Unformatted text preview: dwarfs, and the clouds aren't detectable emitters of Hα. There is strong evidence that the Lyman α lines are underabundant at redshifts close to that of the background quasar, the proximity effect , usually taken to mean that the QSO ionizes all the material within some megaparsecs too highly to see the absorption. This provides a way to estimate the ambient ionizing-radiation intensity as a function of redshift, using the better-known QSO radiation as a point of comparison and seeing how far away it makes a significant difference. Sizes: (or more precisely correlation scales): look at pairs of QSOs along similar lines of sight, appearing within a few arcseconds as we see them, and count the coincident absorption systems and those that don't match. Gravitational lenses are excellent for this. The few cases for which this is possible suggest a typical dimension of some tens of kiloparsecs....
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- Fall '10
- Astronomy, Redshift, Quasar, Lyman α systems, low redshift, HST FOS data