Journal Article

A first direct measurement of the intergalactic medium temperature around a quasar at <i>z</i>= 6

James S. Bolton, George D. Becker, J. Stuart B. Wyithe, Martin G. Haehnelt and Wallace L. W. Sargent

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 1, pages 612-625
Published in print July 2010 | ISSN: 0035-8711
Published online July 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16701.x
A first direct measurement of the intergalactic medium temperature around a quasar at z= 6

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The thermal state of the intergalactic medium (IGM) provides an indirect probe of both the H i and He ii reionization epochs. Current constraints on the IGM temperature from the Lyα forest are restricted to the redshift range 2 ≤z≤ 4.5, limiting the ability to probe the thermal memory of H i reionization towards higher redshift. In this work, we present the first direct measurement of the IGM temperature around a z= 6 quasar by analyzing the Doppler widths of Lyα absorption lines in the proximity zone of SDSS J0818+1722. We use a high-resolution (R= 40 000) Keck/HIRES spectrum in combination with detailed numerical modelling to obtain the temperature at mean density, T0= 23 600 ±50006900 K (±92009300 K) at 68 (95) per cent confidence assuming a prior probability following H i and He ii reionization. This enables us to place an upper limit on the redshift of H i reionization, zH, within 33 comoving Mpc of SDSS J0818+1722. If the quasar reionizes the He ii in its vicinity, then in the limit of instantaneous reionization we infer zH < 9.0(11.0) at 68 (95) per cent confidence assuming photoheating is the dominant heat source and that H i reionization is driven by ionizing sources with soft spectra, typical of Population II stars. If the H i and He ii in the IGM around SDSS J0818+1722 are instead reionized simultaneously by a population of massive metal-free stars, characterized by very hard ionizing spectra, we obtain a tighter upper limit of zH < 8.4(9.4). Initiating reionization at higher redshifts produces temperatures which are too low with respect to our constraint unless the H i ionizing sources or the quasar itself has spectra significantly harder than typically assumed.

Keywords: methods: numerical; intergalactic medium; quasars: absorption lines

Journal Article.  10150 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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