The effect of peculiar velocities on the epoch of reionization (EoR)
  21-cm signal
  We have used semi-numerical simulations of reionization to study the
behaviour of the power spectrum of the EoR 21-cm signal in redshift space. We
have considered two models of reionization, one which has homogeneous
recombination (HR) and the other incorporating inhomogeneous recombination
(IR). We have estimated the observable quantities --- quadrupole and monopole
moments of HI power spectrum at redshift space from our simulated data. We find
that the magnitude and nature of the ratio between the quadrupole and monopole
moments of the power spectrum ($P^s_2 /P^s_0$) can be a possible probe for the
epoch of reionization. We observe that this ratio becomes negative at large
scales for $x_{HI} \leq 0.7$ irrespective of the reionization model, which is a
direct signature of an inside-out reionization at large scales. It is possible
to qualitatively interpret the results of the simulations in terms of the
fluctuations in the matter distribution and the fluctuations in the neutral
fraction which have power spectra and cross-correlation $P_{\Delta \Delta}(k)$,
$P_{xx}(k)$ and $P_{\Delta x}(k)$ respectively. We find that at large scales
the fluctuations in matter density and neutral fraction is exactly
anti-correlated through all stages of reionization. This provides a simple
picture where we are able to qualitatively interpret the behaviour of the
redshift space power spectra at large scales with varying $x_{HI}$ entirely in
terms of a just two quantities, namely $x_{HI}$ and the ratio $P_{xx}/P_{\Delta
\Delta}$. The nature of $P_{\Delta x}$ becomes different for HR and IR
scenarios at intermediate and small scales. We further find that it is possible
to distinguish between an inside-out and an outside-in reionization scenario
from the nature of the ratio $P^s_2 /P^s_0$ at intermediate length scales.
