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Galaxy protoclusters, which will eventually grow into the massive clusters we see in the local universe, are usually traced by locating overdensities of galaxies. Large spectroscopic surveys of distant galaxies now exist, but their sensitivity depends mainly on a galaxy's star formation activity and dust content rather than its mass. Tracers of massive protoclusters that do not rely on their galaxy constituents are therefore needed. Here we report observations of Lyman-$\alpha$ absorption in the spectra of a dense grid of background galaxies, which we use to locate a substantial number of candidate protoclusters at redshifts 2.2-2.8 via their intergalactic gas. We find that the structures producing the most absorption, most of which were previously unknown, contain surprisingly few galaxies compared to the dark matter content of their analogs in cosmological simulations. Nearly all are expected to be protoclusters, and we infer that half of their expected galaxy members are missing from our survey because they are unusually dim at rest-frame ultraviolet wavelengths. We attribute this to an unexpectedly strong and early influence of the protocluster environment on the evolution of these galaxies that reduced their star formation or increased their dust content., Comment: Published in Nature. The version of record is available at https://www.nature.com/articles/s41586-022-04681-6 or view-only at https://rdcu.be/cPIIX

Despite significant progress both observationally and theoretically, the origin of high-ionization nebular HeII emission in galaxies dominated by stellar photoionization remains unclear. Accretion-powered radiation from high-mass X-ray binaries (HMXBs) is still one of the leading proposed explanations for the missing $\mathrm{He^+}$-ionizing photons, but this scenario has yet to be conclusively tested. In this paper, we present nebular line predictions from a grid of photoionization models with input SEDs containing the joint contribution of both stellar atmospheres and a multi-color disk model for HMXBs. This grid demonstrates that HMXBs are inefficient producers of the photons necessary to power HeII, and can only boost this line substantially in galaxies with HMXB populations large enough to power X-ray luminosities of $10^{42}$ erg/s per unit star formation rate (SFR). To test this, we assemble a sample of eleven low-redshift star-forming galaxies with high-quality constraints on both X-ray emission from Chandra and HeII emission from deep optical spectra, including new observations with the MMT. These data reveal that the HMXB populations of these nearby systems are insufficient to account for the observed HeII strengths, with typical X-ray luminosities or upper limits thereon of only $10^{40}$-$10^{41}$ erg/s per SFR. This indicates that HMXBs are not the dominant source of $\mathrm{He^+}$ ionization in these metal-poor star-forming galaxies. We suggest that the solution may instead reside in revisions to stellar wind predictions, softer X-ray sources, or very hot products of binary evolution at low metallicity., Comment: 18 pages, 9 figures, published in MNRAS

We present an analysis of 10 ks snapshot Chandra observations of 12 shocked post-starburst galaxies, which provide a window into the unresolved question of active galactic nuclei (AGN) activity in post-starburst galaxies and its role in the transition of galaxies from actively star forming to quiescence. While 7/12 galaxies have statistically significant detections (with 2 more marginal detections), the brightest only obtained 10 photons. Given the wide variety of hardness ratios in this sample, we chose to pursue a forward modeling approach to constrain the intrinsic luminosity and obscuration of these galaxies rather than stacking. We constrain intrinsic luminosity of obscured power-laws based on the total number of counts and spectral shape, itself mostly set by the obscuration, with hardness ratios consistent with the data. We also tested thermal models. While all the galaxies have power-law models consistent with their observations, a third of the galaxies are better fit as an obscured power-law and another third are better fit as thermal emission. If these post-starburst galaxies, early in their transition, contain AGN, then these are mostly confined to a lower obscuration ($n_H \leq10^{23}$ cm$^{-2}$) and lower luminosity ($L_{2-10~ \rm keV}\leq10^{42}$erg s$^{-1}$). Two galaxies, however, are clearly best fit as significantly obscured AGN. At least half of this sample show evidence of at least low luminosity AGN activity, though none could radiatively drive out the remaining molecular gas reservoirs. Therefore, these AGN are more likely along for the ride, having been fed gas by the same processes driving the transition., Comment: 16 pages, 6 figures, 3 tables, accepted for publication in ApJ

Galaxy protoclusters, which will eventually grow into the massive clusters we see in the local Universe, are usually traced by locating overdensities of galaxies

We constrain the evolution of the brightest cluster galaxy plus intracluster light (BCG + ICL) using an ensemble of 42 galaxy groups and clusters that span redshifts of z = 0.05−1.75 and masses of M500,c= 2 × 1013−1015 M⊙. Specifically, we measure the relationship between the BCG + ICL stellar mass M⋆ and M500,c at projected radii 10 < r < 100 kpc for three different epochs. At intermediate redshift ($\bar{z}=0.40$), where we have the best data, we find M⋆ ∝ M500,c0.48 ± 0.06. Fixing the exponent of this power law for all redshifts, we constrain the normalization of this relation to be 2.08 ± 0.21 times higher at $\bar{z}=0.40$ than at high redshift ($\bar{z}=1.55$). We find no change in the relation from intermediate to low redshift ($\bar{z}=0.10$). In other words, for fixed M500,c, M⋆ at 10 < r < 100 kpc increases from $\bar{z}=1.55$ to $\bar{z}=0.40$ and not significantly thereafter. Theoretical models predict that the physical mass growth of the cluster from z = 1.5 to z = 0 within r500,c is 1.4×, excluding evolution due to definition of r500,c. We find that M⋆ within the central 100 kpc increases by ∼3.8× over the same period. Thus, the growth of M⋆ in this central region is more than a factor of 2 greater than the physical mass growth of the cluster as a whole. Furthermore, the concentration of the BCG + ICL stellar mass, defined by the ratio of stellar mass within 10 kpc to the total stellar mass within 100 kpc, decreases with increasing M500,c at all z. We interpret this result as evidence for inside–out growth of the BCG + ICL over the past 10 Gyr, with stellar mass assembly occurring at larger radii at later times.

(Abridged) We present a systematic investigation of physical conditions and elemental abundances in four optically thick Lyman-limit systems (LLSs) at $z=0.36-0.6$ discovered within the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS LLSs exhibit multi-component kinematic structure and a complex mix of multiphase gas, with associated metal transitions from multiple ionization states that span several hundred km/s in line-of-sight velocity. Specifically, higher column density components (log N(HI)>16) in all four absorbers comprise dynamically cool gas with $\langle T \rangle =(2\pm1) \times10^4\,$K and modest non-thermal broadening of $5\pm3\,$ km/s. The high quality of the QSO absorption spectra allows us to infer the physical conditions of the gas, using a detailed ionization modeling that takes into account the resolved component structures of HI and metal transitions. The range of inferred gas densities indicates that these absorbers consist of spatially compact clouds with a median line-of-sight thickness of $160^{+140}_{-50}$ pc. While obtaining robust metallicity constraints for the low-density, highly ionized phase remains challenging due to the uncertain N(HI), we demonstrate that the cool-phase gas in LLSs has a median metallicity of $\mathrm{[\alpha/H]_{1/2}}=-0.7^{+0.1}_{-0.2}$, with a 16-84 percentile range of $\mathrm{[\alpha/H]}=(-1.3,-0.1)$. Furthermore, the wide range of inferred elemental abundance ratios ($\mathrm{[C/\alpha]}$, $\mathrm{[N/\alpha]}$, and $\mathrm{[Fe/\alpha]}$) indicate a diversity of chemical enrichment histories. Combining the absorption data with deep galaxy survey data characterizing the galaxy environment of these absorbers, we discuss the physical connection between star-forming regions in galaxies and diffuse gas associated with optically thick absorption systems in the $z, Comment: Accepted for publication in MNRAS after a minor revision. 18 pages, 11 figures, and a nine-page Appendix with four additional figures

We present a detailed study of two partial Lyman limit systems (pLLSs) of neutral hydrogen column density $N_\mathrm{H\,I}\approx(1-3)\times10^{16}\,\mathrm{cm}^{-2}$ discovered at $z=0.5$ in the Cosmic Ultraviolet Baryon Survey (CUBS). Available far-ultraviolet spectra from the Hubble Space Telescope Cosmic Origins Spectrograph and optical echelle spectra from MIKE on the Magellan Telescopes enable a comprehensive ionization analysis of diffuse circumgalactic gas based on resolved kinematics and abundance ratios of atomic species spanning five different ionization stages. These data provide unambiguous evidence of kinematically aligned multi-phase gas that masquerades as a single-phase structure and can only be resolved by simultaneous accounting of the full range of observed ionic species. Both systems are resolved into multiple components with inferred $\alpha$-element abundance varying from $[\alpha/\text{H}]\approx\!{-0.8}$ to near solar and densities spanning over two decades from $\log n_\mathrm{H}\mathrm{cm}^{-3}\approx\!-2.2$ to $, Comment: Accepted for publication in MNRAS, 27 pages, 21 figures

We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS is designed to map diffuse baryonic structures at redshift z~ 17.2 over a total redshift survey pathlength of dz=9.3, and a number density of n(z)=0.43 (-0.18, +0.26). Considering all absorbers with log N(HI)/cm^-2 > 16.5 leads to n(z)=1.08 (-0.25, +0.31) at z, Comment: 26 pages, 14 figures, MNRAS in press

We report the serendipitous detection of an H$_{2}$-bearing damped Lyman-$��$ absorber at z = 0.576 in the spectrum of the QSO J0111-0316 in the Cosmic Ultraviolet Baryon Survey. Spectroscopic observations from HST-COS in the far-ultraviolet reveal a damped absorber with log[N(HI)/cm^-2] = 20.1 +/- 0.2 and log[N(H$_{2}$)/cm^-2] = 18.97 (-0.06, +0.05). The diffuse molecular gas is found in two velocity components separated by dv = 60 km/s, with >99.9% of the total H$_{2}$ column density concentrated in one component. At a metallicity of $\approx$ 50% of solar, there is evidence for Fe enhancement and dust depletion, with a dust-to-gas ratio $��_{\text{O}} \approx$ 0.4. A galaxy redshift survey conducted with IMACS and LDSS-3C on Magellan reveals an overdensity of nine galaxies at projected distance d, 19 pages, 6 figures. Accepted for publication in ApJ

With Hubble Space Telescope imaging, we investigate the progenitor population and formation mechanisms of the intracluster light (ICL) for 23 galaxy groups and clusters ranging from 3$\times10^{13}10^{11.6}$ M$_\odot$), while by 100 kpc this colour is equivalent to that of a 10$^{10}$ M$_\odot$ galaxy. Additionally, we find 75% of the total BCG+ICL luminosity is consistent in color of galaxies with L$>$0.2 L$_*$ (log(M$_\bigstar$[M$_\odot$])$>$10.4), assuming conservatively that these galaxies are completely disrupted. We conclude that tidal stripping of massive galaxies is the likely source of the intracluster light from 10-100 kpc (0.008-0.23 r$_{500,c}$) for galaxy groups and clusters., Comment: Accepted for publication in MNRAS

Quasars at early redshifts ($z > 6$) with companion galaxies offer unique insights into the growth and evolution of the first supermassive black holes. Here, we report on a 150 ks Chandra observation of PSO J308.0416$-$21.2339, a $z=6.23$ quasar with a merging companion galaxy identified in [C II] and rest-frame UV emission. With $72.3^{+9.6}_{-8.6}$ net counts, we find that PSO J308.0416$-$21.2339 is powerful ($L_X = 2.31^{+1.14}_{-0.76} \times 10^{45}\ \textrm{erg}\,\textrm{s}^{-1}\,\textrm{cm}^{-2}$ in rest-frame $2.0-10.0$ keV) yet soft (spectral power-law index $\Gamma=2.39^{+0.37}_{-0.36}$ and optical-to-X-ray slope $\alpha_{\rm OX} = -1.41 \pm 0.11$). In addition, we detect three hard-energy photons $2.''0$ to the west of the main quasar, cospatial with the brightest UV emission of the merging companion. As no soft-energy photons are detected in the same area, this is potentially indicative of a highly-obscured source. With conservative assumptions, and accounting for both background fluctuations and the extended wings of the quasar's emission, these photons only have a probability $P=0.021$ of happening by chance. If confirmed by deeper observations, this system is the first high redshift quasar and companion individually detected in X-rays and is likely a dual AGN., Comment: 8 pages, 4 figures, published in the Astrophysical Journal. Revised to reflect accepted version

A key obstacle to developing a satisfying theory of galaxy evolution is the difficulty in extending analytic descriptions of early structure formation into full nonlinearity, the regime in which galaxy growth occurs. Extant techniques, though powerful, are based on approximate numerical methods whose Monte Carlo-like nature hinders intuition building. Here, we develop a new solution to this problem and its empirical validation. We first derive closed-form analytic expectations for the evolution of fixed percentiles in the real-space cosmic density distribution, {\it averaged over representative volumes observers can track cross-sectionally\}. Using the Lagrangian forms of the fluid equations, we show that percentiles in $\delta$---the density relative to the median---should grow as $\delta(t)\propto\delta_{0}^{\alpha}\,t^{\beta}$, where $\alpha\equiv2$ and $\beta\equiv2$ for Newtonian gravity at epochs after the overdensities transitioned to nonlinear growth. We then use 9.5 sq. deg. of Carnegie-Spitzer-IMACS Redshift Survey data to map {\it galaxy\} environmental densities over $0.2, Comment: 13 pages, 12 figures, submitted to Monthly Notices of the Royal Astronomical Society, 23 August 2019, and accepted for publication, 9 January 2020. Some more typo(s) fixed

Author(s): Schlegel, David J; Kollmeier, Juna A; Aldering, Greg; Bailey, Stephen; Baltay, Charles; Bebek, Christopher; BenZvi, Segev; Besuner, Robert; Blanc, Guillermo; Bolton, Adam S; Bouri, Mohamed; Brooks, David; Buckley-Geer, Elizabeth; Cai, Zheng; Crane, Jeffrey; Dey, Arjun; Doel, Peter; Fan, Xiaohui; Ferraro, Simone; Font-Ribera, Andreu; Gutierrez, Gaston; Guy, Julien; Heetderks, Henry; Huterer, Dragan; Infante, Leopoldo; Jelinsky, Patrick; Johns, Matthew; Karagiannis, Dionysios; Kent, Stephen M; Kim, Alex G; Kneib, Jean-Paul; Kronig, Luzius; Konidaris, Nick; Lahav, Ofer; Lampton, Michael L; Lang, Dustin; Leauthaud, Alexie; Liguori, Michele; Linder, Eric V; Magneville, Christophe; Martini, Paul; Mateo, Mario; McDonald, Patrick; Miller, Christopher J; Moustakas, John; Myers, Adam D; Mulchaey, John; Newman, Jeffrey A; Nugent, Peter E; Palanque-Delabrouille, Nathalie; Padmanabhan, Nikhil; Piro, Anthony L; Poppett, Claire; Prochaska, Jason X; Pullen, Anthony R; Rabinowitz, David; Ramirez, Solange; Rix, Hans-Walter; Ross, Ashley J; Samushia, Lado; Schaan, Emmanuel; Schubnell, Michael; Seljak, Uros; Seo, Hee-Jong; Shectman, Stephen A; Silber, Joseph; Simon, Joshua D; Slepian, Zachary; Soares-Santos, Marcelle; Tarle, Greg; Thompson, Ian; Valluri, Monica; Wechsler, Risa H; White, Martin; Wilson, Michael J; Yeche, Christophe; Zaritsky, Dennis | Abstract: MegaMapper is a proposed ground-based experiment to measure Inflation parameters and Dark Energy from galaxy redshifts at 2

As an evolutionary phase of galaxies, active galactic nuclei (AGN) over a large range of redshift have been utilized for understanding cosmic evolution. In particular, the population and evolution of AGNs have been investigated through the study of the cosmic X-ray background in various fields. As one of the deep fields observed by Chandra with a total of 2.8 Msec exposures, Abell 133 is a special region to investigate AGNs, providing a testbed for probing the environmental effect on AGN trigger, since cluster environments can be different from field environments. The achieved flux limit of data at 50% completeness level of 6.95x10^(-16), 1.43x10^(-16), and 1.57x10^(-15) ergs cm^(-2) in 0.5-8, 0.5-2, and 2-8 keV. Using the wavdetect and no-source binomial probability (i.e., p, Accepted for publication in ApJ. 11 pages, 12 figures

We report the discovery of six spatially extended (10-100 kpc) line-emitting nebulae in the z=0.57 galaxy group hosting PKS0405-123, one of the most luminous quasars at z, 9 pages, 3 figures, 2 tables. Accepted to ApJ Letters

We present the analysis of deep optical imaging of the galaxy cluster Abell 133 with the IMACS instrument on Magellan. Our multi-band photometry enables stellar mass measurements in the cluster member galaxies down to a mass limit of $M_\star=3\times10^8\,M_\odot$ ($\approx 0.1$ of the Large Magellanic Cloud stellar mass). We observe a clear difference in the spatial distribution of large and dwarf galaxies within the cluster. Modeling these galaxies populations separately, we can confidently track the distribution of stellar mass locked in the galaxies to the cluster's virial radius. The extended envelope of the cluster's brightest galaxy can be tracked to $\sim 200$ kpc. The central galaxy contributes $\sim 1/3$ of the the total cluster stellar mass within the radius $r_{500c}$.

We introduce LATIS, the Ly$\alpha$ Tomography IMACS Survey, a spectroscopic survey at Magellan designed to map the z=2.2-2.8 intergalactic medium (IGM) in three dimensions by observing the Ly$\alpha$ forest in the spectra of galaxies and QSOs. Within an area of 1.7 deg${}^2$, we will observe approximately half of $\gtrsim L^*$ galaxies at z=2.2-3.2 for typically 12 hours, providing a dense network of sightlines piercing the IGM with an average transverse separation of 2.5 $h^{-1}$ comoving Mpc (1 physical Mpc). At these scales, the opacity of the IGM is expected to be closely related to the dark matter density, and LATIS will therefore map the density field in the $z \sim 2.5$ universe at $\sim$Mpc resolution over the largest volume to date. Ultimately LATIS will produce approximately 3800 spectra of z=2.2-3.2 galaxies that probe the IGM within a volume of $4 \times 10^6 h^{-3}$ Mpc${}^3$, large enough to contain a representative sample of structures from protoclusters to large voids. Observations are already complete over one-third of the survey area. In this paper, we describe the survey design and execution. We present the largest IGM tomographic maps at comparable resolution yet made. We show that the recovered matter overdensities are broadly consistent with cosmological expectations based on realistic mock surveys, that they correspond to galaxy overdensities, and that we can recover structures identified using other tracers. LATIS is conducted in Canada-France-Hawaii Telescope Legacy Survey fields, including COSMOS. Coupling the LATIS tomographic maps with the rich data sets collected in these fields will enable novel studies of environment-dependent galaxy evolution and the galaxy-IGM connection at cosmic noon.

Filaments of the cosmic web have long been associated with the threadlike structures seen in galaxy redshift surveys. However, despite their baryon content being dominated by hot gas, these filaments have been an elusive target for X-ray observations. Recently, detections of filaments in very deep (2.4 Msec) observations with Chandra were reported around Abell 133 (z=0.0559). To verify these claims, we conducted a multi-object spectrographic campaign on the Baade 6.5m telescope around Abell 133; this resulted in a catalog of ${\sim}3000$ new redshift measurements, of which 254 are of galaxies near the cluster. We investigate the kinematic state of Abell 133 and identify the physical locations of filamentary structure in the galaxy distribution. Contrary to previous studies, we see no evidence that Abell 133 is dynamically disturbed; we reject the hypothesis that there is a kinematically distinct subgroup (p=0.28) and find no velocity offset between the central galaxy and the cluster ($\textrm{Z}_\textrm{score}=0.041^{+0.111}_{-0.106}$). The spatial distribution of galaxies traces the X-ray filaments, as confirmed by angular cross correlation with a significance of ${\sim}5\sigma$. A similar agreement is found in the angular density distribution, where two X-ray structures have corresponding galaxy enhancements. We also identify filaments in the large-scale structure of galaxies; these filaments approach the cluster from the direction the X-ray structures are seen. While more members between $\textrm{R}_{200}$ and $2\times\textrm{R}_{200}$ are required to clarify which large scale filaments connect to the X-ray gas, we argue that this is compelling evidence that the X-ray emission is indeed associated with cosmic filaments., Comment: 25 pages, 10 figures. Accepted for publication in ApJ

We present a 45 ks Chandra observation of the quasar ULAS J1342+0928 at z=7.54. We detect 14.0^{+4.8}_{-3.7} counts from the quasar in the observed-frame energy range 0.5-7.0 keV (6-sigma detection), representing the most distant non-transient astronomical source identified in X-rays to date. The present data are sufficient only to infer rough constraints on the spectral parameters. We find an X-ray hardness ratio of HR = -0.51^{+0.26}_{-0.28} between the 0.5-2.0 keV and 2.0-7.0 keV ranges and derive a power-law photon index of Gamma = 1.95^{+0.55}_{-0.53}. Assuming a typical value for high-redshift quasars of Gamma = 1.9, ULAS J1342+0928 has a 2-10 keV rest-frame X-ray luminosity of L_{2-10} = 11.6^{+4.3}_{-3.5} x 10^{44} erg/s. Its X-ray-to-optical power-law slope is alpha_{OX}=-1.67^{+0.16}_{-0.10}, consistent with the general trend indicating that the X-ray emission in the most bolometrically powerful quasars is weaker relative to their optical emission., Comment: Accepted for publication in the Astrophysical Journal Letters

Gas metallicity is a key quantity used to determine the physical conditions of gaseous clouds in a wide range of astronomical environments, including interstellar and intergalactic space. In particular, considerable effort in circumgalactic medium (CGM) studies focuses on metallicity measurements, because gas metallicity serves as a critical discriminator for whether the observed heavy ions in the CGM originate in chemically-enriched outflows or in more chemically-pristine gas accreted from the intergalactic medium. However, because the gas is ionized, a necessary first step in determining CGM metallicity is to constrain the ionization state of the gas which, in addition to gas density, depends on the ultraviolet background radiation field (UVB). While it is generally acknowledged that both the intensity and spectral slope of the UVB are uncertain, the impact of an uncertain spectral slope has not been properly addressed in the literature. This Letter shows that adopting a different spectral slope can result in an order of magnitude difference in the inferred CGM metallicity. Specifically, a harder UVB spectrum leads to a higher estimated gas metallicity for a given set of observed ionic column densities . Therefore, such systematic uncertainties must be folded into the error budget for metallicity estimates of ionized gas. An initial study shows that empirical diagnostics are available for discriminating between hard and soft ionizing spectra. Applying these diagnostics helps reduce the systematic uncertainties in CGM metallicity estimates., 7 pages, 4 figures; Accepted for publication in ApJ Letters

The relationship between galaxies and the state/chemical enrichment of the warm-hot intergalactic medium (WHIM) expected to dominate the baryon budget at low-z provides sensitive constraints on structure formation and galaxy evolution models. We present a deep redshift survey in the field of 1ES1553+113, a blazar with a unique combination of UV+X-ray spectra for surveys of the circum-/intergalactic medium (CGM/IGM). Nicastro et al. 2018 reported the detection of two O VII WHIM absorbers at $z=0.4339$ and $0.3551$ in its spectrum, suggesting that the WHIM is metal-rich and sufficient to close the missing baryons problem. Our survey indicates that the blazar is a member of a $z=0.433$ group and that the higher-$z$ O VII candidate arises from its intragroup medium. The resulting bias precludes its use in baryon censuses. The $z=0.3551$ candidate occurs in an isolated environment 630 kpc from the nearest galaxy (with stellar mass $\log M_*/M_\odot \approx 9.7$) which we show is unexpected for the WHIM. Finally, we characterize the galactic environments of broad H I Ly$\alpha$ absorbers (Doppler widths of $b=40-80$ \kms; $T\lesssim4\times10^5$ K) which provide metallicity independent WHIM probes. On average, broad Ly$\alpha$, absorbers are ${\approx}2\times$ closer to the nearest luminous ($L>0.25 L_*$) galaxy (700 kpc) than narrow ($b, Comment: Accepted to ApJ Letters; 10 pages, 4 figures, 1 table with the full version available on the journal webpage (or by request); v2 corrects one reference

In the local universe, a large fraction of the baryon content is believed to exist as diffuse gas in filaments. While this gas is directly observable in X-ray emission around clusters of galaxies, it is primarily studied through its UV absorption. Recently, X-ray observations of large-scale filaments connecting to the cosmic web around the nearby ($z=0.05584$) cluster Abell 133 were reported. One of these filaments is intersected by the sightline to quasar [VV98] J010250.2$-$220929, allowing for a first-ever census of cold, cool, and warm gas in a filament of the cosmic web where hot gas has been seen in X-ray emission. Here, we present UV observations with the Cosmic Origins Spectrograph and optical observations with the Magellan Echellette spectrograph of [VV98] J010250.2$-$220929. We find no evidence of cold, cool, or warm gas associated with the filament. In particular, we set a $2\sigma$ upper limit on Ly$\alpha$ absorption of $\log(N_{HI} / \textrm{cm}^{-2}) < 13.7$, assuming a Doppler parameter of $b=20\,\textrm{km}\,\textrm{s}^{-1}$. As this sightline is ${\sim}1100\,\textrm{pkpc}$ ($0.7R_\textrm{vir}$) from the center of Abell 133, we suggest that all gas in the filament is hot at this location, or that any warm, cool, or cold components are small and clumpy. A broader census of this system -- combining more UV sightlines, deeper X-ray observations, and a larger redshift catalog of cluster members -- is needed to better understand the roles of filaments around clusters., Comment: Published in the Astrophysical Journal Letters; 9 Pages, 4 Figures, 1 Table. v2 corrects one reference

We examine galaxy groups from the present epoch to z = 1 to explore the impact of group dynamics on galaxy evolution. We use group catalagues from the Sloan Digital Sky Survey (SDSS), the Group Environment and Evolution Collaboration (GEEC) and the high redshift GEEC2 sample to study how the observed member properties depend on galaxy stellar mass, group dynamical mass and dynamical state of the host group. We find a strong correlation between the fraction of non-star-forming (quiescent) galaxies and galaxy stellar mass, but do not detect a significant difference in the quiescent fraction with group dynamical mass, within our sample halo mass range of 10^13-10^14.5 M_sun, or with dynamical sate. However, at a redshift of approximately 0.4 we do see some evidence that the quiescent fraction in low mass galaxies (log(M_star/M_sun) < 10.5) is lower in groups with substructure. Additionally, our results show that the fraction of groups with non-Gaussian velocity distributions increases with redshift to roughly z = 0.4, while the amount of detected substructure remains constant to z = 1. Based on these results, we conclude that for massive galaxies (log(M_star/M_sun_ > 10.5), evolution is most strongly correlated to the stellar mass of a galaxy with little or no additional effect related to either the group dynamical mass or dynamical state. For low mass galaxies, we do see some evidence of a correlation between the quiescent fraction and the amount of detected substructure, highlighting the need to probe further down the stellar mass function to elucidate the role of the environment in galaxy evolution., 14 pages, 6 figures, MNRAS accepted

We present new absorption-line analysis and new galaxy survey data obtained for the field around PKS0405-123 at z=0.57. Combining previously known OVI absorbers with new identifications in the higher S/N UV spectra obtained with COS, we have established a sample of 7 OVI absorbers and 12 individual components at z=0.0918-0.495 along the sightline toward PKS0405-123. We complement the available UV absorption spectra with galaxy survey data that reach 100% completeness at projected distances rho0.04L* at rho0.3L* at rho13.6 and no detectable OVI absorption features. The Lya-only absorbers serve as a control sample in seeking the discriminating galactic features that result in the observed OVI absorbing gas at large galactic radii. We find a clear distinction in the radial profiles of mean galaxy surface brightness around different absorbers. Specifically, OVI absorbers are found to reside in regions of higher mean surface brightness at rho, Comment: 16 pages, 7 figures; accepted to Monthly Notices of the Royal Astronomical Society

We present the Palomar Transient Factory discoveries and the photometric and spectroscopic observations of PTF11kmb and PTF12bho. We show that both transients have properties consistent with the class of calcium-rich gap transients, specifically lower peak luminosities and rapid evolution compared to ordinary supernovae, and a nebular spectrum dominated by [Ca II] emission. A striking feature of both transients is their host environments: PTF12bho is an intra-cluster transient in the Coma Cluster, while PTF11kmb is located in a loose galaxy group, at a physical offset ~150 kpc from the most likely host galaxy. Deep Subaru imaging of PTF12bho rules out an underlying host system to a limit of $M_R > -8.0$ mag, while Hubble Space Telescope imaging of PTF11kmb reveals a marginal counterpart that, if real, could be either a background galaxy or a globular cluster. We show that the offset distribution of Ca-rich gap transients is significantly more extreme than that seen for Type Ia supernovae or even short-hard gamma-ray bursts (sGRBs). Thus, if the offsets are caused by a kick, they require larger kick velocities and/or longer merger times than sGRBs. We also show that almost all Ca-rich gap transients found to date are in group and cluster environments with elliptical host galaxies, indicating a very old progenitor population; the remote locations could partially be explained by these environments having the largest fraction of stars in the intra-group/intra-cluster light following galaxy-galaxy interactions., Matches published version. Minor changes to previous version following referee report; conclusions unchanged

We present the first comprehensive archival study of the X-ray properties of ultracompact dwarf (UCD) galaxies, with the goal of identifying weakly-accreting central black holes in UCDs. Our study spans 578 UCDs distributed across thirteen different host systems, including clusters, groups, fossil groups, and isolated galaxies. Of the 336 spectroscopically-confirmed UCDs with usable archival Chandra imaging observations, 21 are X-ray-detected. Imposing a completeness limit of $L_X>2\times10^{38}$ erg s$^{-1}$, the global X-ray detection fraction for the UCD population is $\sim3\%$. Of the 21 X-ray-detected UCDs, seven show evidence of long-term X-ray time variability on the order of months to years. X-ray-detected UCDs tend to be more compact than non-X-ray-detected UCDs, and we find tentative evidence that the X-ray detection fraction increases with surface luminosity density and global stellar velocity dispersion. The X-ray emission of UCDs is fully consistent with arising from a population of low-mass X-ray binaries (LMXBs). In fact, there are fewer X-ray sources than expected using a naive extrapolation from globular clusters. Invoking the fundamental plane of black hole activity for SUCD1 near the Sombrero galaxy, for which archival Jansky Very Large Array imaging at 5 GHz is publicly available, we set an upper limit on the mass of a hypothetical central black hole in that UCD to be $\lesssim10^5M_{\odot}$. While the majority of our sources are likely LMXBs, we cannot rule out central black holes in some UCDs based on X-rays alone, and so we address the utility of follow-up radio observations to find weakly-accreting central black holes., 20 pages, 6 figures, re-submitted to ApJ after minor revisions

We present a compilation of UBVRIz light curves of 51 type II supernovae discovered during the course of four different surveys during 1986-2003: the Cerro Tololo Supernova Survey, the Calán/Tololo Supernova Program (C&T), the Supernova Optical and Infrared Survey (SOIRS), and the Carnegie Type II Supernova Survey (CATS). The photometry is based on template-subtracted images to eliminate any potential host galaxy light contamination, and calibrated from foreground stars. This work presents these photometric data, studies the color evolution using different bands, and explores the relation between the magnitude at maximum brightness and the brightness decline parameter (s) from maximum light through the end of the recombination phase. This parameter is found to be shallower for redder bands and appears to have the best correlation in the B band. In addition, it also correlates with the plateau duration, being shorter (longer) for larger (smaller) s values., La lista completa de autores que integran el documento puede consultarse en el archivo., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local environment at $z10^{10.4-10.6}$ $M_{\odot}$), across all environments. At high redshift ( $0.5, Comment: 14 pages, 14 figures, accepted for publication in MNRAS

We investigate the optical and Wide-field Survey Explorer (WISE) colors of "E+A" identified post-starburst galaxies, including a deep analysis on 190 post-starbursts detected in the 2{\mu}m All Sky Survey Extended Source Catalog. The post-starburst galaxies appear in both the optical green valley and the WISE Infrared Transition Zone (IRTZ). Furthermore, we find that post-starbursts occupy a distinct region [3.4]-[4.6] vs. [4.6]-[12] WISE colors, enabling the identification of this class of transitioning galaxies through the use of broad-band photometric criteria alone. We have investigated possible causes for the WISE colors of post-starbursts by constructing a composite spectral energy distribution (SED), finding that mid-infrared (4-12{\mu}m) properties of post-starbursts are consistent with either 11.3{\mu}m polycyclic aromatic hydrocarbon emission, or Thermally Pulsating Asymptotic Giant Branch (TP-AGB) and post-AGB stars. The composite SED of extended post- starburst galaxies with 22{\mu}m emission detected with signal to noise >3 requires a hot dust component to produce their observed rising mid-infrared SED between 12 and 22{\mu}m. The composite SED of WISE 22{\mu}m non-detections (S/N, Comment: 13 pages, 11 figures, accepted for publication in the Astrophysical Journal

We present coarse but robust star formation histories (SFHs) derived from spectro-photometric data of the Carnegie-Spitzer-IMACS Survey, for 22,494 galaxies at 0.3, Comment: 17 pages, 10 figures; accepted by ApJ; version 2 - no substantive changes; clarifications and corrections

The presence of substructure in galaxy groups and clusters is believed to be a sign of recent galaxy accretion and can be used not only to probe the assembly history of these structures, but also the evolution of their member galaxies. Using the Dressler-Shectman (DS) Test, we study substructure in a sample of intermediate redshift (z ~ 0.4) galaxy groups from the Group Environment and Evolution Collaboration (GEEC) group catalog. We find that 4 of the 15 rich GEEC groups, with an average velocity dispersion of ~525 km s-1, are identified as having significant substructure. The identified regions of localized substructure lie on the group outskirts and in some cases appear to be infalling. In a comparison of galaxy properties for the members of groups with and without substructure, we find that the groups with substructure have a significantly higher fraction of blue and star-forming galaxies and a parent colour distribution that resembles that of the field population rather than the overall group population. In addition, we observe correlations between the detection of substructure and other dynamical measures, such as velocity distributions and velocity dispersion profiles. Based on this analysis, we conclude that some galaxy groups contain significant substructure and that these groups have properties and galaxy populations that differ from groups with no detected substructure. These results indicate that the substructure galaxies, which lie preferentially on the group outskirts and could be infalling, do not exhibit signs of environmental effects, since little or no star-formation quenching is observed in these systems.

We examine the star formation properties of group and field galaxies in two surveys, the Sloan Digital Sky Survey (SDSS; at z ~ 0.08) and the Group Environment and Evolution Collaboration (GEEC; at z ~ 0.4). Using UV imaging from the GALEX space telescope, along with optical and, for GEEC, near infrared photometry, we compare the observed spectral energy distributions to large suites of stellar population synthesis models. This allows us to accurately determine star formation rates and stellar masses. We find that star forming galaxies of all environments undergo a systematic lowering of their star formation rate between z=0.4 and z=0.08 regardless of mass. Nonetheless, the fraction of passive galaxies is higher in groups than the field at both redshifts. Moreover, the difference between the group and field grows with time and is mass-dependent, in the sense the the difference is larger at low masses. However, the star formation properties of star forming galaxies, as measured by their average specific star formation rates, are consistent within the errors in the group and field environment at fixed redshift. The evolution of passive fraction in groups between z=0.4 and z=0 is consistent with a simple accretion model, in which galaxies are environmentally affected 3 Gyrs after falling into a ~ 10E13 Msun group. This long timescale appears to be inconsistent with the need to transform galaxies quickly enough to ensure that star forming galaxies appear similar in both the group and field, as observed.

(abridged) We introduce our survey of galaxy groups at 0.85 15 members. The dynamical mass estimates are in good agreement with the masses estimated from the X-ray luminosity, with most of the groups having 13 1E10.1 Msun, and for blue galaxies we sample masses as low as Mstar=1E8.8 Msun. Like lower-redshift groups, these systems are dominated by red galaxies, at all stellar masses Mstar>1E10.1 Msun. Few group galaxies inhabit the "blue cloud" that dominates the surrounding field; instead, we find a large and possibly distinct population of galaxies with intermediate colours. The "green valley" that exists at low redshift is instead well-populated in these groups, containing ~30 per cent of galaxies. These do not appear to be exceptionally dusty galaxies, and about half show prominent Balmer-absorption lines. Furthermore, their HST morphologies appear to be intermediate between those of red-sequence and blue-cloud galaxies of the same stellar mass. We postulate that these are a transient population, migrating from the blue cloud to the red sequence, with a star formation rate that declines with an exponential timescale 0.6 Gyr< tau < 2 Gyr. Their prominence among the group galaxy population, and the marked lack of blue, star-forming galaxies, provides evidence that the group environment either directly reduces star formation in member galaxies, or at least prevents its rejuvenation during the normal cycle of galaxy evolution.

The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify galaxies in the transitional phase between actively star-forming and quiescence with nebular lines that are excited from shocks rather than star formation processes. We explored the ultraviolet (UV) properties of objects with near-ultraviolet (NUV) and far-ultraviolet (FUV) photometry from archival GALEX data; 444 objects were detected in both bands, 365 in only the NUV, and 24 in only the FUV, for a total of 833 observed objects. We compared SPOGs to samples of star-forming galaxies (SFs), quiescent galaxies (Qs), classical E+A post-starburst galaxies, active galactic nuclei (AGN) host galaxies, and interacting galaxies. We found that SPOGs have a larger range in their FUV–NUV and NUV–r colors compared with most of the other samples, although all of our comparison samples occupied color space inside of the SPOGs region. On the basis of their UV colors, SPOGs are a heterogeneous group, possibly made up of a mixture of SFs, Qs, and/or AGN. Using Gaussian mixture models, we are able to recreate the distribution of FUV–NUV colors of SPOGs and E + A galaxies with different combinations of SFs, Qs, and AGN. We find that the UV colors of SPOGs require a >60% contribution from SFs, with either Qs or AGN representing the remaining contribution, while UV colors of E + A galaxies required a significantly lower fraction of SFs, supporting the idea that SPOGs are at an earlier point in their transition from quiescent to star-forming than E + A galaxies.

We present the first mid-IR study of galaxy groups in the nearby Universe based on Spitzer MIPS observations of a sample of nine redshift-selected groups from the XMM-IMACS (XI) project, at z=0.06. We find that on average the star-forming (SF) galaxy fraction in the groups is about 30% lower than the value in the field and 30% higher than in clusters. The SF fractions do not show any systematic dependence on group velocity dispersion, total stellar mass, or the presence of an X-ray emitting intragroup medium, but a weak anti-correlation is seen between SF fraction and projected galaxy density. However, even in the densest regions, the SF fraction in groups is still higher than that in cluster outskirts, suggesting that preprocessing of galaxies in group environments is not sufficient to explain the much lower SF fraction in clusters. The typical specific star formation rates (SFR/M*) of SF galaxies in groups are similar to those in the field across a wide range of stellar mass (M*>10^9.6 msun), favoring a quickly acting mechanism that suppresses star formation to explain the overall smaller fraction of SF galaxies in groups. If galaxy-galaxy interactions are responsible, then the extremely low starburst galaxy fraction (10^10 Msun), possibly as a consequence of ram pressure stripping being less efficient in removing gas from more massive galaxies., 19 pages, 7 figures, 1 table. Accepted by ApJ

We have performed a systematic search for X-ray cavities in the hot gas of 51 galaxy groups with Chandra archival data. The cavities are identified based on two methods: subtracting an elliptical beta model fitted to the X-ray surface brightness, and performing unsharp masking. 13 groups in the sample 25% are identified as clearly containing cavities, with another 13 systems showing tentative evidence for such structures. We find tight correlations between the radial and tangential radii of the cavities, and between their size and projected distance from the group center, in quantitative agreement with the case for more massive clusters. This suggests that similar physical processes are responsible for cavity evolution and disruption in systems covering a large range in total mass. We see no clear association between the detection of cavities and the current 1.4 GHz radio luminosity of the central brightest group galaxy, but there is a clear tendency for systems with a cool core to be more likely to harbor detectable cavities. To test the efficiency of the adopted cavity detection procedures, we employ a set of mock images designed to mimic typical Chandra data of our sample, and find that the model-fitting approach is generally more reliable than unsharp masking for recovering cavity properties. Finally, we find that the detectability of cavities is strongly influenced by a few factors, particularly the signal-to-noise ratio of the data, and that the real fraction of X-ray groups with prominent cavities could be substantially larger than the 25--50% suggested by our analysis., Comment: 19 pages, 16 figures, 2 tables, accepted by ApJ

We present the first luminous, spatially resolved binary quasar that clearly inhabits an ongoing galaxy merger. SDSS J125455.09+084653.9 and SDSS J125454.87+084652.1 (SDSS J1254+0846 hereafter) are two luminous z=0.44 radio quiet quasars, with a radial velocity difference of just 215 km/s, separated on the sky by 21 kpc in a disturbed host galaxy merger showing obvious tidal tails. The pair was targeted as part of a complete sample of binary quasar candidates with small transverse separations drawn from SDSS DR6 photometry. We present follow-up optical imaging which shows broad, symmetrical tidal arm features spanning some 75 kpc at the quasars' redshift. Numerical modeling suggests that the system consists of two massive disk galaxies prograde to their mutual orbit, caught during the first passage of an active merger. This demonstrates rapid black hole growth during the early stages of a merger between galaxies with pre-existing bulges. Neither of the two luminous nuclei show significant instrinsic absorption by gas or dust in our optical or X-ray observations, illustrating that not all merging quasars will be in an obscured, ultraluminous phase. We find that the Eddington ratio for the fainter component B is rather normal, while for the A component L/LEdd is quite (>3sigma) high compared to quasars of similar luminosity and redshift, possibly evidence for strong merger-triggered accretion. More such mergers should be identifiable at higher redshifts using binary quasars as tracers., 15 pages, 5 figures, accepted to the Astrophysical Journal for the February 2010 - 20 v710 issue. Latest version corrects author list

(Abridged) We present new optical and near-infrared imaging for a sample of 98 spectroscopically-selected galaxy groups at 0.25, Comment: Resubmitted to MNRAS following referee report

We present an imaging and spectroscopic survey of galaxies in fields around QSOs HE 0226-4110, PKS 0405-123, and PG 1216+069. The fields are selected to have ultraviolet echelle spectra available, which uncover 195 Ly{alpha} absorbers and 13 O{sub VI} absorbers along the three sightlines. We obtain robust redshifts for 1104 galaxies of rest-frame absolute magnitude M{sub R} - 5log h {approx} =}14 and O{sub VI} absorbers exhibit a comparable clustering amplitude as emission-line-dominated galaxies and a factor of {approx} 6 weaker amplitude than absorption-line-dominated galaxies on comoving projected distance scales of r{sub p} 70 mA.« less

To better understand the mechanism or mechanisms that lead to AGN activity today, we measure the X-ray AGN fraction in a new sample of nearby clusters and examine how it varies with galaxy properties, projected cluster-centric radius, and cluster velocity dispersion. We present new wide-field Chandra X-ray Observatory observations of Abell 85, Abell 754 and the background cluster Abell 89B out to their virial radii. Out of seventeen X-ray sources associated with galaxies in these clusters, we classify seven as X-ray AGN with L_{X,B} > 10^{41} erg/s. Only two of these would be classified as AGN based on their optical spectra. We combine these observations with archival data to create a sample of X-ray AGN from six z 10^{41} erg/s. We find that more X-ray AGN are detected in more luminous galaxies and attribute this to larger spheriods in more luminous galaxies and increased sensitivity to lower Eddington-rate accretion from black holes in those spheroids. At a given X-ray luminosity limit, more massive black holes can be accreting less efficiently, yet still be detected. If interactions between galaxies are the principal drivers of AGN activity, then the AGN fraction should be higher in lower velocity dispersion clusters and the outskirts of clusters. However, the tendency of the most massive and early-type galaxies to lie in the centers of the richest clusters could dilute such trends. While we find no variation in the AGN fraction with projected cluster-centric radius, we do find that the AGN fraction increases significantly from 2.6+1.0/-0.8% in rich clusters to 10.0+6.2/-4.3% in those with lower velocity dispersions.

We use Chandra observations of 13 nearby groups of galaxies to investigate the hot gas content of their member galaxies. We find that a large fraction of near-IR bright, early-type galaxies in groups have extended X-ray emission, indicating that they retain significant hot gas halos even in these dense environments. In particular, we detect hot gas halos in ~80% of L_K > L_star galaxies. We do not find a significant difference in the L_K-L_X relation for detected group and cluster early-type galaxies. However, we detect X-ray emission from a significantly higher fraction of galaxies brighter than L_star in groups compared to clusters, indicating that a larger fraction of galaxies in clusters experience significant stripping of their hot gas. In addition, group and cluster galaxies appear to be X-ray faint compared to field galaxies, though a Chandra based field sample is needed to confirm this result. The near-IR bright late-types galaxies in clusters and groups appear to follow the L_K-L_X relation for early-type galaxies, while near-IR fainter late-type galaxies are significantly more X-ray luminous than this relation likely due to star formation. Finally, we find individual examples of ongoing gas stripping of group galaxies. One galaxy shows a 40-50 kpc X-ray tail, and two merging galaxy systems show tidal bridges/tails of X-ray emission. Therefore, stripping of hot galactic gas through both ram pressure and tidal forces does occur in groups and clusters, but the frequency or efficiency of such events must be moderate enough to allow hot gas halos in a large fraction of bright galaxies to survive even in group and cluster cores., 33 pages, 7 figures, accepted to ApJ, for version with full resolution figures see http://www.ucolick.org/~tesla/groupgals.ps.gz

We present a detailed analysis of the intergalactic metal-line absorption systems in the archival HST/STIS and FUSE ultraviolet spectra of the low-redshift quasar PKS1302-102 (z_QSO = 0.2784). We supplement the archive data with CLOUDY ionization models and a survey of galaxies in the quasar field. There are 15 strong Lya absorbers with column densities logN_HI > 14. Of these, six are associated with at least CIII 977 absorption (logN(C^++) > 13); this implies a redshift density dN_CIII/dz = 36+13/-9 (68% confidence limits) for the five detections with rest equivalent width W_r > 50 mA. Two systems show OVI 1031,1037 absorption in addition to CIII (logN(O^+5) > 14). One is a partial Lyman limit system (logN_HI = 17) with associated CIII, OVI, and SiIII 1206 absorption. There are three tentative OVI systems that do not have CIII detected. For one OVI doublet with both lines detected at 3 sigma with W_r > 50 mA, dN_OVI/dz = 7+9/-4. We also search for OVI doublets without Lya absorption but identify none. From CLOUDY modeling, these metal-line systems have metallicities spanning the range -4 < [M/H] < -0.3. The two OVI systems with associated CIII absorption cannot be single-phase, collisionally-ionized media based on the relative abundances of the metals and kinematic arguments. From the galaxy survey, we discover that the absorption systems are in a diverse set of galactic environments. Each metal-line system has at least one galaxy within 500 km/s and 600 h^-1 kpc with L > 0.1 L_*., 21 pages in emulatepj form, 24 figures, 10 tables, accepted to ApJ

We present a study of the distribution of AGN in clusters of galaxies with a uniformly selected, spectroscopically complete sample of 35 AGN in eight clusters at z = 0.06 to 0.31. We find that the 12 AGN with L_X > 10^42 erg/s in galaxies more luminous than a rest-frame M_R 10^41 erg/s do not show evidence for greater concentration than inactive members, nor evidence for a different kinematic or substructure distribution. As we do see clear differences in the spatial and kinematic distributions of the blue Butcher-Oemler and red galaxy populations, any difference in the AGN and inactive galaxy population must be less distinct than that between these two pairs of populations. Comparison of the AGN fraction selected via X-ray emission in this study to similarly-selected AGN in the field indicates that the AGN fraction is not significantly lower in clusters, contrary to AGN identified via visible-wavelength emission lines, but similar to the approximately constant radio-selected AGN fraction in clusters and the field. We also find significant evidence for variation between clusters and explore the dependence of cluster AGN fraction on redshift, velocity dispersion, cluster substructure, and Butcher-Oemler fraction. While we see weak evidence for several trends, correlations between these four parameters in our small sample precludes identification of which one(s) most strongly influence the cluster AGN fraction.

We investigate the galaxy populations in seven X-ray selected, intermediate-redshift groups (0.2, Comment: 50 pages, 8 figures, minor revisons to make consistent with published version, for version with full resolution figures, see http://www.ociw.edu/~tesla/groups.ps.gz

We present an analysis of galaxies in groups and clusters at $0.810^{10.3}M_\odot$, we find $f_{\rm convert}\sim 0.4$ in the groups and $\sim 0.6$ in the clusters, similar to comparable measurements at $z=0$. This means the time between first accretion into a more massive halo and final star formation quenching is $t_p\sim 2$ Gyr. This is substantially longer than the estimated time required for a galaxy's star formation rate to become zero once it starts to decline, suggesting there is a long delay time during which little differential evolution occurs. In contrast with local observations we find evidence that this delay timescale may depend on stellar mass, with $t_p$ approaching $t_{\rm Hubble}$ for $M_{\rm star}\sim 10^{9.5}M_\odot$. The result suggests that the delay time must not only be much shorter than it is today, but may also depend on stellar mass in a way that is not consistent with a simple evolution in proportion to the dynamical time. Instead, we find the data are well-matched by a model in which the decline in star formation is due to "overconsumption", the exhaustion of a gas reservoir through star formation and expulsion via modest outflows in the absence of cosmological accretion. Dynamical gas removal processes, which are likely dominant in quenching newly accreted satellites today, may play only a secondary role at $z=1$., Comment: Submitted to MNRAS; revised Oct 23 following referee report