450 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
Implementation of a Fourier Matched Filter in CMB Analyses. Application to ISW Studies
Aims: Implement a matched filter (MF) cross-correlation algorithm in
multipole space and compare it to the standard Angular Cross Power Spectrum
(ACPS) method. Apply both methods on a Integrated Sachs Wolfe (ISW) - Large
Scale Structure (LSS) cross correlation scenario and study how sky masks
influence the multipole range where signal arises and its comparison to
theoretical predictions.
Methods: The MF requires the inversion of a multipole covariance matrix that
if is generally non-diagonal and singular. We use a SVD
approach that focuses on those modes carrying most of the information. We
compare the MF to the ACPS in ISW-LSS Monte Carlo simulations, paying attention
on the effect that a limited sky coverage has on the cross-correlation results.
Results: Within the linear data model for which the MF is defined, the MF
performs comparatively better than the ACPS for smaller values of and
scale dependent (non-Poissonian) noise fields. In the context of ISW studies
both methods are comparable, although the MF performs slightly more sensitively
under more restrictive masks. A preliminary study predicts that most of the
ISW--LSS cross correlation S/N ratio should be found in the very large scales
(50% of the S/N at , 90% at ), and this is confirmed by
Monte Carlo simulations. The statistical significance of our cross-correlation
statistics reaches its maximum when considering , with
for all values of observed, despite of the
smoothing and power aliasing that aggressive masks introduce in Fourier space.
This -confinement of the ISW-LSS cross correlation should enable a safe
distinction from other secondary effects arising at smaller angular scales.Comment: 9 pages, 5 figures, submitted to A&
Revisiting the WMAP - NVSS angular cross correlation. A skeptic's view
In the context of the study of the ISW, we revisit the angular cross
correlation of WMAP CMB data with the NVSS radio survey. We compute 2-point
cross functions between the two surveys in real and in Fourier space, paying
particular attention on the dependence of results on the flux of NVSS radio
sources, the angular scales where correlations arise and the comparison with
theoretical expectations. We reproduce previous results that claim an excess of
correlation in the angular correlation function (ACF), and we also find some
(low significance) similarity between the CMB and radio galaxy data in the
multipole range \el \in [10, 25]. However, the S/N in the ACFs increases
with higher flux thresholds for NVSS sources, but drops a 30 - 50% in
separations of the order of a pixel size, suggesting some residual point source
contribution. When restricting our analyses to multipoles \el \gt 60, we fail
to find any evidence for cross correlation in the range \el \in [2,10], where
according to the model predictions and our simulations 50% of the S/N is
supposed to arise. Also, the accumulated S/N for \el \lt 60 is below 1, far
from the theoretical expectation of S/N. Part of this disagreement may
be caused by an inaccurate modeling of the NVSS source population: as in
previous works, we find a level of large scale (\el \lt 70) clustering in the
NVSS catalog that seems incompatible with a high redshift population. This is
unlikely to be caused by contaminants or systematics, since it is independent
of flux threshold, and hence present for the brightest () NVSS
sources. Either our NVSS catalogs are not probing the high redshift, large
scale gravitational potential wells, or there is a clear mismatch between the
ISW component present in WMAP data and theoretical expectations.Comment: 16 pages, one extra figure (13 total), matches accepted version in
A&
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&
Evidence of the missing baryons from the kinematic Sunyaev-Zeldovich effect in Planck data
Under the terms of the Creative Commons Attribution license.-- et al.We estimate the amount of the missing baryons detected by the Planck measurements of the cosmic microwave background in the direction of central galaxies (CGs) identified in the Sloan galaxy survey. The peculiar motion of the gas inside and around the CGs unveils values of the Thomson optical depth Ï„T in the range 0.2-2×10-4, indicating that the regions probed around CGs contain roughly half of the total amount of baryons in the Universe at the epoch where the CGs are found. If baryons follow dark matter, the measured Ï„T's are compatible with the detection of all of the baryons existing inside and around the CGs.C. H.-M. acknowledges the support of Ramón y Cajal Fellowship No. RyC-2011-08262, Marie Curie Career Integration Grant No. 294183, and Spanish Ministerio de EconomÃa y Competitividad Project No. AYA2012-30789. Y.-Z. M thanks ERC for its support through Starting Grant No. 307209.Peer Reviewe
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
The ISW-tSZ cross correlation: ISW extraction out of pure CMB data
If Dark Energy introduces an acceleration in the universal expansion then
large scale gravitational potential wells should be shrinking, causing a
blueshift in the CMB photons that cross such structures (Integrated Sachs-Wolfe
effect, [ISW]). Galaxy clusters are known to probe those potential wells. In
these objects, CMB photons also experience inverse Compton scattering off the
hot electrons of the intra-cluster medium, and this results in a distortion
with a characteristic spectral signature of the CMB spectrum (the so-called
thermal Sunyaev-Zel'dovich effect, [tSZ]). Since both the ISW and the tSZ
effects take place in the same potential wells, they must be spatially
correlated. We present how this cross ISW-tSZ signal can be detected in a
CMB-data contained way by using the frequency dependence of the tSZ effect in
multi frequency CMB experiments like {\it Planck}, {\em without} requiring the
use of external large scale structure tracers data. We find that by masking low
redshift clusters, the shot noise level decreases significantly, boosting the
signal to noise ratio of the ISW--tSZ cross correlation. We also find that
galactic and extragalactic dust residuals must be kept at or below the level of
~0.04 muK^2 at l=10, a limit that is a factor of a few below {\it Planck}'s
expectations for foreground subtraction. If this is achieved, CMB observations
of the ISW-tSZ cross correlation should also provide an independent probe for
the existence of Dark Energy and the amplitude of density perturbations.Comment: submitted to MNRA
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
The cosmic dawn and the epoch of reionization
In this chapter we briefly describe the physics behind the HI 21 cm line in terms of the interplay of the HI gas with the ionized plasma and the Cosmic Microwave Background, and the different phases the system undergoes as the ambient density and UV background evolve with cosmological time. We also address the problematics associated to the metal enrichment of the IGM and the implications for the models of galaxy formation and evolution. We briefly discuss possible synergies with other reionization probes like E-ELT, JWST and ALMA, and conclude by listing a number of cosmological scenarios describing some type of energetic injection in the Universe, scenarios to whose understanding SKA should be able to (at least partially) contribute.The authors acknowledge partial support from the Spanish Ministerio de EconomÃa y Competitividad (MICINN) through projects AYA2013-48623-C2-2, AYA2007-68058-C03-01, AYA2010-21766-C03-02, AYA2012-30789, and the Consolider-Ingenio project CSD2010-00064 (EPI: Exploring the Physics of Inflation). We also acknowledge the support of the Ramón y Cajal fellowship (RyC 2011 148062) awarded by the Spanish MICINN and the Marie Curie Career Integration Grant (CIG 294183).Peer reviewe
- …