Abstract

ABSTRACT We make use of deep 1.2 mm continuum observations (12.7 μ Jy beam −1 rms) of a 1 arcmin 2 region in the Hubble Ultra Deep Field to probe dust-enshrouded star formation from 330 Lyman-break galaxies spanning the redshift range z = 2–10 (to ∼2–3 M ⊙ yr −1 at 1 σ over the entire range). Given the depth and area of ASPECS, we would expect to tentatively detect 35 galaxies, extrapolating the Meurer z ∼ 0 IRX– β relation to z ≥ 2 (assuming dust temperature T d ∼ 35 K). However, only six tentative detections are found at z ≳ 2 in ASPECS, with just three at >3 σ . Subdividing our z = 2–10 galaxy samples according to stellar mass, UV luminosity, and UV-continuum slope and stacking the results, we find a significant detection only in the most massive (>10 9.75 M ⊙ ) subsample, with an infrared excess (IRX = L IR / L UV ) consistent with previous z ∼ 2 results. However, the infrared excess we measure from our large selection of sub- L ∗ (<10 9.75 M ⊙ ) galaxies is ± 0.34 (bootstrap and formal uncertainties) and ± 0.18 at z = 2–3 and z = 4–10, respectively, lying below even an IRX– β relation for the Small Magellanic Cloud (95% confidence). These results demonstrate the relevance of stellar mass for predicting the IR luminosity of z ≳ 2 galaxies. We find that the evolution of the IRX–stellar mass relationship depends on the evolution of the dust temperature. If the dust temperature increases monotonically with redshift ( ) such that T d ∼ 44–50 K at z ≥ 4, current results are suggestive of little evolution in this relationship to z ∼ 6. We use these results to revisit recent estimates of the z ≥ 3 star formation rate density.