Limits on dust in damped Lyman-alpha systems and the obscuration of quasars

Details Limits on dust in damped Lyman-alpha systems and the obscuration of quasars Limits on dust in damped Lyman-alpha systems and the obscuration of quasars

Feb 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...337....7f&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 337, Feb. 1, 1989, p. 7-20.

Astronomy and Astrophysics

Astrophysics

74

Cosmic Dust, Cosmology, Intergalactic Media, Lyman Alpha Radiation, Quasars, Continuous Spectra, Gases, Interstellar Extinction, Optical Thickness, Radiation Absorption, Red Shift

Scientific paper

A new method to determine or set limits on the dust-to-gas ratio k in damped Ly-alpha systems and any obscuration they cause along random lines of sight is introduced. The spectra of quasars in the survey of Wolfe et al. (1986) that have damped Ly-alpha are compared with those that do not have damped Ly-alpha to obtain statistical information about the reddening by dust. At the 95 percent confidence level, it is found that k is 0.41 for the Galaxy, 0.29 or less for the LMC, and 0.19 or less for the SMC. The upper limits on the dust-to-gas ratio in the sampled Ly-alpha systems are half the observed value in the Galaxy but are several times larger than the observed values in the Magellanic Clouds. A new method to set limits on the mean and the variance of the optical depth along random lines of sight is developed, including a correction for the effect that highly obscured quasars are less likely to be included in optically selected samples than quasars with little dust in the foreground.

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