LUMINOUS INFRARED GALAXIES WITH THE SUBMILLIMETER ARRAY. IV. {sup 12}CO J = 6-5 OBSERVATIONS OF VV 114
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada)
- Institut de Radio Astronomie Millimetrique, 300 Rue de la Piscine, Domaine Universitaire, F-38406 Saint Martin d'Heres (France)
- Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
- Chile Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
- University of Helsinki, FI-00014 Helsinki (Finland)
- Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China)
- National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States)
- Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
We present high-resolution (∼2.''5) observations of {sup 12}CO J = 6-5 toward the luminous infrared galaxy VV 114 using the Submillimeter Array. We detect {sup 12}CO J = 6-5 emission from the eastern nucleus of VV 114 but do not detect the western nucleus or the central region. We combine the new {sup 12}CO J = 6-5 observations with previously published or archival low-J CO observations, which include {sup 13}CO J = 1-0 Atacama Large Millimeter/submillimeter Array cycle 0 observations, to analyze the beam-averaged physical conditions of the molecular gas in the eastern nucleus. We use the radiative transfer code RADEX and a Bayesian likelihood code to constrain the temperature (T{sub kin}), density (n{sub H{sub 2}}), and column density (N{sub {sup 1}{sup 2}CO}) of the molecular gas. We find that the most probable scenario for the eastern nucleus is a cold (T{sub kin} = 38 K), moderately dense (n{sub H{sub 2}} = 10{sup 2.89} cm{sup –3}) molecular gas component. We find that the most probable {sup 12}CO to {sup 13}CO abundance ratio ([{sup 12}CO]/[{sup 13}CO]) is 229, which is roughly three times higher than the Milky Way value. This high abundance ratio may explain the observed high {sup 12}CO/ {sup 13}CO line ratio (>25). The unusual {sup 13}CO J = 2-1/J = 1-0 line ratio of 0.6 is produced by a combination of moderate {sup 13}CO optical depths (τ = 0.4-1.1) and extremely subthermal excitation temperatures. We measure the CO-to-H{sub 2} conversion factor, α{sub CO}, to be 0.5{sup +0.6}{sub -0.3} M{sub ☉} (K km s{sup –1} pc{sup 2}){sup –1}, which agrees with the widely used factor for ultra luminous infrared galaxies of Downes and Solomon (α{sub CO} = 0.8 M{sub ☉} (K km s{sup –1} pc{sup 2}){sup –1})
- OSTI ID:
- 22270582
- Journal Information:
- Astrophysical Journal, Vol. 777, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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