# Exploring galaxy dark matter halos across redshifts with strong quasar absorbers

## TL;DR

This study investigates how the velocity widths of absorption lines in quasar spectra relate to galaxy dark matter halos across different redshifts, revealing that steeper dark matter profiles better match observations and that massive galaxy halos contain bound DLAs.

## Contribution

It introduces a normalized velocity ratio to compare absorbers across galaxies and finds that steeper dark matter profiles fit the data better than shallower ones.

## Key findings

- Velocity ratio decreases with projected distance from host galaxies.
- Steeper dark matter profiles better fit the observed velocity dispersions.
- Massive galaxy halos (around 10^{12} solar masses) mostly contain gravitationally bound DLAs.

## Abstract

Quasar lines of sight intersect intervening galaxy discs or circum-galactic environments at random impact parameters and potential well depths. Absorption line velocity widths ($\Delta v_{90}$) are known to scale with host galaxy stellar masses, and inversely with the projected separation from the quasar line of sight. Its dependence on stellar mass can be eliminated by normalising with the emission-line widths of the host galaxies, $\sigma_{em}$, so that absorbers with a range of $\Delta v_{90}$ values can be compared directly. Using a sample of DLA systems at 0.2 < z < 3.2 with spectroscopically confirmed host galaxies, we find that the velocity ratio $\Delta v_{90}/\sigma_{em}$ decreases with projected distances from the hosts. We compare the data with expectations of line-of-sight velocity dispersions derived for different dark matter halo mass distributions, and find that models with steeper radial dark matter profiles provide a better fit to the observations, although the scatter remains large. Gas outflows from the galaxies may cause an increased scatter, or scale radii of dark matter halo models may not be representative for the galaxies. We demonstrate by computing virial velocities, that metal-rich DLAs that belong to massive galaxy halos (M$_{halo} \approx 10^{12}$ M$_{\odot}$) mostly remain gravitationally bound to the halos.