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A deep ALMA image of the Hubble Ultra Deep Field.

Dunlop, J. S. and McLure, R. J. and Biggs, A. D. and Geach, J. E. and Michałowski, M. J. and Ivison, R. J. and Rujopakarn, W. and van Kampen, E. and Kirkpatrick, A. and Pope, A. and Scott, D. and Swinbank, A. M. and Targett, T. A. and Aretxaga, I. and Austermann, J. E. and Best, P. N. and Bruce, V. A. and Chapin, E. L. and Charlot, S. and Cirasuolo, M. and Coppin, K. and Ellis, R. S. and Finkelstein, S. L. and Hayward, C. C. and Hughes, D. H. and Ibar, E. and Jagannathan, P. and Khochfar, S. and Koprowski, M. P. and Narayanan, D. and Nyland, K. and Papovich, C. and Peacock, J. A. and Rieke, G. H. and Robertson, B. and Vernstrom, T. and van der Werf, P. P. and Wilson, G. W. and Yun, M. (2017) 'A deep ALMA image of the Hubble Ultra Deep Field.', Monthly notices of the Royal Astronomical Society., 466 (1). pp. 861-883.


We present the results of the first, deep Atacama Large Millimeter Array (ALMA) imaging covering the full ≃4.5 arcmin2 of the Hubble Ultra Deep Field (HUDF) imaged with Wide Field Camera 3/IR on HST. Using a 45-pointing mosaic, we have obtained a homogeneous 1.3-mm image reaching σ1.3 ≃ 35 μJy, at a resolution of ≃0.7 arcsec. From an initial list of ≃50 > 3.5σ peaks, a rigorous analysis confirms 16 sources with S1.3 > 120 μJy. All of these have secure galaxy counterparts with robust redshifts (〈z〉 = 2.15). Due to the unparalleled supporting data, the physical properties of the ALMA sources are well constrained, including their stellar masses (M*) and UV+FIR star formation rates (SFR). Our results show that stellar mass is the best predictor of SFR in the high-redshift Universe; indeed at z ≥ 2 our ALMA sample contains seven of the nine galaxies in the HUDF with M* ≥ 2 × 1010 M⊙, and we detect only one galaxy at z > 3.5, reflecting the rapid drop-off of high-mass galaxies with increasing redshift. The detections, coupled with stacking, allow us to probe the redshift/mass distribution of the 1.3-mm background down to S1.3 ≃ 10 μJy. We find strong evidence for a steep star-forming ‘main sequence’ at z ≃ 2, with SFR ∝M* and a mean specific SFR ≃ 2.2 Gyr−1. Moreover, we find that ≃85 per cent of total star formation at z ≃ 2 is enshrouded in dust, with ≃65 per cent of all star formation at this epoch occurring in high-mass galaxies (M* > 2 × 1010 M⊙), for which the average obscured:unobscured SF ratio is ≃200. Finally, we revisit the cosmic evolution of SFR density; we find this peaks at z ≃ 2.5, and that the star-forming Universe transits from primarily unobscured to primarily obscured at z ≃ 4.

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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:25 November 2016
Date deposited:09 March 2017
Date of first online publication:30 November 2016
Date first made open access:09 March 2017

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