Abstract
We report on the gas-phase metallicity gradients of a sample of 238 star-forming galaxies at 0.6 <
z
< 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. ...The observations include 12 orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Ly
α
Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies in this sample are consistent with having a zero or slightly positive metallicity gradient (
dZ
/
dR
≥ 0, i.e., increasing with radius) across the full mass range probed (8.5 < log
M
*
/
M
⊙
< 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass—consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider—including star formation rates, sizes, star formation rate surface densities, and star formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models.
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 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.
CLEAR: Survey Overview, Data Analysis, and Products Simons, Raymond C.; Papovich, Casey; Momcheva, Ivelina G. ...
The Astrophysical journal. Supplement series,
05/2023, Volume:
266, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
We present an overview of the CANDELS Ly
α
Emission At Reionization (CLEAR) survey. CLEAR is a 130 orbit program of the Hubble Space Telescope using the Wide Field Camera 3 (WFC3) IR G102 ...grism. CLEAR targets 12 pointings divided between the GOODS-N and GOODS-S fields of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). Combined with existing spectroscopic data from other programs, the full CLEAR data set includes spectroscopic imaging of these fields over 0.8–1.7
μ
m. In this paper, we describe the CLEAR survey, the survey strategy, the data acquisition, reduction, processing, and science products and catalogs released alongside this paper. The catalogs include emission line fluxes and redshifts derived from the combination of the photometry and grism spectroscopy for 6048 galaxies, primarily ranging from 0.2 ≲
z
≲ 3. We also provide an overview of CLEAR’s science goals and results. In conjunction with this paper we provide links to electronic versions of the data products, including 1D+2D extracted spectra and emission line maps.
Abstract
We use deep spectroscopy from the Hubble Space Telescope Wide-Field-Camera 3 IR grisms combined with broadband photometry to study the stellar populations, gas ionization and chemical ...abundances in star-forming galaxies at
z
∼ 1.1–2.3. The data stem from the CANDELS Ly
α
Emission At Reionization (CLEAR) survey. At these redshifts, the grism spectroscopy measure the O
II
λ
λ
3727, 3729, O
III
λ
λ
4959, 5008, and H
β
strong emission features, which constrain the ionization parameter and oxygen abundance of the nebular gas. We compare the line-flux measurements to predictions from updated photoionization models (MAPPINGS V; Kewley et al.), which include an updated treatment of nebular gas pressure,
log
P
/
k
=
n
e
T
e
. Compared to low-redshift samples (
z
∼ 0.2) at fixed stellar mass,
log
M
*
/
M
⊙
=
9.4–9.8, the CLEAR galaxies at
z
= 1.35 (1.90) have lower gas-phase metallicity,
Δ
(
log
Z
)
= 0.25 (0.35) dex, and higher ionization parameters,
Δ
(
log
q
)
= 0.25 (0.35) dex, where
U
≡
q
/
c
. We provide updated analytic calibrations between the O
III
, O
II
, and H
β
emission-line ratios, metallicity, and ionization parameter. The CLEAR galaxies show that at fixed stellar mass, the gas ionization parameter is correlated with the galaxy specific star formation rates, where
Δ
log
q
≃
0.4
×
Δ
(
log
sSFR
)
, derived from changes in the strength of galaxy H
β
equivalent width. We interpret this as a consequence of higher gas densities, lower gas covering fractions, combined with a higher escape fraction of H-ionizing photons. We discuss both tests to confirm these assertions and implications this has for future observations of galaxies at higher redshifts.
CLEAR: Emission-line Ratios at Cosmic High Noon Backhaus, Bren E.; Trump, Jonathan R.; Cleri, Nikko J. ...
Astrophysical journal/The Astrophysical journal,
02/2022, Volume:
926, Issue:
2
Journal Article
Peer reviewed
Open access
Abstract
We use Hubble Space Telescope Wide Field Camera 3 G102 and G141 grism spectroscopy to measure rest-frame optical emission-line ratios of 533 galaxies at
z
∼ 1.5 in the CANDELS Ly
α
Emission ...at Reionization survey. We compare O
iii
/H
β
versus S
ii
/(H
α
+ N
ii
) as an “unVO87” diagram for 461 galaxies and O
iii
/H
β
versus Ne
iii
/O
ii
as an “OHNO” diagram for 91 galaxies. The unVO87 diagram does not effectively separate active galactic nuclei (AGN) and Ne
v
sources from star-forming galaxies, indicating that the unVO87 properties of star-forming galaxies evolve with redshift and overlap with AGN emission-line signatures at
z
> 1. The OHNO diagram does effectively separate X-ray AGN and Ne
v
-emitting galaxies from the rest of the population. We find that the O
iii
/H
β
line ratios are significantly anticorrelated with stellar mass and significantly correlated with
log
(
L
H
β
)
, while S
ii
/(H
α
+ N
ii
) is significantly anticorrelated with
log
(
L
H
β
)
. Comparison with MAPPINGS V photoionization models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-star formation rate (SFR) galaxies. We do not find evidence for redshift evolution of the emission-line ratios outside of the correlations with mass and SFR. Our results suggest that the OHNO diagram of O
iii
/H
β
versus Ne
iii
/O
ii
will be a useful indicator of AGN content and gas conditions in very high-redshift galaxies to be observed by the James Webb Space Telescope.
Abstract
We investigate spatially resolved emission-line ratios in a sample of 219 galaxies (0.6 <
z
< 1.3) detected using the G102 grism on the Hubble Space Telescope Wide Field Camera 3 taken as ...part of the CANDELS Ly
α
Emission at Reionization survey to measure ionization profiles and search for low-luminosity active galactic nuclei (AGN). We analyze O
iii
and H
β
emission-line maps, enabling us to spatially resolve the O
iii
/H
β
emission-line ratio across the galaxies in the sample. We compare the O
iii
/H
β
ratio in galaxy centers and outer annular regions to measure ionization differences and investigate the potential of sources with nuclear ionization to host AGN. We investigate some of the individual galaxies that are candidates to host strong nuclear ionization and find that they often have low stellar mass and are undetected in X-rays, as expected for low-luminosity AGN in low-mass galaxies. We do not find evidence for a significant population of off-nuclear AGN or other clumps of off-nuclear ionization. We model the observed distribution of O
iii
/H
β
spatial profiles and find that most galaxies are consistent with a small or zero difference between their nuclear and off-nuclear line ratios, but 6%–16% of galaxies in the sample are likely to host nuclear O
iii
/H
β
that is ∼0.5 dex higher than in their outer regions. This study is limited by large uncertainties in most of the measured O
iii
/H
β
spatial profiles; therefore, deeper data, e.g., from deeper HST/WFC3 programs or from JWST/NIRISS, are needed to more reliably measure the spatially resolved emission-line conditions of individual high-redshift galaxies.
Abstract
Using spatially resolved H
α
emission line maps of star-forming galaxies, we study the spatial distribution of star formation over a wide range in redshift (0.5 ≲
z
≲ 1.7). Our
z
∼ 0.5 ...measurements come from deep Hubble Space Telescope (HST) Wide Field Camera 3 G102 grism spectroscopy obtained as part of the CANDELS Ly
α
Emission at Reionization Experiment. For star-forming galaxies with log(
M
*
/
M
⊙
) ≥ 8.96, the mean H
α
effective radius is 1.2 ± 0.1 times larger than that of the stellar continuum, implying inside-out growth via star formation. This measurement agrees within 1
σ
with those measured at
z
∼ 1 and
z
∼ 1.7 from the 3D-HST and KMOS
3D
surveys, respectively, implying no redshift evolution. However, we observe redshift evolution in the stellar mass surface density within 1 kpc (Σ
1kpc
). Star-forming galaxies at
z
∼ 0.5 with a stellar mass of log(
M
*
/
M
⊙
) = 9.5 have a ratio of Σ
1kpc
in H
α
relative to their stellar continuum that is lower by (19 ± 2)% compared to
z
∼ 1 galaxies. Σ
1kpc,H
α
/Σ
1kpc,Cont
decreases toward higher stellar masses. The majority of the redshift evolution in Σ
1kpc,H
α
/Σ
1kpc,Cont
versus stellar mass stems from the fact that log(Σ
1kpc,H
α
) declines twice as much as log(Σ
1kpc,Cont
) from
z
∼ 1 to 0.5 (at a fixed stellar mass of log(
M
*
/
M
⊙
) = 9.5). By comparing our results to the TNG50 cosmological magneto-hydrodynamical simulation, we rule out dust as the driver of this evolution. Our results are consistent with inside-out quenching following in the wake of inside-out growth, the former of which drives the significant drop in Σ
1kpc,H
α
from
z
∼ 1 to
z
∼ 0.5.
Abstract
We use Paschen-
β
(Pa
β
; 1282 nm) observations from the Hubble Space Telescope G141 grism to study the star formation and dust-attenuation properties of a sample of 29 low-redshift (
z
< ...0.287) galaxies in the CANDELS Ly
α
Emission at Reionization survey. We first compare the nebular attenuation from Pa
β
/H
α
with the stellar attenuation inferred from the spectral energy distribution, finding that the galaxies in our sample are consistent with an average ratio of the continuum attenuation to the nebular gas of 0.44, but with a large amount of excess scatter beyond the observational uncertainties. Much of this scatter is linked to a large variation between the nebular dust attenuation as measured by (space-based) Pa
β
to (ground-based) H
α
to that from (ground-based) H
α
/H
β
. This implies there are important differences between attenuation measured from grism-based/wide-aperture Pa
β
fluxes and the ground-based/slit-measured Balmer decrement. We next compare star formation rates (SFRs) from Pa
β
to those from dust-corrected UV. We perform a survival analysis to infer a census of Pa
β
emission implied by both detections and nondetections. We find evidence that galaxies with lower stellar mass have more scatter in their ratio of Pa
β
to attenuation-corrected UV SFRs. When considering our Pa
β
detection limits, this observation supports the idea that lower-mass galaxies experience “burstier” star formation histories. Together, these results show that Pa
β
is a valuable tracer of a galaxy’s SFR, probing different timescales of star formation and potentially revealing star formation that is otherwise missed by UV and optical tracers.
Reionization is an inhomogeneous process, thought to begin in small ionized bubbles of the intergalactic medium (IGM) around overdense regions of galaxies. Recent Lyα studies during the epoch of ...reionization show evidence that ionized bubbles formed earlier around brighter galaxies, suggesting higher IGM transmission of Lyα from these galaxies. We investigate this problem using IR slitless spectroscopy from the Hubble Space Telescope (HST) Wide-Field Camera 3 (WFC3) G102 grism observations of 148 galaxies selected via photometric redshifts at 6.0 < z < 8.2. These galaxies have spectra extracted from the CANDELS Lyα Emission at Reionization (CLEAR) survey. We combine the CLEAR data for 275 galaxies with the Keck Deep Imaging Multi-Object Spectrograph and MOSFIRE data set from the Texas Spectroscopic Search for Lyα Emission at the End of Reionization Survey. We constrain the Lyα equivalent width (EW) distribution at 6.0 < z < 8.2, which is described by an exponential form, dN / dEW ∝ exp(-EW) W(sub 0), with the characteristic e-folding scale width (W(sub 0)). We confirm a significant drop in the Lyα strength (i.e., W(sub 0)) at z > 6. Furthermore, we compare the redshift evolution of W(sub 0) between galaxies at different UV luminosities. UV-bright (M(sub UV) < −21 i.e., L(sub UV) > L*) galaxies show weaker evolution with a decrease of 0.4 ( ± 0.2) dex in W(sub 0) at z > 6, while UV-faint (M(sub UV) > −21 LUV < L*) galaxies exhibit a significant drop of 0.7–0.8 (±0.2) dex in W(sub 0) from z < 6 to z > 6. If the change in W(sub 0) is proportional to the change in the IGM transmission for Lyα photons, then this is evidence that the transmission is “boosted” around UV-brighter galaxies, suggesting that reionization proceeds faster in regions around such galaxies.
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