289 research outputs found
Temperature Anisotropies and Distortions Induced by Hot Intracluster Gas on the Cosmic Microwave Background
The power spectrum of temperature anisotropies induced by hot intracluster
gas on the cosmic background radiation is calculated. For low multipoles it
remains constant while at multipoles above it is exponentially damped.
The shape of the radiation power spectrum is almost independent of the average
intracluster gas density profile, gas evolution history or clusters virial
radii; but the amplitude depends strongly on those parameters and could be as
large as 20% that of intrinsic contribution. The exact value depends on the
global properties of the cluster population and the evolution of the
intracluster gas. The distortion on the Cosmic Microwave Background black body
spectra varies in a similar manner. The ratio of the temperature anisotropy to
the mean Comptonization parameters is shown to be almost independent of the
cluster model and, in first approximation, depends only on the number density
of clusters.Comment: 10 pages, Latex, 3 figures; to be published in Ap
Constraining f(R) gravity with PLANCK data on galaxy cluster profiles
Models of gravity that introduce corrections to the Newtonian
potential in the weak field limit are tested at the scale of galaxy clusters.
These models can explain the dynamics of spiral and elliptical galaxies without
resorting to dark matter. We compute the pressure profiles of 579 galaxy
clusters assuming that the gas is in hydrostatic equilibrium within the
potential well of the modified gravitational field. The predicted profiles are
compared with the average profile obtained by stacking the data of our cluster
sample in the Planck foreground clean map SMICA. We find that the resulting
profiles of these systems fit the data without requiring a dominant dark matter
component, with model parameters similar to those required to explain the
dynamics of galaxies. Our results do not rule out that clusters are dynamically
dominated by Dark Matter but support the idea that Extended Theories of Gravity
could provide an explanation to the dynamics of self-gravitating systems and to
the present period of accelerated expansion, alternative to the concordance
cosmological model.Comment: 10 pages, 5 figures, accepted for publication in MNRA
Measuring cosmological bulk flows via the kinematic Sunyaev-Zeldovich effect in the upcoming cosmic microwave background maps
We propose a new method to measure the possible large-scale bulk flows in the
Universe from the cosmic microwave background (CMB) maps from the upcoming
missions, MAP and Planck. This can be done by studying the statistical
properties of the CMB temperature field at many X-ray cluster positions. At
each cluster position, the CMB temperature fluctuation will be a combination of
the Sunyaev-Zeldovich (SZ) kinematic and thermal components, the cosmological
fluctuations and the instrument noise term. When averaged over many such
clusters the last three will integrate down, whereas the first one will be
dominated by a possible bulk flow component. In particular, we propose to use
all-sky X-ray cluster catalogs that should (or could) be available soon from
X-ray satellites, and then to evaluate the dipole component of the CMB field at
the cluster positions. We show that for the MAP and Planck mission parameters
the dominant contributions to the dipole will be from the terms due to the SZ
kinematic effect produced by the bulk flow (the signal we seek) and the
instrument noise (the noise in our signal). Computing then the expected
signal-to-noise ratio for such measurement, we get that at the 95 % confidence
level the bulk flows on scales >100h^{-1} Mpc can be probed down to the
amplitude of km/sec with the MAP data and down to only 30 km/sec with
the Planck mission.Comment: Astrophysical Journal Letters, in pres
On the Number Density of Sunyaev-Zel'dovich Clusters of Galaxies
If the mean properties of clusters of galaxies are well described by the
entropy-driven model, the distortion induced by the cluster population on the
blackbody spectrum of the Cosmic Microwave Background radiation is proportional
to the total amount of intracluster gas while temperature anisotropies are
dominated by the contribution of clusters of about 10^{14} solar masses. This
result depends marginally on cluster parameters and it can be used to estimate
the number density of clusters with enough hot gas to produce a detectable
Sunyaev-Zel'dovich effect. Comparing different cosmological models, the
relation depends mainly on the density parameter Omega_m. If the number density
of clusters could be estimated by a different method, then this dependence
could be used to constrain Omega_m.Comment: 8 pages, 3 figures, submitted to ApJ Letter
Observational constraints on interacting quintessence models
We determine the range of parameter space of Interacting Quintessence Models
that best fits the recent WMAP measurements of Cosmic Microwave Background
temperature anisotropies. We only consider cosmological models with zero
spatial curvature. We show that if the quintessence scalar field decays into
cold dark matter at a rate that brings the ratio of matter to dark energy
constant at late times,the cosmological parameters required to fit the CMB data
are: \Omega_x = 0.43 \pm 0.12, baryon fraction \Omega_b = 0.08 \pm 0.01, slope
of the matter power spectrum at large scals n_s = 0.98 \pm 0.02 and Hubble
constant H_0 = 56 \pm 4 km/s/Mpc. The data prefers a dark energy component with
a dimensionless decay parameter c^2 =0.005 and non-interacting models are
consistent with the data only at the 99% confidence level. Using the Bayesian
Information Criteria we show that this exra parameter fits the data better than
models with no interaction. The quintessence equation of state parameter is
less constrained; i.e., the data set an upper limit w_x \leq -0.86 at the same
level of significance. When the WMAP anisotropy data are combined with
supernovae data, the density parameter of dark energy increases to \Omega_x
\simeq 0.68 while c^2 augments to 6.3 \times 10^{-3}. Models with quintessence
decaying into dark matter provide a clean explanation for the coincidence
problem and are a viable cosmological model, compatible with observations of
the CMB, with testable predictions. Accurate measurements of baryon fraction
and/or of matter density independent of the CMB data, would support/disprove
these models.Comment: 16 pages, Revtex4, 5 eps figures, to appear in Physical Review
Matter density perturbations in interacting quintessence models
Models with dark energy decaying into dark matter have been proposed to solve
the coincidence problem in cosmology. We study the effect of such coupling in
the matter power spectrum. Due to the interaction, the growth of matter density
perturbations during the radiation dominated regime is slower compared to
non-interacting models with the same ratio of dark matter to dark energy today.
This effect introduces a damping on the power spectrum at small scales
proportional to the strength of the interaction and similar to the effect
generated by ultrarelativistic neutrinos. The interaction also shifts
matter--radiation equality to larger scales. We compare the matter power
spectrum of interacting quintessence models with the measurments of 2dFGRS. We
particularize our study to models that during radiation domination have a
constant dark matter to dark energy ratio.Comment: 11 pages, 4 figures, accepted for publication in Phys. Rev.
The contribution of the kinematic Sunyaev-Zel'dovich Effect from the Warm Hot Intergalactic Medium to the Five-Year WMAP Data
We study the contribution of the kinematic Sunyaev-Zel'dovich (kSZ) effect,
generated by the warm-hot intergalactic medium (WHIM), to the cosmic microwave
background (CMB) temperature anisotropies in the Five-Year Wilkinson Microwave
Anisotropy Probe (WMAP) data. We explore the concordance LambdaCDM cosmological
model, with and without this kSZ contribution, using a Markov chain Monte Carlo
algorithm. Our model requires a single extra parameter to describe this new
component. Our results show that the inclusion of the kSZ signal improves the
fit to the data without significantly altering the best-fit cosmological
parameters except Obh^2. The improvement is localized at the l>500 multipoles.
For the best-fit model, this extra component peaks at l~450 with an amplitude
of 129 muK^2, and represents 3.1% of the total power measured by the Wilkinson
Microwave Anisotropy Probe. Nevertheless, at the 2-sigma level a null kSZ
contribution is still compatible with the data. Part of the detected signal
could arise from unmasked point sources and/or Poissonianly distributed
foreground residuals. A statistically more significant detection requires the
wider frequency coverage and angular resolution of the forthcoming Planck
mission.Comment: 16 pages, 4 figures. Accepted for publication in Ap
Probing gravity with PLANCK data on cluster pressure profiles
Analytical -gravity models introduce Yukawa-like corrections to the
Newtonian potential in the weak field limit. These models can explain the
dynamics of galaxies and cluster of galaxies without requiring dark matter. To
test the model, we have computed the pressure profile of 579 X-ray galaxy
clusters assuming the gas is in hydrostatic equilibrium within the potential
well of the modified gravitational potential. We have compared those profiles
with the ones measured in the foreground cleaned SMICA released by the Planck
Collaboration. Our results show that Extended Theories of Gravity explain the
dynamics of self-gravitating systems at cluster scales and represent an
alternative to dark matter haloes.Comment: 6 pages, 3 figures, 1 table. To be published in Journal of Physics:
Conference Series (JPCS) as the Proceedings of Spanish Relativity Meeting
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