408 research outputs found
High resolution CMB power spectrum from the complete ACBAR data set
In this paper, we present results from the complete set of cosmic microwave
background (CMB) radiation temperature anisotropy observations made with the
Arcminute Cosmology Bolometer Array Receiver (ACBAR) operating at 150 GHz. We
include new data from the final 2005 observing season, expanding the number of
detector-hours by 210% and the sky coverage by 490% over that used for the
previous ACBAR release. As a result, the band-power uncertainties have been
reduced by more than a factor of two on angular scales encompassing the third
to fifth acoustic peaks as well as the damping tail of the CMB power spectrum.
The calibration uncertainty has been reduced from 6% to 2.1% in temperature
through a direct comparison of the CMB anisotropy measured by ACBAR with that
of the dipole-calibrated WMAP5 experiment. The measured power spectrum is
consistent with a spatially flat, LambdaCDM cosmological model. We include the
effects of weak lensing in the power spectrum model computations and find that
this significantly improves the fits of the models to the combined ACBAR+WMAP5
power spectrum. The preferred strength of the lensing is consistent with
theoretical expectations. On fine angular scales, there is weak evidence (1.1
sigma) for excess power above the level expected from primary anisotropies. We
expect any excess power to be dominated by the combination of emission from
dusty protogalaxies and the Sunyaev-Zel'dovich effect (SZE). However, the
excess observed by ACBAR is significantly smaller than the excess power at ell
> 2000 reported by the CBI experiment operating at 30 GHz. Therefore, while it
is unlikely that the CBI excess has a primordial origin; the combined ACBAR and
CBI results are consistent with the source of the CBI excess being either the
SZE or radio source contamination.Comment: Submitted to ApJ; Changed to apply a WMAP5-based calibration. The
cosmological parameter estimation has been updated to include WMAP
Joint Elastic Side-Scattering Lidar and Raman Lidar Measurements of Aerosol Optical Properties in South East Colorado
We describe an experiment, located in south-east Colorado, USA, that measured
aerosol optical depth profiles using two Lidar techniques. Two independent
detectors measured scattered light from a vertical UV laser beam. One detector,
located at the laser site, measured light via the inelastic Raman
backscattering process. This is a common method used in atmospheric science for
measuring aerosol optical depth profiles. The other detector, located
approximately 40km distant, viewed the laser beam from the side. This detector
featured a 3.5m2 mirror and measured elastically scattered light in a bistatic
Lidar configuration following the method used at the Pierre Auger cosmic ray
observatory. The goal of this experiment was to assess and improve methods to
measure atmospheric clarity, specifically aerosol optical depth profiles, for
cosmic ray UV fluorescence detectors that use the atmosphere as a giant
calorimeter. The experiment collected data from September 2010 to July 2011
under varying conditions of aerosol loading. We describe the instruments and
techniques and compare the aerosol optical depth profiles measured by the Raman
and bistatic Lidar detectors.Comment: 34 pages, 16 figure
QUaD: A High-Resolution Cosmic Microwave Background Polarimeter
We describe the QUaD experiment, a millimeter-wavelength polarimeter designed
to observe the Cosmic Microwave Background (CMB) from a site at the South Pole.
The experiment comprises a 2.64 m Cassegrain telescope equipped with a
cryogenically cooled receiver containing an array of 62 polarization-sensitive
bolometers. The focal plane contains pixels at two different frequency bands,
100 GHz and 150 GHz, with angular resolutions of 5 arcmin and 3.5 arcmin,
respectively. The high angular resolution allows observation of CMB temperature
and polarization anisotropies over a wide range of scales. The instrument
commenced operation in early 2005 and collected science data during three
successive Austral winter seasons of observation.Comment: 23 pages, author list and text updated to reflect published versio
Galaxy clusters discovered with a Sunyaev-Zel'dovich effect survey
The South Pole Telescope (SPT) is conducting a Sunyaev-Zel'dovich (SZ) effect
survey over large areas of the southern sky, searching for massive galaxy
clusters to high redshift. In this preliminary study, we focus on a 40
square-degree area targeted by the Blanco Cosmology Survey (BCS), which is
centered roughly at right ascension 5h30m, declination -53 degrees. Over two
seasons of observations, this entire region has been mapped by the SPT at 95
GHz, 150 GHz, and 225 GHz. We report the four most significant SPT detections
of SZ clusters in this field, three of which were previously unknown and,
therefore, represent the first galaxy clusters discovered with an SZ survey.
The SZ clusters are detected as decrements with greater than 5-sigma
significance in the high-sensitivity 150 GHz SPT map. The SZ spectrum of these
sources is confirmed by detections of decrements at the corresponding locations
in the 95 GHz SPT map and non-detections at those locations in the 225 GHz SPT
map. Multiband optical images from the BCS survey demonstrate significant
concentrations of similarly colored galaxies at the positions of the SZ
detections. Photometric redshift estimates from the BCS data indicate that two
of the clusters lie at moderate redshift (z ~ 0.4) and two at high redshift (z
>~ 0.8). One of the SZ detections was previously identified as a galaxy cluster
using X-ray data from the ROSAT All-Sky Survey (RASS). Potential RASS
counterparts (not previously identified as clusters) are also found for two of
the new discoveries. These first four galaxy clusters are the most significant
SZ detections from a subset of the ongoing SPT survey. As such, they serve as a
demonstration that SZ surveys, and the SPT in particular, can be an effective
means for finding galaxy clusters.Comment: 11 pages, 3 figures, revised to match published version, uses
emulateap
SPIDER: a balloon-borne CMB polarimeter for large angular scales
We describe SPIDER, a balloon-borne instrument to map the polarization of the
millimeter-wave sky with degree angular resolution. Spider consists of six
monochromatic refracting telescopes, each illuminating a focal plane of
large-format antenna-coupled bolometer arrays. A total of 2,624 superconducting
transition-edge sensors are distributed among three observing bands centered at
90, 150, and 280 GHz. A cold half-wave plate at the aperture of each telescope
modulates the polarization of incoming light to control systematics. Spider's
first flight will be a 20-30-day Antarctic balloon campaign in December 2011.
This flight will map \sim8% of the sky to achieve unprecedented sensitivity to
the polarization signature of the gravitational wave background predicted by
inflationary cosmology. The Spider mission will also serve as a proving ground
for these detector technologies in preparation for a future satellite mission.Comment: 12 pages, 6 figures; as published in the conference proceedings for
SPIE Millimeter, Submillimeter, and Far-Infrared Detectors and
Instrumentation for Astronomy V (2010
A Millimeter-Wave Galactic Plane Survey With The BICEP Polarimeter
In addition to its potential to probe the Inflationary cosmological paradigm,
millimeter-wave polarimetry is a powerful tool for studying the Milky Way
galaxy's composition and magnetic field structure. Towards this end, presented
here are Stokes I, Q, and U maps of the Galactic plane from the millimeter-wave
polarimeter BICEP covering the Galactic longitude range 260 - 340 degrees in
three atmospheric transmission windows centered on 100, 150, and 220 GHz. The
maps sample an optical depth 1 < AV < 30, and are consistent with previous
characterizations of the Galactic millimeter-wave frequency spectrum and the
large-scale magnetic field structure permeating the interstellar medium.
Polarized emission is detected over the entire region within two degrees of the
Galactic plane and indicates that the large-scale magnetic field is oriented
parallel to the plane of the Galaxy. An observed trend of decreasing
polarization fraction with increasing total intensity rules out the simplest
model of a constant Galactic magnetic field throughout the Galaxy. Including
WMAP data in the analysis, the degree-scale frequency spectrum of Galactic
polarization fraction is plotted between 23 and 220 GHz for the first time. A
generally increasing trend of polarization fraction with electromagnetic
frequency is found, which varies from 0.5%-1.5%at frequencies below 50 GHz to
2.5%-3.5%above 90 GHz. The BICEP and WMAP data are fit to a two-component
(synchrotron and dust) model showing that the higher frequency BICEP data are
necessary to tightly constrain the amplitude and spectral index of Galactic
dust. Furthermore, the dust amplitude predicted by this two-component fit is
consistent with model predictions of dust emission in the BICEP bands
280 GHz Focal Plane Unit Design and Characterization for the SPIDER-2 Suborbital Polarimeter
We describe the construction and characterization of the 280 GHz bolometric
focal plane units (FPUs) to be deployed on the second flight of the
balloon-borne SPIDER instrument. These FPUs are vital to SPIDER's primary
science goal of detecting or placing an upper limit on the amplitude of the
primordial gravitational wave signature in the cosmic microwave background
(CMB) by constraining the B-mode contamination in the CMB from Galactic dust
emission. Each 280 GHz focal plane contains a 16 x 16 grid of corrugated
silicon feedhorns coupled to an array of aluminum-manganese transition-edge
sensor (TES) bolometers fabricated on 150 mm diameter substrates. In total, the
three 280 GHz FPUs contain 1,530 polarization sensitive bolometers (765 spatial
pixels) optimized for the low loading environment in flight and read out by
time-division SQUID multiplexing. In this paper we describe the mechanical,
thermal, and magnetic shielding architecture of the focal planes and present
cryogenic measurements which characterize yield and the uniformity of several
bolometer parameters. The assembled FPUs have high yields, with one array as
high as 95% including defects from wiring and readout. We demonstrate high
uniformity in device parameters, finding the median saturation power for each
TES array to be ~3 pW at 300 mK with a less than 6% variation across each array
at one standard deviation. These focal planes will be deployed alongside the 95
and 150 GHz telescopes in the SPIDER-2 instrument, slated to fly from McMurdo
Station in Antarctica in December 2018
The South Pole Telescope
A new 10 meter diameter telescope is being constructed for deployment at the
NSF South Pole research station. The telescope is designed for conducting
large-area millimeter and sub-millimeter wave surveys of faint, low contrast
emission, as required to map primary and secondary anisotropies in the cosmic
microwave background. To achieve the required sensitivity and resolution, the
telescope design employs an off-axis primary with a 10m diameter clear
aperture. The full aperture and the associated optics will have a combined
surface accuracy of better than 20 microns rms to allow precision operation in
the submillimeter atmospheric windows. The telescope will be surrounded with a
large reflecting ground screen to reduce sensitivity to thermal emission from
the ground and local interference. The optics of the telescope will support a
square degree field of view at 2mm wavelength and will feed a new 1000-element
micro-lithographed planar bolometric array with superconducting transition-edge
sensors and frequency-multiplexed readouts. The first key project will be to
conduct a survey over approximately 4000 degrees for galaxy clusters using the
Sunyaev-Zel'dovich Effect. This survey should find many thousands of clusters
with a mass selection criteria that is remarkably uniform with redshift. Armed
with redshifts obtained from optical and infrared follow-up observations, it is
expected that the survey will enable significant constraints to be placed on
the equation of state of the dark energy.Comment: Written prior to SPIE conference, June 21-25, 2004. 19 pages, 13
figures. Also available (with higher resolution figures) at
http://spt.uchicago.edu
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