2016/03/22 by Kristian Finlator, K. Finlator, Benjamin D. Oppenheimer +9 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gamma-ray bursts and supernovae #Physics #QSOS #Quasar #Redshift #Reionization #Stars #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stw805
13 pages, 10 figures, re-submitted to MNRAS after incorporating referee's suggestions
arxiv created 2016/03/22 · openalex publication_date 2016/04/07 · arxiv updated 2016/04/20 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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 ∼ 6 versus predictions from a cosmological hydrodynamic simulation using three different UVBs: a soft, spatially inhomogeneous ‘galaxies+QSOs’ UVB; a homogeneous ‘galaxies+QSOs’ UVB, and a ‘QSOs-only’ model. All UVBs reproduce the observed column density distributions of |\mathrmC \small ii|, |\mathrmSi \small iv|, and |\mathrmC \small iv| 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 |\mathrmSi \small iv/\mathrmC \small iv| and |\mathrmC \small ii/\mathrmC \small iv| distributions. The QSOs-only UVB overpredicts both |\mathrmC \small iv/\mathrmC \small ii| and |\mathrmC \small iv/\mathrmSi \small iv|, indicating that it is too hard. The Haardt & Madau (2012) UVB underpredicts |\mathrmC \small iv/\mathrmSi \small iv|, 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 2 deeper in metal column density will distinguish between the soft, fluctuating and QSOs-only UVBs.