The ESO UVES Advanced Data Products Quasar Sample-V. Identifying the Galaxy Counterpart to the sub-Damped Ly-alpha System towards Q2239-2949

TL;DR

This study combines absorption and emission observations to identify and analyze the galaxy counterpart of a sub-Damped Ly-alpha system at z=1.825, revealing its metallicity, star formation rate, and gas kinematics.

Contribution

It presents the first detection of the galaxy counterpart to a specific sub-DLA using combined emission and absorption data, providing insights into its properties.

Findings

Metallicity of the sub-DLA is [M/H] > -0.75.

Galaxy counterpart detected at 20.8 kpc impact parameter.

Star formation rate estimated at ~0.13 solar masses per year.

Abstract

Gas flows in and out of galaxies are one of the key unknowns in todays' galaxy evolution studies. Because gas flows carry mass, energy and metals, they are believed to be closely connected to the star formation history of galaxies. Most of these processes take place in the circum-galactic medium (CGM) which remains challenging to observe in emission. A powerful tool to study the CGM gas is offered by combining observations of the gas traced by absorption lines in quasar spectra with detection of the stellar component of the same absorbing-galaxy. To this end, we have targeted the zabs=1.825 sub-Damped Ly-alpha absorber (sub-DLA) towards the zem=2.102 quasar 2dF J 223941.8-294955 (hereafter Q2239-2949) with the ESO VLT/X-Shooter spectrograph. Our aim is to investigate the relation between its properties in emission and in absorption. The derived metallicity of the sub-DLA with log N(HI) = 19.84+/-0.14 cm-2 is [M/H] >-0.75. Using the Voigt profile optical depth method, we measure Delta_v90(FeII)=64 kms-1. The sub-DLA galaxy counterpart is located at an impact parameter of 2."4+/-0."2 (20.8+/-1.7 kpc at z = 1.825). We have detected Ly-alpha and marginal [OII] emissions. The mean measured flux of the Ly-alpha line is F(Ly-alpha) ~ 5.7x10^-18 erg s-1 cm-2 A-1, corresponding to a dust uncorrected SFR of ~ 0.13 M(solar) yr-1.