A survey of the cold molecular gas in gravitationally lensed star-forming galaxies at z > 2
Using the Australia Telescope Compact Array, we conducted a survey of CO J = 1 − 0 and J = 2 − 1 line emission towards strongly lensed high-redshift dusty star-forming galaxies (DSFGs) previously discovered with the South Pole Telescope (SPT). Our sample comprises 17 sources that had CO-based spectroscopic redshifts obtained with the Atacama Large Millimeter/submillimeter Array and the Atacama Pathfinder Experiment. We detect all sources with known redshifts in either CO J = 1 − 0 or J = 2 − 1. 12 sources are detected in the 7-mm continuum. The derived CO luminosities imply gas masses in the range (0.5–11) × 10^(10) M⊙ and gas depletion time-scales t_(dep) < 200 Myr, using a CO to gas mass conversion factor αCO = 0.8 M⊙ (K km s^(−1) pc^2)^(−1). Combining the CO luminosities and dust masses, along with a fixed gas-to-dust ratio, we derive α_(CO) factors in the range 0.4–1.8 M⊙ (K km s^(−1) pc^2)^(−1), similar to what is found in other starbursting systems. We find small scatter in αCO values within the sample, even though inherent variations in the spatial distribution of dust and gas in individual cases could bias the dust-based α_(CO) estimates. We find that lensing magnification factors based on the CO linewidth to luminosity relation (μCO) are highly unreliable, but particularly when μ < 5. Finally, comparison of the gas and dynamical masses suggest that the average molecular gas fraction stays relatively constant at z = 2–5 in the SPT DSFG sample.
© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 February 1. Received 2016 January 31; in original form 2015 November 4. First published online February 9, 2016. MA acknowledges partial support from FONDECYT through grant 1140099. JSS, DPM and JDV acknowledge support from the US National Science Foundation under grant no. AST-1312950. JSS acknowledges support through award SOSPA1-006 from the NRAO. The Australia Telescope is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. The SPT is supported by the National Science Foundation through grant ANT-0638937, with partial support through PHY-1125897, the Kavli Foundation and the Gordon and Betty Moore Foundation.
Submitted - 1602.00652v1.pdf
Published - MNRAS-2016-Aravena-4406-20.pdf