CO Line Emission from Compact Nuclear Starburst Disks Around Active
  Galactic Nuclei
  There is substantial evidence for a connection between star formation in the
nuclear region of a galaxy and growth of the central supermassive black hole.
Furthermore, starburst activity in the region around an active galactic nucleus
(AGN) may provide the obscuration required by the unified model of AGN.
Molecular line emission is one of the best observational avenues to detect and
characterize dense, star-forming gas in galactic nuclei over a range of
redshift. This paper presents predictions for the carbon monoxide (CO) line
features from models of nuclear starburst disks around AGN. These small scale
($\la 100$ pc), dense and hot starbursts have CO luminosities similar to
scaled-down ultra-luminous infrared galaxies and quasar host galaxies. Nuclear
starburst disks that exhibit a pc-scale starburst and could potentially act as
the obscuring torus show more efficient CO excitation and higher brightness
temperature ratios than those without such a compact starburst. In addition,
the compact starburst models predict strong absorption when $J_{\mathrm{Upper}}
\ga 10$, a unique observational signature of these objects. These findings
allow for the possibility that CO SLEDs could be used to determine if starburst
disks are responsible for the obscuration in $z \la 1$ AGN. Directly isolating
the nuclear CO line emission of such compact regions around AGN from
galactic-scale emission will require high resolution imaging or selecting AGN
host galaxies with weak galactic-scale star formation. Stacking individual CO
SLEDs will also be useful in detecting the predicted high-$J$ features.
