Spatially resolved velocity maps of halo gas around two intermediate-redshift galaxies

Absorption-line spectroscopy of multiply-lensed QSOs near a known foreground galaxy provides a unique opportunity to go beyond the traditional one-dimensional application of QSO probes and establish a crude three-dimensional map of halo gas around the galaxy that records the line-of-sight velocity field at different locations in the gaseous halo. Two intermediate-redshift galaxies are targeted in the field around the quadruply-lensed QSO HE 0435-1223 at redshift z = 1.689, and absorption spectroscopy along each of the lensed QSOs is carried out in the vicinities of these galaxies. One galaxy is a typical, star-forming L_* galaxy at z = 0.4188 and projected distance of ρ = 50 kpc from the lensing galaxy. The other is a super-L_* barred spiral at z = 0.7818 and ρ = 33 kpc. Combining known orientations of the quadruply-lensed QSO to the two foreground galaxies with the observed Mg II λλ2796, 2803 absorption profiles along individual QSO sightlines has for the first time led to spatially resolved kinematics of tenuous halo gas on scales of 5-10 kpc at z > 0.2. A Mg II absorber is detected in every sightline observed through the haloes of the two galaxies, and the recorded absorber strength is typical of what is seen in previous close QSO-galaxy pair studies. While the multisightline study confirms the unity covering fraction of Mg II absorbing gas at ρ < 50 kpc from star-forming discs, the galaxies also present two contrasting examples of complex halo gas kinematics. Different models, including a rotating disc, collimated outflows and gaseous streams from either accretion or tidal/ram-pressure stripping, are considered for comparisons with the absorption-line observations, and infalling streams/stripped gas of width ≳10 kpc are found to best describe the observed gas kinematics across multiple sightlines. In addition, the observed velocity dispersion between different sightlines offers a crude estimate of turbulence in the Mg II absorbing halo gas. The observations presented here demonstrate that multiple-QSO probes enable studies of spatially resolved gas kinematics around distant galaxies, which provide key insights into the physical nature of circumgalactic gas beyond the nearby Universe.