1,649 research outputs found
The Standard Cosmological Model and CMB Anisotropies
This is a course on cosmic microwave background (CMB) anisotropies in the
standard cosmological model, designed for beginning graduate students and
advanced undergraduates. ``Standard cosmological model'' in this context means
a Universe dominated by some form of cold dark matter (CDM) with adiabatic
perturbations generated at some initial epoch, e.g., Inflation, and left to
evolve under gravity alone (which distinguishes it from defect models). The
course is primarily theoretical and concerned with the physics of CMB
anisotropies in this context and their relation to structure formation. Brief
presentations of the uniform Big Bang model and of the observed large--scale
structure of the Universe are given. The bulk of the course then focuses on the
evolution of small perturbations to the uniform model and on the generation of
temperature anisotropies in the CMB. The theoretical development is performed
in the (pseudo--)Newtonian gauge because it aids intuitive understanding by
providing a quick reference to classical (Newtonian) concepts. The fundamental
goal of the course is not to arrive at a highly exact nor exhaustive
calculation of the anisotropies, but rather to a good understanding of the
basic physics that goes into such calculations.Comment: Course given at the International School of Space Science: 3K
Cosmology, held in L'Aquila, Italy, September 1998. 44 pages with 4 figure
Measuring cluster masses with CMB lensing: a statistical approach
We present a method for measuring the masses of galaxy clusters using the
imprint of their gravitational lensing signal on the cosmic microwave
background (CMB) temperature anisotropies. The method first reconstructs the
projected gravitational potential with a quadratic estimator and then applies a
matched filter to extract cluster mass. The approach is well-suited for
statistical analyses that bin clusters according to other mass proxies. We find
that current experiments, such as Planck, the South Pole Telescope and the
Atacama Cosmology Telescope, can practically implement such a statistical
methodology, and that future experiments will reach sensitivities sufficient
for individual measurements of massive systems. As illustration, we use
simulations of Planck observations to demonstrate that it is possible to
constrain the mass scale of a set of 62 massive clusters with prior information
from X-ray observations, similar to the published Planck ESZ-XMM sample. We
examine the effect of the thermal (tSZ) and kinetic (kSZ) Sunyaev-Zeldovich
(SZ) signals, finding that the impact of the kSZ remains small in this context.
The stronger tSZ signal, however, must be actively removed from the CMB maps by
component separation techniques prior to reconstruction of the gravitational
potential. Our study of two such methods highlights the importance of broad
frequency coverage for this purpose. A companion paper presents application to
the Planck data on the ESZ-XMM sample.Comment: 9 pages, 5 figures, version accepted for publication in A&
Point Source Confusion in SZ Cluster Surveys
We examine the effect of point source confusion on cluster detection in
Sunyaev-Zel'dovich (SZ) surveys. A filter matched to the spatial and spectral
characteristics of the SZ signal optimally extracts clusters from the
astrophysical backgrounds. We calculate the expected confusion (point source
and primary cosmic microwave background [CMB]) noise through this filter and
quantify its effect on the detection threshold for both single and multiple
frequency surveys. Extrapolating current radio counts, we estimate that
confusion from sources below 100 microJy limits single-frequency surveys to
1-sigma detection thresholds of Y 3.10^{-6} arcmin^2 at 30 GHz and Y 10^{-5}
arcmin^2 at 15 GHz (for unresolved clusters in a 2 arcmin beam); these numbers
are highly uncertain, and an extrapolation with flatter counts leads to much
lower confusion limits. Bolometer surveys must contend with an important
population of infrared point sources. We find that a three-band matched filter
with 1 arcminute resolution (in each band) efficiently reduces confusion, but
does not eliminate it: residual point source and CMB fluctuations contribute
significantly the total filter noise. In this light, we find that a 3-band
filter with a low-frequency channel (e.g, 90+150+220 GHz) extracts clusters
more effectively than one with a high frequency channel (e.g, 150+220+300 GHz).Comment: Accepted for publication in Astronomy & Astrophysics; Updated grant
information in acknowledgement
SZ Surveys are Coming: What should we do?
Galaxy clusters furnish extremely rich information on the contents and
structure of our universe. The potential of galaxy cluster studies to constrain
dark energy, for example, motivates a number of ambitious cluster surveys.
Among these, surveys based on the Sunyaev-Zel'dovich (SZ) effect are
particularly powerful for their ability to cleanly select clusters out to
redshifts z>1. Now poised to begin surveying substantial areas of sky,
dedicated interferometers, bolometer cameras and the Planck satellite will soon
produce large cluster catalogs that will provide a precise measure of the
cosmic expansion rate over a range of redshifts and precipitate a new
understanding of structure and galaxy formation. I review the science potential
of these surveys and examine some issues of SZ cluster catalog construction.Comment: Review talk given at the Rencontres de Moriond, "Contents and
Structures of the Universe", La Thuile, Italy, March 18-25, 200
redMaPPer III: A Detailed Comparison of the Planck 2013 and SDSS DR8 RedMaPPer Cluster Catalogs
We compare the Planck Sunyaev-Zeldovich (SZ) cluster sample (PSZ1) to the
Sloan Digital Sky Survey (SDSS) redMaPPer catalog, finding that all Planck
clusters within the redMaPPer mask and within the redshift range probed by
redMaPPer are contained in the redMaPPer cluster catalog. These common clusters
define a tight scaling relation in the richness-SZ mass (--)
plane, with an intrinsic scatter in richness of . The corresponding intrinsic scatter in true cluster halo mass
at fixed richness is . The regularity of this scaling relation is
used to identify failures in both the redMaPPer and Planck cluster catalogs. Of
the 245 galaxy clusters in common, we identify three failures in redMaPPer and
36 failures in the PSZ1. Of these, at least 12 are due to clusters whose
optical counterpart was correctly identified in the PSZ1, but where the quoted
redshift for the optical counterpart in the external data base used in the PSZ1
was incorrect. The failure rates for redMaPPer and the PSZ1 are and
respectively, or 9.8% in the PSZ1 after subtracting the external data
base errors. We have further identified 5 PSZ1 sources that suffer from
projection effects (multiple rich systems along the line-of-sight of the SZ
detection) and 17 new high redshift () cluster candidates of
varying degrees of confidence. Should all of the high-redshift cluster
candidates identified here be confirmed, we will have tripled the number of
high redshift Planck clusters in the SDSS region. Our results highlight the
power of multi-wavelength observations to identify and characterize systematic
errors in galaxy cluster data sets, and clearly establish photometric data both
as a robust cluster finding method, and as an important part of defining clean
galaxy cluster samples.Comment: comments welcom
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