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The AT-LESS CO(1–0) survey of submillimetre galaxies in the Extended Chandra Deep Field South : first results on cold molecular gas in galaxies at z ∼ 2.

Huynh, Minh T. and Emonts, B. H. C. and Kimball, A. E. and Seymour, N. and Smail, Ian and Swinbank, A. M. and Brandt, W. N. and Casey, C. M. and Chapman, S. C. and Dannerbauer, H. and Hodge, J. A. and Ivison, R. J. and Schinnerer, E. and Thomson, A. P. and van der Werf, P. and Wardlow, J. L. (2017) 'The AT-LESS CO(1–0) survey of submillimetre galaxies in the Extended Chandra Deep Field South : first results on cold molecular gas in galaxies at z ∼ 2.', Monthly notices of the Royal Astronomical Society., 467 (1). pp. 1222-1230.

Abstract

We present the first results from our ongoing Australia Telescope Compact Array survey of 12CO(1–0) in Atacama Large Millimeter Array (ALMA)-identified submillimetre galaxies (SMGs) in the Extended Chandra Deep Field South. Strong detections of 12CO(1–0) emission from two SMGs, ALESS 122.1 (z = 2.0232) and ALESS 67.1 (z = 2.1230), were obtained. We estimate gas masses of Mgas ∼ 1.3 × 1011 M⊙ and Mgas ∼ 1.0 × 1011 M⊙ for ALESS 122.1 and ALESS 67.1, respectively, adopting αCO = 1.0. Dynamical mass estimates from the kinematics of the 12CO(1–0) line yields Mdyn sin2 i = (2.1 ± 1.1) × 1011 M⊙ and (3.2 ± 0.9) × 1011 M⊙ for ALESS 122.1 and ALESS 67.1, respectively. This is consistent with the total baryonic mass estimates of these two systems. We examine star formation efficiency, using the LFIR versus L′CO(1−0) LCO(1−0)′ relation for samples of local ultraluminous infrared galaxies (ULIRGs) and Luminous Infrared Galaxies (LIRGs), and more distant star-forming galaxies, with 12CO(1–0) detections. We find some evidence of a shallower slope for ULIRGs and SMGs compared to less luminous systems, but a larger sample is required for definite conclusions. We determine gas-to-dust ratios of 170 ± 30 and 140 ± 30 for ALESS 122.1 and ALESS 67.1, respectively, showing that ALESS 122.1 has an unusually large gas reservoir. By combining the 38.1 GHz continuum detection of ALESS 122.1 with 1.4 and 5.5 GHz data, we estimate that the free–free contribution to radio emission at 38.1 GHz is 34 ± 17 μJy, yielding a star formation rate (1400 ± 700 M⊙ yr−1) consistent with that from the infrared luminosity.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1093/mnras/stx156
Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:17 January 2017
Date deposited:09 March 2017
Date of first online publication:22 January 2017
Date first made open access:09 March 2017

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