Journal Article

The ATLAS<sup>3D</sup> project – XI. Dense molecular gas properties of CO-luminous early-type galaxies*

Alison Crocker, Melanie Krips, Martin Bureau, Lisa M. Young, Timothy A. Davis, Estelle Bayet, Katherine Alatalo, Leo Blitz, Maxime Bois, Frédéric Bournaud, Michele Cappellari, Roger L. Davies, P. T. de Zeeuw, Pierre-Alain Duc, Eric Emsellem, Sadegh Khochfar, Davor Krajnović, Harald Kuntschner, Pierre-Yves Lablanche, Richard M. McDermid, Raffaella Morganti, Thorsten Naab, Tom Oosterloo, Marc Sarzi, Nicholas Scott, Paolo Serra and Anne-Marie Weijmans

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 421, issue 2, pages 1298-1314
Published in print April 2012 | ISSN: 0035-8711
Published online March 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.20393.x
The ATLAS3D project – XI. Dense molecular gas properties of CO-luminous early-type galaxies*

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Surveying 18 12CO-bright galaxies from the ATLAS3D early-type galaxy sample with the Institut de Radio Astronomie Millimétrique (IRAM) 30-m telescope, we detect 13CO(1–0) and 13CO(2–1) in all 18 galaxies, HCN(1–0) in 12/18 and HCO+(1–0) in 10/18. We find that the line ratios 12CO(1–0)/13CO(1–0) and 12CO(1–0)/HCN(1–0) are clearly correlated with several galaxy properties: total stellar mass, luminosity-weighted mean stellar age, molecular-to-atomic gas ratio, dust temperature and dust morphology. We suggest that these correlations are primarily governed by the optical depth in the 12CO lines; interacting, accreting and/or starbursting early-type galaxies have more optically thin molecular gas while those with settled dust and gas discs host optically thick molecular gas. The ranges of the integrated line intensity ratios generally overlap with those of spirals, although we note some outliers in the 12CO(1–0)/13CO(1–0), 12CO(2–1)/13CO(2–1) and HCN/HCO+(1–0) ratios. In particular, three galaxies are found to have very low 12CO(1–0)/13CO(1–0) and 12CO(2–1)/13CO(2–1) ratios. Such low ratios may signal particularly stable molecular gas which creates stars less efficiently than ‘normal’ (i.e. below Schmidt–Kennicutt prediction), consistent with the low dust temperatures seen in these galaxies.

Keywords: galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: ISM; galaxies: kinematics and dynamics; galaxies: stellar content

Journal Article.  10452 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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