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Published September 21, 2015 | Published
Journal Article Open

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

Abstract

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) × 10^(10) M_⊙ which is comparable to the total molecular gas masses of (2.7 ± 0.5) × 10^(10) M_⊙ and (3.5 ± 0.6) × 10^(10) 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 ± 80 M⊙ 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.

Additional Information

© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 June 26. Received 2015 June 25. In original form 2015 April 13. First published online July 24, 2015. SD acknowledges financial support from the Midland Physics Alliance and STFC. CF acknowledges funding from CAPES (proc. 12203-1). MN acknowledges financial support by PRIN-INAF 2012 project 'Looking into the dust-obscured phase of galaxy formation through cosmic zoom lenses in the H-ATLAS'. LD, RJI and IO acknowledge support from the European Research Council (ERC) in the form of the Advanced Investigator Program, COSMICISM. IRS acknowledges support from STFC (ST/L00075X/1), the ERC Advanced Investigator programme DUSTYGAL 321334 and a Royal Society/Wolfson Merit Award. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00016.SV. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The work in this paper is based on observations made with the NASA/ESA Hubble Space Telescope under the HST programme #12194.

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August 22, 2023
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