10(9.7) M-circle dot to similar to 80% at M-star=10(11.0) M-circle dot. Nonetheless, the shapes of the SMFs of the two individual galaxy types, star-forming and quiescent galaxies, are identical between cluster and field to high statistical precision. Nevertheless, along with the different quiescent fractions, the total galaxy SMF is also environmentally dependent, with a relative deficit of low-mass galaxies in the clusters. These results are in stark contrast with findings in the local Universe, and therefore require a substantially different quenching mode to operate at early times. We discuss these results in light of several popular quenching models.
    • The GOGREEN survey: post-infall environmental quenching fails to predict the observed age difference between quiescent field and cluster galaxies at z > 1

      Webb, Kristi; Balogh, Michael L; Leja, Joel; van der Burg, Remco F J; Rudnick, Gregory; Muzzin, Adam; Boak, Kevin; Cerulo, Pierluigi; Gilbank, David; Lidman, Chris; et al. (OXFORD UNIV PRESS, 2020-09-10)
      We study the star formation histories (SFHs) and mass-weighted ages of 331 UVJ-selected quiescent galaxies in 11 galaxy clusters and in the field at 1 < z < 1.5 from the Gemini Observations of Galaxies in Rich Early ENvironments (GOGREEN) survey. We determine the SFHs of individual galaxies by simultaneously fitting rest-frame optical spectroscopy and broad-band photometry to stellar population models. We confirm that the SFHs are consistent with more massive galaxies having on average earlier formation times. Comparing galaxies found in massive clusters with those in the field, we find galaxies with M-* < 10(11.3) M-circle dot in the field have more extended SFHs. From the SFHs we calculate the mass-weighted ages, and compare age distributions of galaxies between the two environments, at fixed mass. We constrain the difference in mass-weighted ages between field and cluster galaxies to 0.31(-0.33)(+0.51) Gyr, in the sense that cluster galaxies are older. We place this result in the context of two simple quenching models and show that neither environmental quenching based on time since infall (without pre-processing) nor a difference in formation times alone can reproduce both the average age difference and relative quenched fractions. This is distinctly different from local clusters, for which the majority of the quenched population is consistent with having been environmentally quenched upon infall. Our results suggest that quenched population in galaxy clusters at z > 1 has been driven by different physical processes than those at play at z = 0.
    • The GOGREEN survey: the environmental dependence of the star-forming galaxy main sequence at 1.0 < z < 1.5

      Old, Lyndsay J; Balogh, Michael L; van der Burg, Remco F J; Biviano, Andrea; Yee, Howard K C; Pintos-Castro, Irene; Webb, Kristi; Muzzin, Adam; Rudnick, Gregory; Vulcani, Benedetta; et al. (OXFORD UNIV PRESS, 2020-03-04)
      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 [O 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 (similar to 3.3 sigma) across the stellar mass range: 9.0 < log (M-*/M-circle dot) < 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.
    • The Local Cluster Survey. I. Evidence of Outside-in Quenching in Dense Environments

      Finn, Rose A.; Desai, Vandana; Rudnick, Gregory; Balogh, Michael; Haynes, Martha P.; Jablonka, Pascale; Koopmann, Rebecca A.; Moustakas, John; Peng, Chien Y.; Poggianti, Bianca; et al. (IOP PUBLISHING LTD, 2018-08-01)
      The goal of the Local Cluster Survey is to look for evidence of environmentally driven quenching among star-forming galaxies in nearby galaxy groups and clusters. Quenching is linked with environment and stellar mass, and much of the current observational evidence comes from the integrated properties of galaxies. However, the relative size of the stellar and star-forming disk is sensitive to environmental processing and can help identify the mechanisms that lead to a large fraction of quenched galaxies in dense environments. Toward this end, we measure the size of the star-forming disks for 224 galaxies in nine groups and clusters (0.02 < z < 0.04; SFR > 0.1 M-circle dot yr(-1)) using 24 mu m imaging from the Spitzer Space Telescope. We normalize the 24 mu m effective radius (R-24) by the size of the stellar disk (R-d). We find that star-forming galaxies with higher bulge-to-total ratios (BIT) and galaxies in more dense environments have more centrally concentrated star formation. Comparison with H mass fractions and NUV - r colors indicates that a galaxy's transition from gas-rich and blue to depleted and red is accompanied by an increase in the central concentration of star formation. We build a simple model to constrain the timescale over which the star-forming disks shrink in the cluster environment. Our results are consistent with a long-timescale (>2 Gyr) mechanism that produces outside-in quenching, such as the removal of the extended gas halo or weak stripping of the cold disk gas.
    • Preprocessing among the Infalling Galaxy Population of EDisCS Clusters

      Just, Dennis W.; Kirby, Matthew; Zaritsky, Dennis; Rudnick, Gregory; Desjardins, Tyler; Cool, Richard; Moustakas, John; Clowe, Douglas; Lucia, Gabriella De; Aragón-Salamanca, Alfonso; et al. (IOP PUBLISHING LTD, 2019-10-24)
      We present results from a low-resolution spectroscopic survey for 21 galaxy clusters at 0.4 < z < 0.8 selected from the ESO Distant Cluster Survey. We measured spectra using the low-dispersion prism in IMACS on the Magellan Baade telescope and calculate redshifts with an accuracy of sigma(z) = 0.007. We find 1763 galaxies that are brighter than R = 22.9 in the large-scale cluster environs. We identify the galaxies expected to be accreted by the clusters as they evolve to z = 0 using spherical infall models and find that similar to 30%-70% of the z = 0 cluster population lies outside the virial radius at z similar to 0.6. For analogous clusters at z = 0, we calculate that the ratio of galaxies that have fallen into the clusters since z similar to 0.6 to those that were already in the core at that redshift is typically between similar to 0.3 and 1.5. This wide range of ratios is due to intrinsic scatter and is not a function of velocity dispersion, so a variety of infall histories is to be expected for clusters with current velocity dispersions of 300 km s(-1) less than or similar to sigma less than or similar to 1200 km s(-1). Within the infall regions of z similar to 0.6 clusters, we find a larger red fraction of galaxies than in the field and greater clustering among red galaxies than blue. We interpret these findings as evidence of "preprocessing," where galaxies in denser local environments have their star formation rates affected prior to their aggregation into massive clusters, although the possibility of backsplash galaxies complicates the interpretation.