Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.264..705m&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 264, NO. 3/OCT1, P. 705, 1993
Astronomy and Astrophysics
Astronomy
22
Quasars: Absorption Lines - Cosmology: Observations - Dark Matter
Scientific paper
According to the minihalo model for the Lyα forest, the absorption lines arise from photoionized gas gravitationally confined in dark matter haloes of low circular velocity. Using the Press-Schechter formalism, we find that, in the CDM model, the number of Lyα clouds and their evolution with redshift are in agreement with observations if we assume a constant intensity for the ionizing background and a constant temperature for the gas in the minihaloes against changes in redshift. This is a generic consequence of the shape and the amplitude of the CDM spectrum on subgalactic scales; the evolution is due to the disappearance of the minihaloes as they merge into larger systems, although other effects may also modify the evolution rate. The stringent upper limits on the Gunn-Peterson absorption currently available are not a serious problem for the model, since the space between haloes producing absorption lines is mostly filled by highly underdense voids.
If the minihaloes giving rise to the absorption lines were as clustered as the mass, their autocorrelation should be about three times larger than the upper limits found by Rauch et al. (depending on the bias parameter). Most minihaloes, however, would have already merged into larger structures at the epoch when the Lyα forest is observed, the surviving ones being preferentially in low-density regions. In fact, using an analytical model based on the Press-Schechter formalism, we find that the crosscorrelation between minihaloes and mass can be much smaller than the autocorrelation of mass. We also discuss the amplitude of the autocorrelation function of minihaloes.
Miralda-Escude' Jordi
Mo Hou-Jun
Rees Martin J.
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