UV Luminosity Density Results at z>8 from the First JWST/NIRCam Fields: Limitations of Early Data Sets and the Need for Spectroscopy

We have derived luminosity functions, and set constraints on the UV luminosity and SFR density from z~17 to z~8, using the three most-studied JWST/NIRCam data sets, the SMACS0723, GLASS Parallel, and CEERS fields. We first used our own selections on two independent reductions of these datasets using the latest calibrations. 18 z~8, 12 z~10, 5 z~13, and 1 z~17 candidate galaxies are identified over these fields in our primary reductions, with a similar number of candidates in our secondary reductions. We then use these two reductions, applying a quantitative discriminator, to segregate the full set of z>~8 candidates reported over these fields from the literature, into three different samples, ``robust,'' ``solid,'' and ``possible''. Using all of these samples we then derive UV LF and luminosity density results at $z\geq8$, finding substantial differences. For example, including the full set of ``solid'' and ``possible'' z>~12 candidates from the literature, we find UV luminosity densities which are ~7x and ~20x higher than relying on the ``robust'' candidates alone. These results indicate the evolution of the UV LF and luminosity densities at z>~8 is still extremely uncertain, emphasizing the need for spectroscopy and deeper NIRCam+optical imaging to obtain reliable results. Nonetheless, even with the very conservative ``robust'' approach to selections, both from our own and those of other studies, we find the luminosity density from luminous (M(UV)<-19) galaxies to be ~2x larger than is easily achievable using constant star-formation efficiency models, similar to what other early JWST results have suggested.Comment: 26 pages, 10 figures, 15 tables, accepted for publication in MNRAS, figure 7 shows the key result

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Ellis and Magee (2007) provide a very compelling analysis of the meta-and macrocontingencies that have developed around the implementation of the No Child Left Behind (NCLB) Act. They point out what in my articl

The Rest Frame UV to Optical Colors and SEDs of z~4-7 Galaxies

We use the ultra-deep HUDF09 and the deep ERS data from the HST WFC3/IR camera, along with the wide area Spitzer/IRAC data from GOODS-S to derive SEDs of star-forming galaxies from the rest-frame UV to the optical over a wide luminosity range (M_1500 ~ -21 to M_1500 ~ -18) from z ~ 7 to z ~ 4. The sample contains ~ 400 z ~ 4, ~ 120 z ~ 5, ~ 60 z ~ 6, and 36 prior z ~ 7 galaxies. Median stacking enables the first comprehensive study of very faint high-z galaxies at multiple redshifts (e.g., [3.6] = 27.4 +/- 0.1 AB mag for the M_1500 ~ -18 sources at z ~ 4). At z ~ 4 our faint median-stacked SEDs reach to ~ 0.06 L*(z=4) and are combined with recently published results at high luminosity L > L* that extend to M_1500 ~ -23. We use the observed SEDs and template fits to derive rest frame UV-to-optical colors (U - V) at all redshifts and luminosities. We find that this color does not vary significantly with redshift at a fixed luminosity. The UV-to-optical color does show a weak trend with luminosity, becoming redder at higher luminosities. This is most likely due to dust. At z >~ 5 we find blue colors [3.6]-[4.5] ~ -0.3 mag that are most likely due to rest-frame optical emission lines contributing to the flux in the IRAC filter bandpasses. The scatter across our derived SEDs remains substantial, but the results are most consistent with a lack of any evolution in the SEDs with redshift at a given luminosity. The similarity of the SEDs suggests a self-similar mode of evolution over a timespan from 0.7 Gyr to 1.5 Gyr that encompasses very substantial growth in the stellar mass density in the universe (from ~ 4x10^6 to ~ 2x10^7 Msun Mpc^-3).Comment: 15 pages, 11 figures, 3 tables, submitted to Ap

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z~7 galaxy candidates from NICMOS observations over the HDF South and the CDF-S and HDF-N GOODS fields

We use ~88 arcmin**2 of deep (>~26.5 mag at 5 sigma) NICMOS data over the two GOODS fields and the HDF South to conduct a search for bright z>~7 galaxy candidates. This search takes advantage of an efficient preselection over 58 arcmin**2 of NICMOS H-band data where only plausible z>~7 candidates are followed up with NICMOS J-band observations. ~248 arcmin**2 of deep ground-based near-infrared data (>~25.5 mag, 5 sigma) is also considered in the search. In total, we report 15 z-dropout candidates over this area -- 7 of which are new to these search fields. Two possible z~9 J-dropout candidates are also found, but seem unlikely to correspond to z~9 galaxies. The present z~9 search is used to set upper limits on the prevalence of such sources. Rigorous testing is undertaken to establish the level of contamination of our selections by photometric scatter, low mass stars, supernovae (SNe), and spurious sources. The estimated contamination rate of our z~7 selection is ~24%. Through careful simulations, the effective volume available to our z>~7 selections is estimated and used to establish constraints on the volume density of luminous (L*(z=3), or -21 mag) galaxies from these searches. We find that the volume density of luminous star-forming galaxies at z~7 is 13_{-5}^{+8}x lower than at z~4 and >25x lower (1 sigma) at z~9 than at z~4. This is the most stringent constraint yet available on the volume density of >~L* galaxies at z~9. The present wide-area, multi-field search limits cosmic variance to <20%. The evolution we find at the bright end of the UV LF is similar to that found from recent Subaru Suprime-Cam, HAWK-I or ERS WFC3/IR searches. The present paper also includes a complete summary of our final z~7 z-dropout sample (18 candidates) identified from all NICMOS observations to date (over the two GOODS fields, the HUDF, galaxy clusters).Comment: 13 pages, 6 figures, 6 tables, accepted for publication in the Astrophysical Journal, replaced to match accepted version, see http://firstgalaxies.org/astronomers-area/ for a link to a complete reduction of the NICMOS observations over the two GOODS field

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Slow Evolution of the Specific Star Formation Rate at z>2: The Impact of Dust, Emission Lines, and A Rising Star Formation History

We measure the evolution of the specific star formation rate (sSFR = SFR / Mstellar) between redshift 4 and 6 to investigate the previous reports of "constant" sSFR at z>2. We obtain photometry on a large sample of galaxies at z~4-6 located in the GOODS-S field that have high quality imaging from HST and Spitzer. We have derived stellar masses and star formation rates (SFRs) through stellar population modeling of their spectral energy distributions (SEDs). We estimate the dust extinction from the observed UV colors. In the SED fitting process we have studied the effects of assuming a star formation history (SFH) both with constant SFR and one where the SFR rises exponentially with time. The latter SFH is chosen to match the observed evolution of the UV luminosity function. We find that neither the mean SFRs nor the mean stellar masses change significantly when the rising SFR (RSF) model is assumed instead of the constant SFR model. When focusing on galaxies with Mstar ~ 5x10^9 Msun, we find that the sSFR evolves weakly with redshift (sSFR(z) \propto (1+z)^(0.6+/-0.1) Gyr^-1), consistent with previous results and with recent estimates of the sSFR at z~2-3 using similar assumptions. We have also investigated the impact of optical emission lines on our results. We estimate that the contribution of emission lines to the rest-frame optical fluxes is only modest at z~4 and 5 but it could reach ~50% at z~6. When emission lines of this strength are taken into account, the sSFR shows somewhat higher values at high redshifts, according to the relation sSFR(z) \propto (1+z)^(1.0+/-0.1) Gyr^-1, i.e., ~2.3x higher at z~6 than at z~2. However, the observed evolution is substantially weaker than that found at z<2 or that expected from current models (which corresponds to sSFR(z) \propto (1+z)^(2.5) Gyr^-1). -abridged-Comment: 15 pages, 10 figures, 2 tables. Update from v1: after second referee report, improved (larger) sample at z~

3D-HST: A wide-field grism spectroscopic survey with the Hubble Space Telescope

We present 3D-HST, a near-infrared spectroscopic Treasury program with the Hubble Space Telescope for studying the processes that shape galaxies in the distant Universe. 3D-HST provides rest-frame optical spectra for a sample of ~7000 galaxies at 1<z<3.5, the epoch when 60% of all star formation took place, the number density of quasars peaked, the first galaxies stopped forming stars, and the structural regularity that we see in galaxies today must have emerged. 3D-HST will cover 3/4 (625 sq.arcmin) of the CANDELS survey area with two orbits of primary WFC3/G141 grism coverage and two to four parallel orbits with the ACS/G800L grism. In the IR these exposure times yield a continuum signal-to-noise of ~5 per resolution element at H~23.1 and a 5sigma emission line sensitivity of 5x10-17 erg/s/cm2 for typical objects, improving by a factor of ~2 for compact sources in images with low sky background levels. The WFC3/G141 spectra provide continuous wavelength coverage from 1.1-1.6 um at a spatial resolution of ~0."13, which, combined with their depth, makes them a unique resource for studying galaxy evolution. We present the preliminary reduction and analysis of the grism observations, including emission line and redshift measurements from combined fits to the extracted grism spectra and photometry from ancillary multi-wavelength catalogs. The present analysis yields redshift estimates with a precision of sigma(z)=0.0034(1+z), or sigma(v)~1000 km/s. We illustrate how the generalized nature of the survey yields near-infrared spectra of remarkable quality for many different types of objects, including a quasar at z=4.7, quiescent galaxies at z~2, and the most distant T-type brown dwarf star known. The CANDELS and 3D-HST surveys combined will provide the definitive imaging and spectroscopic dataset for studies of the 1<z<3.5 Universe until the launch of the James Webb Space Telescope.Comment: Replacement reflects version now accepted by ApJS. A preliminary data release intended to provide a general illustration of the WFC3 grism data is available at http://3dhst.research.yale.edu

A massive quiescent galaxy at redshift 4.658

A. C. Carnall thanks the Leverhulme Trust for their support via a Leverhulme Early Career Fellowship. R. J. McLure, J. S. Dunlop, D. J. McLeod, V. Wild, R. Begley, C. T. Donnan and M. L. Hamadouche acknowledge the support of the Science and Technology Facilities Council. F. Cullen acknowledges support from a UKRI Frontier Research Guarantee Grant (grant reference EP/X021025/1). A. Cimatti acknowledges support from the grant PRIN MIUR 2017 - 20173ML3WW 001.The extremely rapid assembly of the earliest galaxies during the first billion years of cosmic history is a major challenge for our understanding of galaxy formation physics (1; 2; 3; 4; 5). The advent of JWST has exacerbated this issue by confirming the existence of galaxies in significant numbers as early as the first few hundred million years (6; 7; 8). Perhaps even more surprisingly, in some galaxies, this initial highly efficient star formation rapidly shuts down, or quenches, giving rise to massive quiescent galaxies as little as 1.5 billion years after the Big Bang (9; 10), however, due to their faintness and red colour, it has proven extremely challenging to learn about these extreme quiescent galaxies, or to confirm whether any exist at earlier times. Here we report the spectroscopic confirmation of a massive quiescent galaxy, GS-9209, at redshift, z = 4.658, just 1.25 billion years after the Big Bang, using JWST NIRSpec. From these data we infer a stellar mass of M∗ = 3.8 ± 0.2 × 1010 M⊙, which formed over a ≃ 200 Myr period before this galaxy quenched its star formation activity at z=6.5+0.2−0.5, when the Universe was ≃ 800 million years old. This galaxy is both a likely descendent of the highest-redshift submillimetre galaxies and quasars, and a likely progenitor for the dense, ancient cores of the most massive local galaxies.PostprintPeer reviewe

The HDUV Survey: A Revised Assessment of the Relationship between UV Slope and Dust Attenuation for High-redshift Galaxies

We use a newly assembled sample of 3545 star-forming galaxies with secure spectroscopic, grism, and photometric redshifts at z = 1.5–2.5 to constrain the relationship between UV slope (β) and dust attenuation (L IR/L UV ≡ IRX). Our sample significantly extends the range of L UV and β probed in previous UV-selected samples, including those as faint as M 1600 = −17.4 ($\simeq 0.05{L}_{\mathrm{UV}}^{* }$) and −2.6 lesssim β lesssim 0.0. IRX is measured using stacks of deep Herschel data, and the results are compared with predictions of the IRX−β relation for different assumptions of the stellar population model and obscuration curve. We find that z = 1.5–2.5 galaxies have an IRX−β relation that is consistent with the predictions for an SMC curve if we invoke subsolar-metallicity models currently favored for high-redshift galaxies, while the commonly assumed starburst curve overpredicts the IRX at a given β by a factor of gsim3. IRX is roughly constant with L UV for L UV gsim 3 × 109 L ⊙. Thus, the commonly observed trend of fainter galaxies having bluer β may simply reflect bluer intrinsic slopes for such galaxies, rather than lower obscurations. The IRX−β relation for young/low-mass galaxies at z gsim 2 implies a dust curve that is steeper than the SMC. The lower attenuations and higher ionizing photon output for low-metallicity stellar populations point to Lyman continuum production efficiencies, ξ ion, that may be elevated by a factor of ≈2 relative to the canonical value for L* galaxies, aiding in their ability to keep the universe ionized at z ~ 2