Using the most recent measurements of the ultraviolet (UV) luminosity functions (LFs) and dust estimates of early galaxies, we derive updated dust-corrected star formation rate functions (SFRFs) at ...z ∼ 4–8, which we model to predict the evolution to higher redshifts, z > 8. We employ abundance matching techniques to calibrate a relation between galaxy star formation rate (SFR) and host halo mass M
h
by mapping the shape of the observed SFRFs at z ∼ 4–8 to that of the halo mass function. The resulting scaling law remains roughly constant over this redshift range. We apply the average SFR–M
h
relation to reproduce the observed SFR functions at 4 ≲ z ≲ 8 and also derive the expected UV LFs at higher redshifts. At z ∼ 9 and z ∼ 10 these model LFs are in excellent agreement with current observed estimates. Our predicted number densities and UV LFs at z > 10 indicate that James Webb Space Telescope will be able to detect galaxies out to z ∼ 15 with an extensive treasury sized program. We also derive the redshift evolution of the star formation rate density (SFRD) and associated reionization history by galaxies. Models which integrate down to the current HUDF12/XDF detection limit (M
UV ∼ −17.7 mag) result in a SFRD that declines as (1 + z)−10.4 ± 0.3 at high redshift and fail to reproduce the observed cosmic microwave background electron scattering optical depth, τ ≃ 0.066, to within 1σ. On the other hand, we find that the inclusion of galaxies with SFRs well below the current detection limit (M
UV < −5.7 mag) leads to a fully reionized universe by z ∼ 6.5 and an optical depth of τ ≃ 0.054, consistent with the recently derived Planck value at the 1σ level.
The protagonists of the last great phase transition of the universe-cosmic reionization-remain elusive. Faint star-forming galaxies are leading candidates because they are found to be numerous and ...may have significant ionizing photon escape fractions ( ). Here we update this picture via an empirical model that successfully predicts latest observations (e.g., the rapid drop in star-formation density ( at ). We generate an ionizing spectrum for each galaxy in our model and constrain by leveraging latest measurements of the reionization timeline (e.g., Ly damping of quasars and galaxies at z > 7). Assuming a constant across all sources at z > 6, we find < −13.5 galaxies need = to complete reionization. The inferred Intergalactic Medium neutral fraction is 0.9, 0.5, 0.1 at -that is, the bulk of reionization transpires rapidly in 300 Myr, driven by the z > 8 SFR and favored by high neutral fractions (∼60%-90%) measured at z ∼ 7-8. Inspired by the emergent sample of Lyman Continuum (LyC) leakers spanning z ∼ 0-6.6 that overwhelmingly displays higher-than-average star-formation surface density ( ), we propose a physically motivated model relating to and find . Since falls by ∼2.5 dex between z = 8 and z = 0, our model explains the humble upper limits on at lower redshifts and its required evolution to ∼ 0.2 at z > 6. Within this model, strikingly, <5% of galaxies with < −18 and log(M /M ) > 8 (the "oligarchs") account for 80% of the reionization budget-a stark departure from the canonical "democratic" reionization led by copious faint sources. In fact, faint sources ( > −16) must be relegated to a limited role in order to ensure high neutral fractions at z = 7-8. Shallow faint-end slopes of the UV luminosity function ( > −2) and/or distributions skewed toward massive galaxies produce the required late and rapid reionization. We predict that LyC leakers like COLA1 (z = 6.6, ∼ 30%, = −21.5) will become increasingly common toward z ∼ 6 and that the drivers of reionization do not lie hidden across the faint end of the luminosity function but are already known to us.
Abstract
We present new stellar mass functions at
z
∼ 6,
z
∼ 7,
z
∼ 8,
z
∼ 9 and, for the first time,
z
∼ 10, constructed from ∼800 Lyman-break galaxies previously identified over the eXtreme Deep ...Field and Hubble Ultra-Deep Field parallel fields and the five Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields. Our study is distinctive due to (1) the much deeper (∼200 hr) wide-area Spitzer/Infrared Array Camera (IRAC) imaging at 3.6
μ
m and 4.5
μ
m from the Great Observatories Origins Deep Survey Re-ionization Era Wide-area Treasury from Spitzer program (GREATS) and (2) consideration of
z
∼ 6–10 sources over a 3× larger area than those of previous Hubble Space Telescope+Spitzer studies. The Spitzer/IRAC data enable ≥2
σ
rest-frame optical detections for an unprecedented 50% of galaxies down to a stellar mass limit of
∼
10
8
⊙
across all redshifts. Schechter fits to our volume densities suggest a combined evolution in the characteristic mass
*
and normalization factor
ϕ
*
between
z
∼ 6 and
z
∼ 8. The stellar mass density (SMD) increases by ∼1000× in the ∼500 Myr between
z
∼ 10 and
z
∼ 6, with indications of a steeper evolution between
z
∼ 10 and
z
∼ 8, similar to the previously reported trend of the star formation rate density. Strikingly, abundance matching to the Bolshoi–Planck simulation indicates halo mass densities evolving at approximately the same rate as the SMD between
z
∼ 10 and
z
∼ 4. Our results show that the stellar-to-halo mass ratios, a proxy for the star formation efficiency, do not change significantly over the huge stellar mass buildup occurred from
z
∼ 10 to
z
∼ 6, indicating that the assembly of stellar mass closely mirrors the buildup in halo mass in the first ∼1 Gyr of cosmic history. The James Webb Space Telescope is poised to extend these results into the “first galaxy” epoch at
z
≳ 10.
ABSTRACT
The infrared (IR) spectral energy distributions (SEDs) of main-sequence galaxies in the early Universe (z > 4) is currently unconstrained as IR continuum observations are time-consuming and ...not feasible for large samples. We present Atacama Large Millimetre Array Band 8 observations of four main-sequence galaxies at z ∼ 5.5 to study their IR SED shape in detail. Our continuum data (rest-frame 110 $\rm \mu m$, close to the peak of IR emission) allows us to constrain luminosity-weighted dust temperatures and total IR luminosities. With data at longer wavelengths, we measure for the first time the emissivity index at these redshifts to provide more robust estimates of molecular gas masses based on dust continuum. The Band 8 observations of three out of four galaxies can only be reconciled with optically thin emission redward of rest-frame $100\, {\rm \mu m}$. The derived dust peak temperatures at z ∼ 5.5 ($30\!-\!43\, {\rm K}$) are elevated compared to average local galaxies, however, $\sim 10\, {\rm K}$ below what would be predicted from an extrapolation of the trend at z < 4. This behaviour can be explained by decreasing dust abundance (or density) towards high redshifts, which would cause the IR SED at the peak to be more optically thin, making hot dust more visible to the external observer. From the $850{\hbox{-}}{\rm \mu m}$ dust continuum, we derive molecular gas masses between 1010 and $10^{11}\, {\rm M_{\odot }}$ and gas fractions (gas over total mass) of $30\!-\!80{{\ \rm per\ cent}}$ (gas depletion times of $100\!-\!220\, {\rm Myr}$). All in all, our results provide a first measured benchmark SED to interpret future millimetre observations of normal, main-sequence galaxies in the early Universe.
Abstract
The first few 100 Myr at
z
> 10 mark the last major uncharted epoch in the history of the universe, where only a single galaxy (GN-z11 at
z
≈ 11) is currently spectroscopically confirmed. ...Here we present a search for luminous
z
> 10 galaxies with JWST/NIRCam photometry spanning ≈1–5
μ
m and covering 49 arcmin
2
from the public JWST Early Release Science programs (CEERS and GLASS). Our most secure candidates are two
M
UV
≈ −21 systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt ≳1.8 mag breaks in their spectral energy distributions (SEDs), consistent with complete absorption of flux bluewards of Ly
α
that is redshifted to
z
=
12.4
−
0.3
+
0.1
and
z
=
10.4
−
0.5
+
0.4
. Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at >5
σ
in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up ∼10
9
solar masses in stars over the ≲300–400 Myr after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of
r
50
≈ 0.7 kpc. These sources, if confirmed, join GN-z11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area >10× larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep JWST observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated.
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 (LIR/LUV IRX). Our sample significantly extends the range of LUV and β probed in previous UV-selected samples, including those as faint as M1600 = −17.4 ( ) and −2.6 β 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 3. IRX is roughly constant with LUV for LUV 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 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, 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.
Abstract
Deep rest-optical observations are required to accurately constrain the stellar populations of
z
∼ 8 galaxies. Due to significant limitations in the availability of such data for ...statistically complete samples, observational results have been limited to modest numbers of bright or lensed sources. To revolutionize the present characterization of
z
∼ 8 galaxies, we exploit the ultradeep (∼27 mag, 3
σ
) Spitzer/Infrared Array Camera (IRAC) 3.6 and 4.5
μ
m data, probing the rest-frame optical at
z
∼ 8, over ∼200 arcmin
2
of the GOODS fields from the recently completed GOODS Re-ionization Era wide-Area Treasury from Spitzer program (GREATS), combined with observations in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)/Ultra Deep Survey (UDS) and CANDELS/Cosmic Evolution Survey (COSMOS) fields. We stacked ≳100
z
∼ 8 Lyman-break galaxies in four bins of UV luminosity (
M
UV
∼ −20.7 to −18.4 mag) and study their
H
160
− 3.6 and 3.6–4.5 colors. We find young ages (≲100 Myr) for the three faintest stacks, inferred from their blue
H
160
− 3.6 ∼ 0 mag colors, consistent with a negative Balmer break. Meanwhile, the redder
H
160
− 3.6 color seen in the brightest stack is suggestive of slightly older ages. We explored the existence of a correlation between the UV luminosity and age, and find either no trend or fainter galaxies being younger. The stacked SEDs also exhibit very red 3.6–4.5 ∼ 0.5 mag colors, indicative of intense O
iii
+H
β
nebular emission and star formation rate (SFR). The correspondingly high specific SFRs, sSFR ≳10 Gyr
−1
, are consistent with recent determinations at similar redshifts and higher luminosities, and support the coevolution between the sSFR and the specific halo mass accretion rate.
ABSTRACT
Recent work has suggested that extreme O iii emitting star-forming galaxies are important to reionization. Relatedly, O iii/O ii has been put forward as an indirect estimator of the Lyman ...Continuum (LyC) escape fraction (fesc) at z ≳ 4.5 when the opaque IGM renders LyC photons unobservable. Using deep archival U-band (VLT/VIMOS) imaging of a recently confirmed overdensity at z∼ 3.5, we calculate tight constraints on fesc for a sample (N = 73) dominated by extreme O iii emitters. We find no LyC signal ($f_{\rm esc}^{\rm rel} < 6.3^{+0.7}_{-0.7} \hbox{ per cent}$ at 1σ) in a deep U-band stack of our sample (31.98 mag at 1σ). This constraint is in agreement with recent studies of star-forming galaxies spanning z ∼ 1–4 that have found very low average fesc. Despite the galaxies in our study having an estimated average rest-frame EW(O iiiλ5007) ∼ 400 Å and O iii/O ii ∼ 4 from composite SED fitting, we find no LyC detection, which brings into question the potential of O iii/O ii as an effective probe of the LyC – a majority of LyC emitters have O iii/O ii > 3, but we establish here that O iii/O ii > 3 does not guarantee significant LyC leakage for a population. Since even extreme star-forming galaxies are unable to produce the $f_{\rm esc}\sim 10{-}15\hbox{ per cent}$ required by most theoretical calculations for star-forming galaxies to drive reionization, there must either be a rapid evolution of fesc between z∼ 3.5 and the epoch of reionization, or hitherto observationally unstudied sources e.g. ultrafaint low-mass galaxies with log (M/M⊙) ∼ 7–8.5 must make an outsized contribution to reionization.
Abstract
We present the first spatially resolved measurements of galaxy properties in the JWST ERO SMACS 0723 field. We perform a comprehensive analysis of five 5 <
z
< 9 galaxies with spectroscopic ...redshifts from NIRSpec observations. We perform spatially resolved spectral energy distribution fitting with
Bagpipes
, using six NIRCam imaging bands spanning the wavelength range 0.8–5
μ
m. This approach allows us to study the internal structure and assembly of the first generations of galaxies. We find clear gradients both in the empirical color maps and in most of the estimated physical parameters. We find regions of considerably different specific star formation rates across each galaxy, which points to very bursty star formation happening on small scales, not galaxy-wide. The integrated light is dominated by these bursty regions, which exhibit strong line emission, with the equivalent width of O
iii
+H
β
reaching up to ∼3000–4000 Å rest frame. Studying these galaxies in an integrated approach yields extremely young inferred ages of the stellar population (<10 Myr), which outshine older stellar populations that are only distinguishable in the spatially resolved maps. This leads to inferring ∼0.5–1 dex lower stellar masses by using single-aperture photometry, when compared to resolved analyses. Such systematics would have strong implications in the shape and evolution of the stellar mass function at these early times, particularly while samples are limited to small numbers of the brightest candidates. Furthermore, the evolved stellar populations revealed in this study imply an extended process of early galaxy formation that could otherwise be hidden behind the light of the most recently formed stars.
ABSTRACT
Cosmic dust is an essential component shaping both the evolution of galaxies and their observational signatures. How quickly dust builds up in the early Universe remains an open question ...that requires deep observations at (sub-)millimetre wavelengths to resolve. Here, we use Atacama Large Millimeter Array observations of 45 galaxies from the Reionization Era Bright Emission Line Survey (REBELS) and its pilot programs, designed to target C ii and dust emission in UV-selected galaxies at z ∼ 7, to investigate the dust content of high-redshift galaxies through a stacking analysis. We find that the typical fraction of obscured star formation fobs = SFRIR/SFRUV+IR depends on stellar mass, similar to what is observed at lower redshift, and ranges from fobs ≈ 0.3 − 0.6 for galaxies with log10(M⋆/M⊙) = 9.4–10.4. We further adopt the z ∼ 7 stellar mass function from the literature to extract the obscured cosmic star formation rate density (SFRD) from the REBELS survey. Our results suggest only a modest decrease in the SFRD between 3 ≲ z ≲ 7, with dust-obscured star formation still contributing ${\sim}30{{\ \rm per\ cent}}$ at z ∼ 7. While we extensively discuss potential caveats, our analysis highlights the continued importance of dust-obscured star formation even well into the epoch of reionization.
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