Bolton, James S. and Becker, George D. and Wyithe, J. Stuart B. and Haehnelt, Martin G. and Sargent, Wallace L. W. (2010) A first direct measurement of the intergalactic medium temperature around a quasar at z = 6. Monthly Notices of the Royal Astronomical Society, 406 (1). pp. 612-625. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20100805-090447372
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The thermal state of the intergalactic medium (IGM) provides an indirect probe of both the HI 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 HI 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, T_0 = 23 600 ± ^(5000)_(6900) K (±^(9200)_(9300) K) at 68 (95) per cent confidence assuming a prior probability 13 500K ≤ T_0 ≤ 38 500K following HI and He II reionization. This enables us to place an upper limit on the redshift of HI reionization, zH, within 33 comovingMpc of SDSS J0818+1722. If the quasar reionizes the He II in its vicinity, then in the limit of instantaneous reionization we infer z_H < 9.0(11.0) at 68 (95) per cent confidence assuming photoheating is the dominant heat source and that HI reionization is driven by ionizing sources with soft spectra, typical of Population II stars. If the HI 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 z_H < 8.4(9.4). Initiating reionization at higher redshifts produces temperatures which are too low with respect to our constraint unless the HI ionizing sources or the quasar itself has spectra significantly harder than typically assumed.
|Additional Information:||© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 March 17. Received 2010 March 17; in original form 2010 January 14. We thank Benedetta Ciardi and Peng Oh for valuable conversations during the course of this work. The hydrodynamical simulations used in this work were performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England. JSB acknowledges the support of an ARC Australian postdoctoral fellowship (DP0984947), and GDB thanks the Kavli foundation for financial support.|
|Subject Keywords:||methods: numerical; intergalactic medium; quasars: absorption lines|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||05 Aug 2010 17:49|
|Last Modified:||26 Dec 2012 12:17|
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