Was the Universe neutral beyond redshift six?

S. Gallerani, A. Ferrara, Xiaohui Fan, T. Roy Choudhury, R. Salvaterra

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

We provide measurements of the neutral hydrogen fraction xHI at z ≈ 6, by comparing semi-analytical models of the Lyα forest with observations of high-z quasars and gamma-ray bursts absorption spectra. We analyze the transmitted flux in a sample of 17 QSOs spectra at 5.74 ≤ z em ≤ 6.42 studying separately the narrow transmission windows (peaks) and the wide dark portions (gaps) in the observed absorption spectra. By comparing the statistics of these spectral features with our models, we conclude that xHI evolves smoothly from 10-4.4 at z = 5.3 to 10-4.2 at z = 5.6, with a robust upper limit xHI < 0.36 at z = 6.3. We show the results of the first-ever detected transverse proximity effect in the HI Lyα forest, produced by the HII region of the faint quasar RD J1148+5253 at z = 5.70 intervening along the LOS of SDSS J1148+5251 at z = 6.42. Moreover, we propose a novel method to study cosmic reionization using absorption line spectra of high-redshift GRBs afterglows. We show that the time evolution and the statistics of gaps in the observed spectra represent exquisite tools to discriminate among different reionization models. By applying our methods to GRB 050904 detected at z = 6.29, we show that the observation of this burst provides strong indications of a highly ionized intergalactic medium at z ∼ 6, with an estimated mean neutral hydrogen fraction xHI = 6.4 ± 0.3 × 10-5 along that line of sight.

Original languageEnglish (US)
Pages (from-to)977-983
Number of pages7
JournalIl Nuovo Cimento B
Volume122
Issue number9-11
DOIs
StatePublished - Sep 2007

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quasars
universe
absorption spectra
statistics
intergalactic media
hydrogen
afterglows
gamma ray bursts
line of sight
line spectra
bursts
indication

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Gallerani, S., Ferrara, A., Fan, X., Choudhury, T. R., & Salvaterra, R. (2007). Was the Universe neutral beyond redshift six? Il Nuovo Cimento B, 122(9-11), 977-983. https://doi.org/10.1393/ncb/i2008-10432-y

Was the Universe neutral beyond redshift six? / Gallerani, S.; Ferrara, A.; Fan, Xiaohui; Choudhury, T. Roy; Salvaterra, R.

In: Il Nuovo Cimento B, Vol. 122, No. 9-11, 09.2007, p. 977-983.

Research output: Contribution to journalArticle

Gallerani, S, Ferrara, A, Fan, X, Choudhury, TR & Salvaterra, R 2007, 'Was the Universe neutral beyond redshift six?', Il Nuovo Cimento B, vol. 122, no. 9-11, pp. 977-983. https://doi.org/10.1393/ncb/i2008-10432-y
Gallerani S, Ferrara A, Fan X, Choudhury TR, Salvaterra R. Was the Universe neutral beyond redshift six? Il Nuovo Cimento B. 2007 Sep;122(9-11):977-983. https://doi.org/10.1393/ncb/i2008-10432-y
Gallerani, S. ; Ferrara, A. ; Fan, Xiaohui ; Choudhury, T. Roy ; Salvaterra, R. / Was the Universe neutral beyond redshift six?. In: Il Nuovo Cimento B. 2007 ; Vol. 122, No. 9-11. pp. 977-983.
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