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

Sangeeta Malhotra

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

The broad absorption bump at 2175 Å 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 rest frame 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 Å (FWHM), or 0.4-0.6 μm-1, and the central wavelength is 2240 Å. These are somewhat different from the central wavelength of 2176 Å and FWHM = 0.8-1.25 μm-1 found in the Galaxy. Simulations show that this discrepancy between the properties of the 2175 Å feature in Mg II absorbers and the Galactic interstellar medium can be mostly explained by the different methods used to measure them.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume488
Issue number2 PART II
StatePublished - 1997
Externally publishedYes

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absorbers
dust
galaxies
wavelength
composite materials
Magellanic clouds
wavelengths
quasars
detection
emission spectra
simulation

Keywords

  • Dust, extinction
  • Intergalactic medium
  • Quasars: absorption lines

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Detection of the 2175 Å dust feature in Mg II absorption systems. / Malhotra, Sangeeta.

In: Astrophysical Journal, Vol. 488, No. 2 PART II, 1997.

Research output: Contribution to journalArticle

Malhotra, Sangeeta. / Detection of the 2175 Å dust feature in Mg II absorption systems. In: Astrophysical Journal. 1997 ; Vol. 488, No. 2 PART II.
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abstract = "The broad absorption bump at 2175 {\AA} 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 rest frame 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 {\AA} (FWHM), or 0.4-0.6 μm-1, and the central wavelength is 2240 {\AA}. These are somewhat different from the central wavelength of 2176 {\AA} and FWHM = 0.8-1.25 μm-1 found in the Galaxy. Simulations show that this discrepancy between the properties of the 2175 {\AA} feature in Mg II absorbers and the Galactic interstellar medium can be mostly explained by the different methods used to measure them.",
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