2022ApJ...928...31S

We make use of Atacama Large Millimeter/submillimeter Array continuum observations of 15 luminous Lyman-break galaxies at z ∼ 7-8 to probe their dust-obscured star formation. These observations are sensitive enough to probe obscured star formation rates (SFRs) of 20 M_☉ yr^–1 (3σ). Six of the targeted galaxies show significant (>=3σ) dust-continuum detections, more than doubling the number of known dust-detected galaxies at z > 6.5. Their IR luminosities range from 2.7 x 10¹¹L_☉ to 1.1 x 10¹²L_☉, equivalent to obscured SFRs of 25 to 101 M_☉ yr^–1. We use our results to quantify the correlation of the infrared excess (IRX) on the UV-continuum slope β_UV and stellar mass. Our results are most consistent with a Small Magellanic Cloud (SMC) attenuation curve for intrinsic UV-slopes β_UV,intr of -2.63 and most consistent with an attenuation curve in between SMC and Calzetti for β_UV,intr slopes of -2.23, assuming a dust temperature T_d of 50 K. Our fiducial IRX-stellar mass results at z ∼ 7-8 are consistent with marginal evolution from z ∼ 0. We then show how both results depend on T_d. For our six dust-detected sources, we estimate their dust masses and find that they are consistent with dust production from supernovae if the dust destruction is low (<90%). Finally we determine the contribution of dust-obscured star formation to the SFR density for UV luminous (H←21.5 mag: >=1.7 L^*_UV) z ∼ 7-8 galaxies, finding that the total SFR density at z ∼ 7 and z ∼ 8 from bright galaxies is {0.20}_{-0.10}^{+0.10} dex and {0.23}_{-0.09}^{+0.06} dex higher, respectively; i.e., ∼1{3} of the star formation in >=1.7 L^*_UV galaxies at z ∼ 7-8 is obscured by dust.