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

TL;DR

This study uses ALMA observations to analyze dust-obscured star formation in UV-selected galaxies from redshift 1.5 to 10, revealing how infrared excess correlates with stellar mass and UV slope, impacting high-redshift star formation estimates.

Contribution

It provides new empirical relations between IRX, stellar mass, and UV slope, improving understanding of dust obscuration and star formation at high redshift.

Findings

Detection fraction increases with stellar mass, reaching 85% at >10^{10} Msolar.

Stacking low-mass galaxies yields a tight upper limit on obscured SFR.

IRX correlates with stellar mass and UV slope, following Calzetti-like and SMC-like relations.

Abstract

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.