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An ALMA survey of CO in submillimetre galaxies: companions, triggering, and the environment in blended sources

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posted on 23.05.2019, 10:37 by JL Wardlow, JM Simpson, I Smail, AM Swinbank, AW Blain, WN Brandt, SC Chapman, C-C Chen, EA Cooke, H Dannerbauer, B Gullberg, JA Hodge, RJ Ivison, KK Knudsen, D Scott, AP Thomson, A Weiss, PP van der Werf
We present ALMA observations of the mid-J 12CO emission from six single-dish selected 870-μm sources in the Extended Chandra Deep Field-South and UKIDSS Ultra-Deep Survey fields. These six single-dish submillimetre sources were selected based on previous ALMA continuum observations, which showed that each comprised a blend of emission from two or more individual submillimetre galaxies (SMGs), separated on 5–10 arcsec scales. The six single-dish submillimetre sources targeted correspond to a total of 14 individual SMGs, of which seven have previously measured robust optical/near-infrared spectroscopic redshifts, which were used to tune our ALMA observations. We detect CO(3–2) or CO(4–3) at z = 2.3– 3.7 in 7 of the 14 SMGs, and in addition serendipitously detect line emission from three gas-rich companion galaxies, as well as identify four new 3.3 mm selected continuum sources in the six fields. Joint analysis of our CO spectroscopy and existing data suggests that 64(±18) per cent of the SMGs in blended submillimetre sources are unlikely to be physically associated. However, three of the SMG fields (50 per cent) contain new, serendipitously detected CO-emitting (but submillimetre-faint) sources at similar redshifts to the 870 μm selected SMGs we targeted. These data suggest that the SMGs inhabit overdense regions, but that these are not sufficiently overdense on ∼100 kpc scales to influence the source blending given the short lifetimes of SMGs. We find that 21 ± 12 per cent of SMGs have spatially distinct and kinematically close companion galaxies (∼8–150 kpc and 300 km s−1), which may have enhanced their star formation via gravitational interactions.


JLW acknowledges support from a Science and Technology Facilities Council (STFC) Ernest Rutherford Fellowship (ST/P004784/1) and from a European Union COFUND/Durham Junior Research Fellowship under EU grant agreement number 609412. IRS, EAC, and BG acknowledge support from the European Research Council (ERC) Advanced Grant DUSTYGAL (#321334), and IRS also recognizes support from a Royal Society/Wolfsom Merit Award. JLW, IRS, AMS, EAC, and BG also acknowledge support from STFC (ST/P000541/1). HD acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under the 2014 Ramón y Cajal programme MINECO RYC-2014-15686, and JH acknowledges support of the VIDI research programme with project number 639.042.611, which is (partly) financed by the Netherlands Organisation for Scientific Research (NWO). This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.00754.S. 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. Based in part on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 094.A-0811(A).



Monthly Notices of the Royal Astronomical Society, 2018, 479 (3), pp. 3879-3891 (13)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society





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The raw and pipeline-processed data used in this paper are available from the ALMA Science Archive, and the raw XSHOOTER data are available from the ESO Science Archive Facility.