A low-luminosity type-1 QSO sample: IV. Molecular gas contents and
  conditions of star formation in three nearby Seyfert galaxies
  We present a pilot study of ~ 3" resolution observations of low CO
transitions with the Submillimeter Array in three nearby Seyfert galaxies,
which are part of the low-luminosity quasi-stellar object (LLQSOs) sample
consisting of 99 nearby (z = 0.06) type-1 active galactic nuclei (AGN) taken
from the Hamburg/ESO quasi-stellar object (QSO) survey. Two sources were
observed in 12CO(2-1) and 13CO(2-1) and the third in 12CO(3-2) and HCO+(4-3).
None of the sources is detected in continuum emission. More than 80% of the
12CO detected molecular gas is concentrated within a diameter (FWHM) < 1.8 kpc.
13CO is tentatively detected, while HCO+ emission could not be detected. All
three objects show indications of a kinematically decoupled central unresolved
molecular gas component. The molecular gas masses of the three galaxies are in
the range M_mol = (0.7 - 8.7) x 10^9 M_sun. We give lower limits for the
dynamical masses of M_dyn > 1.5 x 10^9 M_sun and for the dust masses of M_dust
> 1.6 x 10^6 M_sun. The R21 =12CO/13CO(2-1) line luminosity ratios show
Galactic values of R21 ~ 5 - 7 in the outskirts and R21 > 20 in the central
region, similar to starbursts and (ultra)luminous infrared galaxies ((U)LIRGs;
i.e. LIRGs and ULIRGs), implying higher temperatures and stronger turbulence.
All three sources show indications of 12CO(2-1)/12CO(1-0) ratios of ~ 0.5,
suggesting a cold or diffuse gas phase. Strikingly, the 12CO(3-2)/(1-0) ratio
of ~ 1 also indicates a higher excited phase. Since these galaxies have high
infrared luminosities of L_IR > 10^11 L_sun and seem to contain a circumnuclear
starburst with minimum surface densities of gas and star formation rate (SFR)
around {\Sigma}_mol = 50 - 550 M_sun pc^-2 and {\Sigma}_SFR = 1.1 - 3.1 M_sun
kpc^-2 yr^-1, we conclude that the interstellar medium in the centers of these
LIRG Seyferts is strongly affected by violent star formation and better ...
