Galactic Winds and Extended Lya Emission from the Host Galaxies of High Column Density QSO Absorption Systems

TL;DR

This study uses 3D radiative transfer simulations based on cosmological galaxy models to predict the spatial and spectral properties of Lyman-alpha emission from high-redshift galaxy hosts of dense absorption systems, highlighting complex gas dynamics and wind effects.

Contribution

It provides the first detailed simulation of Lyman-alpha emission considering realistic galaxy formation and wind models, revealing how gas dynamics influence observable properties.

Findings

Lyman-alpha emission is spatially extended up to several arcseconds.

Spectral width can reach over a thousand km/s, with profiles varying by viewing angle.

Galactic winds significantly affect the spatial extent and spectral shape of the emission.

Abstract

We present 3D resonant radiative transfer simulations of the spatial and spectral diffusion of the Lya radiation from a central source in the host galaxies of high column density absorption systems at z ~ 3. The radiative transfer simulations are based on a suite of cosmological galaxy formation simulations that reproduce a wide range of observed properties of damped Lya absorption systems. The Lya emission is predicted to be spatially extended up to several arcsec, and the spectral width of the Lya emission is broadened to several hundred (in some case more than thousand) km/s. The distribution and the dynamical state of the gas in the simulated galaxies is complex, the latter with significant contributions from rotation and both in- and out-flows. The emerging Lya radiation extends to gas with column densities of N_HI ~ 10^{18} cm^{-2} and its spectral shape varies strongly with viewing angle. The strong dependence on the central \hi column density and the HI velocity field suggests that the Lya emission will also vary strongly with time on timescales of a few dynamical times of the central region. Such variations with time should be especially pronounced at times where the host galaxy undergoes a major merger and/or starburst. Depending on the pre-dominance of in- or out-flow along a given sightline and the central column density, the spectra show prominent blue peaks, red peaks or double-peaked profiles. Both spatial distribution and spectral shape are very sensitive to details of the galactic wind implementation. Stronger galactic winds result in more spatially extended Lya emission and - somewhat counterintuitively - a narrower spectral distribution.