Probing the intergalactic medium during the Epoch of Reionization using 21 cm signal power spectra

¹ Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
e-mail: ghara.raghunath@gmail.com
² ARCO (Astrophysics Research Center), Department of Natural Sciences, The Open University of Israel, 1 University Road, PO Box 808, Ra’anana 4353701, Israel
e-mail: abinashkumarshaw@gmail.com
³ Haverford College, 370 Lancaster Ave, Haverford, PA 19041, USA
⁴ Center for Particle Cosmology, Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
⁵ Department of Computer Science, University of Nevada, Las Vegas, Nevada 89154, USA
⁶ Department of Natural Sciences, The Open University of Israel, 1 University Road, Ra’anana 4353701, Israel
⁷ Max-Planck Institute for Astrophysics, Karl-Schwarzschild-Straße 1, 85748 Garching, Germany
⁸ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden
⁹ Center for Fundamental Physics of the Universe, Department of Physics, Brown University, Providence, 02914 RI, USA
¹⁰ Nordita, KTH Royal Institute of Technology and Stockholm University, Hannes Alfvéns väg 12, 106 91 Stockholm, Sweden
¹¹ Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Pevensey II Building, Brighton BN1 9QH, UK
¹² School of Physics and Electronic Science, Guizhou Normal University, Guiyang 550001, PR China
¹³ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, 75014 Paris, France

Received: 31 January 2024
Accepted: 16 April 2024

Abstract

Context. The redshifted 21 cm signal from the Epoch of Reionization (EoR) directly probes the ionization and thermal states of the intergalactic medium during that period. In particular, the distribution of the ionized regions around the radiating sources during EoR introduces scale-dependent features in the spherically averaged EoR 21 cm signal power spectrum.

Aims. The goal is to study these scale-dependent features at different stages of reionization using numerical simulations and to build a source model-independent framework to probe the properties of the intergalactic medium using EoR 21 cm signal power spectrum measurements.

Methods. Under the assumption of high spin temperature, we modeled the redshift evolution of the ratio of the EoR 21 cm brightness temperature power spectrum to the corresponding density power spectrum using an ansatz consisting of a set of redshift and scale-independent parameters. This set of eight parameters probes the redshift evolution of the average ionization fraction and the quantities related to the morphology of the ionized regions.

Results. We tested this ansatz on different reionization scenarios generated using different simulation algorithms and found that it is able to recover the redshift evolution of the average neutral fraction within an absolute deviation ≲0.1.

Conclusions. Our framework allows us to interpret 21 cm signal power spectra in terms of parameters related to the state of the IGM. This source model-independent framework is able to efficiently constrain reionization scenarios using multi-redshift power spectrum measurements with ongoing and future radio telescopes such as LOFAR, MWA, HERA, and SKA. This will add independent information regarding the EoR IGM properties.