Compact Molecular Gas Distribution in Quasar Host Galaxies
  We use Atacama Large Millimeter/submillimeter Array CO(2-1) observations of
six low-redshift Palomar-Green quasars to study the distribution and kinematics
of the molecular gas of their host galaxies at kpc-scale resolution. While the
molecular gas content, molecular gas fraction, and star formation rates are
similar to those of nearby massive, star-forming galaxies, the quasar host
galaxies possess exceptionally compact, disky molecular gas distributions with
a median half-light radius of 1.8 kpc and molecular gas mass surface densities
$\gtrsim 22$ $M_\odot$pc$^{-2}$. While the overall velocity field of the
molecular gas is dominated by regular rotation out to large radii, with
rotation velocity-to-velocity dispersion ratio $\gtrsim 9$, the nuclear region
displays substantial kinematic complexity associated with small-scale
substructure in the gas distribution. A tilted-ring analysis reveals that the
kinematic and photometric position angles are misaligned on average by $\sim 34
\pm 26^\circ$, and provides evidence of kinematic twisting. These observations
provide tantalizing clues to the detailed physical conditions of the
circumnuclear environments of actively accreting supermassive black holes.
