ABSTRACT
In this paper, we discuss measurements of the stellar population and star-forming properties for 43 spectroscopically confirmed publicly available high-redshift z > 7 JWST galaxies in the ...JADES and CEERS observational programs. We carry out a thorough study investigating the relationship between spectroscopic features and photometrically derived ones, including from spectral energy distribution (SED) fitting of models, as well as morphological and structural properties. We find that the star formation rates (SFRs) measured from H β line emission are higher than those estimated from Bayesian SED fitting and ultraviolet (UV) luminosity, with ratios SFRH β/SFRUV ranging from ∼2 to 13. This is a sign that the star formation history is consistently rising given the time-scales of H β versus UV star formation probes. In addition, we investigate how well equivalent widths (EWs) of H β λ4861, O iii λ4959, and O iii λ5007 can be measured from photometry, finding that, on average, the EW derived from photometric excesses in filters is 30 per cent smaller than the direct spectroscopic measurement. We also discover that a stack of the line emitting galaxies shows a distinct morphology after subtracting imaging that contains only the continuum. This gives us a first view of the line or ionized gas emission from z > 7 galaxies, demonstrating that this material has a similar distribution, statistically, as the continuum. We also compare the derived SFRs and stellar masses for both parametric and non-parametric star formation histories, where we find that 35 per cent of our sample formed at least 30 per cent of their stellar mass in recent (<10 Myr) starburst events.
Abstract
We present early results regarding the morphological and structural properties of galaxies seen with the James Webb Space Telescope (JWST) at
z
> 3 in the Early Release Observations toward ...the SMACS 0723 cluster field. Using JWST we investigate, for the first time, the optical morphologies of a significant number of
z
> 3 galaxies with accurate photometric redshifts in this field to determine the form of galaxy structure in the relatively early universe. We use visual morphologies and M
orfometryka
measures to perform quantitative morphology measurements, both parametric with light profile fitting (Sérsic indices) and nonparametric (concentration, asymmetry, and smoothness (CAS) values). Using these, we measure the relative fraction of disk, spheroidal, and peculiar galaxies at 3 <
z
< 8. We discover the surprising result that at
z
> 1.5 disk galaxies dominate the overall fraction of morphologies, with a factor of ∼10 relative higher number of disk galaxies than seen by the Hubble Space Telescope at these redshifts. Our visual morphological estimates of galaxies align closely with their locations in CAS parameter space and their Sérsic indices.
We present Hubble Space Telescope WFC3-IR imaging in the fields of six apparently bright dusty star-forming galaxies (DSFGs) at z = 2-4 identified by their rest-frame far-infrared colors using the ...Planck and Herschel space facilities. We detect near-infrared counterparts for all six submillimeter sources, allowing us to undertake strong-lensing analyses. One field in particular stands out for its prominent giant arcs, PLCK G165.7+67.0 (G165). After combining the color and morphological information, we identify 11 sets of image multiplicities in this one field. We construct a strong-lensing model constrained by this lensing evidence, which uncovers a bimodal spatial mass distribution, and from which we measure a mass of (2.6 0.11) × 1014 M within ∼250 kpc. The bright (S350 750 mJy) DSFG appears as two images: a giant arc with a spatial extent of that is merging with the critical curve, and a lower-magnification counterimage that is detected in our new longer-wavelength ground- and space-based imaging data. Using our ground-based spectroscopy, we calculate a dynamical mass of M to the same fixed radius, although this value may be inflated relative to the true value if the velocity distribution is enhanced in the line-of-sight direction. We suggest that the bimodal mass taken in combination with the weak X-ray flux and low SZ decrement may be explained as a pre-merger for which the intracluster gas is diluted along the line of sight, while the integrated surface mass density is supercritical to strong-lensing effects.
We present a study on the stellar mass growth of the progenitors of local massive galaxies with a variety of number density selections with n ≤ 1 × 10−4 Mpc−3 (corresponding to M
* = 1011.24 M⊙ at ...z = 0.3) in the redshift range 0.3 < z < 3.0. We select the progenitors of massive galaxies using a constant number density selection, and one which is adjusted to account for major mergers. We find that the progenitors of massive galaxies grow by a factor of 4 in total stellar mass over this redshift range. On average the stellar mass added via the processes of star formation, major and minor mergers account for 24 ± 8, 17 ± 15 and 34 ± 14 per cent, respectively, of the total galaxy stellar mass at z = 0.3. Therefore 51 ± 20 per cent of the total stellar mass in massive galaxies at z = 0.3 is created externally to their z = 3 progenitors. We explore the implication of these results on the cold gas accretion rate and size evolution of the progenitors of most massive galaxies over the same redshift range. We find an average gas accretion rate of ∼66 ± 32 M⊙ yr−1 over the redshift range of 1.5 < z < 3.0. We find that the size evolution of a galaxy sample selected this way is on average lower than the findings of other investigations.
Understanding the role of mergers in galaxy formation is one of the most outstanding problems in extragalactic astronomy. While we now have an idea for how the merger fraction evolves at redshifts z ...< 3, converting this merger fraction into merger rates, and therefore how many mergers an average galaxy undergoes during its history, is still uncertain. The main reason for this is that the inferred number of mergers depends highly upon the time-scale observational methods are sensitive for finding ongoing or past mergers. While there are several theoretical and model-based estimates of merger times, there is currently no empirical measure of this time-scale. We present the first observationally based measurement of merger times utilizing the observed decline in the galaxy major merger fraction at z < 1.2 based on >20 000 galaxies in the Extended Groth Strip Survey and Cosmic Evolution Survey. Using a new methodology described in this Letter, we are able to determine how long a galaxy remains identifiable as a merging system within the CAS system. We find a maximum CAS major merger time-scale of 1.1 ± 0.3 Gyr at z < 1.2, and a most likely CAS merger time-scale of 0.6 ± 0.3 Gyr, in good agreement with results from N-body simulations. Utilizing this time-scale, we are able to measure the number of major mergers galaxies with masses M* > 1010 M⊙ undergo at z < 1.2, with a total number Nm= 0.90+0.44−0.23. We further show that this time-scale is inconsistent with a star formation origin for ultrahigh asymmetries, thereby providing further evidence that structural methods are able to locate mostly merging galaxies.
Abstract
Being able to distinguish between galaxies that have recently undergone major-merger events, or are experiencing intense star formation, is crucial for making progress in our understanding ...of the formation and evolution of galaxies. As such, we have developed a machine-learning framework based on a convolutional neural network to separate star-forming galaxies from post-mergers using a data set of 160,000 simulated images from IllustrisTNG100 that resemble observed deep imaging of galaxies with Hubble. We improve upon previous methods of machine learning with imaging by developing a new approach to deal with the complexities of contamination from neighboring sources in crowded fields and define a quality control limit based on overlapping sources and background flux. Our pipeline successfully separates post-mergers from star-forming galaxies in IllustrisTNG 80% of the time, which is an improvement by at least 25% in comparison to a classification using the asymmetry (
A
) of the galaxy. Compared with measured Sérsic profiles, we show that star-forming galaxies in the CANDELS fields are predominantly disk-dominated systems while post-mergers show distributions of transitioning disks to bulge-dominated galaxies. With these new measurements, we trace the rate of post-mergers among asymmetric galaxies in the universe, finding an increase from 20% at
z
= 0.5 to 50% at
z
= 2. Additionally, we do not find strong evidence that the scattering above the star-forming main sequence can be attributed to major post-mergers. Finally, we use our new approach to update our previous measurements of galaxy merger rates
=
0.022
±
0.006
×
(
1
+
z
)
2.71
±
0.31
.
In this paper we present a detailed study of the structures and morphologies of a sample of 1188 massive galaxies with M
* ≥ 1010 M between redshifts z = 1 and 3 within the Ultra Deep Survey (UDS) ...region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Using this sample we determine how galaxy structure and morphology evolve with time, and investigate the nature of galaxy structure at high redshift. We visually classify our sample into discs, ellipticals and peculiar systems and correct for redshift effects on these classifications through simulations. We find significant evolution in the fractions of galaxies at a given visual classification as a function of redshift. The peculiar population is dominant at z > 2 with a substantial spheroid population, and a negligible disc population. We compute the transition redshift, z
trans, where the combined fraction of spheroidal and disc galaxies is equal to that of the peculiar population, as z
trans = 1.86 ± 0.62 for galaxies in our stellar mass range. We find that this transition changes as a function of stellar mass, with Hubble-type galaxies becoming dominant at higher redshifts for higher mass galaxies (z
trans = 2.22 ± 0.82), than for the lower mass galaxies (z
trans = 1.73 ± 0.57). Higher mass galaxies become morphologically settled before their lower mass counterparts, a form of morphological downsizing. We furthermore compare our visual classifications with the Sérsic index, the concentration, asymmetry and clumpiness (CAS) parameters, star formation rate and rest-frame U − B colour. We find links between the colour of a galaxy, its star formation rate and how extended or peculiar it appears. Finally, we discuss the negligible z > 2 disc fraction based on visual morphologies and speculate that this is an effect of forming disc appearing peculiar through processes such as violent disc instabilities or mergers. We conclude that to properly define and measure high-redshift morphology and structure a new and more exact classification scheme is needed.
We present our analysis of the Lyman continuum (LyC) emission and escape fraction of 111 spectroscopically verified galaxies with and without active galactic nuclei (AGN) from 2.26 < z < 4.3. We ...extended our ERS sample from Smith et al. with 64 galaxies in the GOODS North and South fields using WFC3/UVIS F225W, F275W, and F336W mosaics we independently drizzled using the HDUV, CANDELS, and UVUDF data. Among the 17 AGN from the 111 galaxies, one provided a LyC detection in F275W at = 23.19 mag (signal-to-noise ratio, S/N, 133) and GALEX NUV at = 23.77 mag (S/N 13). We simultaneously fit SDSS and Chandra spectra of this AGN to an accretion disk and Comptonization model, and find values of and . For the remaining 110 galaxies, we stack image cutouts that capture their LyC emission using the F225W, F275W, and F336W data of the GOODS and ERS samples, and both combined, as well as subsamples of galaxies with and without AGN, and all galaxies. We find the stack of 17 AGN dominate the LyC production from 2.3-4.3 by a factor of ∼10 compared to all 94 galaxies without AGN. While the IGM of the early universe may have been reionized mostly by massive stars, there is evidence that a significant portion of the ionizing energy came from AGN.
Abstract
We use the energy-balance code magphys to determine stellar and dust masses, and dust corrected star formation rates for over 200 000 GAMA galaxies, 170 000 G10-COSMOS galaxies, and 200 000 ...3D-HST galaxies. Our values agree well with previously reported measurements and constitute a representative and homogeneous data set spanning a broad range in stellar-mass (108–1012 M⊙), dust-mass (106–109 M⊙), and star formation rates (0.01–100 M⊙yr−1), and over a broad redshift range (0.0 < z < 5.0). We combine these data to measure the cosmic star formation history (CSFH), the stellar-mass density (SMD), and the dust-mass density (DMD) over a 12 Gyr timeline. The data mostly agree with previous estimates, where they exist, and provide a quasi-homogeneous data set using consistent mass and star formation estimators with consistent underlying assumptions over the full time range. As a consequence our formal errors are significantly reduced when compared to the historic literature. Integrating our CSFH we precisely reproduce the SMD
with an interstellar medium replenishment factor of 0.50 ± 0.07, consistent with our choice of Chabrier initial mass function plus some modest amount of stripped stellar mass. Exploring the cosmic dust density evolution, we find a gradual increase in dust density with lookback time. We build a simple phenomenological model from the CSFH to account for the dust-mass evolution, and infer two key conclusions: (1) For every unit of stellar mass which is formed 0.0065–0.004 units of dust mass is also formed. (2) Over the history of the Universe approximately 90–95 per cent of all dust formed has been destroyed and/or ejected.
Evolutionary studies that compare galaxy structure as a function of redshift are complicated by the fact that any particular galaxy's appearance depends in part on the rest-frame wavelength of the ...observation. This leads to the necessity for a "morphological k-correction" between different passbands, especially when comparing the rest-frame optical or infrared (IR) to the ultraviolet (UV). This is of particular concern for high-redshift studies that are conducted in the rest-frame UV. We investigate the effects of this "bandpass shifting" out of the UV by quantifying nearby galaxy structure via concentration, asymmetry, and clumpiness (CAS) parameters. For this study we combine panchromatic data from the UV through the near-IR with Galaxy Evolution Explorer (GALEX) data of 2073 nearby galaxies in the "near-UV" (NUV; ∼230 nm) and 1127 in the "far-UV" (FUV; ∼150 nm), providing the largest study of this kind in the mid- to far-UV. We find a relationship between the CAS parameters and observed rest-frame wavelength that make galaxies appear more late-type at shorter wavelengths, particularly in the UV. The effect is strongest for E/S0 galaxies in the far-UV, which have concentrations and asymmetries that more closely resemble those of spiral and peculiar/merging galaxies in the optical. This may be explained by extended disks containing recent star formation. Here, we also release the CAS values of the galaxies imaged in GALEX NUV and FUV for use in comparisons with deep Hubble Space Telescope imaging and the James Webb Space Telescope in the future.
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