VLA imaging of 12CO J = 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, G. A. van Moorsel

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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 L CO 3-2′/L CO 1-0′=0.95±0.12, 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.

Original languageEnglish (US)
Pages (from-to)2203-2211
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Sep 21 2012

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Active
  • Galaxies
  • General
  • High-redshift
  • ISM
  • Molecules
  • Starburst
  • Submillimetre


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