300 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
Lyman-tomography of cosmic infrared background fluctuations with Euclid: probing emissions and baryonic acoustic oscillations at z>10
The Euclid space mission, designed to probe evolution of the Dark Energy,
will map a large area of the sky at three adjacent near-IR filters, Y, J and H.
This coverage will also enable mapping source-subtracted cosmic infrared
background (CIB) fluctuations with unprecedented accuracy on sub-degree angular
scales. Here we propose methodology, using the Lyman-break tomography applied
to the Euclid-based CIB maps, to accurately isolate the history of CIB
emissions as a function of redshift from 10 < z < 20, and to identify the
baryonic acoustic oscillations (BAOs) at those epochs. To identify the BAO
signature, we would assemble individual CIB maps over conservatively large
contiguous areas of >~ 400 sq deg. The method can isolate the CIB spatial
spectrum by z to sub-percent statistical accuracy. We illustrate this with a
specific model of CIB production at high z normalized to reproduce the measured
Spitzer-based CIB fluctuation. We show that even if the latter contain only a
small component from high-z sources, the amplitude of that component can be
accurately isolated with the methodology proposed here and the BAO signatures
at z>~ 10 are recovered well from the CIB fluctuation spatial spectrum. Probing
the BAO at those redshifts will be an important test of the underlying
cosmological paradigm, and would narrow the overall uncertainties on the
evolution of cosmological parameters, including the Dark Energy. Similar
methodology is applicable to the planned WFIRST mission, where we show that a
possible fourth near-IR channel at > 2 micron would be beneficial.Comment: comments welcom
Looking at cosmic near-infrared background radiation anisotropies
The cosmic infrared background (CIB) contains emissions accumulated over the
entire history of the Universe, including from objects inaccessible to
individual telescopic studies. The near-IR (~1-10 mic) part of the CIB, and its
fluctuations, reflects emissions from nucleosynthetic sources and
gravitationally accreting black holes (BHs). If known galaxies are removed to
sufficient depths the source-subtracted CIB fluctuations at near-IR can reveal
sources present in the first-stars-era and possibly new stellar populations at
more recent times. This review discusses the recent progress in this newly
emerging field which identified, with new data and methodology, significant
source-subtracted CIB fluctuations substantially in excess of what can be
produced by remaining known galaxies. The CIB fluctuations further appear
coherent with unresolved cosmic X-ray background (CXB) indicating a very high
fraction of BHs among the new sources producing the CIB fluctuations. These
observations have led to intensive theoretical efforts to explain the
measurements and their properties. While current experimental configurations
have limitations in decisively probing these theories, their potentially
remarkable implications will be tested in the upcoming CIB measurements with
the ESA's Euclid dark energy mission. We describe the goals and methodologies
of LIBRAE (Looking at Infrared Background Radiation with Euclid), a
NASA-selected project for CIB science with Euclid, which has the potential for
transforming the field into a new area of precision cosmology.Comment: Reviews of Modern Physics, to appea
The Effect of Hot Gas in WMAP's First Year Data
By cross-correlating templates constructed from the 2 Micron All Sky Survey
(2MASS) Extended Source (XSC) catalogue with WMAP's first year data, we search
for the thermal Sunyaev-Zel'dovich signature induced by hot gas in the local
Universe. Assuming that galaxies trace the distribution of hot gas, we select
regions on the sky with the largest projected density of galaxies. Under
conservative assumptions on the amplitude of foreground residuals, we find a
temperature decrement of -35 7 K ( detection level,
the highest reported so far) in the 26 square degrees of the sky
containing the largest number of galaxies per solid angle. We show that most of
the reported signal is caused by known galaxy clusters which, when convolved
with the average beam of the WMAP W band channel, subtend a typical angular
size of 20--30 arcmins. Finally, after removing from our analyses all pixels
associated with known optical and X-ray galaxy clusters, we still find a tSZ
decrement of -96 37 K in pixels subtending about 0.8 square
degrees on the sky. Most of this signal is coming from five different cluster
candidates in the Zone of Avoidance (ZoA), present in the Clusters In the ZoA
(CIZA) catalogue. We found no evidence that structures less bound than clusters
contribute to the tSZ signal present in the WMAP data.Comment: 10 pages, 4 figures, matches accepted version in ApJ Letter
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
Measurement of the electron-pressure profile of galaxy clusters in Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data
Using WMAP 3-year data at the locations of close to X-ray selected
clusters we have detected the amplitude of the thermal Sunyaev-Zeldovich (TSZ)
effect at the 15 level, the highest statistical significance reported
so far. Owing to the large size of our cluster sample, we are able to detect
the corresponding CMB distortions out to large cluster-centric radii. The
region over which the TSZ signal is detected is, on average, four times larger
in radius than the X-ray emitting region, extending to Mpc.
We show that an isothermal model does not fit the electron pressure at
large radii; instead, the baryon profile is consistent with the
Navarro-Frenk-White profile, expected for dark matter in the concordance
CDM model. The X-ray temperature at the virial radius of the clusters
falls by a factor from the central value, depending on the cluster
concentration parameter. Our results suggest that cluster dynamics at large
radii is dominated by dark matter and is well described by Newtonian gravity.Comment: ApJ Lett, to be published on March 10th, 200
Constraining the redshift evolution of the Cosmic Microwave Background black-body temperature with PLANCK data
We constrain the deviation of adiabatic evolution of the Universe using the
data on the Cosmic Microwave Background (CMB) temperature anisotropies measured
by the {\it Planck} satellite and a sample of 481 X-ray selected clusters with
spectroscopically measured redshifts. To avoid antenna beam effects, we bring
all the maps to the same resolution. We use a CMB template to subtract the
cosmological signal while preserving the Thermal Sunyaev-Zeldovich (TSZ)
anisotropies; next, we remove galactic foreground emissions around each cluster
and we mask out all known point sources. If the CMB black-body temperature
scales with redshift as , we constrain deviations of
adiabatic evolution to be , consistent with the
temperature-redshift relation of the standard cosmological model. This result
could suffer from a potential bias associated with the CMB
template, that we quantify it to be and with the same
sign than the measured value of , but is free from those biases
associated with using TSZ selected clusters; it represents the best constraint
to date of the temperature-redshift relation of the Big-Bang model using only
CMB data, confirming previous results.Comment: ApJ, in press. Manuscript matches the accepted version: 10 pages, 7
figures, 3 table
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
Use of ensemble based on GA for imbalance problem
In real-world applications, it has been observed that class imbalance (significant differences in class prior probabilities) may produce an important deterioration of the classifier performance, in particular with patterns belonging to the less represented classes. One method to tackle this problem consists to resample the original training set, either by over-sampling the minority class and/or under-sampling the majority class. In this paper, we propose two ensemble models (using a modular neural network and the nearest neighbor rule) trained on datasets under-sampled with genetic algorithms. Experiments with real datasets demonstrate the effectiveness of the methodology here propose
Missing baryons, bulk flows and the E-mode polarization of the Cosmic Microwave Background
If the peculiar motion of galaxy groups and clusters indeed resembles that of
the surrounding baryons, then the kinetic Sunyaev-Zel'dovich (kSZ) pattern of
those massive halos should be closely correlated to the kSZ pattern of all
surrounding electrons. Likewise, it should also be correlated to the CMB E-mode
polarization field generated via Thomson scattering after reionization. We
explore the cross-correlation of the kSZ generated in groups and clusters to
the all sky E-mode polarization in the context of upcoming CMB experiments like
Planck, ACT, SPT or APEX. We find that this cross-correlation is effectively
probing redshifts below (where most of baryons cannot be seen), and
that it arises in the very large scales (). The significance with which
this cross-correlation can be measured depends on the Poissonian uncertainty
associated to the number of halos where the kSZ is measured and on the accuracy
of the kSZ estimations themselves. Assuming that Planck can provide a cosmic
variance limited E-mode polarization map at and S/N kSZ
estimates can be gathered for all clusters more massive than , then this cross-correlation should be measured at the 2--3
level. Further, if an all-sky ACT or SPT type CMB experiment provides similar
kSZ measurements for all halos above , then the
cross-correlation total signal to noise (S/N) ratio should be at the level of
4--5. A detection of this cross-correlation would provide direct and definite
evidence of bulk flows and missing baryons simultaneously.Comment: 6 pages, 2 figures, submitted to A&
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