We investigate the properties of HI-rich galaxies detected in blind radio surveys within the hierarchical structure formation scenario using a semi-analytic model of galaxy formation .
By drawing a detailed comparison between the properties of HI-selected galaxies and HI absorption systems , we argue a link between the local galaxy population and quasar absorption systems , particularly for damped Ly \alpha absorption ( DLA ) systems and sub-DLA systems .
First , we evaluate how many HI-selected galaxies exhibit HI column densities as high as those of DLA systems .
We find that HI-selected galaxies with HI masses M _ { HI } \gtrsim 10 ^ { 8 } M _ { \odot } have gaseous disks that produce HI column densities comparable to those of DLA systems .
We conclude that DLA galaxies where the HI column densities are as high as those of DLA systems , contribute significantly to the population of HI-selected galaxies at M _ { HI } \gtrsim 10 ^ { 8 } M _ { \odot } .
Second , we find that star formation rates ( SFRs ) correlate tightly with HI masses ( M _ { HI } ) rather than B - ( and J - ) band luminosities : SFR \propto M _ { HI } ^ { \alpha } , \alpha = 1.25 - 1.40 for 10 ^ { 6 } \leq M _ { HI } / M _ { \odot } \leq 10 ^ { 11 } .

In the low-mass range M _ { HI } \lesssim 10 ^ { 8 } M _ { \odot } , sub-DLA galaxies replace DLA galaxies as the dominant population .
The number fraction of sub-DLA galaxies relative to galaxies reaches 40 \% - 60 \% for M _ { HI } \sim 10 ^ { 8 } M _ { \odot } and 30 \% - 80 \% for M _ { HI } \sim 10 ^ { 7 } M _ { \odot } .
The HI-selected galaxies at M _ { HI } \sim 10 ^ { 7 } M _ { \odot } are a strong probe of sub-DLA systems that place stringent constraints on galaxy formation and evolution .