With a goal toward deriving the physical conditions in external galaxies, we present a study of the ammonia (NH3) emission and absorption in a sample of starburst systems. Results from a survey of mainly nearby galaxies measured using the GBT (Mangum et al. 2008, 2013) have shown that Formaldehyde (H2CO) is a reliable and accurate density probe for extragalactic environments where the kinetic temperature is known. The inversion transitions of NH3 and the rotational transitions of H2CO possess very similar excitation conditions, thus likely trace similar dense gas environments. Using the unique sensitivities to kinetic temperature afforded by the excitation characteristics of several inversion transitions of NH3, we have continued our characterization of the dense gas in starburst galaxies by measuring the kinetic temperature in a sample of 23 galaxies and one galaxy offset position selected for their high infrared luminosity. With these measurements we derive kinetic temperatures toward 13 galaxies, 9 of which possess multiple kinetic temperature and/or velocity components. Eight of these galaxies exhibit kinetic temperatures > 100K, which is in many cases at least a factor of two larger than kinetic temperatures derived previously. Furthermore, the derived kinetic temperatures in our galaxy sample, which are in many cases at least a factor of two larger than derived dust temperatures, point to a problem with the common assumption that dust and gas kinetic temperatures are equivalent. As previously suggested, the use of dust emission at wavelengths greater than 160 μm to derive dust temperatures, or dust heating from older stellar populations, may be skewing derived dust temperatures in these galaxies to lower values.
We confirm the detection of high-excitation OH 2P3/2 J=9/2 absorption toward Arp220 (Ott et al. 2011). We also report the first detections of non-metastable NH3 inversion transitions toward external galaxies in the (2,1) (NGC253, NGC660, IC342, and IC860), (3,1), (3,2), (4,3), (5,4) (all in NGC 660) and (10,9) (Arp 220) transitions.