20 research outputs found
The Imprint of Proper Motion of Nonlinear Structures on the Cosmic Microwave Background
We investigate the imprint of nonlinear matter condensations on the Cosmic
Microwave Background (CMB) in an , Cold Dark Matter (CDM) model
universe. Temperature anisotropies are obtained by numerically evolving matter
inhomogeneities and CMB photons from the beginning of decoupling until the
present epoch. The underlying density field produced by the inhomogeneities is
followed from the linear, through the weakly clustered, into the fully
nonlinear regime. We concentrate on CMB temperature distortions arising from
variations in the gravitational potentials of nonlinear structures. We find two
sources of temperature fluctuations produced by time-varying potentials: (1)
anisotropies due to intrinsic changes in the gravitational potentials of the
inhomogeneities and (2) anisotropies generated by the peculiar, bulk motion of
the structures across the microwave sky. Both effects generate CMB anisotropies
in the range of 10^{-7} \siml \Delta T/T \siml 10^{-6} on scales of . For isolated structures, anisotropies due to proper motion exhibit
a dipole-like signature in the CMB sky that in principle could yield
information on the transverse velocity of the structures.Comment: 9 pages, 7 figures (included), uuencoded postcript fil
Cosmic Microwave Background Anisotropies from the Rees-Sciama Effect in Universes
We investigate the imprint of nonlinear matter condensations on the Cosmic
Microwave Background (CMB) in cold dark matter (CDM) model
universes. We consider simulation domains ranging from Mpc to
Mpc in size. We concentrate on the secondary temperature
anisotropies induced by time varying gravitational potentials occurring after
decoupling. Specifically, we investigate the importance of the Rees-Sciama
effect due to: (1) intrinsic changes in the gravitational potential of forming,
nonlinear structures, (2) proper motion of nonlinear structures, and (3) late
time decay of gravitational potential perturbations in open universes. CMB
temperature anisotropies are obtained by numerically evolving matter
inhomogeneities and CMB photons from an early, linear epoch () to the
present, nonlinear epoch . We test the dependence and relative
importance of these secondary temperature anisotropies as a function of the
scale of the underlying matter (voids, superclusters) and as a function of
. The results of the models are compared to a
similarly executed simulation. We find that in low density
models all three sources of anisotropy could be relevant and reach levels of
. In particular, we find that for at
large scales, secondary temperature anisotropies are dominated by the decaying
potential.Comment: 20 pages + 7 figures + 4 plates, self-expanding uuencoded compressed
tar archive of postscript file
CMB anisotropy: deviations from Gaussianity due to non-linear gravity
Non-linear evolution of cosmological energy density fluctuations triggers
deviations from Gaussianity in the temperature distribution of the cosmic
microwave background. A method to estimate these deviations is proposed. N-body
simulations -- in a CDM cosmology -- are used to simulate the strongly
non-linear evolution of cosmological structures. It is proved that these
simulations can be combined with the potential approximation to calculate the
statistical moments of the CMB anisotropies produced by non-linear gravity.
Some of these moments are computed and the resulting values are different from
those corresponding to Gaussianity.Comment: 6 latex pages with mn.sty, 3 eps figures. Accepted in MNRA
Time-Delay Effect on the cOsmic Background Radiation by Static Gravitational Potential of Clusters
We present a quantitative analysis of the time-delay effect on the cosmic
background radiation (CBR) by static gravitational potential of galaxy
clusters. This is primarily motivated by growing observational evidence that
clusters have essentially experienced no-evolution since redshift ,
indicating that the contribution of a time-dependent potential to CBR
anisotropy discussed in literature could be rather small for the
dynamically-relaxed clusters. Using the softened isothermal sphere model and
the universal density profile for the mass distribution of rich clusters, we
calculate the CBR anisotropy by the time-delay effect and compare it with those
generated by the thermal and kinematic S-Z effects as well as by the transverse
motion of clusters. While it is unlikely that the time-delay effect is
detectable in the current S-Z measurement because of its small amplitude of
- and its achromaticity, it nevertheless leads to an
uncertainty of in the measurement of the kinematic S-Z effect of
clusters. Future cosmological application of the peculiar velocity of clusters
to be measured through the S-Z effect should therefore take this uncertainty
into account.Comment: 15pages,1figures,accepted by Astrophysical Journa
Extragalactic Foregrounds of the Cosmic Microwave Background: Prospects for the MAP Mission
(Abridged) While the major contribution to the Cosmic Microwave Background
(CMB) anisotropies are the sought-after primordial fluctuations produced at the
surface of last scattering, other effects produce secondary fluctuations at
lower redshifts. Here, we study the extragalactic foregrounds of the CMB in the
context of the upcoming MAP mission. We first survey the major extragalactic
foregrounds and show that discrete sources, the Sunyaev-Zel'dovich (SZ) effect,
and gravitational lensing are the most dominant ones for MAP. We then show that
MAP will detect (>5 sigma) about 46 discrete sources and 10 SZ clusters
directly with 94 GHz fluxes above 2 Jy. The mean SZ fluxes of fainter clusters
can be probed by cross-correlating MAP with cluster positions extracted from
existing catalogs. For instance, a MAP-XBACs cross-correlation will be
sensitive to clusters with S(94GHz)>200mJy, and will thus provide a test of
their virialization state and a measurement of their gas fraction. Finally, we
consider probing the hot gas on supercluster scales by cross-correlating the
CMB with galaxy catalogs. Assuming that galaxies trace the gas, we show that a
cross-correlation between MAP and the APM catalog should yield a marginal
detection, or at least a four-fold improvement on the COBE upper limits for the
rms Compton y-parameter.Comment: 27 LaTeX pages, including 5 ps figures and 2 tables. To appear in
ApJ. Minor revisions to match accepted version. Color figures and further
links available at http://www.astro.princeton.edu/~refreg
Contributions to the Power Spectrum of Cosmic Microwave Background from Fluctuations Caused by Clusters of Galaxies
We estimate the contributions to the cosmic microwave background radiation
(CMBR) power spectrum from the static and kinematic Sunyaev-Zel'dovich (SZ)
effects, and from the moving cluster of galaxies (MCG) effect. We conclude, in
agreement with other studies, that at sufficiently small scales secondary
fluctuations caused by clusters provide important contributions to the CMBR. At
, these secondary fluctuations become important relative to
lensed primordial fluctuations. Gravitational lensing at small angular scales
has been proposed as a way to break the ``geometric degeneracy'' in determining
fundamental cosmological parameters. We show that this method requires the
separation of the static SZ effect, but the kinematic SZ effect and the MCG
effect are less important. The power spectrum of secondary fluctuations caused
by clusters of galaxies, if separated from the spectrum of lensed primordial
fluctuations, might provide an independent constraint on several important
cosmological parameters.Comment: LateX, 41 pages and 10 figures. Accepted for publication in the
Astrophysical Journa
On the Rees-Sciama effect: maps and statistics
Small maps of the Rees-Sciama (RS) effect are simulated by using an
appropriate N-body code and a certain ray-tracing procedure. A method designed
for the statistical analysis of cosmic microwave background (CMB) maps is
applied to study the resulting simulations. These techniques, recently proposed
--by our team-- to consider lens deformations of the CMB, are adapted to deal
with the RS effect. This effect and the deviations from Gaussianity associated
to it seem to be too small to be detected in the near future. This conclusion
follows from our estimation of both the RS angular power spectrum and the RS
reduced n-direction correlation functions for n<7.Comment: 11 pages, 13 figures, to appear in MNRA
Cosmic Microwave Background anisotropies from second order gravitational perturbations
This paper presents a complete analysis of the effects of second order
gravitational perturbations on Cosmic Microwave Background anisotropies, taking
explicitly into account scalar, vector and tensor modes. We also consider the
second order perturbations of the metric itself obtaining them, for a universe
dominated by a collision-less fluid, in the Poisson gauge, by transforming the
known results in the synchronous gauge. We discuss the resulting second order
anisotropies in the Poisson gauge, and analyse the possible relevance of the
different terms. We expect that, in the simplest scenarios for structure
formation, the main effect comes from the gravitational lensing by scalar
perturbations, that is known to give a few percent contribution to the
anisotropies at small angular scales.Comment: 15 pages, revtex, no figures. Version to be published in Phys. Rev.
The Effect of Weak Gravitational Lensing on the Cosmic Microwave Background Anisotropy: Flat versus Open Universes
We have studied the effect of gravitational lensing on the Cosmic Microwave
Background (CMB) anisotropy in flat and open universes. We develop a formalism
to calculate the changes on the radiation power spectrum induced by lensing in
the Newtonian and synchronous-comoving gauges. The previously considered
negligible contribution to the CMB radiation power spectrum of the anisotropic
term of the lensing correlation is shown to be appreciable. However,
considering the nonlinear evolution of the matter power spectrum produces only
slight differences on the results based on linear evolution. The general
conclusion for flat as well as open universes is that lensing slightly smoothes
the radiation power spectrum. For a given range of multipoles the effect of
lensing increases with Omega but for the same acoustic peak it decreases with
. The maximum contribution of lensing to the radiation power spectrum
for is 5% for values in the range 0.1-1.Comment: latex file in ApJ style, 17 pages, 3 ps figure
Non-linear Integrated Sachs-Wolfe Effect
We discuss the non-linear extension to the integrated Sachs-Wolfe effect
(ISW) resulting from the divergence of the large scale structure momentum
density field. The non-linear ISW effect leads to an increase in the total ISW
contribution by roughly two orders of magnitude at l ~ 1000. This increase,
however, is still below the cosmic variance limit of the primary anisotropies;
at further small angular scales, secondary effects such as gravitational
lensing and the kinetic Sunyaev-Zel'dovich (SZ) effect dominates the non-linear
ISW power spectrum. We show this second-order non-linear ISW contribution is
effectively same as the contribution previously described as a lensing effect
due to the transverse motion of gravitational lenses and well known as the
Kaiser-Stebbins effect under the context of cosmic strings. Due to geometrical
considerations, there is no significant three point correlation function, or a
bispectrum, between the linear ISW effects and its non-linear extension. The
non-linear ISW contribution can be potentially used as a probe of the
transverse velocity of dark matter halos such as galaxy clusters. Due to the
small contribution to temperature fluctuations, of order few tenths of micro
Kelvin, however, extrating useful measurements on velocities will be
challenging.Comment: 12 pages, 8 figures; submitted to Phys. Rev.