ABSTRACT
We reliably extend the stellar mass–size relation over 0.2 ≤ z ≤ 2 to low stellar mass galaxies by combining the depth of Hubble Frontier Fields with the large volume covered by CANDELS. ...Galaxies are simultaneously modelled in multiple bands using the tools developed by the MegaMorph project, allowing robust size (i.e. half-light radius) estimates even for small, faint, and high redshift galaxies. We show that above 107 M⊙, star-forming galaxies are well represented by a single power law on the mass–size plane over our entire redshift range. Conversely, the stellar mass–size relation is steep for quiescent galaxies with stellar masses $\ge 10^{10.3}\, {\rm M}_\odot$ and flattens at lower masses, regardless of whether quiescence is selected based on star-formation activity, rest-frame colours, or structural characteristics. This flattening occurs at sizes of ∼1 kpc at z ≤ 1. As a result, a double power law is preferred for the stellar mass–size relation of quiescent galaxies, at least above 10$^7\, {\rm M}_\odot$. We find no strong redshift dependence in the slope of the relation of star-forming galaxies as well as of high mass quiescent galaxies. We also show that star-forming galaxies with stellar masses $\ge 10^{9.5}\, {\rm M}_\odot$ and quiescent galaxies with stellar masses $\ge 10^{10.3}\, {\rm M}_\odot$ have undergone significant size growth since z ∼ 2, as expected; however, low mass galaxies have not. Finally, we supplement our data with predominantly quiescent dwarf galaxies from the core of the Fornax cluster, showing that the stellar mass–size relation is continuous below 10$^7\, {\rm M}_\odot$, but a more complicated functional form is necessary to describe the relation.
ABSTRACT We present photometry and derived redshifts from up to eleven bandpasses for 9927 galaxies in the Hubble Ultra Deep field (UDF), covering an observed wavelength range from the ...near-ultraviolet (NUV) to the near-infrared (NIR) with Hubble Space Telescope observations. Our Wide Field Camera 3 (WFC3)/UV F225W, F275W, and F336W image mosaics from the ultra-violet UDF (UVUDF) imaging campaign are newly calibrated to correct for charge transfer inefficiency, and use new dark calibrations to minimize background gradients and pattern noise. Our NIR WFC3/IR image mosaics combine the imaging from the UDF09 and UDF12 campaigns with CANDELS data to provide NIR coverage for the entire UDF field of view. We use aperture-matched point-spread function corrected photometry to measure photometric redshifts in the UDF, sampling both the Lyman break and Balmer break of galaxies at - , and one of the breaks over the rest of the redshift range. Our comparison of these results with a compilation of robust spectroscopic redshifts shows an improvement in the galaxy photometric redshifts by a factor of two in scatter and a factor three in outlier fraction (OLF) over previous UDF catalogs. The inclusion of the new NUV data is responsible for a factor of two decrease in the OLF compared to redshifts determined from only the optical and NIR data, and improves the scatter at and at . The panchromatic coverage of the UDF from the NUV through the NIR yields robust photometric redshifts of the UDF, with the lowest OLF available.
We examine the fraction of massive ( ) compact star-forming galaxies (cSFGs) that host an active galactic nucleus (AGN) at . These cSFGs are likely the direct progenitors of the compact quiescent ...galaxies observed at this epoch, which are the first population of passive galaxies to appear in large numbers in the early Universe. We identify cSFGs that host an AGN using a combination of Hubble WFC3 imaging and Chandra X-ray observations in four fields: the Chandra Deep Fields, the Extended Groth Strip, and the UKIDSS Ultra Deep Survey field. We find that (65/166) of cSFGs at host an X-ray detected AGN. This fraction is 3.2 times higher than the incidence of AGN in extended star-forming galaxies with similar masses at these redshifts. This difference is significant at the level. Our results are consistent with models in which cSFGs are formed through a dissipative contraction that triggers a compact starburst and concurrent growth of the central black hole. We also discuss our findings in the context of cosmological galaxy evolution simulations that require feedback energy to rapidly quench cSFGs. We show that the AGN fraction peaks precisely where energy injection is needed to reproduce the decline in the number density of cSFGs with redshift. Our results suggest that the first abundant population of massive quenched galaxies emerged directly following a phase of elevated supermassive black hole growth and further hints at a possible connection between AGN and the rapid quenching of star formation in these galaxies.
We study the evolution of the scaling relations that compare the effective density ( ) and core density ( kpc) to the stellar masses of star-forming galaxies (SFGs) and quiescent galaxies. These ...relations have been fully in place since and have exhibited almost constant slope and scatter since that time. For SFGs, the zero points in and decline by only . This fact plus the narrowness of the relations suggests that galaxies could evolve roughly along the scaling relations. Quiescent galaxies follow different scaling relations that are offset to higher densities at the same mass and redshift. Furthermore, the zero point of their core density has declined by only since , while the zero point of the effective density declines by . When galaxies quench, they move from the star-forming relations to the quiescent relations. This involves an increase in the core and effective densities, which suggests that SFGs could experience a phase of significant core growth relative to the average evolution along the structural relations. The distribution of massive galaxies relative to the SFR-M and the quiescent relations exhibits an L-shape that is independent of redshift. The knee of this relation consists of a subset of "compact" SFGs that are the most likely precursors of quiescent galaxies forming at later times. The compactness selection threshold in exhibits a small variation from z = 3 to 0.5, M kpc−2, allowing the most efficient identification of compact SFGs and quiescent galaxies at every redshift.
Abstract We study a new population of extremely red objects (EROs) recently discovered by the James Webb Space Telescope (JWST) based on their NIRCam colors F277W − F444W > 1.5 mag. We find 37 EROs ...in the Cosmic Evolution Early Release Science Survey (CEERS) field with F444W < 28 mag and photometric redshifts between 5 < z < 7, with median z = 6.9 − 1.6 + 1.0 . Surprisingly, despite their red long-wavelength colors, these EROs have blue short-wavelength colors (F150W − F200W ∼ 0 mag) indicative of bimodal spectral energy distributions (SEDs) with a red, steep slope in the rest-frame optical, and a blue, flat slope in the rest-frame UV. Moreover, all these EROs are unresolved, point-like sources in all NIRCam bands. We analyze the SEDs of eight of them with MIRI and NIRSpec observations using stellar population models and active galactic nucleus (AGN) templates. We find that dusty galaxies or obscured AGNs provide similarly good SED fits but different stellar properties: massive and dusty, log M ⋆ / M ⊙ ∼ 10 and A V ≳ 3 mag, or low mass and obscured, log M ⋆ / M ⊙ ∼ 7.5 and A V ∼ 0 mag, hosting an obscured quasi-stellar object (QSO). SED modeling does not favor either scenario, but their unresolved sizes are more suggestive of AGNs. If any EROs are confirmed to have log M ⋆ / M ⊙ ≳ 10.5, it would increase the pre-JWST number density at z > 7 by up to a factor ∼60. Similarly, if they are QSOs with luminosities in the L bol > 10 45–46 erg s −1 range, their number would exceed that of bright blue QSOs by more than three orders of magnitude. Additional photometry at mid-infrared wavelengths will reveal the true nature of the red continuum emission in these EROs and will place this puzzling population in the right context of galaxy evolution.
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.
We analyze the dependence of galaxy structure (size and Sersic index) and mode of star formation ( Delta *SSFR and SFRIR/SFRUV) on the position of galaxies in the star formation rate (SFR) versus ...mass diagram. Our sample comprises roughly 640,000 galaxies at z ~ 0.1, 130,000 galaxies at z ~ 1, and 36,000 galaxies at z ~ 2. Structural measurements for all but the z ~ 0.1 galaxies are based on Hubble Space Telescope imaging, and SFRs are derived using a Herschel-calibrated ladder of SFR indicators. We find that a correlation between the structure and stellar population of galaxies (i.e., a 'Hubble sequence') is already in place since at least z ~ 2.5. At all epochs, typical star-forming galaxies on the main sequence are well approximated by exponential disks, while the profiles of quiescent galaxies are better described by de Vaucouleurs profiles. In the upper envelope of the main sequence, the relation between the SFR and Sersic index reverses, suggesting a rapid buildup of the central mass concentration in these starbursting outliers. We observe quiescent, moderately and highly star-forming systems to co-exist over an order of magnitude or more in stellar mass. At each mass and redshift, galaxies on the main sequence have the largest size. The rate of size growth correlates with specific SFR, and so does Delta *SSFR at each redshift. A simple model using an empirically determined star formation law and metallicity scaling, in combination with an assumed geometry for dust and stars, is able to relate the observed Delta *SSFR and SFRIR/SFRUV, provided a more patchy dust geometry is assumed for high-redshift galaxies.
Abstract We combine deep imaging data from the CEERS early release JWST survey and Hubble Space Telescope imaging from CANDELS to examine the size–mass relation of star-forming galaxies and the ...morphology–quenching relation at stellar masses M ⋆ ≥ 10 9.5 M ⊙ over the redshift range 0.5 < z < 5.5. In this study with a sample of 2450 galaxies, we separate star-forming and quiescent galaxies based on their star formation activity and confirm that star-forming and quiescent galaxies have different morphologies out to z = 5.5, extending the results of earlier studies out to higher redshifts. We find that star-forming and quiescent galaxies have typical Sérsic indices of n ∼ 1.3 and n ∼ 4.3, respectively. Focusing on star-forming galaxies, we find that the slope of the size–mass relation is nearly constant with redshift, as was found previously, but shows a modest increase at z ∼ 4.2. The intercept in the size–mass relation declines out to z = 5.5 at rates that are similar to what earlier studies found. The intrinsic scatter in the size–mass relation is relatively constant out to z = 5.5.
We compare multi-wavelength star formation rate (SFR) indicators out to z ~ 3 in the GOODS-South field. Our analysis uniquely combines U to 8 Delta *mm photometry from FIREWORKS, MIPS 24 Delta *mm ...and PACS 70, 100, and 160 Delta *mm photometry from the PEP, and H Delta *a spectroscopy from the SINS survey. We describe a set of conversions that lead to a continuity across SFR indicators. A luminosity-independent conversion from 24 Delta *mm to total infrared luminosity yields estimates of L IR that are in the median consistent with the L IR derived from PACS photometry, albeit with significant scatter. Dust correction methods perform well at low-to-intermediate levels of star formation. They fail to recover the total amount of star formation in systems with large SFRIR/SFRUV ratios, typically occuring at the highest SFRs (SFRUV + IR 100 M yr--1) and redshifts (z 2.5) probed. Finally, we confirm that H Delta *a-based SFRs at 1.5 < z < 2.6 are consistent with SFRSED and SFRUV + IR provided extra attenuation toward H II regions is taken into account (A V, neb = A V, continuum/0.44). With the cross-calibrated SFR indicators in hand, we perform a consistency check on the star formation histories inferred from spectral energy distribution (SED) modeling. We compare the observed SFR-M relations and mass functions at a range of redshifts to equivalents that are computed by evolving lower redshift galaxies backward in time. We find evidence for underestimated stellar ages when no stringent constraints on formation epoch are applied in SED modeling. We demonstrate how resolved SED modeling, or alternatively deep UV data, may help to overcome this bias. The age bias is most severe for galaxies with young stellar populations and reduces toward older systems. Finally, our analysis suggests that SFHs typically vary on timescales that are long (at least several 100 Myr) compared to the galaxies' dynamical time.
The shutdown of star formation in galaxies is generally termed "quenching." This paper addresses quenching by searching for traces of possible quenching processes through their effects on galaxy ...structural parameters such as stellar mass (M sub(*)), M sub(*)/r sub(e), surface stellar mass density (~M sub(*)/r super(2) sub(e)), and Sersic index (n). We analyze the rest-frame U-B color correlations versus these structural parameters using a sample of galaxies in the redshift range 0.5 < or =, slant z < 0.8 from the DEEP2/AEGIS survey. We assess the tightness of the color relationships by measuring their "overlap regions," defined as the area in color-parameter space in which red and blue galaxies overlap; the parameter that minimizes these overlap regions is considered to be the most effective color discriminator. We discuss a two-stage model for quenching in which galaxy star formation rates are controlled by their dark halos while they are still in the blue cloud and a second quenching process sets in later, associated with the central stellar mass buildup.
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