The Dust-to-Gas Ratio in the Damped Ly alpha Clouds toward the Gravitationally Lensed QSO 0957+561

Details The Dust-to-Gas Ratio in the Damped Ly alpha Clouds toward the Gravitationally Lensed QSO 0957+561 The Dust-to-Gas Ratio in the Damped Ly alpha Clouds toward the Gravitationally Lensed QSO 0957+561

Mar 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...477..568z&link_type=abstract

Astrophysical Journal v.477, p.568

Astronomy and Astrophysics

Astronomy

28

Galaxies: Ism, Galaxies: Quasars: Individual Alphanumeric: Qso 0957+561, Cosmology: Gravitational Lensing, Galaxies: Quasars: Absorption Lines

Scientific paper

We present HST/FOS 1 spectra of the two bright images (A and B) of the gravitationally lensed QSO 0957+561 in the wavelength range 2200--3300 A. We find that the absorption system (zabs = 1.3911) near zem is a weak, damped Ly alpha system with strong Ly alpha absorption lines seen in both images. However, the H I column densities are different, with the line of sight to image A intersecting a larger column density. The continuum shapes of the two spectra differ in the sense that the flux level of image A increases more slowly toward shorter wavelengths than that of image B. We explain this as the result of differential reddening by dust grains in the damped Ly alpha absorber. A direct outcome of this explanation is a determination of the dust-to-gas ratio, k, in the damped Ly alpha system. We derive k = 0.55 +/- 0.18 for a simple 1/ lambda extinction law and k = 0.31 +/- 0.10 for the Galactic extinction curve. For gravitationally lensed systems with damped Ly alpha absorbers, our method is a powerful tool for determining the values and dispersion of k, and the shapes of extinction curves, especially in the FUV and EUV regions. We compare our results with previous work.

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