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| Paper: |
How Normal Disk Galaxies Ionize their Surroundings |
| Volume: |
230, Galaxy Disks and Disk Galaxies |
| Page: |
299 |
| Authors: |
Beckman, J. E.; Zurita, A.; Rozas, M. |
| Abstract: |
We examine using numerical examples and conservative assumptions, the consequences of the fractal structure of the interstellar medium in a disk galaxy in permitting the propagation of the ionizing radiation emitted by its massive stellar population. We compare the Strömgren sphere in a homogeneous medium with its equivalent in a clumpy medium, taking densities typical of HII regions, to show that there is always a fractional escape of Lyman continuum photons from an HII region, and that this fraction should increase for regions with high luminosities. The calculation is extended to deal with a clumpy medium at densities typical of the diffuse interstellar gas in disks, showing how propagation over kpc scales from OB associations is in no way ruled out. Finally, showing that at densities typical of the IGM clumpiness should play a less critical role, we estimate the volume and mass of gas around a Milky Way sized galaxy which should be ionized by photons escaping from its disk, and draw a parallel with recent results from high-z galaxies. |
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