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

We have obtained Keck HIRES spectra of three images of the gravitationallylensed QSO 2237+0305 to study low ionization absorption systems and theirdifferences in terms of projected velocity and column density across the linesof sight. We detect CaII absorption from our Galaxy, and a system of HighVelocity Clouds from the lensing galaxy (z=0.039). CaII components with totalequivalent widths similar to those of Galactic intermediate and high velocityclouds are spread out over several hundred km/s at impact parameters of lessthan one kpc from the center of the lensing galaxy. We have also studied threelow ionization MgII-FeII systems in detail. All three systems cover all threelines of sight, suggesting that the gaseous structures giving rise to MgIIcomplexes are larger than about 0.5 kpc. However, in most cases it is difficultto trace individual MgII `cloudlets' over distances larger than 200-300 pc,indicating that typical sizes of the MgII cloudlets are smaller than the sizesinferred earlier for the individual CIV high ionization gas clouds. Wetentatively interpret the absorption pattern of the strongest MgII system interms of an expanding bubble or galactic wind and show that the possible locioccupied by the model bubble in radius-velocity space overlap with the observedcharacteristics of Galactic supershells. (abridged).Comment: 40 latex pages, 12 postscript figures. Accepted for publication by Ap