The effect of peculiar velocities on the epoch of reionization 21-cm signal

Abstract

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 H I 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 forx H i ≤ 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 ∆∆ (k), P xx (k) and P ∆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 varyingx H i entirely in terms of a just two quantities, namelyx H i and the ratio P xx /P ∆∆ . The nature of P ∆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.

The visibility-based tapered gridded estimator (TGE) for the redshifted 21-cm power spectrum

“…independent of the direction of k. However, the signal is assumed to be statistically isotropic in the plane of the sky, and the binning in k ⊥ is exactly identical to the binning that we have used earlier for C ℓ . This distinction between k ⊥ and k is useful to quantify the effect of redshift space distortion (Bharadwaj, Nath and Sethi 2001;Bharadwaj & Ali 2004;Barkana & Loeb 2005;Mao 2012;Majumdar, Bharadwaj & Choudhury 2013;Jensen et al 2016) and also to distinguish the foregrounds from the HI signal (Morales & Hewitt 2004). We have used eq.…”

Effects of the sources of reionization on 21-cm redshift-space distortions

“…Mao et al (2012), Jensen et al (2013) or Majumdar, Bharadwaj & Choudhury (2013). We implement the redshift-space distortions using the same method as in Jensen et al (2013).…”

“…The estimation of each multipole moment through Equation (5) will be independent of the other, as this representation is in an orthonormal basis. Under the quasi-linear model of Mao et al (2012), only the first three even multipole moments will have nonzero values (Majumdar, Bharadwaj & Choudhury 2013;Majumdar et al 2014):…”

“…If reionization is strongly inside-out, this quantity will decrease quickly as reionization progresses, and take on a negative value (see e.g. Jensen et al 2013;Majumdar, Bharadwaj & Choudhury 2013;.…”

The rich complexity of 21-cm fluctuations produced by the first stars

“…This anisotropy adds some overall power to the 21-cm fluctuations (Bharadwaj & Ali 2004), but more importantly, it allows several power spectrum components to be separately measured, in principle allowing much more information to be extracted about the various sources of 21-cm fluctuations (Barkana & Loeb 2005a). We note that the line-ofsight anisotropy has been previously studied during reionization (Mesinger, Furlanetto & Cen 2011;Mao et al 2012;Shapiro et al 2013;Majumdar et al 2013), but we discuss it over a wide redshift range that includes various cosmic epochs. Finally, we make sure to sample a wide range of parameters.…”