The ionizing photon production efficiency, ion, is a critical parameter that provides a number of physical constraints to the nature of the early universe, including the contribution of galaxies to ...the timely completion of the reionization of the universe. Here, we use KECK/MOSFIRE and ZFOURGE multiband photometric data to explore the ion of a population of galaxies at z ∼ 2 with . Our 130 H detections show a median of 24.8 0.5 when dust corrected using a Calzetti et al. dust prescription. Our values are typical of mass/magnitude selected ion values observed in the z ∼ 2 universe. Using BPASSv2.2.1 and Starburst99 stellar population models with simple parametric star formation histories (SFH), we find that even with models that account for effects of stellar evolution with binaries/stellar rotation, model galaxies at have low H equivalent widths (EWs) and redder colors compared to our z ∼ 2 observed sample. We find that introducing starbursts to the SFHs resolve the tension with the models; however, due to the rapid time evolution of ion, H EWs, and rest-frame optical colors, our Monte Carlo simulations of starbursts show that random distributions of starbursts in evolutionary time of galaxies are unlikely to explain the observed distribution. Thus, either our observed sample is specially selected based on their past SFH, or stellar models require additional mechanisms to reproduce the observed high UV luminosity of galaxies for a given production rate of hydrogen ionizing photons.
Abstract
We report detections of the O
iii
λ
4364 auroral emission line for 16 galaxies at
z
= 2.1–8.7, measured from JWST/NIRSpec observations obtained as part of the Cosmic Evolution Early Release ...Science (CEERS) survey program. We combine this CEERS sample with 9 objects from the literature at
z
= 4−9 with auroral-line detections from JWST/NIRSpec and 21 galaxies at
z
= 1.4−3.7 with auroral-line detections from ground-based spectroscopy. We derive electron temperature (
T
e
) and direct-method oxygen abundances for the combined sample of 46 star-forming galaxies at
z
= 1.4−8.7. We use these measurements to construct the first high-redshift empirical
T
e
-based metallicity calibrations for the strong-line ratios O
iii
/H
β
, O
ii
/H
β
, R23 = (O
iii
+O
ii
)/H
β
, O
iii
/O
ii
, and Ne
iii
/O
ii
. These new calibrations are valid over 12+log(O/H) = 7.4−8.3 and can be applied to samples of star-forming galaxies at
z
= 2−9, leading to an improvement in the accuracy of metallicity determinations at Cosmic Noon and in the Epoch of Reionization. The high-redshift strong-line relations are offset from calibrations based on typical
z
∼ 0 galaxies or H
ii
regions, reflecting the known evolution of ionization conditions between
z
∼ 0 and
z
∼ 2. Deep spectroscopic programs with JWST/NIRSpec promise to improve statistics at the low and high ends of the metallicity range covered by the current sample, as well as to improve the detection rate of N
ii
λ
6585 and thus allow the future assessment of N-based indicators. These new high-redshift calibrations will enable accurate characterizations of metallicity scaling relations at high redshift, improving our understanding of feedback and baryon cycling in the early Universe.
Abstract
We present electron temperature (
T
e
) maps for the edge-on system Mrk 1486, affording “direct-method” gas-phase metallicity measurements across 5.″8 (4.1 kpc) along the minor axis and 9.″9 ...(6.9 kpc) along the major axis. These maps, enabled by strong detections of the O
iii
λ
4363 auroral emission line across a large spatial extent of Mrk 1486, reveal a clear negative minor-axis
T
e
gradient in which temperature decreases with increasing distance from the disk plane. We find that the lowest metallicity spaxels lie near the extremes of the major axis, while the highest metallicity spaxels lie at large spatial offsets along the minor axis. This is consistent with a picture in which low-metallicity inflows dilute the metallicity at the edges of the major axis of the disk, while star formation drives metal-enriched outflows along the minor axis. We find that the outflow metallicity in Mrk 1486 is 0.20 dex (1.6 times) higher than the average insterstellar medium (ISM) metallicity, and more than 0.80 dex (6.3 times) higher than metal-poor inflowing gas, which we observe to be below 5%
Z
⊙
. This is the first example of metallicity measurements made simultaneously for inflowing, outflowing, and inner disk ISM gas using consistent
T
e
-based methodology. These measurements provide unique insight into how baryon-cycle processes contribute to the assembly of a galaxy like Mrk 1486.
Abstract
The Lyman continuum (LyC) cannot be observed at the epoch of reionization (
z
≳ 6) owing to intergalactic H
i
absorption. To identify LyC emitters (LCEs) and infer the fraction of escaping ...LyC, astronomers have developed various indirect diagnostics of LyC escape. Using measurements of the LyC from the Low-redshift Lyman Continuum Survey (LzLCS), we present the first statistical test of these diagnostics. While optical depth indicators based on Ly
α
, such as peak velocity separation and equivalent width, perform well, we also find that other diagnostics, such as the O
iii
/O
ii
flux ratio and star formation rate surface density, predict whether a galaxy is an LCE. The relationship between these galaxy properties and the fraction of escaping LyC flux suggests that LyC escape depends strongly on H
i
column density, ionization parameter, and stellar feedback. We find that LCEs occupy a range of stellar masses, metallicities, star formation histories, and ionization parameters, which may indicate episodic and/or different physical causes of LyC escape.
Abstract
We present JWST Extragalactic Medium-band Survey, the first public medium-band imaging survey carried out using JWST/NIRCam and NIRISS. These observations use ∼2 and ∼4
μ
m medium-band ...filters (NIRCam F182M, F210M, F430M, F460M, F480M; and NIRISS F430M and F480M in parallel) over 15.6 arcmin
2
in the Hubble Ultra Deep Field (UDF), thereby building on the deepest multiwavelength public data sets available anywhere on the sky. We describe our science goals, survey design, NIRCam and NIRISS image reduction methods, and describe our first data release of the science-ready mosaics, which reach 5
σ
point-source limits (AB mag) of ∼29.3–29.4 in 2
μ
m filters and ∼28.2–28.7 at 4
μ
m. Our chosen filters create a JWST imaging survey in the UDF that enables novel analysis of a range of spectral features potentially across the redshift range of 0.3 <
z
< 20, including Paschen-
α
, H
α
+N
ii
, and O
iii
+H
β
emission at high spatial resolution. We find that our JWST medium-band imaging efficiently identifies strong line emitters (medium-band colors >1 mag) across redshifts 1.5 <
z
< 9.3, most prominently H
α
+N
ii
and O
iii
+H
β
. We present our first data release including science-ready mosaics of each medium-band image available to the community, adding to the legacy value of past and future surveys in the UDF. This survey demonstrates the power of medium-band imaging with JWST, informing future extragalactic survey strategies using JWST observations.
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