The Maximum Effect of Thermal Instability on Galactic Outflows

We have investigated steady, radial gas outflows (or winds) from galaxies and the development of thermal instability in the hot gas. In order to see the maximum influence of the instability on the global structure of the galactic outflows, we study inhomogeneous comoving flows and the non-linear fate of the fluctuations in the flows. We compare the results with solutions for homogeneous flows. In the case of supersonic flows, the global structure of inhomogeneous flows is not much different from that of homogeneous flows. However, detailed investigation shows that the average density of inhomogeneous flows decreases faster than that of homogeneous flows, because local thermal instability removes overdense regions in the inhomogeneous flows and reduces the mass flux. We also find that when the gravity of a galaxy is strong, the cold clouds formed from the removed gas are distributed in the galactic halo. In the case of subsonic flows, the form of inhomogeneous flows is different from that of homogeneous flows near the regions where the flows terminate. The density rise appearing near the regions where the homogeneous flows terminate is not seen in the inhomogeneous flows because the local thermal instability decreases the mass flux. The cold clouds formed through thermal instability in the inhomogeneous flow almost all coast to the same maximum radius. Subject headings: galaxies: ISM—ISM: jets and outflows—ISM: kinematics and dynamics