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The majority of massive disk galaxies in the local Universe show a stellar barred structure in their central regions, including our Milky Way 1 , 2 . Bars are supposed to develop in dynamically cold stellar disks at low redshift, as the strong gas turbulence typical of disk galaxies at high redshift suppresses or delays bar formation 3 , 4 . Moreover, simulations predict bars to be almost absent beyond z  = 1.5 in the progenitors of Milky Way-like galaxies 5 , 6 . Here we report observations of ceers-2112, a barred spiral galaxy at redshift z phot  ≈ 3, which was already mature when the Universe was only 2 Gyr old. The stellar mass ( M ★  = 3.9 × 10 9  M ⊙ ) and barred morphology mean that ceers-2112 can be considered a progenitor of the Milky Way 7 – 9 , in terms of both structure and mass-assembly history in the first 2 Gyr of the Universe, and was the closest in mass in the first 4 Gyr. We infer that baryons in galaxies could have already dominated over dark matter at z  ≈ 3, that high-redshift bars could form in approximately 400 Myr and that dynamically cold stellar disks could have been in place by redshift z  = 4–5 (more than 12 Gyrs ago) 10 , 11 . We report observations of ceers-2112 that show that this galaxy, at a redshift of 3, unexpectedly has a barred spiral structure.

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\\le z\\le2.5\\) and \\(10.1 \\le \\log{M_*/M_\\odot}\\le11.6\\) in three CANDELS fields. We exploit deep multi-band HST 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 \\(\\Sigma_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.

[Shortened for arXiv] We conduct a systematic search for \\(\\log(M_\\ast/M_\\odot) \\geq 9.5\\) quiescent galaxies at \\(z > 3\\) in six extragalactic deep fields observed with NIRCam, with the goal of extracting their physical and statistical features in a uniform and self-consistent manner. We exploit the ASTRODEEP-JWST photometric catalogs to single out robust candidates, including sources quenched only a few tens of Myr before the observation. We apply a SED-fitting procedure which explores three functional forms of star formation history and the \\(\\chi^2\\) probabilities of the solutions, with additional checks to minimise the contamination from interlopers, tuning our selection criteria against available spectroscopic data from the DAWN archive and simulated catalogs. We select 633 candidates, which we rank by a reliability parameter based on the probabilities of the quiescent and alternative star-forming solutions, with 291 candidates tagged as \"gold\". According to the best-fit models, 79\\% of the massive (\\(\\log(M_\\ast/M_\\odot) \\geq 10.5\\)) quiescent galaxies at \\(3 < z < 5\\) stopped forming stars at least 150 Myr before the time of observation, while 89\\% of low-mass sources have been quenched for less than 150 Myr. The abundance of low-mass old quiescent systems does not increase significantly with time from \\(z = 5\\) to 3: low-mass objects seem to be experiencing a short episode of quenching followed by rejuvenation (``breathing''), consistent with a downsizing scenario of galaxy formation. We also find an abrupt drop in the density of massive quiescent candidates at \\(z > 5\\). We derive estimates for the number density of early passive galaxies up to \\(z = 10\\) and compare them against various models: tensions with data remain in the modeling of the observed bimodality of time passed since quenching as a function of mass.

We use high-resolution, multi-band 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 which 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 semi-analytic galaxy models. Further detailed, consistent comparisons with simulations are required to place these results in context.

We present measurements of morphological parameters from fitting 53,885 galaxies detected to a magnitude limit of F356W\\(< 28.5\\) in the CEERS NIRCam imaging with galfit in six broadband filters: F115W, F150W, F200W, F277W, F356W, and F444W. We provide a public catalog of Sérsic index, effective semi-major axis, axis ratio, integrated magnitude, and position angle for these galaxies in each of the filters. Uncertainties in the measured parameters are estimated from simulated galaxies that have similar noise and background properties as the observed galaxies. We compare our measurements with those in the CANDELS/EGS field measured with HST/WFC3 and find that the sizes agree to within 0.09 dex and the Sérsic indices agree to within 0.13 dex. We further present the evolution in the size-mass relation, and find that the evolution to \\(z9\\) is consistent with previous results derived at lower redshift. Finally, we look at the color gradients of galaxies at \\(12.5\\)), the color gradients are nearly flat with no dependence on mass, indicating that the stellar populations are more uniform throughout. The structural measurements presented are accurate to \\(20\\%\\) or better for most galaxies with F356W \\(<27.0\\) mag and will enable further studies of galaxy morphology to \\(z10\\).

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: 7,006 galaxies in the CANDELS fields at 1.0 < z < 2.5. The sample includes both star-forming and quiescent galaxies with stellar masses 9.0 < log(M_* / M_) < 11.5. We test three methods for calculating half-mass radii from multi-band PSF-matched HST imaging: two based on spatially-resolved SED 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 r_e,mass < r_e,light). 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 r_mass-M_* relations are 10-40% smaller than the corresponding r_light-M_* relations; the slopes are ~0.1-0.3 dex shallower. Finally, the half-mass radii of star-forming and quiescent galaxies at M_* = 10^10.5M_ 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 investigate how the environment affects the assembly history of massive galaxies. For that purpose, we make use of SHARDS and HST spectro-photometric data, whose depth, spectral resolution, and wavelength coverage allow to perform a detailed analysis of the stellar emission as well as obtaining unprecedentedly accurate photometric redshifts. This expedites a sufficiently accurate estimate of the local environment and a robust derivation of the star formation histories of a complete sample of 332 massive galaxies (\\(\\mathrm{>10^{10}M_{\\odot}}\\)) at redshift \\(1\\leq z \\leq 1.5\\) in the GOODS-N field. We find that massive galaxies in this redshift range avoid the lowest density environments. Moreover, we observed that the oldest galaxies in our sample with with mass-weighted formation redshift \\(\\mathrm{\\overline{z}_{M-w} \\geq 2.5}\\), avoid the highest density regions, preferring intermediate environments. Younger galaxies, including those with active star formation, tend to live in denser environments (\\(\\Sigma = \\mathrm{5.0_{1.1}^{24.8}\\times 10^{10}M_{\\odot}Mpc^{-2}}\\)). This behavior could be expected if those massive galaxies starting their formation first would merge with neighbors and sweep their environment earlier. On the other hand, galaxies formed more recently (\\(\\overline{z}_{M-w} < 2.5\\)) are accreted into large scale structures at later times and we are observing them before sweeping their environment or, alternatively, they are less likely to affect their environment. However, given that both number and mass surface densities of neighbor galaxies is relatively low for the oldest galaxies, our results reveal a very weak correlation between environment and the first formation stages of the earliest massive galaxies.

Some recent observations seem to disagree with hierarchical theories of galaxy formation on the role of major mergers in a late build-up of massive early-type galaxies. We re-address this question by analysing the morphology, structural distortion level, and star formation enhancement of a sample of massive galaxies (M* > 5 × 1010M⊙) lying on the Red Sequence and its surroundings at 0.3 < z < 1.5. We have used an initial sample of ~1800 sources with Ks < 20.5 mag over an area ~155 arcmin2 on the Groth Strip, combining data from the Rainbow Extragalactic Database and the GOYA Survey. Red galaxy classes that can be directly associated to intermediate stages of major mergers and to their final products have been defined. For the first time we report observationally the existence of a dominant evolutionary path among massive red galaxies at 0.6 < z < 1.5, consisting in the conversion of irregular disks into irregular spheroids, and of these ones into regular spheroids. This result points to: 1) the massive red regular galaxies at low redshifts derive from the irregular ones populating the Red Sequence and its neighbourhood at earlier epochs up to z ~ 1.5; 2) the progenitors of the bulk of present-day massive red regular galaxies have been blue disks that have migrated to the Red Sequence majoritarily through major mergers at 0.6 < z < 1.2 (these mergers thus starting at z ~ 1.5); 3) the formation of E-S0's that end up with M* > 1011M⊙ at z = 0 through gas-rich major mergers has frozen since z ~ 0.6. Our results support that major mergers have played the dominant role in the definitive build-up of present-day E-S0's with M* > 1011M⊙ at 0.6 < z < 1.2, in good agreement with the hierarchical scenario proposed in the Eliche-Moral et al. (2010a) model (see also Eliche-Moral et al. 2010b). This study is published in Prieto et al. (2012). Supported by the Spanish Ministry of Science and Innovation (MICINN) under projects AYA2009-10368, AYA2006-12955, AYA2010-21887-C04-04, and AYA2009-11137, by the Madrid Regional Government through the AstroMadrid Project (CAM S2009/ESP-1496), and by the Spanish MICINN under the Consolider-Ingenio 2010 Program grant CSD2006-00070: “First Science with the GTC” (http://www.iac.es/consolider-ingenio-gtc/). S. D. H. & G.

Strong galactic winds are ubiquitous at \\(z\\gtrsim 1\\). However, it is not well known where inside galaxies these winds are launched from. We study the cool winds (\\(\\sim 10^4\\)\\,K) in two spatial regions of a massive galaxy at \\(z=1.3\\), which we nickname the \"Baltimore Oriole's Nest.\" The galaxy has a stellar mass of \\(10^{10.3\\pm 0.3} M_\\odot\\), is located on the star-forming main sequence, and has a morphology indicative of a recent merger. Gas kinematics indicate a dynamically complex system with velocity gradients ranging from 0 to 60 \\(\\mathrm{km}\\cdot\\mathrm{s}^{-1}\\). The two regions studied are: a dust-reddened center (Central region), and a blue arc at 7 kpc from the center (Arc region). We measure the \\ion{Fe}{2} and \\ion{Mg}{2} absorption line profiles from deep Keck/DEIMOS spectra. Blueshifted wings up to 450 km\\(\\cdot\\)s\\(^{-1}\\) are found for both regions. The \\ion{Fe}{2} column densities of winds are \\(10^{14.7\\pm 0.2}\\,\\mathrm{cm}^{-2}\\) and \\(10^{14.6\\pm 0.2}\\,\\mathrm{cm}^{-2}\\) toward the Central and Arc regions, respectively. Our measurements suggest that the winds are most likely launched from both regions. The winds may be driven by the spatially extended star formation, the surface density of which is around 0.2 \\(M_\\odot\\,\\mathrm{yr}^{-1}\\cdot \\mathrm{kpc}^{-2}\\) in both regions. The mass outflow rates are estimated to be \\(4\\,M_\\odot\\,\\mathrm{yr}^{-1}\\) and \\(3\\,M_\\odot\\,\\mathrm{yr}^{-1}\\) for the Central and Arc regions, with uncertainties of one order-of-magnitude or more. Findings of this work and a few previous studies suggest that the cool galactic winds at \\(z\\gtrsim 1\\) might be commonly launched from the entire spatial extents of their host galaxies due to extended galaxy star formation.

We study how half-mass radii, central mass densities (\\(\\Sigma_1\\)), and color gradients change as galaxies evolve. We separate \\(\\sim7,000\\) galaxies into sixteen 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 \\(\\Sigma_1\\)-mass space. The nine star-forming groups lie along the integrated star-forming \\(\\Sigma_1\\)-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 \\(\\Sigma_1\\)-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 which requires structural change and operates primarily at high redshift. Green valley galaxies have negative color gradients, and are both larger and more numerous towards lower redshift. These galaxies are consistent with slow quenching without significant structural change. We find that dusty star-forming galaxies at \\(z\\gtrsim2\\) are very compact, and may represent the \"burst\" before post-starburst galaxies; at \\(z\\lesssim2\\), 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 \\sig-mass relation until (a) they naturally reach the high \\(\\Sigma_1\\) values required for quiescence, or (b) a compaction-type event rapidly increases their \\(\\Sigma_1\\).