A deep ALMA image of the Hubble Ultra Deep Field

• Published in: Monthly notices of the Royal Astronomical Society Vol. 466; no. 1; pp. 861 - 883
• Main Authors: Dunlop, J. S., McLure, R. J., Biggs, A. D., Geach, J. E., Michałowski, M. J., Ivison, R. J., Rujopakarn, W., van Kampen, E., Kirkpatrick, A., Pope, A., Scott, D., Swinbank, A. M., Targett, T. A., Aretxaga, I., Austermann, J. E., Best, P. N., Bruce, V. A., Chapin, E. L., Charlot, S., Cirasuolo, M., Coppin, K., Ellis, R. S., Finkelstein, S. L., Hayward, C. C., Hughes, D. H., Ibar, E., Jagannathan, P., Khochfar, S., Koprowski, M. P., Narayanan, D., Nyland, K., Papovich, C., Peacock, J. A., Rieke, G. H., Robertson, B., Vernstrom, T., Werf, P. P. van der, Wilson, G. W., Yun, M.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 01-04-2017; Oxford University Press (OUP): Policy P - Oxford Open Option A
• Subjects: Galaxies; Physical properties; Radio telescopes; Red shift; Sciences of the Universe; Space telescopes; Star & galaxy formation; Star formation; Stellar mass; Transits; Universe; galaxies: starburst; cosmology: observations; submillimetre: galaxies; galaxies: evolution; galaxies: high-redshift; Astrophysics - Astrophysics of Galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw3088

Abstract
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 S
1.3 > 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 S
1.3 ≃ 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.