Detailed structure of expanding photoionized Ly-alpha clouds

Details Detailed structure of expanding photoionized Ly-alpha clouds Detailed structure of expanding photoionized Ly-alpha clouds

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.260...67p&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 260, no. 1, p. 67-76.

Astronomy and Astrophysics

Astronomy

15

Absorption Spectra, Interstellar Gas, Lyman Alpha Radiation, Photoionization, Quasars, Astronomical Models, Density Distribution, Doppler Effect, Metallicity, Red Shift

Scientific paper

To investigate the properties of high-redshift Ly-alpha systems, we use a detailed photoionization code to examine spherical gaseous clouds with very low metallicity and bounded by an external pressure. The density variations through the cloud are governed by gravity. As the confining pressure decreases with time because of the expansion of the Universe, the cloud expands with a surface velocity in the range 5-15 km/s. The corresponding additional cooling rate happens to be negligible in the central part of the cloud, where the temperature can be as high as 30,000 K, but it induces a decrease in the temperature and pressure in the outer layers of the cloud. The column density and Doppler parameter distributions inferred from high-resolution data can be reproduced only by a population of clouds with different central densities, radii and masses, in which case there is a trend for high column densities to be associated with large b values. If confirmed, the tight correlation between b and N/(H I) claimed by Pettini et al. would imply an uncomfortably narrow range for the cloud parameters.

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