279 research outputs found
Final Results from the BIMA CMB Anisotropy Survey and Search for Signature of the SZ effect
We report the final results of our study of the cosmic microwave background
(CMB) with the BIMA array. Over 1000 hours of observation were dedicated to
this project exploring CMB anisotropy on scales between 1' and 2' in eighteen
6.6' FWHM fields. In the analysis of the CMB power spectrum, the visibility
data is divided into two bins corresponding to different angular scales.
Modeling the observed excess power as a flat band of average multipole ell=
5237, we find Delta T_1^2=220_{-120}^{+140} muK^2 at 68% confidence and Delta
T_1^2 >0 muK^2 with 94.7% confidence. In a second band with average multipole
of ell = 8748, we find Delta T_2^2 consistent with zero, and an upper limit 880
muK^2 at 95% confidence. An extensive series of tests and supplemental
observations with the VLA provide strong evidence against systematic errors or
radio point sources being the source of the observed excess power. The dominant
source of anisotropy on these scales is expected to arise from the
Sunyaev-Zel'dovich (SZ) effect in a population of distant galaxy clusters. If
the excess power is due to the SZ effect, we can place constraints on the
normalization of the matter power spectrum sigma_8 = 1.03^{+0.20}_{-0.29} at
68% confidence. The distribution of pixel fluxes in the BIMA images are found
to be consistent with simulated observations of the expected SZ background and
rule out instrumental noise or radio sources as the source of the observed
excess power with similar confidence to the detection of excess power.
Follow-up optical observations to search for galaxy over-densities
anti-correlated with flux in the BIMA images, as might be expected from the SZ
effect, proved to be inconclusive.Comment: Accepted by ApJ, 17 page
Shelterbelts: a row of trees or the next best thing to mitigating GHGs on prairie landscapes
Non-Peer Reviewe
Fast-Neutron Activation of Long-Lived Isotopes in Enriched Ge
We measured the production of \nuc{57}{Co}, \nuc{54}{Mn}, \nuc{68}{Ge},
\nuc{65}{Zn}, and \nuc{60}{Co} in a sample of Ge enriched in isotope 76 due to
high-energy neutron interactions. These isotopes, especially \nuc{68}{Ge}, are
critical in understanding background in Ge detectors used for double-beta decay
experiments. They are produced by cosmogenic-neutron interactions in the
detectors while they reside on the Earth's surface. These production rates were
measured at neutron energies of a few hundred MeV. We compared the measured
production to that predicted by cross-section calculations based on CEM03.02.
The cross section calculations over-predict our measurements by approximately a
factor of three depending on isotope. We then use the measured cosmic-ray
neutron flux, our measurements, and the CEM03.02 cross sections to predict the
cosmogenic production rate of these isotopes. The uncertainty in extrapolating
the cross section model to higher energies dominates the total uncertainty in
the cosmogenic production rate.Comment: Revised after feedback and further work on extrapolating cross
sections to higher energies in order to estimate cosmic production rates.
Also a numerical error was found and fixed in the estimate of the Co-57
production rat
A Preliminary Detection of Arcminute Scale Cosmic Microwave Background Anisotropy with the BIMA Array
We have used the Berkeley-Illinois-Maryland-Association (BIMA) array
outfitted with sensitive cm-wave receivers to expand our search for arcminute
scale anisotropy of the Cosmic Microwave Background (CMB). The interferometer
was placed in a compact configuration toobtain high brightness sensitivity on
arcminute scales over its 6.6' FWHM field of view. The sensitivity of this
experiment to flat band power peaks at a multipole of l=5530 which corresponds
to an angular scale of ~2'. We present the analysis of a total of 470 hours of
on-source integration time on eleven independent fields which were selected
based on their low IR contrast and lack of bright radio sources. Applying a
Bayesian analysis to the visibility data, we find CMB anisotropy flat band
power Q_flat = 6.1(+2.8/-4.8) microKelvin at 68% confidence. The confidence of
a non- zero signal is 76% and we find an upper limit of Q_flat < 12.4
microKelvin at 95% confidence. We have supplemented our BIMA observations with
concurrent observations at 4.8 GHz with the VLA to search for and remove point
sources. We find the point sources make an insignificant contribution to the
observed anisotropy.Comment: 8 pages, 2 figures, submitted to Astrophysical Journa
Determination of the Cosmic Distance Scale from Sunyaev-Zel'dovich Effect and Chandra X-ray Measurements of High Redshift Galaxy Clusters
We determine the distance to 38 clusters of galaxies in the redshift range
0.14 < z < 0.89 using X-ray data from Chandra and Sunyaev-Zeldovich Effect data
from the Owens Valley Radio Observatory and the Berkeley-Illinois-Maryland
Association interferometric arrays. The cluster plasma and dark matter
distributions are analyzed using a hydrostatic equilibrium model that accounts
for radial variations in density, temperature and abundance, and the
statistical and systematic errors of this method are quantified. The analysis
is performed via a Markov chain Monte Carlo technique that provides
simultaneous estimation of all model parameters. We measure a Hubble constant
of 76.9 +3.9-3.4 +10.0-8.0 km/s/Mpc (statistical followed by systematic
uncertainty at 68% confidence) for an Omega_M=0.3, Omega_Lambda=0.7 cosmology.
We also analyze the data using an isothermal beta model that does not invoke
the hydrostatic equilibrium assumption, and find H_0=73.7 +4.6-3.8 +9.5-7.6
km/s/Mpc; to avoid effects from cool cores in clusters, we repeated this
analysis excluding the central 100 kpc from the X-ray data, and find H_0=77.6
+4.8-4.3 +10.1-8.2 km/s/Mpc. The consistency between the models illustrates the
relative insensitivity of SZE/X-ray determinations of H_0 to the details of the
cluster model. Our determination of the Hubble parameter in the distant
universe agrees with the recent measurement from the Hubble Space Telescope key
project that probes the nearby universe.Comment: ApJ submitted (revised version
X-ray and Sunyaev-Zel'dovich Effect Measurements of the Gas Mass Fraction in Galaxy Clusters
We present gas mass fractions of 38 massive galaxy clusters spanning
redshifts from 0.14 to 0.89, derived from Chandra X-ray data and OVRO/BIMA
interferometric Sunyaev-Zel'dovich Effect measurements. We use three models for
the gas distribution: (1) an isothermal beta-model fit jointly to the X-ray
data at radii beyond 100 kpc and to all of the SZE data,(2) a non-isothermal
double beta-model fit jointly to all of the X-ray and SZE data, and (3) an
isothermal beta-model fit only to the SZE spatial data. We show that the simple
isothermal model well characterizes the intracluster medium (ICM) outside of
the cluster core in clusters with a wide range of morphological properties. The
X-ray and SZE determinations of mean gas mass fractions for the 100 kpc-cut
isothermal beta-model are fgas(X-ray)=0.110 +0.003-0.003 +0.006-0.018 and
fgas(SZE)=0.116 +0.005-0.005 +0.009-0.026, where uncertainties are statistical
followed by systematic at 68% confidence. For the non-isothermal double
beta-model, fgas(X-ray)=0.119 +0.003-0.003 +0.007-0.014 and fgas(SZE)=0.121
+0.005-0.005 +0.009-0.016. For the SZE-only model, fgas(SZE)=0.120 +0.009-0.009
+0.009-0.027. Our results indicate that the ratio of the gas mass fraction
within r2500 to the cosmic baryon fraction is 0.68 +0.10-0.16 where the range
includes statistical and systematic uncertainties. By assuming that cluster gas
mass fractions are independent of redshift, we find that the results are in
agreement with standard LambdaCDM cosmology and are inconsistent with a flat
matter dominated universe.Comment: ApJ, submitted. 47 pages, 5 figures, 8 table
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