The ESO UVES Advanced Data Products quasar sample - V. Identifying the galaxy counterpart to the sub-damped Lyα system towards Q 2239-2949

Gas flows in and out of galaxies are one of the key unknowns in today's 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 Lyα absorber (sub-DLA) towards the zem = 2.102 quasar 2dF J 223941.8-294955 (hereafter Q 2239-2949) 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(H I) = 19.84 ± 0.14 cm⁻² is [M/H] > −0.75. Using the Voigt profile optical depth method, we measure Δv90(Fe II) = 64 km s⁻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 Lyα and marginal [O II] emissions. The mean measured flux of the Lyα line is FLy α ∼ 5.7 × 10−18 erg s⁻¹ cm⁻² Å⁻¹, corresponding to a dust uncorrected SFR of ∼0.13 M⊙ yr⁻¹.