We present a detailed stellar population analysis of 11 bright (H < 26.6) galaxies at z=9−11 (three spectroscopically confirmed) to constrain the chemical enrichment and growth of stellar mass of ...early galaxies. We use the flexible Bayesian spectral energy distribution (SED) fitting code Prospector with a range of star-formation histories (SFHs), a flexible dust attenuation law and a self-consistent modeling of emission lines. This approach allows us to assess how different priors affect our results, and how well we can break degeneracies between dust attenuation, stellar ages, metallicity and emission lines using data which probe only the rest-frame ultraviolet to optical wavelengths. We measure a median observed ultraviolet spectral slope β= −1.87+0.35−0.43 for relatively massive star-forming galaxies (9<log(M?/M)<10), consistent with no change from z=4 to z=9−10 at these stellar masses, implying rapid enrichment. Our SED-fitting results are consistent with a star-forming main sequence with sub-linear slope (0.7±0.2) and specific star-formation rates of 3−10 Gyr−1. However, the stellar ages and SFHs are less well constrained. Using different SFH priors, we cannot distinguish between median mass-weighted ages of ∼50−150 Myr, which corresponds to 50% formation redshifts of z50∼10−12 atz∼9 and is of the order of the dynamical timescales of these systems. Importantly, the models with different SFH priors are able to fit the data equally well. We conclude that the current observational data cannot tightly constrain the mass-buildup timescales of these z=9−11 galaxies, with our results consistent with SFHs implying both a shallow and steep increase of the cosmic SFR density with time at z >10
Galaxy mergers are expected to have a significant role in the mass assembly of galaxies in the early universe, but there are very few observational constraints on the merger history of galaxies at z ...> 2. We present the first study of galaxy major mergers (mass ratios <1:4) in mass-selected samples out to z 6. Using all five fields of the Hubble Space Telescope/CANDELS survey and a probabilistic pair-count methodology that incorporates the full photometric redshift posteriors and corrections for stellar mass completeness, we measure galaxy pair-counts for projected separations between 5 and 30 kpc in stellar mass selected samples at 9.7 < log10(M /M ) < 10.3 and log10(M /M ) > 10.3. We find that the major merger pair fraction rises with redshift to z 6 proportional to (1 + z)m, with m = 0.8 0.2 (m = 1.8 0.2) for log10(M /M ) > 10.3 (9.7 < log10(M /M ) < 10.3). Investigating the pair fraction as a function of mass ratio between 1:20 and 1:1, we find no evidence for a strong evolution in the relative numbers of minor to major mergers out to z < 3. Using evolving merger timescales, we find that the merger rate per galaxy ( ) rises rapidly from 0.07 0.01 Gyr−1 at z < 1 to 7.6 2.7 Gyr−1 at z = 6 for galaxies at log10(M /M ) > 10.3. The corresponding comoving major merger rate density remains roughly constant during this time, with rates of Γ 10−4 Gyr−1 Mpc−3. Based on the observed merger rates per galaxy, we infer specific mass accretion rates from major mergers that are comparable to the specific star formation rates for the same mass galaxies at z > 3 - observational evidence that mergers are as important a mechanism for building up mass at high redshift as in situ star formation.
Abstract
We present the data release and data reduction process for the Epoch 1 NIRCam observations for the Cosmic Evolution Early Release Science Survey (CEERS). These data consist of NIRCam imaging ...in six broadband filters (F115W, F150W, F200W, F277W, F356W and F444W) and one medium-band filter (F410M) over four pointings, obtained in parallel with primary CEERS MIRI observations. We reduced the NIRCam imaging with the JWST Calibration Pipeline, with custom modifications and reduction steps designed to address additional features and challenges with the data. Here we provide a detailed description of each step in our reduction and a discussion of future expected improvements. Our reduction process includes corrections for known prelaunch issues such as 1/
f
noise, as well as in-flight issues including snowballs, wisps, and astrometric alignment. Many of our custom reduction processes were first developed with prelaunch simulated NIRCam imaging over the full 10 CEERS NIRCam pointings. We present a description of the creation and reduction of this simulated data set in the Appendix. We provide mosaics of the real images in a public release, as well as our reduction scripts with detailed explanations to allow users to reproduce our final data products. These represent one of the first official public data sets released from the Directors Discretionary Early Release Science (DD-ERS) program.
Abstract We report on the discovery of two low-luminosity, broad-line active galactic nuclei (AGNs) at z > 5 identified using JWST NIRSpec spectroscopy from the Cosmic Evolution Early Release Science ...(CEERS) survey. We detect broad H α emission in the spectra of both sources, with FWHM of 2060 ± 290 km s −1 and 1800 ± 200 km s −1 , resulting in virial black hole (BH) masses that are 1–2 dex below those of existing samples of luminous quasars at z > 5. The first source, CEERS 2782 at z = 5.242, is 2–3 dex fainter than known quasars at similar redshifts and was previously identified as a candidate low-luminosity AGN based on its morphology and rest-frame optical spectral energy distribution (SED). We measure a BH mass of M BH = (1.3 ± 0.4) × 10 7 M ⊙ , confirming that this AGN is powered by the least massive BH known in the Universe at the end of cosmic reionization. The second source, CEERS 746 at z = 5.624, is inferred to be a heavily obscured, broad-line AGN caught in a transition phase between a dust-obscured starburst and an unobscured quasar. We estimate its BH mass to be in the range of M BH ≃ (0.9–4.7) × 10 7 M ⊙ , depending on the level of dust obscuration assumed. We perform SED fitting to derive host stellar masses, M ⋆ , allowing us to place constraints on the BH–galaxy mass relationship in the lowest mass range yet probed in the early Universe. The M BH / M ⋆ ratio for CEERS 2782, in particular, is consistent with or higher than the empirical relationship seen in massive galaxies at z = 0. We examine the narrow emission line ratios of both sources and find that their location on the BPT and OHNO diagrams is consistent with model predictions for moderately low metallicity AGNs with Z / Z ⊙ ≃ 0.2–0.4. The spectroscopic identification of low-luminosity, broad-line AGNs at z > 5 with M BH ≃ 10 7 M ⊙ demonstrates the capability of JWST to push BH masses closer to the range predicted for the BH seed population and provides a unique opportunity to study the early stages of BH–galaxy assembly.
This is the first in a series of papers examining the demographics of star-forming (SF) galaxies at 0.2 < z < 2.5 in CANDELS. We study 9100 galaxies from GOODS-S and UDS, having published values of ...redshifts, masses, star formation rates (SFRs), and dust attenuation (AV) derived from UV-optical spectral energy distribution fitting. In agreement with previous works, we find that the UVJ colors of a galaxy are closely correlated with its specific star formation rate (SSFR) and AV. We define rotated UVJ coordinate axes, termed SSED and CSED, that are parallel and perpendicular to the SF sequence and derive a quantitative calibration that predicts SSFR from CSED with an accuracy of ∼0.2 dex. SFRs from UV-optical fitting and from UV+IR values based on Spitzer/MIPS 24 m agree well overall, but systematic differences of order 0.2 dex exist at high and low redshifts. A novel plotting scheme conveys the evolution of multiple galaxy properties simultaneously, and dust growth, as well as star formation decline and quenching, exhibit "mass-accelerated evolution" ("downsizing"). A population of transition galaxies below the SF main sequence is identified. These objects are located between SF and quiescent galaxies in UVJ space, and have lower AV and smaller radii than galaxies on the main sequence. Their properties are consistent with their being in transit between the two regions. The relative numbers of quenched, transition, and SF galaxies are given as a function of mass and redshift.
Abstract
We study galactic star formation activity as a function of environment and stellar mass over 0.5 <
z
< 2.0 using the FourStar Galaxy Evolution (ZFOURGE) survey. We estimate the galaxy ...environment using a Bayesian-motivated measure of the distance to the third nearest neighbor for galaxies to the stellar mass completeness of our survey,
at
z
= 1.3 (2.0). This method, when applied to a mock catalog with the photometric-redshift precision (
) of ZFOURGE, accurately recovers galaxies in low- and high-density environments. We quantify the environmental quenching efficiency and show that at
, it depends on galaxy stellar mass, demonstrating that the effects of quenching related to (stellar) mass and environment are not separable. In high-density environments, the mass and environmental quenching efficiencies are comparable for massive galaxies (
) at all redshifts. For lower-mass galaxies (
), the environmental quenching efficiency is very low at
, but increases rapidly with decreasing redshift. Environmental quenching can account for nearly all quiescent lower-mass galaxies (
), which appear primarily at
. The morphologies of lower-mass quiescent galaxies are inconsistent with those expected of recently quenched star-forming galaxies. Some environmental process must transform the morphologies on similar timescales as the environmental quenching itself. The evolution of the environmental quenching favors models that combine gas starvation (as galaxies become satellites) with gas exhaustion through star formation and outflows (“overconsumption”), and additional processes such as galaxy interactions, tidal stripping, and disk fading to account for the morphological differences between the quiescent and star-forming galaxy populations.
The rate of major galaxy-galaxy merging is theoretically predicted to steadily increase with redshift during the peak epoch of massive galaxy development (1 ≤ z ≤ 3). We use close-pair statistics to ...objectively study the incidence of massive galaxies (stellar M1 > 2 × 1010 M⊙) hosting major companions (1 ≤ M1/M2 ≤ 4; i.e. <4:1) at six epochs spanning 0 < z < 3. We select companions from a nearly complete, mass-limited (≥5 × 109 M⊙) sample of 23 696 galaxies in the five Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey fields and the Sloan Digital Sky Survey. Using 5-50 kpc projected separation and close redshift proximity criteria, we find that the major companion fraction fmc(z) based on stellar mass-ratio (MR) selection increases from 6 per cent (z ∼ 0) to 16 per cent (z ∼ 0.8), then turns over at z ∼ 1 and decreases to 7 per cent (z ∼ 3). Instead, if we use a major F160W flux-ratio (FR) selection, we find that fmc(z) increases steadily until z = 3 owing to increasing contamination from minor (MR > 4:1) companions at z > 1. We show that these evolutionary trends are statistically robust to changes in companion proximity. We find disagreements between published results are resolved when selection criteria are closely matched. If we compute merger rates using constant fraction-to-rate conversion factors (Cmerg,pair = 0.6 and Tobs,pair = 0.65 Gyr), we find that MR rates disagree with theoretical predictions at z > 1.5. Instead, if we use an evolving Tobs,pair(z) ∝ (1 + z)-2 from Snyder et al., our MR-based rates agree with theory at 0 < z < 3. Our analysis underscores the need for detailed calibration of Cmerg,pair and Tobs,pair as a function of redshift, mass, and companion selection criteria to better constrain the empirical major merger history.
ABSTRACT Although there has been much progress in understanding how galaxies evolve, we still do not understand how and when they stop forming stars and become quiescent. We address this by applying ...our galaxy spectral energy distribution models, which incorporate physically motivated star formation histories (SFHs) from cosmological simulations, to a sample of quiescent galaxies at . A total of 845 quiescent galaxies with multi-band photometry spanning rest-frame ultraviolet through near-infrared wavelengths are selected from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) data set. We compute median SFHs of these galaxies in bins of stellar mass and redshift. At all redshifts and stellar masses, the median SFHs rise, reach a peak, and then decline to reach quiescence. At high redshift, we find that the rise and decline are fast, as expected, because the universe is young. At low redshift, the duration of these phases depends strongly on stellar mass. Low-mass galaxies ( ) grow on average slowly, take a long time to reach their peak of star formation ( Gyr), and then the declining phase is fast ( Gyr). Conversely, high-mass galaxies ( ) grow on average fast ( Gyr), and, after reaching their peak, decrease the star formation slowly ( ). These findings are consistent with galaxy stellar mass being a driving factor in determining how evolved galaxies are, with high-mass galaxies being the most evolved at any time (i.e., downsizing). The different durations we observe in the declining phases also suggest that low- and high-mass galaxies experience different quenching mechanisms, which operate on different timescales.
We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at in the rest-frame far-ultraviolet (FUV) using Hubble Space Telescope Wide Field Camera 3 broadband imaging in F225W, ...F275W, and F336W. An analysis of 1404 galaxies yields 209 galaxies that host 403 kpc scale clumps. These host galaxies appear to be typical star-forming galaxies, with an average of 2 clumps per galaxy and reaching a maximum of 8 clumps. We measure the photometry of the clumps and determine the mass, age, and star formation rates (SFR) using the spectral energy distribution fitting code FAST. We find that clumps make an average contribution of 19% to the total rest-frame FUV flux of their host galaxy. Individually, clumps contribute a median of 5% to the host galaxy SFR and an average of ∼4% to the host galaxy mass, with total clump contributions to the host galaxy stellar mass ranging widely from lower than 1% up to 93%. Clumps in the outskirts of galaxies are typically younger, with higher SFRs, than clumps in the inner regions. The results are consistent with clump migration theories in which clumps form through violent gravitational instabilities in gas-rich turbulent disks, eventually migrate toward the center of the galaxies, and coalesce into the bulge.
We describe the TFIT software package to measure galaxy photometry using prior information from high‐resolution observations. Our basic methodology is similar in principle but different in detail ...from previous procedures for crowded field photometry. We use the spatial positions and morphologies of objects in an image with higher angular resolution to construct object templates, which are then fitted to a lower resolution image, solving for the object fluxes as free parameters. Using extensive experiments on both simulated and real data, we show that this template‐fitting method measures accurate object photometry to the limiting sensitivity of the image. In this limit, our method derives robust flux upper limits for objects fainter than the limiting image surface brightness. We describe the challenges encountered in applying this technique to real data, and methods to cope with some of them.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, UL, UM, UPUK
PDF
