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.
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 investigate the evolution of galaxy gas-phase metallicity (O/H) over the range
z
= 0–3.3 using samples of ∼300 galaxies at
z
∼ 2.3 and ∼150 galaxies at
z
∼ 3.3 from the MOSDEF survey. ...This analysis crucially utilizes different metallicity calibrations at
z
∼ 0 and
z
> 1 to account for evolving interstellar medium (ISM) conditions. We find significant correlations between O/H and stellar mass (
M
*
) at
z
∼ 2.3 and
z
∼ 3.3. The low-mass power-law slope of the mass–metallicity relation (MZR) is remarkably invariant over
z
= 0–3.3, such that O/H ∝
at all redshifts in this range. At fixed
M
*
, O/H decreases with increasing redshift as
d
log(O/H)/
dz
= −0.11 ± 0.02. We find no evidence that the fundamental metallicity relation between
M
*
, O/H, and star formation rate evolves out to
z
∼ 3.3. We employ analytic chemical evolution models to place constraints on the mass and metal loading factors of galactic outflows. The efficiency of metal removal increases toward lower
M
*
at fixed redshift and toward higher redshift at fixed
M
*
. These models suggest that the slope of the MZR is primarily set by the scaling of the outflow metal loading factor with
M
*
, not by the change in gas fraction as a function of
M
*
. The evolution toward lower O/H at fixed
M
*
with increasing redshift is driven by both higher gas fraction (leading to stronger dilution of ISM metals) and higher metal removal efficiency. These results suggest that the processes governing the smooth baryonic growth of galaxies via gas flows and star formation hold in the same form over at least the past 12 Gyr.
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.
Using observations from the MOSFIRE Deep Evolution Field survey, we investigate the physical conditions of star-forming regions in z ~ 2.3 galaxies, specifically the electron density and ionization ...state. From measurements of the OIIlambdalambda3726,3729 and SIIlambdalambda6716,6731 doublets, we find a median electron density of ~250 cm super(-3) at z ~ 2.3, an increase of an order of magnitude compared to measurements of galaxies at z ~ 0. While z ~ 2.3 galaxies are offset toward significantly higher O sub(32) values relative to local galaxies at fixed stellar mass, we find that the high-redshift sample follows a similar distribution to the low-metallicity tail of the local distribution in the O sub(32) versus R sub(23) and O3N2 diagrams. Based on these results, we propose that z ~ 2.3 star-forming galaxies have the same ionization parameter as local galaxies at fixed metallicity. In combination with simple photoionization models, the position of local and z ~ 2.3 galaxies in excitation diagrams suggests that there is no significant change in the hardness of the ionizing spectrum at fixed metallicity from z ~ 0 to z ~ 2.3. We find that z ~ 2.3 galaxies show no offset compared to low-metallicity local galaxies in emission line ratio diagrams involving only lines of hydrogen, oxygen, and sulfur, but show a systematic offset in diagrams involving NIIlambda6584. We conclude that the offset of z ~ 2.3 galaxies from the local star-forming sequence in the NII BPT diagram is primarily driven by elevated N/O at fixed O/H compared to local galaxies. These results suggest that the local gas-phase and stellar metallicity sets the ionization state of star-forming regions at z ~ 0 and z ~ 2.
Abstract
We investigate the nature of the relation among stellar mass, star formation rate, and gas-phase metallicity (the
–SFR–
Z
relation) at high redshifts using a sample of 260 star-forming ...galaxies at
z
∼ 2.3 from the MOSDEF survey. We present an analysis of the high-redshift
–SFR–
Z
relation based on several emission-line ratios for the first time. We show that a
–SFR–
Z
relation clearly exists at
z
∼ 2.3. The strength of this relation is similar to predictions from cosmological hydrodynamical simulations. By performing a direct comparison of stacks of
z
∼ 0 and
z
∼ 2.3 galaxies, we find that
z
∼ 2.3 galaxies have ∼0.1 dex lower metallicity at fixed
and SFR. In the context of chemical evolution models, this evolution of the
–SFR–
Z
relation suggests an increase with redshift of the mass-loading factor at fixed
, as well as a decrease in the metallicity of infalling gas that is likely due to a lower importance of gas recycling relative to accretion from the intergalactic medium at high redshifts. Performing this analysis simultaneously with multiple metallicity-sensitive line ratios allows us to rule out the evolution in physical conditions (e.g., N/O ratio, ionization parameter, and hardness of the ionizing spectrum) at fixed metallicity as the source of the observed trends with redshift and with SFR at fixed
at
z
∼ 2.3. While this study highlights the promise of performing high-order tests of chemical evolution models at high redshifts, detailed quantitative comparisons ultimately await a full understanding of the evolution of metallicity calibrations with redshift.
We use extensive spectroscopy from the MOSFIRE Deep Evolution Field survey to investigate the relationships between rest-frame optical emission line equivalent widths (W) and a number of galaxy and ...interstellar medium (ISM) characteristics for a sample of 1134 star-forming galaxies at redshifts 1.4 z 3.8. We examine how the equivalent widths of , , λλ4960, 5008, + Hβ, , and , depend on stellar mass, UV slope, age, star formation rate (SFR) and specific SFR (sSFR), ionization parameter and excitation conditions (O32 and /Hβ), gas-phase metallicity, and ionizing photon production efficiency ( ion). The trend of increasing W with decreasing stellar mass is strongest for (and +Hβ). More generally, the equivalent widths of all the lines increase with redshift at a fixed stellar mass or fixed gas-phase metallicity, suggesting that high equivalent width galaxies are common at high redshift. This redshift evolution in equivalent widths can be explained by the increase in SFR and decrease in metallicity with redshift at a fixed stellar mass. Consequently, the dependence of W on sSFR is largely invariant with redshift, particularly when examined for galaxies of a given metallicity. Our results show that high equivalent width galaxies, specifically those with high , have low stellar masses, blue UV slopes, young ages, high sSFRs, ISM line ratios indicative of high ionization parameters, high ion, and low metallicities. As these characteristics are often attributed to galaxies with high ionizing escape fractions, galaxies with high W are likely candidates for the population that dominates cosmic reionization.
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.
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.
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