Ion densities of cold clouds driven by galactic outflows

Abstract

Observations of the circumgalactic medium (CGM) often display coincident absorption from species with widely varying ionization states, providing direct evidence for complex, multiphase interactions. Motivated by these measurements, we perform a series of cloud-crushing simulations that model cold clouds travelling through the hot CGM. We analyse the ion distributions of these clouds under the assumption of ionization equilibrium in the presence of a photoionizing background, generate mock absorption spectra, and study their implications on quasar (QSO) absorption observations. Our results show multiphase features, in which ions with significantly different ionization potentials exist in the same absorber and share similar spectral features. However, our simulations are unable to explain high ions such as O vi and their coexistence with lower ions as observed in many QSO absorption systems.