On observational constraints on the shape of the dark matter distribution in the model of dark matter confined Ly$\alpha$ clouds
Session 115 -- Cosmology and Dark Matter
Oral presentation, Saturday, January 15, 10:15-11:45, Salon III Room (Crystal Gateway)

## [115.02] On observational constraints on the shape of the dark matter distribution in the model of dark matter confined Ly$\alpha$ clouds

V. Khersonsky, D. A. Turnshek (University of Pittsburgh)

\hspace*{0.5cm}A promising model of the Ly$\alpha$ clouds seen in absorption in quasar spectra was developed by Rees (1986, MNRAS, 218, 25p) [see also Ikeuchi (1991, Adv Space Res, 11, No.2, 245) and Miralda-Escud\'{e} and Rees (1993, MNRAS, 260, 617)]. In this model `minihalos' of dark matter (DM) are postulated to provide potential wells which stabilize the Ly$\alpha$ clouds. In this contribution we show that available observational data can be used to obtain some constraints on the radial distributions of the DM density inside the minihalos and we discuss several important points with regard to this problem. First, we combine the shape of the density distribution of HI in a typical cloud (which can be derived from the distribution of cloud numbers as a function of column density) with results from the study of Black (1981, MNRAS, 197, 553) on the physical conditions in hot photoionized Ly$\alpha$ clouds. For gas in hydrostatic equilibrium in a DM potential well we show that the radial distribution of the density of DM can be decribed analytically as function of two parameters. One parameter is related to the slope of the distribution of cloud numbers as a function of column density. The second parameter is the ratio of the DM density in the center of a cloud to the background density of DM outside the cloud. To obtain some constraints on the second parameter we use observational results on the distribution of Doppler parameters, the variation of cloud numbers with redshift, and assumptions about how the distribution of cloud numbers varies with cloud mass. With this information we are able to derive the redshift dependence of the distribution of DM potential well parameters.
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