Speaker
Mr
Raghunath Raghunath Ghara
(NCRA-TIFR)
Description
Observations of redshifted 21 cm radiation from the epoch of
reionization promises to provide information on the physical processes
during that epoch. Many low frequency interferometers are trying to
provide statistical measurements of this signal, such as its power
spectrum. Beside observations numerical simulations are essential to
derive tight constraints on different aspects of reionization like the
nature of first sources, relative level of emission from UV and X-ray
sources etc. We present a formalism for generating the $\delta T_b$
distribution using dark matter simulations and an one-dimensional
radiative transfer code. Our analysis is able to account for the spin
temperature $T_{\rm S}$ fluctuations arising from inhomogeneous X-ray
heating and $Ly{\alpha}$ coupling during cosmic dawn. The $\delta T_b$
power spectrum amplitude at large scales ($k \sim 0.1$ Mpc$^{-1}$) is
maximum when $\sim 10\%$ of the gas (by volume) is heated above the
CMB temperature. The power spectrum shows a “bump”-like feature during
cosmic dawn and its location measures the typical sizes of heated
regions. Also, one need to consider the effect of peculiar velocities
of gas (redshift space distortion) while generating $\delta T_b$
distribution. We find that the effect of peculiar velocities on the
power spectrum is negligible at large scales for most part of the
reionization history. During early stages (when the volume averaged
ionization fraction $\le 0.2$) this is because the signal is
dominated by fluctuations in $T_{\rm S}$. For reionization models that
are solely driven by stars within high mass ($\gt 10^9 M_{\odot}$)
haloes, the peculiar velocity effects are prominent only at smaller
scales ($k \gt 0.4$ Mpc$^{-1}$) where patchiness in the neutral
hydrogen density dominates the signal. The conclusions are unaffected
by changes in the amplitude or steepness in the X-ray spectra of the
sources. We also study the effect of the evolution of the signal along
the line-of-sight.
Author
Mr
Raghunath Raghunath Ghara
(NCRA-TIFR)
Co-authors
Dr
Kanan Kanan K. Datta
(Presidency University)
Dr
Tirthankar Tirthankar Roy Choudhury
(NCRA-TIFR)
