Exploring the thermal state of the low-density intergalactic medium at $z$ = 3 with an ultrahigh signal-to-noise QSO spectrum
Monthly Notices of the Royal Astronomical Society
Oxford University Press
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Rorai, A., Becker, G., Haehnelt, M., Carswell, R., Bolton, J., Cristiani, S., D'Odorico, V., et al. (2017). Exploring the thermal state of the low-density intergalactic medium at $z$ = 3 with an ultrahigh signal-to-noise QSO spectrum. Monthly Notices of the Royal Astronomical Society, 466 (3), 2690-2709. https://doi.org/10.1093/mnras/stw2917
At low densities, the standard ionization history of the intergalactic medium (IGM) predicts a decreasing temperature of the IGM with decreasing density once hydrogen (and helium) reionization is complete. Heating the high-redshift, low-density IGM above the temperature expected from photoheating is difficult, and previous claims of high/rising temperatures in lowdensity regions of the Universe based on the probability density function (PDF) of the opacity in Ly $\alpha$ forest data at 2 < $z$ < 4 have been met with considerable scepticism, particularly since they appear to be in tension with other constraints on the temperature–density relation (TDR). We utilize here an ultrahigh signal-to-noise spectrum of the Quasi-stellar object HE0940-1050 and a novel technique to study the low opacity part of the PDF. We show that there is indeed evidence (at 90 per cent confidence level) that a significant volume fraction of the underdense regions at $z$ ~ 3 has temperatures as high or higher than those at densities comparable to the mean and above. We further demonstrate that this conclusion is nevertheless consistent with measurements of a slope of the TDR in overdense regions that imply a decreasing temperature with decreasing density, as expected if photoheating of ionized hydrogen is the dominant heating process. We briefly discuss implications of our findings for the need to invoke either spatial temperature fluctuations, as expected during helium reionization, or additional processes that heat a significant volume fraction of the low-density IGM.
intergalactic medium, quasars: absorption lines
We thank Volker Springel for making GADGET-3 available. This work made use of the Distributed Research utilising Advanced Computing High Performance Computing System (HPCS) and the COSMOlogy Supercomputer shared memory service at the University of Cambridge. These are operated on behalf of the Science and Technology Facilities Council (STFC) DiRAC HPC facility. This equipment is funded by Department for Business, Innovation and Skills National E-infrastructure capital grant ST/J005673/1 and STFC grants ST/H008586/1, ST/K00333X/1. We acknowledge Partnership for Advanced Computing in Europe for awarding us access to the Curie supercomputer, based in France at the Tres Grand Centre de Calcul (TGCC), through the 8th regular call. Support by the European Research Council Advanced Grant 320596 ‘The Emergence of structure during the epoch of reionization’ is gratefully acknowledged. ET is supported by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. AR thanks Joseph F. Hennawi and the ENIGMA group at the Max Planck institute for Astronomy for helpful comments and discussion. MV and TSK acknowledges funding support to the European Research Council Starting Grant ‘Cosmology with the IGM’ through grant GA-257670. PB is supported by the Istituto Nazionale di Astrofisica PRIN-2014 grant ”Windy black holes combing galaxy evolution”.
European Research Council (320596)
SCIENCE & TECHNOLOGY FACILITIES COUNCIL (ST/N000927/1)
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External DOI: https://doi.org/10.1093/mnras/stw2917
This record's URL: https://www.repository.cam.ac.uk/handle/1810/262333