Properties of Molecular Gas in Galaxies in Early and Mid Stages of the Interaction. I. Distribution of Molecular Gas

Abstract

Abstract We present the results of $ ^{12}$ CO (J$ =$ 1–0) mapping observations toward four interacting galaxies in early and mid stages of the interaction in order to understand the behavior of molecular gas in galaxy–galaxy interactions. The observations were carried out using the 45-m telescope at Nobeyama Radio Observatory (NRO). We compared our CO total flux to those previously obtained with single-dish observations, and found that there is no discrepancy between them. By applying a typical CO–H$ _{2}$ conversion factor, it was found that all constituent galaxies have molecular gas mass of more than 10$ ^{9}$ . Comparisons to H I, K$ _{\rm s}$, and tracers of star formation, such as H$ \alpha$ , FUV, 8 $ \mu$ m, and 24 $ \mu$ m, revealed that the distribution of molecular gas in interacting galaxies in the early stage of the interaction differs from atomic gas, stars, and star-forming regions. These differences can not be explained without the result of the interaction. The central concentration of molecular gas of interacting galaxies in the early stage of the interaction is lower than that of isolated galaxies, which suggests that molecular gas is distributed off-centre, and/or extends in the beginning of the interaction.