Significant H I and Metal Differences around the z = 0.83 Lens Galaxy Towards the Doubly Lensed Quasar SBS 0909+532

Abstract

We report a large difference in neutral hydrogen (H I) and metal column densities between the two sight lines probing opposite sides of the lensing galaxy at $z_\mathrm{lens}$ = 0.83 toward the doubly lensed quasar SBS 0909+532. Using archival HST-STIS and Keck HIRES spectra of the lensed quasar images, we measure log $N_\mathrm{H\;I}$ = 18.77 $\pm$ 0.12 cm$^{-2}$ toward the brighter image ($A$) at an impact parameter of $r_A$ = 3.15 kpc and log $N_\mathrm{H\;I}$ = 20.38 $\pm$ 0.20 cm$^{-2}$ toward the fainter image ($B$) at an impact parameter of $r_B$ = 5.74 kpc. This difference by a factor of $\sim$41 is the highest difference between sight lines for a lens galaxy in which H I has been measured, suggesting patchiness and/or anisotropy on these scales. We estimate an average Fe abundance gradient between the sight lines to be $\geq$ +0.35 dex kpc$^{-1}$. The $N_\mathrm{Fe\;II}$/$N_\mathrm{Mg\;II}$ ratios for the individual components detected in the Keck HIRES spectra have supersolar values for all components in sight line $A$ and for 11 out of 18 components in sight line $B$, suggesting that Type Ia supernovae may have contributed to the chemical enrichment of the galaxy's environment. Additionally, these observations provide complementary information to detections of cold gas in early-type galaxies and the tension between these and some models of cloud survival.