Milky-Way-Like 2175 Å Dust Extinction Feature Observed toward the Quasar SDSS J0916[formula omitted]2921

Abstract

Spectral observations indicated that the quasar SDSS J091613.60+ 292106.1 (simply called as J0916+2921, with the system redshift of zem=1.1418±0.0018) has a Milky-Way-like 2715Å dust extinction feature, its strength is obviously greater than the average value of the Galaxy. At the same time, a plenty of gas absorption lines in association with dust were detected, their system redshift is determined to be zabs=1.1413±0.0002, in consistence with the quasar redshift. The ratios of column densities of gaseous metal ions relative to the Solar metallicity are [Al/Zn]=−1.68±0.10, [Cr/Zn]=−0.49±0.10, and [Fe/Zn]=−0.81±0.18. The significant effect of dust dissipation indicates that the absorber is heavily dusty, supporting the detection of the 2175Å dust extinction feature. The Milky-Way-like dust extinction was usually observed in the intervening quasar absorbers, but its existence in the quasar intrinsic absorber has never been confirmed before. The associated dust absorber toward the quasar SDSS J0916+2921 is one of the several intrinsic 2175Å absorber candidates. The X-ray radiation of the quasar is greater than the average value. This may provide a natural laboratory for further studying the equilibrium of formation and dissociation of 2175Å dust grains under the irradiation of strong high-energy radiations, so that their chemical composition, physical structure, and origin can be revealed.