35 research outputs found
On the ages of bright galaxies Myr after the Big Bang: insights into star formation activity at with JWST
With JWST, new opportunities to study the formation and evolution of galaxies
in the early Universe are now emerging. Spitzer constraints on rest-optical
properties of galaxies demonstrated the power of using stellar
masses and star formation histories (SFHs) of galaxies to indirectly infer the
star formation history of the Universe. However, only the brightest individual
objects at could be detected with Spitzer, making it difficult to
robustly constrain past activity at . Here, we leverage the
greatly improved rest-optical sensitivity of JWST at to constrain
the ages and SFHs of eleven UV-bright () galaxies
selected to lie at , then investigate implications for star
formation activity at . We infer the properties of individual
objects in our sample with two spectral energy distribution modelling codes,
then infer a distribution of ages for bright galaxies. We
find a median age of Myr, younger than that inferred at
with a similar analysis, which is consistent with an evolution towards larger
specific star formation rates at early times. The age distribution suggests
that only percent of bright galaxies would be
similarly luminous at , implying that the number density of
bright galaxies declines by approximately an order of magnitude between and . This evolution is challenging to reconcile with some
early JWST results suggesting that the abundance of bright galaxies does not
significantly decrease towards very early times, but we suggest this tension
may be eased if young stellar populations form on top of older stellar
components, or if bright galaxies at are observed during a burst of
star formation.Comment: 13 pages, 9 figure
Insight from JWST/NIRCam into galaxy overdensities around bright Ly emitters during reionization: implications for ionized bubbles at
Several studies have detected Lyman-alpha (Ly) from bright
() galaxies during the early stages of reionization
despite the significantly neutral intergalactic medium. To explain these
detections, it has been suggested that Ly emitters (LAEs) inhabit
physical Mpc (pMpc)-scale ionized regions powered by overdensities of faint
galaxies, but systematic searches for these overdensities near LAEs have been
challenging. Here, we use CEERS JWST/NIRCam imaging to search for large-scale
galaxy overdensities near two very UV-bright, LAEs in the EGS field. We
colour select 27 candidates, including the one LAE in the footprint
(EGSY8p7). From SED models, we infer moderately faint UV luminosities
() and stellar masses of
M. All are efficient ionizing agents
( Hz erg) and are generally
morphologically simple with only one compact ( to pc)
star-forming component. 13 candidates lie within 5 arcmin of EGSY8p7, leading
to a factor-of-four galaxy overdensity at arcmin (
projected pMpc at ) separations from EGSY8p7. Separations of
arcmin ( projected pMpc) are consistent with an average field. The
spatial distribution of our sample may qualitatively suggest an pMpc
ionized bubble encompassing both LAEs in EGS, which is theoretically unexpected
but may be possible for a galaxy population more numerous than the
average to create with moderate escape fractions ()
over long times ( Myr). Upcoming spectroscopic follow-up will
characterize the size of any ionized bubble that may exist and the properties
of the galaxies powering such a bubble.Comment: 20 pages, 7 main figures, 3 appendices, accepted to MNRA
Searching for Extremely Blue UV Continuum Slopes at in JWST/NIRCam Imaging: Implications for Stellar Metallicity and Ionizing Photon Escape in Early Galaxies
The ultraviolet (UV) continuum slope ( where f) of galaxies is sensitive to a variety of properties, from the
metallicity and age of the stellar population to the attenuation from dust
through the galaxy. Considerable attention has focused on identifying
reionization-era galaxies with very blue UV slopes (). Not only do
such systems provide a signpost of low metallicity stars, but they also
identify galaxies that likely have ionizing photons leaking from their HII
regions as such blue UV slopes can only be seen if the reddening effect of
nebular continuum has been diminished. In this paper we present a search for
reionization-era galaxies with very blue UV colors in recent JWST/NIRCam
imaging of the EGS field. We characterize UV slopes for a large sample of
galaxies, finding a median value of . Three of the
lower luminosity (M) and lower stellar mass
(5-6M) systems exhibit both extremely blue UV slopes
( to ) and rest-optical photometry indicating weak nebular
line emission. Each system is very compact (r260 pc) with very high star
formation rate surface densities. We model the SEDs with a suite of BEAGLE
models with varying levels of ionizing photon escape. The SEDs cannot be
reproduced with our fiducial (f=0) or alpha enhanced
(Z) models. The combined blue UV slopes and weak nebular
emission are best-fit by models with significant ionizing photon escape from
HII regions (f=0.6-0.8) and extremely low metallicity massive
stars (Z=0.01-0.06 Z). The discovery of these galaxies highlights
the potential for JWST to identify large numbers of candidate Lyman Continuum
leaking galaxies in the reionization era and suggests low metallicity stellar
populations may be veryComment: 11 pages, 8 figures, 2 tables; Submitted to Ap
JWST spectroscopy of UV-selected galaxies: New constraints on the evolution of the Ly escape fraction in the reionization era
We describe {\it JWST}/NIRSpec prism measurements of Ly emission in
galaxies. We identify Ly detections in 10 out of 69
galaxies with robust rest-optical emission line redshift measurements at in the CEERS and DDT-2750 observations of the EGS field. Galaxies at
with faint continuum (F150W 27--29 mag) are found with
extremely large rest-frame Ly equivalent widths (ranging up to 286 A).
Likely Ly detections are also seen in two new galaxies ( 7.49
and 7.17) from the second epoch of CEERS observations, both showing large
Ly equivalent widths that likely indicate significant transmission
through the IGM. We measure high Ly escape fractions in the 12
Ly emitters in our sample (median 0.28), two of which show near unity (). We find that % of
galaxies with [OIII]+H EW 1000 A have , consistent with the fractions found in lower-redshift
samples with matched [OIII]+H EWs. While uncertainties are still
significant, we find that only % of galaxies with similarly
strong rest optical emission lines show such large , as may be expected if IGM attenuation of Ly increases
towards higher redshifts. We identify photometric galaxy overdensities near the
Ly emitters, potentially providing the ionizing flux
necessary to create large ionized sightlines that facilitate Ly
transmission. Finally, we investigate the absence of Ly emission in a
comparable (and spectroscopically confirmed) galaxy overdensity at in
the Abell 2744 field, discussing new prism spectra of the field obtained with
the UNCOVER program.Comment: main text 20 pages, 13 figures; accepted for publication by MNRA
A JWST/NIRCam Study of Key Contributors to Reionization: The Star-forming and Ionizing Properties of UV-faint Galaxies
Spitzer/IRAC imaging has revealed that the brightest galaxies
often exhibit young ages and strong nebular line emission, hinting at high
ionizing efficiency among early galaxies. However, IRAC's limited sensitivity
has long hindered efforts to study the fainter, more numerous population often
thought largely responsible for reionization. Here we use CEERS JWST/NIRCam
data to characterize 116 UV-faint (median M)
galaxies. The SEDs are typically dominated by young (10-50 Myr), low-mass
() stellar populations, and we find no need for
extremely high stellar masses (). Considering previous
studies of UV-bright (M) galaxies, we find evidence
for a strong (5-10) increase in specific star formation rate toward
lower luminosities (median sSFR=103 Gyr in CEERS). The larger sSFRs
imply a more dominant contribution from OB stars in the relatively numerous
UV-faint population, perhaps suggesting that these galaxies are very efficient
ionizing agents (median erg Hz). In spite of their
much larger sSFRs, we find no significant increase in [OIII]H EWs
towards fainter M (median 780 ). If confirmed,
this may indicate that a substantial fraction of our CEERS galaxies possess
extremely low metallicities (3% ) where [OIII] emission is
suppressed. Alternatively, high ionizing photon escape fractions or bursty star
formation histories can also weaken the nebular lines in a subset of our CEERS
galaxies. While the majority of our objects are very blue (median
), we identify a significant tail of very dusty galaxies
() at 0.5 which may contribute significantly
to the star formation rate density.Comment: Accepted in MNRAS. Updated to use the most recent NIRCam zeropoints.
There are no significant changes to the conclusions relative to v
JADES: Using NIRCam Photometry to Investigate the Dependence of Stellar Mass Inferences on the IMF in the Early Universe
The detection of numerous and relatively bright galaxies at redshifts z > 9
has prompted new investigations into the star-forming properties of
high-redshift galaxies. Using local forms of the initial mass function (IMF) to
estimate stellar masses of these galaxies from their light output leads to
galaxy masses that are at the limit allowed for the state of the LambdaCDM
Universe at their redshift. We explore how varying the IMF assumed in studies
of galaxies in the early universe changes the inferred values for the stellar
masses of these galaxies. We infer galaxy properties with the SED fitting code
Prospector using varying IMF parameterizations for a sample of 102 galaxies
from the JWST Advanced Deep Extragalactic Survey (JADES) spectroscopically
confirmed to be at z > 6.7, with additional photometry from the JWST
Extragalactic Medium Band Survey (JEMS) for twenty-one galaxies. We demonstrate
that models with stellar masses reduced by a factor of three or more do not
affect the modeled spectral energy distribution (SED).Comment: The Significance statement is required for PNAS submissio
The UV continuum slopes of early star-forming galaxies in JADES
© 2024 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 (CC BY), https://creativecommons.org/licenses/by/4.0/The power-law slope of the rest-ultraviolet (UV) continuum (fλ ∝ λβ) is a key metric of early star-forming galaxies, providing one of our only windows into the stellar populations and physical conditions of z ≳ 10 galaxies. Expanding upon previous studies with limited sample sizes, we leverage deep imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to investigate the UV slopes of 179 z ≳ 9 galaxies with apparent magnitudes of mF200W ≃ 26–31, which display a median UV slope of β = −2.4. We compare to a statistical sample of z ≃ 5–9 galaxies, finding a shift towards bluer rest-UV colours at all . The most UV-luminous z ≳ 9 galaxies are significantly bluer than their lower redshift counterparts, representing a dearth of moderately red galaxies within the first 500 Myr. At yet earlier times, the z ≳ 11 galaxy population exhibits very blue UV slopes, implying very low impact from dust attenuation. We identify a robust sample of 44 galaxies with β ≲ −2.8, which have spectral energy distributions requiring models of density-bounded H ii regions and median ionizing photon escape fractions of 0.51 to reproduce. Their rest-optical colours imply that this sample has weaker emission lines (median mF356W − mF444W = 0.19 mag) than typical galaxies (median mF356W − mF444W = 0.39 mag), consistent with the inferred escape fractions. This sample consists of relatively low stellar masses (median ), and specific star formation rates (sSFRs; median ) nearly twice that of our full galaxy sample (median sSFRs ), suggesting these objects are more common among systems experiencing a recent upturn in star formation. We demonstrate that the shutoff of star formation provides an alternative solution for modelling of extremely blue UV colours, making distinct predictions for the rest-optical emission of these galaxies. Future spectroscopy will be required to distinguish between these physical pictures.Peer reviewe
The UV Continuum Slopes of Early Star-Forming Galaxies in JADES
The power-law slope of the rest-UV continuum
() is a key metric of early star forming
galaxies, providing one of our only windows into the stellar populations and
physical conditions of galaxies. Expanding upon previous studies with
limited sample sizes, we leverage deep imaging from JADES to investigate the UV
slopes of 179 galaxies with apparent magnitudes of ,
which display a median UV slope of . We compare to a statistical
sample of galaxies, finding a shift toward bluer rest-UV colors at all
. The most UV-luminous galaxies are significantly bluer than
their lower-redshift counterparts, representing a dearth of moderately-red
galaxies in the first Myr. At yet earlier times, the galaxy
population exhibits very blue UV slopes, implying very low attenuation from
dust. We identify a robust sample of 44 galaxies with , which have
SEDs requiring models of density-bounded HII regions and median ionizing photon
escape fractions of to reproduce. Their rest-optical colors imply that
this sample has weaker emission lines (median mag) than typical galaxies (median mag), consistent with the inferred escape fractions. This sample
has relatively low stellar masses (median ), and
specific star-formation rates (median) nearly twice that of our
full sample (median), suggesting they are more common among systems
experiencing a recent upturn in star formation. We demonstrate that the shutoff
of star formation provides an alternative solution for modelling of extremely
blue UV colors, making distinct predictions for the rest-optical emission of
these galaxies. Future spectroscopy will be required to distinguish between
these physical pictures.Comment: 17 pages, 13 figures; submitted to MNRA
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic Star Formation Rate Density 300 Myr after the Big Bang
© 2024 The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We characterize the earliest galaxy population in the JADES Origins Field, the deepest imaging field observed with JWST. We make use of ancillary Hubble Space Telescope optical images (five filters spanning 0.4–0.9 μm) and novel JWST images with 14 filters spanning 0.8−5 μm, including seven medium-band filters, and reaching total exposure times of up to 46 hr per filter. We combine all our data at >2.3 μm to construct an ultradeep image, reaching as deep as ≈31.4 AB mag in the stack and 30.3–31.0 AB mag (5σ, r = 0.″1 circular aperture) in individual filters. We measure photometric redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts z = 11.5−15. These objects show compact half-light radii of R 1/2 ∼ 50−200 pc, stellar masses of M ⋆ ∼ 107−108 M ☉, and star formation rates ∼ 0.1−1 M ☉ yr−1. Our search finds no candidates at 15 < z < 20, placing upper limits at these redshifts. We develop a forward-modeling approach to infer the properties of the evolving luminosity function without binning in redshift or luminosity that marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the impact of nondetections. We find a z = 12 luminosity function in good agreement with prior results, and that the luminosity function normalization and UV luminosity density decline by a factor of ∼2.5 from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical models for evolution of the dark matter halo mass function.Peer reviewe