Probing the ionization state of the universe at z > 6

Richard L. White, Robert H. Becker, Xiaohui Fan, Michael A. Strauss

Research output: Contribution to journalArticle

238 Citations (Scopus)

Abstract

We present high signal-to-noise ratio Keck ESI spectra of the two quasars known to have Gunn-Peterson absorption troughs, SDSS J1030+0524 (z = 6.28) and SDSS J1148+5251 (z = 6.37). The Lyα and Lyβ troughs for SDSS J1030+0524 are very black and show no evidence of any emission over a redshift interval of ∼0.2, starting at z = 6. On the other hand, SDSS J1148+5251 shows a number of emission peaks in the Lyβ Gunn-Peterson trough along with a single weak peak in the Lyα trough. The Lyα emission has corresponding Lyβ emission, suggesting that it is indeed a region of lower optical depth in the intergalactic medium at z = 6.08. The stronger Lyβ peaks in the spectrum of SDSS J1148+5251 could also conceivably be the result of "leaks" in the intergalactic medium (IGM), but we suggest instead that they are Lyα emission from an intervening galaxy at z = 4.9. This hypothesis gains credence from a strong complex of C IV absorption at the same redshift and from the detection of continuum emission in the Lyα trough at the expected brightness. If this proposal is correct, the quasar light has probably been magnified through gravitational lensing by the intervening galaxy. The Strömgren sphere observed in the absorption spectrum of SDSS J1148+5251 is significantly smaller than expected on the basis of its brightness, which is consistent with the hypothesis that the quasar is lensed. If our argument for lensing is correct, the optical depths derived from the troughs of SDSS J1148+5251 are only lower limits [albeit still quite strong, with τ(Lyα) > 16 inferred from the Lyβ trough]. The Lyβ absorption trough of SDSS J1030+0524 gives the single best measurement of the IGM transmission at z > 6, with an inferred optical depth of τ(Lyα) > 22.

Original languageEnglish (US)
Pages (from-to)1-14
Number of pages14
JournalAstronomical Journal
Volume126
Issue number1 1771
DOIs
StatePublished - Jul 2003

Fingerprint

troughs
trough
ionization
universe
intergalactic media
optical thickness
quasars
optical depth
brightness
galaxies
absorption spectrum
signal-to-noise ratio
proposals
signal to noise ratios
continuums
intervals
absorption spectra

Keywords

  • Cosmology: observations
  • Early universe
  • Intergalactic medium
  • Quasars: general

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

White, R. L., Becker, R. H., Fan, X., & Strauss, M. A. (2003). Probing the ionization state of the universe at z > 6. Astronomical Journal, 126(1 1771), 1-14. https://doi.org/10.1086/375547

Probing the ionization state of the universe at z > 6. / White, Richard L.; Becker, Robert H.; Fan, Xiaohui; Strauss, Michael A.

In: Astronomical Journal, Vol. 126, No. 1 1771, 07.2003, p. 1-14.

Research output: Contribution to journalArticle

White, RL, Becker, RH, Fan, X & Strauss, MA 2003, 'Probing the ionization state of the universe at z > 6', Astronomical Journal, vol. 126, no. 1 1771, pp. 1-14. https://doi.org/10.1086/375547
White, Richard L. ; Becker, Robert H. ; Fan, Xiaohui ; Strauss, Michael A. / Probing the ionization state of the universe at z > 6. In: Astronomical Journal. 2003 ; Vol. 126, No. 1 1771. pp. 1-14.
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AB - We present high signal-to-noise ratio Keck ESI spectra of the two quasars known to have Gunn-Peterson absorption troughs, SDSS J1030+0524 (z = 6.28) and SDSS J1148+5251 (z = 6.37). The Lyα and Lyβ troughs for SDSS J1030+0524 are very black and show no evidence of any emission over a redshift interval of ∼0.2, starting at z = 6. On the other hand, SDSS J1148+5251 shows a number of emission peaks in the Lyβ Gunn-Peterson trough along with a single weak peak in the Lyα trough. The Lyα emission has corresponding Lyβ emission, suggesting that it is indeed a region of lower optical depth in the intergalactic medium at z = 6.08. The stronger Lyβ peaks in the spectrum of SDSS J1148+5251 could also conceivably be the result of "leaks" in the intergalactic medium (IGM), but we suggest instead that they are Lyα emission from an intervening galaxy at z = 4.9. This hypothesis gains credence from a strong complex of C IV absorption at the same redshift and from the detection of continuum emission in the Lyα trough at the expected brightness. If this proposal is correct, the quasar light has probably been magnified through gravitational lensing by the intervening galaxy. The Strömgren sphere observed in the absorption spectrum of SDSS J1148+5251 is significantly smaller than expected on the basis of its brightness, which is consistent with the hypothesis that the quasar is lensed. If our argument for lensing is correct, the optical depths derived from the troughs of SDSS J1148+5251 are only lower limits [albeit still quite strong, with τ(Lyα) > 16 inferred from the Lyβ trough]. The Lyβ absorption trough of SDSS J1030+0524 gives the single best measurement of the IGM transmission at z > 6, with an inferred optical depth of τ(Lyα) > 22.

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KW - Quasars: general

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