A Look at Luminous Infrared Galaxies with the SMA
We are using high-resolution CO observations and the radiative transfer code, RADEX (van der Tak et al. 2007) to constrain the physical conditions of the molecular gas such as density, column density and temperature of 14 local (DL < 200 Mpc) luminous infrared galaxies (LIRGs). The SMA was used to observe 12 CO J=2-1 and J=3-2 and 13 CO J=2-1 in the sample and the short spacings of the 12 CO J=2-1 and J=3-2 have been recovered using JCMT observations. Currently, we have implemented this method on two LIRGs in the sample: Arp 299 and VV 114. Arp 299 has three major concentrations of molecular gas where two are associated with the nuclei of the merging galaxies and the third is believed to be an overlap region. We find that the kiloparsec-scale overlap region has very similar physical conditions to those of giant molecular clouds in M33. The analysis of VV 114 also included 13 CO J=1-0 observed with ALMA in cycle 0. We find an unusually high 12 CO-to-13 CO abundance ratio ([12 CO/13 CO] = 229) in VV 114, roughly 3 times higher than the local ISM value. We use the RADEX analysis results to measure the CO-to-H2 conversion factor, alphaCO , and we find that the alphaCO values for Arp 299 and VV 114 agree with the widely used ULIRG value.
Warm and cold molecular in nearby galaxies: Excited CO and [CI] in the Antennae (NGC 4038/39)
At a distance of only 22 Mpc, the Antennae (NGC 4038/39) represents the nearest example of a major merger between gas-rich galaxies, providing us with an excellent laboratory in which to study merger-triggered star formation. I will be presenting recently published observations of the Antennae using the SPIRE Fourier Transform Spectrometer (FTS) onboard the now defunct Herschel Space Observatory. We detect 5 CO transitions (J=4-3 to J=8-7) and both [CI] transitions across the system, all of which trace molecular gas. We model these transitions, along with ground based observations of the CO J=1-0 to J=3-2 transitions, using the publicly available radiative transfer code RADEX. We find that there is both cold (Tkin ~ 10-30 K) and warm (Tkin > 100 K) molecular gas throughout the system. Finally, we investigate possible sources for heating, including photon dominated regions (PDRs), supernova and stellar winds, and turbulent heating.