35 research outputs found
Radio Sources from a 31 GHz Sky Survey with the Sunyaev-Zel'dovich Array
We present the first sample of 31-GHz selected sources to flux levels of 1
mJy. From late 2005 to mid 2007, the Sunyaev-Zel'dovich Array (SZA) observed
7.7 square degrees of the sky at 31 GHz to a median rms of 0.18 mJy/beam. We
identify 209 sources at greater than 5 sigma significance in the 31 GHz maps,
ranging in flux from 0.7 mJy to ~200 mJy. Archival NVSS data at 1.4 GHz and
observations at 5 GHz with the Very Large Array are used to characterize the
sources. We determine the maximum-likelihood integrated source count to be
N(>S) = (27.2 +- 2.5) deg^-2 x (S_mJy)^(-1.18 +- 0.12) over the flux range 0.7
- 15 mJy. This result is significantly higher than predictions based on 1.4-GHz
selected samples, a discrepancy which can be explained by a small shift in the
spectral index distribution for faint 1.4-GHz sources. From comparison with
previous measurements of sources within the central arcminute of massive
clusters, we derive an overdensity of 6.8 +- 4.4, relative to field sources.Comment: 13 pages, 5 figure
Cosmological Constraints from a 31 GHz Sky Survey with the Sunyaev-Zel'dovich Array
We present the results of a 6.1 square degree survey for clusters of galaxies
via their Sunyaev- Zel'dovich (SZ) effect at 31 GHz. From late 2005 to mid 2007
the Sunyaev-Zel'dovich Array (SZA) observed four fields of roughly 1.5 square
degrees each. One of the fields shows evidence for significant diffuse Galactic
emission, and we therefore restrict our analysis to the remaining 4.4 square
degrees. We estimate the cluster detectability for the survey using mock
observations of simulations of clusters of galaxies; and determine that, at
intermediate redshifts (z ~ 0.8), the survey is 50% complete to a limiting mass
(M200 rho mean) of ~ 6.0 x 10^14M_{solar}, with the mass limit decreasing at
higher redshifts. We detect no clusters at a significance greater than 5 times
the RMS noise level in the maps, and place an upper limit on \sigma_8, the
amplitude of mass density fluctuations on a scale of 8h^-1 Mpc, of 0.84 + 0.07
at 95% confidence, where the uncertainty reflects calibration and systematic
effects. This result is consistent with estimates from other cluster surveys
and CMB anisotropy experiments.Comment: 10 pages, 7 figures, 3 table
Observations of High-Redshift X-Ray Selected Clusters with the Sunyaev-Zel'dovich Array
We report measurements of the Sunyaev-Zel'dovich (SZ) effect in three high-redshift (0.89 ≤ z ≤ 1.03), X-ray selected galaxy clusters. The observations were obtained at 30 GHz during the commissioning period of a new, eight-element interferometer—the Sunyaev-Zel'dovich Array (SZA)—built for dedicated SZ effect observations. The SZA observations are sensitive to angular scales larger than those subtended by the virial radii of the clusters. Assuming isothermality and hydrostatic equilibrium for the intracluster medium and gas-mass fractions consistent with those for clusters at moderate redshift, we calculate electron temperatures, gas masses, and total cluster masses from the SZ data. The SZ-derived masses, integrated approximately to the virial radii, are 1.9^(+0.5)_(-0.4) × 10^(14) M_☉ for Cl J1415.1+3612, 3.4^(+0.6)_(-0.5) × 10^(14) M_☉ for Cl J1429.0+4241, and 7.2^(+1.3)_(-0.9) × 10^(14) M_☉ for Cl J1226.9+3332. The SZ-derived quantities are in good agreement with the cluster properties derived from X-ray measurements
Absolute polarization angle calibration using polarized diffuse Galactic emission observed by BICEP
We present a method of cross-calibrating the polarization angle of a
polarimeter using BICEP Galactic observations. \bicep\ was a ground based
experiment using an array of 49 pairs of polarization sensitive bolometers
observing from the geographic South Pole at 100 and 150 GHz. The BICEP
polarimeter is calibrated to +/-0.01 in cross-polarization and less than +/-0.7
degrees in absolute polarization orientation. BICEP observed the temperature
and polarization of the Galactic plane (R.A= 100 degrees ~ 270 degrees and Dec.
= -67 degrees ~ -48 degrees). We show that the statistical error in the 100 GHz
BICEP Galaxy map can constrain the polarization angle offset of WMAP Wband to
0.6 degrees +\- 1.4 degrees. The expected 1 sigma errors on the polarization
angle cross-calibration for Planck or EPIC are 1.3 degrees and 0.3 degrees at
100 and 150 GHz, respectively. We also discuss the expected improvement of the
BICEP Galactic field observations with forthcoming BICEP2 and Keck
observations.Comment: 13 pages, 10 figures and 2 tables. To appear in Proceedings of SPIE
Astronomical Telescopes and Instrumentation 201
LoCuSS: A Comparison of Sunyaev-Zel'dovich Effect and Gravitational Lensing Measurements of Galaxy Clusters
We present the first measurement of the relationship between the
Sunyaev-Zel'dovich effect signal and the mass of galaxy clusters that uses
gravitational lensing to measure cluster mass, based on 14 X-ray luminous
clusters at z~0.2 from the Local Cluster Substructure Survey. We measure the
integrated Compton y-parameter, Y, and total projected mass of the clusters
(M_GL) within a projected clustercentric radius of 350 kpc, corresponding to
mean overdensities of 4000-8000 relative to the critical density. We find
self-similar scaling between M_GL and Y, with a scatter in mass at fixed Y of
32%. This scatter exceeds that predicted from numerical cluster simulations,
however, it is smaller than comparable measurements of the scatter in mass at
fixed T_X. We also find no evidence of segregation in Y between disturbed and
undisturbed clusters, as had been seen with T_X on the same physical scales. We
compare our scaling relation to the Bonamente et al. relation based on mass
measurements that assume hydrostatic equilibrium, finding no evidence for a
hydrostatic mass bias in cluster cores (M_GL = 0.98+/-0.13 M_HSE), consistent
with both predictions from numerical simulations and lensing/X-ray-based
measurements of mass-observable scaling relations at larger radii. Overall our
results suggest that the Sunyaev-Zel'dovich effect may be less sensitive than
X-ray observations to the details of cluster physics in cluster cores.Comment: Minor changes to match published version: 2009 ApJL 701:114-11
Joint analysis of X-ray and Sunyaev Zel'dovich observations of galaxy clusters using an analytic model of the intra-cluster medium
We perform a joint analysis of X-ray and Sunyaev Zel'dovich (SZ) effect data
using an analytic model that describes the gas properties of galaxy clusters.
The joint analysis allows the measurement of the cluster gas mass fraction
profile and Hubble constant independent of cosmological parameters. Weak
cosmological priors are used to calculate the overdensity radius within which
the gas mass fractions are reported. Such an analysis can provide direct
constraints on the evolution of the cluster gas mass fraction with redshift. We
validate the model and the joint analysis on high signal-to-noise data from the
Chandra X-ray Observatory and the Sunyaev-Zel'dovich Array for two clusters,
Abell 2631 and Abell 2204.Comment: ApJ in pres
Sunyaev Zel'dovich Effect Observations of Strong Lensing Galaxy Clusters: Probing the Over-Concentration Problem
We have measured the Sunyaev Zel'dovich (SZ) effect for a sample of ten
strong lensing selected galaxy clusters using the Sunyaev Zel'dovich Array
(SZA). The SZA is sensitive to structures on spatial scales of a few
arcminutes, while the strong lensing mass modeling constrains the mass at small
scales (typically < 30"). Combining the two provides information about the
projected concentrations of the strong lensing clusters. The Einstein radii we
measure are twice as large as expected given the masses inferred from SZ
scaling relations. A Monte Carlo simulation indicates that a sample randomly
drawn from the expected distribution would have a larger median Einstein radius
than the observed clusters about 3% of the time. The implied overconcentration
has been noted in previous studies with smaller samples of lensing clusters. It
persists for this sample, with the caveat that this could result from a
systematic effect such as if the gas fractions of the strong lensing clusters
are substantially below what is expected.Comment: submitte
Comparison of Pressure Profiles of Massive Relaxed Galaxy Clusters using Sunyaev-Zel'dovich and X-ray Data
We present Sunyaev-Zel'dovich (SZ) effect observations of a sample of 25
massive relaxed galaxy clusters observed with the Sunyaev-Zel'dovich Array
(SZA), an 8-element interferometer that is part of the Combined Array for
Research in Millimeter-wave Astronomy (CARMA). We perform an analysis of new
SZA data and archival Chandra observations of this sample to investigate the
integrated pressure -- a proxy for cluster mass -- determined from X-ray and SZ
observations, two independent probes of the intra-cluster medium. This analysis
makes use of a model for the intra-cluster medium introduced by Bulbul (2010)
which can be applied simultaneously to SZ and X-ray data. With this model, we
estimate the pressure profile for each cluster using a joint analysis of the SZ
and X-ray data, and using the SZ data alone. We find that the integrated
pressures measured from X-ray and SZ data are consistent. This conclusion is in
agreement with recent results obtained using WMAP and Planck data, confirming
that SZ and X-ray observations of massive clusters detect the same amount of
thermal pressure from the intra-cluster medium. To test for possible biases
introduced by our choice of model, we also fit the SZ data using the universal
pressure profile proposed by Arnaud (2010), and find consistency between the
two models out to r500 in the pressure profiles and integrated pressures.Comment: Accepted for New Journal of Physics, Focus Issue on Galaxy Cluster
LoCuSS: The Sunyaev-Zel'dovich Effect and Weak Lensing Mass Scaling Relation
We present the first weak-lensing-based scaling relation between galaxy
cluster mass, M_wl, and integrated Compton parameter Y_sph. Observations of 18
galaxy clusters at z~0.2 were obtained with the Subaru 8.2-m telescope and the
Sunyaev-Zel'dovich Array. The M_wl-Y_sph scaling relations, measured at
Delta=500, 1000, and 2500 rho_c, are consistent in slope and normalization with
previous results derived under the assumption of hydrostatic equilibrium (HSE).
We find an intrinsic scatter in M_wl at fixed Y_sph of 20%, larger than both
previous measurements of M_HSE-Y_sph scatter as well as the scatter in true
mass at fixed Y_sph found in simulations. Moreover, the scatter in our
lensing-based scaling relations is morphology dependent, with 30-40% larger
M_wl for undisturbed compared to disturbed clusters at the same Y_sph at r_500.
Further examination suggests that the segregation may be explained by the
inability of our spherical lens models to faithfully describe the
three-dimensional structure of the clusters, in particular, the structure along
the line-of-sight. We find that the ellipticity of the brightest cluster
galaxy, a proxy for halo orientation, correlates well with the offset in mass
from the mean scaling relation, which supports this picture. This provides
empirical evidence that line-of-sight projection effects are an important
systematic uncertainty in lensing-based scaling relations.Comment: Accepted versio
A Measurement of Arcminute Anisotropy in the Cosmic Microwave Background with the Sunyaev-Zel'dovich Array
We present 30 GHz measurements of the angular power spectrum of the cosmic
microwave background (CMB) obtained with the Sunyaev-Zel'dovich Array. The
measurements are sensitive to arcminute angular scales, where secondary
anisotropy from the Sunyaev-Zel'dovich effect (SZE) is expected to dominate.
For a broad bin centered at multipole 4066 we find 67+77-50 uK^2, of which
26+/-5 uK^2 is the expected contribution from primary CMB anisotropy and
80+/-54 uK^2 is the expected contribution from undetected radio sources. These
results imply an upper limit of 155 uK^2 (95% CL) on the secondary contribution
to the anisotropy in our maps. This level of SZE anisotropy power is consistent
with expectations based on recent determinations of the normalization of the
matter power spectrum, i.e., sigma_8~0.8.Comment: ApJ, 713, 82-89, (2010