ALMA Explorations of Warm Dense Molecular Gas in Nearby LIRGs

We present results of ALMA (Cycle-0) observations of the CO (6-5) line emission and the 435μm continuum of two nearby luminous infrared galaxies (LIRGs) NGC 34 (a major merger with an AGN) and NGC 1614 (a minor merger with a circum-nuclear starburst). Using receivers in the highest frequency ALMA band available (Band-9), these observations achieved the best angular resolutions (∼ 0′′.25) for ALMA Cycle-0 observations and resolved for the first time distributions of warm dense molecular gas (n > 10 cm−3 , T > 100 K) in LIRGs with spatial resolutions better than 100 pc. Our ALMA data show a very tight correlation between the CO (6-5) line emission and the 435μm dust continuum emission, suggesting the warm dense molecular gas dominates the ISM in the central kpc of LIRGs, and gas heating and dust heating in the warm dense gas cores are strongly coupled. On the other hand, we saw very different spatial distributions and kinematic properties of warm dense gas in the two LIRGs, indicating that physical conditions in the ISM can be very different in different LIRGs.