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Significant Dust-Obscured Star Formation in Luminous Lyman-break Galaxies at $z$$\sim$$7$$-$$8$

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(2021)cite arxiv:2105.12133Comment: 21 pages, 12 figures, 2 tables. Submitted to ApJ.

Abstract

We make use of ALMA continuum observations of $15$ luminous Lyman-break galaxies at $z$$\sim$$7$$-$$8$ to probe their dust-obscured star-formation. These observations are sensitive enough to probe to obscured SFRs of $20$ $M_ødot$$/$$yr$ ($3\sigma$). Six of the targeted galaxies show significant ($\geq$$3$$\sigma$) dust continuum detections, more than doubling the number of known dust-detected galaxies at $z$$>$$6.5$. Their IR luminosities range from $2.7$$\times$$10^11$ $L_ødot$ to $1.1$$\times$$10^12$ $L_ødot$, equivalent to obscured SFRs of $20$ to $105$ $M_ødot$$/$$yr$. We use our results to quantify the correlation of the infrared excess IRX on the UV-continuum slope $\beta_UV$ and stellar mass. Our results are most consistent with an SMC attenuation curve for intrinsic $UV$-slopes $\beta_UV,intr$ of $-2.63$ and most consistent with an attenuation curve in-between SMC and Calzetti for $\beta_UV,intr$ slopes of $-2.23$, assuming a dust temperature $T_d$ of $50$ K. Our fiducial IRX-stellar mass results at $z$$\sim$$7$$-$$8$ are consistent with marginal evolution from $z$$\sim$$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 SNe if the dust destruction is low ($<$$90$%). Finally we determine the contribution of dust-obscured star formation to the star formation rate density for $UV$ luminous ($<$$-$$21.5$ mag: $\gtrsim$$1.7$$L_UV ^*$) $z$$\sim$$7$$-$$8$ galaxies, finding that the total SFR density at $z$$\sim$$7$ and $z$$\sim$$8$ from bright galaxies is $0.18_-0.10^+0.08$ dex and $0.20_-0.09^+0.05$ dex higher, respectively, i.e. $\sim$$13$ of the star formation in $\gtrsim$$1.7$$L_UV ^*$ galaxies at $z$$\sim$$7$$-$$8$ is obscured by dust.

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