We present new \sim 1 \arcsec resolution data of the dense molecular gas in the central 50 - 100 pc of four nearby Seyfert galaxies .
PdBI observations of HCN and , in 2 of the 4 sources , simultaneously HCO ^ { + } allow us to carefully constrain the dynamical state of the dense gas surrounding the AGN .
Analysis of the kinematics shows large line widths of 100–200 km/s FWHM that can only partially arise from beam smearing of the velocity gradient .
The observed morphological and kinematic parameters ( dimensions , major axis position angle , red and blue channel separation , and integrated line width ) are well reproduced by a thick disk , where the emitting dense gas has a large intrinsic dispersion ( 20–40 km/s ) , implying that it exists at significant scale heights ( 25–30 % of the disk radius ) .
To put the observed kinematics in the context of the starburst and AGN evolution , we estimate the Toomre Q parameter .
We find this is always greater than the critical value , i.e .
Q is above the limit such that the gas is stable against rapid star formation .
This is supported by the lack of direct evidence , in these 4 Seyfert galaxies , for on-going star formation close around the AGN .
Instead , any current star formation tends to be located in a circumnuclear ring .
We conclude that the physical conditions are indeed not suited to star formation within the central \sim 100 pc .