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1. The ALPINE-ALMA [C II] survey: Little to no evolution in the [C II]–SFR relation over the last 13 Gyr

   https://doi.org/10.1051/0004-6361/202037617  

   Schaerer, D. ; Ginolfi, M. ; Béthermin, M. ; Fudamoto, Y. ; Oesch, P. A. ; Le Fèvre, O. ; Faisst, A. ; Capak, P. ; Cassata, P. ; Silverman, J. D. ; et al ( November 2020 , Astronomy & Astrophysics)

   The [C  II ] 158 μ m line is one of the strongest IR emission lines, which has been shown to trace the star formation rate (SFR) of galaxies in the nearby Universe, and up to z  ∼ 2. Whether this is also the case at higher redshift and in the early Universe remains debated. The ALPINE survey, which targeted 118 star-forming galaxies at 4.4 <   z  <  5.9, provides a new opportunity to examine this question with the first statistical dataset. Using the ALPINE data and earlier measurements from the literature, we examine the relation between the [C  II ] luminosity and the SFR over the entire redshift range from z  ∼ 4 − 8. ALPINE galaxies, which are both detected in [C  II ] and in dust continuum, show good agreement with the local L ([CII])–SFR relation. Galaxies undetected in the continuum by ALMA are found to be over-luminous in [C  II ] when the UV SFR is used. After accounting for dust-obscured star formation, by an amount of SFR(IR) ≈ SFR(UV) on average, which results from two different stacking methods and SED fitting, the ALPINE galaxies show an L ([CII])–SFR relation comparable to the local one. When [C  II ] non-detections are taken into account, the slope may be marginally steeper at high- z , although this is still somewhat uncertain. When compared homogeneously, the z  >  6 [C  II ] measurements (detections and upper limits) do not behave very differently to the z  ∼ 4 − 6 data. We find a weak dependence of L ([CII])/SFR on the Ly α equivalent width. Finally, we find that the ratio L ([CII])/ L IR ∼ (1 − 3) × 10 −3 for the ALPINE sources, comparable to that of “normal” galaxies at lower redshift. Our analysis, which includes the largest sample (∼150 galaxies) of [C  II ] measurements at z  > 4 available so far, suggests no or little evolution of the [C  II ]–SFR relation over the last 13 Gyr of cosmic time. 

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2. The ALMA REBELS survey: obscured star formation in massive Lyman-break galaxies at z = 4–8 revealed by the IRX–β and M ⋆ relations

   https://doi.org/10.1093/mnras/stad3578  

   Bowler, R. A. A. ; Inami, H. ; Sommovigo, L. ; Smit, R. ; Algera, H. S. B. ; Aravena, M. ; Barrufet, L. ; Bouwens, R. ; da Cunha, E. ; Cullen, F. ; et al ( November 2023 , Monthly Notices of the Royal Astronomical Society)

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

    

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3. 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)

   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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4. The ALPINE–ALMA [C ii] Survey: The Infrared–Radio Correlation and Active Galactic Nucleus Fraction of Star-forming Galaxies at z ∼ 4.4–5.9

   https://doi.org/10.3847/1538-4357/ac81c5  

   Shen, Lu ; Lemaux, Brian C. ; Lubin, Lori M. ; Liu, Guilin ; Béthermin, Matthieu ; Boquien, Médéric ; Cucciati, Olga ; Le Fèvre, Olivier ; Talia, Margherita ; Vergani, Daniela ; et al ( August 2022 , The Astrophysical Journal)

   We present the radio properties of 66 spectroscopically confirmed normal star-forming galaxies (SFGs) at 4.4 <z< 5.9 in the COSMOS field that were [Cii]-detected in the Atacama Large Millimeter/submillimeter Array Large Program to INvestigate [Cii] at Early times (ALPINE). We separate these galaxies (“Cii-detected-all”) into lower-redshift (“Cii-detected-lz”; 〈z〉 = 4.5) and higher-redshift (“Cii-detected-hz”; 〈z〉 = 5.6) subsamples, and stack multiwavelength imaging for each subsample from X-ray to radio bands. A radio signal is detected in the stacked 3 GHz images of the Cii-detected-all and lz samples at ≳3σ. We find that the infrared–radio correlation of our sample, quantified byq_TIR, is lower than the local relation for normal SFGs at a ∼3σsignificance level, and is instead broadly consistent with that of bright submillimeter galaxies at 2 <z< 5. Neither of these samples show evidence of dominant active galactic nucleus activity in their stacked spectral energy distributions (SEDs), UV spectra, or stacked X-ray images. Although we cannot rule out the possible effects of the assumed spectral index and applied infrared SED templates in causing these differences, at least partially, the lower obscured fraction of star formation than at lower redshift can alleviate the tension between our stackedq_TIRs and those of local normal SFGs. It is possible that the dust buildup, which primarily governs the infrared emission, in addition to older stellar populations, has not had enough time to occur fully in these galaxies, whereas the radio emission can respond on a more rapid timescale. Therefore, we might expect a lowerq_TIRto be a general property of high-redshift SFGs.

    

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5. The dust-to-gas mass ratio of luminous galaxies as a function of their metallicity at cosmic noon

   Popping, Gergö ; Shivaei, Irene ; Sanders, Ryan L. ; Jones, Tucker ; Pope, Alexandra ; Reddy, Naveen A. ; Shapley, Alice E. ; Coil, Alison L. ; Kriek, Mariska ( February 2023 , Astronomy & Astrophysics)

   Aims. We aim to quantify the relation between the dust-to-gas mass ratio (DTG) and gas-phase metallicity of z  = 2.1 − 2.5 luminous galaxies and contrast this high-redshift relation against analogous constraints at z  = 0. Methods. We present a sample of ten star-forming main-sequence galaxies in the redshift range 2.1 <  z  < 2.5 with rest-optical emission-line information available from the MOSDEF survey and with ALMA 1.2 millimetre and CO J  = 3 − 2 follow-up observations. The galaxies have stellar masses ranging from 10 10.3 to 10 10.6   M ⊙ and cover a range in star-formation rate from 35 to 145 M ⊙ yr −1 . We calculated the gas-phase oxygen abundance of these galaxies from rest-optical nebular emission lines (8.4 < 12 + log(O/H) < 8.8, corresponding to 0.5−1.25 Z ⊙ ). We estimated the dust and H 2 masses of the galaxies (using a metallicity-dependent CO-to-H 2 conversion factor) from the 1.2 mm and CO J  = 3 − 2 observations, respectively, from which we estimated a DTG. Results. We find that the galaxies in this sample follow the trends already observed between CO line luminosity and dust-continuum luminosity from z  = 0 to z  = 3, extending such trends to fainter galaxies at 2.1 <  z  < 2.5 than observed to date. We find no second-order metallicity dependence in the CO – dust-continuum luminosity relation for the galaxies presented in this work. The DTGs of main-sequence galaxies at 2.1 <  z  < 2.5 are consistent with an increase in the DTG with gas-phase metallicity. The metallicity dependence of the DTG is driven by the metallicity dependence of the CO-to-H 2 conversion factor. Galaxies at z  = 2.1 − 2.5 are furthermore consistent with the DTG-metallicity relation found at z  = 0 (i.e. with no significant evolution), providing relevant constraints for galaxy formation models. These results furthermore imply that the metallicity of galaxies should be taken into account when estimating cold-gas masses from dust-continuum emission, which is especially relevant when studying metal-poor low-mass or high-redshift galaxies. 

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