Significant H i and Metal Differences around the z = 0.83 Lens Galaxy toward 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 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 H I = 18.77 ± 0.12 cm −2 toward the brighter image ( A ) at an impact parameter of r A = 3.15 kpc and log N H I = 20.38 ± 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 ∼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 ≥+0.35 dex kpc −1 . The N Fe II / N 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.