VLA imaging of 12CO J=1-0 and free-free emission in lensed submillimetre galaxies
Résumé
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 (SMM?J16359, SMM?J14009 and SMM?J02399) at z = 2.52.9. These galaxies span LIR = 10111013?L?, 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 240 X 109?M? 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 SMM?J14009 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 3s \textless 6 X 108?M? for the Lyman break galaxy, A2218 #384, located in the same field as SMM?J16359 at z = 2.515. Finally, we use the rest-frame similar to 115?GHz freefree flux densities for SMM?J14009 and SMM?J02399 measurements tied directly to the photoionization rate of massive stars, and made possible by VLA's bandwidth to estimate star formation rates (SFRs) of 400600?M??yr-1 and to estimate the fraction of LIR due to AGN.