The gravitational lens system 2237 + 0305 consists of a low-redshift barred spiral galaxy (z = 0.0394) centered on a more distant quasar (z = 1.695). Because the lensing galaxy is nearly face on, spectroscopy of the background quasar affords a unique opportunity to study the interstellar medium in the galaxy's center and buW:. We report moderate-resolution spectroscopy of QS02237 + 0305 yielding a 3u upper limit of 72 rnA forthe rest equivalent width of Ca II K absorption d);le to gas in the intervening galaxy. Since gas in the Milky Way "thick disk" typically produces 220 mA Ca II lines along lines of sight at high galactic latitude, while our line of sight to QSO 2237 + 0305 is effectively the weighted mean of four lines of sight, each of which transects an entire halo diameter in the lensing galaxy rather than just a radius, our Ca II upper limit argues against the presence. of such a thick disk near the center of the lensing galaxy. Also, published studies indicate that at 8200 A, QSO 2237 + 0305 suffers roughly 0.5 mag of extinction due to the lensing galaxy. Assuming a normal gas-to-dust ratio and allowing for various sources of uncertainty, this absorption estimate combined with our Ca II Kupper limit implies that calcium is depleted with respect to hydrogen by at least 2.7-3.7 dex, compared to solar abundances. This depletion is similar to the more extreme cases seen in our own galaxy, and higher-dispersion observations may further decrease the upper limit on Ca II absorption.
Hintzen, P., Maran, S.P., Michalitsianos, A.G., Foltz, C.B., Chafee, F.H., Kafatos, M. (1990). Moderate-Resolution Spectroscopy of the Lensed Quasar 2237+0305: A search for Ca ii Absorption Due to the Interstellar Medium in the Foreground Lensing Galaxy, Astrophysical Journal Supplement Series, 99:45-48. doi: 10.1086/115310