Search

Dwarf galaxies hold the key to crucial frontiers of astrophysics, however, their faintness renders spectroscopy challenging. Here we present the JWST Cycle 2 survey, All the Little Things (ALT, PID 3516), which is designed to seek late-forming Pop III stars and the drivers of reionization at $z\sim6-7$. ALT has acquired the deepest NIRCam grism spectroscopy yet (7-27 hr), at JWST's most sensitive wavelengths (3-4 $\mu$m), covering the powerful lensing cluster Abell 2744. Over the same 30 arcmin$^2$, ALT's ultra-deep F070W+F090W imaging ($\sim$30 mag) enables selection of very faint sources at $z>6$. We demonstrate the success of ALT's novel ``butterfly" mosaic to solve spectral confusion and contamination, and introduce the ``Allegro" method for emission line identification. By collecting spectra for every source in the field of view, ALT has measured precise ($R\sim1600$) redshifts for 1630 sources at $z=0.2-8.5$. This includes one of the largest samples of distant dwarf galaxies: [1015, 475, 50] sources less massive than the SMC, Fornax, and Sculptor with $\log(M_{*}/M_{\odot})<$[8.5, 7.5, 6.5]. We showcase ALT's discovery space with: (i) spatially resolved spectra of lensed clumps in galaxies as faint as $M_{\rm{UV}}\sim-15$; (ii) large-scale clustering -- overdensities at $z$=[2.50, 2.58, 3.97, 4.30, 5.66, 5.77, 6.33] hosting massive galaxies with striking Balmer breaks; (iii) small-scale clustering -- a system of satellites around a Milky Way analog at $z\sim6$; (iv) spectroscopically confirmed multiple images that help constrain the lensing model underlying all science in this legacy field; (v) sensitive star-formation maps based on dust-insensitive tracers such as Pa$\alpha$; (vi) direct spectroscopic discovery of rare sources such as AGN with ionized outflows. These results provide a powerful proof of concept for how grism surveys maximize the potential of strong lensing fields., Comment: Submitted to the Open Journal of Astrophysics. Figs. 6 and 10 illustrate the quality of the spectra and imaging, while Fig. 12 summarizes the yield of the survey. Comments warmly welcomed and greatly appreciated. The ALT DR1 catalog is available at https://zenodo.org/records/13871850

We present the properties of a massive, large, dusty, metal-rich, star-forming galaxy at z_spec=6.73. GOODSN-100182 was observed with JWST/NIRSpec as part of the AURORA survey, and is also covered by public multi-wavelength HST and JWST imaging. While the large mass of GOODSN-100182 (~10^10 M_sun) was indicated prior to JWST, NIRCam rest-optical imaging now reveals the presence of an extended disk (r_eff~1.5 kpc). In addition, the NIRSpec R~1000 spectrum of GOODSN-100182 includes the detection of a large suite of rest-optical nebular emission lines ranging in wavelength from [OII]3727 up to [NII]6583. The ratios of Balmer lines suggest significant dust attenuation (E(B-V)_gas=0.40+0.10/-0.09), consistent with the red rest-UV slope inferred for GOODSN-100182 (beta=-0.50+/-0.09). The star-formation rate based on dust-corrected H-alpha emission is log(SFR(H-alpha)/ M_sun/yr)=2.02+0.13/-0.14, well above the z~7 star-forming main sequence in terms of specific SFR. Strikingly, the ratio of [NII]6583/H-alpha emission suggests almost solar metallicity, as does the ratio ([OIII]5007/H-beta)/([NII]6583/H-alpha) and the detection of the faint [FeII]4360 emission feature, whereas the [OIII]5007/[OII]3727 ratio suggests roughly 50% solar metallicity. Overall, the excitation and ionization properties of GOODSN-100182 more closely resemble those of typical star-forming galaxies at z~2-3 rather than z~7. Based on public spectroscopy of the GOODS-N field, we find that GOODSN-100182 resides within a significant galaxy overdensity, and is accompanied by a spectroscopically-confirmed neighbor galaxy. GOODSN-100182 demonstrates the existence of mature, chemically-enriched galaxies within the first billion years of cosmic time, whose properties must be explained by galaxy formation models., Comment: 16 pages, 13 figures, submitted to ApJ

We report the first successful ALMA follow-up observations of a secure $z > 10$ JWST-selected galaxy, by robustly detecting ($6.6\sigma$) the [OIII]$_{88\mu m}\,$ line in JADES-GS-z14-0 (hereafter GS-z14). The ALMA detection yields a spectroscopic redshift of $z=14.1793\pm0.0007$, and increases the precision on the prior redshift measurement of $z=14.32_{-0.20}^{+0.08}$ from NIRSpec by $\gtrsim$180$\times$. Moreover, the redshift is consistent with that previously determined from a tentative detection ($3.6\sigma$) of CIII]$_{1907,1909}$ ($z=14.178\pm0.013$), solidifying the redshift determination via multiple line detections. We measure a line luminosity of $L_\mathrm{[OIII]88} = (2.1 \pm 0.5)\times10^8\,L_\odot$, placing GS-z14 at the lower end, but within the scatter of, the local $L_\mathrm{[OIII]88}$-star formation rate relation. No dust continuum from GS-z14 is detected, suggesting an upper limit on the dust-to-stellar mass ratio of $< 2 \times 10^{-3}$, consistent with dust production from supernovae with a yield $y_d < 0.3\,M_\odot$. Combining a previous JWST/MIRI photometric measurement of the [OIII]$\lambda\lambda$4959,5007$\mathrm{\mathring{A}}$ and H$\beta$ lines with Cloudy models, we find GS-z14 to be surprisingly metal-enriched ($Z\sim0.05 - 0.2\,Z_\odot$) a mere $300\,\mathrm{Myr}$ after the Big Bang. The detection of a bright oxygen line in GS-z14 thus reinforces the notion that galaxies in the early Universe undergo rapid evolution., Comment: 11 Pages, 6 Figures, 1 Table. Submitted to The Astrophysical Journal

The H{\alpha} nebular emission line is an optimal tracer for recent star formation in galaxies. With the advent of JWST, this line has recently become observable at z>3 for the first time. We present a catalog of 1013 H{\alpha} emitters at 3.73 obtained based purely on spectroscopic data, robustly tracing galaxy star formation rates (SFRs) beyond the peak of the cosmic star formation history. We compare our results with theoretical predictions from three different simulations and find good agreement at z~4-6. The UV LFs of this spectroscopically-confirmed sample are in good agreement with pre-JWST measurements obtained with photometrically-selected objects. Finally, we derive SFR functions and integrate these to compute the evolution of the cosmic star-formation rate densities across z~4-6, finding values in good agreement with recent UV estimates from Lyman-break galaxies, which imply a continuous decrease in SFR density by a factor of 3x over z~4 to z~6. Our work shows the power of NIRCam grism observations to efficiently provide new tests for early galaxy formation models based on emission line statistics., Comment: 17 pages, 14 figures

We use JWST/NIRSpec observations from the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) survey to constrain the shape of the nebular attenuation curve of a star-forming galaxy at z=4.41, GOODSN-17940. We utilize 11 unblended HI recombination lines to derive the attenuation curve spanning optical to near-infrared wavelengths (3751-9550 \r{A}). We then leverage a high-S/N spectroscopic detection of the rest-frame ultraviolet continuum in combination with rest-UV photometric measurements to constrain the shape of the curve at ultraviolet wavelengths. While this UV constraint is predominantly based on stellar emission, the large measured equivalent widths of H$\alpha$ and H$\beta$ indicate that GOODSN-17940 is dominated by an extremely young stellar population <10 Myr in age such that the UV stellar continuum experiences the same attenuation as the nebular emission. The resulting combined nebular attenuation curve spans 1400-9550 \r{A} and has a shape that deviates significantly from commonly assumed dust curves in high-redshift studies. Relative to the Milky Way, SMC, and Calzetti curves, the new curve has a steeper slope at long wavelengths ($\lambda>5000$ \r{A}) while displaying a similar slope across blue-optical wavelengths ($\lambda=3750-5000$ \r{A}). In the ultraviolet, the new curve is shallower than the SMC and Calzetti curves and displays no significant 2175 \r{A} bump. This work demonstrates that the most commonly assumed dust curves are not appropriate for all high-redshift galaxies. These results highlight the ability to derive nebular attenuation curves for individual high-redshift sources with deep JWST/NIRSpec spectroscopy, thereby improving the accuracy of physical properties inferred from nebular emission lines., Comment: 21 pages, 6 figures, 1 table, submitted to ApJ

We present new multi-frequency ALMA continuum observations of the massive [$\log_{10}(M_\star/M_\odot) = 10.3_{-0.2}^{+0.1}$], UV-luminous [$M_\mathrm{UV} = -21.7 \pm 0.2$] $z=7.31$ galaxy REBELS-25 in Bands 3, 4, 5, and 9. Combining the new observations with previously-taken data in Bands 6 and 8, we cover the dust continuum emission of the galaxy in six distinct bands -- spanning rest-frame $50-350\,\mu$m -- enabling simultaneous constraints on its dust mass ($M_\mathrm{dust}$), temperature ($T_\mathrm{dust}$) and emissivity index ($\beta_\mathrm{IR}$) via modified blackbody fitting. Given a fiducial model of optically thin emission, we infer a cold dust temperature of $T_\mathrm{dust} = 32_{-6}^{+9}\,$K and a high dust mass of $\log_{10}(M_\mathrm{dust}/M_\odot) = 8.2_{-0.4}^{+0.6}$, and moderately optically thick dust does not significantly alter these estimates. If we assume dust production is solely through supernovae (SNe), the inferred dust yield would be high, $y = 0.7_{-0.4}^{+2.3}\,M_\odot$ per SN. Consequently, we argue grain growth in the interstellar medium of REBELS-25 also contributes to its dust build-up. This is supported by the steep dust emissivity index $\beta_\mathrm{IR} = 2.5 \pm 0.4$ we measure for REBELS-25, as well as by its high stellar mass, dense interstellar medium, and metal-rich nature. Our results suggest that constraining the dust emissivity indices of high-redshift galaxies is important not only to mitigate systematic uncertainties in their dust masses and obscured star formation rates, but also to assess if dust properties evolve across cosmic time. We present an efficient observing setup to do so with ALMA, combining observations of the peak and Rayleigh-Jeans tail of the dust emission., Comment: 14 pages main text, 6 figures + appendices; re-submitted to MNRAS after a positive referee report

We present results on the emission-line properties of z=1.4-7.5 star-forming galaxies in the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) Cycle 1 JWST/NIRSpec program. Based on its depth, continuous wavelength coverage from 1--5 microns, and medium spectral resolution (R~1000), AURORA includes detections of a large suite of nebular emission lines spanning a broad range in rest wavelength. We investigate the locations of AURORA galaxies in multiple different emission-line diagrams, including traditional "BPT" diagrams of [OIII]/Hbeta vs. [NII]/Halpha, [SII]/Halpha, and [OI]/Halpha, and the "ionization-metallicity" diagram of [OIII]/[OII] (O32) vs. ([OIII]+[OII])/Hbeta (R23). We also consider a bluer rest-frame "ionization-metallicity" diagram introduced recently to characterize z>10 galaxies: [NeIII]/[OII] vs. ([NeIII]+[OII])/Hdelta; as well as longer-wavelength diagnostic diagrams extending into the rest-frame near-IR: [OIII]/Hbeta vs. [SIII]/[SII] (S32); and HeI/Pagamma and [SIII]/Pagamma vs. [FeII]/Pabeta. With a significant boost in signal-to-noise and large, representative samples of individual galaxy detections, the AURORA emission-line diagrams presented here definitively confirm a physical picture in which chemically-young, alpha-enhanced, massive stars photoionize the ISM in distant galaxies with a harder ionizing spectrum at fixed nebular metallicity than in their z~0 counterparts. We also uncover previously unseen evolution prior to z~2 in the [OIII]/Hbeta vs. [NII]/Halpha diagram, which motivates deep NIRSpec observations at even higher redshift. Finally, we present the first statistical sample of rest-frame near-IR emission-line diagnostics in star-forming galaxies at high redshift. In order to truly interpret rest-frame near-IR line ratios including [FeII], we must obtain better constraints on dust depletion in the high-redshift ISM., Comment: 17 pages, 8 figures, submitted to ApJ

We present high resolution ($\sim0.14$" = 710 pc) ALMA [CII] 158$\mu$m and dust continuum follow-up observations of REBELS-25, a [CII]-luminous ($L_{\mathrm{[CII]}}=(1.7\pm0.2)\times 10^9 \mathrm{L_{\odot}}$) galaxy at redshift $z=7.3065\pm0.0001$. These high resolution, high signal-to-noise observations allow us to study the sub-kpc morphology and kinematics of this massive ($M_* = 8^{+4}_{-2} \times 10^9 \mathrm{M_{\odot}}$) star-forming (SFR$_{\mathrm{UV+IR}} = 199^{+101}_{-63} \mathrm{M_{\odot}} \mathrm{yr}^{-1}$) galaxy in the Epoch of Reionisation. By modelling the kinematics with $^{\mathrm{3D}}$BAROLO, we find it has a low velocity dispersion ($\bar{\sigma} = 33 \pm 9$ km s$^{-1}$) and a high ratio of ordered-to-random motion ($V_{\mathrm{rot, ~max}}/\bar{\sigma} = 11 ^{+8}_{-4}$), indicating that REBELS-25 is a dynamically cold disc. Additionally, we find that the [CII] distribution is well fit by a near-exponential disc model, with a S\'ersic index, $n$, of $1.3 \pm 0.2$, and we see tentative evidence of more complex non-axisymmetric structures suggestive of a bar in the [CII] and dust continuum emission. By comparing to other high spatial resolution cold gas kinematic studies, we find that dynamically cold discs seem to be more common in the high redshift Universe than expected based on prevailing galaxy formation theories, which typically predict more turbulent and dispersion-dominated galaxies in the early Universe as an outcome of merger activity, gas accretion and more intense feedback. This higher degree of rotational support seems instead to be consistent with recent cosmological simulations that have highlighted the contrast between cold and warm ionised gas tracers, particularly for massive galaxies. We therefore show that dynamically settled disc galaxies can form as early as 700 Myr after the Big Bang., Comment: Submitted to MNRAS

Combining the public JWST/NIRCam imaging programs CEERS, PRIMER and JADES, spanning a total area of $\sim500\,{\rm arcmin}^2$, we obtain a sample of $>$30,000 galaxies at $z_{\rm phot}\sim4-9$ that allows us to perform a complete, rest-optical selected census of the galaxy population at $z>3$. Comparing the stellar mass $M_*$ and the UV-slope $\beta$ distributions between JWST- and HST-selected samples, we generally find very good agreement and no significant biases. Nevertheless, JWST enables us to probe a new population of UV-red galaxies that was missing from previous HST-based Lyman Break Galaxy (LBG) samples. We measure galaxy stellar mass functions (SMFs) at $z\sim4-9$ down to limiting masses of $10^{7.5}-10^{8.5}\,{\rm M_\odot}$, finding steep low mass slopes over the entire redshift range, reaching values of $\alpha\approx-2$ at $z\gtrsim6$. At the high-mass end, UV-red galaxies dominate at least out to $z\sim6$. The implied redshift evolution of the SMF suggests a rapid build-up of massive dust-obscured or quiescent galaxies from $z\sim6$ to $z\sim4$ as well as an enhanced efficiency of star formation towards earlier times ($z\gtrsim6$). Finally, we show that the galaxy mass density grows by a factor $\sim20\times$ from $z\sim9$ to $z\sim4$. Our results emphasize the importance of rest-frame optically-selected samples in inferring accurate distributions of physical properties and studying the mass build-up of galaxies in the first 1.5 Gyr of cosmic history., Comment: 31 pages, 17 figures, published in MNRAS

We present the morphological parameters and global properties of dust-obscured star formation in typical star-forming galaxies at z=4-6. Among 26 galaxies composed of 20 galaxies observed by the Cycle-8 ALMA Large Program, CRISTAL, and six galaxies from archival data, we have individually detected rest-frame 158$\mu$m dust continuum emission from 19 galaxies, nine of which are reported for the first time. The derived far-infrared luminosities are in the range $\log_{10} L_{\rm IR}\,[L_{\odot}]=$10.9-12.4, an order of magnitude lower than previously detected massive dusty star-forming galaxies (DSFGs). The average relationship between the fraction of dust-obscured star formation ($f_{\rm obs}$) and the stellar mass is consistent with previous results at z=4-6 in a mass range of $\log_{10} M_{\ast}\,[M_{\odot}]\sim$9.5-11.0 and show potential evolution from z=6-9. The individual $f_{\rm obs}$ exhibits a significant diversity, and it shows a correlation with the spatial offset between the dust and the UV continuum, suggesting the inhomogeneous dust reddening may cause the source-to-source scatter in $f_{\rm obs}$. The effective radii of the dust emission are on average $\sim$1.5 kpc and are $\sim2$ times more extended than the rest-frame UV. The infrared surface densities of these galaxies ($\Sigma_{\rm IR}\sim2.0\times10^{10}\,L_{\odot}\,{\rm kpc}^{-2}$) are one order of magnitude lower than those of DSFGs that host compact central starbursts. On the basis of the comparable contribution of dust-obscured and dust-unobscured star formation along with their similar spatial extent, we suggest that typical star-forming galaxies at z=4-6 form stars throughout the entirety of their disks.

ALMA observations revealed the presence of significant amounts of dust in the first Gyr of Cosmic time. However, the metal and dust buildup picture remains very uncertain due to the lack of constraints on metallicity. JWST has started to reveal the metal content of high-redshift targets, which may lead to firmer constraints on high-redshift dusty galaxies evolution. In this work, we use detailed chemical and dust evolution models to explore the evolution of galaxies within the ALMA REBELS survey, testing different metallicity scenarios that could be inferred from JWST observations. In the models, we track the buildup of stellar mass by using non-parametric SFHs for REBELS galaxies. Different scenarios for metal and dust evolution are simulated by allowing different prescriptions for gas flows and dust processes. The model outputs are compared with measured dust scaling relations, by employing metallicity-dependent calibrations for the gas mass based on the [CII]158micron line. Independently of the galaxies metal content, we found no need for extreme dust prescriptions to explain the dust masses revealed by ALMA. However, different levels of metal enrichment will lead to different dominant dust production mechanisms, with stardust production dominant over other ISM dust processes only in the metal-poor case. This points out how metallicity measurements from JWST will significantly improve our understanding of the dust buildup in high-redshift galaxies. We also show that models struggle to reproduce observables such as dust-to-gas and dust-to-stellar ratios simultaneously, possibly indicating an overestimation of the gas mass through current calibrations, especially at high metallicities., Comment: 16 pages + appendices, 9 Figures, 1 Table. Resubmitted to MNRAS after moderate revision

We report the detection of a 13$\sigma$ H$\alpha$ emission line from HDF850.1 at $z=5.188\pm0.001$ using the FRESCO NIRCam F444W grism observations. Detection of H$\alpha$ in HDF850.1 is noteworthy, given its high far-IR luminosity, substantial dust obscuration, and the historical challenges in deriving its redshift. HDF850.1 shows a clear detection in the F444W imaging data, distributed between a northern and southern component, mirroring that seen in [CII] from the Plateau de Bure Interferometer. Modeling the SED of each component separately, we find that the northern component has a higher mass, star formation rate (SFR), and dust extinction than the southern component. The observed H$\alpha$ emission appears to arise entirely from the less-obscured southern component and shows a similar $\Delta$v$\sim$+130 km/s velocity offset to that seen for [CII] relative to the source systemic redshift. Leveraging H$\alpha$-derived redshifts from FRESCO observations, we find that HDF850.1 is forming in one of the richest environments identified to date at $z>5$, with 100 $z=5.17-5.20$ galaxies distributed across 10 structures and a $\sim$(15 cMpc)$^3$ volume. Based on the evolution of analogous structures in cosmological simulations, the $z=5.17-5.20$ structures seem likely to collapse into a single $>$10$^{14}$ $M_{\odot}$ cluster by $z\sim0$. Comparing galaxy properties forming within this overdensity with those outside, we find the masses, SFRs, and $UV$ luminosities inside the overdensity to be clearly higher. The prominence of H$\alpha$ line emission from HDF850.1 and other known highly-obscured $z>5$ galaxies illustrates the potential of NIRCam-grism programs to map both the early build-up of IR-luminous galaxies and overdense structures., Comment: Submitted to MNRAS. 20 pages, 10 figures and 8 tables (including appendices)

Recent JWST observations have revealed an unexpected abundance of massive galaxy candidates in the early Universe, extending further in redshift and to lower luminosity than what had previously been found by sub-millimeter surveys. These JWST candidates have been interpreted as challenging the $\Lambda$CDM cosmology, but, so far, they have mostly relied only on rest-frame ultraviolet data and lacked spectroscopic confirmation of their redshifts. Here we report a systematic study of 36 massive dust-obscured galaxies with spectroscopic redshifts between $z_{\rm spec}=5-9$ from the JWST FRESCO survey. We find no tension with the $\Lambda$CDM model in our sample. However, three ultra-massive galaxies (log$M_{\star}/M_{\odot}$ $\gtrsim11.0$) require an exceptional fraction of 50% of baryons converted into stars -- two to three times higher than even the most efficient galaxies at later epochs. The contribution from an active nucleus is unlikely because of their extended emission. Ultra-massive galaxies account for as much as 17% of the total cosmic star formation rate density at $z\sim5-6$., Comment: Nature in press. Updated to the accepted version. 24 pages, 4 main figures, 7 supplementary figures, 3 supplementary tables

Characterising the prevalence and properties of faint active galactic nuclei (AGN) in the early Universe is key for understanding the formation of supermassive black holes (SMBHs) and determining their role in cosmic reionization. We perform a spectroscopic search for broad H$\alpha$ emitters at $z\approx4-6$ using deep JWST/NIRCam imaging and wide field slitless spectroscopy from the EIGER and FRESCO surveys. We identify 20 H$\alpha$ lines at $z=4.2-5.5$ that have broad components with line widths from $\sim1200-3700$ km s$^{-1}$, contributing $\sim30-90$ % of the total line flux. We interpret these broad components as being powered by accretion onto SMBHs with implied masses $\sim10^{7-8}$ M$_{\odot}$. In the UV luminosity range M$_{\rm UV}=-21$ to $-18$, we measure number densities of $\approx10^{-5}$ cMpc$^{-3}$. This is an order of magnitude higher than expected from extrapolating quasar UV luminosity functions. Yet, such AGN are found in only $<1$ % of star-forming galaxies at $z\sim5$. The SMBH mass function agrees with large cosmological simulations. In two objects we detect narrow red- and blue-shifted H$\alpha$ absorption indicative, respectively, of dense gas fueling SMBH growth and outflows. We may be witnessing early AGN feedback that will clear dust-free pathways through which more massive blue quasars are seen. We uncover a strong correlation between reddening and the fraction of total galaxy luminosity arising from faint AGN. This implies that early SMBH growth is highly obscured and that faint AGN are only minor contributors to cosmic reionization., Comment: 26 pages, 20 figures. Accepted for publication in ApJ. Various improvements and updated citations. Main additions: colours (Fig 11), broad Halpha LF (Fig 18, Sect 5.2), comparisons to simulations (Sect 5.3)

We present the H{\alpha} luminosity function (LF) derived from a large sample of Lyman break galaxies at z {\sim} 4.5 over the GOODS-South and North fields. This study makes use of the new, full-depth Spitzer/IRAC [3.6] and [4.5] imaging from the GOODS Re-ionization Era wide-Area Treasury from the Spitzer program. The H{\alpha} flux is derived from the offset between the continuum flux estimated from the best-fit spectral energy distribution, and the observed photometry in IRAC [3.6]. From these measurements, we build the H{\alpha} LF and study its evolution providing the best constraints of this property at high redshift, where spectroscopy of H{\alpha} is not yet available. Schechter parameterizations of the H{\alpha} LF show a decreasing evolution of {\Phi^\star} with redshift, increasing evolution in L{^\star}, and no significant evolution in the faint-end slope at high z. We find that star formation rates (SFRs) derived from H{\alpha} are higher than those derived from the rest-frame UV for low SFR galaxies but the opposite happens for the highest SFRs. This can be explained by lower mass galaxies (also lower SFR) having, on average, rising star formation histories (SFHs), while at the highest masses the SFHs may be declining. The SFR function is steeper, and because of the excess SFR(H{\alpha}) compared to SFR(UV) at low SFRs, the SFR density estimated from H{\alpha} is higher than the previous estimates based on UV luminosities., Comment: Astrophysical Journal, Accepted, 17 pages, 16 figures

We present updated measurements of the [O III] 88 $\mu$m, [C II] 158 $\mu$m, and dust continuum emission from a star-forming galaxy at $z=7.212$, SXDF-NB1006-2, by utilizing Atacama Large Millimeter/submillimeter Array (ALMA) archival data sets analysed in previous studies and data sets that have not been analysed before. The follow-up ALMA observations with higher angular resolution and sensitivity reveal a clumpy structure of the [O III] emission on a scale of $0.32-0.85\,\rm{kpc}$. We also combined all the ALMA [O III] ([C II]) data sets and updated the [O III] ([C II]) detection to $5.9\sigma$ ($3.6\sigma-4.5\sigma$). The non-detection of [C II] with data from the REBELS large program implies the incompleteness of spectral-scan surveys using [C II] to detect galaxies with high star formation rates (SFRs) but marginal [C II] emission at high-$z$. The dust continuum at 90 $\mu$m and 160 $\mu$m remains undetected, indicating little dust content of $<3.9\times10^{6}\,M_\odot\,(3\sigma)$, and we obtained a more stringent constraint on the total infrared luminosity. We updated the [O III]/[C II] luminosity ratios to $10.2\pm4.7~(6.1\pm3.5$) and $20\pm12~(9.6\pm6.1$) for $4.5\sigma$ and $3.6\sigma$ [C II] detections, respectively, where the ratios in the parentheses are corrected for the surface brightness dimming effect on the extended [C II] emission. We also found a strong [C II] deficit ($0.6-1.3$ dex) between SXDF-NB1006-2 and the mean $L_{\rm{[CII]}}-\rm{SFR}$ relation of galaxies at $0

We present new ALMA Band 8 (rest-frame $90\,\mu$m) observations of three massive ($M_\star \approx 10^{10}\,M_\odot$) galaxies at $z\approx7$ previously detected in [CII]$158\,\mu$m and underlying dust continuum emission in the Reionization Era Bright Emission Line Survey (REBELS). We detect the dust continuum emission of two of our targets in Band 8 (REBELS-25 and REBELS-38), while REBELS-12 remains undetected. Through modified blackbody fitting we determine cold dust temperatures ($T_\mathrm{dust} \approx 30 - 35\,$K) in both of the dual-band detected targets, given a fiducial model of optically thin emission with $\beta = 2.0$. Their dust temperatures are lower than most $z\sim7$ galaxies in the literature, and consequently their dust masses are higher ($M_\mathrm{dust} \approx 10^{8}\,M_\odot$). Nevertheless, these large dust masses are still consistent with predictions from models of dust production in the early Universe. In addition, we target and detect [OIII]$88\,\mu$m emission in both REBELS-12 and REBELS-25, and find $L_\mathrm{[OIII]} / L_\mathrm{[CII]}$ ratios of approximately unity, low compared to the $L_\mathrm{[OIII]} / L_\mathrm{[CII]} \gtrsim 2 - 10$ observed in the known $z\gtrsim6$ population thus far. We argue the lower line ratios are due to a comparatively weaker ionizing radiation field resulting from the less starbursty nature of our targets. This low burstiness supports the cold dust temperatures and below average $\mathrm{[OIII]}\lambda\lambda4959,5007 + \mathrm{H}\beta$ equivalent widths of REBELS-25 and REBELS-38, compared to the known high-redshift population. Overall, this provides evidence for the existence of a massive, dust-rich galaxy population at $z\approx7$ which has previously experienced vigorous star formation, but is currently forming stars in a steady, as opposed to bursty, manner., Comment: 18 pages + appendices; 8 figures in main text; Submitted to MNRAS on 27 Dec 2022

We have derived luminosity functions, and set constraints on the UV luminosity and SFR density from z~17 to z~8, using the three most-studied JWST/NIRCam data sets, the SMACS0723, GLASS Parallel, and CEERS fields. We first used our own selections on two independent reductions of these datasets using the latest calibrations. 18 z~8, 12 z~10, 5 z~13, and 1 z~17 candidate galaxies are identified over these fields in our primary reductions, with a similar number of candidates in our secondary reductions. We then use these two reductions, applying a quantitative discriminator, to segregate the full set of z>~8 candidates reported over these fields from the literature, into three different samples, ``robust,'' ``solid,'' and ``possible''. Using all of these samples we then derive UV LF and luminosity density results at $z\geq8$, finding substantial differences. For example, including the full set of ``solid'' and ``possible'' z>~12 candidates from the literature, we find UV luminosity densities which are ~7x and ~20x higher than relying on the ``robust'' candidates alone. These results indicate the evolution of the UV LF and luminosity densities at z>~8 is still extremely uncertain, emphasizing the need for spectroscopy and deeper NIRCam+optical imaging to obtain reliable results. Nonetheless, even with the very conservative ``robust'' approach to selections, both from our own and those of other studies, we find the luminosity density from luminous (M(UV)<-19) galaxies to be ~2x larger than is easily achievable using constant star-formation efficiency models, similar to what other early JWST results have suggested., Comment: 26 pages, 10 figures, 15 tables, accepted for publication in MNRAS, figure 7 shows the key results

We present the first constraints on the prevalence of z>10 galaxies in the Hubble Ultra Deep Field (HUDF) leveraging new NIRCam observations from JEMS (JWST Extragalactic Medium-band Survey). These NIRCam observations probe redward of 1.6$\mu$m, beyond the wavelength limit of HST, allowing us to search for galaxies to z>10. These observations indicate that the highest redshift candidate identified in the HUDF09 data with HST, UDFj-39546284, has a redshift of z>11.5, as had been suggested in analyses of the HUDF12/XDF data. This has now been confirmed with JWST NIRSpec. This source is thus the most distant galaxy discovered by HST in its >30 years of operation. Additionally, we identify nine other z~8-13 candidate galaxies over the HUDF, two of which are new discoveries that appear to lie at z~11-12. We use these results to characterize the evolution of the UV luminosity function (LF) from z~15 to z~8.7. While our LF results at z~8.7 and z~10.5 are consistent with previous findings over the HUDF, our new LF estimates at z~12.6 are higher than other results in the literature, potentially pointing to a milder evolution in the UV luminosity density from z~12.6. We emphasize that our LF results are uncertain given the small number of z~12.6 sources and limited volume probed. The new NIRCam data also indicate that the faint z~8-13 galaxies in the HUDF/XDF show blue UV-continuum slopes beta~-2.7, high specific star formation rates ~24.5 Gyr**-1, and high EW (~1300A) [OIII]+H$\beta$ emission, with two z~8.5 sources showing [OIII]+H$\beta$ EWs of ~2300 A., Comment: 21 pages, 14 figures, 7 tables, resubmitted to MNRAS, after replying to the referee report

Cosmic dust is an essential component shaping both the evolution of galaxies and their observational signatures. How quickly dust builds up in the early Universe remains an open question that requires deep observations at (sub-)millimeter wavelengths to resolve. Here we use Atacama Large Millimeter Array observations of 45 galaxies from the Reionization Era Bright Emission Line Survey (REBELS) and its pilot programs, designed to target [CII] and dust emission in UV-selected galaxies at $z\sim7$, to investigate the dust content of high-redshift galaxies through a stacking analysis. We find that the typical fraction of obscured star formation $f_\mathrm{obs} = \mathrm{SFR}_\mathrm{IR} / \mathrm{SFR}_\mathrm{UV + IR}$ depends on stellar mass, similar to what is observed at lower redshift, and ranges from $f_\mathrm{obs} \approx 0.3 - 0.6$ for galaxies with $\log_{10}\left(M_\star / M_\odot\right) = 9.4 - 10.4$. We further adopt the $z\sim7$ stellar mass function from the literature to extract the obscured cosmic star formation rate density (SFRD) from the REBELS survey. Our results suggest only a modest decrease in the SFRD between $3\lesssim z \lesssim 7$, with dust-obscured star formation still contributing $\sim30\%$ at $z\sim7$. While we extensively discuss potential caveats, our analysis highlights the continued importance of dust-obscured star formation even well into the epoch of reionization., Comment: MNRAS Accepted (01 Nov 2022)

$JWST$'s first glimpse of the $z>10$ Universe has yielded a surprising abundance of luminous galaxy candidates. Here we present the most extreme of these systems: CEERS-1749. Based on $0.6-5\mu$m photometry, this strikingly luminous ($\approx$26 mag) galaxy appears to lie at $z\approx17$. This would make it an $M_{\rm{UV}}\approx-22$, $M_{\rm{\star}}\approx5\times10^{9}M_{\rm{\odot}}$ system that formed a mere $\sim220$ Myrs after the Big Bang. The implied number density of this galaxy and its analogues challenges virtually every early galaxy evolution model that assumes $\Lambda$CDM cosmology. However, there is strong environmental evidence supporting a secondary redshift solution of $z\approx5$: all three of the galaxy's nearest neighbors at $<2.5$" have photometric redshifts of $z\approx5$. Further, we show that CEERS-1749 may lie in a $z\approx5$ protocluster that is $\gtrsim5\times$ overdense compared to the field. Intense line emission at $z\approx5$ from a quiescent galaxy harboring ionized gas, or from a dusty starburst, may provide satisfactory explanations for CEERS-1749's photometry. The emission lines at $z\approx5$ conspire to boost the $>2\mu$m photometry, producing an apparent blue slope as well as a strong break in the SED. Such a perfectly disguised contaminant is possible only in a narrow redshift window ($\Delta z\lesssim0.1$), implying that the permitted volume for such interlopers may not be a major concern for $z>10$ searches, particularly when medium-bands are deployed. If CEERS-1749 is confirmed to lie at $z\approx5$, it will be the highest-redshift quiescent galaxy, or one of the lowest mass dusty galaxies of the early Universe detected to-date. Both redshift solutions of this intriguing galaxy hold the potential to challenge existing models of early galaxy evolution, making spectroscopic follow-up of this source critical., Comment: Submitted to ApJL. Fig. 1 shows the "superposed" state, Fig. 2 presents the potential z~5 protocluster, Fig. 3 shows some atypical z~5 SEDs, Fig. 4 studies the morphology, Fig. 5 summarizes the extraordinary situation at z~17, and Fig. 6 argues for why such interlopers may not be a major issue for z>10 searches. Comments warmly welcomed

The first few hundred Myrs at $z>10$ mark the last major uncharted epoch in the history of the Universe, where only a single galaxy (GNz11 at $z\approx11$) is currently spectroscopically confirmed. Here we present a search for luminous $z>10$ galaxies with $JWST$/NIRCam photometry spanning $\approx1-5\mu$m and covering 49 arcmin$^{2}$ from the public Early Release Science programs (CEERS and GLASS). Our most secure candidates are two $M_{\rm{UV}}\approx-21$ systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt $\gtrsim1.8$ mag breaks in their spectral energy distributions, consistent with complete absorption of flux bluewards of Lyman-$\alpha$ that is redshifted to $z=12.4^{+0.1}_{-0.3}$ and $z=10.4^{+0.4}_{-0.5}$. Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at $>5\sigma$ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up $\sim 10^9$ solar masses in stars over the $\lesssim300-400$ Myrs after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of $r_{\rm{50}}\approx0.7$ kpc. These sources, if confirmed, join GNz11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area $>10\times$ larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep $JWST$ observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated., Comment: Accepted for publication in ApJL. Analysis updated with in-flight NIRCam chip-wise zero-points -- Figure 6 shows a comparison with v1

We present new [O III] 88 ${\rm \mu}$m observations of five bright $z \sim 7$ Lyman-break galaxies spectroscopically confirmed by ALMA through the [C II] 158 ${\rm \mu}$m line, unlike recent [O III] detections where Lyman-${\rm \alpha}$ was used. This nearly doubles the sample of Epoch of Reionisation galaxies with robust ($5 \sigma$) detections of [C II] and [O III]. We perform a multi-wavelength comparison with new deep HST images of the rest-frame UV, whose compact morphology aligns well with [O III] tracing ionised gas. By contrast, we find more spatially extended [C II] emission likely produced in neutral gas, as indicated by a [N II] 205 ${\rm \mu}$m non-detection in one source. We find a positive correlation between the equivalent width of the optical [O III] and H${\rm \beta}$ lines and the [O III]/[C II] ratio, as seen in local metal-poor dwarf galaxies. Cloudy models of a nebula of typical density harbouring a young stellar population with a high ionisation parameter appear to adequately reproduce the far-infrared lines. Surprisingly, however, our models fail to reproduce the strength of [O III] 88 ${\rm \mu}$m, unless we assume an ${\rm \alpha}$/Fe enhancement and a near-solar nebular oxygen abundance. On spatially resolved scales, we find [O III]/[C II] shows a tentative anti-correlation with infrared excess, $L_{\rm IR}/L_{\rm UV}$, also seen on global scales in the local Universe. Finally, we introduce the far-infrared spectral energy distribution fitting code MERCURIUS to show that dust-continuum measurements of one source appear to favour a low dust temperature coupled with a high dust mass. This implies a high stellar metallicity yield and may point towards the need of dust production or grain-growth mechanisms beyond supernovae., Comment: 23 pages, 11 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society

We present the deepest constraints yet on the median rest-UV+optical SED of $z\sim10$ galaxies, prior to JWST science operations. We constructed stacks based on four robust $J_{125}$-dropouts, previously identified across the GOODS fields. We used archival HST/WFC3 data and the full depth Spitzer/IRAC mosaics from the GREATS program, the deepest coverage at $\sim3-5\mu$m to date. The most remarkable feature of the SED is a blue IRAC $[3.6]-[4.5]=-0.18\pm0.25$ mag color. We also find a nearly flat $H_{160}-[3.6]=0.07\pm0.22$ mag color, corresponding to a UV slope $\beta= -1.92\pm0.25$. This is consistent with previous studies, and indicative of minimal dust absorption. The observed blue IRAC color and SED fitting suggest that $z\sim10$ galaxies have very young (few $\times10$ Myr) stellar populations, with $80\%$ of stars being formed in the last $\lesssim 160$ Myr ($2\sigma$). While an exciting result, the uncertainties on the SED are too large to allow us to place strong constraints on the presence of a nebular continuum in $z\sim10$ galaxies (as might be suggested by the blue $[3.6]-[4.5] < 0$ mag color). The resulting sSFR is consistent with the specific accretion rate of dark matter halos, indicative of a star-formation efficiency showing quite limited evolution at such early epochs., Comment: Submitted to ApJ. 9 pages, 3 figures. Comments welcome

We present band 6 ALMA observations of a heavily-obscured radio-loud ($L_{1.4\ \mathrm{GHz}}=10^{25.4}$ W Hz$^{-1}$) AGN candidate at $z_\mathrm{phot}=6.83\pm0.06$ found in the 1.5 deg$^2$ COSMOS field. The ALMA data reveal detections of exceptionally strong [CII]158$\mu$m ($z_\mathrm{[CII]}=6.8532$) and underlying dust continuum emission from this object (COS-87259), where the [CII] line luminosity, line width, and 158$\mu$m continuum luminosity are comparable to that seen from $z\sim7$ sub-mm galaxies and quasar hosts. The 158$\mu$m continuum detection suggests a total infrared luminosity of $9\times10^{12}$ $L_\odot$ with corresponding very large obscured star formation rate (1300 $M_\odot$/yr) and dust mass ($2\times10^9$ $M_\odot$). The strong break seen between the VIRCam and IRAC photometry perhaps suggests that COS-87259 is an extremely massive reionization era galaxy with $M_\ast\approx1.7\times10^{11}$ $M_\odot$. Moreover, the MIPS, PACS, and SPIRE detections imply that this object harbors an AGN that is heavily obscured ($\tau_{_{\mathrm{9.7\mu m}}}=2.3$) with a bolometric luminosity of approximately $5\times10^{13}$ $L_\odot$. Such a very high AGN luminosity suggests this object is powered by an $\approx$1.6 $\times$ 10$^9$ $M_\odot$ black hole if accreting near the Eddington limit, and is effectively a highly-obscured version of an extremely UV-luminous ($M_{1450}\approx-27.3$) $z\sim7$ quasar. Notably, these $z\sim7$ quasars are an exceedingly rare population ($\sim$0.001 deg$^{-2}$) while COS-87259 was identified over a relatively small field. Future very wide-area surveys with, e.g., Roman and Euclid have the potential to identify many more extremely red yet UV-bright $z\gtrsim7$ objects similar to COS-87259, providing richer insight into the occurrence of intense obscured star formation and supermassive black hole growth among this population., Comment: 12 pages, 7 figures, 1 table. Updated to accepted version (MNRAS)

We measure, for the first time, the median equivalent width (EW) of H$\alpha$+[N II] in star-forming galaxies at $z\sim8$. Our estimate leverages the unique photometric depth of the Spitzer/IRAC $5.8\mu$m-band mosaics (probing $\approx 5500 - 7100$ A at $z\sim8$) of the GOODS Reionization Era Wide Area Treasury from Spitzer (GREATS) program. We median stacked the stamps of $102$ Lyman-break galaxies in the $3.6, 4.5, 5.8$ and $8.0\mu$m bands, after carefully removing potential contamination from neighbouring sources. We infer an extreme rest-frame EW$_0$(H$\alpha$+[N II])$=2328^{+1326}_{-1127}$ A from the measured red $[3.6]-[5.8]=0.82\pm0.27$ mag, consistent with young ($\lesssim10^7$ yr) average stellar population ages at $z\sim8$. This implies an ionizing photon production efficiency of $\log(\xi_{\mathrm{ion},0}/\mathrm{erg\ Hz}^{-1})=25.97^{+0.18}_{-0.28}$. Such a high value for photo production, similar to the highest values found at $z\lesssim4$, indicates that only modest escape fractions $f_\mathrm{esc}\lesssim0.3$ (at $2\sigma$) are sufficient for galaxies brighter than $M_\mathrm{UV}<-18$ mag to re-ionize the neutral Hydrogen at $z\sim8$. This requirement is relaxed even more to $f_\mathrm{esc}\le 0.1$ when considering galaxies brighter than $M_\mathrm{UV}\approx -13$ mag, consistent with recent luminosity functions and as typically assumed in studies addressing re-ionization. These exceptional results clearly indicate that galaxies can be the dominant source of reionizing photons, and provide us with an exciting glimpse into what we might soon learn about the early universe, and particularly about the Reionization Epoch, from forthcoming JWST/MIRI and NIRCam programs., Comment: Submitted to ApJ. 12 pages, 5 figures (main) + appendix. Comments welcome

We report 18 dust continuum detections ($\geq 3.3\sigma$) at $\sim88{\rm \mu m}$ and $158{\rm \mu m}$ out of 49 ultraviolet(UV)-bright galaxies ($M_{\rm UV} < -21.3$ mag) at $z>6.5$, observed by the Cycle-7 ALMA Large Program, REBELS and its pilot programs. This has more than tripled the number of dust continuum detections known at $z>6.5$. Out of these 18 detections, 12 are reported for the first time as part of REBELS. In addition, 15 of the dust continuum detected galaxies also show a [CII]$_{\rm 158{\rm \mu m}}$ emission line, providing us with accurate redshifts. We anticipate more line emission detections from six targets (including three continuum detected targets) where observations are still ongoing. The dust continuum detected sources in our sample tend to have a redder UV spectral slope than the ones without a dust continuum detection. We estimate that all of the sources have an infrared (IR) luminosity ($L_{\rm IR}$) in a range of $3-8 \times 10^{11} L_\odot$, except for one with $L_{\rm IR} = 1.5^{+0.8}_{-0.5} \times 10^{12}\,L_{\odot}$. Their fraction of obscured star formation is significant at $\gtrsim 50\%$. Some of the dust continuum detected galaxies show spatial offsets ($\sim 0.5-1.5''$) between the rest-UV and far-IR emission peaks. These separations appear to have an increasing trend against an indicator that suggests spatially decoupled phases of obscured and unobscured star formation. REBELS offers the best available statistical constraints on obscured star formation in UV-bright, massive galaxies at $z > 6.5$., Comment: 17 pages, 9 figures, 4 tables, Accepted for publication in MNRAS

We present specific star-formation rates for 40 UV-bright galaxies at $z\sim7-8$ observed as part of the Reionization Era Bright Emission Line Survey (REBELS) ALMA large program. The sSFRs are derived using improved measures of SFR and stellar masses, made possible by measurements of far-infrared (FIR) continuum emission and [CII]-based spectroscopic redshifts. For each source in the sample, we derive stellar masses from SED fitting and total SFRs from calibrations of the UV and FIR emission. The median sSFR is $18_{-5}^{+7}$ Gyr$^{-1}$, significantly larger than literature measurements lacking constraints in the FIR. The increase in sSFR reflects the larger obscured SFRs we derive from the dust continuum relative to that implied by the UV+optical SED. We suggest that such differences may reflect spatial variations in dust across these luminous galaxies, with the component dominating the FIR distinct from that dominating the UV. We demonstrate that the inferred stellar masses (and hence sSFRs) are strongly-dependent on the assumed star formation history (SFH) in reionization-era galaxies. When large sSFR galaxies are modeled with non-parametric SFHs, the derived stellar masses can increase by an order of magnitude relative to constant star formation models, owing to the presence of a significant old stellar population that is outshined by the recent burst. The [CII] line widths in the largest sSFR systems are often very broad, suggesting dynamical masses that are easily able to accommodate the dominant old stellar population suggested by non-parametric models. Regardless of these systematic uncertainties in the derived parameters, we find that the sSFR increases rapidly toward higher redshifts for massive galaxies ($9.6<\log(\rm M_*/M_{\odot})<9.8$), with a power law that goes as $(1+z)^{1.7\pm0.3}$, broadly consistent with expectations from the evolving baryon accretion rates., Comment: 18 pages, 10 figures, submitted to MNRAS

The [CII]$_{158\mu m}$ line has long been proposed as a promising line to spectroscopically confirm galaxies in the epoch of reionization. In this paper we present the results of new ALMA observations spectral scanning for [CII] in six particularly luminous Lyman Break Galaxies at $z\sim7$. The six sources were drawn from a sample of bright $z\sim7$ galaxies identified using the wide-area optical, near-IR, and Spitzer/IRAC data over the COSMOS/UltraVISTA field and were targeted on the basis of tight constraints on their redshifts from their IRAC [3.6]-[4.5] colors. We detect significant ($>9\sigma$) [CII] lines in three of our six targets ($50\%$) co-spatial with the rest-$UV$ emission from the ground/space-based near-IR imaging. The luminosities of the [CII] lines lie in the range $5.6$ to $8.8\times10^{8}L_{\odot}$, consistent with the local [CII]-SFR relation. Meanwhile, their [CII]/$L_{IR}\sim1-3\times10^{-3}$ ratios are slightly elevated compared to local (U)LIRGS. This could be due to lower dust-to-gas or dust-to-metal ratios. We also find that our sources display a large kinematic diversity, with one source showing signs of rotation, one source a likely major merger and one dispersion dominated source that might contain a bright star-forming clump. Our results highlight the effectiveness of spectral scans with ALMA in spectroscopically confirming luminous galaxies in the epoch of reionization, something that is being be applied on a significantly larger sample in the on-going REBELS large program., Comment: 16 pages, 7 figures, 3 tables. Submitted to ApJ

Recent work has shown that UV-luminous reionization-era galaxies often exhibit strong Lyman-alpha emission despite being situated at redshifts where the IGM is thought to be substantially neutral. It has been argued that this enhanced Ly$\alpha$ transmission reflects the presence of massive galaxies in overdense regions which power large ionized bubbles. An alternative explanation is that massive galaxies shift more of their Ly$\alpha$ profile to large velocities (relative to the systemic redshift) where the IGM damping wing absorption is reduced. Such a mass-dependent trend is seen at lower redshifts, but whether one exists at $z\sim7$ remains unclear owing to the small number of existing systemic redshift measurements in the reionization era. This is now changing with the emergence of [CII]-based redshifts from ALMA. Here we report MMT/Binospec Ly$\alpha$ spectroscopy of eight UV-bright ($\mathrm{M_{UV}}^{}\sim-22$) galaxies at $z\simeq7$ selected from the ALMA REBELS survey. We detect Ly$\alpha$ in 4 of 8 galaxies and use the [CII] systemic redshifts to investigate the Ly$\alpha$ velocity profiles. The Ly$\alpha$ lines are significantly redshifted from systemic (average velocity offset=223 km/s) and broad (FWHM$\approx$300$-$650 km/s), with two sources showing emission extending to $\approx$750 km/s. We find that the broadest Ly$\alpha$ profiles are associated with the largest [CII] line widths, suggesting a potential link between the Ly$\alpha$ FWHM and the dynamical mass. Since Ly$\alpha$ photons at high velocities transmit efficiently through the $z=7$ IGM, our data suggest that velocity profiles play a significant role in boosting the Ly$\alpha$ visibility of the most UV-luminous reionization-era galaxies., Comment: 17 pages, 7 figures, submitted to MNRAS

We present the deepest Spitzer/IRAC $3.6$, $4.5$, $5.8$ and $8.0\mu$m wide-area mosaics yet over the GOODS-N and GOODS-S fields as part of the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) project. We reduced and mosaicked in a self-consistent way observations taken by the 11 different Spitzer/IRAC programs over the two GOODS fields from 12 years of Spitzer cryogenic and warm mission data. The cumulative depth in the $3.6\mu$m and $4.5\mu$m bands amounts to $\sim 4260$ hr, $\sim 1220$ hr of which are new very deep observations from the GREATS program itself. In the deepest area, the full-depth mosaics reach $\gtrsim200$ hr over an area of $\sim100$ arcmin$^2$, corresponding to a sensitivity of $\sim29$ AB magnitude at $3.6\mu$m ($1\sigma$ for point sources). Archival cryogenic $5.8\mu$m and $8.0\mu$m band data (a cumulative 976 hr) are also included in the release. The mosaics are projected onto the tangential plane of CANDELS/GOODS at a $0.3''$ pixel$^{-1}$ scale. This paper describes the methodology enabling, and the characteristics of, the public release of the mosaic science images, the corresponding coverage maps in the four IRAC bands, and the empirical Point-Spread Functions (PSFs). These PSFs enable mitigation of the source blending effects by taking into account the complex position-dependent variation in the IRAC images. The GREATS data products are in the Infrared Science Archive (IRSA). We also release the deblended $3.6$-to-$8.0\mu$m photometry for $9192$ Lyman-Break galaxies at $z\sim3.5-10$. GREATS will be the deepest mid-infrared imaging until JWST and, as such, constitutes a major resource for characterizing early galaxy assembly., Comment: Accepted for publication on ApJS. Mosaics, PSFs and catalogs are publicly available at https://home.strw.leidenuniv.nl/~stefanon/GREATS/

We report the identification of radio (0.144-3 GHz), mid-IR, far-IR, and sub-mm (24-850$\mu$m) emission at the position of one of 41 UV-bright (M$_\mathrm{UV}^{}\lesssim-21.25$) $z\simeq6.6-6.9$ Lyman-break galaxy candidates in the 1.5 deg$^2$ COSMOS field. This source, COS-87259, exhibits a sharp flux discontinuity (factor $>$3) between two narrow/intermediate bands at 9450 and 9700 Angstroms and is undetected in all nine bands blueward of 9600 Angstroms, as expected from a Lyman-alpha break at $z\simeq6.8$. The full multi-wavelength (X-ray through radio) data of COS-87529 can be self-consistently explained by a very massive (M$_{\ast}=10^{10.8}$ M$_{\odot}$) and extremely red (rest-UV slope $\beta=-0.59$) $z\simeq6.8$ galaxy with hyperluminous infrared emission (L$_{\mathrm{IR}}=10^{13.6}$ L$_{\odot}$) powered by both an intense burst of highly-obscured star formation (SFR$\approx$1800 M$_{\odot}$ yr$^{-1}$) and an obscured ($\tau_{\mathrm{9.7\mu m}}=7.7\pm2.5$) radio-loud (L$_{\mathrm{1.4\ GHz}}\approx10^{25.4}$ W Hz$^{-1}$) AGN. The radio emission is compact (1.04$\pm$0.12 arcsec) and exhibits an ultra-steep spectrum between 1.32-3 GHz ($\alpha=-1.57^{+0.22}_{-0.21}$) that flattens at lower frequencies ($\alpha=-0.86^{+0.22}_{-0.16}$ between 0.144-1.32 GHz), consistent with known $z>4$ radio galaxies. We also demonstrate that COS-87259 may reside in a significant (11$\times$) galaxy overdensity at $z\simeq6.6-6.9$, as common for systems hosting radio-loud AGN. Nonetheless, a spectroscopic redshift will ultimately be required to establish the true nature of COS-87259 as we cannot yet completely rule out low-redshift solutions. If confirmed to lie at $z\simeq6.8$, the properties of COS-87259 would be consistent with a picture wherein AGN and highly-obscured star formation activity are fairly common among very massive (M$_{\ast}>10^{10}$ M$_{\odot}$) reionization-era galaxies., Comment: 14 pages, 6 figures. Accepted in MNRAS with minor revisions. This accepted version considers very recent data from LOFAR and MeerKAT which improve our analyses on the radio slope and luminosity

We study the molecular gas content of 24 star-forming galaxies at $z=3-4$, with a median stellar mass of $10^{9.1}$ M$_{\odot}$, from the MUSE Hubble Ultra Deep Field (HUDF) Survey. Selected by their Lyman-alpha-emission and H-band magnitude, the galaxies show an average EW $\approx 20$ angstrom, below the typical selection threshold for Lyman Alpha Emitters (EW $> 25$ angstrom), and a rest-frame UV spectrum similar to Lyman Break Galaxies. We use rest-frame optical spectroscopy from KMOS and MOSFIRE, and the UV features observed with MUSE, to determine the systemic redshifts, which are offset from Lyman alpha by 346 km s$^{-1}$, with a 100 to 600 km s$^{-1}$ range. Stacking CO(4-3) and [CI](1-0) (and higher-$J$ CO lines) from the ALMA Spectroscopic Survey of the HUDF (ASPECS), we determine $3\sigma$ upper limits on the line luminosities of $4.0\times10^{8}$ K km s$^{-1}$pc$^{2}$ and $5.6\times10^{8}$ K km s$^{-1}$pc$^{2}$, respectively (for a 300 km s$^{-1}$ linewidth). Stacking the 1.2 mm and 3 mm dust continuum flux densities, we find a $3\sigma$ upper limits of 9 $\mu$Jy and $1.2$ $\mu$Jy, respectively. The inferred gas fractions, under the assumption of a 'Galactic' CO-to-H$_{2}$ conversion factor and gas-to-dust ratio, are in tension with previously determined scaling relations. This implies a substantially higher $\alpha_{\rm CO} \ge 10$ and $\delta_{\rm GDR} \ge 1200$, consistent with the sub-solar metallicity estimated for these galaxies ($12 + \log(O/H) \approx 7.8 \pm 0.2$). The low metallicity of $z \ge 3$ star-forming galaxies may thus make it very challenging to unveil their cold gas through CO or dust emission, warranting further exploration of alternative tracers, such as [CII]., Comment: 26 pages, 12 figures, 3 tables. Accepted for publication in ApJ

We make use of ALMA continuum observations of $15$ luminous Lyman-break galaxies at $z$$\sim$$7$$-$$8$ to probe their dust-obscured star-formation. These observations are sensitive enough to probe to obscured SFRs of $20$ $M_{\odot}$$/$$yr$ ($3\sigma$). Six of the targeted galaxies show significant ($\geq$$3$$\sigma$) dust continuum detections, more than doubling the number of known dust-detected galaxies at $z$$>$$6.5$. Their IR luminosities range from $2.7$$\times$$10^{11}$ $L_{\odot}$ to $1.1$$\times$$10^{12}$ $L_{\odot}$, equivalent to obscured SFRs of $20$ to $105$ $M_{\odot}$$/$$yr$. We use our results to quantify the correlation of the infrared excess IRX on the UV-continuum slope $\beta_{UV}$ and stellar mass. Our results are most consistent with an SMC attenuation curve for intrinsic $UV$-slopes $\beta_{UV,intr}$ of $-2.63$ and most consistent with an attenuation curve in-between SMC and Calzetti for $\beta_{UV,intr}$ slopes of $-2.23$, assuming a dust temperature $T_d$ of $50$ K. Our fiducial IRX-stellar mass results at $z$$\sim$$7$$-$$8$ are consistent with marginal evolution from $z$$\sim$$0$. We then show how both results depend on $T_d$. For our six dust-detected sources, we estimate their dust masses and find that they are consistent with dust production from SNe if the dust destruction is low ($<$$90$%). Finally we determine the contribution of dust-obscured star formation to the star formation rate density for $UV$ luminous ($<$$-$$21.5$ mag: $\gtrsim$$1.7$$L_{UV} ^*$) $z$$\sim$$7$$-$$8$ galaxies, finding that the total SFR density at $z$$\sim$$7$ and $z$$\sim$$8$ from bright galaxies is $0.18_{-0.10}^{+0.08}$ dex and $0.20_{-0.09}^{+0.05}$ dex higher, respectively, i.e. $\sim$$\frac{1}{3}$ of the star formation in $\gtrsim$$1.7$$L_{UV} ^*$ galaxies at $z$$\sim$$7$$-$$8$ is obscured by dust., Comment: 21 pages, 12 figures, 2 tables. Submitted to ApJ

We present new stellar mass functions at $z\sim6$, $z\sim7$, $z\sim8$, $z\sim9$ and, for the first time, $z\sim10$, constructed from $\sim800$ Lyman-Break galaxies previously identified over the XDF/UDF, parallels and the five CANDELS fields. Our study is distinctive due to (1) the much deeper ($\sim200$ hour) wide-area Spitzer/IRAC imaging at $3.6\mu$m and $4.5\mu$m from the GOODS Re-ionization Era wide Area Treasury from Spitzer (GREATS) program and (2) consideration of $z\sim6-10$ sources over a $3\times$ larger area than previous HST+Spitzer studies. The Spitzer/IRAC data enable $\ge2\sigma$ rest-frame optical detections for an unprecedented $50\%$ of galaxies down to a stellar mass limit of $\sim10^{8}\mathcal{M}_\odot$ across all redshifts. Schechter fits to our volume densities suggest a combined evolution in characteristic mass $\mathcal{M}^*$ and normalization factor $\phi^*$ between $z\sim6$ and $z\sim8$. The stellar mass density (SMD) increases by $\sim1000\times$ in the $\sim500$ Myr between $z\sim10$ and $z\sim6$, with indications of a steeper evolution between $z\sim10$ and $z\sim8$, similar to the previously-reported trend of the star-formation rate density. Strikingly, abundance matching to the Bolshoi-Planck simulation indicates halo mass densities evolving at approximately the same rate as the SMD between $z\sim10$ and $z\sim4$. Our results show that the stellar-to-halo mass ratios, a proxy for the star-formation efficiency, do not change significantly over the huge stellar mass build-up occurred from $z\sim10$ to $z\sim6$, indicating that the assembly of stellar mass closely mirrors the build-up in halo mass in the first $\sim1$ Gyr of cosmic history. JWST is poised to extend these results into the "first galaxy" epoch at $z\gtrsim10$., Comment: Submitted to ApJ, comments welcome

Deep rest-optical observations are required to accurately constrain the stellar populations of $z\sim8$ galaxies. Due to significant limitations in the availability of such data for statistically complete samples, observational results have been limited to modest numbers of bright or lensed sources. To revolutionize the present characterization of $z\sim8$ galaxies, we exploit the ultradeep ($\sim27$ mag, $3\sigma$) Spitzer/IRAC $3.6\mu$m and $4.5\mu$m data, probing the rest-frame optical at $z\sim8$, over $\sim200$ arcmin$^2$ of the GOODS fields from the recently completed GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) program, combined with observations in the CANDELS UDS and COSMOS fields. We stacked $\gtrsim100$ $z\sim8$ Lyman-Break galaxies in four bins of UV luminosity ($M_\mathrm{UV}\sim -20.7$ to $-18.4$) and study their $H_\mathrm{160}-[3.6]$ and $[3.6]-[4.5]$ colors. We find young ages ($\lesssim100$ Myr) for the three faintest stacks, inferred from their blue $H_\mathrm{160}-[3.6]\sim 0$ mag colors, consistent with a negative Balmer break. Meanwhile, the redder $H_\mathrm{160}-[3.6]$ color seen in the brightest stack is suggestive of slightly older ages. We explored the existence of a correlation between the UV luminosity and age, and find either no trend or fainter galaxies being younger. The stacked SEDs also exhibit very red $[3.6]-[4.5]\sim0.5$ mag colors, indicative of intense [OIII]+H$\beta$ nebular emission and SFR. The correspondingly high specific star-formation rates, sSFR$\gtrsim10$Gyr$^{-1}$, are consistent with recent determinations at similar redshifts and higher luminosities, and support the co-evolution between the sSFR and the specific halo mass accretion rate., Comment: Submitted to ApJ. Comments welcome. See Fig. 2 & 3 for the stacks, Fig. 4 & 6 for the colors/age and Fig. 8 for the sSFR evolution

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Band 6 scan (212-272 GHz) covers potential [CII] emission in galaxies at $6\leq z \leq8$ throughout a 2.9 arcmin$^2$ area. By selecting on known Lyman-$\alpha$ emitters (LAEs) and photometric dropout galaxies in the field, we perform targeted searches down to a 5$\sigma$ [CII] luminosity depth $L_{\mathrm{[CII]}}\sim2.0\times10^8$ L$_{\odot}$, corresponding roughly to star formation rates (SFRs) of $10$-$20$ M$_{\odot}$ yr$^{-1}$ when applying a locally calibrated conversion for star-forming galaxies, yielding zero detections. While the majority of galaxies in this sample are characterized by lower SFRs, the resulting upper limits on [CII] luminosity in these sources are consistent with the current literature sample of targeted ALMA observations of $z=6$-$7$ LAEs and Lyman-break galaxies (LBGs), as well as the locally calibrated relations between $L_{\mathrm{[CII]}}$ and SFR -- with the exception of a single [CII]-deficient, UV luminous LBG. We also perform a blind search for [CII]-bright galaxies that may have been missed by optical selections, resulting in an upper limit on the cumulative number density of [CII] sources with $L_{\mathrm{[CII]}}>2.0\times10^8$ L$_{\odot}$ ($5\sigma $) to be less than $1.8\times10^{-4}$ Mpc$^{-3}$ (90% confidence level). At this luminosity depth and volume coverage, we present an observed evolution of the [CII] luminosity function from $z=6$-$8$ to $z\sim0$ by comparing the ASPECS measurement to literature results at lower redshift., Comment: 16 pages, 6 figures, accepted for publication in ApJ

Reionization-era galaxies tend to exhibit weak Ly$\alpha$ emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this picture, with strong Ly$\alpha$ emission now known in four of the most massive z=7$-$9 galaxies in the CANDELS fields, all of which also exhibit intense [OIII]$+$H$\beta$ emission (EW$>$800 $\mathrm{\mathring{A}}$). To better understand why Ly$\alpha$ is anonymously strong in a subset of massive z$\simeq$7$-$9 galaxies, we have initiated an MMT/Binospec survey targeting a larger sample (N=22) of similarly luminous ($\simeq$1$-$6 L$^{\ast}_{\mathrm{UV}}$) z$\simeq$7 galaxies selected over very wide-area fields ($\sim$3 deg$^2$). We confidently ($>$7$\sigma$) detect Ly$\alpha$ in 78% (7/9) of galaxies with strong [OIII]$+$H$\beta$ emission (EW$>$800 $\mathrm{\mathring{A}}$) as opposed to only 8% (1/12) of galaxies with more moderate (EW=200$-$800 $\mathrm{\mathring{A}}$) [OIII]$+$H$\beta$. We argue that the higher Ly$\alpha$ EWs of the strong [OIII]$+$H$\beta$ population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs ($\gtrsim$30 Gyr$^{-1}$). We also find evidence that Ly$\alpha$ transmission from massive galaxies declines less rapidly over $6

We combine the recent determination of the evolution of the cosmic density of molecular gas (H_2) using deep, volumetric surveys, with previous estimates of the cosmic density of stellar mass, star formation rate and atomic gas (HI), to constrain the evolution of baryons associated with galaxies averaged over cosmic time and space. The cosmic HI and H_2 densities are roughly equal at z~1.5. The H_2 density then decreases by a factor 6^{+3}_{-2} to today's value, whereas the HI density stays approximately constant. The stellar mass density is increasing continuously with time and surpasses that of the total gas density (HI and H_2) at redshift z~1.5. The growth in stellar mass cannot be accounted for by the decrease in cosmic H_2 density, necessitating significant accretion of additional gas onto galaxies. With the new H_2 constraints, we postulate and put observational constraints on a two step gas accretion process: (i) a net infall of ionized gas from the intergalactic/circumgalactic medium to refuel the extended HI reservoirs, and (ii) a net inflow of HI and subsequent conversion to H_2 in the galaxy centers. Both the infall and inflow rate densities have decreased by almost an order of magnitude since z~2. Assuming that the current trends continue, the cosmic molecular gas density will further decrease by about a factor of two over the next 5 Gyr, the stellar mass will increase by approximately 10%, and cosmic star formation activity will decline steadily toward zero, as the gas infall and accretion shut down., Comment: Accepted for publication in The Astrophysical Journal

We make use of sensitive (9.3 microJy/beam RMS) 1.2mm-continuum observations from the ASPECS ALMA large program of the Hubble Ultra Deep Field (HUDF) to probe dust-enshrouded star formation from 1362 Lyman-break galaxies spanning the redshift range z=1.5-10 (to ~7-28 Msolar/yr at 4 sigma over the entire range). We find that the fraction of ALMA-detected galaxies in our z=1.5-10 samples increases steeply with stellar mass, with the detection fraction rising from 0% at 10^9 Msolar to 85(-18)(+9)% at >10^{10} Msolar. Moreover, stacking all 1253 low-mass (<10^{9.25} Msolar) galaxies over the ASPECS footprint, we find a mean continuum flux of -0.1+/-0.4 microJy/beam, implying a hard upper limit on the obscured SFR of <0.6 Msolar/yr (4 sigma) in a typical low-mass galaxy. The correlation between the infrared excess IRX of UV-selected galaxies (L(IR)/L(UV)) and the UV-continuum slope is also seen in our ASPECS data and shows consistency with a Calzetti-like relation at >10^{9.5} M_{solar} and a SMC-like relation at lower masses. Using stellar-mass and beta measurements for z~2 galaxies over CANDELS, we derive a new empirical relation between beta and stellar mass and then use this correlation to show that our IRX-beta and IRX-stellar mass relations are consistent with each other. We then use these constraints to express the infrared excess as a bivariate function of beta and stellar mass. Finally, we present updated estimates of star-formation rate density determinations at z>3, leveraging current improvements in the measured infrared excess and recent probes of ultra-luminous far-IR galaxies at z>2., Comment: 32 pages, 22 figures, 11 pages, accepted for publication in the Astrophysical Journal, key results shown in Figures 7, 8, 11, and 20, updated to match version in press

Spectroscopic surveys of massive galaxy clusters reveal the properties of faint background galaxies, thanks to the magnification provided by strong gravitational lensing. We present a systematic analysis of integral-field-spectroscopy observations of 12 massive clusters, conducted with the Multi Unit Spectroscopic Explorer (MUSE). All data were taken under very good seeing conditions (0.6") in effective exposure times between two and 15 hrs per pointing, for a total of 125 hrs. Our observations cover a total solid angle of ~23 arcmin$^2$ in the direction of clusters, many of which were previously studied by the MACS, Frontier Fields, GLASS and CLASH programs. The achieved emission line detection limit at 5$\sigma$ for a point source varies between (0.77--1.5)$\times$10$^{-18}$ erg\,s$^{-1}$\,cm$^{-2}$ at 7000\AA. We present our developed strategy to reduce these observational data, detect sources and determine their redshifts. We construct robust mass models for each cluster to further confirm our redshift measurements using strong-lensing constraints, and identify a total of 312 strongly lensed sources producing 939 multiple images. The final redshift catalogs contain more than 3300 robust redshifts, of which 40\% are for cluster members and $\sim$30\% for lensed Lyman-$\alpha$ emitters. 14\% of all sources are line emitters not seen in the available HST images, even at the depth of the FFs ($\sim29$ AB). We find that the magnification distribution of the lensed sources in the high-magnification regime ($\mu{=}$ 2--25) follows the theoretical expectation of $N(z)\propto\mu^{-2}$. The quality of this dataset, number of lensed sources, and number of strong-lensing constraints enables detailed studies of the physical properties of both the lensing cluster and the background galaxies. The full data products from this work are made available to the community. [abridged], Comment: 47 pages, 13 figures, 18 tables. Accepted for publication in A&A. Data Release products available on CDS and at https://cral-perso.univ-lyon1.fr/labo/perso/johan.richard/MUSE_data_release

We investigate the CO excitation and interstellar medium (ISM) conditions in a cold gas mass-selected sample of 22 star-forming galaxies at $z=0.46-3.60$, observed as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). Combined with VLA follow-up observations, we detect a total of 34 CO $J \rightarrow J-1$ transitions with $J=1$ up to $8$ (and an additional 21 upper limits, up to $J=10$) and six [C I] ${^3P}_1 \rightarrow {^3P}_0$ and ${^3P}_2 \rightarrow {^3P}_1$ transitions (and 12 upper limits). The CO(2-1) and CO(3-2)-selected galaxies, at $z=1.2$ and $2.5$, respectively, exhibit a range in excitation in their mid-$J=4,5$ and high-$J=7,8$ lines, on average lower than ($L_{\rm IR}$-brighter) BzK-color- and submillimeter-selected galaxies at similar redshifts. The former implies that a warm ISM component is not necessarily prevalent in gas mass-selected galaxies at $z=1.2$. We use stacking and Large Velocity Gradient models to measure and predict the average CO ladders at $z<2$ and $z\geq2$, finding $r_{21}=0.75 \pm 0.11$ and $r_{31}=0.77 \pm 0.14$, respectively. From the models, we infer that the galaxies at $z\geq2$ have intrinsically higher excitation than those at $z<2$. This fits a picture in which the global excitation is driven by an increase in the star formation rate surface density of galaxies with redshift. We derive a neutral atomic carbon abundance of $(1.9 \pm 0.4) \times 10^{-5}$, comparable to the Milky Way and main-sequence galaxies at similar redshifts, and fairly high densities ($\geq 10^4$ cm$^{-3}$), consistent with the low-$J$ CO excitation. Our results imply a decrease in the cosmic molecular gas mass density at $z\geq2$ compared to previous ASPECS measurements., Comment: 37 pages, 15 figures, 6 tables. Accepted for publication in the Astrophysical Journal

We propose a new mission called Space Project for Astrophysical and Cosmological Exploration (SPACE) as part on the ESA long term planning Voyage 2050 programme. SPACE will study galaxy evolution at the earliest times, with the key goals of charting the formation of the heavy elements, measuring the evolution of the galaxy luminosity function, tracing the build-up of stellar mass in galaxies over cosmic time, and finding the first super-massive black holes (SMBHs) to form. The mission will exploit a unique region of the parameter space, between the narrow ultra-deep surveys with HST and JWST, and shallow wide-field surveys such as Roman Space Telescope and EUCLID, and should yield by far the largest sample of any current or planned mission of very high redshift galaxies at z > 10 which are sufficiently bright for detailed follow-up spectroscopy. Crucially, we propose a wide-field spectroscopic near-IR + mid-IR capability which will greatly enhance our understanding of the first galaxies by detecting and identifying a statistical sample of the first galaxies and the first SMBH, and to chart the metal enrichment history of galaxies in the early Universe - potentially finding signatures of the very first stars to form from metal-free primordial gas. The wide-field and wavelength range of SPACE will also provide us a unique opportunity to study star formation by performing a wide survey of the Milky Way in the near-IR + mid-IR. This science project can be enabled either by a stand-alone ESA-led M mission or by an instrument for an L mission (with ESA and/or NASA, JAXA and other international space agencies) with a wide-field (sub-)millimetre capability at wavelength > 500 microns., Comment: Submitted to Experimental Astronomy as one of the proposals for the European Space Agency Voyage 2050 Programme

We present a characterization of the physical properties of a sample of 35 securely-detected, dusty galaxies in the deep ALMA 1.2-mm image obtained as part of the ALMA Spectroscopic Survey in the {\it Hubble} Ultra Deep Field (ASPECS) Large Program. This sample is complemented by 26 additional sources identified via an optical/infrared source positional prior. Using their well-characterized spectral energy distributions, we derive median stellar masses and star formation rates (SFR) of $4.8\times10^{10}~M_\odot$ and 30 $M_\odot$ yr$^{-1}$, and interquartile ranges of $(2.4-11.7)\times10^{10}~M_\odot$ and $20-50~M_\odot$ yr$^{-1}$, respectively. We derive a median spectroscopic redshift of 1.8 with an interquartile range $1.1-2.6$, significantly lower than submillimeter galaxies detected in shallower, wide-field surveys. We find that 59\%$\pm$13\%, 6\%$\pm$4\%, and 34\%$\pm$9\% of our sources are within, above and below $\pm0.4$ dex from the SFR-stellar mass relation or main-sequence (MS), respectively. The ASPECS galaxies closely follow the SFR-molecular gas mass relation and other previously established scaling relations, confirming a factor of five increase of the gas-to-stellar mass ratio from $z=0.5$ to $z=2.5$ and a mild evolution of the gas depletion timescales with a typical value of 0.7 Gyr at $z=1-3$. ASPECS galaxies located significantly below the MS, a poorly exploited parameter space, have low gas-to-stellar-mass ratios of $\sim0.1-0.2$ and long depletion timescales $>1$ Gyr. Galaxies along the MS dominate the cosmic density of molecular gas at all redshifts. Systems above the main sequence have an increasing contribution to the total gas reservoirs from $z<1$ to $z=2.5$, while the opposite is found for galaxies below the MS., Comment: ApJ published on Sept. 24, 2020. Contains 36 pages, 17 figures. Final version matching the proof reviewed article

While low-luminosity galaxies dominate number counts at all redshifts, their contribution to cosmic Reionization is poorly understood due to a lack of knowledge of their physical properties. We isolate a sample of 35 z~4-5 continuum-faint Lyman-alpha emitters from deep VLT/MUSE spectroscopy and directly measure their Halpha emission using stacked Spitzer/IRAC Ch. 1 photometry. Based on Hubble Space Telescope imaging, we determine that the average UV continuum magnitude is fainter than -16 (~0.01 L_star), implying a median Lyman-alpha equivalent width of 249 Angstroms. By combining the Halpha measurement with the UV magnitude we determine the ionizing photon production efficiency, xi_ion, a first for such faint galaxies. The measurement of log (xi_ion [Hz/erg]) = 26.28 (+0.28; -0.40) is in excess of literature measurements of both continuum- and emission line-selected samples, implying a more efficient production of ionizing photons in these lower-luminosity, Lyman-alpha-selected systems. We conclude that this elevated efficiency can be explained by stellar populations with metallicities between 4e-4 and 0.008, with light-weighted ages less than 3 Myr., Comment: 12 Pages, 6 Figures; Accepted for publication in MNRAS

We use Hubble Space Telescope (HST) imaging and near-infrared spectroscopy from Keck/MOSFIRE to study the sub-structure around the progenitor of a Milky Way-mass galaxy in the Hubble Frontier Fields (HFF). Specifically, we study an $r_e = 40^{+70}_{-30}$pc, $M_{\star} \sim 10^{8.2} M_{\odot}$ rest-frame ultra-violet luminous "clump" at a projected distance of $\sim$100~pc from a $M_{\star} \sim 10^{9.8}$M$_{\odot}$ galaxy at $z = 2.36$ with a magnification $\mu = 5.21$. We measure the star formation history of the clump and galaxy by jointly modeling the broadband spectral energy distribution from HST photometry and H$\alpha$ from MOSFIRE spectroscopy. Given our inferred properties (e.g., mass, metallicity, dust) of the clump and galaxy, we explore scenarios in which the clump formed \emph{in-situ} (e.g., a star forming complex) or \emph{ex-situ} (e.g., a dwarf galaxy being accreted). If it formed \emph{in-situ}, we conclude that the clump is likely a single entity as opposed to a aggregation of smaller star clusters, making it one of the most dense star clusters cataloged. If it formed \emph{ex-situ}, then we are witnessing an accretion event with a 1:40 stellar mass ratio. However, our data alone are not informative enough to distinguish between \emph{in-situ} and \emph{ex-situ} scenarios to a high level of significance. We posit that the addition of high-fidelity metallicity information, such as [OIII]4363\AA, which can be detected at modest S/N with only a few hours of JWST/NIRSpec time, may be a powerful discriminant. We suggest that studying larger samples of moderately lensed sub-structures across cosmic time can provide unique insight into the hierarchical formation of galaxies like the Milky Way., Comment: Accepted to MNRAS

We present the results from the 1.2 mm continuum image obtained as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). The 1.2 mm continuum image has a size of 2.9 (4.2) arcmin$^2$ within a primary beam response of 50% (10%) and a rms value of $9.3\thinspace{\rm\mu Jy\thinspace beam^{-1}}$. We detect 35 sources at high significance (Fidelity $\geq0.5$), 32 of these have well characterized near-infrared HST counterparts. We estimate the 1.2 mm number counts to flux levels of $<30\thinspace{\rm\mu Jy}$ in two different ways: we first use the detected sources to constrain the number counts and find a significant flattening of the counts below $S_\nu \sim 0.1$ mJy. In a second approach, we constrain the number counts by using a probability of deflection statistics (P(D)) analysis. For this latter approach, we describe new methods to accurately measure the noise in interferometric imaging (employing jack-knifing in the cube and in the visibility plane). This independent measurement confirms the flattening of the number counts. Our analysis of the differential number counts shows that we are detecting $\sim$93% ($\sim$100% if we include the lower fidelity detections) of the total continuum dust emission associated to galaxies in the HUDF. The ancillary data allows us to study the dependence of the 1.2 mm number counts on redshift ($z=0-4$), galaxy dust mass (${\rm M}_{\rm dust}=10^{7}-10^{9}{\rm M}_{\odot}$), stellar mass (${\rm M}_{*}=10^{9}-10^{12}{\rm M}_{\odot}$), and star-formation rate (${\rm SFR}=1-1000\thinspace{\rm M}_{\odot}\thinspace{\rm yr^{-1}}$). In an accompanying paper we show that the number counts are crucial to constrain galaxy evolution models and the understanding of star-forming galaxies at high redshift., Comment: Accepted for publication in ApJ

The Beyond Ultra-deep Frontier Fields and Legacy Observations (BUFFALO) is a 101 orbit + 101 parallel Cycle 25 Hubble Space Telescope Treasury program taking data from 2018-2020. BUFFALO will expand existing coverage of the Hubble Frontier Fields (HFF) in WFC3/IR F105W, F125W, and F160W and ACS/WFC F606W and F814W around each of the six HFF clusters and flanking fields. This additional area has not been observed by HST but is already covered by deep multi-wavelength datasets, including Spitzer and Chandra. As with the original HFF program, BUFFALO is designed to take advantage of gravitational lensing from massive clusters to simultaneously find high-redshift galaxies which would otherwise lie below HST detection limits and model foreground clusters to study properties of dark matter and galaxy assembly. The expanded area will provide a first opportunity to study both cosmic variance at high redshift and galaxy assembly in the outskirts of the large HFF clusters. Five additional orbits are reserved for transient followup. BUFFALO data including mosaics, value-added catalogs and cluster mass distribution models will be released via MAST on a regular basis, as the observations and analysis are completed for the six individual clusters., Comment: Accepted ApJS; MAST archive will be live concurrent with publication

The ionizing photon production efficiency, $\xi_{ion}$, is a critical parameter that provides a number of physical constraints to the nature of the early Universe, including the contribution of galaxies to the timely completion of the reionization of the Universe. Here we use KECK/MOSFIRE and ZFOURGE multi-band photometric data to explore the $\xi_{ion}$ of a population of galaxies at $z\sim2$ with $log_{10}(M_*/M_\odot)\sim9.0-11.5$. Our 130 \Halpha\ detections show a median $log_{10}(\xi_{ion}[Hz/erg])$ of $24.8\pm0.5$ when dust corrected using a Calzetti et al. (2000) dust prescription. Our values are typical of mass/magnitude selected $\xi_{ion}$ values observed in the $z\sim2$ Universe. Using BPASSv2.2.1 and Starburst99 stellar population models with simple parametric star-formation-histories (SFH), we find that even with models that account for effects of stellar evolution with binaries/stellar rotation, model galaxies at $log_{10}(\xi_{ion}[Hz/erg])\lesssim25.0$ have low H$\alpha$ equivalent widths (EW) and redder colors compared to our $z\sim2$ observed sample. We find that introducing star-bursts to the SFHs resolve the tension with the models, however, due to the rapid time evolution of $\xi_{ion}$, H$\alpha$ EWs, and rest-frame optical colors, our Monte Carlo simulations of star-bursts show that random distribution of star-bursts in evolutionary time of galaxies are unlikely to explain the observed distribution. Thus, either our observed sample is specially selected based on their past SFH or stellar models require additional mechanisms to reproduce the observed high UV luminosity of galaxies for a given production rate of hydrogen ionizing photons., Comment: Accepted for publication in the ApJ, 8 figures, 15 pages