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
We present Keck/MOSFIRE H-band spectroscopy targeting C iii λ1907, 1909 in a z = 7.5056 galaxy previously identified via Ly emission. We detect strong line emission at with a line flux of (2.63 0.52) ...× 10−18 erg s−1 cm−2. We tentatively identify this line as C iii λ1907, but we are unable to detect C iii λ1909 owing to sky emission at the expected location. This gives a galaxy systemic redshift, , with a velocity offset to Ly of = 88 27 km s−1. The ratio of combined C iii/Ly is 0.30-0.45, one of the highest values measured for any z > 2 galaxy. We do not detect Si iii λλ1883, 1892, and place an upper limit on Si iii/C iii < 0.35 (2 ). Comparing our results to photoionization models, the C iii equivalent width (WC iii = 16.23 2.32 ), low Si iii/C iii ratio, and high implied O iii equivalent width (from the Spitzer/IRAC 3.6-4.5 0.8 mag color) require subsolar metallicities (Z 0.1-0.2 Z ) and a high ionization parameter, log U −1.5. These results favor models that produce higher ionization, such as the bpass models for the photospheres of high-mass stars, and that include both binary stellar populations and/or an IMF that extends to 300 M . The combined C iii equivalent width and 3.6-4.5 color are more consistent with ionization from young stars than active galactic nuclei (AGNs); however, we cannot rule out ionization from a combination of an AGN and young stars. We make predictions for James Webb Space Telescope spectroscopy using these different models, which will ultimately test the nature of the ionizing radiation in this source.
Abstract
The selection of high-redshift galaxies often involves spectral energy distribution (SED) fitting to photometric data, an expectation for contamination levels, and measurement of sample ...completeness—all vetted through comparison to spectroscopic redshift measurements of a sub-sample. The first JWST data are now being taken over several extragalactic fields to different depths and across various areas, which will be ideal for the discovery and classification of galaxies out to distances previously uncharted. As spectroscopic redshift measurements for sources in this epoch will not be initially available to compare with the first photometric measurements of
z
> 8 galaxies, robust photometric redshifts are of the utmost importance. Galaxies at
z
> 8 are expected to have bluer rest-frame ultraviolet (UV) colors than typically used model SED templates, which could lead to catastrophic photometric redshift failures. We use a combination of BPASS and
Cloudy
models to create a supporting set of templates that match the predicted rest-UV colors of
z
> 8 simulated galaxies. We test these new templates by fitting simulated galaxies in a mock catalog, Yung et al., which mimic expected field depths and areas of the JWST Cosmic Evolution Early Release Science Survey (
m
5
σ
∼ 28.6 over ∼100 arcmin
2
). We use EAZY to highlight the improvements in redshift recovery with the inclusion of our new template set and suggest criteria for selecting galaxies at 8 <
z
< 10 with the JWST, providing an important test case for observers venturing into this new era of astronomy.
Abstract
We present the results from a new search for candidate galaxies at
z
≈ 8.5–11 discovered over the 850 arcmin
2
area probed by the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy ...Survey (CANDELS). We use a photometric-redshift selection including both Hubble and Spitzer Space Telescope photometry to robustly identify galaxies in this epoch at
H
160
< 26.6. We use a detailed vetting procedure, including screening against persistence and stellar contamination, and the inclusion of ground-based imaging and follow-up Hubble Space Telescope imaging to build a robust sample of 11 candidate galaxies, three presented here for the first time. The inclusion of Spitzer/IRAC photometry in the selection process reduces contamination, and yields more robust redshift estimates than Hubble alone. We constrain the evolution of the rest-frame ultraviolet luminosity function via a new method of calculating the observed number densities without choosing a prior magnitude bin size. We find that the abundance at our brightest probed luminosities (
M
UV
= − 22.3) is consistent with predictions from simulations that assume that galaxies in this epoch have gas depletion times at least as short as those in nearby starburst galaxies. Due to large Poisson and cosmic variance uncertainties, we cannot conclusively rule out either a smooth evolution of the luminosity function continued from
z
= 4–8, or an accelerated decline at
z
> 8. We calculate that the presence of seven galaxies in a single field Extended Groth Strip is an outlier at the 2
σ
significance level, implying the discovery of a significant over-density. These scenarios will be imminently testable to high confidence within the first year of observations of the James Webb Space Telescope.
Abstract
We present the results from a spectroscopic survey using the MOSFIRE near-infrared spectrograph on the 10 m Keck telescope to search for Ly
α
emission from candidate galaxies at
z
∼ 9–10 in ...four of the CANDELS fields (GOODS-N, EGS, UDS, and COSMOS). We observed 11 target galaxies, detecting Ly
α
from one object in ∼8.1 hr of integration, at
z
= 8.665 ± 0.001 with an integrated signal-to-noise ratio > 7. This galaxy is in the CANDELS Extended Groth Strip (EGS) field and lies physically close (3.5 physical Mpc pMpc) to another confirmed galaxy in this field with Ly
α
detected at
z
= 8.683. The detection of Ly
α
suggests the existence of large (∼1 pMpc) ionized bubbles fairly early in the reionization process. We explore the ionizing output needed to create bubbles of this size at this epoch and find that such a bubble requires more than the ionizing power provided by the full expected population of galaxies (by integrating the UV luminosity function down to
M
UV
= −13). The Ly
α
we detect would be able to escape the predominantly neutral intergalactic medium at this epoch if our detected galaxy is inhabiting an overdensity, which would be consistent with the photometric overdensity previously identified in this region by Finkelstein et al. This implies that the CANDELS EGS field is hosting an overdensity at
z
= 8.7 that is powering one or more ionized bubbles, a hypothesis that will be imminently testable with forthcoming James Webb Space Telescope observations in this field.
Lyα emission from galaxies can be utilized to characterize the ionization state in the intergalactic medium (IGM). We report our search for Lyα emission at z > 7 using a comprehensive Keck/MOSFIRE ...near-infrared spectroscopic data set, as part of the Texas Spectroscopic Search for Lyα Emission at the End of Reionization Survey. We analyze data from 10 nights of MOSFIRE observations which together target 72 high-z candidate galaxies in the GOODS-N field, all with deep exposure times of 4.5–19 hr. Utilizing an improved automated emission-line search, we report 10 Lyα emission lines detected (>4σ) at z > 7, significantly increasing the spectroscopically confirmed sample. Our sample includes large equivalent-width (EW) Lyα emitters (>50 Å), and additional tentative Lyα emission lines detected at 3σ–4σ from five additional galaxies. We constrain the Lyα EW distribution at z ~ 7.6, finding a significant drop from z ≲ 6, suggesting an increasing fraction of neutral hydrogen (H I) in the IGM in this epoch. We estimate the Lyα transmission through the IGM (=EW(z)~7.6/EW(z~2–6)) and infer an IGM H I fraction (X(HI)) of 49 (+19,-19)% at z ~ 7.6, which is lower in modest tension (>1σ) with recent measurements at z ~ 7.6. The spatial distribution of the detected Lyα emitters implies the presence of a potential highly ionized region at z ~ 7.55, which hosts four Lyα emitters within a ∼40 cMpc spatial separation. The prominence of this ionized region in our data set could explain our lower inferred value of X(HI), though our analysis is also sensitive to the chosen reference Lyα EW distribution values and reionization models.
Abstract
We analyze a sample of 25 Ne
v
(
λ
3426) emission-line galaxies at 1.4 <
z
< 2.3 using Hubble Space Telescope/Wide Field Camera 3 G102 and G141 grism observations from the CANDELS Ly
α
...Emission at Reionization (CLEAR) survey. Ne
v
emission probes extremely energetic photoionization (creation potential of 97.11 eV) and is often attributed to energetic radiation from active galactic nuclei (AGNs), shocks from supernovae, or an otherwise very hard ionizing spectrum from the stellar continuum. In this work, we use Ne
v
in conjunction with other rest-frame UV/optical emission lines (O
ii
λ
λ
3726, 3729, Ne
iii
λ
3869, H
β
, O
iii
λ
λ
4959, 5007, H
α
+N
ii
λ
λ
6548, 6583, S
ii
λ
λ
6716, 6731), deep (2–7 Ms) X-ray observations (from Chandra), and mid-infrared imaging (from Spitzer) to study the origin of this emission and to place constraints on the nature of the ionizing engine. The majority of the Ne
v
-detected galaxies have properties consistent with ionization from AGNs. However, for our Ne
v
-selected sample, the X-ray luminosities are consistent with local (
z
≲ 0.1) X-ray-selected Seyferts, but the Ne
v
luminosities are more consistent with those from
z
∼ 1 X-ray-selected QSOs. The excess Ne
v
emission requires either reduced hard X-rays or a ∼0.1 keV excess. We discuss possible origins of the apparent Ne
v
excess, which could be related to the “soft (X-ray) excess” observed in some QSOs and Seyferts and/or be a consequence of a complex/anisotropic geometry for the narrow-line region, combined with absorption from a warm, relativistic wind ejected from the accretion disk. We also consider implications for future studies of extreme high-ionization systems in the epoch of reionization (
z
≳ 6) with the James Webb Space Telescope.
Abstract
Spectroscopic studies of extreme-ionization galaxies (EIGs) are critical to our understanding of exotic systems throughout cosmic time. These EIGs exhibit spectral features requiring >54.42 ...eV photons: the energy needed to ionize helium into He
2+
fully and emit He
ii
recombination lines. Spectroscopic studies of EIGs can probe exotic stellar populations or accretion onto intermediate-mass black holes (∼10
2
–10
5
M
⊙
), which are the possibly key contributors to the reionization of the Universe. To facilitate the use of EIGs as probes of high-ionization systems, we focus on ratios constructed from several rest-frame UV/optical emission lines: O
iii
λ
5008, H
β
, Ne
iii
λ
3870, O
ii
λ
λ
3727, 3729, and Ne
v
λ
3427. These lines probe the relative intensity at energies of 35.12, 13.62, 40.96, 13.62, and 97.12 eV, respectively, covering a wider range of ionization than traced by other common rest-frame UV/optical techniques. We use the ratios of these lines (Ne
v
/Ne
iii
≡ Ne53, O
iii
/H
β
, and Ne
iii
/O
ii
), which are nearby in wavelength, mitigating the effects of dust attenuation and uncertainties in flux calibration. We make predictions from photoionization models constructed from
Cloudy
that use a broad range of stellar populations and black hole accretion models to explore the sensitivity of these line ratios to changes in the ionizing spectrum. We compare our models to observations from the Hubble Space Telescope and JWST of galaxies with strong high-ionization emission lines at
z
∼ 0,
z
∼ 2, and 5 <
z
< 8.5. We show that the Ne53 ratio can separate galaxies with ionization from “normal” stellar populations from those with active galactic nuclei and even “exotic” Population III models. We introduce new selection methods to identify galaxies with photoionization driven by Population III stars or intermediate-mass black hole accretion disks that could be identified in upcoming high-redshift spectroscopic surveys.
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.
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