AAS 200th meeting, Albuquerque, NM, June 2002
Session 86. Cosmology and IGM
Oral, Thursday, June 6, 2002, 2:00-3:30pm, Ballroom B

[86.06D] The Search for Intergalactic Hydrogen Clouds in Voids

C. V. Manning (UC Berkeley)

My dissertation research is divided into two parts. The first part is the utilization of published HST data on HI absorption systems in spectra of low redshift AGN and galaxy redshift catalogs, to separate clouds according to their proximity to galaxies by use of the calculated scalar tidal field. I discover a robust population of clouds located in cosmic voids and detail the differences between void and non-void clouds. By noting the correspondence of the tidal fields at which the transition between void and non-void cloud Doppler parameter characteristics, and equivalent width distribution function slope characteristics occur, I am able to determine a filling factor for voids fV~q 0.9. I show that void clouds dominate the line density for equivalent widths less than 32 mÅ. The second part of my research is a modeling of the history'' of clouds seen as sub-galactic perturbations which expand in response to the re-ionization of the universe at z ~q 6.5 using a 1-D Lagrangian hydro/gravity code. The results of this modeling can be used to explain the observed cloud distribution function, and so estimate the matter density in voids. The observed EW distribution can be explained if 1) a truncated isothermal halo approximately 5 times more massive than NFW halos of the same halo circular velocity are utilized, and 2) the distribution of clouds with velocities in the range 10 \leq vc \leq 25 km/s are very steep ( ie, most mass at small velocities). This fit implies \Omegam ~q 0.11 in voids. This estimate excludes possible contributions from a possible diffuse gaseous/DM component and galaxies, and must be regarded as a lower limit.

I gratefully acknowledge the support of the UC Berkeley Department of Astronomy, and NSF grant # AST-0097163.