Absorption spectrum of the Z = 3.78 QSO 2000-330. II - The redshift and equivalent width distributions of primordial hydrogen clouds

Details Absorption spectrum of the Z = 3.78 QSO 2000-330. II - The redshift and equivalent width distributions of primordial hydrogen clouds Absorption spectrum of the Z = 3.78 QSO 2000-330. II - The redshift and equivalent width distributions of primordial hydrogen clouds

Oct 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986apj...309...19m&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 309, Oct. 1, 1986, p. 19-32.

Astronomy and Astrophysics

Astrophysics

221

Cosmology, Galactic Evolution, Hydrogen Clouds, Intergalactic Media, Lyman Alpha Radiation, Quasars, Absorption Spectra, Bl Lacertae Objects, Red Shift, Spectral Line Width

Scientific paper

We present an analysis of the distribution in redshift z and equivalent width W of the number density of Lyman-α lines detected in the spectra of high-redshift QSOs. We use a sample which is reasonably homogeneous as regards spectral resolution and signal-to-noise ratio and covers a wider range of z (1.50-3.78) than previous studies. This is achieved principally by including results from the z = 3.78 QSO 2000-330. We extend the lower end of the range by including data down to 3040 Å from the bright z = 1.7 BL Lac object 0215 + 015. Unlike previous studies, we exclude from our Lyα sample those Lyα lines which occur in known heavy-element (metal-line) systems. However, we also present results with these lines included and thereby demonstrate that this has a marked effect on the distribution of the number density of lines with redshift. Our analysis, which uses the method of maximum likelihood, has led to a reappraisal of much of the previous work. Our conclusions are: (1) There is incontrovertible evidence for evolution in the number density of Lyα lines of the form dN/dz ∝ (1 + z)γ, with γ = 2.17 ± 0.36. (2) However, within individual QSOs we find a countervailing trend in dN/dz which previous studies have failed to recognize. (3) We attribute this trend to the influence of luminous QSOs on their environment over distances of order 4 Mpc. (4) We confirm previous results that the distribution in equivalent width W is well represented by an exponential increase in the number density of lines with decreasing W for W > 0.2 Å. However, we show that the line density rises even more steeply for W <0.2 Å. (5) From our results for the distributions in number density and equivalent width we deduce strong evolution with epoch in the H I column density of individual clouds, as indeed suggested by current theoretical models.

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