177 research outputs found
A new parameterization of the reionisation history
Motivated by the current constraints on the epoch of reionisation from recent
cosmic microwave background observations, ionising background measurements of
star-forming galaxies, and low redshifts line-of-sight probes, we propose a new
data-motivated parameterisation of the history of the average ionisation
fraction. This parameterisation describes a flexible redshift-asymmetric
reionisation process in two regimes that is capable of fitting all the current
constraints.Comment: 5 page
SKA Deep Polarization and Cosmic Magnetism
Deep surveys with the SKA1-MID array offer for the first time the opportunity
to systematically explore the polarization properties of the microJy source
population. Our knowledge of the polarized sky approaching these levels is
still very limited. In total intensity the population will be dominated by
star-forming and normal galaxies to intermediate redshifts (), and
low-luminosity AGN to high redshift. The polarized emission from these objects
is a powerful probe of their intrinsic magnetic fields and of their magnetic
environments. For redshift of order 1 and above the broad bandwidth of the
mid-bands span the Faraday thick and thin regimes allowing study of the
intrinsic polarization properties of these objects as well as depolarization
from embedded and foreground plasmas. The deep field polarization images will
provide Rotation Measures data with very high solid angle density allowing a
sensitive statistical analysis of the angular variation of RM on critical
arc-minute scales from a magnetic component of Large Scale Structure of the
Universe.Comment: 9 pages, 3 figures; to appear as part of 'Cosmic Magnetism' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)11
Biases on the cosmological parameters and thermal SZ residuals
We examine the biases induced on cosmological parameters when the presence of
secondary anisotropies is not taken into account in Cosmic Microwave Background
analyses. We first develop an exact analytical expression for computing the
biases on parameters when any additive signal is neglected in the analysis. We
then apply it in the context of the forthcoming Planck experiment. For
illustration, we investigate the effect of the sole residual thermal
Sunyaev--Zel'dovich signal that remains after cluster extraction. We find in
particular that analyses neglecting the presence of this contribution introduce
on the cosmological parameters n_s and tau biases, at least 6.5 and 2.9 times
their one sigma confidence intervals. The Omega_b parameter is also biased to a
lesser extent.Comment: 7 pages, 5 figures, published in MNRA
The Sunyaev-Zel'dovich effect and Faraday rotation contributions of galaxy groups to the CMB angular power spectrum
The S-Z effect and Faraday rotation from halos are examined over a wide mass
range, an including gas condensation and magnetic field evolution.
Contributions to the CMB angular power spectrum are evaluated for galaxy
clusters, galaxy groups and galaxies. Smaller mass halos are found to play a
more important role than massive halos for the B-mode polarisation associated
with the S-Z CMB anisotropies. The B-modes from Faraday rotation dominate the
secondary B-modes caused by gravitational lensing at l > 3000. Measurement of
B-mode polarisation in combination with the S-Z power spectrum can potentially
provide important constraints on intracluster magnetic field and gas evolution
at early epochs.Comment: submitted to MNRA
Detectability of the 21 cm-CMB cross-correlation from the EoR
The 21-cm line fluctuations and the cosmic microwave background (CMB) are
powerful probes of the epoch of reionisation of the universe. We study the
potential of the cross-correlation between 21-cm line fluctuations and CMB
anisotropy to obtain further constraints on the reionisation history. We
compute analytically the 21-cm cross-correlation with the CMB temperature
anisotropy and polarisation, and we calculate the signal-to-noise (SN) ratio
for its detection with Planck together with LOFAR, MWA and SKA. We find, on the
one hand, that the 21-cm cross-correlation signal with CMB polarisation from
the instant reionisation can be detected with an SN ratio of for LOFAR
and for SKA. On the other hand, we confirm that the detection of the
21-cm cross-correlation with CMB polarisation is practically infeasible.Comment: 12 figure
The cross-correlation of the CMB polarisation and the 21-cm line fluctuations from cosmic reionisation
The cosmic microwave background (CMB) polarisation and the 21 cm line
fluctuations are powerful probes of cosmological reionisation. We study how the
cross-correlation between the CMB polarisation (E-modes) and the 21 cm line
fluctuations can be used to gain further understanding of the reionisation
history, within the framework of inhomogeneous reionisation. Since the E-mode
polarisation reflects the amplitude of the quadrupole component of the CMB
temperature fluctuations, the angular power spectrum of the cross-correlation
exhibits oscillations at all multipoles. The first peak of the power spectrum
appears at the scale corresponding to the quadrupole at the redshift that is
probed by the 21 cm line fluctuations. The peak reaches its maximum value in
redshift when the average ionisation fraction of the universe is about half. On
the other hand, on small scales, there is a damping that depends on the
duration of reionisation. Thus, the cross-correlation between the CMB
polarisation and the 21 cm line fluctuations has the potential to constrain
accurately the epoch and the duration of reionisation
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