Investigating X-ray sources during the epoch of reionization with the 21 cm signal

Abstract

Heating of neutral gas by energetic sources is crucial for the prediction of the 21 cm signal during the epoch of reionization (EoR). To investigate differences induced on statistics of the 21 cm signal by various source types, we use five radiative transfer simulations which have the same stellar UV emission model and varying combinations of more energetic sources, such as X-ray binaries (XRBs), accreting nuclear black holes (BHs) and hot interstellar medium emission (ISM). We find that the efficient heating from the ISM increases the average global 21 cm signal, while reducing its fluctuations and thus power spectrum. A clear impact is also observed in the bispectrum in terms of scale and timing of the transition between a positive and a negative value. The impact of XRBs is similar to that of the ISM, although it is delayed in time and reduced in intensity because of the less efficient heating. Due to the paucity of nuclear BHs, the behaviour of the 21 cm statistics in their presence is very similar to that of a case when only stars are considered, with the exception of the latest stages of reionization, when the effect of BHs is clearly visible. We find that differences between the source scenarios investigated here are larger than the instrumental noise of SKA1-low at z 7 − 8, suggesting that in the future it might be possible to constrain the spectral energy distribution of the sources contributing to the reionization process.

The Epoch of Reionization 21-cm Bispectrum: The impact of light-cone effects and detectability

“…We would like to start by pointing out that all previous studies presenting error predictions for the SABS (see e.g. Yoshiura et al 2015;Watkinson et al 2019;Ma et al 2021;Watkinson et al 2021) have assumed the errors to behave as if the observed signal was a Gaussian random field. This assumption, however, is counter-intuitive and also under-predicts the CV errors (e.g.…”

“…Both CV and system noise have previously only been considered through approximations and/or for a limited set of triangle shapes (see e.g. Yoshiura et al 2015;Watkinson et al 2019;Ma et al 2021;Watkinson et al 2021 etc. ).…”

Cosmological 21cm line observations to test scenarios of super-Eddington accretion on to black holes being seeds of high-redshifted supermassive black holes

“…Another possibility would be assuming a super-Eddington accretion rate 2 on to a light seed BH [28,[67][68][69][70][71][72][73][74][75][76][77][78]. 3 To test consistencies of the theoretical disk models for the (super-)Eddington accretions with observations, in principle we can use cosmological 21cm line emissions/absorptions which were produced in the dark ages at z ∼ O(10) − O( 102 ) (e.g., see [80][81][82][83][84] for earlier works). So far, the EDGES collaboration has reported the observational data for the absorption feature of the cosmological global 21cm line spectrum at around z ∼ 17 [85].…”