Small Scale Structure at High Redshift: IV. Low Ionization Gas Intersecting Three Lines of Sight to Q2237+0305

Abstract

We have obtained Keck HIRES spectra of three images of the gravitationally lensed QSO 2237+0305 to study low ionization absorption systems and their differences in terms of projected velocity and column density across the lines of sight. We detect CaII absorption from our Galaxy, and a system of High Velocity Clouds from the lensing galaxy (z=0.039). CaII components with total equivalent widths similar to those of Galactic intermediate and high velocity clouds are spread out over several hundred km/s at impact parameters of less than one kpc from the center of the lensing galaxy. We have also studied three low ionization MgII-FeII systems in detail. All three systems cover all three lines of sight, suggesting that the gaseous structures giving rise to MgII complexes are larger than about 0.5 kpc. However, in most cases it is difficult to trace individual MgII `cloudlets' over distances larger than 200-300 pc, indicating that typical sizes of the MgII cloudlets are smaller than the sizes inferred earlier for the individual CIV high ionization gas clouds. We tentatively interpret the absorption pattern of the strongest MgII system in terms of an expanding bubble or galactic wind and show that the possible loci occupied by the model bubble in radius-velocity space overlap with the observed characteristics of Galactic supershells. (abridged).