2012MNRAS.425.2203T

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 L_IR= 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 x 10⁹M_☉ using a method that assumes canonical underlying brightness temperature (T_b) ratios for star-forming and non-star-forming gas phases and a maximal star formation efficiency. A more simplistic method – using X_CO= 0.8 and the measured T_b ratios – yields gas masses twice as high. In SMMJ14009 we find \mi L\mi CO\mn 3\mo –\mn 2\mo '\mo/\mi L\mi CO\mn 1\mo –\mn 0\mo '\mn 0.95=±\mn 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 x 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 400–600M_☉/yr and to estimate the fraction of L_IR due to AGN.