We derive constraints on the thermal and ionization states of the intergalactic medium (IGM) at redshift ≈ 9.1 using new upper limits on the 21-cm power spectrum measured by the LOFAR radio telescope and a prior on the ionized fraction at that redshift estimated from recent cosmic microwave background (CMB) observations. We have used results from the reionization simulation code GRIZZLY and a Bayesian inference framework to constrain the parameters which describe the physical state of the IGM. We find that, if the gas heating remains negligible, an IGM with ionized fraction ≿0.13 and a distribution of the ionized regions with a characteristic size ≿ 8 h−1 comoving megaparsec (Mpc) and a full width at half-maximum (FWHM) ≿16 h−1 Mpc is ruled out. For an IGM with a uniform spin temperature TS ≿ 3 K, no constraints on the ionized component can be computed. If the large-scale fluctuations of the signal are driven by spin temperature fluctuations, an IGM with a volume fraction ≾0.34 of heated regions with a temperature larger than CMB, average gas temperature 7–160 K, and a distribution of the heated regions with characteristic size 3.5–70 h−1 Mpc and FWHM of ≾110 h−1 Mpc is ruled out. These constraints are within the 95 per cent credible intervals. With more stringent future upper limits from LOFAR at multiple redshifts, the constraints will become tighter and will exclude an increasingly large region of the parameter space.
Bibliographical noteFunding Information:
The authors would like to thank Jens Jasche and Daniel J. Mortlock for useful discussions, and an anonymous referee for insightful comments. We acknowledge that the results in this paper have been achieved using the PRACE Research Infrastructure resources Curie based at the Très Grand Centre de Calcul (TGCC) operated by CEA near Paris, France and Marenostrum based in the Barcelona Supercomputing Center, Spain. Time on these resources was awarded by PRACE under PRACE4LOFAR grants 2012061089 and 2014102339 as well as under the Multiscale Reionization grants 2014102281 and 2015122822. We have used resources provided by the Swedish National Infrastructure for Computing (SNIC) (proposal number SNIC 2018/3-40) at PDC, Royal Institute of Technology, Stockholm. GM, RG, and SKG are thankful for support by Swedish Research Council grant 2016-03581. RG and SZ furthermore acknowledge support by the Israel Science Foundation (grant no. 255/18). VJ acknowledges support by the Croatian Science Foundation for a project IP-2018-01-2889 (LowFreqCRO). FGM and LVEK acknowledge support from a SKA-NL roadmap grant from the Dutch Ministry of OCW. EC acknowledges support from the Royal Society via the Dorothy Hodgkin Fellowship.
© 2020 The Author(s) Published by Oxford University Press on behalf of The Royal Astronomical Society.
- Cosmology: theory
- Dark ages, reionization, first stars
- Galaxies: formation
- Intergalactic medium
- Radiative transfer
- X-rays: galaxies