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  1. OA@INAF
  2. PRODOTTI RICERCA INAF
  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
  4. 1.01 Articoli in rivista
Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/29187
Title: The Evolution of O I over 3.2 < z < 6.5: Reionization of the Circumgalactic Medium
Authors: Becker, George D.
Pettini, Max
Rafelski, Marc
D'ODORICO, Valentina 
BOERA, ELISA
Christensen, Lise
CUPANI, Guido 
Ellison, Sara L.
Farina, Emanuele Paolo
FUMAGALLI, MICHELE
López, Sebastian
Neeleman, Marcel
Ryan-Weber, Emma V.
Worseck, Gábor
Issue Date: 2019
Journal: THE ASTROPHYSICAL JOURNAL 
Number: 883
Issue: 2
First Page: 163
Abstract: We present a survey for metal absorption systems traced by neutral oxygen over 3.2 < z < 6.5. Our survey uses Keck/ESI and VLT/X-Shooter spectra of 199 QSOs with redshifts up to 6.6. In total, we detect 74 O I absorbers, of which 57 are separated from the background QSO by more than 5000 km s<SUP>-1</SUP>. We use a maximum likelihood approach to fit the distribution of O I λ1302 equivalent widths in bins of redshift and from this determine the evolution in number density of absorbers with W <SUB>1302</SUB> > 0.05 Å, of which there are 49 nonproximate systems in our sample. We find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. The number density over 4.9 < z < 5.7 is a factor of 1.7-4.1 lower (68% confidence) than that over 5.7 < z < 6.5, with a lower value at z < 5.7 favored with 99% confidence. This decrease suggests that the fraction of metals in a low-ionization phase is larger at z ∼ 6 than at lower redshifts. Absorption from highly ionized metals traced by C IV is also weaker in higher-redshift O I systems, supporting this picture. The evolution of O I absorbers implies that metal-enriched circumgalactic gas at z ∼ 6 is undergoing an ionization transition driven by a strengthening ultraviolet background. This in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch.
URI: http://hdl.handle.net/20.500.12386/29187
URL: https://iopscience.iop.org/article/10.3847/1538-4357/ab3eb5
ISSN: 0004-637X
DOI: 10.3847/1538-4357/ab3eb5
Bibcode ADS: 2019ApJ...883..163B
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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