Toward Detecting the 2175 Å Dust Feature Associated with Strong High-redshift Mg II Absorption Lines

• Published in: The Astrophysical journal Vol. 732; no. 2; pp. 110 - jQuery1323908817801='48'
• Main Authors: Jiang, Peng, Ge, Jian, Zhou, Hongyan, Wang, Junxian, Wang, Tinggui
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 10.05.2011; IOP
• Subjects: ABSORPTION; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC DUST; COSMIC RADIO SOURCES; DETECTION; DUSTS; Earth, ocean, space; ELEMENTS; Exact sciences and technology; GALAXIES; MANGANESE; METALS; QUASARS; RED SHIFT; SIMULATION; SORPTION; TRANSITION ELEMENTS; Quasars; Red shift; Galaxies; Optical models; quasars: absorption lines; Equivalent width; Lyman alpha forest; Parameterization; Milky Way; Absorption line; Upper bound; dust, extinction; Lyman alpha line; galaxies: ISM; Extinction curve; Sky surveys; Large Magellanic Cloud
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/732/2/110

We report detections of 39 2175 A dust extinction bump candidates associated with strong Mg II absorption lines at z~ 1-1.8 on quasar spectra in Sloan Digital Sky Survey (SDSS) DR3. These strong Mg II absorption line systems are detected among 2951 strong Mg II absorbers with a rest equivalent width Wr Delta *l2796> 1.0 A at 1.0 < z < 1.86, which is part of a full sample of 7421 strong Mg II absorbers compiled by Prochter et al. The redshift range of the absorbers is chosen to allow the 2175 A extinction features to be completely covered within the SDSS spectrograph operation wavelength range. An upper limit of the background quasar emission redshift at z = 2.1 is set to prevent the Ly Delta *a forest lines from contaminating the sensitive spectral region for the 2175 A bump measurements. The FM90 parameterization is applied to model the optical/UV extinction curve in the rest frame of Mg II absorbers of the 2175 A bump candidates. The simulation technique developed by Jiang et al. is used to derive the statistical significance of the candidate 2175 A bumps. A total of 12 absorbers are detected with 2175 A bumps at a 5 Delta *s level of statistical significance, 10 are detected at a 4 Delta *s level, and 17 are detected at a 3 Delta *s level. Most of the candidate bumps in this work are similar to the relatively weak 2175 A bumps observed in the Large Magellanic Cloud LMC2 supershell rather than the strong ones observed in the Milky Way. This sample has greatly increased the total number of 2175 A extinction bumps measured on SDSS quasar spectra. Follow-up observations may rule out some of the possible false detections and reveal the physical and chemical natures of 2175 A quasar absorbers.