Astronomy and Astrophysics – Astrophysics
Scientific paper
1997-01-29
Astronomy and Astrophysics
Astrophysics
25 pages, 8 figures, final version accepted for publication in ApJ
Scientific paper
10.1086/304806
The damped Lyman alpha absorbers (DLAs) in quasar spectra are believed to be the progenitors of present-day disk galaxies. We examine the probability for microlensing of background quasars by stars in their DLAs. Microlensing by an individual star should magnify the continuum but not the broad emission lines of the quasars. Consequently, the equivalent width distribution of microlensed quasars would be distorted. We model a representative spiral galaxy as a closed system composed of a bulge, a disk, and a halo, and evolve the mass fraction of stars in the disk based on the observed metallicity of DLAs at high redshifts. The microlensing signatures are stronger if the halo of the galaxy is made of Massive Compact Halo Objects (MACHOs). In this case, the distortion imprinted by microlensing on the equivalent width distribution of quasar emission lines can be detected with high significance in a sample of about 10 DLAs with HI column densities N>10^21 cm^-2 and absorption redshifts z_abs<1. About a tenth of all quasars with DLAs (N>10^20 cm^-2) might show excess variability on timescales shorter than five years. A search for these signals would complement microlensing searches in local galaxies and calibrate the MACHO mass fraction in galactic halos at high redshifts.
Loeb Abraham
Perna Rosalba
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