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Session 84 - IGM.
Display session, Friday, January 09
While it is possible to explain Ly\alpha absorber counts at low redshift using gas which is associated with moderately extended galaxies (Linder 1997), absorbers are often observed to be associated with galaxies at larger impact parameters from quasar lines of sight than are expected from calculated galaxy absorption cross sections in such absorber-galaxy models. However, a large fraction of absorption is expected to arise in lines sight through galaxies which are low in luminosity and/or surface brightness, so that they are unlikely to be detected in surveys for galaxies close to quasar lines of sight. Given that it is impossible to be certain that any particular absorber has been matched to the correct galaxy, I show that it is possible to simulate plots of absorption covering factors around luminous galaxies which resemble observed plots more by assuming that absorption often originates in unidentified galaxies. Many absorbers may arise in low surface brightness galaxies which are weakly clustered around luminous, high surface brightness galaxies, so that the clustering properties of galaxies must be included within the simulations in order to determine the shape of covering factor plots more accurately.
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