Large gas reservoirs and free–free emission in two lensed star-forming galaxies at z = 2.7

Abstract

We report the detection of CO(1-0) line emission in the bright, lensed star-forming galaxies SPT-S 233227-5358.5 (z = 2.73) and SPT-S 053816-5030.8 (z = 2.78), using the Australia Telescope Compact Array. Both galaxies were discovered in a large-area millimetre survey with the South Pole Telescope (SPT) and found to be gravitationally lensed by intervening structures. The measured CO intensities imply galaxies with molecular gas masses of (3.2 0.5) 10 10 (/15) -1 (X CO /0.8) and (1.7 0.3) 10 10 (/20) -1 (X CO /0.8) M , and gas depletion time-scales of 4.9 10 7 (X CO /0.8) and 2.6 10 7 (X CO /0.8) yr, respectively, where corresponds to the lens magnification and X CO is the CO luminosity to gas mass conversion factor. In the case of SPT-S 053816-5030.8, we also obtained significant detections of the rest-frame 115.7 and 132.4 GHz radio continuum. Based on the radio-to-infrared spectral energy distribution and an assumed synchrotron spectral index, we find that 42 10 and 55