738 research outputs found
Likelihood Functions for Galaxy Cluster Surveys
Galaxy cluster surveys offer great promise for measuring cosmological
parameters, but survey analysis methods have not been widely studied. Using
methods developed decades ago for galaxy clustering studies, it is shown that
nearly exact likelihood functions can be written down for galaxy cluster
surveys. The sparse sampling of the density field by galaxy clusters allows
simplifications that are not possible for galaxy surveys. An application to
counts in cells is explicitly tested using cluster catalogs from numerical
simulations and it is found that the calculated probability distributions are
very accurate at masses above several times 10^{14}h^{-1} solar masses at z=0
and lower masses at higher redshift.Comment: 6 pages, 3 figures, updated key referenc
The unusual smoothness of the extragalactic unresolved radio background
If the radio background is coming from cosmological sources, there should be
some amount of clustering due to the large scale structure in the universe.
Simple models for the expected clustering combined with the recent measurement
by ARCADE-2 of the mean extragalactic temperature lead to predicted clustering
levels that are substantially above upper limits from searches for anisotropy
on arcminute scales using ATCA and the VLA. The rms temperature variations in
the cosmic radio background appear to be more than a factor of 10 smaller (in
temperature) than the fluctuations in the cosmic infrared background. It is
therefore extremely unlikely that this background comes from galaxies, galaxy
clusters, or any sources that trace dark matter halos at z<5, unless typical
sources are smooth on arcminute scales, requiring typical sizes of several Mpc.Comment: 4 pages, 1 figur
Radio Point Sources and the Thermal SZ Power Spectrum
Radio point sources are strongly correlated with clusters of galaxies, so a
significant fraction of the thermal Sunyaev-Zel'dovich (SZ) effect signal could
be affected by point source contamination. Based on empirical estimates of the
radio galaxy population, it is shown that the rms temperature fluctuations of
the thermal SZ effect could be underestimated by as much as 30% at an observing
frequency of 30 GHz at l>1000. The effect is larger at higher multipoles. If
the recent report of excess power at small angular scales is to be explained by
the thermal SZ effect, then radio point sources at an observing frequency of 30
GHz must be a surprisingly weak contaminant of the SZ effect for low-mass
clusters.Comment: 5 pages, minor changes to match accepted ApJ versio
Searching for patchy reionization from cosmic microwave background with hybrid quadratic estimators
We propose a hybrid quadratic estimator to measure cross correlations between
gravitational lensing of the cosmic microwave background (CMB) and differential
screening effects arising from fluctuations in the electron column density,
such as could arise from patchy reionization. The hybrid quadratic estimators
are validated by simulated data sets with both Planck and CMB-Stage 4 (CMB-S4)
instrumental properties and found to be able to recover the cross-power spectra
with almost no biases. We apply this technique to Planck 2015 temperature data
and obtain cross-power spectra between gravitational lensing and differential
screening effects. Planck data alone cannot detect the
patchy-reionization-induced cross-power spectrum but future experiment like
CMB-S4 will be able to robustly measure the expected signal and deliver new
insights on reionization.Comment: 6 pages, 6 figure
An excess of non-Gaussian fluctuations in the cosmic infrared background consistent with gravitational lensing
The cosmic infrared background (CIB) is gravitationally lensed. A
quadratic-estimator technique that is inherited from lensing analyses of the
cosmic microwave background (CMB) can be applied to detect the CIB lensing
effects. However, the CIB fluctuations are intrinsically strongly non-Gaussian,
making CIB lensing reconstruction highly biased. We perform numerical
simulations to estimate the intrinsic non-Gaussianity and establish a
cross-correlation approach to precisely extract the CIB lensing signal from raw
data. We apply this technique to CIB data from the Planck satellite and
cross-correlate the resulting lensing estimate with the CIB data, galaxy number
counts and the CMB lensing potential. We detect an excess that is consistent
with a lensing contribution at .Comment: 13 pages, 7 figure
Enhanced global signal of neutral hydrogen due to excess radiation at cosmic dawn
We revisit the global 21cm signal calculation incorporating a possible radio
background at early times, and find that the global 21cm signal shows a much
stronger absorption feature, which could enhance detection prospects for future
21 cm experiments. In light of recent reports of a possible low-frequency
excess radio background, we propose that detailed 21 cm calculations should
include a possible early radio background.Comment: 4 pages, 4 figure
A Method for Mapping the Temperature Profile of X-ray Clusters Through Radio Observations
Many of the most luminous extragalactic radio sources are located at the
centers of X-ray clusters, and so their radiation must be scattered by the
surrounding hot gas. We show that radio observations of the highly-polarized
scattered radiation (which depends on the electron density distribution) in
combination with the thermal Sunyaev-Zeldovich effect (which measures the
electron pressure distribution), can be used to determine the radial profile of
the electron temperature within the host cluster. The sensitivity levels
expected from current instruments will allow radio measurements of
mass-weighted cluster temperature profiles to better than roughly 1 keV
accuracy, as long as the central radio source is steady over several million
years. Variable or beamed sources will leave observable signatures in the
scattered emission. For clusters with a central point source brighter than
about 1 mJy, the scattered polarization signal is stronger than competing
effects due to the cosmic microwave background.Comment: 5 pages, 2 figures, to be submitted to ApJ
The Polarization Signature of Local Bulk Flows
A large peculiar velocity of the intergalactic medium produces a Doppler
shift of the cosmic microwave background with a frequency-dependent quadrupole
term. This quadrupole will act as a source for polarization of the cosmic
microwave background, creating a large-scale polarization anisotropy if the
bulk flow is local and coherent on large scales. In the case where we are near
the center of the moving region, the polarization signal is a pure quadrupole.
We show that the signal is small, but detectable with future experiments for
bulk flows as large as some recent reports.Comment: 5 pages, 3 figures. Accepted by Ap
Detecting Electron Density Fluctuations from Cosmic Microwave Background Polarization using a Bispectrum Approach
Recent progress in high sensitivity Cosmic Microwave Background (CMB)
polarization experiments opens up a window on large scale structure (LSS), as
CMB polarization fluctuations on small angular scales can arise from a
combination of LSS and ionization fluctuations in the late universe.
Gravitational lensing effects can be extracted from CMB datasets with quadratic
estimators but reconstructions of electron density fluctuations (EDFs) with
quadratic estimators are found to be significantly biased by the much larger
lensing effects in the secondary CMB fluctuations. In this paper we establish a
bispectrum formalism using tracers of LSS to extract the subdominant EDFs from
CMB polarization data. We find that this bispectrum can effectively reconstruct
angular band-powers of cross correlation between EDFs and LSS tracers. Next
generation CMB polarization experiments in conjunction with galaxy surveys and
cosmic infrared background experiments can detect signatures of EDFs with high
significance.Comment: 6 pages, 3 figure
Globular Cluster Microlensing: Globular Clusters as Microlensing Targets
We investigate the possibility of using globular clusters as targets for
microlensing searches. Such searches will be challenging and require more
powerful telescopes than now employed, but are feasible in the 0 future.
Although expected event rates are low, we show that the wide variety of lines
of sight to globular clusters greatly enhances the ability to distinguish
between halo models using microlensing observations as compared to LMC/SMC
observations alone.Comment: 6 pages, uses mn.sty, 2 figure
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