Direct Detection of Dust and Diffuse Interstellar Bands in a QSO Absorption-Line System

Details Direct Detection of Dust and Diffuse Interstellar Bands in a QSO Absorption-Line System Direct Detection of Dust and Diffuse Interstellar Bands in a QSO Absorption-Line System

May 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...194.7101c&link_type=abstract

American Astronomical Society, 194th AAS Meeting, #71.01; Bulletin of the American Astronomical Society, Vol. 31, p.942

Astronomy and Astrophysics

Astronomy

10

Scientific paper

We have identified unambiguous signatures of dust and diffuse interstellar bands at z=0.524 in the spectrum of AO 0235+164. AO 0235+164 is a BL Lac object at zem=0.94 which is known to have two metal-line absorption systems, at z=0.524 and z=0.851. The lower redshift system has 21 cm absorption, indicative of very high column density. There are two galaxies within 2" of A0235+164 which may be the sites of the z=0.524 absorption system. One of these is itself an unusual object, with a UV spectrum dominated by high-ionization, BAL-like absorption lines. We have obtained a low resolution spectrum covering from 1600 Angstroms to beyond 1mu with STIS and HST. The two dominant features are the damped Lyalpha line at z=0.524 and a strong, broad feature centered near 3300 Angstroms. This feature can only be identified as the lambda =2175 Angstroms feature due to interstellar dust extinction at z=0.524. The model that most closely approximates the spectrum is parametrized as a broken power law with Galactic type extinction at z=0 and z=0.524 in addition to the absorption lines. We derive N_H ~ 5 x 10(21) \ cm(-2) and E(B-V) ~ 0.25. This indicates that the dust-to-gas ratio is considerably lower than in the Galaxy. The fit to the lambda =2175 Angstroms feature suggests there are differences from the average Galactic curve. Acceptable fits with R > 3.1 are also possible, but they imply an extremely high luminosity for AO 0235+164. From a low-resolution, but very high signal-to-noise spectrum obtained with LRIS at Keck Observatory, we have detected a feature which we identify as the lambda =4428 Angstroms diffuse interstellar band at z=0.524, with a rest equivalent width of 0.8 Angstroms. The strength of the DIB and E(B-V) ~ 0.25 are consistent with the Galactic relationship. This work was supported by NASA through a grant from STScI.

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