Dust and Diffuse Interstellar Bands in the z(sub a) = 0.524 Absorption System toward AO 0235+164.

[摘要] The authors present new HST STIS NUV-MAMA and STIS CCD observations of the BL Lac object AO 0235+164 and the intervening damped Ly (alpha) (DLA) line at z(sub (alpha)) = 0.524. The line profile gives N(HI) = 5 (+-) 1 x 10(sup 21) cm(sup -2) and, combined with the H I 21 cm absorption data leads to a spin temperature of Ts = 220 K (+-) 60 K. Those spectra also show a strong, broad feature at the expected position of the 2175 (angstrom) graphitic dust feature at z(sup (alpha)) = 0.524. Assuming a Galactic type dust extinction curve at z(sub (alpha)) = 0.524 gives a dust-to-gas ratio of 0.19 Galactic, but the fit, assuming the underlying, un-reddened spectrum is a single power-law, is poor in the far-UV. A dust-to-gas ratio of 0.19 Galactic is similar to the LMC, but the AO 0235+164 spectrum does not fit the LMC extinction curve, or the SMC extinction curve (which has practically no 2175 (angstrom) feature). A possible interpretation includes dust similar to Galactic, but with less of the small particles that produce the far-UV extinction. The metallicity of the z(sub (alpha)) = 0.524 absorber, estimated from the observed N(HI) and excess X-ray absorption (beyond Galactic) derived from contemporaneous and archival ASCA and ROSAT.

[发布机构] Technical Information Center Oak Ridge Tennessee

[学科分类] 工程和技术（综合）

[关键词] Interstellar grains;Cosmic dust;Spin;Absorption spectra;X-ray spectra