Radial mass-to-light ratio gradients cause the half-mass and half-light radii of galaxies to differ, potentially biasing studies that use half-light radii. Here we present the largest catalog to date ...of galaxy half-mass radii at z > 1: 7006 galaxies in the CANDELS fields at 1.0 ≤ z ≤ 2.5. The sample includes both star-forming and quiescent galaxies with stellar masses . We test three methods for calculating half-mass radii from multiband PSF-matched Hubble Space Telescope (HST) imaging: two based on spatially resolved spectral energy distribution modeling, and one that uses a rest-frame color profile. All three methods agree, with scatter 0.3 dex. In agreement with previous studies, most galaxies in our sample have negative color gradients (the centers are redder than the outskirts, and ). We find that color gradient strength has significant trends with increasing stellar mass, half-light radius, U − V color, and stellar mass surface density. These trends have not been seen before at z > 1. Furthermore, color gradients of star-forming and quiescent galaxies show a similar redshift evolution: they are flat at z 2, then steeply decrease as redshift decreases. This affects the galaxy mass-size relation. The normalizations of the star-forming and quiescent relations are 10%-40% smaller than the corresponding relations; the slopes are ∼0.1-0.3 dex shallower. Finally, the half-mass radii of star-forming and quiescent galaxies at M* = 1010.5 M only grow by ∼1% and ∼8% between z ∼ 2.25 and z ∼ 1.25. This is significantly less than the ∼37% and ∼47% size increases found when using the half-light radius.
Galaxies with stellar masses as high as roughly 10
solar masses have been identified
out to redshifts z of roughly 6, around 1 billion years after the Big Bang. It has been difficult to find massive ...galaxies at even earlier times, as the Balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond 2.5 μm. Here we make use of the 1-5 μm coverage of the James Webb Space Telescope early release observations to search for intrinsically red galaxies in the first roughly 750 million years of cosmic history. In the survey area, we find six candidate massive galaxies (stellar mass more than 10
solar masses) at 7.4 ≤ z ≤ 9.1, 500-700 Myr after the Big Bang, including one galaxy with a possible stellar mass of roughly 10
solar masses. If verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies on the basis of rest-frame ultraviolet-selected samples.
Abstract
The first few 100 Myr at
z
> 10 mark the last major uncharted epoch in the history of the universe, where only a single galaxy (GN-z11 at
z
≈ 11) is currently spectroscopically confirmed. ...Here we present a search for luminous
z
> 10 galaxies with JWST/NIRCam photometry spanning ≈1–5
μ
m and covering 49 arcmin
2
from the public JWST Early Release Science programs (CEERS and GLASS). Our most secure candidates are two
M
UV
≈ −21 systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt ≳1.8 mag breaks in their spectral energy distributions (SEDs), consistent with complete absorption of flux bluewards of Ly
α
that is redshifted to
z
=
12.4
−
0.3
+
0.1
and
z
=
10.4
−
0.5
+
0.4
. Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at >5
σ
in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up ∼10
9
solar masses in stars over the ≲300–400 Myr after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of
r
50
≈ 0.7 kpc. These sources, if confirmed, join GN-z11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area >10× larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep JWST observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated.
We study how half-mass radii, central mass densities (Σ1), and color gradients change as galaxies evolve. We separate ∼7000 galaxies into 16 groups with similar spectral shapes; each group represents ...a different evolutionary stage. We find that different galaxy types populate different regions of both size–mass and Σ1–mass space. The nine star-forming groups lie along the integrated star-forming Σ1–mass relation. However, these star-forming groups form steep parallel relations in the size–mass plane, with slopes similar to the quiescent size–mass relation. These steep slopes can be explained as a transformation of the star-forming Σ1–mass relation and its scatter. We identify three types of transitional galaxies. Green valley and post-starburst galaxies are similarly compact at z > 1.5; however, their distinct color gradients indicate that the two populations represent different pathways to quenching. Post-starburst galaxies have flat color gradients and compact structures, consistent with a fast quenching pathway that requires structural change and operates primarily at high redshift. Green valley galaxies have negative color gradients, and are both larger and more numerous toward lower redshift. These galaxies are consistent with slow quenching without significant structural change. We find that dusty star-forming galaxies at z ≳ 2 are very compact and may represent the “burst” before post-starburst galaxies; at z ≲ 2, dusty star-forming galaxies are extended and have shallow color gradients consistent with slow quenching. Our results suggest that star-forming galaxies grow gradually up the Σ1–mass relation until (a) they naturally reach the high Σ1 values required for quiescence or (b) a compaction-type event rapidly increases their Σ1.
Abstract
We use high-resolution, multiband imaging of ∼16,500 galaxies in the CANDELS fields at 0 ≲
z
≤ 2.5 to study the evolution of color gradients and half-mass radii over cosmic time. We find ...that galaxy color gradients at fixed mass evolve rapidly between
z
∼ 2.5 and
z
∼ 1, but remain roughly constant below
z
∼ 1. This result implies that the sizes of both star-forming and quiescent galaxies increase much more slowly than previous studies found using half-light radii. The half-mass radius evolution of quiescent galaxies is fully consistent with a model that uses observed minor merger rates to predict the increase in sizes due to the accretion of small galaxies. Progenitor bias may still contribute to the growth of quiescent galaxies, particularly if we assume a slower timescale for the minor merger growth model. The slower half-mass radius evolution of star-forming galaxies is in tension with cosmological simulations and semianalytic galaxy models. Further detailed, consistent comparisons with simulations are required to place these results in context.
Abstract
We present the first spatially resolved measurements of galaxy properties in the JWST ERO SMACS 0723 field. We perform a comprehensive analysis of five 5 <
z
< 9 galaxies with spectroscopic ...redshifts from NIRSpec observations. We perform spatially resolved spectral energy distribution fitting with
Bagpipes
, using six NIRCam imaging bands spanning the wavelength range 0.8–5
μ
m. This approach allows us to study the internal structure and assembly of the first generations of galaxies. We find clear gradients both in the empirical color maps and in most of the estimated physical parameters. We find regions of considerably different specific star formation rates across each galaxy, which points to very bursty star formation happening on small scales, not galaxy-wide. The integrated light is dominated by these bursty regions, which exhibit strong line emission, with the equivalent width of O
iii
+H
β
reaching up to ∼3000–4000 Å rest frame. Studying these galaxies in an integrated approach yields extremely young inferred ages of the stellar population (<10 Myr), which outshine older stellar populations that are only distinguishable in the spatially resolved maps. This leads to inferring ∼0.5–1 dex lower stellar masses by using single-aperture photometry, when compared to resolved analyses. Such systematics would have strong implications in the shape and evolution of the stellar mass function at these early times, particularly while samples are limited to small numbers of the brightest candidates. Furthermore, the evolved stellar populations revealed in this study imply an extended process of early galaxy formation that could otherwise be hidden behind the light of the most recently formed stars.
This Letter examines how the sizes, structures, and color gradients of galaxies change along the quiescent sequence. Our sample consists of ∼400 quiescent galaxies at 1.0 ≤ z ≤ 2.5 and in three ...CANDELS fields. We exploit deep multi-band Hubble Space Telescope imaging to derive accurate mass profiles and color gradients, then use an empirical calibration from rest-frame UVJ colors to estimate galaxy ages. We find that-contrary to previous results-the youngest quiescent galaxies are not significantly smaller than older quiescent galaxies at fixed stellar mass. These "post-starburst" galaxies only appear smaller in half-light radii because they have systematically flatter color gradients. The strength of color gradients in quiescent galaxies is a clear function of age, with older galaxies exhibiting stronger negative color gradients (i.e., redder centers). Furthermore, we find that the central mass surface density 1 is independent of age at fixed stellar mass, and only weakly depends on redshift. This finding implies that the central mass profiles of quiescent galaxies do not significantly change with age; however, we find that older quiescent galaxies have additional mass at large radii. Our results support the idea that building a massive core is a necessary requirement for quenching beyond z = 1, and indicate that post-starburst galaxies are the result of a rapid quenching process that requires structural change. Furthermore, our observed color gradient and mass profile evolution supports a scenario where quiescent galaxies grow inside-out via minor mergers.
The physical mechanisms that quench star formation, turning blue star-forming galaxies into red quiescent galaxies, remain unclear. In this Letter, we investigate the role of gas supply in ...suppressing star formation by studying the molecular gas content of post-starburst galaxies. Leveraging the wide area of the Sloan Digital Sky Survey, we identify a sample of massive intermediate-redshift galaxies that have just ended their primary epoch of star formation. We present Atacama Large Millimeter/submillimeter Array CO(2-1) observations of two of these post-starburst galaxies at z ∼ 0.7 with . Their molecular gas reservoirs of and are an order of magnitude larger than comparable-mass galaxies in the local universe. Our observations suggest that quenching does not require the total removal or depletion of molecular gas, as many quenching models suggest. However, further observations are required both to determine if these apparently quiescent objects host highly obscured star formation and to investigate the intrinsic variation in the molecular gas properties of post-starburst galaxies.
Abstract
With just a month of data, JWST is already transforming our view of the universe, revealing and resolving starlight in unprecedented populations of galaxies. Although “HST-dark” galaxies ...have previously been detected at long wavelengths, these observations generally suffer from a lack of spatial resolution, which limits our ability to characterize their sizes and morphologies. Here we report on a first view of starlight from a subset of the HST-dark population that is bright with JWST/NIRCam (4.4
μ
m < 24.5 mag) and very faint or even invisible with HST (<1.6
μ
m). In this Letter we focus on a dramatic and unanticipated population of physically extended galaxies (≳0.″25). These 12 galaxies have photometric redshifts 2 <
z
< 6, high stellar masses
M
⋆
≳ 10
10
M
⊙
, and significant dust-attenuated star formation. Surprisingly, the galaxies have elongated projected axis ratios at 4.4
μ
m, suggesting that the population is disk dominated or prolate and we hence refer to them as ultrared flattened objects. Most of the galaxies appear red at all radii, suggesting significant dust attenuation throughout. With
R
e
(F444W) ∼ 1–2 kpc, the galaxies are similar in size to compact massive galaxies at
z
∼ 2 and the cores of massive galaxies and S0s at
z
∼ 0. The stellar masses, sizes, and morphologies of the sample suggest that some could be progenitors of lenticular or fast-rotating galaxies in the local universe. The existence of this population suggests that our previous censuses of the universe may have missed massive, dusty edge-on disks, in addition to dust-obscured starbursts.
Abstract
The first JWST data revealed an unexpected population of red galaxies that appear to have redshifts of
z
∼ 7–9 and high masses of
M
*
≳ 10
10
M
☉
. Here we fit Sérsic profiles to the F200W ...NIRCam images of the 13 massive galaxy candidates of Labbé et al., to determine their structural parameters. Satisfactory fits were obtained for nine galaxies. We find that their effective radii are extremely small, ranging from
r
e
∼ 80 pc to
r
e
∼ 300 pc, with a mean of 〈
r
e
〉 ≈ 150 pc. For their apparent stellar masses, the galaxies are smaller than any other galaxy population that has been observed at any other redshift. We use the fits to derive circularized three-dimensional stellar mass profiles of the galaxies, and compare these to the mass profiles of massive quiescent galaxies at
z
∼ 2.3 and nearby elliptical galaxies. Despite the fact that the high-redshift galaxies have 10–20 times smaller half-light radii than their putative descendants, the central stellar densities are very similar. The most straightforward interpretation is that the dense compact inner regions of the most massive ellipticals today were already in place ∼600 Myr after the Big Bang. We caution that the redshifts and masses of the galaxies remain to be confirmed, and that the complex NIRCam point-spread function is not yet fully characterized.
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