1999/04/06 by Yoshiaki Taniguchi, Youichi Ohyama, D. B. Sanders · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1086/307650
published as Astrophys.J. 522 (1999) 214-219 · 12 pages, 2 tables, and 6 figures. Accepted for publications in The Astrophysical Journal, Part 1
arxiv created 1999/04/06 · openalex publication_date 1999/09/01 · arxiv updated 2009/12/01 · openalex created_date 2022/10/02 · openalex updated_date 2026/08/01
It is known that merging galaxies with luminous starbursts and high far-infrared luminosities tend to have higher R 1-0 = 12 CO ( J = 1-0)/ 13 CO ( J = 1-0) integrated line intensity ratios ( R 1-0 ≃ 20-50) than normal spiral galaxies ( R 1-0 ≃ 5-15). Comparing far-infrared luminosities [ L (FIR)] with those of 12 CO ( J = 1-0) and 13 CO ( J = 1-0) for a sample of normal and starburst galaxies, Taniguchi & Ohyama found that the observed high R 1-0 values for the luminous starburst mergers are attributed to their lower (by a factor of 3 on average) 13 CO line intensities. They suggested the following two possibilities: in the luminous starburst mergers (1) 13 CO is underabundant with respect to 12 CO, or (2) exitation and/or optical depth effects are responsible for the change in R 1-0 . In this paper, we investigate the second possibility, using higher transition data of both 12 CO and 13 CO emission lines. Applying the same method proposed by Taniguchi & Ohyama to both 12 CO ( J = 2-1) and 13 CO ( J = 2-1), we find that 13 CO ( J = 2-1) is also depressed with respect to 12 CO ( J = 2-1). This suggests that the 13 CO gas may be underabundant in the high- R 1-0 starburst mergers, although we cannot rule out the possibility that excitation and optical depth effects are still affecting R 2-1 , for example, as a result of the large velocity widths in the CO emission lines. Additional observations of both 12 CO and 13 CO lines at J ≥ 3 are required to better constrain the conditions of the molecular gas in luminous starburst galaxies.