We present a detailed stellar population analysis of 11 bright (H < 26.6) galaxies at z=9−11 (three spectroscopically confirmed) to constrain the chemical enrichment and growth of stellar mass of ...early galaxies. We use the flexible Bayesian spectral energy distribution (SED) fitting code Prospector with a range of star-formation histories (SFHs), a flexible dust attenuation law and a self-consistent modeling of emission lines. This approach allows us to assess how different priors affect our results, and how well we can break degeneracies between dust attenuation, stellar ages, metallicity and emission lines using data which probe only the rest-frame ultraviolet to optical wavelengths. We measure a median observed ultraviolet spectral slope β= −1.87+0.35−0.43 for relatively massive star-forming galaxies (9<log(M?/M)<10), consistent with no change from z=4 to z=9−10 at these stellar masses, implying rapid enrichment. Our SED-fitting results are consistent with a star-forming main sequence with sub-linear slope (0.7±0.2) and specific star-formation rates of 3−10 Gyr−1. However, the stellar ages and SFHs are less well constrained. Using different SFH priors, we cannot distinguish between median mass-weighted ages of ∼50−150 Myr, which corresponds to 50% formation redshifts of z50∼10−12 atz∼9 and is of the order of the dynamical timescales of these systems. Importantly, the models with different SFH priors are able to fit the data equally well. We conclude that the current observational data cannot tightly constrain the mass-buildup timescales of these z=9−11 galaxies, with our results consistent with SFHs implying both a shallow and steep increase of the cosmic SFR density with time at z >10
Abstract
The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the Epoch of Reionization ...is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with the Hubble Space Telescope Cosmic Origins Spectrograph for a
z
= 0.2–0.4 sample of 66 galaxies. After careful processing of the far-UV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.
Abstract
We present the data release and data reduction process for the Epoch 1 NIRCam observations for the Cosmic Evolution Early Release Science Survey (CEERS). These data consist of NIRCam imaging ...in six broadband filters (F115W, F150W, F200W, F277W, F356W and F444W) and one medium-band filter (F410M) over four pointings, obtained in parallel with primary CEERS MIRI observations. We reduced the NIRCam imaging with the JWST Calibration Pipeline, with custom modifications and reduction steps designed to address additional features and challenges with the data. Here we provide a detailed description of each step in our reduction and a discussion of future expected improvements. Our reduction process includes corrections for known prelaunch issues such as 1/
f
noise, as well as in-flight issues including snowballs, wisps, and astrometric alignment. Many of our custom reduction processes were first developed with prelaunch simulated NIRCam imaging over the full 10 CEERS NIRCam pointings. We present a description of the creation and reduction of this simulated data set in the Appendix. We provide mosaics of the real images in a public release, as well as our reduction scripts with detailed explanations to allow users to reproduce our final data products. These represent one of the first official public data sets released from the Directors Discretionary Early Release Science (DD-ERS) program.
ABSTRACT We present a robust measurement and analysis of the rest-frame ultraviolet (UV) luminosity functions at z = 4-8. We use deep Hubble Space Telescope imaging over the Cosmic Assembly ...Near-infrared Deep Extragalactic Legacy Survey/GOODS fields, the Hubble Ultra Deep Field, and the Hubble Frontier Field deep parallel observations near the Abell 2744 and MACS J0416.1-2403 clusters. The combination of these surveys provides an effective volume of 0.6-1.2 × 106 Mpc3 over this epoch, allowing us to perform a robust search for faint 18) and bright (M 21) high-redshift galaxies. We select candidate galaxies using a well-tested photometric redshift technique with careful screening of contaminants, finding a sample of 7446 candidate galaxies at 3.5 8.5, with >1000 galaxies at 6-8. We measure both a stepwise luminosity function for candidate galaxies in our redshift samples, and a Schechter function, using a Markov Chain Monte Carlo analysis to measure robust uncertainties. At the faint end, our UV luminosity functions agree with previous studies, yet we find a higher abundance of UV-bright candidate galaxies at 6. Our best-fit value of the characteristic magnitude is consistent with −21 at 5, which is different than that inferred based on previous trends at lower redshift, and brighter at ∼2 significance than previous measures at z = 6 and 7. At z = 8, a single power law provides an equally good fit to the UV luminosity function, while at z = 6 and 7 an exponential cutoff at the bright end is moderately preferred. We compare our luminosity functions to semi-analytical models, and find that the lack of evolution in is consistent with models where the impact of dust attenuation on the bright end of the luminosity function decreases at higher redshift, although a decreasing impact of feedback may also be possible. We measure the evolution of the cosmic star-formation rate (SFR) density by integrating our observed luminosity functions to , correcting for dust attenuation, and find that the SFR density declines proportionally to (1 ) at 4, which is consistent with observations at 9. Our observed luminosity functions are consistent with a reionization history that starts at 10, completes at 6, and reaches a midpoint (x 0.5) at 6.7 9.4. Finally, using a constant cumulative number density selection and an empirically derived rising star-formation history, our observations predict that the abundance of bright z = 9 galaxies is likely higher than previous constraints, although consistent with recent estimates of bright 10 galaxies.
Abstract
We present JWST NIRSpec spectroscopy for 11 galaxy candidates with photometric redshifts of
z
≃ 9 − 13 and
M
UV
∈ −21, −18 newly identified in NIRCam images in the Cosmic Evolution Early ...Release Science Survey. We confirm emission line redshifts for 7 galaxies at
z
= 7.762–8.998 using spectra at ∼1–5
μ
m either with the NIRSpec prism or its three medium-resolution (
R
∼ 1000) gratings. For
z
≃ 9 photometric candidates, we achieve a high confirmation rate of ≃90%, which validates the classical dropout selection from NIRCam photometry. No robust emission lines are identified in three galaxy candidates at
z
> 10, where the strong O
iii
and H
β
lines would be redshifted beyond the wavelength range observed by NIRSpec, and the Ly
α
continuum break is not detected with the sensitivity of the current data. Compared with Hubble Space Telescope-selected bright galaxies (
M
UV
≃ −22) that are similarly spectroscopically confirmed at
z
≃ 8 − 9, these NIRCam-selected galaxies are characterized by lower star formation rates (SFRs; SFR ≃ 4
M
⊙
yr
−1
) and lower stellar masses (≃10
8
M
⊙
), but with higher specific SFR (≃40 Gyr
−1
), higher O
iii
+H
β
equivalent widths (≃1100 Å), and elevated production efficiency of ionizing photons (
log
(
ξ
ion
/
Hz
erg
−
1
)
≃
25.8
) induced by young stellar populations (<10 Myr) accounting for ≃20% of the galaxy mass, highlighting the key contribution of faint galaxies to cosmic reionization. Taking advantage of the homogeneous selection and sensitivity, we also investigate metallicity and ISM conditions with empirical calibrations using the O
iii
5008
/H
β
ratio. We find that galaxies at
z
≃ 8 − 9 have higher SFRs and lower metallicities than galaxies at similar stellar masses at
z
≃ 2 − 6, which is generally consistent with the current galaxy formation and evolution models.
The origin of the correlations between mass, morphology, quenched fraction, and formation history in galaxies is difficult to define, primarily due to the uncertainties in galaxy star formation ...histories (SFHs). SFHs are better constrained for higher redshift galaxies, observed closer to their formation and quenching epochs. Here we use "nonparametric" SFHs and a nested sampling method to derive constraints on the formation and quenching timescales of quiescent galaxies at . We model deep HST grism spectroscopy and photometry from the CLEAR (CANDELS Ly Emission at Reionization) survey. The galaxy formation redshifts, z50 (defined as the point where they had formed 50% of their stellar mass) range from (shortly prior to the observed epoch) up to . We find that early formation redshifts are correlated with high stellar-mass surface densities, , where 1 is the stellar mass within 1 pkpc (proper kpc). Quiescent galaxies with the highest stellar-mass surface density, , show a minimum formation redshift: all such objects in our sample have . Quiescent galaxies with lower surface density, , show a range of formation epochs ( ), implying these galaxies experienced a range of formation and assembly histories. We argue that the surface density threshold uniquely identifies galaxies that formed in the first few Gyr after the big bang, and we discuss the implications this has for galaxy formation models.
Abstract
We present JWST/NIRSpec prism spectroscopy of seven galaxies selected from Cosmic Evolution Early Release Science (CEERS) survey NIRCam imaging with photometric redshifts
z
phot
> 8. We ...measure emission line redshifts of
z
= 7.65 and 8.64 for two galaxies. For two other sources without securely detected emission lines we measure
z
=
9.77
−
0.29
+
0.37
and
10.01
−
0.19
+
0.14
by fitting model spectral templates to the prism data, from which we detect continuum breaks consistent with Ly
α
opacity from a mostly neutral intergalactic medium. The presence of strong breaks and the absence of strong emission lines give high confidence that these two galaxies have redshifts
z
> 9.6, but the redshift values derived from the breaks alone have large uncertainties given the low spectral resolution and relatively low S/N of the CEERS NIRSpec prism data. The two
z
∼ 10 sources observed are relatively luminous (
M
UV
< −20), with blue continua (−2.3 ≲
β
≲ −1.9) and low dust attenuation (
A
V
≃
0.15
−
0.1
+
0.3
); and at least one of them has a high stellar mass for a galaxy at that redshift (
log
(
M
⋆
/
M
⊙
)
≃
9.3
−
0.3
+
0.2
). Considered together with spectroscopic observations of other CEERS NIRCam-selected high-
z
galaxy candidates in the literature, we find a high rate of redshift confirmation and low rate of confirmed interlopers (8%). Ten out of 35
z
> 8 candidates with CEERS NIRSpec spectroscopy do not have secure redshifts, but the absence of emission lines in their spectra is consistent with redshifts
z
> 9.6. We find that
z
> 8 photometric redshifts are generally in agreement (within their uncertainties) with the spectroscopic values, but also that the photometric redshifts tend to be slightly overestimated (〈Δ
z
〉 = 0.45 ± 0.11), suggesting that current templates do not fully describe the spectra of very-high-
z
sources. Overall, the spectroscopy solidifies photometric redshift evidence for a high spatial density of bright galaxies at
z
> 8 compared to theoretical model predictions, and further disfavors an accelerated decline in the integrated UV luminosity density at
z
> 8.
We explore star formation histories (SFHs) of galaxies based on the evolution of the star formation rate stellar mass relation (SFR-M). Using data from the FourStar Galaxy Evolution Survey (ZFOURGE) ...in combination with far-IR imaging from the Spitzer and Herschel observatories we measure the SFR-M relation at 0.5 < z <. Similar to recent works we find that the average infrared spectral energy distributions of galaxies are roughly consistent with a single infrared template across a broad range of redshifts and stellar masses, with evidence for only weak deviations. We find that these two estimates are in broad qualitative agreement, but that there is room for improvement at a more detailed level. At early times the SFHs suggest mass growth rates that are as much as 10 x higher than inferred from the SMF. However, at later times the SFHs under-predict the inferred evolution, as is expected in the case of additional growth due to mergers.
Abstract
We report on the discovery of two low-luminosity, broad-line active galactic nuclei (AGNs) at
z
> 5 identified using JWST NIRSpec spectroscopy from the Cosmic Evolution Early Release Science ...(CEERS) survey. We detect broad H
α
emission in the spectra of both sources, with FWHM of 2060 ± 290 km s
−1
and 1800 ± 200 km s
−1
, resulting in virial black hole (BH) masses that are 1–2 dex below those of existing samples of luminous quasars at
z
> 5. The first source, CEERS 2782 at
z
= 5.242, is 2–3 dex fainter than known quasars at similar redshifts and was previously identified as a candidate low-luminosity AGN based on its morphology and rest-frame optical spectral energy distribution (SED). We measure a BH mass of
M
BH
= (1.3 ± 0.4) × 10
7
M
⊙
, confirming that this AGN is powered by the least massive BH known in the Universe at the end of cosmic reionization. The second source, CEERS 746 at
z
= 5.624, is inferred to be a heavily obscured, broad-line AGN caught in a transition phase between a dust-obscured starburst and an unobscured quasar. We estimate its BH mass to be in the range of
M
BH
≃ (0.9–4.7) × 10
7
M
⊙
, depending on the level of dust obscuration assumed. We perform SED fitting to derive host stellar masses,
M
⋆
, allowing us to place constraints on the BH–galaxy mass relationship in the lowest mass range yet probed in the early Universe. The
M
BH
/
M
⋆
ratio for CEERS 2782, in particular, is consistent with or higher than the empirical relationship seen in massive galaxies at
z
= 0. We examine the narrow emission line ratios of both sources and find that their location on the BPT and OHNO diagrams is consistent with model predictions for moderately low metallicity AGNs with
Z
/
Z
⊙
≃ 0.2–0.4. The spectroscopic identification of low-luminosity, broad-line AGNs at
z
> 5 with
M
BH
≃ 10
7
M
⊙
demonstrates the capability of JWST to push BH masses closer to the range predicted for the BH seed population and provides a unique opportunity to study the early stages of BH–galaxy assembly.
Abstract
We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to ...measure the redshifts of over a million Ly
α
emitting galaxies between 1.88 <
z
< 3.52, in a 540 deg
2
area encompassing a comoving volume of 10.9 Gpc
3
. No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.
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