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1. Infrared Spectral Energy Distributions and Dust Masses of Sub-solar Metallicity Galaxies at z ∼ 2.3

   https://doi.org/10.3847/1538-4357/ac54a9  

   Shivaei, Irene; Popping, Gergö; Rieke, George; Reddy, Naveen; Pope, Alexandra; Kennicutt, Robert; Mobasher, Bahram; Coil, Alison; Fudamoto, Yoshinobu; Kriek, Mariska; et al (March 2022, The Astrophysical Journal)

   Abstract We present results from Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm continuum observations of a sample of 27 star-forming galaxies at z = 2.1–2.5 from the MOSFIRE Deep Evolution Field survey with metallicity and star formation rate measurements from optical emission lines. Using stacks of Spitzer, Herschel, and ALMA photometry (rest frame ∼8–400 μ m), we examine the infrared (IR) spectral energy distributions (SED) of z ∼ 2.3 subsolar-metallicity (∼0.5 Z ⊙ ) luminous infrared galaxies (LIRGs). We find that the data agree well with an average template of higher-luminosity local low-metallicity dwarf galaxies (reduced χ 2 = 1.8). When compared with the commonly used templates for solar-metallicity local galaxies or high-redshift LIRGs and ultraluminous IR galaxies, even in the most favorable case (with reduced χ 2 = 2.8), the templates are rejected at >98% confidence. The broader and hotter IR SED of both the local dwarfs and high-redshift subsolar-metallicity galaxies may result from different grain properties or a harder/more intense ionizing radiation field that increases the dust temperature. The obscured star formation rate (SFR) indicated by the far-IR emission of the subsolar-metallicity galaxies is only ∼60% of the total SFR, considerably lower than that of the local LIRGs with ∼96%–97% obscured fractions. Due to the evolving IR SED shape, the local LIRG templates fit to mid-IR data overestimate the Rayleigh–Jeans tail measurements by a factor of 2–20. These templates underestimate IR luminosities if fit to the observed ALMA fluxes by >0.4 dex. At a given stellar mass or metallicity, dust masses at z ∼ 2.3 are an order of magnitude higher than z ∼ 0. Given the predicted molecular gas fractions, the observed z ∼ 2.3 dust-to-stellar mass ratios suggest lower dust-to-molecular gas masses than in local galaxies with similar metallicities. 

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2. The ALMA REBELS Survey: specific star formation rates in the reionization era

   https://doi.org/10.1093/mnras/stac2291  

   Topping, Michael W; Stark, Daniel P; Endsley, Ryan; Bouwens, Rychard J; Schouws, Sander; Smit, Renske; Stefanon, Mauro; Inami, Hanae; Bowler, Rebecca_A A; Oesch, Pascal; et al (August 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present specific star formation rates (sSFRs) for 40 ultraviolet (UV)-bright galaxies at z ∼ 7–8 observed as part of the Reionization Era Bright Emission Line Survey (REBELS) Atacama Large Millimeter/submillimeter Array (ALMA) large programme. The sSFRs are derived using improved star formation rate (SFR) calibrations and spectral energy distribution (SED)-based stellar masses, made possible by measurements of far-infrared (FIR) continuum emission and [C ii]-based spectroscopic redshifts. The median sSFR of the sample is $$18_{-5}^{+7}$$ Gyr−1, significantly larger than literature measurements lacking constraints in the FIR, reflecting the larger obscured SFRs derived 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 in reionization-era galaxies. When large sSFR galaxies (a population that is common at z > 6) are modelled with non-parametric star formation histories, 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 [C ii] line widths in the largest sSFR systems are often very broad, suggesting dynamical masses capable of accommodating an old stellar population suggested by non-parametric models. Regardless of these systematic uncertainties among derived parameters, we find that sSFRs increase rapidly toward higher redshifts for massive galaxies (9.6 < log (M*/M⊙) < 9.8), evolving as (1 + z)1.7 ± 0.3, broadly consistent with expectations from the evolving baryon accretion rates. 

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3. The ALPINE-ALMA [CII] survey: Obscured star formation rate density and main sequence of star-forming galaxies at z  > 4

   https://doi.org/10.1051/0004-6361/202038944  

   Khusanova, Y.; Bethermin, M.; Le Fèvre, O.; Capak, P.; Faisst, A. L.; Schaerer, D.; Silverman, J. D.; Cassata, P.; Yan, L.; Ginolfi, M.; et al (May 2021, Astronomy & Astrophysics)

   Star formation rate (SFR) measurements at z  > 4 have relied mostly on the rest-frame far-ultraviolet (FUV) observations. The corrections for dust attenuation based on the IRX- β relation are highly uncertain and are still debated in the literature. Hence, rest-frame far-infrared (FIR) observations are necessary to constrain the dust-obscured component of the SFR. In this paper, we exploit the rest-frame FIR continuum observations collected by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) to directly constrain the obscured SFR in galaxies at 4.4 <  z  < 5.9. We used stacks of continuum images to measure average infrared luminosities taking both detected and undetected sources into account. Based on these measurements, we measured the position of the main sequence of star-forming galaxies and the specific SFR (sSFR) at z  ∼ 4.5 and z  ∼ 5.5. We find that the main sequence and sSFR do not significantly evolve between z  ∼ 4.5 and z  ∼ 5.5, as opposed to lower redshifts. We developed a method to derive the obscured SFR density (SFRD) using the stellar masses or FUV-magnitudes as a proxy of FIR fluxes measured on the stacks and combining them with the galaxy stellar mass functions and FUV luminosity functions from the literature. We obtain consistent results independent of the chosen proxy. We find that the obscured fraction of SFRD is decreasing with increasing redshift, but even at z  ∼ 5.5 it constitutes around 61% of the total SFRD. 

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4. ALMA characterizes the dust temperature of z ∼ 5.5 star-forming galaxies

   https://doi.org/10.1093/mnras/staa2545  

   Faisst, Andreas L; Fudamoto, Yoshinobu; Oesch, Pascal A; Scoville, Nick; Riechers, Dominik A; Pavesi, Riccardo; Capak, Peter (September 2020, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The infrared (IR) spectral energy distributions (SEDs) of main-sequence galaxies in the early Universe (z > 4) is currently unconstrained as IR continuum observations are time-consuming and not feasible for large samples. We present Atacama Large Millimetre Array Band 8 observations of four main-sequence galaxies at z ∼ 5.5 to study their IR SED shape in detail. Our continuum data (rest-frame 110 $$\rm \mu m$$, close to the peak of IR emission) allows us to constrain luminosity-weighted dust temperatures and total IR luminosities. With data at longer wavelengths, we measure for the first time the emissivity index at these redshifts to provide more robust estimates of molecular gas masses based on dust continuum. The Band 8 observations of three out of four galaxies can only be reconciled with optically thin emission redward of rest-frame $$100\, {\rm \mu m}$$. The derived dust peak temperatures at z ∼ 5.5 ($$30\!-\!43\, {\rm K}$$) are elevated compared to average local galaxies, however, $$\sim 10\, {\rm K}$$ below what would be predicted from an extrapolation of the trend at z < 4. This behaviour can be explained by decreasing dust abundance (or density) towards high redshifts, which would cause the IR SED at the peak to be more optically thin, making hot dust more visible to the external observer. From the $$850{\hbox{-}}{\rm \mu m}$$ dust continuum, we derive molecular gas masses between 1010 and $$10^{11}\, {\rm M_{\odot }}$$ and gas fractions (gas over total mass) of $$30\!-\!80{{\ \rm per\ cent}}$$ (gas depletion times of $$100\!-\!220\, {\rm Myr}$$). All in all, our results provide a first measured benchmark SED to interpret future millimetre observations of normal, main-sequence galaxies in the early Universe. 

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5. The MOSDEF Survey: calibrating the relationship between H α star formation rate and radio continuum luminosity at 1.4 < z < 2.6

   https://doi.org/10.1093/mnras/staa2561  

   Duncan, Kenneth J; Shivaei, Irene; Shapley, Alice E; Reddy, Naveen A; Mobasher, Bahram; Coil, Alison L; Kriek, Mariska; Siana, Brian (September 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT The observed empirical relation between the star formation rates (SFR) of low-redshift galaxies and their radio continuum luminosity offers a potential means of measuring SFR in high-redshift galaxies that is unaffected by dust obscuration. In this study, we make the first test for redshift evolution in the SFR-radio continuum relation at high redshift using dust-corrected H α SFR. Our sample consists of 178 galaxies from the MOSFIRE Deep Evolution Field (MOSDEF) Survey at 1.4 < z < 2.6 with rest-frame optical spectroscopy and deep 1.5 GHz radio continuum observations from the Karl G. Jansky Very Large Array (VLA) GOODS North field. Using a stacking analysis, we compare the observed radio continuum luminosities with those predicted from the dust-corrected H α SFR assuming a range of z ∼ 0 relations. We find no evidence for a systematic evolution with redshift, when stacking the radio continuum as a function of dust-corrected H α SFR and when stacking both optical spectroscopy and radio continuum as a function of stellar mass. We conclude that locally calibrated relations between SFR and radio continuum luminosity remain valid out to z ∼ 2. 

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