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We present a new determination of the star-forming main sequence (MS), obtained through stacking 100k K-band-selected galaxies in the far-infrared (FIR) Herschel and James Clerk Maxwell Telescope (JCMT) imaging. By fitting the dust emission curve to the stacked FIR photometry, we derive the IR luminosities (LIR), and hence the star formation rates (SFRs) out to z ≲ 5.7. The functional form of the MS is found, with the linear SFR-M* relation that flattens at high stellar masses and the normalization that increases exponentially with redshift. We derive the corresponding redshift evolution of the specific star formation rate (sSFR) and compare our findings with the recent literature. We find our MS to be exhibiting slightly lower normalization at z ≲ 2 and to flatten at somewhat larger stellar masses at high redshifts. By deriving the relationship between the peak dust temperature (Td) and redshift, where Td increases linearly from ∼20 K at z = 0.5 to ∼50 K at z = 5, we conclude that the apparent inconsistencies in the shapes of the MS are most likely caused by the different dust temperatures assumed when deriving SFRs in the absence of FIR data. Finally, we investigate the derived shape of the star-forming MS by simulating the time evolution of the observed galaxy stellar mass function (GSMF). While the simulated GSMF is in good agreement with the observed one, some inconsistencies persist. In particular, we find the simulated GSMF to be slightly overpredicting the number density of low-mass galaxies at z ≳ 2. [ABSTRACT FROM AUTHOR]

We report ultra-deep, medium-resolution spectroscopic observations for four quiescent galaxies with log |$_{10}(M_*/\mathrm{M_\odot })\gt 11$| at |$3 \lt z \lt 5$|⁠. These data were obtained with JWST NIRSpec as part of the Early eXtragalactic Continuum and Emission Line Science (EXCELS) survey, which we introduce in this work. The first two galaxies are newly selected from PRIMER UDS imaging, both at |$z=4.62$| and separated by 860 pkpc on the sky, within a larger structure for which we confirm several other members. Both formed at |$z\simeq 8-10$|⁠. These systems could plausibly merge by the present day to produce a local massive elliptical galaxy. The other two ultra-massive quiescent galaxies are previously known at |$z=3.99$| and 3.19, with the latter (ZF-UDS-7329) having been the subject of debate as potentially too old and too massive to be accommodated by the |$\Lambda$| -CDM halo-mass function. Both exhibit high stellar metallicities, and for ZF-UDS-7329 we are able to measure the |$\alpha -$| enhancement, obtaining [Mg/Fe] = |$0.42^{+0.19}_{-0.17}$|⁠. We finally evaluate whether these four galaxies are consistent with the |$\Lambda$| -CDM halo-mass function using an extreme value statistics approach. We find that the |$z=4.62$| objects and the |$z=3.19$| object are unlikely within our area under the assumption of standard stellar fractions (⁠|$f_*\simeq 0.1-0.2$|⁠). However, these objects roughly align with the most massive galaxies expected under the assumption of 100 per cent conversion of baryons to stars (⁠|$f_*$| =1). Our results suggest extreme galaxy formation physics during the first billion years, but no conflict with |$\Lambda$| -CDM cosmology. [ABSTRACT FROM AUTHOR]

We present a new determination of the evolving galaxy ultraviolet (UV) luminosity function (LF) over the redshift range |$8.5< z< 15.5$| using a combination of several major Cycle-1 JWST imaging programmes – Public Release IMaging for Extragalactic Research, JWST Advanced Deep Extragalactic Survey, and Next Generation Deep Extragalactic Exploratory Public Survey. This multifield approach yields a total of |$\simeq 370$| arcmin2 of JWST /NIRCam imaging, reaching (5- |$\sigma$|⁠) depths of |$\simeq 30$| AB mag in the deepest regions. We select a sample of 2548 galaxies with a significant probability of lying at high redshift (⁠|$p(z> 8.5)> 0.05$|⁠) to undertake a statistical calculation of the UV LF. Our new measurements span |$\simeq 4$|  mag in UV luminosity at |$z=9-12.5$|⁠ , placing new constraints on both the shape and evolution of the LF at early times. Our measurements yield a new estimate of the early evolution of cosmic star-formation rate density (⁠|$\rho _{\rm {SFR}}$|⁠) confirming the gradual decline deduced from early JWST studies, at least out to |$z \simeq 12$|⁠. Finally we show that the observed early evolution of the galaxy UV LF (and |$\rho _{\rm {SFR}}$|⁠) can be reproduced in a |${\rm \Lambda }$| cold dark matter Universe, with no change in dust properties or star-formation efficiency required out to |$z \simeq 12$|⁠. Instead, a progressive trend towards younger stellar population ages can reproduce the observations, and the typical ages required at |$z \simeq$| 8, 9, 10, and 11 all converge on |$\simeq 380-330$|  Myr after the big bang, indicative of a rapid emergence of early galaxies at |$z \simeq 12 - 13$|⁠. This is consistent with the first indications of a steeper drop-off in |$\rho _{\rm {SFR}}$| we find beyond |$z \simeq 13$|⁠ , possibly reflecting the rapid evolution of the halo mass function at earlier times. [ABSTRACT FROM AUTHOR]

We present determinations of the gas-phase and stellar metallicities of a sample of 65 star-forming galaxies at |$z \simeq 3.5$| using rest-frame far-ultraviolet (FUV) spectroscopy from the VANDELS survey in combination with follow-up rest-frame optical spectroscopy from VLT /KMOS and Keck/MOSFIRE. We infer gas-phase oxygen abundances (⁠|$Z_{\mathrm{g}}$|⁠ ; tracing O/H) via strong optical nebular lines and stellar iron abundances (⁠|$Z_{\star }$|⁠ ; tracing Fe/H) from full spectral fitting to the FUV continuum. Our sample spans the stellar mass range |$8.5 \lt \mathrm{log}(M_{\star }/\mathrm{M}_{\odot }) \lt 10.5$| and shows clear evidence for both a stellar and gas-phase mass-metallicity relation (MZR). We find that our O and Fe abundance estimates both exhibit a similar mass-dependence, such that |$\mathrm{Fe/H}\propto M_{\star }^{0.30\pm 0.11}$| and |$\mathrm{O/H}\propto M_{\star }^{0.32\pm 0.09}$|⁠. At fixed |$M_{\star }$| we find that, relative to their solar values, O abundances are systematically larger than Fe abundances (i.e. α-enhancement). We estimate an average enhancement of |$\mathrm{(O/Fe)} = 2.65 \pm 0.16 \times \mathrm{(O/Fe)_\odot }$| which appears to be independent of |$M_{\star }$|⁠. We employ analytic chemical evolution models to place a constraint on the strength of galactic-level outflows via the mass-outflow factor (⁠|$\eta$|⁠). We show that outflow efficiencies that scale as |$\eta \propto M_{\star }^{-0.32}$| can simultaneously explain the functional form of of the stellar and gas-phase MZR, as well as the degree of α-enhancement at fixed Fe/H. Our results add further evidence to support a picture in which α-enhanced abundance ratios are ubiquitous in high-redshift star-forming galaxies, as expected for young systems whose interstellar medium is primarily enriched by core-collapse supernovae. [ABSTRACT FROM AUTHOR]

We present an analysis of the ultraviolet (UV) continuum slopes (β) for a sample of 172 galaxy candidates at 8 < z phot < 16 selected from a combination of JWST NIRCam imaging and COSMOS/UltraVISTA ground-based near-infrared imaging. Focusing primarily on a new sample of 121 galaxies at 〈 z 〉 ≃ 11 selected from ≃ 320 arcmin2 of public JWST imaging data across 15 independent data sets, we investigate the evolution of β in the galaxy population at z ≥ 9. We find a significant trend between β and redshift, with the inverse-variance weighted mean UV slope evolving from 〈β〉 = −2.17 ± 0.06 at z  = 9.5 to 〈β〉 = −2.59 ± 0.06 at z  = 11.5. Based on a comparison with stellar population models including nebular continuum emission, we find that at z > 10.5 the average UV continuum slope is consistent with the intrinsic blue limit of dust-free stellar populations (βint ≃ −2.6). These results suggest that the moderately dust-reddened galaxy population at z < 10 was essentially unattenuated at z ≃ 11. The extremely blue galaxies being uncovered at z > 10 place important constraints on dust attenuation in galaxies in the early Universe, and imply that the already observed galaxy population is likely supplying an ionizing photon budget capable of maintaining ionized intergalactic medium fractions of ≳ 5 per cent at z ≃ 11. [ABSTRACT FROM AUTHOR]

We investigate the degree of dust obscured star formation in 49 massive (log10(M ⋆/M⊙) > 9) Lyman-break galaxies (LBGs) at z  = 6.5–8 observed as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Reionization Era Bright Emission Line Survey (REBELS) large program. By creating deep stacks of the photometric data and the REBELS ALMA measurements we determine the average rest-frame ultraviolet (UV), optical, and far-infrared (FIR) properties which reveal a significant fraction (f obs = 0.4–0.7) of obscured star formation, consistent with previous studies. From measurements of the rest-frame UV slope, we find that the brightest LBGs at these redshifts show bluer (β ≃ −2.2) colours than expected from an extrapolation of the colour–magnitude relation found at fainter magnitudes. Assuming a modified blackbody spectral energy distribution (SED) in the FIR (with dust temperature of |$T_{\rm d} = 46\, {\rm K}$| and βd = 2.0), we find that the REBELS sources are in agreement with the local 'Calzetti-like' starburst Infrared-excess (IRX)–β relation. By re-analysing the data available for 108 galaxies at z ≃ 4–6 from the ALMA Large Program to Investigate C+ at Early Times (ALPINE) using a consistent methodology and assumed FIR SED, we show that from z ≃ 4–8, massive galaxies selected in the rest-frame UV have no appreciable evolution in their derived IRX–β relation. When comparing the IRX– M ⋆ relation derived from the combined ALPINE and REBELS sample to relations established at z < 4, we find a deficit in the IRX, indicating that at z > 4 the proportion of obscured star formation is lower by a factor of ≳ 3 at a given a M ⋆. Our IRX–β results are in good agreement with the high-redshift predictions of simulations and semi-analytic models for z ≃ 7 galaxies with similar stellar masses and star formation rates. [ABSTRACT FROM AUTHOR]

We present a new determination of the evolving galaxy ultraviolet (UV) luminosity function (LF) over the redshift range 9.5 < z < 12.5 based on a wide-area (>250 arcmin2) data set of JWST NIRCam near-infrared imaging assembled from 13 public JWST surveys. Our relatively large-area search allows us to uncover a sample of 61 robust z > 9.5 candidates detected at ≥8σ, and hence place new constraints on the intermediate-to-bright end of the UV LF. When combined with our previous JWST  + UltraVISTA results, this allows us to measure the form of the LF over a luminosity range corresponding to four magnitudes (M 1500). At these early times we find that the galaxy UV LF is best described by a double power-law function, consistent with results obtained from recent ground-based and early JWST studies at similar redshifts. Our measurements provide further evidence for a relative lack of evolution at the bright-end of the UV LF at z  = 9–11, but do favour a steep faint-end slope (α ≤ −2). The luminosity-weighted integral of our evolving UV LF provides further evidence for a gradual smooth (exponential) decline in co-moving star-formation rate density (ρSFR) at least out to z ≃ 12, with our determination of ρSFR(z  = 11) lying significantly above the predictions of many theoretical models of galaxy evolution. [ABSTRACT FROM AUTHOR]

Recently, intense emission from nebular C III] and C IV emission lines have been observed in galaxies in the epoch of reionization (z > 6) and have been proposed as the prime way of measuring their redshift and studying their stellar populations. These galaxies might represent the best examples of cosmic reionizers, as suggested by recent low-z observations of Lyman continuum emitting galaxies, but it is hard to directly study the production and escape of ionizing photons at such high redshifts. The ESO spectroscopic public survey VANDELS offers the unique opportunity to find rare examples of such galaxies at cosmic noon (z ∼ 3), thanks to the ultra deep observations available. We have selected a sample of 39 galaxies showing C IV emission, whose origin (after a careful comparison to photoionization models) can be ascribed to star formation and not to active galactic nuclei. By using a multiwavelength approach, we determined their physical properties including metallicity and the ionization parameter and compared them to the properties of the parent population to understand what the ingredients are that could characterize the analogs of the cosmic reionizers. We find that C IV emitters are galaxies with high photon production efficiency and there are strong indications that they might also have a large escape fraction: given the visibility of C IV in the epoch of reionization, this could become the best tool to pinpoint the cosmic reioinzers. [ABSTRACT FROM AUTHOR]

We present a spectrophotometric study of a mass-complete sample of quiescent galaxies at 1.0 < z < 1.3 with |$\mathrm{log_{10}}(M_{\star }/\mathrm{{\rm M}_{\odot }}) \ge 10.3$| drawn from the VANDELS survey, exploring the relationship between stellar mass, age, and star-formation history. Within our sample of 114 galaxies, we derive a stellar–mass versus stellar–age relation with a slope of |$1.20^{+0.28}_{-0.27}$| Gyr per decade in stellar mass. When combined with recent literature results, we find evidence that the slope of this relation remains consistent over the redshift interval 0 < z < 4. The galaxies within the VANDELS quiescent sample display a wide range of star-formation histories, with a mean quenching time-scale of 1.4 ± 0.1 Gyr. We also find a large scatter in the quenching time-scales of the VANDELS quiescent galaxies, in agreement with previous evidence that galaxies at z ∼ 1 cease star formation via multiple mechanisms. We then focus on the oldest galaxies in our sample, finding that the number density of galaxies that quenched before z = 3 with stellar masses |$\mathrm{log_{10}}(M_{\star }/\mathrm{{\rm M}_{\odot }}) \ge 10.6$| is |$1.12_{-0.72}^{+1.47} \times 10^{-5} \ \mathrm{Mpc}^{-3}$|⁠. Although uncertain, this estimate is in good agreement with the latest observational results at 3 < z < 4, tentatively suggesting that neither rejuvenation nor merger events are playing a major role in the evolution of the oldest massive quiescent galaxies within the redshift interval 1 < z < 3. [ABSTRACT FROM AUTHOR]

We study the rest-frame ultraviolet (UV) continuum slopes (β) of galaxies at redshifts 8 < z < 16 (〈 z 〉 = 10), using a combination of JWST ERO and ERS NIRCam imaging and ground-based near-infrared imaging of the COSMOS field. The combination of JWST and ground-based imaging provides a wide baseline in both redshift and absolute UV magnitude (−22.6 < M UV < −17.9), sufficient to allow a meaningful comparison to previous results at lower redshift. Using a power-law fitting technique, we find that our full sample (median M UV = −19.3 ± 1.3) returns an inverse-variance weighted mean value of 〈β〉 = −2.10 ± 0.05, with a corresponding median value of β  = −2.29 ± 0.09. These values imply that the UV colours of galaxies at z > 8 are, on average , no bluer than the bluest galaxies in the local universe (e.g. NGC 1705; β  = −2.46). We find evidence for a β − M UV relation, such that brighter UV galaxies display redder UV slopes (⁠|$\rm {d}\beta / \rm {d} M_{\rm UV} = -0.17 \pm 0.05$|⁠). Comparing to results at lower redshift, we find that the slope of our β − M UV relation is consistent with the slope observed at z ≃ 5 and that, at a given M UV, our 8 < z < 16 galaxies are bluer than their z ≃ 5 counterparts, with an inverse-variance weighted mean offset of 〈Δβ〉 = −0.38 ± 0.09. We do not find strong evidence that any objects in our sample display ultra-blue UV continuum slopes (i.e. β ≲ −3) that would require their UV emission to be dominated by ultra-young, dust-free stellar populations with high Lyman-continuum escape fractions. Comparing our results to the predictions of theoretical galaxy formation models, we find that the galaxies in our sample are consistent with the young, metal-poor, and moderately dust-reddened galaxies expected at z > 8. [ABSTRACT FROM AUTHOR]

We reduce and analyse the available JWST ERO and ERS NIRCam imaging (SMACS0723, GLASS, CEERS) in combination with the latest deep ground-based near-infrared imaging in the COSMOS field (provided by UltraVISTA DR5) to produce a new measurement of the evolving galaxy UV luminosity function (LF) over the redshift range z  = 8 − 15. This yields a new estimate of the evolution of UV luminosity density (ρUV), and hence cosmic star formation rate density (ρSFR) out to within <300 Myr of the Big Bang. Our results confirm that the high-redshift LF is best described by a double power law (rather than a Schechter) function up to z ∼ 10, and that the LF and the resulting derived ρUV (and thus ρSFR), continues to decline gradually and steadily up to z ∼ 15 (as anticipated from previous studies which analysed the pre-existing data in a consistent manner to this study). We provide details of the 61 high-redshift galaxy candidates, 47 of which are new, that have enabled this new analysis. Our sample contains 6 galaxies at z ≥ 12, one of which appears to set a new redshift record as an apparently robust galaxy candidate at z ≃ 16.4, the properties of which we therefore consider in detail. The advances presented here emphasize the importance of achieving high dynamic range in studies of early galaxy evolution, and re-affirm the enormous potential of forthcoming larger JWST programmes to transform our understanding of the young Universe. [ABSTRACT FROM AUTHOR]

We present a first-look analysis of the JWST ERO data in the SMACS J0723.3-7327 cluster field. We begin by reporting 10 new spectroscopic redshifts from λobs = 1.8–5.2 μm NIRSpec medium-resolution (R  = λ/Δλ = 1000) data. These are determined via multiple high-SNR emission line detections with five objects at 1 < z < 3 displaying multiple rest-frame near-infrared Hydrogen Paschen lines, and five objects at 5 < z < 9 displaying rest-frame optical Oxygen and Hydrogen Balmer lines. For the five higher-redshift galaxies we extract fluxes in six NIRCam bands spanning λobs = 0.8–5 μm and perform spectral energy distribution fitting in combination with existing HST photometry. The 7 < z < 9 objects exhibit a U-shaped pattern across the F 277 W, F 356 W , and F 444 W bands, indicating a Balmer break seen in emission (Balmer jump) and high-equivalent-width [O  iii ] emission. This indicates an extremely young stellar population with the bulk of the current mass having formed within the past 10 Myr. We report robust stellar masses and mean stellar ages from our spectral fitting with the four z > 6 galaxies exhibiting low-stellar masses from log10 (M */M⊙) = 7.1–8.2, and correspondingly young mean stellar ages of only a few Myr. This work highlights the critical importance of combining large upcoming NIRCam surveys with NIRSpec follow-up to measure the spectroscopic redshifts necessary to robustly constrain physical parameters. [ABSTRACT FROM AUTHOR]

We present a study designed to measure the average Lyman-continuum escape fraction (〈 f esc〉) of star-forming galaxies at z ≃ 3.5. We assemble a sample of 148 galaxies from the VANDELS spectroscopic survey at 3.35 ≤  z spec ≤ 3.95, selected to minimize line-of-sight contamination of their photometry. For this sample, we use ultra-deep, ground-based, U -band imaging and Hubble Space Telescope V -band imaging to robustly measure the distribution of |$\mathcal {R_{\rm obs}}\, =(L_{\rm LyC}/L_{\rm UV})_{\rm obs}$|⁠. We then model the |$\mathcal {R_{\rm obs}}$| distribution as a function of 〈 f esc〉, carefully accounting for attenuation by dust, the intergalactic medium and the circumgalactic medium. A maximum likelihood fit to the |$\mathcal {R_{\rm obs}}$| distribution returns a best-fitting value of |$\langle f_{\rm esc}\rangle =0.07^{+0.02}_{-0.02}$|⁠ , a result confirmed using an alternative Bayesian inference technique (both techniques exclude 〈 f esc〉 = 0.0 at >3σ). By splitting our sample in two, we find evidence that 〈 f esc〉 is positively correlated with Ly α equivalent width (W λ(Ly α)), with high and low W λ(Lyα) subsamples returning values of |$\langle f_{\rm esc}\rangle =0.12^{+0.06}_{-0.04}$| and |$\langle f_{\rm esc} \rangle =0.02^{+0.02}_{-0.01}$|⁠ , respectively. In contrast, we find evidence that 〈 f esc〉 is anticorrelated with intrinsic UV luminosity and UV dust attenuation; with low UV luminosity and dust attenuation subsamples both returning best fits in the range 0.10 ≤ 〈 f esc〉 ≤ 0.22. We do not find a clear correlation between f esc and galaxy stellar mass, suggesting stellar mass is not a primary indicator of f esc. Although larger samples are needed to further explore these trends, our results suggest that it is entirely plausible that the low dust, low-metallicity galaxies found at z ≥ 6 will display the 〈 f esc〉 ≥ 0.1 required to drive reionization. [ABSTRACT FROM AUTHOR]

We study the relationships between stellar mass, size, and age within the quiescent population, using two mass-complete spectroscopic samples with log10(M ⋆/M⊙) > 10.3, taken from VANDELS at 1.0 < z < 1.3, and LEGA-C at 0.6 < z < 0.8. Using robust Dn4000 values, we demonstrate that the well-known 'downsizing' signature is already in place by z ≃ 1.1, with Dn4000 increasing by ≃ 0.1 across a ≃ 1 dex mass interval for both VANDELS and LEGA-C. We then proceed to investigate the evolution of the quiescent galaxy stellar mass–size relation from z ≃ 1.1 to z ≃ 0.7. We find the median size increases by a factor of 1.9 ± 0.1 at log10(M ⋆/M⊙) = 10.5, and see tentative evidence for flattening of the relation, finding slopes of α = 0.72 ± 0.06 and |$\alpha =\, 0.56\pm 0.04$| for VANDELS and LEGA-C, respectively. We finally split our sample into galaxies above and below our fitted mass–size relations, to investigate how size and Dn4000 correlate. For LEGA-C, we see a clear difference, with larger galaxies found to have smaller Dn4000 at fixed stellar mass. Due to the faintness and smaller numbers of the VANDELS sample, we cannot confirm whether a similar relation exists at z ≃ 1.1. We consider whether differences in stellar age or metallicity are most likely to drive this size–Dn4000 relation, finding that any metallicity differences are unlikely to fully explain the observed offset, meaning smaller galaxies must be older than their larger counterparts. We find the observed evolution in size, mass, and Dn4000 across the ≃ 2 Gyr from z ∼ 1.1 to z ∼ 0.7 can be explained by a simple toy model in which VANDELS galaxies evolve passively whilst experiencing a series of minor mergers. [ABSTRACT FROM AUTHOR]

We present deep ALMA dust continuum observations for a sample of luminous (M UV < −22) star-forming galaxies at z ≃ 7. We detect five of the six sources in the far-infrared (FIR), providing key constraints on the obscured star formation rate (SFR) and the infrared-excess-β (IRX–β) relation without the need for stacking. Despite the galaxies showing blue rest-frame ultraviolet (UV) slopes (β ≃ −2) we find that 35–75 per cent of the total SFR is obscured. We find the IRX–β relation derived for these z ≃ 7 sources is consistent with that found for local starburst galaxies. Using our relatively high-resolution (FWHM |$\simeq 0.7\, {\rm arcsec}$|⁠) observations we identify a diversity of dust morphologies in the sample. We find both compact emission that appears offset relative to the unobscured components and extended dust emission that is co-spatial with the rest-frame UV light. In the majority of the sources, we detect strong rest-frame UV colour gradients (with up to Δβ ≃ 0.7–1.4) as probed by the multiband UltraVISTA ground-based data. The observed redder colours are spatially correlated with the location of the FIR detection. Our results show that even in bright Lyman-break galaxies at z ≃ 7 the peak of the star formation is typically hosted by the fainter, redder, regions in the rest-frame UV, which have an obscured fraction of f obs ≥ 0.8. As well as demonstrating the importance of dust obscured star formation within the Epoch of Reionization, these observations provide an exciting taster of the rich spatially resolved data sets that will be obtained from  JWST and high-resolution ALMA follow-up at these redshifts. [ABSTRACT FROM AUTHOR]

We present results from the NIRVANDELS survey on the gas-phase metallicity (Z g, tracing O/H) and stellar metallicity (Z ⋆, tracing Fe/H) of 33 star-forming galaxies at redshifts 2.95 < z < 3.80. Based on a combined analysis of deep optical and near-IR spectra, tracing the rest-frame far-ultraviolet (FUV; 1200–2000 Å) and rest-frame optical (3400–5500 Å), respectively, we present the first simultaneous determination of the stellar and gas-phase mass–metallicity relationships (MZRs) at z ≃ 3.4. In both cases, we find that metallicity increases with increasing stellar mass (M ⋆) and that the power-law slope at M ⋆ ≲ 1010M⊙ of both MZRs scales as |$Z \propto M_{\star }^{0.3}$|⁠. Comparing the stellar and gas-phase MZRs, we present direct evidence for super-solar O/Fe ratios (i.e. α-enhancement) at z > 3, finding (O/Fe) = 2.54 ± 0.38 × (O/Fe)⊙, with no clear dependence on M ⋆. [ABSTRACT FROM AUTHOR]

We present a new determination of the galaxy stellar-mass function (GSMF) over the redshift interval 0.25 ≤ z ≤ 3.75, derived from a combination of ground-based and Hubble Space Telescope (HST) imaging surveys. Based on a near-IR-selected galaxy sample selected over a raw survey area of 3 deg2 and spanning ≥4 dex in stellar mass, we fit the GSMF with both single and double Schechter functions, carefully accounting for Eddington bias to derive both observed and intrinsic parameter values. We find that a double Schechter function is a better fit to the GSMF at all redshifts, although the single and double Schechter function fits are statistically indistinguishable by z  = 3.25. We find no evidence for significant evolution in M ⋆, with the intrinsic value consistent with |$\log _{10}(M^{\star }/\hbox{$\rm \, M_{\odot }$})=10.55\pm {0.1}$| over the full redshift range. Overall, our determination of the GSMF is in good agreement with recent simulation results, although differences persist at the highest stellar masses. Splitting our sample according to location on the UVJ plane, we find that the star-forming GSMF can be adequately described by a single Schechter function over the full redshift range, and has not evolved significantly since z ≃ 2.5. In contrast, both the normalization and the functional form of the passive GSMF evolve dramatically with redshift, switching from a single to a double Schechter function at z ≤ 1.5. As a result, we find that while passive galaxies dominate the integrated stellar-mass density at z ≤ 0.75, they only contribute ≲10 per cent by z ≃ 3. Finally, we provide a simple parametrization that provides an accurate estimate of the GSMF, both observed and intrinsic, at any redshift within the range 0 ≤ z ≤ 4. [ABSTRACT FROM AUTHOR]

We present a sample of 151 massive (M * > 1010 M⊙) quiescent galaxies at 2 < z < 5, based on a sophisticated Bayesian spectral energy distribution fitting analysis of the CANDELS UDS and GOODS-South fields. Our sample includes a robust sub-sample of 61 objects for which we confidently exclude low-redshift and star-forming solutions. We identify 10 robust objects at z > 3, of which 2 are at z > 4. We report formation redshifts, demonstrating that the oldest objects formed at z > 6; however, individual ages from our photometric data have significant uncertainties, typically ∼0.5 Gyr. We demonstrate that the UVJ colours of the quiescent population evolve with redshift at z > 3, becoming bluer and more similar to post-starburst galaxies at lower redshift. Based upon this, we construct a model for the time evolution of quiescent galaxy UVJ colours, concluding that the oldest objects are consistent with forming the bulk of their stellar mass at z  ∼ 6–7 and quenching at z  ∼ 5. We report spectroscopic redshifts for two of our objects at z  = 3.440 and 3.396, which exhibit extremely weak Ly α emission in ultra-deep VANDELS spectra. We calculate star formation rates based on these line fluxes, finding that these galaxies are consistent with our quiescent selection criteria, provided their Ly α escape fractions are >3 and >10 per cent, respectively. We finally report that our highest redshift robust object exhibits a continuum break at λ ∼ 7000 Å in a spectrum from VUDS, consistent with our photometric redshift of |$z_\mathrm{phot}=4.72^{+0.06}_{-0.04}$|⁠. If confirmed as quiescent, this object would be the highest redshift known quiescent galaxy. To obtain stronger constraints on the times of the earliest quenching events, high-SNR spectroscopy must be extended to z  ≳ 3 quiescent objects. [ABSTRACT FROM AUTHOR]

We present the results of a new study investigating the relationship between observed Ly α equivalent width (W λ(Ly α)) and the metallicity of the ionizing stellar population (  Z ⋆) for a sample of 768 star-forming galaxies at 3 ≤ z ≤ 5 drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame W λ(Ly α) across the range |$-58 \,\rm {\mathring{\rm A}} \lesssim$| W λ(Ly α) |$\lesssim 110 \,\rm {\mathring{\rm A}}$|⁠ , we determine   Z ⋆ from full spectral fitting of composite far-ultraviolet spectra and find a clear anticorrelation between W λ(Ly α) and   Z ⋆. Our results indicate that   Z ⋆ decreases by a factor ≳ 3 between the lowest W λ(Ly α) quartile (〈 W λ(Ly α) |$\rangle =-18\,\rm {\mathring{\rm A}}$|⁠) and the highest W λ(Ly α) quartile (〈 W λ(Ly α) |$\rangle =24\,\rm {\mathring{\rm A}}$|⁠). Similarly, galaxies typically defined as Lyman alpha emitters (LAEs; W λ(Ly α) |$\gt 20\,\rm {\mathring{\rm A}}$|⁠) are, on average, metal poor with respect to the non-LAE galaxy population (W λ(Ly α) |$\le 20\,\rm {\mathring{\rm A}}$|⁠) with   Z ⋆non-LAE ≳ 2 ×   Z ⋆LAE. Finally, based on the best-fitting stellar models, we estimate that the increasing strength of the stellar ionizing spectrum towards lower   Z ⋆ is responsible for |${\simeq}15{-}25{{\ \rm per\ cent}}$| of the observed variation in W λ(Ly α) across our sample, with the remaining contribution (⁠|${\simeq}75{-}85{{\ \rm per\ cent}}$|⁠) being due to a decrease in the H  i /dust covering fractions in low-  Z ⋆ galaxies. [ABSTRACT FROM AUTHOR]

We measure the rest-frame ultraviolet (UV) luminosity function (LF) at z ∼ 4 self-consistently over a wide range in absolute magnitude (−27 ≲ M UV ≲ −20). The LF is measured with 46 904 sources selected using a photometric redshift approach over ∼6  |$\, {\rm deg}^2$|  of the combined Cosmological Evolution Survey and XMM–Newton Large-Scale Structure fields. We simultaneously fit for both active galactic nuclei (AGNs) and galaxy LFs using a combination of Schechter or double power law (DPL) functions alongside a single power law for the faint-end slope of the AGN LF. We find a lack of evolution in the shape of the bright end of the Lyman-break galaxy (LBG) component when compared to other studies at z ≃ 5 and evolutionary recipes for the UV LF. Regardless of whether the LBG LF is fit with a Schechter function or DPL, AGNs are found to dominate at M UV < −23.5. We measure a steep faint-end slope of the AGN LF with |$\alpha _{\mathrm{ AGN}} = -2.09^{+0.35}_{-0.38}$| (⁠|$-1.66^{+0.29}_{-0.58}$|⁠) when fit alongside a Schechter function (DPL) for the galaxies. Our results suggest that if AGNs are morphologically selected it results in a bias to lower number densities. Only by considering the full galaxy population over the transition region from AGN to LBG domination can an accurate measurement of the total LFs be attained. [ABSTRACT FROM AUTHOR]

We present a comparative analysis of the properties of active galactic nuclei (AGNs) emitting at radio and X-ray wavelengths. The study is performed on 907 X-ray AGNs and 100 radio AGNs selected on the CDFS and UDS fields and makes use of new and ancillary data available to the VANDELS collaboration. Our results indicate that the mass of the host galaxy is a fundamental quantity that determines the level of AGN activity at the various wavelengths. Indeed, large stellar masses are found to be connected with AGN radio emission, as virtually all radio-active AGNs reside within galaxies of M * > 1010 M⊙. Large stellar masses also seem to favour AGN activity in the X-ray, even though X-ray AGNs present a mass distribution that is more spread out and with a non-negligible tail at M * ≲ 109 M⊙. Stellar mass alone is also observed to play a fundamental role in simultaneous radio and X-ray emission: the percentage of AGNs active at both wavelengths increases from around 1 per cent of all X-ray AGNs residing within hosts of M * < 1011 M⊙ to ∼13 per cent in more massive galaxies. In the case of radio-selected AGNs, such a percentage moves from ∼15 per cent to ∼45 per cent (but up to ∼80 per cent in the deepest fields). Neither cosmic epoch, nor radio luminosity, X-ray luminosity, Eddington ratio or star formation rate of the hosts are found to be connected to an enhanced probability for joint radio + X-ray emission of AGN origin. Furthermore, only a loose relation is observed between X-ray and radio luminosity in those AGNs that are simultaneously active at both frequencies. [ABSTRACT FROM AUTHOR]

We utilize deep near-infrared survey data from the UltraVISTA fourth data release (DR4) and the VIDEO survey, in combination with overlapping optical and  Spitzer data, to search for bright star-forming galaxies at z ≳ 7.5. Using a full photometric redshift fitting analysis applied to the ∼6 |$\, {\rm deg}^2$|  of imaging searched, we find 27 Lyman break galaxies (LBGs), including 20 new sources, with best-fitting photometric redshifts in the range 7.4 < z < 9.1. From this sample, we derive the rest-frame UV luminosity function at z = 8 and z = 9 out to extremely bright UV magnitudes (M UV ≃ −23) for the first time. We find an excess in the number density of bright galaxies in comparison to the typically assumed Schechter functional form derived from fainter samples. Combined with previous studies at lower redshift, our results show that there is little evolution in the number density of very bright (M UV ∼ −23) LBGs between z ≃ 5 and z ≃ 9. The tentative detection of an LBG with best-fitting photometric redshift of z = 10.9 ± 1.0 in our data is consistent with the derived evolution. We show that a double power-law fit with a brightening characteristic magnitude (Δ M */Δ z ≃ −0.5) and a steadily steepening bright-end slope (Δβ/Δ z ≃ −0.5) provides a good description of the z > 5 data over a wide range in absolute UV magnitude (−23 < M UV < −17). We postulate that the observed evolution can be explained by a lack of mass quenching at very high redshifts in combination with increasing dust obscuration within the first |${\sim}1 \, {\rm Gyr}$| of galaxy evolution. [ABSTRACT FROM AUTHOR]

We present a Bayesian full-spectral-fitting analysis of 75 massive (⁠|$M_* \gt 10^{10.3} \, \mathrm{M_\odot }$|⁠) UVJ-selected galaxies at redshifts of 1.0 < z < 1.3, combining extremely deep rest-frame ultraviolet spectroscopy from VANDELS with multiwavelength photometry. By the use of a sophisticated physical plus systematic uncertainties model, constructed within the bagpipes code, we place strong constraints on the star-formation histories (SFHs) of individual objects. We first constrain the stellar mass versus stellar age relationship, finding a steep trend towards earlier average formation time with increasing stellar mass (downsizing) of |$1.48^{+0.34}_{-0.39}$| Gyr per decade in mass, although this shows signs of flattening at |$M_* \gt 10^{11} \, \mathrm{M_\odot }$|⁠. We show that this is consistent with other spectroscopic studies from 0 < z < 2. This relationship places strong constraints on the AGN-feedback models used in cosmological simulations. We demonstrate that, although the relationships predicted by simba and illustristng agree well with observations at z = 0.1, they are too shallow at z = 1, predicting an evolution of ≲0.5 Gyr per decade in mass. Secondly, we consider the connections between green-valley, post-starburst, and quiescent galaxies, using our inferred SFH shapes and the distributions of galaxy physical properties on the UVJ diagram. The majority of our lowest-mass galaxies (⁠|$M_* \sim 10^{10.5} \, \mathrm{M_\odot }$|⁠) are consistent with formation in recent (z < 2), intense starburst events, with time-scales of ≲500 Myr. A second class of objects experience extended star-formation epochs before rapidly quenching, passing through both green-valley and post-starburst phases. The most massive galaxies in our sample are extreme systems: already old by z = 1, they formed at z ∼ 5 and quenched by z = 3. However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity. [ABSTRACT FROM AUTHOR]

We present the results of a study utilizing ultradeep, rest-frame UV, spectroscopy to quantify the relationship between stellar mass and stellar metallicity for 681 star-forming galaxies at 2.5 < z < 5.0 (〈 z 〉 = 3.5 ± 0.6) drawn from the VANDELS survey. Via a comparison with high-resolution stellar population synthesis models, we determine stellar metallicities (Z ∗, here a proxy for the iron abundance) for a set of high signal-to-noise ratio composite spectra formed from subsamples selected by mass and redshift. Across the stellar mass range |$8.5\,\, \lt\,\, \mathrm{log}(\langle M_{\ast } \rangle /\rm {M}_{\odot })\,\, \lt\,\, 10.2$|⁠ , we find a strong correlation between stellar metallicity (Z ∗/Z⊙) and stellar mass, with stellar metallicity monotonically increasing from Z ∗/Z⊙ < 0.09 at |$\langle M_{\ast } \rangle = 3.2 \times 10^{8}\, \rm {M}_{\odot }$| to Z ∗/Z⊙ = 0.27 at |$\langle M_{\ast } \rangle = 1.7 \times 10^{10}\, \rm {M}_{\odot }$|⁠. In contrast, at a given stellar mass, we find no evidence for significant metallicity evolution across the redshift range of our sample. However, comparing our results to the z  = 0 stellar mass–metallicity relation for star-forming galaxies, we find that the 〈 z 〉 = 3.5 relation is consistent with being shifted to lower metallicities by ≃0.6 dex at all stellar masses. Contrasting our derived stellar metallicities with estimates of the gas-phase metallicities of galaxies at similar redshifts and stellar masses, we find evidence for enhanced |$\rm {O}/\rm {Fe}$| ratios in z  ≳ 2.5 star-forming galaxies of the order (O/Fe) ≳ 1.8 × (O/Fe)⊙. Finally, by comparing our results to the predictions of three cosmological simulations, we find that the 〈 z 〉 = 3.5 stellar mass–metallicity relation is consistent with current predictions for how outflow strength scales with galaxy stellar mass. This conclusion is supported by an analysis of one-zone analytic chemical evolution models, and suggests that the mass-loading parameter (⁠|$\eta =\dot{M}_{\mathrm{outflow}}/M_{\ast }$|⁠) scales as |$\eta \propto M_{\ast }^{\beta }$| with β ≃ −0.4. [ABSTRACT FROM AUTHOR]

We present a new analysis of the potential power of deep, near-infrared, imaging surveys with the James Webb Space Telescope (JWST) to improve our knowledge of galaxy evolution. In this work we properly simulate what can be achieved with realistic survey strategies, and utilize rigorous signal-to-noise ratio calculations to calculate the resulting posterior constraints on the physical properties of galaxies. We explore a broad range of assumed input galaxy types (>20 000 models, including extremely dusty objects) across a wide redshift range (out to z  ≃ 12), while at the same time considering a realistic mix of galaxy properties based on our current knowledge of the evolving population (as quantified through the Empirical Galaxy Generator). While our main focus is on imaging surveys with NIRCam, spanning |$\lambda _{\mathrm{ obs}} = 0.8\!-\!5.0\, \mu$| m, an important goal of this work is to quantify the impact/added-value of: (i) parallel imaging observations with MIRI at longer wavelengths, and (ii) deeper supporting optical/UV imaging with HST (potentially prior to JWST launch) in maximizing the power and robustness of a major extragalactic NIRCam survey. We show that MIRI parallel 7.7- |$\mu$| m imaging is of most value for better constraining the redshifts and stellar masses of the dustiest (AV > 3) galaxies, while deep B -band imaging (reaching ≃ 28.5 AB mag) with ACS on HST is vital for determining the redshifts of the large numbers of faint/low-mass, z < 5 galaxies that will be detected in a deep JWST NIRCam survey. [ABSTRACT FROM AUTHOR]

We present Atacama Large Millimeter/Submillimeter Array observations of the rest-frame far-infrared (FIR) dust continuum emission of six bright Lyman-break galaxies (LBGs) at |$z$| ≃ 7. One LBG is detected (5.2σ at peak emission), whilst the others remain individually undetected at the 3σ level. The average FIR luminosity of the sample is found to be |$L_{\rm FIR} \simeq 2 \times 10^{11}\, {\rm L}_{\odot }$|⁠, corresponding to an obscured star formation rate (SFR) that is comparable to that inferred from the unobscured UV emission. In comparison to the infrared excess (IRX |$\, =L_{\rm FIR}/L_{\rm UV}$|⁠)–β relation, our results are consistent with a Calzetti-like attenuation law (assuming a dust temperature of T = 40–50 K). We find a physical offset of |$3\, {\rm kpc}$| between the dust continuum emission and the rest-frame UV light probed by Hubble Space Telescope imaging for galaxy ID65666 at |$z=7.17^{+0.09}_{-0.06}$|⁠. The offset is suggestive of an inhomogeneous dust distribution, where 75 per cent of the total star formation activity (SFR |$\, \simeq 70\, {\rm M}_{\odot }/{\rm yr}$|⁠) of the galaxy is completely obscured. Our results provide direct evidence that dust obscuration plays a key role in shaping the bright end of the observed rest-frame UV luminosity function at |$z$| ≃ 7, in agreement with cosmological galaxy formation simulations. The existence of a heavily obscured component of galaxy ID65666 indicates that dusty star-forming regions, or even entire galaxies, that are 'UV dark' are significant even in the |$z$| ≃ 7 galaxy population. [ABSTRACT FROM AUTHOR]

We present Bayesian Analysis of Galaxies for Physical Inference and Parameter EStimation, or bagpipes, a new python tool that can be used to rapidly generate complex model galaxy spectra and to fit these to arbitrary combinations of spectroscopic and photometric data using the multinest nested sampling algorithm. We extensively test our ability to recover realistic star formation histories (SFHs) by fitting mock observations of quiescent galaxies from the mufasa simulation. We then perform a detailed analysis of the SFHs of a sample of 9289 quiescent galaxies from UltraVISTA with stellar masses, M * > 1010 M⊙ and redshifts 0.25 < |$z$| < 3.75. The majority of our sample exhibit SFHs that rise gradually then quench relatively rapidly over 1−2 Gyr. This behaviour is consistent with recent cosmological hydrodynamic simulations, where AGN-driven feedback in the low-accretion (jet) mode is the dominant quenching mechanism. At |$z$| > 1, we also find a class of objects with SFHs that rise and fall very rapidly, with quenching time-scales of <1 Gyr, consistent with quasar-mode AGN feedback. Finally, at |$z$| < 1 we find a population with SFHs which quench more slowly than they rise, over >3 Gyr, which we speculate to be the result of diminishing overall cosmic gas supply. We confirm the mass-accelerated evolution (downsizing) trend, and a trend towards more rapid quenching at higher stellar masses. However, our results suggest that the latter is a natural consequence of mass-accelerated evolution, rather than a change in quenching physics with stellar mass. We find 61 ± 8 per cent of |$z$| > 1.5 massive-quenched galaxies undergo significant further evolution by |$z$|  = 0.5. bagpipes is available at bagpipes.readthedocs.io. [ABSTRACT FROM AUTHOR]

We use a sample of 4209 Lyman-break galaxies (LBGs) at z ≃ 3, 4, and 5 in the UKIRT Infrared Deep Sky Survey Ultra Deep Survey field to investigate the relationship between the observed slope of the stellar continuum emission in the ultraviolet, β, and the thermal dust emission, as quantified via the so-called ‘infrared excess’ (IRX ≡ L IR/ L UV). Through a stacking analysis, we directly measure the 850- $$\mu$$ m flux density of LBGs in our deep (0.9 mJy) James Clerk Maxwell Telescope SCUBA-2 850- $${\rm \mu m}$$ map as well as deep public Herschel /SPIRE 250-, 350-, and 500- $${\rm \mu m}$$ imaging. We establish functional forms for the IRX–β relation to z ∼ 5, confirming that there is no significant redshift evolution of the relation, and that the resulting average IRX–β curve is consistent with a Calzetti-like attenuation law. Comparing our results with recent works in the literature, we confirm that discrepancies in the slope of the IRX–β relation are driven by biases in the methodology used to determine the ultraviolet slopes. Consistent results are found when IRX–β is evaluated by stacking in bins of stellar mass, and we argue that the near-linear IRX– M ⋆ relationship is a better proxy for correcting observed ultraviolet luminosities to total star formation rates, provided an accurate handle on M ⋆ and also gives clues as to the physical driver of the role of dust-obscured star formation in high-redshift galaxies. [ABSTRACT FROM AUTHOR]

We present the results of a new study of dust attenuation at redshifts 3 <  z  < 4 based on a sample of 236 star-forming galaxies from the VANDELS spectroscopic survey. Motivated by results from the First Billion Years (FiBY) simulation project, we argue that the intrinsic spectral energy distributions (SEDs) of star-forming galaxies at these redshifts have a self-similar shape across the mass range 8.2 ≤ log (M⋆/M⊙) ≤ 10.6 probed by our sample. Using FiBY data, we construct a set of intrinsic SED templates which incorporate both detailed star formation and chemical abundance histories, and a variety of stellar population synthesis (SPS) model assumptions. With this set of intrinsic SEDs, we present a novel approach for directly recovering the shape and normalization of the dust attenuation curve. We find, across all of the intrinsic templates considered, that the average attenuation curve for star-forming galaxies at z ≃ 3.5 is similar in shape to the commonly adopted Calzetti starburst law, with an average total-to-selective attenuation ratio of RV  = 4.18 ± 0.29. In contrast, we find that an average attenuation curve as steep as the SMC extinction law is strongly disfavoured. We show that the optical attenuation (AV) versus stellar mass (M ⋆) relation predicted using our method is consistent with recent ALMA observations of galaxies at 2 <  z  < 3 in the Hubble Ultra Deep Field (HUDF), as well as empirical AV  −  M ⋆ relations predicted by a Calzetti-like law. In fact, our results, combined with other literature data, suggest that the AV – M ⋆ relation does not evolve over the redshift range 0 <  z  < 5, at least for galaxies with log(M ⋆/M⊙) ≳ 9.5. Finally, we present tentative evidence which suggests that the attenuation curve may become steeper at lower masses log(M ⋆/M⊙) ≲ 9.0. [ABSTRACT FROM AUTHOR]

We present the results of a new study of the relationship between infrared excess (IRX ≡ L IR/ L UV), ultraviolet (UV) spectral slope (β) and stellar mass at redshifts 2 <  z  < 3, based on a deep Atacama Large Millimeter Array (ALMA) 1.3-mm continuum mosaic of the Hubble Ultra Deep Field. Excluding the most heavily obscured sources, we use a stacking analysis to show that z ≃ 2.5 star-forming galaxies in the mass range |$9.25\le \log (M_{\ast }/\rm M_{{\odot }}) \le 10.75$| are fully consistent with the IRX–β relation expected for a relatively grey attenuation curve, similar to the commonly adopted Calzetti law. Based on a large, mass-complete sample of 2 ≤ z ≤ 3 star-forming galaxies drawn from multiple surveys, we proceed to derive a new empirical relationship between β and stellar mass, making it possible to predict UV attenuation (A 1600) and IRX as a function of stellar mass, for any assumed attenuation law. Once again, we find that z ≃ 2.5 star-forming galaxies follow A 1600– M * and IRX– M * relations consistent with a relatively grey attenuation law, and find no compelling evidence that star-forming galaxies at this epoch follow a reddening law as steep as the Small Magellanic Cloud (SMC) extinction curve. In fact, we use a simple simulation to demonstrate that previous determinations of the IRX–β relation may have been biased towards low values of IRX at red values of β, mimicking the signature expected for an SMC-like dust law. We show that this provides a plausible mechanism for reconciling apparently contradictory results in the literature and that, based on typical measurement uncertainties, stellar mass provides a cleaner prediction of UV attenuation than β. Although the situation at lower stellar masses remains uncertain, we conclude that for 2 <  z  < 3 star-forming galaxies with |$\log (M_{\ast }/\rm M_{{\odot }}) \ge 9.75$|⁠, both the IRX–β and IRX– M * relations are well described by a Calzetti-like attenuation law. [ABSTRACT FROM AUTHOR]