Publication Date:
2017-01-12
Description:
We present the results of the first, deep Atacama Large Millimeter Array (ALMA) imaging covering the full ~=4.5 arcmin 2 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 1.3 ~= 35 μJy, at a resolution of ~=0.7 arcsec. From an initial list of ~=50 〉 3.5 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 x 10 10 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 x 10 10 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.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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