The Cosmological Bias Factor of Damped Lyman Alpha systems: Dependence on Metal Line Strength

TL;DR

This study measures how the clustering bias of Damped Lyman Alpha systems varies with their metal line strength, revealing a correlation with host galaxy mass and confirming the physical link between bias and halo properties.

Contribution

It introduces a method to relate DLA metal strength to host halo mass via bias factor measurements, accounting for measurement errors and metallicity effects.

Findings

Bias increases with metal strength, indicating more massive host halos.

Weak metal line DLAs are consistent with dwarf galaxy hosts (~10^{10} M_sun).

Strong metal line DLAs suggest massive galaxy or group hosts (~10^{12} M_sun).

Abstract

We measure the cosmological bias factor of DLAs from their cross-correlation with the Ly$\alpha$ forest absorption, as a function of the DLA metal strength, defined from an average of equivalent widths of the strongest detectable low-ionization metal lines. A clear increase of the bias factor with metal strength is detected, as expected from a relation of metallicity and velocity dispersion with host halo mass. The relation is stronger after the metal strength is corrected for the HI column density, to make it more related to metallicity instead of metal column density. After correcting for the effects of measurement errors of the metal strength parameter, we find that the bias factor of DLAs with the weakest metal lines is close to unity, consistent with an origin in dwarf galaxies with host halo masses $\sim10^{10} M_{\odot}$, whereas the most metal rich DLAs have a bias factor as large as $b_{\rm DLA} \sim 3$, indicative of massive galaxies or galaxy groups in host halos with masses $\sim 10^{12} M_{\odot}$. Our result confirms the physical origin of the relation of bias factors measured from cross-correlation studies to the host halos of the absorbers.