Shintaro Yoshiura

Studying 21cm power spectrum with one-point statistics

The redshifted 21cm line signal from neutral hydrogens is a promising tool to probe the cosmic dawn and the epoch of reionization (EoR). Ongoing and future low-frequency radio experiments are expected to detect its fluctuations, especially through the power spectrum. In this paper, we give a physical interpretation of the time evolution of the power spectrum of the 21cm brightness temperature fluctuations, which can be decomposed into dark matter density, spin temperature and neutral fraction of hydrogen fluctuations. From the one-point statistics of the fluctuations, such as variance and skewness, we find that the peaks and dips in the time evolution are deeply related to X-ray heating of the intergalactic gas, which controls the spin temperature. We suggest the skewness of the brightness temperature distribution is a key observable to identify the onset of X-ray heating.

21 cm line bispectrum as a method to probe cosmic dawn and epoch of reionization

Redshifted 21cm signal is a promising tool to investigate the state of intergalactic medium (IGM) in the Cosmic Dawn (CD) and Epoch of Reionization(EoR). In our previous work (Shimabukuro et al 2015), we studied the variance and skewness to give a clear interpretation of 21cm power spectrum and found that skewness is a good indicator of the epoch when X-ray heating becomes effective. Thus, the non-Gaussian feature of the spatial distribution of the 21cm signal is expected to be useful to investigate the astrophysical effects in the CD and EoR. In this paper, in order to investigate such a non-Gaussian feature in more detail, we focus on the bispectrum of the 21cm signal. It is expected that the 21cm brightness temperature bispectrum is produced by non-gaussianity due to the various astrophysical effects such as Wouthysen-Field (WF) effect, X-ray heating and reionization. We study the various properties of 21cm bispectrum such as scale dependence, shape dependence and redshift evolution. And also we study the contribution from each component of 21cm bispectrum. We find that the contribution from each component has characteristic scale-dependent feature, and it is expected that we could obtain more detailed information on the IGM in the CD and EoR by using the 21cm bispectrum in the future experiments, combined with the power spectrum and skewness.

Constraining the Contribution of Galaxies and Active Galactic Nuclei to Cosmic Reionization

Understanding the detailed process of cosmic reionization is one of the remaining problems in astrophysics and cosmology. Here we construct a model of cosmic reionization that includes contribution from high-

Sensitivity for 21 cm bispectrum from Epoch of Reionization

z

Constraining the epoch-of-reionization model parameters with the 21-cm bispectrum

galaxies and active galactic nuclei (AGNs), and calculate the reionization and thermal histories with the model. To keep the model to be general and realistic, we vary the escape fraction of ionizing photons,

Detectability of the 21-cm signal during the epoch of reionization with 21-cm Lyman α emitter cross-correlation – I

f_{\rm esc}

Expected constraints on models of the epoch of reionization with the variance and skewness in redshifted 21 cm-line fluctuations

, and the faint-end slope of the AGN luminosity function at high redshifts,

The variance of dispersion measure of high-redshift transient objects as a probe of ionized bubble size during reionization

\alpha_{\rm hz}

Studying topological structure of 21-cm line fluctuations with 3D Minkowski functionals before reionization

, within the constraints from the observed cosmic star formation history and the observed bright-end UV luminosity functions at

Japanese Cosmic Dawn/Epoch of Reionization Science with the Square Kilometre Array

z \leq 6