Lyman-\alpha absorption beyond the disk of simulated spiral galaxies

TL;DR

This study analyzes the circum-galactic medium of simulated spiral galaxies, revealing the origins of gas, its properties, and how Lyman-alpha absorption compares with observations, introducing a new analysis tool.

Contribution

It introduces the novel analysis tool pygad for ion abundance and absorption spectra computation and provides detailed insights into CGM composition and absorption characteristics.

Findings

CGM is composed of recycled and accreted gas with distinct radial dominance.

Simulated Lyman-alpha absorption matches observations well at large radii.

Effective line-width for absorbers is 50-70 km/s, increasing with halo mass.

Abstract

We present an analysis of the origin and properties of the circum-galactic medium (CGM) in a suite of 11 cosmological zoom simulations resembling present day spiral galaxies. On average the galaxies retain about 50\% of the cosmic fraction in baryons, almost equally divided into disc (interstellar medium) gas, cool CGM gas and warm-hot CGM gas. At radii smaller than 50 kpc the CGM is dominated by recycled warm-hot gas injected from the central galaxy, while at larger radii it is dominated by cool gas accreted onto the halo. The recycled gas typically accounts for one-third of the CGM mass. We introduce the novel publicly available analysis tool \textsc{pygad} to compute ion abundances and mock absorption spectra. For Lyman-${\alpha}$ absorption we find good agreement of the simulated equivalent width (EW) distribution and observations out to large radii. Disc galaxies with quiescent assembly histories show significantly more absorption along the disc major axis. By comparing the EW and HI column densities we find that CGM Lyman-${\alpha}$ absorbers are best represented by an effective line-width $b\approx 50 - 70$ km s$^{-1}$ that increases mildly with halo mass, larger than typically assumed.