64 research outputs found
The [OIII] equivalent width distribution at z : The redshift evolution of the extreme emission line galaxies
We determine the [OIII] equivalent width (EW) distribution of
rest-frame UV-selected (M) star-forming
galaxies in the GOODS North and South fields. We make use of deep HDUV
broadband photometry catalogues for selection and 3D-HST WFC3/IR grism spectra
for measurement of line properties. The [OIII] EW distribution
allows us to measure the abundance of extreme emission line galaxies (EELGs)
within this population. We model a log-normal distribution to the
[OIII] rest-frame equivalent widths of galaxies in our sample,
with location parameter and variance parameter . This EW distribution has a mean [OIII] EW of
168. The fractions of rest-UV-selected galaxies with
[OIII] EWs greater than and are measured to
be , , and
respectively. The EELG fractions do not vary strongly with UV luminosity in the
range () considered in this paper, consistent with
findings at higher redshifts. We compare our results to and
studies where candidate EELGs have been discovered through
Spitzer/IRAC colours, and we identify rapid evolution with redshift in the
fraction of star-forming galaxies observed in an extreme emission line phase (a
rise by a factor between and ). This
evolution is consistent with an increased incidence of strong bursts in the
galaxy population of the reionisation era. While this population makes a
sub-dominant contribution of the ionising emissivity at , EELGs
are likely to dominate the ionising output in the reionisation era.Comment: Submitted to MNRAS. 13 pages, 6 figure
First insights into the ISM at z > 8 with JWST: possible physical implications of a high [O III] λ4363/[O III] λ5007
© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.We present a detailed analysis of the rest-frame optical emission line ratios for three spectroscopically confirmed galaxies at z > 7.5. The galaxies were identified in the James Webb Space Telescope (JWST) Early Release Observations field SMACS J0723.3 − 7327. By quantitatively comparing Balmer and oxygen line ratios of these galaxies with various low-redshift ‘analogue’ populations (e.g. Green Peas, Blueberries, etc.), we show that no single analogue population captures the diversity of line ratios of all three galaxies observed at z > 7.5. We find that S06355 at z = 7.67 and S10612 at z = 7.66 are similar to local Green Peas and Blueberries. In contrast, S04590 at z = 8.50 appears to be significantly different from the other two galaxies, most resembling extremely low-metallicity systems in the local Universe. Perhaps the most striking spectral feature in S04590 is the curiously high [O III] λ4363/[O III] λ5007 ratio (RO3) of 0.048 (or 0.055 when dust-corrected), implying either extremely high electron temperatures, >3 × 104 K, or gas densities >104 cm−3. Observed line ratios indicate that this galaxy is unlikely to host an AGN. Using photoionization modelling, we show that the inclusion of high-mass X-ray binaries or a high cosmic ray background in addition to a young, low-metallicity stellar population can provide the additional heating necessary to explain the observed high RO3 while remaining consistent with other observed line ratios. Our models represent a first step at accurately characterizing the dominant sources of photoionization and heating at very high redshifts, demonstrating that non-thermal processes may become important as we probe deeper into the Epoch of Reionization.Peer reviewe
Early results from GLASS-JWST XVI: Discovering a bluer z~4-7 Universe through UV slopes
We use the GLASS-JWST Early Release Science NIRCam parallel observations to
provide a first view of the UV continuum properties of NIRCam/F444W selected
galaxies at 4<z<7. By combining multiwavelength NIRCam observations, we
constrain the UV continuum slope for a sample of 401 galaxies with stringent
quality controls. We find that >99% of the galaxies are blue star-forming
galaxies with very low levels of dust (Avbeta~0.01+/-0.33). We find no
statistically significant correlation for UV slope with redshift or UV
magnitude. However, we find that in general galaxies at higher redshifts and
fainter UV magnitudes have steeper UV slopes. We find a statistically
significant correlation for UV slope with stellar mass, with galaxies with
higher stellar mass showing shallower UV slopes. Individual fits to some of our
galaxies reach the bluest UV slopes of beta~-3.1 allowed by stellar population
models used in this analysis. Therefore, it is likely that stellar population
models with higher amount of Lyman continuum leakage, AGN effects, and/or
Population III contributions are required to accurately reproduce the rest-UV
and optical properties of some of our bluest galaxies. This dust-free early
view confirms that our current cosmological understanding of gradual mass +
dust buildup of galaxies with cosmic time is largely accurate to describe the
~0.7-1.5 Gyr age window of the Universe. The abundance of a large population of
UV faint dust-poor systems may point to a dominance of low-mass galaxies at z>6
playing a vital role in cosmic reionization.Comment: Accepted in ApJ
Early Results from GLASS-JWST. XXI: Rapid assembly of a galaxy at z=6.23 revealed by its C/O abundance
The abundance of carbon relative to oxygen (C/O) is a promising probe of star
formation history in the early universe, as the ratio changes with time due to
production of these elements by different nucleosynthesis pathways. We present
a measurement of (stat) (sys)
in a galaxy observed as part of the GLASS-JWST Early Release Science
Program. Notably, we achieve good precision thanks to the detection of the
rest-frame ultraviolet O III], C III], and C IV emission lines delivered by
JWST/NIRSpec. The C/O abundance is 0.8 dex lower than the solar value and
is consistent with the expected yield from core-collapse supernovae, indicating
that longer-lived intermediate mass stars have not fully contributed to carbon
enrichment. This in turn implies rapid buildup of a young stellar population
with age Myr in a galaxy seen 900 million years after the
Big Bang. Our chemical abundance analysis is consistent with spectral energy
distribution modeling of JWST/NIRCam photometric data, which indicates a
current stellar mass and specific star formation rate sSFR
Gyr. These results showcase the value of chemical abundances and C/O in
particular to study the earliest stages of galaxy assembly.Comment: 16 pages, 4 figures, 2 tables. Accepted for publication in ApJ
The production of ionizing photons in UV-faint z~3-7 galaxies
The demographics of the production and escape of ionizing photons from
UV-faint early galaxies is a key unknown in discovering the primary drivers of
reionization. With the advent of JWST it is finally possible to observe the
rest-frame optical nebular emission from individual sub-L z>3 galaxies to
measure the production of ionizing photons, . Here we study a
sample of 380 z~3-7 galaxies spanning -23 <M < -15.5 (median
M -18) with deep multi-band HST and JWST/NIRCam photometry
covering the rest-UV to optical from the GLASS and UNCOVER JWST surveys. Our
sample includes 109 galaxies with Lyman-alpha emission detected in MUSE
spectroscopy. We use H-alpha fluxes inferred from NIRCam photometry to estimate
the production rate of ionizing photons which do not escape these galaxies
. We find median
, with a broad
intrinsic scatter 0.42 dex, implying a broad range of galaxy properties and
ages in our UV-faint sample. Galaxies detected with Lyman-alpha have ~0.1 dex
higher , which is explained by their higher
H-alpha EW distribution, implying younger ages, higher sSFR and thus more O/B
stars. We find significant trends of increasing
with increasing H-alpha EW, decreasing UV
luminosity, and decreasing UV slope, implying the production of ionizing
photons is enhanced in young, low metallicity galaxies. We find no significant
evidence for sources with very high ionizing escape fraction
(>0.5) in our sample, based on their photometric properties,
even amongst the Lyman-alpha selected galaxies. This work demonstrates that
considering the full distribution of across galaxy
properties is important for assessing the primary drivers of reionization.Comment: 10 pages, 7 figures, submitted to A&
The ionising photon production efficiency at z~6 for a sample of bright Lyman-alpha emitters using JEMS and MUSE
We study the ionising photon production efficiency at the end of the Epoch of
Reionisation () for a sample of 35 bright Lyman-
emitters, this quantity is crucial to infer the ionising photon budget of the
Universe. These objects were selected to have reliable spectroscopic redshifts,
assigned based on the profile of their Lyman- emission line, detected
in the MUSE deep fields. We exploit medium-band observations from the JWST
extragalactic medium band survey (JEMS) to find the flux excess corresponding
to the redshifted \ha\ emission line. We estimate the UV luminosity by fitting
the full JEMS photometry, along with several HST photometric points, with
\texttt{Prospector}. We find a median ultra-violet continuum slope of for the sample, indicating young stellar populations
with little-to-no dust attenuation. Supported by this, we derive
with no dust attenuation and find a median value of
log. If we
perform dust attenuation corrections and assume a Calzetti attenuation law, our
values are lowered by dex. Our results suggest Lyman-
emitters at the Epoch of Reionisation have enhanced compared to
previous estimations from literature, in particular, when compared to the
non-Lyman- emitting population. This initial study provides a promising
outlook on the characterisation of ionising photon production in the early
Universe. In the future, a more extensive study will be performed on the entire
dataset provided by the JWST Advanced Deep Extragalactic Survey (JADES). Thus,
for the first time, allowing us toComment: 11 pages, 5 figures in main paper. 10 pages, 30 figures in appendix.
Submitted to MNRA
The Galaxies Missed by Hubble and ALMA: The Contribution of Extremely Red Galaxies to the Cosmic Census at 3 < z < 8
Using deep JWST imaging from JADES, JEMS, and SMILES, we characterize optically faint and extremely red galaxies at z > 3 that were previously missing from galaxy census estimates. The data indicate the existence of abundant, dusty, and poststarburst-like galaxies down to 108 M ⊙, below the sensitivity limit of Spitzer and the Atacama Large Millimeter/submillimeter Array (ALMA). Modeling the NIRCam and Hubble Space Telescope (HST) photometry of these red sources can result in extremely high values for both stellar mass and star formation rate (SFR); however, including seven MIRI filters out to 21 μm results in decreased masses (median 0.6 dex for log10(M∗/M⊙) > 10) and SFRs (median 10× for SFR > 100 M ⊙ yr−1). At z > 6, our sample includes a high fraction of “little red dots” (LRDs; NIRCam-selected dust-reddened active galactic nucleus (AGN) candidates). We significantly measure older stellar populations in the LRDs out to rest-frame 3 μm (the stellar bump) and rule out a dominant contribution from hot dust emission, a signature of AGN contamination to stellar population measurements. This allows us to measure their contribution to the cosmic census at z > 3, below the typical detection limits of ALMA (L IR < 1012 L ⊙). We find that these sources, which are overwhelmingly missed by HST and ALMA, could effectively double the obscured fraction of the star formation rate density at 4 < z < 6 compared to some estimates, showing that prior to JWST, the obscured contribution from fainter sources could be underestimated. Finally, we identify five sources with evidence for Balmer breaks and high stellar masses at 5.5 < z < 7.7. While spectroscopy is required to determine their nature, we discuss possible measurement systematics to explore with future data
Early results from GLASS-JWST. III: Galaxy candidates at z9-15
We present the results of a first search for galaxy candidates at
z9--15 on deep seven-bands NIRCam imaging acquired as part of the
GLASS-JWST Early Release Science Program on a flanking field of the Frontier
Fields cluster A2744. Candidates are selected via two different renditions of
the Lyman-break technique, isolating objects at z9-11, and z9-15,
respectively, supplemented by photometric redshifts obtained with two
independent codes. We find six color-selected candidates at z9, plus one
additional candidate with photometric redshift z9. In particular,
we identify two bright candidates at that are
unambiguously placed at and , respectively. The
total number of galaxies discovered at is in line with the predictions of
a non-evolving LF. The two bright ones at are unexpected given the
survey volume, although cosmic variance and small number statistics limits
general conclusions. This first search demonstrates the unique power of JWST to
discover galaxies at the high redshift frontier. The candidates are ideal
targets for spectroscopic follow-up in cycle.Comment: Submitted to ApJL, 9 pages, 4 figure
The GLASS-JWST Early Release Science Program. II. Stage I release of NIRCam imaging and catalogs in the Abell 2744 region
We present images and a multi-wavelength photometric catalog based on all of
the JWST NIRCam observations obtained to date in the region of the Abell 2744
galaxy cluster. These data come from three different programs, namely the
GLASS-JWST Early Release Science Program, UNCOVER, and Director's Discretionary
Time program 2756. The observed area in the NIRCam wide-band filters - covering
the central and extended regions of the cluster, as well as new parallel fields
- is 46.5 arcmin in total. All images in eight bands (F090W, F115W, F150W,
F200W, F277W, F356W, F410M, F444W) have been reduced adopting the latest
calibration and reference files available. Data reduction has been performed
using an augmented version of the official JWST pipeline, with improvements
aimed at removing or mitigating defects in the raw images and improving the
background subtraction and photometric accuracy. We obtain a F444W-detected
multi-band catalog, including all NIRCam and available HST data, adopting
forced aperture photometry on PSF-matched images. The catalog is intended to
enable early scientific investigations and is optimized for the study of faint
galaxies; it contains 24389 sources, with a 5 limiting magnitude in the
F444W band ranging from 28.5 AB to 30.5 AB, as a result of the varying exposure
times of the surveys that observed the field. We publicly release the reduced
NIRCam images, associated multi-wavelength catalog and code adopted for
noise removal with the aim of aiding users to familiarize themselves with JWST
NIRCam data and identify suitable targets for follow-up observations.Comment: Accepted for publication in The Astrophysical Journal. Revised
analysis with updated comparison
First Sample of H+[O III] 5007 Line Emitters at through JWST/NIRCam Slitless Spectroscopy: Physical Properties and Line Luminosity Functions
We present a sample of four emission-line galaxies at that were
serendipitously discovered using the commissioning data for the JWST/NIRCam
wide-field slitless spectroscopy (WFSS) mode. One of them (at ) has
been reported previously while the others are new discoveries. These sources
are selected by the secure detections of both [O III] 5007 and
H lines with other fainter lines tentatively detected in some cases
(e.g., [O II] 3727, [O III] 4959 and [N II] 6583).
In the [O III]/H - [N II]/H Baldwin-Phillips-Terlevich diagram,
these galaxies occupy the same parameter space as that of star-forming
galaxies, indicating that they have been enriched rapidly to sub-solar
metallicities (0.6 ), similar to galaxies with comparable
stellar masses at much lower redshifts. The detection of strong H lines
suggests a higher ionizing photon production efficiency within galaxies in the
early Universe. We find brightening of the [O III] 5007 line
luminosity function (LF) from to 6, and no or weak redshift evolution of
the H line LF from to 6. Both LFs are under-predicted at
by a factor of 10 in certain cosmological simulations. This further
indicates a global Ly photon escape fraction of 5-7% at , much
lower than previous estimates through the comparison of the UV-derived
star-formation rate density and Ly luminosity density. Our sample
recovers % of galaxies in the survey volume with
stellar masses greater than , suggesting the ubiquity
of strong H and [O III] line emitters in the Epoch of Reionization,
which will be further uncovered in the era of JWST.Comment: 25 pages, 11 figures, submitted to Ap
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