43 research outputs found
CMB Comptonization by Energetic Nonthermal Electrons in Clusters of Galaxies
Use of the Sunyaev-Zeldovich effect as a precise cosmological probe
necessitates a realistic assessment of all possible contributions to
Comptonization of the cosmic microwave background in clusters of galaxies. We
have calculated the additional intensity change due to various possible
populations of energetic electrons that have been proposed in order to account
for measurements of intracluster radio, nonthermal X-ray and (possibly also)
EUV emission. Our properly normalized estimates of (the highly model dependent
value of) the predicted intensity change due to these electrons is well below
and of the usual Sunyaev-Zeldovich effect due to electrons
in the hot gas in Coma and A2199, respectively. These levels constitute high
upper limits since they are based on energetic electron populations whose
energy densities are {\it comparable} to those of the thermal gas. The main
impact of nonthermal Comptonization is a shift of the crossover frequency
(where the thermal effect vanishes) to higher values. Such a shift would have
important consequences for our ability to measure cluster peculiar velocities
from the kinematic component of the Sunyaev-Zeldovich effect.Comment: 15 pages, 2 figure
The Cosmic Background Imager
The Cosmic Background Imager (CBI) is an instrument designed to make images of the cosmic microwave background radiation and to measure its statistical properties on angular scales from about 3 arc minutes to one degree (spherical harmonic scales from l Ë 4250 down to l Ë 400). The CBI is a 13-element interferometer mounted on a 6 meter platform operating in ten 1-GHz frequency bands from 26 GHz to 36 GHz. The instantaneous field of view of the instrument is 45 arcmin (FWHM) and its resolution ranges from 3 to 10 arcmin; larger fields can be imaged by mosaicing. At this frequency and resolution, the primary foreground is due to discrete extragalactic sources, which are monitored at the Owens Valley Radio Observatory and subtracted from the CBI visibility measurements.
The instrument has been making observations since late 1999 of both primordial CMB fluctuations and the Sunyaev-Zeldovich effect in clusters of galaxies from its site at an altitude of 5080 meters near San Pedro de Atacama, in northern Chile. Observations will continue until August 2001 or later. We present preliminary results from the first few months of observations
First Intrinsic Anisotropy Observations with the Cosmic Background Imager
We present the first results of observations of the intrinsic anisotropy of
the cosmic microwave background radiation with the Cosmic Background Imager
from a site at 5080 m altitude in northern Chile. Our observations show a sharp
decrease in C_l in the range l=400 - 1500. The broadband amplitudes we have
measured are deltaT(band) = 58.7 (-6.3, +7.7) microK for l = 603 (-166, +180)
and 29.7 (-4.2, +4.8) microK for l = 1190 (-224, +261), where these are
half-power widths in l. Such a decrease in power at high l is one of the
fundamental predictions of the standard cosmological model, and these are the
first observations which cover a broad enough l range to show this decrease in
a single experiment. The C_l we have measured enable us to place limits on the
density parameter, Omega(tot) = 0.7 (90% confidence).Comment: 5 pages including 2 figures. Corrected an error in the comparison
with Boomerang and Maxim
Preliminary Results from the Cosmic Background Imager
The Cosmic Background Imager (CBI) is a 13-element interferometer designed to
image intrinsic anisotropies in the cosmic microwave background (CMB) on
arcminute scales. A review of the capabilities of the instrument is presented,
together with a discussion of observations which have been taken over the past
9 months from the Atacama desert of Chile. We present preliminary
high-resolution mosaiced images of the CMB obtained from recent CBI data and
discuss topics which the CBI will address in the near future.Comment: 4 pp, 2 figures, submitted to Proc. 9th Marcel Grossman Mtg.
(electronic version
Evidence for Ordered Magnetic Fields in the Quasar Environment
At a distance of 20 pc from the purported supermassive black hole powering
quasars, temperatures and densities are inferred from optical observations to
be ~10**4 K and ~10**4 cm**-3. Here we present Very Long Baseline
Interferometry radio observations revealing organized magnetic fields on the
parsec scale in the hot plasma surrounding the quasar OQ172 (1442+101). These
magnetic fields rotate the plane of polarization of the radio emission coming
from the core and inner jet of the quasar. The derived rotation measure (RM) is
40,000 rad m**-2 in the rest frame of the quasar. Only 10 mas (a projected
distance of 68 pc) from the nucleus the jet absolute values of RM fall to less
than 100 rad m**-2.Comment: in press at ApJ Letters, 12 page LaTeX document includes 4 postscript
figure
The Sunyaev-Zeldovich effect in CMB-calibrated theories applied to the Cosmic Background Imager anisotropy power at l > 2000
We discuss the nature of the possible high-l excess in the Cosmic Microwave
Background (CMB) anisotropy power spectrum observed by the Cosmic Background
Imager (CBI). We probe the angular structure of the excess in the CBI deep
fields and investigate whether it could be due to the scattering of CMB photons
by hot electrons within clusters, the Sunyaev-Zeldovich (SZ) effect. We
estimate the density fluctuation parameters for amplitude, sigma_8, and shape,
Gamma, from CMB primary anisotropy data and other cosmological data. We use the
results of two separate hydrodynamical codes for Lambda-CDM cosmologies,
consistent with the allowed sigma_8 and Gamma values, to quantify the expected
contribution from the SZ effect to the bandpowers of the CBI experiment and
pass simulated SZ effect maps through our CBI analysis pipeline. The result is
very sensitive to the value of sigma_8, and is roughly consistent with the
observed power if sigma_8 ~ 1. We conclude that the CBI anomaly could be a
result of the SZ effect for the class of Lambda-CDM concordance models if
sigma_8 is in the upper range of values allowed by current CMB and Large Scale
Structure (LSS) data.Comment: Accepted by The Astrophysical Journal; 17 pages including 12 color
figures. v2 matches accepted version. Additional information at
http://www.astro.caltech.edu/~tjp/CBI
An Unbiased Measurement of H_0 through Cosmic Background Imager Observations of the Sunyaev-Zel'dovich Effect in Nearby Galaxy Clusters
We present H_0 results from Cosmic Background Imager (CBI) observations of the Sunyaev-Zel'dovich effect (SZE) in seven galaxy clusters, A85, A399, A401, A478, A754, A1651, and A2597. These observations are part of a program to study a complete, volume-limited sample of low-redshift (z < 0.1), X-ray-selected clusters. Our focus on nearby objects allows us to study a well-defined, orientation-unbiased sample, minimizing systematic errors due to cluster asphericity. We use density models derived from ROSAT imaging data and temperature measurements from ASCA and BeppoSAX spectral observations. We quantify in detail sources of error in our derivation of H_0, including calibration of the CBI data, density, and temperature models from the X-ray data, cosmic microwave background primary anisotropy fluctuations, and residuals from radio point source subtraction. From these seven clusters we obtain a result of H_0 = 67_(-18-6)^(+30+15) km s^(-1) Mpc^(-1) for an unweighted sample average. The respective quoted errors are random and systematic uncertainties at 68% confidence. The dominant source of error is confusion from intrinsic anisotropy fluctuations