ALMA observations have revealed the presence of dust in the first generations
of galaxies in the Universe. However, the dust temperature $T_d$ remains mostly
unconstrained due to the few available ...FIR continuum data at redshift $z>5$.
This introduces large uncertainties in several properties of high-$z$ galaxies,
namely their dust masses, infrared luminosities, and obscured fraction of star
formation. Using a new method based on simultaneous CII 158$\mu$m line and
underlying dust continuum measurements, we derive $T_ d$ in the continuum and
CII detected $z\approx 7$ galaxies in the ALMA Large Project REBELS sample.
We find $39\ \mathrm{K} < T_d < 58\ \mathrm{K}$, and dust masses in the narrow
range $M_d = (0.9-3.6)\times 10^7 M_{\odot}$. These results allow us to extend
for the first time the reported $T_d(z)$ relation into the Epoch of
Reionization. We produce a new physical model that explains the increasing $T_
d(z)$ trend with the decrease of gas depletion time,
$t_{dep}=M_g/\mathrm{SFR}$, induced by the higher cosmological accretion rate
at early times; this hypothesis yields $T_d \propto (1+z)^{0.4}$. The model
also explains the observed $T_d$ scatter at a fixed redshift. We find that dust
is warmer in obscured sources, as a larger obscuration results in more
efficient dust heating. For UV-transparent (obscured) galaxies, $T_d$ only
depends on the gas column density (metallicity), $T_d \propto N_H^{1/6}$ ($T_d
\propto Z^{-1/6}$). REBELS galaxies are on average relatively transparent, with
effective gas column densities around $N_H \simeq (0.03-1)\times 10^{21}
\mathrm{cm}^{-2}$. We predict that other high-$z$ galaxies (e.g. MACS0416-Y1,
A2744-YD4), with estimated $T_d \gg 60$ K, are significantly obscured,
low-metallicity systems. In fact $T_d$ is higher in metal-poor systems due to
their smaller dust content, which for fixed $L_{ IR}$ results in warmer
temperatures.
We present the multi-wavelength counterparts of 850-$\mu$m selected
submillimetre sources over a 2-deg$^2$ field centred on the North Ecliptic
Pole. In order to overcome the large beam size (15 ...arcsec) of the 850-$\mu$m
images, deep optical to near-infrared (NIR) photometric data and
arcsecond-resolution 20-cm images are used to identify counterparts of
submillimetre sources. Among 647 sources, we identify 514 reliable counterparts
for 449 sources (69 per cent in number), based either on probabilities of
chance associations calculated from positional offsets or offsets combined with
the optical-to-NIR colours. In the radio imaging, the fraction of 850-$\mu$m
sources having multiple counterparts is 7 per cent. The photometric redshift,
infrared luminosity, stellar mass, star-formation rate (SFR), and the AGN
contribution to the total infrared luminosity of the identified counterparts
are investigated through spectral energy distribution fitting. The SMGs are
infrared-luminous galaxies at an average $\langle z\rangle=2.5$ with
$\mathrm{log}_{10} (L_\mathrm{IR}/\mathrm{L}_\odot)=11.5-13.5$, with a mean
stellar mass of $\mathrm{log}_{10} (M_\mathrm{star}/\mathrm{M}_\odot)=10.90$
and SFR of $\mathrm{log}_{10} (\mathrm{SFR/M_\odot\,yr^{-1}})=2.34$. The SMGs
show twice as large SFR as galaxies on the star-forming main sequence, and
about 40 per cent of the SMGs are classified as objects with bursty star
formation. At $z\ge4$, the contribution of AGN luminosity to total luminosity
for most SMGs is larger than 30 per cent. The FIR-to-radio correlation
coefficient of SMGs is consistent with that of main-sequence galaxies at
$z\simeq2$.
We present the average CII $158\,\rm{\mu m}$ emission line sizes of
UV-bright star-forming galaxies at $z\sim7$. Our results are derived from a
stacking analysis of CII $158\,\rm{\mu m}$ emission ...lines and dust continua
observed by ALMA, taking advantage of the large program Reionization Era Bright
Emission Line Survey (REBELS). We find that the average CII emission at
$z\sim7$ has an effective radius $r_e$ of $2.2\pm0.2\,\rm{kpc}$. It is
$\gtrsim2\times$ larger than the dust continuum and the rest-frame UV emission,
in agreement with recently reported measurements for $z\lesssim6$ galaxies.
Additionally, we compared the average CII size with $4<z<6$ galaxies observed
by the ALMA Large Program to INvestigate CII at Early times (ALPINE). By
analysing CII sizes of $4<z<6$ galaxies in two redshift bins, we find an
average CII size of $r_{\rm e}=2.2\pm0.2\,\rm{kpc}$ and $r_{\rm
e}=2.5\pm0.2\,\rm{kpc}$ for $z\sim5.5$ and $z\sim4.5$ galaxies, respectively.
These measurements show that star-forming galaxies, on average, show no
evolution in the size of the CII $158\,{\rm \mu m}$ emitting regions at
redshift between $z\sim7$ and $z\sim4$. This finding suggest that the
star-forming galaxies could be morphologically dominated by gas over a wide
redshift range.
We present the first detailed analysis of three extragalactic fields (IRAC Dark Field, ELAIS-N1, ADF-S) observed by the infrared satellite, AKARI, using an optimised data analysis toolkit ...specifically for the processing of extragalactic point sources. The InfraRed Camera (IRC) on AKARI complements the Spitzer space telescope via its comprehensive coverage between 8-24 microns filling the gap between the Spitzer IRAC and MIPS instruments. Source counts in the AKARI bands at 3.2, 4.1, 7, 11, 15 and 18 microns are presented. At near-infrared wavelengths, our source counts are consistent with counts made in other AKARI fields and in general with Spitzer/IRAC (except at 3.2 microns where our counts lie above). In the mid-infrared (11 - 18 microns) we find our counts are consistent with both previous surveys by AKARI and the Spitzer peak-up imaging survey with the InfraRed Spectrograph (IRS). Using our counts to constrain contemporary evolutionary models we find that although the models and counts are in agreement at mid-infrared wavelengths there are inconsistencies at wavelengths shortward of 7 microns, suggesting either a problem with stellar subtraction or indicating the need for refinement of the stellar population models. We have also investigated the AKARI/IRC filters, and find an AGN selection criteria out to \(z<2\) on the basis of AKARI 4.1, 11, 15 and 18 microns colours.
Deep images and near-IR spectra of galaxies in the field of the lensing cluster SMACS J0723.3-7327 were recently taken in the Early Release Observations program of JWST. Among these, two NIRSpec ...spectra of galaxies at \(z=7.7\) and one at \(z=8.5\) were obtained, revealing for the first time rest-frame optical emission line spectra of galaxies in the epoch of reionization, including the detection of the importantOIII4363 auroral line (see JWST PR 2022-035). We present an analysis of the emission line properties of these galaxies, finding that these galaxies have a high excitation (as indicated by high ratios of OIII/OII, NeIII/OII), strong OIII4363/H\(\gamma\), high equivalent widths, and other properties which are typical of low-metallicity star-forming galaxies. Using the direct method we determine oxygen abundances of \(12+\log(O/H)=7.9\) in two \(z=7.7\) galaxies, and a lower metallicity of \(12+\log(O/H)\approx 7.4-7.5\) in the \(z=8.5\) galaxy using different strong line methods. More accurate metallicity determinations will require better data. With stellar masses estimated from SED fits, we find that the three galaxies lie close to or below the \(z \sim 2\) mass-metallicity relation. Overall, these first galaxy spectra at \(z \sim 8\) show a strong resemblance of the emission lines properties of galaxies in the epoch of reionization with those of relatively rare local analogues previously studied from the SDSS. Clearly, the first JWST observations demonstrate already the incredible power of spectroscopy to reveal properties of galaxies in the early Universe.
Over the past decades, rest-frame ultraviolet (UV) observations have provided large samples of UV luminous galaxies at redshift (z) greater than 6, during the so-called epoch of reionization. While a ...few of these UV identified galaxies revealed significant dust reservoirs, very heavily dust-obscured sources at these early times have remained elusive. They are limited to a rare population of extreme starburst galaxies, and companions of rare quasars. These studies conclude that the contribution of dust-obscured galaxies to the cosmic star formation rate density at \(z>6\) is sub-dominant. Recent ALMA and Spitzer observations have identified a more abundant, less extreme population of obscured galaxies at \(z=3-6\). However, this population has not been confirmed in the reionization epoch so far. Here, we report the discovery of two dust-obscured star forming galaxies at \(z=6.6813\pm0.0005\) and \(z=7.3521\pm0.0005\). These objects are not detected in existing rest-frame UV data, and were only discovered through their far-infrared CII lines and dust continuum emission as companions to typical UV-luminous galaxies at the same redshift. The two galaxies exhibit lower infrared luminosities and star-formation rates than extreme starbursts, in line with typical star-forming galaxies at \(z\sim7\). This population of heavily dust-obscured galaxies appears to contribute 10-25 per cent to the \(z>6\) cosmic star formation rate density.
Dusty high-z galaxies are extreme objects with high star formation rates (SFRs) and luminosities. Characterising the properties of this population and analysing their evolution over cosmic time is ...key to understanding galaxy evolution in the early Universe. We select a sample of high-z dusty star-forming galaxies (DSFGs) and evaluate their position on the main sequence (MS) of star-forming galaxies, the well-known correlation between stellar mass and SFR. We aim to understand the causes of their high star formation and quantify the percentage of DSFGs that lie above the MS. We adopted a multi-wavelength approach with data from optical to submillimetre wavelengths from surveys at the North Ecliptic Pole (NEP) to study a submillimetre sample of high-redshift galaxies. Two submillimetre selection methods were used, including: sources selected at 850\(\mathrm{\, \mu m}\) with the Sub-millimetre Common-User Bolometer Array 2) SCUBA-2 instrument and {\it Herschel}-Spectral and Photometric Imaging Receiver (SPIRE) selected sources (colour-colour diagrams and 500\(\mathrm{\, \mu m}\) risers), finding that 185 have good multi-wavelength coverage. The resulting sample of 185 high-z candidates was further studied by spectral energy distribution (SED) fitting with the CIGALE fitting code. We derived photometric redshifts, stellar masses, SFRs, and additional physical parameters, such as the infrared luminosity and active galactic nuclei (AGN) contribution. We find that the different results in the literature are, only in part, due to selection effects. The difference in measured SFRs affects the position of DSFGs on the MS of galaxies; most of the DSFGs lie on the MS (60\%). Finally, we find that the star formation efficiency (SFE) depends on the epoch and intensity of the star formation burst in the galaxy; the later the burst, the more intense the star formation.
We present a new determination of the evolving galaxy UV luminosity function (LF) over the redshift range \(8.5<z<15.5\) using a combination of several major Cycle-1 JWST imaging programmes - PRIMER, ...JADES and NGDEEP. This multi-field approach yields a total of \(\simeq370\) sq. arcmin of JWST/NIRCam imaging, reaching (5-\(\sigma\)) depths of \(\simeq30\) 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 \(\simeq4\) magnitudes 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 \({\rm \Lambda}\)CDM 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.
With the advent of JWST, we can probe the rest-frame optical emission of galaxies at \(z>3\) with high sensitivity and spatial resolution, making it possible to accurately characterise red, ...optically-faint galaxies and thus move towards a more complete census of the galaxy population at high redshifts. To this end, we present a sample of 148 massive, dusty galaxies from the JWST/CEERS survey, colour-selected using solely JWST bands. With deep JWST/NIRCam data from 1.15\(\mu\)m to 4.44\(\mu\)m and ancillary HST/ACS and WFC3 data, we determine the physical properties of our sample using spectral energy distribution fitting with BAGPIPES. We demonstrate that our selection method efficiently identifies massive (\(\mathrm{\langle \log M_\star/M_\odot \rangle \sim 10}\)) and dusty (\(\mathrm{\langle A_V\rangle \sim 2.7\ mag}\)) sources, with a majority at \(z>3\) and predominantly lying on the galaxy main-sequence. The main results of this work are the stellar mass functions (SMF) of red, optically-faint galaxies from redshifts between \(3<z<8\): these galaxies make up a significant relative fraction of the pre-JWST total SMF at \(3<z<4\) and \(4<z<6\), and dominate the high-mass end of the pre-JWST SMF at \(6<z<8\), suggesting that our census of the galaxy population needs amendment at these epochs. While larger areas need to be surveyed in the future, our results suggest already that the integrated stellar mass density at \(\mathrm{\log M_\star/M_\odot\geq9.25}\) may have been underestimated in pre-JWST studies by up to \(\sim\)15-20\% at \(z\sim3-6\), and up to \(\sim\)45\% at \(z\sim6-8\), indicating the rapid onset of obscured stellar mass assembly in the early universe.
The advent of the JWST has revolutionised our understanding of high-redshift galaxies. In particular, the NIRCam instrument on-board JWST has revealed a population of Hubble Space Telescope ...(HST)-dark galaxies that had previously evaded optical detection, potentially due to significant dust obscuration, quiescence, or simply extreme redshift. Here, we present the first NIRSpec spectra of 23 HST-dark galaxies (\(\mathrm{H-F444W>1.75}\)), unveiling their nature and physical properties. This sample includes both dusty and quiescent galaxies with spectroscopic data from NIRSpec/PRISM, providing accurate spectroscopic redshifts with \(\mathrm{\overline{z}_{spec} = 4.1 \pm 0.7}\). The spectral features demonstrate that, while the majority of HST-dark galaxies are dusty, a substantial fraction, \(\mathrm{13^{+9}_{-6} \%}\), are quiescent. For the dusty galaxies, we have quantified the dust attenuation using the Balmer decrement (\(\mathrm{H\alpha / H\beta}\)), finding attenuations \(\mathrm{A_{V} > 2\ mag}\). We find that HST-dark dusty galaxies are \(\mathrm{H\alpha}\) emitters with equivalent widths spanning the range \(\mathrm{ 68 A < EW_{H\alpha} < 550 A }\), indicative of a wide range of recent star-formation activity. Whether dusty or quiescent, we find that HST-dark galaxies are predominantly massive, with 85\% of the galaxies in the sample having masses \(\mathrm{log(M_{*}/M_{\odot}) > 9.8}\). This pilot NIRSpec program reveals the diverse nature of HST-dark galaxies and highlights the effectiveness of NIRSpec/PRISM spectroscopic follow-up in distinguishing between dusty and quiescent galaxies and properly quantifying their physical properties. Upcoming research utilising higher-resolution NIRSpec data and combining JWST with ALMA observations will enhance our understanding of these enigmatic and challenging sources.
