Ammonia Thermometry of Star Forming Galaxies
  With a goal toward deriving the physical conditions in external galaxies, we
present a study of the ammonia (NH$_3$) emission and absorption in a sample of
star forming systems. Using the unique sensitivities to kinetic temperature
afforded by the excitation characteristics of several inversion transitions of
NH$_3$, we have continued our characterization of the dense gas in star forming
galaxies by measuring the kinetic temperature in a sample of 23 galaxies and
one galaxy offset position selected for their high infrared luminosity. 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 $>100$ K, which are 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
$\mu$m 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 $^2\Pi_{3/2}$
J=9/2 absorption toward Arp220 (Ott et. al. 2011). We also report the first
detections of non-metastable NH$_3$ inversion transitions toward external
galaxies in the (2,1) (NGC253, NGC660, IC342, and IC860), (3,1), (3,2), (4,3),
(5,4) (all in NGC660) and (10,9) (Arp220) transitions.
