ABSTRACT
One of the main goals of the JWST is to study the first galaxies in the Universe. We present a systematic photometric analysis of very distant galaxies in the first JWST deep field towards ...the massive lensing cluster SMACS0723. As a result, we report the discovery of two galaxy candidates at z ∼ 16, only 250 million years after the big bang. We also identify two candidates at z ∼ 12 and six candidates at z ∼ 9−11. Our search extended out to z ≲ 21 by combining colour information across seven near-infrared camera and near-infrared imager and slitless spectrograph filters. By modelling the Spectral Energy Distributions (SEDs) with EAZY and BEAGLE, we test the robustness of the photometric redshift estimates. While their intrinsic (unlensed) luminosity is typical of the characteristic luminosity L* at z > 10, our high-redshift galaxies typically show small sizes and their morphologies are consistent with disks in some cases. The highest-redshift candidates have extremely blue ultraviolet-continuum slopes −3 < β < −2.4, young ages ∼10−100 Myr, and stellar masses around log (M⋆/M⊙) = 8.8 inferred from their spectral energy distribution modelling, which indicate a rapid build-up of their stellar mass. Our search clearly demonstrates the capabilities of JWST to uncover robust photometric candidates up to very high redshifts and peer into the formation epoch of the first galaxies.
Abstract
On 2022 July 8, NASA shared (
https://www.nasa.gov/feature/goddard/2022/nasa-shares-list-of-cosmic-targets-for-webb-telescope-s-first-images
) the list of five public showcase targets that ...have been observed with the new James Webb Space Telescope (JWST) and whose data—at the time of writing—are expected to be released to the public around Tuesday, July 12. One of these targets is the galaxy cluster SMACS J0723.3−7327 (
z
= 0.39), which acts as a gravitational lens and was recently imaged with the Hubble Space Telescope (HST) in the framework of the Reionization Lensing Cluster Survey (RELICS). To facilitate studies by the community with the upcoming JWST data, we publish here a strong-lensing model for SMACS J0723.3−7327—including mass density and magnification maps. We identify five multiple-image families in the HST imaging. For three of them, system membership and redshift are secured by public spectroscopic data. For the remaining two systems, we rely on robust photometric redshift estimates. We use the
Light-Traces-Mass
lens modeling method, which complements the parametric models already available in the RELICS repository and elsewhere and thus helps span a representative range of solutions. The new model published here can be accessed on the RELICS website at MAST. It will be interesting to examine which properties of the mass models change and improve, and by how much, when the JWST data are incorporated.
ABSTRACT
We present new measurements of the very low mass end of the galaxy stellar mass function (GSMF) at z ∼ 6−7 computed from a rest-frame ultraviolet selected sample of dropout galaxies. These ...galaxies lie behind the six Hubble Frontier Field clusters and are all gravitationally magnified. Using deep Spitzer/IRAC and Hubble Space Telescope imaging, we derive stellar masses by fitting galaxy spectral energy distributions and explore the impact of different model assumptions and parameter degeneracies on the resulting GSMF. Our sample probes stellar masses down to $M_{\star }\gt 10^{6}\, \text{M}_{\odot}$ and we find the z ∼ 6−7 GSMF to be best parametrized by a modified Schechter function that allows for a turnover at very low masses. Using a Monte Carlo Markov chain analysis of the GSMF, including accurate treatment of lensing uncertainties, we obtain a relatively steep low-mass end slope $\alpha \simeq -1.96_{-0.08}^{+0.09}$ and a turnover at $\log (M_T/\text{M}_{\odot})\simeq 7.10_{-0.56}^{+0.17}$ with a curvature of $\beta \simeq 1.00_{-0.73}^{+0.87}$ for our minimum assumption model with constant star formation history (SFH) and low dust attenuation, AV ≤ 0.2. We find that the z ∼ 6−7 GSMF, in particular its very low mass end, is significantly affected by the assumed functional form of the star formation history and the degeneracy between stellar mass and dust attenuation. For example, the low-mass end slope ranges from $\alpha \simeq -1.82_{-0.07}^{+0.08}$ for an exponentially rising SFH to $\alpha \simeq -2.34_{-0.10}^{+0.11}$ when allowing AV of up to 3.25. Future observations at longer wavelengths and higher angular resolution with the James Webb Space Telescope are required to break these degeneracies and to robustly constrain the stellar mass of galaxies on the extreme low-mass end of the GSMF.
Abstract
Star cluster formation in the early universe and its contribution to reionization remains largely unconstrained to date. Here we present JWST/NIRCam imaging of the most highly magnified ...galaxy known at
z
∼ 6, the
Sunrise
arc. We identify six young massive star clusters (YMCs) with measured radii spanning from ∼20 down to ∼1 pc (corrected for lensing magnification), estimated stellar masses of ∼10
6–7
M
⊙
, and ages of 1–30 Myr based on SED fitting to photometry measured in eight filters extending to rest frame 7000 Å. The resulting stellar mass surface densities are higher than 1000
M
⊙
pc
−2
(up to a few 10
5
M
⊙
pc
−2
), and their inferred dynamical ages qualify the majority of these systems as gravitationally bound stellar clusters. The star cluster ages map the progression of star formation along the arc, with two evolved systems (≳10 Myr old) followed by very young clusters. The youngest stellar clusters (<5 Myr) show evidence of prominent H
β
+O
iii
emission based on photometry with equivalent widths larger than >1000 Å rest frame and are hosted in a 200 pc sized star-forming complex. Such a region dominates the ionizing photon production with a high efficiency
log
(
ξ
ion
Hz
erg
−
1
)
∼
25.7
. A significant fraction of the recently formed stellar mass of the galaxy (10%–30%) occurred in these YMCs. We speculate that such sources of ionizing radiation boost the ionizing photon production efficiency, which eventually carves ionized channels that might favor the escape of Lyman continuum radiation. The survival of some of the clusters would make them the progenitors of massive and relatively metal-poor globular clusters in the local universe.
Abstract
The James Webb Space Telescope is now detecting early black holes (BHs) as they transition from “seeds” to supermassive BHs. Recently, Bogdan et al. reported the detection of an X-ray ...luminous supermassive BH, UHZ-1, with a photometric redshift at
z
> 10. Such an extreme source at this very high redshift provides new insights on seeding and growth models for BHs given the short time available for formation and growth. Harnessing the exquisite sensitivity of JWST/NIRSpec, here we report the spectroscopic confirmation of UHZ-1 at
z
= 10.073 ± 0.002. We find that the NIRSpec/Prism spectrum is typical of recently discovered
z
≈ 10 galaxies, characterized primarily by star formation features. We see no clear evidence of the powerful X-ray source in the rest-frame UV/optical spectrum, which may suggest heavy obscuration of the central BH, in line with the Compton-thick column density measured in the X-rays. We perform a stellar population fit simultaneously to the new NIRSpec spectroscopy and previously available photometry. The fit yields a stellar-mass estimate for the host galaxy that is significantly better constrained than prior photometric estimates (
M
⋆
∼
1.4
−
0.4
+
0.3
×
10
8
M
⊙
). Given the predicted BH mass (
M
BH
∼ 10
7
–10
8
M
⊙
), the resulting ratio of
M
BH
/
M
⋆
remains 2 to 3 orders of magnitude higher than local values, thus lending support to the heavy seeding channel for the formation of supermassive BHs within the first billion years of cosmic evolution.
ABSTRACT
We investigate the burstiness of star formation and the ionizing efficiency of a large sample of galaxies at 0.7 < z < 1.5 using HST grism spectroscopy and deep ultraviolet (UV) imaging in ...the GOODS-N and GOODS-S fields. The star formation history (SFH) in these strong emission-line low-mass galaxies indicates an elevated star formation rate (SFR) based on the Hα emission line at a given stellar mass when compared to the standard main sequence. Moreover, when comparing the Hα and UV SFR indicators, we find that an excess in SFRHα compared to SFRUV is preferentially observed in lower mass galaxies below 109 M⊙, which are also the highest-EW galaxies. These findings suggest that the burstiness parameters of these strong emission-line galaxies may differ from those inferred from hydrodynamical simulations and previous observations. For instance, a larger burstiness duty cycle would explain the observed SFRHα excess. We also estimate the ionizing photon production efficiency ξion, finding a median value of log(ξion/erg−1 Hz) = 24.80 ± 0.26 when adopting a Galactic dust correction for Hα and an SMC one for the stellar component. We observe an increase of ξion with redshift, further confirming similar results at higher redshifts. We also find that ξion is strongly correlated with EWHα, which provides an approach for deriving ξion in early galaxies. We observe that lower mass, lower luminosity galaxies have a higher ξion. Overall, these results provide further support for faint galaxies playing a major role in the reionization of the Universe.
ABSTRACT
The first deep-field observations of the JWST have immediately yielded a surprisingly large number of very high redshift candidates, pushing the frontier of observability well beyond z ≳ 10. ...We here present a detailed SED-fitting analysis of the 10 gravitationally lensed z ∼ 9–16 galaxy candidates detected behind the galaxy cluster SMACS J0723.3−7327 in a previous paper using the BEAGLE tool. Our analysis makes use of dynamical considerations to place limits on the ages of these galaxies and of all three published SL models of the cluster to account for lensing systematics. We find the majority of these galaxies to have relatively low stellar masses $M_{\star }\sim 10^7-10^8\, \mathrm{M}_{\odot }$ and young ages tage ∼ 10–100 Myr but with a few higher mass exceptions ($M_{\star }\sim 10^9\rm{-}10^{10}\, \mathrm{M}_{\odot }$) due to Balmer-break detections at z ∼ 9–10. Because of their very blue UV-slopes, down to β ∼ −3, all of the galaxies in our sample have extremely low dust attenuations AV ≲ 0.02. Placing the measured parameters into relation, we find a very shallow M⋆ − MUV-slope and high sSFRs above the main sequence of star formation with no significant redshift-evolution in either relation. This is in agreement with the bright UV luminosities measured for these objects and indicates that we are naturally selecting UV-bright galaxies that are undergoing intense star formation at the time they are observed. Finally, we discuss the robustness of our high-redshift galaxy sample regarding low-redshift interlopers and conclude that low-redshift solutions can safely be ruled out for roughly half of the sample, including the highest redshift galaxies at z ∼ 12–16. These objects represent compelling targets for spectroscopic follow-up observations with JWST and ALMA.
Abstract
The first deep field images from the James Webb Space Telescope (JWST) of the galaxy cluster SMACS J0723.3-7327 reveal a wealth of new lensed images at uncharted infrared wavelengths, with ...unprecedented depth and resolution. Here we securely identify 14 new sets of multiply imaged galaxies totaling 42 images, adding to the five sets of bright and multiply imaged galaxies already known from Hubble Space Telescope data. We find examples of arcs crossing critical curves, allowing detailed community follow-up, such as JWST spectroscopy for precise redshift determinations, and measurements of the chemical abundances and of the detailed internal gas dynamics of very distant, young galaxies. One such arc contains a pair of compact knots that are magnified by a factor of hundreds, and features a microlensed transient. We also detect an Einstein cross candidate only visible thanks to JWST’s superb resolution. Our parametric lens model is available through the following link (
https://www.dropbox.com/sh/gwup2lvks0jsqe5/AAC2RRSKce0aX-lIFCc9vhBXa?dl=0
) and will be regularly updated using additional spectroscopic redshifts. The model is constrained by 16 of these sets of multiply imaged galaxies, three of which have spectroscopic redshifts, and reproduces the multiple images to better than an rms of 0.″5, allowing for accurate magnification estimates of high-redshift galaxies. The intracluster light extends beyond the cluster members, exhibiting large-scale features that suggest a significant past dynamical disturbance. This work represents a first taste of the enhanced power JWST will have for lensing-related science.
Abstract
We report the discovery of four galaxy candidates observed 450–600 Myr after the Big Bang with photometric redshifts between
z
∼ 8.3 and 10.2 measured using James Webb Space Telescope (JWST) ...NIRCam imaging of the galaxy cluster WHL0137−08 observed in eight filters spanning 0.8–5.0
μ
m, plus nine Hubble Space Telescope filters spanning 0.4–1.7
μ
m. One candidate is gravitationally lensed with a magnification of
μ
∼ 8, while the other three are located in a nearby NIRCam module with expected magnifications of
μ
≲ 1.1. Using SED fitting, we estimate the stellar masses of these galaxies are typically in the range
log
M
⋆
/
M
⊙
= 8.3–8.7. All appear young, with mass-weighted ages <240 Myr, low dust content
A
V
< 0.15 mag, and specific star formation rates sSFR ∼0.25–10 Gyr
−1
for most. One
z
∼ 9 candidate is consistent with an age <5 Myr and an sSFR ∼10 Gyr
−1
, as inferred from a strong F444W excess, implying O
iii
+H
β
rest-frame equivalent width ∼2000 Å, although an older
z
∼ 10 object is also allowed. Another
z
∼ 9 candidate is lensed into an arc 2.″4 long with a magnification of
μ
∼ 8. This arc is the most spatially resolved galaxy at
z
∼ 9 known to date, revealing structures ∼30 pc across. Follow-up spectroscopy of WHL0137−08 with JWST/NIRSpec will be useful to spectroscopically confirm these high-redshift galaxy candidates and to study their physical properties in more detail.
Abstract
Deep observations with the James Webb Space Telescope (JWST) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black ...hole seeds and observed quasars. In this work, we present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey of a massive accreting black hole at
z
= 8.50 displaying a clear broad-line component as inferred from the H
β
line with FWHM = 3439 ± 413 km s
−1
, typical of the broad-line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. We compute a black hole mass of
log
10
(
M
BH
/
M
⊙
)
=
8.17
±
0.42
and a bolometric luminosity of
L
bol
∼ 6.6 × 10
45
erg s
−1
. These values imply that our object is accreting at ∼40% of the Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from ALMA, indicate an upper limit on the stellar mass of
log
10
(
M
*
/
M
⊙
)
<
8.7
, which would lead to an unprecedented ratio of black hole to host mass of at least ∼30%. This is orders of magnitude higher compared to the local QSOs but consistent with recent AGN studies at high redshift with JWST. This finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-Eddington rate at high redshift. Given the predicted number densities of high-
z
faint AGN, future NIRSpec observations of larger samples will allow us to further investigate galaxy–black hole coevolution in the early Universe.
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