ABSTRACT We make use of deep 1.2 mm continuum observations (12.7 Jy beam−1 rms) of a 1 arcmin2 region in the Hubble Ultra Deep Field to probe dust-enshrouded star formation from 330 Lyman-break ...galaxies spanning the redshift range z = 2-10 (to ∼2-3 M yr−1 at 1 over the entire range). Given the depth and area of ASPECS, we would expect to tentatively detect 35 galaxies, extrapolating the Meurer z ∼ 0 IRX-β relation to z ≥ 2 (assuming dust temperature Td ∼ 35 K). However, only six tentative detections are found at z 2 in ASPECS, with just three at >3 . Subdividing our z = 2-10 galaxy samples according to stellar mass, UV luminosity, and UV-continuum slope and stacking the results, we find a significant detection only in the most massive (>109.75 M ) subsample, with an infrared excess (IRX = LIR/LUV) consistent with previous z ∼ 2 results. However, the infrared excess we measure from our large selection of sub-L∗ (<109.75 M ) galaxies is 0.34 (bootstrap and formal uncertainties) and 0.18 at z = 2-3 and z = 4-10, respectively, lying below even an IRX-β relation for the Small Magellanic Cloud (95% confidence). These results demonstrate the relevance of stellar mass for predicting the IR luminosity of z 2 galaxies. We find that the evolution of the IRX-stellar mass relationship depends on the evolution of the dust temperature. If the dust temperature increases monotonically with redshift ( ) such that Td ∼ 44-50 K at z ≥ 4, current results are suggestive of little evolution in this relationship to z ∼ 6. We use these results to revisit recent estimates of the z ≥ 3 star formation rate density.
ABSTRACT
Reionization-era galaxies tend to exhibit weak Ly α emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this ...picture, with strong Ly α emission now known in four of the most massive z = 7–9 galaxies in the CANDELS fields, all of which also exhibit intense O iii+H β emission (EW > 800 Å). To better understand why Ly α is anomalously strong in a subset of massive z ≃ 7–9 galaxies, we have initiated an MMT/Binospec survey targeting a larger sample (N = 22) of similarly luminous (≃1–6 L$^{\ast }_{\mathrm{UV}}$) z ≃ 7 galaxies selected over very wide-area fields (∼3 deg2). We confidently (>7σ) detect Ly α in 78 per cent (7/9) of galaxies with strong O iii+H β emission (EW > 800 Å) as opposed to only 8 per cent (1/12) of galaxies with more moderate (EW = 200–800 Å) O iii+H β. We argue that the higher Ly α EWs of the strong O iii+H β population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs (≳30 Gyr−1). We also find evidence that Ly α transmission from massive galaxies declines less rapidly over 6 < z < 7 than in low-mass lensed systems. In particular, our data suggest no strong evolution in Ly α transmission, consistent with a picture wherein massive z ≃ 7 galaxies often reside in large ionized regions. We detect three closely separated (R = 1.7 physical Mpc) z ≃ 7 Ly α emitters in our sample, conceivably tracing a large ionized structure that is consistent with this picture. We detect tentative evidence for an overdensity in this region, implying a large ionizing photon budget in the surrounding volume.
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
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.
We present 16 new ultrabright HAB 25 galaxy candidates at z ∼ 8 identified over the COSMOS/UltraVISTA field. The new search takes advantage of the deepest-available ground-based optical and ...near-infrared observations, including the DR3 release of UltraVISTA and full-depth Spitzer/IRAC observations from the SMUVS and SPLASH programs. Candidates are selected using Lyman-break color criteria, combined with strict optical non-detection and SED-fitting criteria, designed to minimize contamination by low-redshift galaxies and low-mass stars. HST/WFC3 coverage from the DASH program reveals that one source evident in our ground-based near-IR data has significant substructure and may actually correspond to 3 separate z ∼ 8 objects, resulting in a total sample of 18 galaxies, 10 of which seem to be fairly robust (with a >97% probability of being at z > 7). The UV-continuum slope β for the bright z ∼ 8 sample is β = −2.2 0.6, bluer but still consistent with that of similarly bright galaxies at z ∼ 6 (β = −1.55 0.17) and z ∼ 7 (β = −1.75 0.18). Their typical stellar masses are M , with the SFRs of yr−1, specific SFR of Gyr−1, stellar ages of Myr, and low dust content mag. Using this sample we constrain the bright end of the z ∼ 8 UV luminosity function. When combined with recent empty field luminosity function estimates at similar redshifts, the resulting z ∼ 8 luminosity function can be equally well represented by either a Schechter or a double-power-law form. Assuming a Schechter parameterization, the best-fit characteristic magnitude is mag with a very steep faint-end slope . These new candidates include some of the brightest objects found at these redshifts, 0.5-1.0 magnitude brighter than those found over CANDELS, and providing excellent targets for spectroscopic and longer-wavelength follow-up studies.
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
We present specific star formation rates (sSFRs) for 40 ultraviolet (UV)-bright galaxies at z ∼ 7–8 observed as part of the Reionization Era Bright Emission Line Survey (REBELS) Atacama ...Large Millimeter/submillimeter Array (ALMA) large programme. The sSFRs are derived using improved star formation rate (SFR) calibrations and spectral energy distribution (SED)-based stellar masses, made possible by measurements of far-infrared (FIR) continuum emission and C ii-based spectroscopic redshifts. The median sSFR of the sample is $18_{-5}^{+7}$ Gyr−1, significantly larger than literature measurements lacking constraints in the FIR, reflecting the larger obscured SFRs derived from the dust continuum relative to that implied by the UV+optical SED. We suggest that such differences may reflect spatial variations in dust across these luminous galaxies, with the component dominating the FIR distinct from that dominating the UV. We demonstrate that the inferred stellar masses (and hence sSFRs) are strongly dependent on the assumed star formation history in reionization-era galaxies. When large sSFR galaxies (a population that is common at z > 6) are modelled with non-parametric star formation histories, the derived stellar masses can increase by an order of magnitude relative to constant star formation models, owing to the presence of a significant old stellar population that is outshined by the recent burst. The C ii line widths in the largest sSFR systems are often very broad, suggesting dynamical masses capable of accommodating an old stellar population suggested by non-parametric models. Regardless of these systematic uncertainties among derived parameters, we find that sSFRs increase rapidly toward higher redshifts for massive galaxies (9.6 < log (M*/M⊙) < 9.8), evolving as (1 + z)1.7 ± 0.3, broadly consistent with expectations from the evolving baryon accretion rates.
Context.
Spectroscopic surveys of massive galaxy clusters reveal the properties of faint background galaxies thanks to the magnification provided by strong gravitational lensing.
Aims.
We present a ...systematic analysis of integral-field-spectroscopy observations of 12 massive clusters, conducted with the Multi Unit Spectroscopic Explorer (MUSE). All data were taken under very good seeing conditions (∼0″.6) in effective exposure times between two and 15 h per pointing, for a total of 125 h. Our observations cover a total solid angle of ∼23 arcmin
2
in the direction of clusters, many of which were previously studied by the MAssive Clusters Survey, Frontier Fields (FFs), Grism Lens-Amplified Survey from Space and Cluster Lensing And Supernova survey with
Hubble
programmes. The achieved emission line detection limit at 5
σ
for a point source varies between (0.77–1.5) × 10
−18
erg s
−1
cm
−2
at 7000 Å.
Methods.
We present our developed strategy to reduce these observational data, detect continuum sources and line emitters in the datacubes, and determine their redshifts. We constructed robust mass models for each cluster to further confirm our redshift measurements using strong-lensing constraints, and identified a total of 312 strongly lensed sources producing 939 multiple images.
Results.
The final redshift catalogues contain more than 3300 robust redshifts, of which 40% are for cluster members and ∼30% are for lensed Lyman-
α
emitters. Fourteen percent of all sources are line emitters that are not seen in the available HST images, even at the depth of the FFs (∼29 AB). We find that the magnification distribution of the lensed sources in the high-magnification regime (
μ
= 2–25) follows the theoretical expectation of
N
(
z
) ∝
μ
−2
. The quality of this dataset, number of lensed sources, and number of strong-lensing constraints enables detailed studies of the physical properties of both the lensing cluster and the background galaxies. The full data products from this work, including the datacubes, catalogues, extracted spectra, ancillary images, and mass models, are made available to the community.
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.
Abstract
We aim at constraining the dust mass in high-z (z ≳ 5) galaxies using the upper limits obtained by Atacama Large Millimetre/submillimetre Array (ALMA) in combination with the rest-frame ...UV–optical spectral energy distributions (SEDs). For SED fitting, because of degeneracy between dust extinction and stellar age, we focus on two extremes: continuous star formation (Model A) and instantaneous star formation (Model B). We apply these models to Himiko (as a representative UV-bright object) and a composite SED of z > 5 Lyman break galaxies (LBGs). For Himiko, Model A requires a significant dust extinction, which leads to a high dust temperature >70 K for consistency with the ALMA upper limit. This high dust temperature puts a strong upper limit on the total dust mass Md ≲ 2 × 106 M⊙, and the dust mass produced per supernova (SN) md,SN ≲ 0.1 M⊙. Such a low md, SN suggests significant loss of dust by reverse shock destruction or outflow, and implies that SNe are not the dominant source of dust at high z. Model B allows Md ∼ 2 × 107 M⊙ and md,SN ∼ 0.3 M⊙. We could distinguish between Models A and B if we observe Himiko at wavelength < 1.2 mm by ALMA. For the LBG sample, we obtain Md ≲ 2 × 106 M⊙ for a typical LBG at z > 5, but this only puts an upper limit for md,SN as ∼2 M⊙. This clarifies the importance of observing UV-bright objects (like Himiko) to constrain the dust production by SNe.
PDF
