Cosmic dust in MgII absorbers
  MgII absorbers induce reddening on background quasars. We measure this effect
and infer the cosmic density of dust residing in these systems to be \Omega\ ~
2e-6, in units of the critical density of the Universe, which is comparable to
the amount of dust found in galactic disks or about half the amount inferred to
exist outside galaxies. We also estimate the neutral hydrogen abundance in MgII
clouds to be \Omega\ ~ 1.5e-4, which is approximately 5% of hydrogen in stars
in galaxies. This implies a dust-to-gas mass ratio for MgII clouds of about
1/100, which is similar to the value for normal galaxies. This would support
the hypothesis of the outflow origin of MgII clouds, which are intrinsically
devoid of stars and hence have no sources of dust. Considerations of the dust
abundance imply that the presence of MgII absorbers around galaxies lasts
effectively for a few Gyr. High redshift absorbers allow us to measure the
rest-frame extinction curve to 900 Angstroms at which the absorption by the
Lyman edge dominates over scattering by dust in the extinction opacity.
