Density Distribution Function from H
نویسندگان
چکیده
The cross-section of sky occupied by a particular neutral hydrogen column density (NHI) provides insight into the nature of Lyα absorption systems. We have measured this column density distribution at z=0 using 21-cm Hi emission from a blind survey. A subsample of HI Parkes All Sky Survey (HIPASS) galaxies have been imaged with the Australia Telescope Compact Array (ATCA). The contribution of low Hi mass galaxies (10 to 10 M⊙) is compared to that of M∗ (10 10 to 10 M⊙) galaxies. We find that the column density distribution function is dominated by low Hi mass galaxies in the range 3×10 < NHI < 2×10 20 cm. This result is not intuitively obvious. M∗ galaxies may contain the bulk of the Hi gas, but the cross-section presented by low Hi mass galaxies (10 to 10 M⊙) is greater at moderate column densities. This result implies that moderate NHI Lyα absorption systems may be caused by a range of galaxy types and not just large spiral galaxies as originally thought.
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