Since the RSD is a direct measure of the velocity field, it is sensitive to the potential fluctuation Φ and thus to the theory of modified gravity (e.g. The RSD is important not only for correctly understanding the distortion of the correlation function to utilize the AP effects in the BAO, but also to gain an independent cosmological information from the BAO. Although the Alcock-Paczynski (AP) test makes the BAO a more powerful tool to constrain cosmological parameters, the systematic effect due to redshift space distortion (RSD) has to be taken into account as it is degenerate with the AP effect.Īs we can observe galaxies only in redshift space, the distance to the galaxies are contaminated by the peculiar velocities of galaxies on large scales, galaxies are coherently attracted towards the overdensity regions that make the anisotropic two-dimensional correlation function squashed, while on small scales, non-linear random motion makes correlation function elongated along the LoS (e.g. ![]() ![]() Another important aspect of the BAO is the combination of parallel and perpendicular components to the line of sight (LoS Alcock & Paczynski 1979). 2007) or the non-trivial couplings among different fluctuation modes due to galaxy bias (e.g. ![]() It is well known that the oscillation peak scale is readily changed by the non-linear clustering of matter (Nishimichi et al. As the BAO is a measurement of the oscillation peak scales, an accurate prediction of the peak scales is required. 2005), significant attention has been paid to constrain the dark energy using BAO in the power spectrum and correlation function (e.g. After the first detection of BAO by the clustering of luminous red galaxies in the Sloan Digital Sky Survey (Eisenstein et al. Because the acceleration only becomes effective at the late epoch of |$z$| ≲ 1, the most promising probe of dark energy or modified gravity is the large-scale structure of the Universe.īaryon acoustic oscillation (BAO) is recognized as a useful technique that is least affected by the systematics to constrain the dark energy models (e.g. One of the most natural explanations of the accelerated expansion is the dark energy in the regime of general relativity or modified theory of gravity (e.g. The acceleration of the Universe has been one of the greatest mysteries since it was first discovered by the observations of Type Ia supernovae (Perlmutter et al. ![]() Hydrodynamics, galaxies: formation, intergalactic medium, cosmology: theory, radio lines: general 1 INTRODUCTION Finally, we compare the results obtained from our simulation and the Illustris simulation, and conclude that the detailed astrophysical effects do not affect the scale dependence of H i bias very much, which implies that the cosmological analysis using 21 cm line of H i will be robust against the uncertainties arising from small-scale astrophysical processes such as star formation and supernova feedback. Fitting to a widely applied theoretical prediction, we find that the constant bias is consistent with that measured directly from the real space power spectra, and the velocity dispersion is marginally consistent with the linear perturbation prediction. We also measure a redshift space distortion (RSD) of H i gas to explore the properties of H i clustering. The redshift evolution of H i bias is relatively slow compared to that of QSOs at similar redshift range. We measure the scale dependence and redshift dependence of 21 cm line emitted from the neutral hydrogen gas at redshift 1 3 on scales of k ≳ 1 h Mpc −1, but it is roughly constant at lower redshift |$z$| < 3.
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