Sizes, Shapes, and Correlations of Lyman Alpha Clouds and Their Evolution in the Lambda CDM Universe

Details Sizes, Shapes, and Correlations of Lyman Alpha Clouds and Their Evolution in the Lambda CDM Universe Sizes, Shapes, and Correlations of Lyman Alpha Clouds and Their Evolution in the Lambda CDM Universe

Jul 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...483....8c&link_type=abstract

Astrophysical Journal v.483, p.8

Astronomy and Astrophysics

Astronomy

33

Cosmology: Large-Scale Structure Of Universe, Cosmology: Theory, Hydrodynamics, Galaxies: Intergalactic Medium, Methods: Numerical, Galaxies: Quasars: Absorption Lines

Scientific paper

This study analyzes the sizes, shapes, and correlations of Ly alpha clouds produced by a hydrodynamic simulation of a spatially flat CDM universe with a nonzero cosmological constant ( Omega 0 = 0.4, Lamda 0 = 0.6, sigma 8 = 0.79) over the redshift range 2 <= z <= 4. The Ly alpha clouds range in size from several kiloparsecs to about a hundred kiloparsecs in proper units, and they range in shape from roundish, high column density regions with NH I >= 1015 cm-2 to low column density sheet-like structures with NH I <= 1013 cm-2 at z = 3. The most common shape found in the simulation resembles that of a flattened cigar. The physical size of a typical cloud grows with time roughly as (1 + z)-3/2, while its shape hardly evolves (except for the most dense regions with rho cut > 30). Collectively, the clouds form large networks of filaments and sheets. Our result indicates that any simple model with a population of spheres (or other shapes) of a uniform size is oversimplified; if such a model agrees with observational evidence, it is probably only by coincidence. We also illustrate why the use of pairs of quasar sight lines to set lower limits on cloud sizes is useful only when the perpendicular sight line separation is small ( Delta r <= 50 h-1 kpc). Finally, we conjecture that high column density Ly alpha clouds (NH I >= 1015 cm-2) may be the progenitors of the lower redshift faint blue galaxies, based on consideration of their correlation, number density, and mass.

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