Study of Lyα absorption lines in the spectra of double line-of-sight (DLOS) quasars holds the promise of diagnosing the nature of the structures that give rise to Lyα absorption. Based on simulations of DLOS with various separations through a single population of absorbers, four tests have been designed to diagnose absorber mass distributions (smoothly varying with radius or irregular), geometries (spherical or disk/slab-like), and kinematics (isotropic or systematic velocities). Applying the tests to existing data at z ∼ 2 we find the following. (1) The observed neutral hydrogen column density (NH) distributions of Lyα lines coincident to both LOSs are consistent with a smooth mass distribution. (2) Observed large anticoincident NH values are not consistent with a single population of smooth spherical absorbers, which should exhibit sharp cutoffs at small NH in the NH distribution. (3) There is marginal evidence that the observed rms value of velocity differences between coincident lines increases with DLOS separation, as is expected for disk/slab-like absorbers that have systematic velocity fields. (4) The observed velocity dispersion along a single LOS is small compared to the rms difference between widely separated LOS, which is not consistent with models of cloudlets moving isotropically within a spherical structure. Overall, only a smooth disk/slab-like model with systematic velocities remains consistent with the inferred properties of a single population of Lyα absorbers.
|Original language||English (US)|
|Issue number||2 PART 2|
|State||Published - Oct 20 1995|
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science