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G.M. Madejski (SLAC), V.T. Junkkarinen, R.D. Cohen, E.A. Beaver, E.M. Burbidge, R.W. Lyons (UCSD)
The well-studied BL Lac object AO 0235+164 is located behind an intervening galaxy at a redshift of 0.524. The ISM of this galaxy causes absorption due to hydrogen by the 21 cm hyperfine transition detected in the radio band, and by the damped Lyman alpha line, detected in our HST STIS UV data with a column of 5 ±1 x 1021 cm-2. The X-ray spectrum shows strong absorption beyond the Galactic value, which we attribute to the intervening system. This absorption is due to reprocessed metals, but also due to helium, which is partially primordial and partially reprocessed. The comparison of the UV and X-ray absorption yields the metallicity of the intervening system to be about 0.7 ± 0.2 Solar. We also comment on the dust content of the intervening system based on the detection of spectral features in the UV and optical.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.