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2000ApJ...539..111D - Astrophys. J., 539, 111-123 (2000/August-2)
Ultraviolet spectral variability and the Lyα forest in the lensed quasar Q0957+561.
DOLAN J.F., MICHALITSIANOS A.G., NGUYEN Q.T. and HILL R.J.
Abstract (from CDS):
The individual spectra of each image were co-added to investigate the properties of the Lyα forest along the two lines of sight to the quasar. Absorption lines having equivalent width Wλ≥0.3 Å in the observer's frame not previously identified by Michalitsianos et al. as interstellar lines, metal lines, or higher order Lyman lines were taken to be Lyα forest lines. The existence of each line in this consistently selected set was then verified by its presence in two archival FOS spectra with ∼1.5 times higher signal to noise than our co-added spectra. Lyα forest lines with Wλ≥0.3 Å appear at 41 distinct wavelengths in the spectra of the two images. One absorption line in the spectrum of image A has no counterpart in the spectrum of image B, and one line in image B has no counterpart in image A. Based on the separation of the lines of sight over the redshift range searched for Lyα forest lines, the density of the absorbing clouds in the direction of Q0957+561 must change significantly over a distance R=160+120–70 h–150 kpc in the simplified model where the absorbers are treated as spherical clouds and the characteristic dimension, R, is the radius. (We adopt H0=50 h50 km.s–1.Mpc–1, q0=(1)/(2), and Λ=0 throughout this paper.) The 95% confidence interval on R extends from 50 to 950 h–150 kpc.
We show in the Appendix that the fraction of Lyα forest lines that appear in only one spectrum can be expressed as a rapidly converging power series in 1/r, where r the ratio of the radius of the cloud to the separation of the two lines of sight at the redshift of the cloud. This power series can be rewritten to give r in terms of the fraction of Lyα forest wavelengths that appear in the spectrum of only one image. A simple linear approximation to the solution that everywhere agrees with the power series solution to better than 0.8% for r≥2 is derived in the Appendix.
Abstract Copyright: ∼
Journal keyword(s): Cosmology: Gravitational Lensing - Galaxies: Quasars: Absorption Lines - Galaxies: Quasars: Emission Lines - Galaxies: Quasars: Individual: Alphanumeric: Q0957+561 - Ultraviolet: Galaxies
Simbad objects: 20
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