Journal Article

VLA imaging of <sup>12</sup>CO <i>J</i> = 1-0 and free-free emission in lensed submillimetre galaxies

A. P. Thomson, R. J. Ivison, Ian Smail, A. M. Swinbank, A. Weiss, J.-P. Kneib, P. P. Papadopoulos, A. J. Baker, C. E. Sharon and G. A. van Moorsel

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 425, issue 3, pages 2203-2211
Published in print September 2012 | ISSN: 0035-8711
Published online September 2012 | e-ISSN: 1365-2966 | DOI:
VLA imaging of 12CO J = 1-0 and free-free emission in lensed submillimetre galaxies

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We present a study using the Karl G. Jansky Very Large Array (VLA) of 12CO J = 1−0 emission in three strongly lensed submillimetre-selected galaxies (SMMJ16359, SMMJ14009 and SMMJ02399) at z = 2.5–2.9. These galaxies span LIR = 1011–1013L, offering an opportunity to compare the interstellar medium of luminous infrared galaxies and ultraluminous infrared galaxies at high redshift. We estimate molecular gas masses in the range of 2–40 × 109M using a method that assumes canonical underlying brightness temperature (Tb) ratios for star-forming and non-star-forming gas phases and a maximal star formation efficiency. A more simplistic method – using XCO = 0.8 and the measured Tb ratios – yields gas masses twice as high. In SMMJ14009 we find , indicative of warm, star-forming gas, possibly influenced by the central active galactic nucleus (AGN). We set a gas mass limit of 3σ < 6 × 108M for the Lyman break galaxy, A2218 #384, located in the same field as SMMJ16359 at z = 2.515. Finally, we use the rest-frame ∼115GHz free–free flux densities for SMMJ14009 and SMMJ02399 – measurements tied directly to the photoionization rate of massive stars, and made possible by VLA's bandwidth – to estimate star formation rates (SFRs) of 400–600Myr−1 and to estimate the fraction of LIR due to AGN.

Keywords: ISM: molecules; galaxies: active; galaxies: high-redshift; galaxies: ISM; galaxies: starburst; submillimetre: general

Journal Article.  6228 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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