paper

Escape of Ionizing Radiation from High-Redshift Galaxies

arXiv:astro-ph/9911316 · doi:10.1086/317775

Abstract

We use a three-dimensional radiation transfer code to calculate the steady-state escape fraction of ionizing photons from disk galaxies as a function of redshift and galaxy mass. The gaseous disks are assumed to be isothermal (with a sound speed ) and radially exponential. Their scale-radius is related to the characteristic spin parameter and virial radius of their host halos, and their vertical structure is dictated by their self-gravity. The sources of radiation are taken to be either stars embedded in the disk, or a central quasar. The predicted increase in the disk density with redshift results in an overall decline of the escape fraction with increasing redshift. For typical parameters of smooth disks, we find that the escape fraction at is $\la 1%$ for stars, but $\ga 30%$ for mini-quasars. Unless the smooth gas content of high-redshift disks was depleted by more than an order of magnitude due to supernovae-driven outflows or fragmentation, the reionization of the universe was most likely dominated by mini-quasars rather than by stars.

33 pages, 13 figures. Accepted for ApJ (December 10, 2000 issue). New section added on escape of ionizing radiation from clumpy disks

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