Abstract
We use the Illustris-1 simulation to explore the capabilities of the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) data to analyze the stellar populations in ...high-redshift galaxies, taking advantage of the combined depth, spatial resolution, and wavelength coverage. For that purpose, we use simulated broadband ACS, WFC3, and NIRCam data and two-dimensional stellar population synthesis (2D-SPS) to derive the integrated star formation history (SFH) of massive (
M
*
> 10
10
M
⊙
) simulated galaxies at 1 <
z
< 4 that evolve into a local
M
*
> 10
11
M
⊙
galaxy. In particular, we explore the potential of HST and JWST data sets reaching a depth similar to those of the CANDELS and ongoing CEERS observations, respectively, and concentrate on determining the capabilities of this data set for characterizing the first episodes in the SFH of local
M
*
> 10
11
M
⊙
galaxies by studying their progenitors at
z
> 1. The 2D-SPS method presented in this paper has been calibrated to robustly recover the cosmic times when the first star formation episodes occurred in massive galaxies, i.e., the first stages in their integrated SFHs. In particular, we discuss the times when the first 1%–50% of their total stellar mass formed in the simulation. We demonstrate that we can recover these ages with typical median systematic offset of less than 5% and scatter around 20%–30%. According to our measurements on Illustris data, we are able to recover that local
M
*
> 10
11
M
⊙
galaxies would have started their formation by
z
= 16, forming the first 5% of their stellar mass present at
z
∼ 1 by
z
= 4.5, 10% by
z
= 3.7, and 25% by
z
= 2.7.
Abstract We study the H α equivalent width (EW(H α )) maps of 19 galaxies at 0.6 < z < 2.2 in the Hubble Ultra Deep Field using NIRISS slitless spectroscopy as part of the Next Generation Deep ...Extragalactic Exploratory Public Survey. Our galaxies mostly lie on the star formation main sequence with stellar masses between 10 9 and 10 11 M ⊙ , characterized as “typical” star-forming galaxies at these redshifts. Leveraging deep Hubble Space Telescope and JWST images, spanning 0.4–4.8 μ m, we perform spatially resolved fitting of the spectral energy distributions for these galaxies and construct specific star formation rate (sSFR) and stellar-mass-weighted age maps with a spatial resolution of ∼1 kpc. The pixel-to-pixel EW(H α ) increases with increasing sSFR and with decreasing age. The average trends are slightly different from the relations derived from integrated fluxes of galaxies from the literature, suggesting complex evolutionary trends within galaxies. We quantify the radial profiles of EW(H α ), sSFR, and age. The majority (84%) of galaxies show positive EW(H α ) gradients, in line with the inside-out quenching scenario. A few galaxies (16%) show inverse (and flat) EW(H α ) gradients, possibly due to merging or starbursts. We compare the distributions of EW(H α ) and sSFR to star formation history (SFH) models as a function of galactocentric radius. We argue that the central regions of galaxies have experienced at least one rapid star formation episode, which leads to the formation of the bulge, while their outer regions (e.g., disks) grow via more smoothly varying SFHs. These results demonstrate the ability to study resolved star formation in distant galaxies with JWST NIRISS.
Abstract
We present a robust sample of very high redshift galaxy candidates from the first epoch of JWST/NIRCam imaging from the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey. ...The NGDEEP NIRCam imaging, spanning 9.7 arcmin
2
in the Hubble Ultra Deep Field Parallel Field 2, reaches
m
= 30.4 (5
σ
, point-source, 2″ diameter apertures corrected to total) in F277W, making it the deepest public JWST GO imaging data set to date. We describe our detailed data reduction process of the six-filter broadband JWST/NIRCam imaging, incorporating custom corrections for systematic effects to produce high-quality calibrated images. Using robust photometric redshift selection criteria, we identify a sample of 38
z
≳ 9 galaxy candidates. These objects span a redshift range of
z
= 8.5–15.8 and apparent magnitudes of
m
F277W
= 27–30.5 AB mag, reaching ∼1.5 mag deeper than previous public JWST imaging surveys. We calculate the rest-frame ultraviolet luminosity function at
z
∼ 9 and 11 and present a new measurement of the luminosity function faint-end slope at
z
∼ 11. We find a faint-end slope of
α
= −2.5 ± 0.4 and −2.2 ± 0.2 at
z
∼ 9 and 11, respectively. This is consistent with no significant evolution in the faint-end slope and number density from
z
= 9 to 11. Comparing our results with theoretical predictions, we find that some models produce better agreement at the faint end than the bright end. These results will help to constrain how stellar feedback impacts star formation at these early epochs.
In recent years, observations have uncovered a population of massive galaxies that are invisible or very faint in deep optical/near-infrared (near-IR) surveys but brighter at longer wavelengths. ...However, the nature of these optically dark or faint galaxies (OFGs; one of several names given to these objects) is highly uncertain. In this work, we investigate the drivers of dust attenuation in the JWST era. In particular, we study the role of stellar mass, size, and orientation in obscuring star-forming galaxies (SFGs) at 3 <
z
< 7.5, focusing on the question of why OFGs and similar galaxies are so faint at optical/near-IR wavelengths. We find that stellar mass is the primary proxy for dust attenuation, among the properties studied. Effective radius and axis ratio do not show a clear link with dust attenuation, with the effect of orientation being close to random. However, there is a subset of highly dust attenuated (
A
V
> 1, typically) SFGs, of which OFGs are a specific case. For this subset, we find that the key distinctive feature is their compact size (for massive systems with log(
M
*
/
M
⊙
) > 10); OFGs exhibit a 30% smaller effective radius than the average SFG at the same stellar mass and redshift. On the contrary, OFGs do not exhibit a preference for low axis ratios (i.e., edge-on disks). The results in this work show that stellar mass is the primary proxy for dust attenuation and compact stellar light profiles behind the thick dust columns obscuring typical massive SFGs.
Aims.
We study the stellar (i.e., rest-optical) and dust-obscured star-forming (i.e., rest-mid-infrared) morphologies (i.e., sizes and Sérsic indices) of star-forming galaxies (SFGs) at 0.1 <
z
< ...2.5.
Methods.
We combined
Hubble
Space Telescope (HST) images from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) with JWST images from the Cosmic Evolution Early Release Science (CEERS) survey to measure the stellar and dust-obscured star formation distributions of 69 SFGs. Rest-mid-infrared (rest-MIR) morphologies were determined using a Markov chain Monte Carlo (MCMC) approach applied to the sharpest Mid-InfraRed Instrument (MIRI) images (i.e., shortest wavelength) dominated by dust emission (
S
ν
dust
/
S
ν
total
> 75%), as inferred for each galaxy from our optical-to-far-infrared spectral energy distribution fits with
CIGALE
. Rest-MIR Sérsic indices were only measured for the brightest MIRI sources, that is, with a signal-to-noise (S/N) greater than 75 (35 galaxies). At a lower S/N, simulations do indeed show that simultaneous measurements of both the size and Sérsic index become less reliable. We extended our study to fainter sources (i.e.,
S
/
N
> 10; 69 galaxies) by restricting our structural analysis to their rest-MIR sizes (
Re
MIR
) and by fixing their Sérsic index to a value of one.
Results.
Our MIRI-selected sample corresponds to a mass-complete sample (> 80%) of SFGs down to stellar masses 10
9.5
, 10
9.5
, and 10
10
M
⊙
at
z
∼ 0.3, 1, and 2, respectively. The rest-MIR Sérsic index of bright galaxies (
S
/
N
> 75) has a median value of 0.7
−0.3
+0.8
(the range corresponds to the 16th and 84th percentiles), which is in good agreement with their median rest-optical Sérsic indices. The Sérsic indices as well as the distribution of the axis ratio of these galaxies suggest that they have a disk-like morphology in the rest-MIR. Galaxies above the main sequence (MS) of star formation (i.e., starbursts) have rest-MIR sizes that are, on average, a factor ∼2 smaller than their rest-optical sizes (
Re
Opt.
). The median rest-optical to rest-MIR size ratio of MS galaxies increases with their stellar mass, from 1.1
−0.2
+0.4
at ∼10
9.8
M
⊙
to 1.6
−0.3
+1.0
at ∼10
11
M
⊙
. This mass-dependent trend resembles the one found in the literature between the rest-optical and rest-near-infrared sizes of SFGs, suggesting that it is primarily due to radial color gradients affecting rest-optical sizes and that the sizes of the stellar and star-forming components of SFGs are, on average, consistent at all masses. There is, however, a small population of SFGs (∼15%) with a compact star-forming component embedded in a larger stellar structure, with Re
Opt.
c
> 1.8 × Re
MIR
. This population could be the missing link between galaxies with an extended stellar component and those with a compact stellar component, the so-called blue nuggets.
Abstract
We present the mid-infrared (MIR) morphologies for 64 star-forming galaxies (SFGs) at 0.2 <
z
< 2.5 with stellar mass
M
*
> 10
9
M
⊙
using James Webb Space Telescope (JWST) Mid-Infrared ...Instrument (MIRI) observations from the Cosmic Evolution Early Release Science survey. The MIRI bands span the MIR (7.7–21
μ
m), enabling us to measure the effective radii (
R
eff
) and Sérsic indexes of these SFGs at rest-frame 6.2 and 7.7
μ
m, which contains strong emission from Polycyclic aromatic hydrocarbon (PAH) features, a well-established tracer of star formation in galaxies. We define a “PAH band” as the MIRI bandpass that contains these features at the redshift of the galaxy. We then compare the galaxy morphologies in the PAH bands to those in the rest-frame near-ultraviolet (NUV) using Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/F435W or ACS/F606W and optical/near-IR using HST WFC3/F160W imaging from UVCANDELS and CANDELS. The
R
eff
of galaxies in the PAH band are slightly smaller (∼10%) than those in F160W for galaxies with
M
*
≳ 10
9.5
M
⊙
at
z
≤ 1.2, but the PAH band and F160W have similar fractions of light within 1 kpc. In contrast, the
R
eff
of galaxies in the NUV band are larger, with lower fractions of light within 1 kpc compared to F160W for galaxies at
z
≤ 1.2. Using the MIRI data to estimate the SFR
IR
surface density, we find that the correlation between the SFR
IR
surface density and stellar mass has a steeper slope than that of the SFR
UV
surface density and stellar mass, suggesting more massive galaxies having increasing amounts of obscured fraction of star formation in their inner regions. This paper demonstrates how the high-angular resolution data from JWST/MIRI can reveal new information about the morphology of obscured star formation.
Abstract
Visual inspections of the first optical rest-frame images from JWST have indicated a surprisingly high fraction of disk galaxies at high redshifts. Here, we alternatively apply ...self-supervised machine learning to explore the morphological diversity at
z
≥ 3. Our proposed data-driven representation scheme of galaxy morphologies, calibrated on mock images from the TNG50 simulation, is shown to be robust to noise and to correlate well with the physical properties of the simulated galaxies, including their 3D structure. We apply the method simultaneously to F200W and F356W galaxy images of a mass-complete sample (
M
*
/
M
⊙
> 10
9
) at 3 ≤
z
≤ 6 from the first JWST/NIRCam CEERS data release. We find that the simulated and observed galaxies do not exactly populate the same manifold in the representation space from contrastive learning. We also find that half the galaxies classified as disks—either convolutional neural network-based or visually—populate a similar region of the representation space as TNG50 galaxies with low stellar specific angular momentum and nonoblate structure. Although our data-driven study does not allow us to firmly conclude on the true nature of these galaxies, it suggests that the disk fraction at
z
≥ 3 remains uncertain and possibly overestimated by traditional supervised classifications. Deeper imaging and spectroscopic follow-ups as well as comparisons with other simulations will help to unambiguously determine the true nature of these galaxies, and establish more robust constraints on the emergence of disks at very high redshift.
Abstract
We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations of a remarkably bright galaxy candidate at
z
phot
=
16.7
−
0.3
+
1.9
(
M
UV
= −21.6), S5-z17-1, identified ...in James Webb Space Telescope (JWST) Early Release Observation data of Stephen’s Quintet. We do not detect the dust continuum at 866
μ
m, ruling out the possibility that S5-z17-1 is a low-
z
dusty starburst with a star formation rate of ≳30
M
⊙
yr
−1
. We detect a 5.1
σ
line feature at 338.726 ± 0.007 GHz exactly coinciding with the JWST source position, with a 2% likelihood of the signal being spurious. The most likely line identification would be O
iii
52
μ
m at
z
= 16.01 or C
ii
158
μ
m at
z
= 4.61, whose line luminosities do not violate the nondetection of the dust continuum in both cases. Together with three other
z
≳ 11–13 candidate galaxies recently observed with ALMA, we conduct a joint ALMA and JWST spectral energy distribution (SED) analysis and find that the high-
z
solution at
z
∼ 11–17 is favored in every candidate as a very blue (UV continuum slope of ≃−2.3) and luminous (
M
UV
≃ − 24:−21) system. Still, we find in several candidates that reasonable SED fits (Δ
χ
2
≲ 4) are reproduced by type II quasar and/or quiescent galaxy templates with strong emission lines at
z
∼ 3–5, where such populations predicted from their luminosity functions and EW(O
iii
+H
β
) distributions are abundant in survey volumes used for the identification of the
z
∼ 11–17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high-
z
solutions, lower-
z
possibilities are not completely ruled out in several of the
z
∼ 11–17 candidates, indicating the need to consider the relative surface densities of the lower-
z
contaminants in the ultra-high-
z
galaxy search.
Abstract Ultraviolet (UV; rest-frame ∼1200–2000 Å) spectra provide a wealth of diagnostics to characterize fundamental galaxy properties, such as their chemical enrichment, the nature of their ...stellar populations, and their amount of Lyman-continuum (LyC) radiation. In this work, we leverage publicly released JWST data to construct the rest-frame UV-to-optical composite spectrum of a sample of 63 galaxies at 5.6 < z < 9, spanning a wavelength range from 1500 to 5200 Å. Based on the composite spectrum, we derive an average dust attenuation E ( B − V ) gas = 0.10 − 0.11 + 0.10 from H β /H γ , an electron density n e = 570 − 290 + 510 cm −3 from the O ii doublet ratio, an electron temperature T e = 16700 − 1500 + 1500 K from the O iii λ 4363/O iii λ 5007 ratio, and an ionization parameter log ( U ) = − 2.15 − 0.03 + 0.03 from the O iii /O ii ratio. Using a direct T e method, we calculate an oxygen abundance 12 + log ( O / H ) = 7.67 ± 0.08 and a carbon-to-oxygen (C/O) abundance ratio log ( C / O ) = − 0.86 − 0.10 + 0.13 . This C/O ratio is smaller than compared to z = 0 and z = 2–4 star-forming galaxies, albeit with moderate significance. This indicates the reionization-era galaxies might be undergoing a rapid buildup of stellar mass with high specific star formation rates. A UV diagnostic based on the ratios of C iii λ λ 1907, 1909/He ii λ 1640 versus O iii λ 1666/He ii λ 1640 suggests that the star formation is the dominant source of ionization, similar to the local extreme dwarf galaxies and z ∼ 2–4 He ii –detected galaxies. The O iii /O ii and C iv /C iii ratios of the composite spectrum are marginally larger than the criteria used to select galaxies as LyC leakers, suggesting that some of the galaxies in our sample are strong contributors to the reionizing radiation.
