2005/04/19 by Desika Narayanan, Christopher K. Walker, Christopher Groppi +2
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Galaxy #Infrared #Luminosity #Luminous infrared galaxy #Physics #Spiral galaxy #Star formation #astro-ph
paper · pdf · doi:10.1086/431171
published as Astrophys.J.630:269-279,2005; Erratum-ibid.642:616,2006; Erratum-ibid.721:921,2010 · 15 Pages, 2 figures, Accepted for Publication in ApJ
arxiv created 2005/04/19 · openalex publication_date 2005/09/01 · arxiv updated 2014/10/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
The role of star formation in luminous and ultraluminous infrared galaxies (LIRGs, L IR ≥ 10 11 L ☉ ; ULIRGs, L IR ≥ 10 12 L ☉ ) is a hotly debated issue: while it is clear that starbursts play a large role in powering the IR luminosity in these galaxies, the relative importance of possible enshrouded AGNs is unknown. It is therefore important to better understand the role of star-forming gas in contributing to the infrared luminosity in IR-bright galaxies. The J = 3 level of 12 CO lies 33 K above ground and has a critical density of ~1.5 × 10 4 cm -3 . The 12 CO J = 3-2 line serves as an effective tracer for warm, dense molecular gas heated by active star formation. Here we report on 12 CO J = 3-2 observations of 17 starburst spiral galaxies, LIRGs, and ULIRGs, which we obtained with the Heinrich Hertz Submillimeter Telescope on Mount Graham, Arizona. Our main results are as follows. (1) We find a nearly linear relation between the infrared luminosity and warm, dense molecular gas such that the infrared luminosity increases as the warm, dense molecular gas to the power 0.92; we interpret this to be roughly consistent with the recent results of Gao & Solomon. (2) We find L IR / M ratios ranging from ~38 to ~482 L ☉ / M ☉ using a modified CO-H 2 conversion factor of 8.3 × 10 19 cm -2 (K km s -1 ) -1 derived in this paper.