H I gas in higher density regions of the IGM

Using H I absorption alone, we attempt to separate H I absorption lines in quasar spectra into two categories; hdls (higher density lines) and ldls (lower density lines), and we discuss the difference in their physical properties. We deblend and fit all H I lines with voigt profiles, and make an unbiased sample of H I lines covering a wide column density range (12 cm^-2). To reduce the influence of line blending, we simultaneously fit several Lyman series lines. As a result of a two-point correlation analysis, we found that higher column density H I lines are clustering at δ v km s^-1, while lower ones at δ v km s^-1. We define hdls as H I lines with 15 cm^-2 and all H I lines within ±200 km s^-1 of a line with log n_HI > 15 cm^-2, and ldls as others with 12 cm^-2. We found that the hdls have smaller minimum b-values for a given column density than the ldls. This difference is successfully reproduced by our hydrodynamic simulation. The ldls seem to be cool or shock-heated difFUSE igm gas, while the hdls are likely to be cooler dense gas near to galaxies.