Journal Article

COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies – I. Relations between H<sub>2</sub>, H <span class="smallCaps">i</span>, stellar content and structural properties

Amélie Saintonge, Guinevere Kauffmann, Carsten Kramer, Linda J. Tacconi, Christof Buchbender, Barbara Catinella, Silvia Fabello, Javier Graciá-Carpio, Jing Wang, Luca Cortese, Jian Fu, Reinhard Genzel, Riccardo Giovanelli, Qi Guo, Martha P. Haynes, Timothy M. Heckman, Mark R. Krumholz, Jenna Lemonias, Cheng Li, Sean Moran, Nemesio Rodriguez-Fernandez, David Schiminovich, Karl Schuster and Albrecht Sievers

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 415, issue 1, pages 32-60
Published in print July 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18677.x
COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies – I. Relations between H2, H i, stellar content and structural properties

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We are conducting COLD GASS, a legacy survey for molecular gas in nearby galaxies. Using the IRAM 30-m telescope, we measure the CO(1−0) line in a sample of ∼350 nearby ( Mpc), massive galaxies (log(M*/M) > 10.0). The sample is selected purely according to stellar mass, and therefore provides an unbiased view of molecular gas in these systems. By combining the IRAM data with Sloan Digital Sky Survey (SDSS) photometry and spectroscopy, GALEX imaging and high-quality Arecibo H i data, we investigate the partition of condensed baryons between stars, atomic gas and molecular gas in 0.1–10L* galaxies. In this paper, we present CO luminosities and molecular hydrogen masses for the first 222 galaxies. The overall CO detection rate is 54 per cent, but our survey also uncovers the existence of sharp thresholds in galaxy structural parameters such as stellar mass surface density and concentration index, below which all galaxies have a measurable cold gas component but above which the detection rate of the CO line drops suddenly. The mean molecular gas fraction of the CO detections is 0.066 ± 0.039, and this fraction does not depend on stellar mass, but is a strong function of (NUV − r) colour. Through stacking, we set a firm upper limit of for red galaxies with NUV − r > 5.0. The average molecular-to-atomic hydrogen ratio in present-day galaxies is 0.3, with significant scatter from one galaxy to the next. The existence of strong detection thresholds in both the H i and CO lines suggests that ‘quenching’ processes have occurred in these systems. Intriguingly, atomic gas strongly dominates in the minority of galaxies with significant cold gas that lie above these thresholds. This suggests that some re-accretion of gas may still be possible following the quenching event.

Keywords: surveys; galaxies: evolution; galaxies: fundamental parameters; galaxies: ISM; radio lines: galaxies

Journal Article.  11498 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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