* Astronomy

Title: Blind detections of CO J = 1--0 in 11 H-ATLAS galaxies at z = 2.1--3.5 with the GBT/Zpectrometer
Authors: A. I. Harris, A. J. Baker, D. T. Frayer, Ian Smail, A. M. Swinbank, D. A. Riechers, P. P. van der Werf, R. Auld, M. Baes, R. S. Bussmann, S. Buttiglione, A. Cava, D. L. Clements, A. Cooray, H. Dannerbauer, A. Dariush, G. DeZotti, L. Dunne, S. Dye, S. Eales, J. Fritz, J. Gonzalez-Nuevo, R. Hopwood, E. Ibar, R. J. Ivison, M. J. Jarvis, S. Maddox, M. Negrello, E. Rigby, D. J. B. Smith, P. Temi, J. Wardlow

We report measurements of the carbon monoxide ground state rotational transition (12C16O J = 1--0) with the Zpectrometer ultra-wideband spectrometer on the 100-m diameter Green Bank Telescope. The sample comprises 11 galaxies with redshifts between z = 2.1 and 3.5 from a total sample of 24 targets identified by Herschel-ATLAS photometric colours from the SPIRE instrument. Nine of the CO measurements are new redshift determinations, substantially adding to the number of detections of galaxies with rest-frame peak submillimetre emission near 100µm. The CO detections confirm the existence of massive gas reservoirs within these luminous dusty star-forming galaxies (DSFGs). The CO redshift distribution of the 350µm-selected galaxies is strikingly similar to the optical redshifts of 850µm-selected submillimetre galaxies (SMGs) in 2.1 < z < 3.5. Spectroscopic redshifts break a temperature-redshift degeneracy; optically thin dust models fit to the far-infrared photometry indicate characteristic dust temperatures near 34 K for most of the galaxies we detect in CO. Detections of two warmer galaxies and statistically significant nondetections hint at warmer or molecule-poor DSFGs with redshifts difficult determine from Herschel-SPIRE photometric colours alone. Many of the galaxies identified by H-ATLAS photometry are expected to be amplified by foreground gravitational lenses. Analysis of CO linewidths and luminosities provides a method for finding approximate gravitational lens magnifications µ from spectroscopic data alone, yielding µ ~ 3--20. Corrected for magnification, most galaxy luminosities are consistent with an ultra-luminous infrared galaxy (ULIRG) classification, but three are candidate hyper-LIRGs with luminosities greater than 10^13 L_sun.

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