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arXiv · 1802.05720

Obscured star-formation in bright z ~ 7 Lyman-break galaxies

R. A. A. Bowler·N. Bourne·J. S. Dunlop·R. J. McLure·D. J. McLeod
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Abstract

We present Atacama Large Millimeter/Submillimeter Array observations of the rest-frame far-infrared (FIR) dust continuum emission of six bright Lyman-break galaxies (LBGs) at $z \simeq 7$. One LBG is detected ($5.2\sigma$ at peak emission), while the others remain individually undetected at the $3\sigma$ level. The average FIR luminosity of the sample is found to be $L_{\rm FIR} \simeq 2 \times 10^{11}\,{\rm L}_{\odot}$, corresponding to an obscured star-formation rate (SFR) that is comparable to that inferred from the unobscured UV emission. In comparison to the infrared excess (IRX$\,=L_{\rm FIR}/L_{\rm UV}$)-$\beta$ relation, our results are consistent with a Calzetti-like attenuation law (assuming a dust temperature of T = 40-50 K). We find a physical offset of 3 kpc between the dust continuum emission and the rest-frame UV light probed by Hubble Space Telescope imaging for galaxy ID65666 at $z = 7.17^{+0.09}_{-0.06}$. The offset is suggestive of an inhomogeneous dust distribution, where 75% of the total star formation activity (SFR$ \,\simeq 70\,{\rm M}_{\odot}/{\rm yr}$) of the galaxy is completely obscured. Our results provide direct evidence that dust obscuration plays a key role in shaping the bright-end of the observed rest-frame UV luminosity function at $z \simeq 7$, in agreement with cosmological galaxy formation simulations. The existence of a heavily-obscured component of galaxy ID65666 indicates that dusty star-forming regions, or even entire galaxies, that are "UV-dark" are significant even in the $z \simeq 7$ galaxy population.

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R. A. A. Bowler, N. Bourne, J. S. Dunlop, R. J. McLure, D. J. McLeod. 2018-02-15. Obscured star-formation in bright z ~ 7 Lyman-break galaxies. https://doi.org/10.1093/mnras/sty2368

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