Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990aj.....99...45h&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 99, Jan. 1990, p. 45-48.
Astronomy and Astrophysics
Astronomy
13
Barred Galaxies, Gravitational Lenses, Quasars, Red Shift, Spiral Galaxies, Stellar Spectra, Cosmic Gases, Galactic Bulge, Galactic Nuclei, Interstellar Matter
Scientific paper
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 . We report moderate-resolution spectroscopy of QSO2237+0305 yielding a 3σ upper limit of 72 mÅ for the rest equivalent width of Ca II K absorption due to gas in the intervening galaxy. Since gas in the Milky Way "thick disk" typically produces 220 mÅ 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 Å, QSO 2237+0305 suffers roughly 0.5 mag of extinction due to the leasing galaxy. Assuming a normal gas-to-dust ratio and allowing for various sources of uncertainty, this absorption estimate combined with our Ca II K upper 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.
Chaffee Frederic H. Jr.
Foltz Craig B.
Hintzen Paul
Kafatos Minas
Maran Stephen P.
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