Redshift Space Distortion of 21cm line at 1<z<5 with Cosmological
  Hydrodynamic Simulations
  We measure the scale dependence and redshift dependence of 21 cm line emitted
from the neutral hydrogen gas at redshift 1<z<5 using full cosmological
hydrodynamic simulations by taking the ratios between the power spectra of
HI-dark matter cross correlation and dark matter auto-correlation. The neutral
hydrogen distribution is computed in full cosmological hydrodynamic simulations
including star formation and supernova feedback under a uniform ultra-violet
background radiation. We find a significant scale dependence of HI bias at z>3
on scales of k>1h/Mpc, but it is roughly constant at lower redshift z<3. The
redshift evolution of HI bias is relatively slow compared to that of QSOs at
similar redshift range. We also measure a redshift space distortion (RSD) of HI
gas to explore the properties of HI clustering. 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.
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 HI bias very much, which implies that the cosmological
analysis using 21 cm line of HI will be robust against the uncertainties
arising from small-scale astrophysical processes such as star formation and
supernova feedback.
