Pressure-confined LY alpha Clouds: Simulation Results versus Observations
Abstract
We use a hydrodynamic numerical code to study the evolution of spherical, optically thin, pressure-confined Lyα clouds in an adiabatically evolving intercloud medium. We use the results to construct the associated synthetic dN/dz and dN/dN_H I_ distributions and compare them against observations as well as to the analytical predictions. We find that the model can largely account for the observed column density distribution with a cloud mass spectrum dN is proportional to M^-δ^dM, δ = 1.90; however, discrepancies are present at high column densities. In particular, the synthetic dH/dN_H I_ exhibits a deficiency of clouds with log (N_H I_) >~ 15.5 and the column density distribution for a restricted redshift range about z ~ 2.7 has an abrupt cutoff not seen in the observations. The synthetic dN/dz is also inconsistent with the data and analytic predictions primarily because the redshift density declines much more rapidly at low redshifts. Both of the above effects arise as a result of the finite mass range for observable clouds, a mass range that shrinks with time. A non-adiabatically evolving ICM cannot alleviate the problems inherent in the model unless the ICM pressure evolves more rapidly than P(z) is proportional to (1 + z)^5^. While effects such as inhomogeneities in the ICM can remedy the situation, a recent study argues against such a hypothesis. Aspherical systems, however, remain a possibility.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1992
- DOI:
- 10.1086/171935
- Bibcode:
- 1992ApJ...399..385W
- Keywords:
-
- Absorption Spectra;
- Hydrogen Clouds;
- Lyman Alpha Radiation;
- Quasars;
- Hydrodynamic Equations;
- Line Spectra;
- Pressure Distribution;
- Space Density;
- Astrophysics;
- HYDRODYNAMICS;
- GALAXIES: QUASARS: ABSORPTION LINES