Detection of the 2175 angstrom dust feature in Mg II absorption systems

Abstract

The broad absorption bump at 2175 angstrom due to dust, which is ubiquitous in the Galaxy and is seen in the Magellanic clouds, is also seen in a composite spectrum of Mg II absorbers. The composite absorber spectrum is obtained by taking the geometric mean of 92 quasar spectra after aligning them in the restframe of 96 absorbers. By aligning the spectra according to absorber redshifts we reinforce the spectral features of the absorbers, and smooth over possible bumps and wiggles in the emission spectra as well as small features in the flat fielding of the spectra. The width of the observed absorption feature is 200-300 angstrom (FWHM), or 0.4-0.6 (micron)^{-1} and the central wavelength is 2240 angstrom. These are somewhat different from the central wavelength of 2176 angstrqom and FWHM=0.8-1.25 (micron)^{-1} found in the Galaxy. Simulations show that this discrepancy between the properties of the 2175 angstrom feature in Mg II absorbers and Galactic ISM can be mostly explained by the different methods used to measure them.

To appear in ApJ(letters). 11 pages, Latex, uses AASTeX v4.0

References in corpus (2)

• Molecular Hydrogen Absorption in the z= 1.97 Damped Lyman alpha Absorption system toward QSO 0013-004
• Abundance Patterns of Heavy Elements in Damped Lyman-Alpha Galaxies

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• Presence of dust with a UV bump in massive, star-forming galaxies at 1 < z < 2.5
• The Number Density of 0.6 < z < 1.7 MgII Systems from CORALS: Observational Biases at Intermediate Redshift
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• The High A(V) Quasar Survey: Reddened quasi-stellar objects selected from optical/near-infrared photometry - II
• Probing Cosmic Dust of the Early Universe through High-Redshift Gamma-Ray Bursts