We report new observations of SL2S J021737-051329, a lens system consisting of a bright arc at z = 1.84435, magnified ∼17× by a massive galaxy at z = 0.65. SL2S0217 is a low-mass (M < 109 M ), ...low-metallicity (Z ∼ 1/20 Z ) galaxy, with extreme star-forming conditions that produce strong nebular UV emission lines in the absence of any apparent outflows. Here we present several notable features from rest-frame UV Keck/LRIS spectroscopy: (1) Very strong narrow emission lines are measured for C iv λλ1548, 1550, He ii λ1640, O iii λλ1661, 1666, Si iii λλ1883, 1892, and C iii λλ1907, 1909. (2) Double-peaked Ly emission is observed with a dominant blue peak and centered near the systemic velocity. (3) The low- and high-ionization absorption features indicate very little or no outflowing gas along the sight line to the lensed galaxy. The relative emission-line strengths can be reproduced with a very high ionization, low-metallicity starburst with binaries, with the exception of He ii, which indicates that an additional ionization source is needed. We rule out large contributions from active galactic nuclei and shocks to the photoionization budget, suggesting that the emission features requiring the hardest radiation field likely result from extreme stellar populations that are beyond the capabilities of current models. Therefore, SL2S0217 serves as a template for the extreme conditions that are important for reionization and thought to be more common in the early universe.
We describe a new program for determining photometric redshifts, dubbed EAZY. The program is optimized for cases where spectroscopic redshifts are not available, or are only available for a biased ...subset of the galaxies. The code combines features from various existing codes: it can fit linear combinations of templates, it includes optional flux- and redshift-based priors, and its user interface is modeled on the popular HYPERZ code. A novel feature is that the default template set, as well as the default functional forms of the priors, are not based on (usually highly biased) spectroscopic samples, but on semianalytical models. Furthermore, template mismatch is addressed by a novel rest-frame template error function. This function gives different wavelength regions different weights, and ensures that the formal redshift uncertainties are realistic. We introduce a redshift quality parameter, image, which provides a robust estimate of the reliability of the photometric redshift estimate. Despite the fact that EAZY is not 'trained' on spectroscopic samples, the code (with default parameters) performs very well on existing public data sets. For K-selected samples in CDF-South and other deep fields, we find a 1 capital sigma scatter in image of 0.034, and we provide updated photometric redshift catalogs for the FIRES, MUSYC, and FIREWORKS surveys.
The 3D-HST and CANDELS programs have provided WFC3 and ACS spectroscopy and photometry over approximate900 arcmin super(2) in five fields: AEGIS, COSMOS, GOODS-North, GOODS-South, and the UKIDSS UDS ...field. All these fields have a wealth of publicly available imaging data sets in addition to the Hubble Space Telescope (HST) data, which makes it possible to construct the spectral energy distributions (SEDs) of objects over a wide wavelength range. In this paper we describe a photometric analysis of the CANDELS and 3D-HST HST imaging and the ancillary imaging data at wavelengths 0.3-8Mum. Objects were selected in the WFC3 near-IR bands, and their SEDs were determined by carefully taking the effects of the point-spread function in each observation into account. A total of 147 distinct imaging data sets were used in the analysis. The photometry is made available in the form of six catalogs: one for each field, as well as a master catalog containing all objects in the entire survey. We also provide derived data products: photometric redshifts, determined with the EAZY code, and stellar population parameters determined with the FAST code. We make all the imaging data that were used in the analysis available, including our reductions of the WFC3 imaging in all five fields. 3D-HST is a spectroscopic survey with the WFC3 and ACS grisms, and the photometric catalogs presented here constitute a necessary first step in the analysis of these grism data. All the data presented in this paper are available through the 3D-HST Web site (http://3dhst.research.yale.edu).
ABSTRACT
We compare the star-forming main sequence (SFMS) of galaxies – both integrated and resolved on 1 kpc scales – between the high-resolution TNG50 simulation of IllustrisTNG and observations ...from the 3D-HST slitless spectroscopic survey at z ∼ 1. Contrasting integrated star formation rates (SFRs), we find that the slope and normalization of the star-forming main sequence in TNG50 are quantitatively consistent with values derived by fitting observations from 3D-HST with the Prospector Bayesian inference framework. The previous offsets of 0.2–1 dex between observed and simulated main-sequence normalizations are resolved when using the updated masses and SFRs from Prospector. The scatter is generically smaller in TNG50 than in 3D-HST for more massive galaxies with M*> 1010 M⊙, by ∼10–40 per cent, after accounting for observational uncertainties. When comparing resolved star formation, we also find good agreement between TNG50 and 3D-HST: average specific star formation rate (sSFR) radial profiles of galaxies at all masses and radii below, on, and above the SFMS are similar in both normalization and shape. Most noteworthy, massive galaxies with M*> 1010.5 M⊙, which have fallen below the SFMS due to ongoing quenching, exhibit a clear central SFR suppression, in both TNG50 and 3D-HST. In contrast, the original Illustris simulation and a variant TNG run without black hole kinetic wind feedback, do not reproduce the central SFR profile suppression seen in data. In TNG, inside-out quenching is due to the supermassive black hole (SMBH) feedback model operating at low accretion rates.
Star formation in half of massive galaxies was quenched by the time the Universe was 3 billion years old.sup.1. Very low amounts of molecular gas seem to be responsible for this, at least in some ...cases.sup.2-7, although morphological gas stabilization, shock heating or activity associated with accretion onto a central supermassive black hole are invoked in other cases.sup.8-11. Recent studies of quenching by gas depletion have been based on upper limits that are insufficiently sensitive to determine this robustly.sup.2-7, or stacked emission with its problems of averaging.sup.8,9. Here we report 1.3 mm observations of dust emission from 6 strongly lensed galaxies where star formation has been quenched, with magnifications of up to a factor of 30. Four of the six galaxies are undetected in dust emission, with an estimated upper limit on the dust mass of 0.0001 times the stellar mass, and by proxy (assuming a Milky Way molecular gas-to-dust ratio) 0.01 times the stellar mass in molecular gas. This is two orders of magnitude less molecular gas per unit stellar mass than seen in star forming galaxies at similar redshifts.sup.12-14. It remains difficult to extrapolate from these small samples, but these observations establish that gas depletion is responsible for a cessation of star formation in some fraction of high-redshift galaxies.
Abstract
We report the detection of a high density of redshift
z
≈ 10 galaxies behind the foreground cluster A2744, selected from imaging data obtained recently with NIRCam on board JWST by three ...programs—GLASS-JWST, UNCOVER, and DDT#2756. To ensure robust estimates of the lensing magnification
μ
, we use an improved version of our model that exploits the first epoch of NIRCam images and newly obtained MUSE spectra and avoids regions with
μ
> 5 where the uncertainty may be higher. We detect seven bright
z
≈ 10 galaxies with demagnified rest frame −22 ≲
M
UV
≲ −19 mag, over an area of ∼37 arcmin
2
. Taking into account photometric incompleteness and the effects of lensing on luminosity and cosmological volume, we find that the density of
z
≈ 10 galaxies in the field is about 10× (3×) larger than the average at
M
UV
≈ −21 ( −20) mag reported so far. The density is even higher when considering only the GLASS-JWST data, which are the deepest and the least affected by magnification and incompleteness. The GLASS-JWST field contains five out of seven galaxies, distributed along an apparent filamentary structure of 2 Mpc in projected length, and includes a close pair of candidates with
M
UV
< −20 mag having a projected separation of only 16 kpc. These findings suggest the presence of a
z
≈ 10 overdensity in the field. In addition to providing excellent targets for efficient spectroscopic follow-up observations, our study confirms the high density of bright galaxies observed in early JWST observations but calls for multiple surveys along independent lines of sight to achieve an unbiased estimate of their average density and a first estimate of their clustering.
We present the second data release of the Large Early Galaxy Astrophysics Census (LEGA-C), an ESO 130−night public spectroscopic survey conducted with VIMOS on the Very Large Telescope. We release ...1988 spectra with typical continuum S/N 20 −1 of galaxies at 0.6 z 1.0, each observed for ∼20 hr and fully reduced with a custom-built pipeline. We also release a catalog with spectroscopic redshifts, emission-line fluxes, Lick/IDS indices, and observed stellar and gas velocity dispersions that are spatially integrated quantities, including both rotational motions and genuine dispersion. To illustrate the new parameter space in the intermediate-redshift regime probed by LEGA-C, we explore relationships between dynamical and stellar population properties. The star-forming galaxies typically have observed stellar velocity dispersions of ∼150 km s−1 and strong Hδ absorption (HδA ∼ 5 ), while passive galaxies have higher observed stellar velocity dispersions (∼200 km s−1) and weak Hδ absorption (HδA ∼ 0 ). Strong O III5007/Hβ ratios tend to occur mostly for galaxies with weak HδA or galaxies with higher observed velocity dispersion. Beyond these broad trends, we find a diversity of possible combinations of rest-frame colors, absorption-line strengths, and emission-line detections, illustrating the utility of spectroscopic measurements to more accurately understand galaxy evolution. By making the spectra and value-added catalogs publicly available we encourage the community to take advantage of this very substantial investment in telescope time provided by ESO.
We present COSMOS-Drift And SHift (DASH), a Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging survey of the COSMOS field in the H160 filter. The survey comprises 456 individual WFC3 ...pointings corresponding to an area of 0.49 deg2 (0.66 deg2 when including archival data) and reaches a 5 point-source limit of H160 = 25.1 (0 3 aperture). COSMOS-DASH is the widest HST/WFC3 imaging survey in the H160 filter, tripling the extragalactic survey area in the near-infrared at HST resolution. We make the reduced H160 mosaic available to the community. We use this data set to measure the sizes of 169 galaxies with at 1.5 < z < 3.0 and augment this sample with 749 galaxies at 0.1 < z < 1.5 using archival ACS imaging. We find that the median size of galaxies in this mass range changes with redshift as kpc. Separating the galaxies into star-forming and quiescent galaxies using their rest-frame U − V and V − J colors, we find no statistical difference between the median sizes of the most massive star-forming and quiescent galaxies at : they are 4.9 0.9 kpc and 4.3 0.3 kpc, respectively. However, we do find a significant difference in the Sèrsic index between the two samples, such that massive quiescent galaxies have higher central densities than star-forming galaxies. We extend the size−mass analysis to lower masses by combining it with the 3D-HST/CANDELS sample of van der Wel et al. and derive empirical relations between size, mass, and redshift. Fitting a relation of the form , with and reff in kpc, we find log A = −0.25 log(1 + z) + 0.80 and = −0.13 log(1 + z) + 0.27. We also provide relations for the subsamples of star-forming and quiescent galaxies. Our results confirm previous studies that were based on smaller samples or ground-based imaging.
Abstract
We present an analysis of the star formation rates (SFRs) and dust attenuation properties of star-forming galaxies at 2.7 ≤
z
< 6.5 drawn from the Cosmic Evolution Early Release Science ...Survey. Our analysis is based on JWST/NIRSpec Micro-Shutter Assembly
R
∼ 1000 spectroscopic observations covering approximately 1–5
μ
m. Our primary rest-frame optical spectroscopic measurements are H
α
/H
β
Balmer decrements, which we use as an indicator of nebular dust attenuation. In turn, we use Balmer decrements to obtain dust-corrected H
α
-based SFRs (i.e., SFR(H
α
)). We construct the relationship between SFR(H
α
) and stellar mass (
M
*
) in three bins of redshift (2.7 ≤
z
< 4.0, 4.0 ≤
z
< 5.0, and 5.0 ≤
z
< 6.5), which represents the first time the star-forming main sequence has been traced at these redshifts using direct spectroscopic measurements of Balmer emission as a proxy for SFR. In tracing the relationship between SFR(H
α
) and
M
*
back to such early times (
z
> 3), it is essential to use a conversion factor between H
α
and SFR that accounts for the subsolar metallicity prevalent among distant galaxies. We also use measured Balmer decrements to investigate the relationship between dust attenuation and stellar mass out to
z
∼ 6. The lack of significant redshift evolution in attenuation at fixed stellar mass, previously confirmed using Balmer decrements out to
z
∼ 2.3, appears to hold out to
z
∼ 6.5. Given the rapidly evolving gas, dust, and metal content of star-forming galaxies at fixed mass, this lack of significant evolution in attenuation provides an ongoing challenge to explain.
We constrain the slope of the star formation rate (SFR; log Psi) to stellar mass (log M sub(*)) relation down to log(M sub(*)/M sub(middot in circle)) = 8.4 (log(M sub(*)/M sub(middot in circle)) = ...9.2) at z = 0.5 (z = 2.5) with a mass-complete sample of 39,106 star-forming galaxies selected from the 3D-HST photometric catalogs, using deep photometry in the CANDELS fields. For the first time, we find that the slope is dependent on stellar mass, such that it is steeper at low masses (log Psi is proportional to log M sub(*)) than at high masses (log Psi is proportional to (0.3-0.6) log M sub(*)). These steeper low-mass slopes are found for three different star formation indicators: the combination of the ultraviolet (UV) and infrared (IR), calibrated from a stacking analysis of Spitzer/MIPS 24 mu m imaging; beta -corrected UV SFRs; and H alpha SFRs. The normalization of the sequence evolves differently in distinct mass regimes as well: for galaxies less massive than log(M sub(*)/M sub(middot in circle)) < 10 the specific SFR (Psi/M sub(*)) is observed to be roughly self-similar with Psi/M sub(*) is proportional to (1 + z) super(1.9), whereas more massive galaxies show a stronger evolution with Psi/M sub(*) is proportional to (1 + z) super(2.2-3.5) for log(M sub(*)/M sub(middot in circle)) = 10.2-11.2. The fact that we find a steep slope of the star formation sequence for the lower mass galaxies will help reconcile theoretical galaxy formation models with the observations.
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