A survey of the cold molecular gas in gravitationally lensed star-forming galaxies at z > 2

• Published in: Monthly Notices of the Royal Astronomical Society
• Main Authors: Aravena, M., Spilker, J. S., Bethermin, M., Bothwell, M., Chapman, S. C., de Breuck, C., Furstenau, R. M., Gónzalez-López, J., Greve, T. R., Litke, K., Ma, J., Malkan, M., Marrone, D. P., Murphy, E. J., Stark, A., Strandet, M., Vieira, J. D., Weiss, A., Welikala, N., Wong, G. F., Collier, J. D.
• Format: Text
• Language: English
• Published: Oxford University Press 2016
• Subjects: Article; South Pole; South pole
• Online Access: http://mnras.oxfordjournals.org/cgi/content/short/457/4/4406; https://doi.org/10.1093/mnras/stw275

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) × 1010 M ⊙ and gas depletion time-scales t dep < 200 Myr, using a CO to gas mass conversion factor α CO = 0.8 M ⊙ (K km s−1 pc2)−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 pc2)−1, similar to what is found in other starbursting systems. We find small scatter in α CO 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 (μ CO ) 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.