176 research outputs found
Aspects of spherically symmetric cosmological models.
Thesis (M.Sc.)-University of Natal, Durban, 1998.In this thesis we consider spherically symmetric cosmological models when the shear
is nonzero and also cases when the shear is vanishing. We investigate the role of
the Emden-Fowler equation which governs the behaviour of the gravitational field.
The Einstein field equations are derived in comoving coordinates for a spherically
symmetric line element and a perfect fluid source for charged and uncharged matter.
It is possible to reduce the system of field equations under different assumptions to
the solution of a particular Emden-Fowler equation. The situations in which the
Emden-Fowler equation arises are identified and studied. We analyse the Emden-Fowler
equation via the method of Lie point symmetries. The conditions under which
this equation is reduced to quadratures are obtained. The Lie analysis is applied to
the particular models of Herlt (1996), Govender (1996) and Maharaj et al (1996) and
the role of the Emden-Fowler equation is highlighted. We establish the uniqueness
of the solutions of Maharaj et al (1996). Some physical features of the Einstein-Maxwell
system are noted which distinguishes charged solutions. A charged analogue
of the Maharaj et al (1993) spherically symmetric solution is obtained. The Gutman-Bespal'ko
(1967) solution is recovered as a special case within this class of solutions
by fixing the parameters and setting the charge to zero. It is also demonstrated
that, under the assumptions of vanishing acceleration and proper charge density,
the Emden-Fowler equation arises as a governing equation in charged spherically
symmetric models
Observing the Sunyaev-Zel'dovich Effect Closer to Home
Hot gas trapped in a dark matter halo will produce a decrement in the surface
brightness of the microwave background, the Sunyaev-Zel'dovich (SZ) effect.
While massive clusters produce the strongest central SZ decrements, we point
out that a local galaxy halo, specifically the halo of M31, may be one of the
brightest integrated SZ sources in the sky. For various realistic gas
distributions consistent with current X-ray limits, we show that the integrated
SZ decrement from M31 will be comparable to decrements already detected in more
distant sources, provided its halo contains an appreciable quantity of hot gas.
A measurement of this decrement would provide direct information on the mass,
spatial distribution and thermodynamic state of hot gas in a low-mass halo, and
could place important constraints on current models of galaxy formation.
Detecting such an extended (~ 10 degree), low-amplitude signal will be
challenging, but should be possible with all-sky SZ maps from satellite
missions such as the Wilkinson Microwave Anisotropy Probe or the Planck
Surveyor.Comment: 5 pages, 3 figures; submitted to MNRA
Measurement of the pairwise kinematic Sunyaev-Zeldovich effect with Planck and BOSS data
We present a new measurement of the kinetic Sunyaev-Zeldovich effect (kSZ)
using Planck cosmic microwave background (CMB) and Baryon Oscillation
Spectroscopic Survey (BOSS) data. Using the `LowZ North/South' galaxy catalogue
from BOSS DR12, and the group catalogue from BOSS DR13, we evaluate the mean
pairwise kSZ temperature associated with BOSS galaxies. We construct a `Central
Galaxies Catalogue' (CGC) which consists of isolated galaxies from the original
BOSS data set, and apply the aperture photometry (AP) filter to suppress the
primary CMB contribution. By constructing a halo model to fit the pairwise kSZ
function, we constrain the mean optical depth to be
for `LowZ North CGC',
for `LowZ South CGC', and
for `DR13 Group'. In
addition, we vary the radius of the AP filter and find that the AP size of
gives the maximum detection for . We also
investigate the dependence of the signal with halo mass and find
and
for `DR13 Group' with halo
mass restricted to, respectively, less and greater than its median halo mass,
. For the `LowZ North CGC' sample restricted
to there is no detection of
the kSZ signal because these high mass halos are associated with the
high-redshift galaxies of the LowZ North catalogue, which have limited
contribution to the pairwise kSZ signals.Comment: 11 pages, 11 figures, 2 table
A cross-bispectrum estimator for CMB-HI intensity mapping correlations
Intensity mapping of 21cm emission from neutral hydrogen (HI) promises to be
a powerful probe of large-scale structure in the post-reionisation epoch.
However, HI intensity mapping (IM) experiments will suffer the loss of
long-wavelength line-of-sight HI modes in the galactic foreground subtraction
process. The loss of these modes is particularly problematic for detecting HI
IM cross-correlations with projected large-scale structure tracers, such as CMB
secondary anisotropies. Here, we propose a cross-bispectrum estimator to
recover the cross-correlation of the HI IM field, with the CMB
lensing field, constructed by correlating the position-dependent HI
power spectrum with the mean overdensity traced by CMB lensing.
We study the cross-bispectrum estimator, in the squeezed limit and forecast its detectability based on HI IM
measurements from HIRAX and CMB lensing measurements from AdvACT. The
cross-bispectrum improves constraints on cosmological parameters; in
particular, the constraint on the dark energy equation-of-state parameter,
improves on the HI IM auto-power spectra constraint by 44\% (to 0.014),
while the constraint on improves by 33\% (to 0.08), assuming Planck
priors in each case. These results are robust to HI IM foreground removal
because they largely derive from small-scale HI modes. The HI-HI-
cross-bispectrum thus provides a novel way to recover HI correlations with CMB
lensing and constrain cosmological parameters at a level that is competitive
with next-generation galaxy redshift surveys. As a striking example of this, we
find that the combined constraint on the sum of the neutrino masses, while
varying all redshift and standard cosmological parameters within a
CDM model, is 5.5 meV.Comment: 11 pages, 4 figure
CMB Lensing Reconstruction in Real Space
We explore the reconstruction of the gravitational lensing field of the
cosmic microwave background in real space showing that very little statistical
information is lost when estimators of short range on the celestial sphere are
used in place of the customary estimators in harmonic space, which are nonlocal
and in principle require a simultaneous analysis of the entire sky without any
cuts or excisions. Because virtually all the information relevant to lensing
reconstruction lies on angular scales close to the resolution scale of the sky
map, the gravitational lensing dilatation and shear fields (which unlike the
deflection field or lensing potential are directly related to the observations
in a local manner) may be reconstructed by means of quadratic combinations
involving only very closely separated pixels. Even though harmonic space
provides a more natural context for understanding lensing reconstruction
theoretically, the real space methods developed here have the virtue of being
faster to implement and are likely to prove useful for analyzing realistic maps
containing a galactic cut and possibly numerous small excisions to exclude
point sources that cannot be reliably subtracted.Comment: 21 pages, 8 figure
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