LUMINOUS INFRARED GALAXIES WITH THE SUBMILLIMETER ARRAY. IV. 12CO J = 6–5 OBSERVATIONS OF VV 114

We present high-resolution (∼2.″5) observations of 12CO J = 6–5 toward the luminous infrared galaxy VV 114 using the Submillimeter Array. We detect 12CO 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 12CO J = 6–5 observations with previously published or archival low-J CO observations, which include 13CO 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 (Tkin), density (), and column density () of the molecular gas. We find that the most probable scenario for the eastern nucleus is a cold (Tkin = 38 K), moderately dense ( = 102.89 cm−3) molecular gas component. We find that the most probable 12CO to 13CO abundance ratio ([12CO]/[13CO]) is 229, which is roughly three times higher than the Milky Way value. This high abundance ratio may explain the observed high 12CO/ 13CO line ratio (>25). The unusual 13CO J = 2–1/J = 1–0 line ratio of 0.6 is produced by a combination of moderate 13CO optical depths (τ = 0.4–1.1) and extremely subthermal excitation temperatures. We measure the CO-to-H2 conversion factor, αCO, to be 0.5 M☉ (K km s−1 pc2)−1, which agrees with the widely used factor for ultra luminous infrared galaxies of Downes & Solomon (αCO = 0.8 M☉ (K km s−1 pc2)−1).