Understanding the galaxy evolution with gaseous halos

A major component of galaxies is the extended hot gaseous halo, with a temperature of the virial temperature and extending to or beyond the virial radius. This component is present in structure formation simulations, where it is a gas reservoir for star formation and a repository for stellar feedback. Also, it may contain a significant amount of the missing baryons and the missing metals. Such a gaseous halo can be traced by various high ionization state ions observationally, such as O VI, O VII, O VIII, Ne VIII, and Mg X. Currently, the UV ions (i.e., O VI, Ne VIII and Mg X) are most available due to the lack of capacity of the X-ray observatories. Based on current observations, we developed a gaseous halo model connecting the galaxy disk and the gaseous halo by assuming the star formation rate on the disk is balanced by the radiative cooling rate of the gaseous halo, including stellar feedback. In addition to a single-temperature gaseous halo in collisional ionization equilibrium, we also consider the photoionization effect and a steady-state cooling model. Photoionization is important for modifying the ion distribution in low-mass galaxies and outskirts of massive galaxies due to the low densities. The multi-phase cooling model dominates the region within the cooling radius, where t_cooling=t_Hubble. Our model reproduces most of the observed high ionization state ions for a wide range of galaxy masses. This gaseous halo model does not close the census of baryonic material or metals within R200. 

Zhijie Qu (University of Michigan)
1st Seminar Room, KIAA-PKU
Tuesday, March 6, 2018 - 5:00pm to 6:00pm