1,961 research outputs found
Determining cosmic microwave background structure from its peak distribution
We present a new method for time-efficient and accurate extraction of the
power spectrum from future cosmic microwave background (CMB) maps based on
properties of peaks and troughs of the Gaussian CMB sky. We construct a
statistic describing their angular clustering - analogously to galaxies, the
2-point angular correlation function, . We show that for
increasing peak threshold, , the is strongly amplified
and becomes measurable for 1 on angular scales . Its
amplitude at every scale depends uniquely on the CMB temperature correlation
function, , and thus the measured can be uniquely inverted
to obtain and its Legendre transform, the power spectrum of the CMB
field. Because in this method the CMB power spectrum is deduced from high
peaks/troughs of the CMB field, the procedure takes only
operations where is the fraction of pixels with
standard deviations in the map of pixels and is e.g. 0.045 and 0.01 for
=2 and 2.5 respectively. We develop theoretical formalism for the method
and show with detailed simulations, using MAP mission parameters, that this
method allows to determine very accurately the CMB power spectrum from the
upcoming CMB maps in only operations.Comment: To be published in Ap.J. Letters. Minor changes to match the journal
versio
On the Presence of Thermal SZ Induced Signal in the First Year WMAP Temperature Maps
Using available optical and X-ray catalogues of clusters and superclusters of
galaxies, we build templates of tSZ emission as they should be detected by the
WMAP experiment. We compute the cross-correlation of our templates with WMAP
temperature maps, and interpret our results separately for clusters and for
superclusters of galaxies. For clusters of galaxies, we claim 2-5
detections in our templates built from BCS Ebeling et al. (1998), NORAS
(Boehringer et al. 2000) and de Grandi et al. (1999) catalogues. In these
templates, the typical cluster temperature decrements in WMAP maps are around
15-35 K in the RJ range (no beam deconvolution applied). Several tests
probing the possible influence of foregrounds in our analyses demonstrate that
our results are robust against galactic contamination. On supercluster scales,
we detect a diffuse component in the V & W WMAP bands which cannot be generated
by superclusters in our catalogues (Einasto et al. 1994, 1997), and which is
not present in the clean map of Tegmark, de Oliveira-Costa & Hamilton (2003).
Using this clean map, our analyses yield, for Einasto's supercluster
catalogues, the following upper limit for the comptonization parameter
associated to supercluster scales: y_{SC} < 2.18 \time s 10^{-8} at the 95%
confidence limit.Comment: MNRAS accepted. New section and minor changes include
Limits on Hot Intracluster Gas Contributions to the Tenerife Temperature Anisotropy Map
We limit the contribution of the hot intracluster gas, by means of the
Sunyaev-Zel'dovich effect, to the temperature anisotropies measured by the
Tenerife experiment. The data is cross-correlated with maps generated from the
ACO cluster catalogue, the ROSAT PSPC catalogue of clusters of galaxies, a
catalogue of superclusters and the HEAO 1 A-1 map of X-ray sources. There is no
evidence of contamination by such sources at an rms level of K at
99% confidence level at angular resolution. We place an upper limit on
the mean Comptonization parameter of at the same
level of confidence. These limits are slightly more restrictive than those
previously found by a similar analysis on the COBE/DMR data and indicate that
most of the signal measured by Tenerife is cosmological.Comment: To be published in ApJ (main journal
Large lianas as hyperdynamic elements of the tropical forest canopy
Lianas (woody vines) are an important component of lowland tropical forests.
We report large liana and tree inventory and dynamics data from Amazonia over periods
of up to 24 years, making this the longest geographically extensive study of liana ecology
to date. We use these results to address basic questions about the ecology of large lianas
in mature forests and their interactions with trees. In one intensively studied site we find
that large lianas (≥10 cm diameter) represent ,5% of liana stems, but 80% of biomass of
well-lit upper canopy lianas. Across sites, large lianas and large trees are both most successful
in terms of structural importance in richer soil forests, but large liana success may
be controlled more by the availability of large tree supports rather than directly by soil
conditions. Long-term annual turnover rates of large lianas are 5–8%, three times those of
trees. Lianas are implicated in large tree mortality: liana-infested large trees are three times
more likely to die than liana-free large trees, and large lianas are involved in the death of
at least 30% of tree basal area. Thus large lianas are a much more dynamic component of
Amazon forests than are canopy trees, and they play a much more significant functional
role than their structural contribution suggests
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&
Galaxy Clusters as mirrors of the distant Universe. Implications for the kSZ and ISW effects
It is well known that Thomson scattering of CMB photons in galaxy clusters
introduces new anisotropies in the CMB radiation field, but however little
attention is payed to the fraction of CMB photons that are scattered off the
line of sight, causing a slight blurring of the CMB anisotropies present at the
moment of scattering. In this work we study this {\it blurring} effect, and
find that it has a non-negligible impact on estimations of the kinetic
Sunyaev-Zel'dovich (kSZ) effect: it induces a 10% correction in 20-40% of the
clusters/groups, and a 100% correction in % of the clusters in an ideal
(noiseless) experiment. We explore the possibility of using this blurring term
to probe the CMB anisotropy field at different epochs in our Universe. In
particular, we study the required precision in the removal of the kSZ that
enables detecting the blurring term in galaxy cluster
populations placed at different redshift shells. By mapping this term in those
shells, we would provide a tomographic probe for the growth of the Integrated
Sachs Wolfe effect (ISW) during the late evolutionary stages of the Universe.
We find that the required precision of the cluster peculiar velocity removal is
of the order of 100 -- 200 km s in the redshift range 0.2 -- 0.8, after
assuming that all clusters more massive than 10 h M are
observable. These errors are comparable to the total expected linear line of
sight velocity dispersion for clusters in WMAPV cosmogony, and correspond to a
residual level of roughly 900 -- 1800 K per cluster, including all
types of contaminants and systematics. Were this precision requirement
achieved, then independent constraints on the intrinsic cosmological dipole
would be simultaneously provided.Comment: Notation clarified and typos and errors corrected in eqs.(2-4
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
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