New simulation of QSO X-ray heating during the Cosmic Dawn

Abstract

The upcoming radio interferometer Square Kilometre Array is expected to directly detect the redshifted 21-cm signal from the Cosmic Dawn for the first time. In this era temperature fluctuations from X-ray heating of the neutral intergalactic medium can impact this signal dramatically. Previously, in Ross et al. (2017), we presented the first large-volume, 244 h −1 Mpc=349 Mpc a side, fully numerical radiative transfer simulations of X-ray heating. This work is a follow-up where we now also consider QSO-like sources in addition to high mass X-ray binaries. Images of the two cases are clearly distinguishable at SKA1-LOW resolution and have RMS fluctuations above the expected noise. The inclusion of QSOs leads to a dramatic increase in non-Gaussianity of the signal, as measured by the skewness and kurtosis of the 21-cm signal. We conclude that this increased non-Gaussianity is a promising signature of early QSOs.

Evaluating the QSO contribution to the 21-cm signal from the Cosmic Dawn

“…Information about the spectral indices of the X-ray sources are given in Table 1, and the source details are outlined in Section 2.2. S1 and S4 have previously been presented in Paper I and S5 in Ross et al (2018). S2 and S3 were run with the new multiphase version of the code.…”

Redshift-space distortions in simulations of the 21-cm signal from the cosmic dawn

“…As we will observe the 21-cm signal in redshift-space, not realspace, it is vital that we include RSDs in our predictions. In this paper, we presented our analysis of the 21-cm signal with and without RSDs from our suite of fully numerical RT simulations presented in Ross et al (2017Ross et al ( , 2018 and Ross et al (2019). We first showed detailed statistics for our fiducial model, emboldened in Table 1, including both the isotropic and anisotropic power spectra, evolution of various wave-numbers and the the anisotropy ratio with redshift, and the one-point statistics (PDFs, RMS, skewness, and kurtosis).…”

“…The details of the source models are outlined in Section 2.2. These simulations have previously been presented in Ross et al (2017), Ross et al (2018) and Ross et al (2019).…”

“…To model the inhomogeneous Ly-α flux background we use a semi-numerical method as a post-processing step, which is outlined in Ghara et al (2016) and Ross et al (2018). This method assumes a spherical profile (showed to be a good approximation even in the presence of density fluctuations by Vonlanthen et al (2011) and drops off as 1/r 2 (Semelin et al 2007;Vonlanthen et al 2011;Higgins & Meiksin 2012).…”