The Mass and Absorption Columns of Galactic Gaseous Halos

The galactic gaseous halo is a gas reservoir for the interstellar medium in the galaxy disk, supplying materials for star formation. We developed a gaseous halo model connecting the galaxy disk and the gaseous halo by assuming that 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 in the outskirts of massive galaxies due to the low densities. The multiphase 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 (i. e., O VI, O VII, Ne VIII, MgX, and O VIII). We find that the O VI column density has a narrow range around approximate to 10(14) cm(-2) for halo masses from M-star approximate to 3 x 10(10) M-circle dot to 6 x 10(12)M(circle dot), which is consistent with some but not all observational studies. For galaxies with halo masses. 3. x. 10(11)M(circle dot), photoionization produces most of the O VI, while for more massive galaxies, the O VI is from the medium that is cooling from higher temperatures. Fitting the Galactic (Milky-Way) O VII and O VIII suggests a gaseous halo model where the metallicity is approximate to 0.55 Z(circle dot) and the gaseous halo has a maximum temperature of approximate to 1.9 x 10(6) K. This gaseous halo model does not close the census of baryonic material within R200.