Abstract
We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy ...formation from
z
∼ 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin
2
, to search for candidate galaxies at
z
> 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at
z
∼ 9–16. These objects are compact with a median half-light radius of ∼0.5 kpc. We present an early estimate of the
z
∼ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at
M
UV
∼ −20 appears to evolve very little from
z
∼ 9 to 11. We also find that the abundance (surface density arcmin
−2
) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at
z
> 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultrahigh-redshift galaxies with which to further explore these conclusions.
We used the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST) to observe the semiforbidden C iii λλ1907, 1909 doublet emission in green pea galaxies at 0.13 ≤ z ≤ 0.3. We ...detect C iii emission in 7/10 galaxies with C iii equivalent widths (EWs) that range from 2 to 10 , confirming that C iii emission is almost ubiquitous in low-mass, low-metallicity (12+log(O/H) < 8.4) galaxies that are characterized by strong optical O iii λ5007 emission. The composite UV spectrum shows evidence for the He ii λ1640 emission line and interstellar absorption features (e.g., C iv λλ1548, 1550, Al iii λλ1854, 1862). We do not detect the O iii λλ1661, 1666 emission with >3 significance. The observed C iii emission line strengths are consistent with the predictions from photoionization models that incorporate the effects of binary stellar evolution with young stellar ages ≤3-5 Myr and high ionization parameters (log U > −2). The hard ionizing radiation from young massive stars and high nebular temperatures at low metallicities can account for the observed high EWs of C iii λ1909 and O iii λ5007 emission lines. Some of the star-forming galaxies at high redshift and local blue compact dwarf galaxies show offsets from the EW(C iii) versus EW(O iii) model grids, indicating an additional contribution to the continuum emission from composite stellar populations or different C/O abundances, nebular temperatures, and electron densities than assumed in the photoionization models. The green pea galaxies do not show a significant correlation between the Ly and C iii EWs, and the observed scatter is likely due to the variations in the optical depth of Ly to the neutral gas. Green pea galaxies are likely to be density-bounded, and we examined the dependence of C iii emission on the Lyman continuum optical depth. The potential LyC leaker galaxies in our sample have high C iii EWs that can only be reproduced by starburst ages as young as <3 Myr and harder ionizing spectra than the nonleakers. Among the galaxies with similar metallicities and ionization parameters, the C iii EW appears to be stronger for those with higher optical depth to LyC, as expected from the photoionization models. There are various factors that affect the C iii emission line strengths, and further investigation of a larger sample of C iii emitters is necessary to calibrate the dependence of C iii emission on the escape of LyC radiation and enable application of the C iii diagnostics to galaxies in the reionization epoch.
Abstract
We present the data release and data reduction process for the Epoch 1 NIRCam observations for the Cosmic Evolution Early Release Science Survey (CEERS). These data consist of NIRCam imaging ...in six broadband filters (F115W, F150W, F200W, F277W, F356W and F444W) and one medium-band filter (F410M) over four pointings, obtained in parallel with primary CEERS MIRI observations. We reduced the NIRCam imaging with the JWST Calibration Pipeline, with custom modifications and reduction steps designed to address additional features and challenges with the data. Here we provide a detailed description of each step in our reduction and a discussion of future expected improvements. Our reduction process includes corrections for known prelaunch issues such as 1/
f
noise, as well as in-flight issues including snowballs, wisps, and astrometric alignment. Many of our custom reduction processes were first developed with prelaunch simulated NIRCam imaging over the full 10 CEERS NIRCam pointings. We present a description of the creation and reduction of this simulated data set in the Appendix. We provide mosaics of the real images in a public release, as well as our reduction scripts with detailed explanations to allow users to reproduce our final data products. These represent one of the first official public data sets released from the Directors Discretionary Early Release Science (DD-ERS) program.
Abstract
The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the Epoch of Reionization ...is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with the Hubble Space Telescope Cosmic Origins Spectrograph for a
z
= 0.2–0.4 sample of 66 galaxies. After careful processing of the far-UV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.
Studying giant star-forming clumps in distant galaxies is important to understand galaxy formation and evolution. At present, however, observers and theorists have not reached a consensus on whether ...the observed "clumps" in distant galaxies are the same phenomenon that is seen in simulations. In this paper, as a step to establish a benchmark of direct comparisons between observations and theories, we publish a sample of clumps constructed to represent the commonly observed "clumps" in the literature. This sample contains 3193 clumps detected from 1270 galaxies at 0.5 ≤ z < 3.0 . The clumps are detected from rest-frame UV images, as described in our previous paper. Their physical properties (e.g., rest-frame color, stellar mass ( M * ), star formation rate (SFR), age, and dust extinction) are measured by fitting the spectral energy distribution (SED) to synthetic stellar population models. We carefully test the procedures of measuring clump properties, especially the method of subtracting background fluxes from the diffuse component of galaxies. With our fiducial background subtraction, we find a radial clump U − V color variation, where clumps close to galactic centers are redder than those in outskirts. The slope of the color gradient (clump color as a function of their galactocentric distance scaled by the semimajor axis of galaxies) changes with redshift and M * of the host galaxies: at a fixed M * , the slope becomes steeper toward low redshift, and at a fixed redshift, it becomes slightly steeper with M * . Based on our SED fitting, this observed color gradient can be explained by a combination of a negative age gradient, a negative E(B − V) gradient, and a positive specific SFR gradient of the clumps. We also find that the color gradients of clumps are steeper than those of intra-clump regions. Correspondingly, the radial gradients of the derived physical properties of clumps are different from those of the diffuse component or intra-clump regions.
The JWST Early Release Observations Pontoppidan, Klaus M.; Barrientes, Jaclyn; Blome, Claire ...
Astrophysical journal. Letters,
09/2022, Volume:
936, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
The James Webb Space Telescope (JWST) Early Release Observations (EROs) is a set of public outreach products created to mark the end of commissioning and the beginning of science operations ...for JWST. Colloquially known as the “Webb First Images and Spectra,” these products were intended to demonstrate to the worldwide public that JWST is ready for science, and is capable of producing spectacular results. The package was released on 2022 July 12 and included images and spectra of the galaxy cluster SMACS J0723.3-7327 and distant lensed galaxies, the interacting galaxy group Stephan’s Quintet, NGC 3324 in the Carina star-forming complex, the Southern Ring planetary nebula NGC 3132, and the transiting hot Jupiter WASP-96b. This paper describes the ERO technical design, observations, and scientific processing of data underlying the colorful outreach products.
Abstract
We present JWST NIRSpec spectroscopy for 11 galaxy candidates with photometric redshifts of
z
≃ 9 − 13 and
M
UV
∈ −21, −18 newly identified in NIRCam images in the Cosmic Evolution Early ...Release Science Survey. We confirm emission line redshifts for 7 galaxies at
z
= 7.762–8.998 using spectra at ∼1–5
μ
m either with the NIRSpec prism or its three medium-resolution (
R
∼ 1000) gratings. For
z
≃ 9 photometric candidates, we achieve a high confirmation rate of ≃90%, which validates the classical dropout selection from NIRCam photometry. No robust emission lines are identified in three galaxy candidates at
z
> 10, where the strong O
iii
and H
β
lines would be redshifted beyond the wavelength range observed by NIRSpec, and the Ly
α
continuum break is not detected with the sensitivity of the current data. Compared with Hubble Space Telescope-selected bright galaxies (
M
UV
≃ −22) that are similarly spectroscopically confirmed at
z
≃ 8 − 9, these NIRCam-selected galaxies are characterized by lower star formation rates (SFRs; SFR ≃ 4
M
⊙
yr
−1
) and lower stellar masses (≃10
8
M
⊙
), but with higher specific SFR (≃40 Gyr
−1
), higher O
iii
+H
β
equivalent widths (≃1100 Å), and elevated production efficiency of ionizing photons (
log
(
ξ
ion
/
Hz
erg
−
1
)
≃
25.8
) induced by young stellar populations (<10 Myr) accounting for ≃20% of the galaxy mass, highlighting the key contribution of faint galaxies to cosmic reionization. Taking advantage of the homogeneous selection and sensitivity, we also investigate metallicity and ISM conditions with empirical calibrations using the O
iii
5008
/H
β
ratio. We find that galaxies at
z
≃ 8 − 9 have higher SFRs and lower metallicities than galaxies at similar stellar masses at
z
≃ 2 − 6, which is generally consistent with the current galaxy formation and evolution models.
Abstract The new capabilities that JWST offers in the near- and mid-infrared (IR) are used to investigate in unprecedented detail the nature of optical/near-IR-faint, mid-IR-bright sources, with ...HST-dark galaxies among them. We gather JWST data from the CEERS survey in the Extended Groth Strip, jointly with HST data, and analyze spatially resolved optical-to-mid-IR spectral energy distributions to estimate photometric redshifts in two dimensions and stellar population properties on a pixel-by-pixel basis for red galaxies detected by NIRCam. We select 138 galaxies with F150W − F356W > 1.5 mag and F356W < 27.5 mag. The nature of these sources is threefold: (1) 71% are dusty star-forming galaxies (SFGs) at 2 < z < 6 with 9 < log M ⋆ / M ⊙ < 11 and a variety of specific SFRs (<1 to >100 Gyr −1 ); (2) 18% are quiescent/dormant (i.e., subject to reignition/rejuvenation) galaxies (QGs) at 3 < z < 5, with log M ⋆ / M ⊙ ∼ 10 and poststarburst mass-weighted ages (0.5–1.0 Gyr); and (3) 11% are strong young starbursts with indications of high equivalent width emission lines (typically, O iii +H β ) at 6 < z < 7 (XELG- z 6) and log M ⋆ / M ⊙ ∼ 9.5 . The sample is dominated by disk-like galaxies with remarkable compactness for XELG- z 6 (effective radii smaller than 0.4 kpc). Large attenuations in SFGs, 2 < A ( V ) < 5 mag, are found within 1.5 times the effective radius, approximately 2 kpc, while QGs present A ( V ) ∼ 0.2 mag. Our SED-fitting technique reproduces the expected dust emission luminosities of IR-bright and submillimeter galaxies. This study implies high levels of star formation activity between z ∼ 20 and z ∼ 10, where virtually 100% of our galaxies had already formed 10 8 M ⊙ , 60% had assembled 10 9 M ⊙ , and 10% up to 10 10 M ⊙ (in situ or ex situ).
Abstract
We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at
z
= 3–9 using early James Webb Space Telescope (JWST) ...CEERS NIRCam observations. Our sample consists of 850 galaxies at
z
> 3 detected in both Hubble Space Telescope (HST)/WFC3 and CEERS JWST/NIRCam images, enabling a comparison of HST and JWST morphologies. We conduct a set of visual classifications, with each galaxy in the sample classified three times. We also measure quantitative morphologies across all NIRCam filters. We find that galaxies at
z
> 3 have a wide diversity of morphologies. Galaxies with disks make up 60% of galaxies at
z
= 3, and this fraction drops to ∼30% at
z
= 6–9, while galaxies with spheroids make up ∼30%–40% across the redshift range, and pure spheroids with no evidence for disks or irregular features make up ∼20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (∼40%–50%), while those that are purely irregular increases from ∼12% to ∼20% at
z
> 4.5. We note that these are apparent fractions, as many observational effects impact the visibility of morphological features at high redshift. On average, Spheroid-only galaxies have a higher Sérsic index, smaller size, and higher axis ratio than disk or irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study, and further work with large samples at higher redshift is needed to quantify when these features first formed.
Although giant clumps of stars are thought to be crucial to galaxy formation and evolution, the most basic demographics of clumps are still uncertain, mainly because the definition of clumps has not ...been thoroughly discussed. In this paper, we carry out a study of the basic demographics of clumps in star-forming galaxies at 0.5 < z < 3, using our proposed physical definition that UV-bright clumps are discrete star-forming regions that individually contribute more than 8% of the rest-frame UV light of their galaxies. Clumps defined this way are significantly brighter than the H II regions of nearby large spiral galaxies, either individually or blended, when physical spatial resolution and cosmological dimming are considered. The clump contribution in the intermediate-mass and massive galaxies is possibly linked to the molecular gas fraction of the galaxies. The clump contribution to the SFR of star-forming galaxies, generally around 4%-10%, also shows dependence on the galaxy M, but for a given galaxy M, its dependence on the redshift is mild.
![The Semiforbidden C iii] λ1...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X_1538-4357/small "The Semiforbidden C iii] λ1909 Emission in the Rest-ultraviolet Spectra of Green Pea Galaxies")
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