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The Evolution of O I over 3.2 < z < 6.5: Reionization of the Circumgalactic Medium | | George D. Becker
; Max Pettini
; Marc Rafelski
; Valentina D'Odorico
; Elisa Boera
; Lise Christensen
; Guido Cupani
; Sara L. Ellison
; Emanuele P. Farina
; Michele Fumagalli
; Sebastian López
; Marcel Neeleman
; Emma V. Ryan-Weber
; Gábor Worseck
; | | Date: |
5 Jul 2019 | | 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. We use a maximum
likelihood approach to fit the distribution of O I $lambda$1302 equivalent
widths in bins of redshift, and from this determine the evolution in number
density of absorbers with $W_{1302} > 0.05$ angstroms. 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 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 $z sim 6$ 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 $z sim 6$ 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. | | Source: | arXiv, 1907.2983 | | Services: | Forum | Review | PDF | Favorites | |
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