%0 Generic %1 munoz2014flatness %A Muñoz, Joseph A. %A Oh, S. Peng %A Davies, Frederick B. %A Furlanetto, Steven R. %D 2014 %K evolution igm ionizing lls mfp uvb %T The Flatness and Sudden Evolution of the Intergalactic Ionizing Background %U http://arxiv.org/abs/1410.2249 %X The ionizing background of cosmic hydrogen is an important probe of the sources and absorbers of ionizing radiation, their evolution and relationship, in the post-reionization universe. Previous studies show that the ionization rate should be very sensitive to changes in the source population: as the emissivity rises, absorbers shrink in size, increasing the ionizing mean free path and, hence, the ionizing background. By contrast, observations of the ionizing background find a very flat evolution from z~2-5, before falling precipitously at z~6. We resolve this discrepancy by pointing out that, at z~2-5, neutral absorbers are associated with the same collapsed halos that additionally host ionizing galactic sources. Thus, an increasing abundance of galaxies is compensated for by a corresponding increase in the absorber population, which moderates the instability in the ionizing background. However, by z~5-6, gas outside of halos dominates the absorption, the coupling between sources and absorbers is lost, and the ionizing background evolves rapidly. Our halo based model reproduces observations of the ionizing background, its flatness and sudden decline, as well as the redshift evolution of the ionizing mean free path. Our work suggests that, through much of their history, both star formation and photoelectric opacity in the universe track halo growth.

@misc{munoz2014flatness, abstract = {The ionizing background of cosmic hydrogen is an important probe of the sources and absorbers of ionizing radiation, their evolution and relationship, in the post-reionization universe. Previous studies show that the ionization rate should be very sensitive to changes in the source population: as the emissivity rises, absorbers shrink in size, increasing the ionizing mean free path and, hence, the ionizing background. By contrast, observations of the ionizing background find a very flat evolution from z~2-5, before falling precipitously at z~6. We resolve this discrepancy by pointing out that, at z~2-5, neutral absorbers are associated with the same collapsed halos that additionally host ionizing galactic sources. Thus, an increasing abundance of galaxies is compensated for by a corresponding increase in the absorber population, which moderates the instability in the ionizing background. However, by z~5-6, gas outside of halos dominates the absorption, the coupling between sources and absorbers is lost, and the ionizing background evolves rapidly. Our halo based model reproduces observations of the ionizing background, its flatness and sudden decline, as well as the redshift evolution of the ionizing mean free path. Our work suggests that, through much of their history, both star formation and photoelectric opacity in the universe track halo growth.}, added-at = {2014-10-10T10:11:53.000+0200}, author = {Muñoz, Joseph A. and Oh, S. Peng and Davies, Frederick B. and Furlanetto, Steven R.}, biburl = {https://www.bibsonomy.org/bibtex/2163f664401450a82b8a9bc1dd1e9cabe/miki}, description = {[1410.2249] The Flatness and Sudden Evolution of the Intergalactic Ionizing Background}, interhash = {5ec670aa9d1ca8fadab54e72e92f1c5d}, intrahash = {163f664401450a82b8a9bc1dd1e9cabe}, keywords = {evolution igm ionizing lls mfp uvb}, note = {cite arxiv:1410.2249Comment: 13 pages, 6 figures, submitted to MNRAS, comments welcome}, timestamp = {2014-10-10T10:11:53.000+0200}, title = {The Flatness and Sudden Evolution of the Intergalactic Ionizing Background}, url = {http://arxiv.org/abs/1410.2249}, year = 2014 }