Large surveys of galaxy clusters with the Hubble Space Telescope (HST) and Spitzer, including the Cluster Lensing And Supernova survey with Hubble and the Frontier Fields, have demonstrated the power ...of strong gravitational lensing to efficiently deliver large samples of high-redshift galaxies. We extend this strategy through a wider, shallower survey named RELICS, the Reionization Lensing Cluster Survey, described here. Our 188-orbit Hubble Treasury Program observed 41 clusters at 0.182 ≤ z ≤ 0.972 with Advanced Camera for Surveys (ACS) and WFC3/IR imaging spanning 0.4-1.7 m. We selected 21 of the most massive clusters known based on Planck PSZ2 estimates and 20 additional clusters based on observed or inferred lensing strength. RELICS observed 46 WFC3/IR pointings (∼200 arcmin2) each with two orbits divided among four filters (F105W, F125W, F140W, and F160W) and ACS imaging as needed to achieve single-orbit depth in each of three filters (F435W, F606W, and F814W). As previously reported by Salmon et al., we discovered over 300 z ∼ 6-10 candidates, including the brightest z ∼ 6 candidates known, and the most distant spatially resolved lensed arc known at z ∼ 10. Spitzer IRAC imaging (945 hr awarded, plus 100 archival, spanning 3.0-5.0 m) has crucially enabled us to distinguish z ∼ 10 candidates from z ∼ 2 interlopers. For each cluster, two HST observing epochs were staggered by about a month, enabling us to discover 11 supernovae, including 3 lensed supernovae, which we followed up with 20 orbits from our program. Reduced HST images, catalogs, and lens models are available on MAST, and reduced Spitzer images are available on IRSA.
Abstract
We investigate the impact of local environment on the galaxy stellar mass function (SMF) spanning a wide range of galaxy densities from the field up to dense cores of massive galaxy ...clusters. Data are drawn from a sample of eight fields from the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. Deep photometry allow us to select mass-complete samples of galaxies down to 109 M⊙. Taking advantage of >4000 secure spectroscopic redshifts from ORELSE and precise photometric redshifts, we construct three-dimensional density maps between 0.55 < z < 1.3 using a Voronoi tessellation approach. We find that the shape of the SMF depends strongly on local environment exhibited by a smooth, continual increase in the relative numbers of high- to low-mass galaxies towards denser environments. A straightforward implication is that local environment proportionally increases the efficiency of (a) destroying lower mass galaxies and/or (b) growth of higher mass galaxies. We also find a presence of this environmental dependence in the SMFs of star-forming and quiescent galaxies, although not quite as strongly for the quiescent subsample. To characterize the connection between the SMF of field galaxies and that of denser environments, we devise a simple semi-empirical model. The model begins with a sample of ≈106 galaxies at z
start = 5 with stellar masses distributed according to the field. Simulated galaxies then evolve down to z
final = 0.8 following empirical prescriptions for star-formation, quenching and galaxy–galaxy merging. We run the simulation multiple times, testing a variety of scenarios with differing overall amounts of merging. Our model suggests that a large number of mergers are required to reproduce the SMF in dense environments. Additionally, a large majority of these mergers would have to occur in intermediate density environments (e.g. galaxy groups).
Abstract
Faint star-forming galaxies at
z
∼ 2–3 can be used as alternative background sources to probe the Ly
α
forest in addition to quasars, yielding high sightline densities that enable 3D ...tomographic reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Ly
α
Mapping And Tomography Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck I telescope. Over an observational footprint of 0.157 deg
2
within the COSMOS field, we used 240 galaxies and quasars at 2.17 <
z
< 3.00, with a mean comoving transverse separation of
, as background sources probing the foreground Ly
α
forest absorption at 2.05 <
z
< 2.55. The Ly
α
forest data was then used to create a Wiener-filtered tomographic reconstruction over a comoving volume of
with an effective smoothing scale of
. In addition to traditional figures, this map is also presented as a virtual-reality visualization and manipulable interactive figure. We see large overdensities and underdensities that visually agree with the distribution of coeval galaxies from spectroscopic redshift surveys in the same field, including overdensities associated with several recently discovered galaxy protoclusters in the volume. Quantitatively, the map signal-to-noise is
over a 3
h
−1
Mpc top-hat kernel based on the variances estimated from the Wiener filter. This data release includes the redshift catalog, reduced spectra, extracted Ly
α
forest pixel data, and reconstructed tomographic map of the absorption. These can be downloaded from Zenodo (
10.5281/zenodo.1292459
).
ABSTRACT
This work presents the first comprehensive study of structure formation at the peak epoch of cosmic star formation over 1.4 ≤ z ≤ 3.6 in the Cosmic Evolution Survey (COSMOS) field, including ...the most massive high-redshift galaxy proto-clusters at that era. We apply the extended COSMIC BIRTH algorithm to account for a multitracer and multisurvey Bayesian analysis at Lagrangian initial cosmic times. Combining the data of five different spectroscopic redshift surveys (zCOSMOS-deep, VUDS, MOSDEF, ZFIRE, and FMOS–COSMOS), we show that the corresponding unbiased primordial density fields can be inferred, if a proper survey completeness computation from the parent photometric catalogues, and a precise treatment of the non-linear and non-local evolution on the light-cone is taken into account, including (i) gravitational matter displacements, (ii) peculiar velocities, and (iii) galaxy bias. The reconstructions reveal a holistic view on the known proto-clusters in the COSMOS field and the growth of the cosmic web towards lower redshifts. The inferred distant dark matter density fields concurrently with other probes like tomographic reconstructions of the intergalactic medium will explore the interplay of gas and dark matter and are ideally suited to study structure formation at high redshifts in the light of upcoming deep surveys.
Measurements of stellar properties of galaxies when the universe was less than one billion years old yield some of the only observational constraints on the onset of star formation. We present here ...the inclusion of Spitzer/IRAC imaging in the fitting of the spectral energy distribution of the seven highest-redshift galaxy candidates selected from the Hubble Space Telescope (HST) imaging of the Reionization Lensing Cluster Survey. We find that for six out of eight HST-selected z ∼ 8 sources, the z ∼ 8 solutions are still strongly preferred over z ∼ 1-2 solutions after the inclusion of Spitzer fluxes, and two prefer a z ∼ 7 solution, which we defer to a later analysis. We find a wide range of intrinsic stellar masses (5 × 106-4 × 109 M ), star formation rates (0.2-14 M yr−1), and ages (30-600 Myr) among our sample. Of particular interest is A1763-1434, which shows evidence of an evolved stellar population (∼500 Myr) at z ∼ 8, implying that its first generation of star formation occurred <100 Myr after the Big Bang. SPT0615-JD, a spatially resolved z ∼ 10 candidate, remains at its high redshift, supported by deep Spitzer/IRAC data, and also shows some evidence for an evolved stellar population. Even with the lensed, bright apparent magnitudes of these z 8 candidates (H = 26.1-27.8 AB mag), only the James Webb Space Telescope will be able to exclude the possibility of abnormally strong nebular emission, large dust content, or some combination thereof, and confirm the presence of evolved stellar populations early in the universe.
ABSTRACT
We present a Bayesian inference on the neutral hydrogen fraction of the intergalactic medium (IGM), $\overline{x}_{\small HI}$, at z ∼ 6–8 using the properties of Lyman break galaxies (LBGs) ...during the epoch of reionization. We use large samples of LBG candidates at 5.5 ≤ z ≤ 8.2 with spectroscopy from Keck/DEIMOS and Keck/MOSFIRE. For each galaxy, we incorporate either the Lyman-α (Lyα) equivalent width (EW) for detections or the EW limit spectrum for non-detections to parametrize the EW distribution at various ultraviolet brightnesses for a given redshift. Using our reference sample of galaxy candidates from the ionized universe at z ∼ 6.0, we are able to infer $\overline{x}_{\small HI}$ at two redshifts: z ∼ 6.7 and z ∼ 7.6. This work includes intrinsically faint, gravitationally lensed galaxies at z ∼ 6.0 in order to constrain the intrinsic faint-end Lyα EW distribution and provide a comparable population of galaxies to counterparts in our sample that are at higher redshift. The inclusion of faint galaxy candidates, in addition to a more sophisticated modelling framework, allows us to better isolate effects of the interstellar medium and circumgalactic medium on the observed Lyα distribution from those of the IGM. We infer an upper limit of $\overline{x}_{\small HI}$ ≤ 0.25 (0.44) at z = 6.7 ± 0.2 and a neutral fraction of $\overline{x}_{\small HI}$ = $0.83^{+0.08}_{-0.11}$ (0.83$^{+0.11}_{-0.21}$) at z = 7.6 ± 0.6, both within 68 per cent (95 per cent) uncertainty, results that favour a moderately late and fairly rapid reionization.
Abstract
We present the second data release of the COSMOS Ly
α
Mapping And Tomography Observations Survey conducted with the Low Resolution Imaging Spectrometer on the Keck I telescope. This project ...used Ly
α
forest absorption in the spectra of faint star-forming galaxies and quasars at
z
∼ 2–3 to trace neutral hydrogen in the intergalactic medium. In particular, we use 320 objects over a footprint of ∼0.2 deg
2
to reconstruct the absorption field at 2.05 <
z
< 2.55 at ∼2
h
−1
Mpc resolution. We apply a Wiener filtering technique to the observed data to reconstruct three-dimensional (3D) maps of the field over a volume of 4.1 × 10
5
h
−3
Mpc
3
. In addition to the filtered flux maps, for the first time we infer the underlying dark matter field through a forward-modeling framework from a joint likelihood of galaxy and Ly
α
forest data, finding clear examples of the detailed cosmic web consisting of cosmic voids, sheets, filaments, and nodes. In addition to traditional figures, we present a number of interactive 3D models to allow exploration of the data and qualitative comparisons to known galaxy surveys. We find that our inferred overdensities are consistent with those found from galaxy fields. We will make all our reduced spectra, extracted Ly
α
forest pixel data, and reconstructed tomographic maps publicly available upon publication.
We report the spectroscopic confirmation of a new protocluster in the COSMOS field at z ∼ 2.2, COSMOS Cluster 2.2 (CC2.2), originally identified as an overdensity of narrowband selected H emitting ...candidates. With only two masks of Keck/MOSFIRE near-IR spectroscopy in both H (∼1.47-1.81 m) and K (∼1.92-2.40 m) bands (∼1.5 hr each), we confirm 35 unique protocluster members with at least two emission lines detected with S/N > 3. Combined with 12 extra members from the zCOSMOS-deep spectroscopic survey (47 in total), we estimate a mean redshift and a line-of-sight velocity dispersion of zmean = 2.23224 0.00101 and los = 645 69 km s−1 for this protocluster, respectively. Assuming virialization and spherical symmetry for the system, we estimate a total mass of Mvir ∼ (1-2) ×1014M for the structure. We evaluate a number density enhancement of δg ∼ 7 for this system and we argue that the structure is likely not fully virialized at z ∼ 2.2. However, in a spherical collapse model, δg is expected to grow to a linear matter enhancement of ∼1.9 by z = 0, exceeding the collapse threshold of 1.69, and leading to a fully collapsed and virialized Coma-type structure with a total mass of Mdyn(z = 0) ∼ 9.2 × 1014M by now. This observationally efficient confirmation suggests that large narrowband emission-line galaxy surveys, when combined with ancillary photometric data, can be used to effectively trace the large-scale structure and protoclusters at a time when they are mostly dominated by star-forming galaxies.
We present the physical extent of C ii 158 m line-emitting gas from 46 star-forming galaxies at z = 4-6 from the ALMA Large Program to INvestigate C ii at Early Times (ALPINE). Using exponential ...profile fits, we measure the effective radius of the C ii line ( ) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum ( ) from Hubble Space Telescope images. The effective radius exceeds by factors of ∼2-3, and the ratio of increases as a function of Mstar. We do not find strong evidence that the C ii line, rest-frame UV, and far-infrared (FIR) continuum are always displaced over 1 kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended C ii component over 10 kpc scales detected at 4.1 -10.9 beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to ∼10 kpc, where the 3D model fit shows the rotating C ii-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended C ii line structure have high star formation rate, high stellar mass (Mstar), low Ly equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Ly line), as compared to galaxies without such extended C ii structures. Although we cannot rule out the possibility that a selection bias toward luminous objects may be responsible for such trends, the star-formation-driven outflow also explains all these trends. Deeper observations are essential to test whether the extended C ii line structures are ubiquitous to high-z star-forming galaxies.
Abstract
We present a study of the star formation rate (SFR)–density relation at $z$ ∼ 0.9 using data drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. We ...find that SFR does depend on environment, but only for intermediate-stellar mass galaxies (1010.1 < M*/M⊙ < 1010.8) wherein the median SFR at the highest densities is 0.2–0.3 dex less than at lower densities at a significance of 4σ. Galaxies that are more/less massive than this have SFRs that vary at most by ${\approx }20{{\ \rm per\ cent}}$ across all environments, but show no statistically significant trend. We further split galaxies into low-redshift ($z$ ∼ 0.8) and high-redshift ($z$ ∼ 1.05) subsamples and observe nearly identical behaviour. We devise a simple toy model to explore possible star formation histories for galaxies evolving between these redshifts. The key assumption in this model is that star-forming galaxies in a given environment-stellar mass bin can be described as a superposition of two exponential time-scales (SFR ∝ e−t/τ): a long−τ time-scale with τ = 4 Gyr to simulate ‘normal’ star-forming galaxies, and a short-τ time-scale with free τ (between 0.3 ≤ τ/Gyr ≤ 2) to simulate galaxies on a quenching trajectory. In general, we find that galaxies residing in low/high environmental densities are more heavily weighted to the long-τ/short-τ pathways, respectively, which we argue is a signature of environmental quenching. Furthermore, for intermediate-stellar mass galaxies this transition begins at intermediate-density environments suggesting that environmental quenching is relevant in group-like haloes and/or cluster infall regions.
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