Revealing the complex nature of the strong gravitationally lensed system H-ATLAS J090311.6+003906 using ALMA

S. Dye, C. Furlanetto, A. M. Swinbank, C. Vlahakis, J. W. Nightingale, L. Dunne, S. A. Eales, Ian Smail, I. Oteo, T. Hunter, M. Negrello, H. Dannerbauer, R. J. Ivison, R. Gavazzi, A. Cooray, P. van der Werf

Research output: Contribution to journalArticlepeer-review


We have modelled Atacama Large Millimetre/sub-millimetre Array (ALMA) long baseline imaging of the strong gravitational lens system H-ATLAS J090311.6+003906 (SDP.81). We have reconstructed the distribution of band 6 and 7 continuum emission in the z = 3.042 source and determined its kinematic properties by reconstructing CO(5-4) and CO(8-7) line emission in bands 4 and 6. The continuum imaging reveals a highly non-uniform distribution of dust with clumps on scales of ~200 pc. In contrast, the CO line emission shows a relatively smooth, disc-like velocity field which is well fitted by a rotating disc model with an inclination angle of (40 ± 5)° and an asymptotic rotation velocity of 320 km s-1. The inferred dynamical mass within 1.5 kpc is (3.5±0.5)×1010 M which is comparable to the total molecular gas masses of (2.7 ± 0.5) × 1010 M and (3.5 ± 0.6) × 1010 M from the dust continuum emission and CO emission, respectively. Our new reconstruction of the lensed Hubble Space Telescope near-infrared emission shows two objects which appear to be interacting, with the rotating disc of gas and dust revealed by ALMA distinctly offset from the near-infrared emission. The clumpy nature of the dust and a low value of the Toomre parameter of Q ~ 0.3 suggest that the disc is in a state of collapse.We estimate a star formation rate in the disc of 470 ± 80M yr-1 with an efficiency ~65 times greater than typical low-redshift galaxies. Our findings add to the growing body of evidence that the most infrared luminous, dust obscured galaxies in the high-redshift Universe represent a population of merger-induced starbursts.

Original languageEnglish
Pages (from-to)2258-2268
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 23 Jul 2015


  • Galaxies: str
  • Gravitational lensing: strong

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