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 quadruply gravitationally lensed quasar Q2237+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 Ca II absorption from our Galaxy and a system of high-velocity clouds from the lensing galaxy (z=0.039) with multiple Ca II components in all three sight lines. Unlike the situation in our Galaxy, there is no prominent Ca II absorption component (with an equivalent width exceeding 60-70 mÅ) close to the velocity centroid of the lensing galaxy Q2237+0305. Instead, Ca II components with total equivalent widths similar to those of Galactic intermediate- and high-velocity clouds are spread out over several hundred kilometers per second in projection along the sight lines at impact parameters of less than 1 kpc through the bulge of the galaxy. A Ca II absorbing thick disk as in our Galaxy does not seem to extend into the bulge region of the 2237+0305 galaxy, whereas high-velocity clouds seem to be a more universal feature. We have also studied three low-ionization Mg II-Fe II systems in detail. All three Mg II systems cover all three lines of sight, suggesting that the gaseous structures giving rise to Mg II complexes are larger than ~0.5 kpc. However, in most cases it is difficult to trace individual Mg II ``cloudlets'' over distances larger than 200-300 h^-1₅₀ pc, indicating that typical sizes of the Mg II cloudlets are smaller than the sizes inferred earlier for the individual clouds of high-ionization gas seen in C IV absorption. We tentatively interpret the absorption pattern of the strongest Mg II 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. The observations were made at the W. M. Keck Observatory, which is operated as a scientific partnership between the California Institute of Technology and the University of California; it was made possible by the generous support of the W. M. Keck Foundation.