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The soft, fluctuating UVB at z similar to 6 as traced by C IV, Si IV, and C II
New Mexico State Univ, MSC 4500, Las Cruces, NM 88003 USA.;Univ Copenhagen, Niels Bohr Inst, Dark Cosmol Ctr, Juliane Maries Vej 30, DK-2100 Copenhagen O, Denmark..
Univ Colorado, Dept Astrophys & Planetary Sci, CASA, 389 UCB, Boulder, CO 80309 USA..
Univ Western Cape, ZA-7535 Cape Town, South Africa.;South African Astron Observ, ZA-7525 Cape Town, South Africa.;African Inst Math Sci, ZA-7545 Cape Town, South Africa..
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
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2016 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 459, no 3, 2299-2310 p.Article in journal (Refereed) PublishedText
Abstract [en]

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 hardUVBwith 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 similar to 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 CII, Si IV, 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 Si IV/CIV and CII/CIV distributions. The QSOs-only UVB overpredicts both CIV/CII and CIV/Si IV, indicating that it is too hard. The Haardt & Madau (2012) UVB underpredicts CIV/Si 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.

Place, publisher, year, edition, pages
2016. Vol. 459, no 3, 2299-2310 p.
Keyword [en]
galaxies: evolution, galaxies: formation, galaxies: high-redshift, intergalactic medium, quasars: absorption lines, cosmology: theory
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:uu:diva-301036DOI: 10.1093/mnras/stw805ISI: 000379840900003OAI: oai:DiVA.org:uu-301036DiVA: diva2:953468
Swedish Research CouncilWenner-Gren FoundationsSwedish National Space Board
Available from: 2016-08-17 Created: 2016-08-17 Last updated: 2016-08-17Bibliographically approved

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Zackrisson, Erik
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