Modeling Photoionized Turbulent Material in the Circumgalactic Medium

Abstract

The circumgalactic medium (CGM) of nearby star-forming galaxies show clear indications of \ion{O}{6} absorption accompanied by little to no \ion{N}{5} absorption. This unusual spectral signature, accompanied by absorption from lower ionization state species whose columns vary by orders of magnitude along \st{difference} \textbf{different} sightlines, indicates that the CGM must be viewed as a dynamic, multiphase medium, such as occurs in the presence of turbulence. To explore this possibility, we carry out a series of chemodynamical simulations of a isotropic turbulent media, using the MAIHEM package. The simulations assume a metallicity of $0.3\ Z_{\odot}$ and a redshift zero metagalatic UV background, and they track ionizations, recombinations, and species-by-species radiative cooling for a wide range of elements. We find that turbulence with a one-dimensional velocity dispersion of $\sigma_{1D} \approx 60$ km/s replicates many of the observed features within the CGM, such as clumping of low ionization-state ions and the existence of \ion{O}{6} at moderate ionization parameters. However, unlike observations, \ion{N}{5} often arises in our simulations with derived column densities of a similar magnitude to those of \ion{O}{6}. While higher values of $\sigma_{1D}$ lead to a thermal runaway in our isotropic simulations, this would not be the case in stratified media, and thus we speculate that more complex models of the turbulence may well match the absence of \ion{N}{5} in the CGM of star-forming galaxies.