Abstract
view Abstract Citations (18) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Origin of H i Absorption Systems of Quasars Murakami, Izumi ; Ikeuchi, Satoru Abstract We examine intergalactic clouds confined by the gravity of cold dark matter (CDM), the so-called minihalo, as a unified model for neutral hydrogen (H I) absorption systems of quasars. The reported H I column density distribution from 10^13^ cm^-2^ of the Lyα forest to 10^22^ cm^-2^ of damped Lyα systems is well reproduced by the evolution of the two-phase nature of minihalos: a neutral core surrounded by an ionized envelope. Shielding effects of diffuse UV flux due to neutral hydrogen in the envelope cause the appearance of a neutral core in a massive minihalo, and this core is detected as a high column density system. Highly ionized envelopes and/or less massive one-phase minihalos correspond to the Lyα forest. In order to reproduce the number density evolution of the Lyα forest and the redshift variation of the continuum depression of high-redshift quasars, minihalos must experience an expansion that is caused by the increase of UV flux with the decrease of redshift at z > 2. Assuming a simplified evolution law of UV flux and mass function of gas clouds, we can reproduce all these observational properties by the minihalo model. At z < 2, the diffuse UV flux decreases and minihalos are apt to contract. The collapse of neutral cores is delayed, especially for small mass clouds, as late as z < 1, and these are considered to become dwarf galaxies. In this picture we present some predictions about low z Lyα clouds for observations of the Hubble Space Telescope. Publication: The Astrophysical Journal Pub Date: May 1993 DOI: 10.1086/172640 Bibcode: 1993ApJ...409...42M Keywords: Absorption Spectra; Dark Matter; H I Regions; Intergalactic Media; Lyman Alpha Radiation; Quasars; Dwarf Galaxies; Line Spectra; Red Shift; Astrophysics; COSMOLOGY: DARK MATTER; GALAXIES: QUASARS: ABSORPTION LINES; GALAXIES: INTERGALACTIC MEDIUM full text sources ADS | data products SIMBAD (3)
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