132 research outputs found
An Analytic Formulation of 21-cm Signal from Early Phase of Epoch of Reionization
We present an analytic formulation to model the fluctuating component of the
HI signal from the epoch of reionization during the phase of partial heating.
During this phase, we assume self-ionized regions, whose size distribution can
be computed using excursion set formalism, to be surrounded by heated regions.
We model the evolution of heating profile around these regions (near zone) and
their merger into the time-dependent background (far zone). We develop a
formalism to compute the two-point correlation function for this topology,
taking into account the heating auto-correlation and heating-ionization
cross-correlation. We model the ionization and X-ray heating using four
parameters: efficiency of ionization, , number of X-ray photons per
stellar baryon, , the spectral index of X-ray photons, ,
and the minimum frequency of X-ray photons, . We compute the HI
signal in the redshift range for the CDM model for a set
of these parameters. We show that the HI signal for a range of scales
show a peak strength
during the partially heated era. The redshift at which the signal makes a
transition to uniformly heated universe depends on modelling parameters, e.g.
if is changed from to , this
transition moves from to . This result, along with
the dependence of the HI signal on modelling parameters, is in reasonable
agreement with existing results from N-body simulations.Comment: 35 pages, 17 figures, published in Ap
Analytic Formulation of 21 cm Signal from Cosmic Dawn: Ly Fluctuations
We present an analytic formalism to compute the fluctuating component of the
\ion{H}{1} signal and extend it to take into account the effects of partial
Lyman- coupling during the era of cosmic dawn. We use excursion set
formalism to calculate the size distribution of randomly distributed
self-ionized regions. These ionization bubbles are surrounded by partially
heated and Lyman- coupled regions, which create spin temperature
fluctuations. We use the ratio of number of Lyman- to ionizing photon
() and number of X-ray photons emitted per stellar baryons () as modeling parameters. Using our formalism, we compute the global
\ion{H}{1} signal, its auto-correlation and power spectrum in the redshift
range for the CDM model. We check the validity of
this formalism for various limits and simplified cases. Our results agree
reasonably well with existing results from N-body simulations, in spite of
following a different approach and requiring orders of magnitude less
computation power and time. We further apply our formalism to study the
fluctuating component corresponding to the recent EDGES observation that shows
an unexpectedly deep absorption trough in global \ion{H}{1} signal in the
redshift range . We show that, generically, the EDGES observation
predicts larger signal in this redshift range but smaller signal at higher
redshifts. We also explore the possibility of negative real-space
auto-correlation of spin temperature and show it can be achieved for partial
Lyman- coupling in many cases corresponding to simplified models and
complete model without density perturbations.Comment: Comments and suggestions are welcome. arXiv admin note: text overlap
with arXiv:1711.0382
Primordial Magnetic Fields in the Post-recombination Era and Early Reionization
We explore the ways in which primordial magnetic fields influence the thermal
and ionization history of the post-recombination universe. After recombination
the universe becomes mostly neutral resulting also in a sharp drop in the
radiative viscosity. Primordial magnetic fields can then dissipate their energy
into the intergalactic medium (IGM) via ambipolar diffusion and, for small
enough scales, by generating decaying MHD turbulence. These processes can
significantly modify the thermal and ionization history of the
post-recombination universe. We show that the dissipation effects of magnetic
fields which redshifts to a present value Gauss
smoothed on the magnetic Jeans scale and below, can give rise to Thomson
scattering optical depths \tau \ga 0.1, although not in the range of
redshifts needed to explain the recent WMAP polarization observations. We also
study the possibility that primordial fields could induce the formation of
subgalactic structures for z \ga 15. We show that early structure formation
induced by nano-Gauss magnetic fields is potentially capable of producing the
early re-ionization implied by the WMAP data. Future CMB observations will be
very useful to probe the modified ionization histories produced by primordial
magnetic field evolution and constrain their strength.Comment: 19 pages, 7 figures, Minor changes to match version accepted in MNRA
Galactic dust polarized emission at high latitudes and CMB polarization
We estimate the dust polarized emission in our galaxy at high galactic
latitudes, which is the dominant foreground for measuring CMB polarization
using the high frequency instrument (HFI) aboard Planck surveyor. We compare it
with the level of CMB polarization and conclude that, for angular scales , the scalar-induced CMB polarization and temperature-polarization
cross-correlation are much larger than the foreground level at . The tensor-induced signals seem to be at best comparable to the
foreground level.}Comment: Latex document, 4 pages, 2 figures, to appear in "Fundamental
parameters in Cosmology", Rencontres de Moriond, 199
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