# The high A_V Quasar Survey: A z=2.027 metal-rich damped Lyman-alpha absorber towards a red quasar at z=3.21

## TL;DR

This study identifies a metal-rich damped Lyman-alpha absorber at z=2.027 towards a dust-reddened quasar at z=3.21, highlighting the impact of dust bias on the census of high-redshift DLAs and their metallicity measurements.

## Contribution

It provides spectroscopic evidence of a dust-rich DLA towards a reddened quasar, demonstrating dust bias affects the detection of metal-rich DLAs at high redshift.

## Key findings

- The DLA has a metallicity of at least 25% of solar.
- The DLA exhibits very strong metal lines and high gas column density.
- Dust reddening and obscuration bias the observed sample of high-z DLAs.

## Abstract

To fully exploit the potential of quasars as probes of cosmic chemical evolution and the internal gas dynamics of galaxies it is important to understand the selection effects behind the quasar samples and in particular if the selection criteria exclude foreground galaxies with certain properties (most importantly a high dust content). Here we present spectroscopic follow-up from the 10.4-m GTC telescope of a dust-reddened quasar, eHAQ0111+0641, from the extended High A_V Quasar (HAQ) survey. We find that the z=3.21 quasar has a foreground Damped Lyman-alpha Absorber (DLA) at z=2.027 along the line of sight. The DLA has very strong metal lines due to a moderately high metallicity (with an inferred lower limit of 25% of the solar metallicity), but a very large gas column density along the line-of-sight in its host galaxy. This discovery is further evidence that there is a dust bias affecting the census of metals, caused by the combined effect of dust obscuration and reddening, in existing samples of z>2 DLAs. The case of eHAQ0111+0641 illustrates that dust bias is not only caused by dust obscuration, but also dust reddening.