Obscured star formation in bright z ≃ 7 Lyman-break galaxies. Issue 2 (31st August 2018)

• Record Type: Journal Article
• Authors: Bowler, R A A; Bourne, N; Dunlop, J S; McLure, R J; McLeod, D J
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 481:Issue 2(2018)
• Page Start: 1631
• Page End: 1644
• Publication Date: 2018-08-31
• Subjects: galaxies: evolution -- galaxies: high-redshift; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty2368
• Languages: English
• ISSNs: 0035-8711

Abstract

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 $z$ ≃ 7. One LBG is detected (5.2σ at peak emission), whilst the others remain individually undetected at the 3σ 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$\, =L_{\rm FIR}/L_{\rm UV}$ )–β 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 $3\, {\rm kpc}$ 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 per cent 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 $z$ ≃ 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 $z$ ≃ 7 galaxy population.