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A consistent and robust measurement of the thermal state of the IGM at 2 ≤ z ≤ 4 from a large sample of Ly α forest spectra: Evidence for late and rapid He ii reionization

Accepted version
Peer-reviewed

Type

Article

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Authors

Srianand, R 
Haehnelt, MG 
Choudhury, TR 

Abstract

We characterise the thermal state of the intergalactic medium (IGM) in ten redshift bins in the redshift range 2≤z≤4 with a sample of 103 high resolution, high S/N Lyα forest spectra using four different flux distribution statistics. Our measurements are calibrated with mock spectra from a large suite of hydrodynamical simulations post-processed with our thermal IGM evolution code CITE, finely sampling amplitude and slope of the expected temperature-density relation. The thermal parameters inferred from our measurements of the flux power spectrum, Doppler parameter distribution, as well as wavelet and curvature statistics agree well within their respective errors and all clearly show the peak in temperature and minimum in slope of the temperature density relation expected from HeII reionization. Combining our measurements from the different flux statistics gives T0=(14750±1322)K for the peak temperature at mean density and a corresponding minimum slope γ=1.225±0.120. The peak in the temperature evolution occurs at z≈3, in agreement with previous measurements that had suggested the presence of such a peak, albeit with a large scatter. Using CITE, we also calculate the thermal state of the IGM predicted by five widely used (spatially homogeneous) UV-background models. The rather rapid thermal evolution inferred by our measurements is well reproduced by two of the models, if we assume (physically well motivated) non-equilibrium evolution with photo-heating rates that are reduced by a moderate factor of ∼0.7−0.8. The other three models predict HeII reionization to be more extended with a somewhat earlier as well as higher temperature peak than our measurements suggest.

Description

Keywords

methods: numerical, intergalactic medium, quasars: absorption lines, large-scale structure of Universe

Journal Title

Monthly Notices of the Royal Astronomical Society

Conference Name

Journal ISSN

0035-8711
1365-2966

Volume Title

506

Publisher

Oxford University Press (OUP)

Rights

All rights reserved
Sponsorship
European Research Council (320596)
Science and Technology Facilities Council (ST/S000623/1)
Science and Technology Facilities Council (ST/H008861/1)
Science and Technology Facilities Council (ST/K00333X/1)
STFC (ST/M007073/1)
Science and Technology Facilities Council (ST/P000673/1)
STFC (ST/T00049X/1)