5,740 research outputs found
Effects of Foreground Contamination on the Cosmic Microwave Background Anisotropy Measured by MAP
We study the effects of diffuse Galactic, far-infrared extragalactic source,
and radio point source emission on the cosmic microwave background (CMB)
anisotropy data anticipated from the MAP experiment. We focus on the
correlation function and genus statistics measured from mock MAP
foreground-contaminated CMB anisotropy maps generated in a spatially-flat
cosmological constant dominated cosmological model. Analyses of the simulated
MAP data at 90 GHz (0.3 deg FWHM resolution smoothed) show that foreground
effects on the correlation function are small compared with cosmic variance.
However, the Galactic emission, even just from the region with |b| > 20 deg,
significantly affects the topology of CMB anisotropy, causing a negative genus
shift non-Gaussianity signal. Given the expected level of cosmic variance, this
effect can be effectively reduced by subtracting existing Galactic foreground
emission models from the observed data. IRAS and DIRBE far-infrared
extragalactic sources have little effect on the CMB anisotropy. Radio point
sources raise the amplitude of the correlation function considerably on scales
below 0.5 deg. Removal of bright radio sources above a 5 \sigma detection limit
effectively eliminates this effect. Radio sources also result in a positive
genus curve asymmetry (significant at 2 \sigma) on 0.5 deg scales. Accurate
radio point source data is essential for an unambiguous detection of CMB
anisotropy non-Gaussianity on these scales. Non-Gaussianity of cosmological
origin can be detected from the foreground-subtracted CMB anisotropy map at the
2 \sigma level if the measured genus shift parameter |\Delta\nu| >= 0.02 (0.04)
or if the measured genus asymmetry parameter |\Delta g| >= 0.03 (0.08) on a 0.3
(1.0) deg FWHM scale.Comment: 26 pages, 7 figures, Accepted for Publication in Astrophysical
Journal (Some sentences and figures modified
Cosmological Parameter Determination in Free-Form Strong Gravitational Lens Modeling
We develop a novel statistical strong lensing approach to probe the
cosmological parameters by exploiting multiple redshift image systems behind
galaxies or galaxy clusters. The method relies on free-form mass inversion of
strong lenses and does not need any additional information other than
gravitational lensing. Since in free-form lensing the solution space is a
high-dimensional convex polytope, we consider Bayesian model comparison
analysis to infer the cosmological parameters. The volume of the solution space
is taken as a tracer of the probability of the underlying cosmological
assumption. In contrast to parametric mass inversions, our method accounts for
the mass-sheet degeneracy, which implies a degeneracy between the steepness of
the profile and the cosmological parameters. Parametric models typically break
this degeneracy, introducing hidden priors to the analysis that contaminate the
inference of the parameters. We test our method with synthetic lenses, showing
that it is able to infer the assumed cosmological parameters. Applied to the
CLASH clusters, the method might be competitive with other probes.Comment: 11 pages, 5 figures. Accepted for publication in MNRA
Testing for Non-Gaussianity in the Wilkinson Microwave Anisotropy Probe Data: Minkowski Functionals and the Length of the Skeleton
The three Minkowski functionals and the recently defined length of the
skeleton are estimated for the co-added first-year Wilkinson Microwave
Anisotropy Probe (WMAP) data and compared with 5000 Monte Carlo simulations,
based on Gaussian fluctuations with the a-priori best-fit running-index power
spectrum and WMAP-like beam and noise properties. Several power
spectrum-dependent quantities, such as the number of stationary points, the
total length of the skeleton, and a spectral parameter, gamma, are also
estimated. While the area and length Minkowski functionals and the length of
the skeleton show no evidence for departures from the Gaussian hypothesis, the
northern hemisphere genus has a chi^2 that is large at the 95% level for all
scales. For the particular smoothing scale of 3.40 degrees FWHM it is larger
than that found in 99.5% of the simulations. In addition, the WMAP genus for
negative thresholds in the northern hemisphere has an amplitude that is larger
than in the simulations with a significance of more than 3 sigma. On the
smallest angular scales considered, the number of extrema in the WMAP data is
high at the 3 sigma level. However, this can probably be attributed to the
effect of point sources. Finally, the spectral parameter gamma is high at the
99% level in the northern Galactic hemisphere, while perfectly acceptable in
the southern hemisphere. The results provide strong evidence for the presence
of both non-Gaussian behavior and an unexpected power asymmetry between the
northern and southern hemispheres in the WMAP data.Comment: 17 pages, 10 figures, accepted for publication in Ap
Topology of Neutral Hydrogen Within the Small Magellanic Cloud
In this paper, genus statistics have been applied to an HI column density map
of the Small Magellanic Cloud in order to study its topology. To learn how
topology changes with the scale of the system, we provide the study of topology
for column density maps at varying resolution. To evaluate the statistical
error of the genus we randomly reassign the phases of the Fourier modes while
keeping the amplitudes. We find, that at the smallest scales studied () the genus shift is in all regions negative,
implying a clump topology. At the larger scales () the topology shift is detected to be negative in 4 cases and positive
(``swiss cheese'' topology) in 2 cases. In 4 regions there is no statistically
significant topology shift at large scales
A low CMB variance in the WMAP data
We have estimated the CMB variance from the three-year WMAP data, finding a
value which is significantly lower than the one expected from Gaussian
simulations using the WMAP best-fit cosmological model, at a significance level
of 98.7 per cent. This result is even more prominent if we consider only the
north ecliptic hemisphere (99.8 per cent). Different analyses have been
performed in order to identify a possible origin for this anomaly. In
particular we have studied the behaviour of single radiometers and single year
data as well as the effect of residual foregrounds and 1/f noise, finding that
none of these possibilities can explain the low value of the variance. We have
also tested the effect of varying the cosmological parameters, finding that the
estimated CMB variance tends to favour higher values of than the one of
the WMAP best-fit model. In addition, we have also tested the consistency
between the estimated CMB variance and the actual measured CMB power spectrum
of the WMAP data, finding a strong discrepancy. A possible interpretation of
this result could be a deviation from Gaussianity and/or isotropy of the CMB.Comment: 13 pages, 5 figures. Some new tests added. Section 5 largely
modified. Accepted for publication in MNRA
High-Resolution Simulations of Cosmic Microwave Background non-Gaussian Maps in Spherical Coordinates
We describe a new numerical algorithm to obtain high-resolution simulated
maps of the Cosmic Microwave Background (CMB), for a broad class of
non-Gaussian models. The kind of non-Gaussianity we account for is based on the
simple idea that the primordial gravitational potential is obtained by a
non-linear but local mapping from an underlying Gaussian random field, as
resulting from a variety of inflationary models. Our technique, which is based
on a direct realization of the potential in spherical coordinates and fully
accounts for the radiation transfer function, allows to simulate non-Gaussian
CMB maps down to the Planck resolution (), with
reasonable memory storage and computational time.Comment: 9 pages, 5 figures. Submitted to ApJ. A version with higher quality
figures is available at http://www.pd.infn.it/~liguori/content.htm
Nonlinear Evolution of the Genus Statistics with Zel'dovich Approximation
Evolution of genus density is calculated from Gaussian initial conditions
using Zel'dovich approximation. A new approach is introduced which formulates
the desired quantity in a rotationally invariant manner. It is shown that
normalized genus density does not depend on the initial spectral shape but is a
function of the fluctuation amplitude only.Comment: 21 pages, 6 Postscript figures, LaTe
Lagrangian bias in the local bias model
It is often assumed that the halo-patch fluctuation field can be written as a
Taylor series in the initial Lagrangian dark matter density fluctuation field.
We show that if this Lagrangian bias is local, and the initial conditions are
Gaussian, then the two-point cross-correlation between halos and mass should be
linearly proportional to the mass-mass auto-correlation function. This
statement is exact and valid on all scales; there are no higher order
contributions, e.g., from terms proportional to products or convolutions of
two-point functions, which one might have thought would appear upon truncating
the Taylor series of the halo bias function. In addition, the auto-correlation
function of locally biased tracers can be written as a Taylor series in the
auto-correlation function of the mass; there are no terms involving, e.g.,
derivatives or convolutions. Moreover, although the leading order coefficient,
the linear bias factor of the auto-correlation function is just the square of
that for the cross-correlation, it is the same as that obtained from expanding
the mean number of halos as a function of the local density only in the
large-scale limit. In principle, these relations allow simple tests of whether
or not halo bias is indeed local in Lagrangian space. We discuss why things are
more complicated in practice. We also discuss our results in light of recent
work on the renormalizability of halo bias, demonstrating that it is better to
renormalize than not. We use the Lognormal model to illustrate many of our
findings.Comment: 14 pages, published on JCA
The Cluster Distribution as a Test of Dark Matter Models. IV: Topology and Geometry
We study the geometry and topology of the large-scale structure traced by
galaxy clusters in numerical simulations of a box of side 320 Mpc, and
compare them with available data on real clusters. The simulations we use are
generated by the Zel'dovich approximation, using the same methods as we have
used in the first three papers in this series. We consider the following models
to see if there are measurable differences in the topology and geometry of the
superclustering they produce: (i) the standard CDM model (SCDM); (ii) a CDM
model with (OCDM); (iii) a CDM model with a `tilted' power
spectrum having (TCDM); (iv) a CDM model with a very low Hubble
constant, (LOWH); (v) a model with mixed CDM and HDM (CHDM); (vi) a
flat low-density CDM model with and a non-zero cosmological
term (CDM). We analyse these models using a variety of
statistical tests based on the analysis of: (i) the Euler-Poincar\'{e}
characteristic; (ii) percolation properties; (iii) the Minimal Spanning Tree
construction. Taking all these tests together we find that the best fitting
model is CDM and, indeed, the others do not appear to be consistent
with the data. Our results demonstrate that despite their biased and extremely
sparse sampling of the cosmological density field, it is possible to use
clusters to probe subtle statistical diagnostics of models which go far beyond
the low-order correlation functions usually applied to study superclustering.Comment: 17 pages, 7 postscript figures, uses mn.sty, MNRAS in pres
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