The quenching of star formation in accretion-driven clumpy turbulent tori of active galactic nuclei

摘要

Galactic gas-gas collisions involving a turbulent multiphase ISM share commonISM properties: dense extraplanar gas visible in CO, large linewidths (>= 50km/s), strong mid-infrared H_2 line emission, low star formation activity, andstrong radio continuum emission. Gas-gas collisions can occur in the form ofICM ram pressure stripping, galaxy head-on collisions, compression of theintragroup gas and/or galaxy ISM by an intruder galaxy which flies through thegalaxy group at a high velocity, or external gas accretion on an existing gastorus in a galactic center. We suggest that the common theme of all thesegas-gas interactions is adiabatic compression of the ISM leading to an increaseof the turbulent velocity dispersion of the gas. The turbulent gas clouds arethen overpressured and star formation is quenched. Within this scenario wedeveloped a model for turbulent clumpy gas disks where the energy to driveturbulence is supplied by external infall or the gain of potential energy byradial gas accretion within the disk. The cloud size is determined by the sizeof a C-type shock propagating in dense molecular clouds with a low ionizationfraction at a given velocity dispersion. We give expressions for the expectedvolume and area filling factors, mass, density, column density, and velocitydispersion of the clouds. The latter is based on scaling relations ofintermittent turbulence whose open parameters are estimated for the CND in theGalactic Center. The properties of the model gas clouds and the external massaccretion rate necessary for the quenching of the star formation rate due toadiabatic compression are consistent with those derived from high-resolutionH_2 line observations. Based on these findings, a scenario for the evolution ofgas tori in galactic centers is proposed and the implications for starformation in the Galactic Center are discussed.