The Evolution of O i over 3.2 < z < 6.5: Reionization of the Circumgalactic Medium
| Autor: | Sara L. Ellison, George D. Becker, Elisa Boera, Sebastian Lopez, Marcel Neeleman, Lise Christensen, Marc Rafelski, Gabor Worseck, Valentina D'Odorico, Max Pettini, Emma V. Ryan-Weber, Guido Cupani, Emanuele Paolo Farina, Michele Fumagalli |
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| Přispěvatelé: | ITA, USA, GBR, DEU, AUS, CAN, CHL, DNK, Becker, G, Pettini, M, Rafelski, M, D'Odorico, V, Boera, E, Christensen, L, Cupani, G, Ellison, S, Farina, E, Fumagalli, M, Lopez, S, Neeleman, M, Ryan-Weber, E, Worseck, G |
| Rok vydání: | 2019 |
| Předmět: |
Physics
Metallicity IGM Number density 010504 meteorology & atmospheric sciences Institut für Physik und Astronomie chemistry.chemical_element Astronomy and Astrophysics Astrophysics medicine.disease_cause 01 natural sciences Oxygen Astrophysics - Astrophysics of Galaxies Redshift chemistry Space and Planetary Science Ionization Phase (matter) 0103 physical sciences medicine ddc:530 Absorption (chemistry) 010303 astronomy & astrophysics Reionization Ultraviolet 0105 earth and related environmental sciences |
| Zdroj: | The Astrophysical Journal Astrophysical journal, 2019, Vol.883(2), pp.163 [Peer Reviewed Journal] |
| ISSN: | 1538-4357 0004-637X 0022-3700 1538-3881 1538-3873 |
| DOI: | 10.3847/1538-4357/ab3eb5 |
| Popis: | 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. Comment: 43 pages, 85 figures, submitted to ApJ |
| Databáze: | OpenAIRE |
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