Modeling Photoionized Turbulent Material in the Circumgalactic Medium. II. Effect of Turbulence within a Stratified Medium

Abstract

The circumgalactic medium (CGM) of nearby star-forming galaxies shows clear indications of O VI absorption accompanied by little to no detectable N V absorption. This unusual spectral signature, accompanied by highly nonuniform absorption from lower-ionization-state species, indicates that the CGM must be viewed as a dynamic, multiphase medium, such as occurs in the presence of turbulence. Motivated by previous isotropic turbulent simulations, we carry out chemodynamical simulations of stratified media in a Navarro-Frenk-White (NFW) gravitational potential with a total mass of 10¹² M_⊙ and turbulence that decreases radially. The simulations assume a metallicity of 0.3 Z_⊙ and a redshift-zero metagalatic UV background, and they track ionizations, recombinations, and species-by-species radiative cooling using the MAIHEM package. We compare a suite of ionic column densities with the COS-Halos sample of low-redshift star-forming galaxies. Turbulence with an average one-dimensional velocity dispersion of ≈40 km s^-1, corresponding to an energy injection rate of ≈4 × 10⁴⁹ erg yr^-1, produces a CGM that matches many of the observed ionic column densities and ratios. In this simulation, the N_{N V}/N_{O VI} ratio is suppressed from its equilibrium value due to a combination of radiative cooling and cooling from turbulent mixing. This level of turbulence is consistent with expectations from observations of better constrained, higher-mass systems and could be sustained by energy input from supernovae, gas inflows, and dynamical friction from dark matter subhalos. We also conduct a higher resolution ≈40 km s^-1 run, which yields smaller-scale structures but remains in agreement with observations.