The ALMA Spectroscopic Survey Large Program: The Infrared Excess of z = 1.5–10 UV-selected Galaxies and the Implied High-redshift Star Formation History

Abstract

We make use of sensitive (9.3 μJy beam −1 rms) 1.2 mm continuum observations from the Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra-Deep Field (ASPECS) large program to probe dust-enshrouded star formation from 1362 Lyman-break galaxies spanning the redshift range z=1.5-10 (to ∼7-28 M e yr −1 at 4σ 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 9.0 M e to-+ 85 18 9 % at >10 10 M e. Moreover, on stacking all 1253 low-mass (<10 9.25 M e) galaxies over the ASPECS footprint, we find a mean continuum flux of −0.1±0.4 μJy beam −1 , implying a hard upper limit on the obscured star formation rate of <0.6 M e yr −1 (4σ) 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 >  M 10 9.5 and an SMC-like relation at lower masses. Using stellar mass and β measurements for z∼2 galaxies over the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we derive a new empirical relation between β and stellar mass and then use this correlation to show that our IRX-β and IRX-stellar mass relations are consistent with each other. We then use these constraints to express the IRX as a bivariate function of β and stellar mass. Finally, we present updated estimates of star formation rate density determinations at z>3, leveraging present improvements in the measured IRX and recent probes of ultraluminous far-IR galaxies at z>2. Unified Astronomy Thesaurus concepts: Lyman-break galaxies (979); Infrared excess (788); High-redshift galaxies (734); Dust continuum emission (412); Far infrared astronomy (529)

The Evolution of the IR Luminosity Function and Dust-obscured Star Formation over the Past 13 Billion Years

“…Our picture of the history of the cosmic star formation is consistent with previous results from long-wavelength (FIR to millimeter) surveys (e.g., Bourne et al 2017;Dunlop et al 2017;Hatsukade et al 2018;Dudzevičiūtė et al 2020), although most of those were limited to z  4. Hence, our results represent significant progress on our understanding of the prevalence of DSFGs during the first 1.5 billion years of the universe and complement the significant efforts carried out using UV/ optically selected galaxies (e.g., Bouwens et al 2020). The inferred SFRD is also in broad agreement with the most recent predictions from galaxy evolution models (like IllustrisTNG and SHARK; Pillepich et al 2018;Lagos et al 2020), which point toward a convergence between models and observations.…”

“…This suggests that the bulk (80%) of the star formation activity in the first billion years of the universe was not dust enshrouded. Given the massive nature of DSFGs, this drop-off of the obscured component is in line with the decreasing number of high-mass galaxies with increasing redshift (see also Dunlop et al 2017;Bouwens et al 2020).…”

“…Other studies based on stacking analysis on (sub)millimeter maps and using samples of UV/optically selected galaxies have also concluded that the fraction of star formation that is obscured by dust decreases at high redshifts (e.g., Capak et al 2015;Bouwens et al 2016;Fudamoto et al 2020). Indeed, Bouwens et al (2020) complemented previous results from the literature with their dust-corrected SFRs to estimate the obscured and unobscured components of the cosmic history of star formation and found that the CSFRD transitions from being primarily unobscured to obscured at z ∼ 5, in relatively good agreement with our estimations 32 from direct millimeterselected samples.…”

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Multiband Constraints on Line-luminosity Functions and the Cosmic Density of Molecular Gas

“…Therefore, we opt not to include this further term into our estimates of the uncertainties. In support of the negligible contribution of cosmic variance, Magnelli et al (2020) and Bouwens et al (2020) find an excellent match between the stellar mass functions and cosmic SFR density in the ASPECS footprint and the ones inferred in the literature from much wider regions in different (physically disconnected) fields at any z0.5.…”

Dependence of the IRX-β Dust Attenuation Relation on Metallicity and Environment *

“…Theoretical studies have shown that the IRX-β scatter may depend on the type of dust, gas metallicity, star formation history (SFH), dust-star geometry, and stellar population age (Popping et al 2017;Safarzadeh et al 2017;Narayanan et al 2018;Schulz et al 2020). Observations have shown that the IRX-β relation varies with stellar mass (Bouwens et al 2016(Bouwens et al , 2020Reddy et al 2018;Fudamoto et al 2020), infrared (IR) luminosity (Buat et al 2012;Casey et al 2014), age (Siana et al 2009;Reddy et al 2010;Shivaei et al 2015), redshift (Capak et al 2015;Pannella et al 2015), and intrinsic β 0 (β for a dust-free system; Boquien et al 2012;Reddy et al 2018;Schulz et al 2020). These variations are linked to the diversity of galaxies' attenuation curves, seen in previous studies (e.g., Kriek & Conroy 2013;Scoville et al 2015;Battisti et al 2020).…”