%0 Generic %1 finlator2016fluctuating %A Finlator, K. %A Oppenheimer, B. D. %A Davé, R. %A Zackrisson, E. %A Thompson, R. %A Huang, S. %D 2016 %K absorber high-z metal uvb %T The Soft, Fluctuating UVB at $z\sim6$ as Traced by C IV, SiIV, and CII %U http://arxiv.org/abs/1603.06651 %X The sources that drove cosmological reionization left clues regarding their identity in the slope and inhomogeneity of the ultraviolet ionizing background (UVB): Bright quasars (QSOs) generate a hard UVB with predominantly large-scale fluctuations while Population II stars generate a softer one with smaller-scale fluctuations. Metal absorbers probe the UVB's slope because different ions are sensitive to different energies. Likewise, they probe spatial fluctuations because they originate in regions where a galaxy-driven UVB is harder and more intense. We take a first step towards studying the reionization-epoch UVB's slope and inhomogeneity by comparing observations of 12 metal absorbers at $z\sim6$ versus predictions from a cosmological hydrodynamic simulation using three different UVBs: a soft, spatially-inhomogeneous "galaxies+QSOs" UVB; a homogeneous "galaxies+QSOs" UVB (Haardt & Madau 2012); and a QSOs-only model. All UVBs reproduce the observed column density distributions of CII, SiIV, and CIV reasonably well although high-column, high-ionization absorbers are underproduced, reflecting numerical limitations. With upper limits treated as detections, only a soft, fluctuating UVB reproduces both the observed SiIV/CIV and CII/CIV distributions. The QSOs-only UVB overpredicts both CIV/CII and CIV/SiIV, indicating that it is too hard. The Haardt & Madau (2012) UVB underpredicts CIV/SiIV, suggesting that it lacks amplifications near galaxies. Hence current observations prefer a soft, fluctuating UVB as expected from a predominantly Population II background although they cannot rule out a harder one. Future observations probing a factor of two deeper in metal column density will distinguish between the soft, fluctuating and QSOs-only UVBs.

@misc{finlator2016fluctuating, abstract = {The sources that drove cosmological reionization left clues regarding their identity in the slope and inhomogeneity of the ultraviolet ionizing background (UVB): Bright quasars (QSOs) generate a hard UVB with predominantly large-scale fluctuations while Population II stars generate a softer one with smaller-scale fluctuations. Metal absorbers probe the UVB's slope because different ions are sensitive to different energies. Likewise, they probe spatial fluctuations because they originate in regions where a galaxy-driven UVB is harder and more intense. We take a first step towards studying the reionization-epoch UVB's slope and inhomogeneity by comparing observations of 12 metal absorbers at $z\sim6$ versus predictions from a cosmological hydrodynamic simulation using three different UVBs: a soft, spatially-inhomogeneous "galaxies+QSOs" UVB; a homogeneous "galaxies+QSOs" UVB (Haardt & Madau 2012); and a QSOs-only model. All UVBs reproduce the observed column density distributions of CII, SiIV, and CIV reasonably well although high-column, high-ionization absorbers are underproduced, reflecting numerical limitations. With upper limits treated as detections, only a soft, fluctuating UVB reproduces both the observed SiIV/CIV and CII/CIV distributions. The QSOs-only UVB overpredicts both CIV/CII and CIV/SiIV, indicating that it is too hard. The Haardt & Madau (2012) UVB underpredicts CIV/SiIV, suggesting that it lacks amplifications near galaxies. Hence current observations prefer a soft, fluctuating UVB as expected from a predominantly Population II background although they cannot rule out a harder one. Future observations probing a factor of two deeper in metal column density will distinguish between the soft, fluctuating and QSOs-only UVBs.}, added-at = {2016-03-23T09:55:43.000+0100}, author = {Finlator, K. and Oppenheimer, B. D. and Davé, R. and Zackrisson, E. and Thompson, R. and Huang, S.}, biburl = {https://www.bibsonomy.org/bibtex/2827ce3bedfdc18e2428055ade0474d7d/miki}, description = {[1603.06651] The Soft, Fluctuating UVB at $z\sim6$ as Traced by C IV, SiIV, and CII}, interhash = {e05bbc2931b4896acc9fc28b821c9279}, intrahash = {827ce3bedfdc18e2428055ade0474d7d}, keywords = {absorber high-z metal uvb}, note = {cite arxiv:1603.06651Comment: 13 pages, 10 figures, re-submitted to MNRAS after incorporating referee's suggestions}, timestamp = {2016-03-23T09:55:43.000+0100}, title = {The Soft, Fluctuating UVB at $z\sim6$ as Traced by C IV, SiIV, and CII}, url = {http://arxiv.org/abs/1603.06651}, year = 2016 }