2020ApJ...902..112B

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_☉ 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_☉ to 85_–18⁺⁹% at >10¹⁰ M_☉. Moreover, on stacking all 1253 low-mass (<10^9.25 M_☉) 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_☉ 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 >10^9.5M_☉ 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.