579 research outputs found
Galaxy Clusters Discovered via the Sunyaev-Zel'dovich Effect in the 2500-Square-Degree SPT-SZ Survey
We present a catalog of galaxy clusters selected via their Sunyaev-Zel'dovich (SZ) effect signature from 2500 deg^2 of South Pole Telescope (SPT) data. This work represents the complete sample of clusters detected at high significance in the 2500 deg^2 SPT-SZ survey, which was completed in 2011. A total of 677 (409) cluster candidates are identified above a signal-to-noise threshold of ξ = 4.5 (5.0). Ground- and space-based optical and near-infrared (NIR) imaging confirms overdensities of similarly colored galaxies in the direction of 516 (or 76%) of the ξ > 4.5 candidates and 387 (or 95%) of the ξ > 5 candidates; the measured purity is consistent with expectations from simulations. Of these confirmed clusters, 415 were first identified in SPT data, including 251 new discoveries reported in this work. We estimate photometric redshifts for all candidates with identified optical and/or NIR counterparts; we additionally report redshifts derived from spectroscopic observations for 141 of these systems. The mass threshold of the catalog is roughly independent of redshift above z ~ 0.25 leading to a sample of massive clusters that extends to high redshift. The median mass of the sample is M_(500c(ρcrit)) ~ 3.5 x 10^(14)M_☉ h_(70)^(-1), the median redshift is z_(med) = 0.55, and the highest-redshift systems are at z > 1.4. The combination of large redshift extent, clean selection, and high typical mass makes this cluster sample of particular interest for cosmological analyses and studies of cluster formation and evolution
The Robinson Gravitational Wave Background Telescope (BICEP): a bolometric large angular scale CMB polarimeter
The Robinson Telescope (BICEP) is a ground-based millimeter-wave bolometric
array designed to study the polarization of the cosmic microwave background
radiation (CMB) and galactic foreground emission. Such measurements probe the
energy scale of the inflationary epoch, tighten constraints on cosmological
parameters, and verify our current understanding of CMB physics. Robinson
consists of a 250-mm aperture refractive telescope that provides an
instantaneous field-of-view of 17 degrees with angular resolution of 55 and 37
arcminutes at 100 GHz and 150 GHz, respectively. Forty-nine pair of
polarization-sensitive bolometers are cooled to 250 mK using a 4He/3He/3He
sorption fridge system, and coupled to incoming radiation via corrugated feed
horns. The all-refractive optics is cooled to 4 K to minimize polarization
systematics and instrument loading. The fully steerable 3-axis mount is capable
of continuous boresight rotation or azimuth scanning at speeds up to 5 deg/s.
Robinson has begun its first season of observation at the South Pole. Given the
measured performance of the instrument along with the excellent observing
environment, Robinson will measure the E-mode polarization with high
sensitivity, and probe for the B-modes to unprecedented depths. In this paper
we discuss aspects of the instrument design and their scientific motivations,
scanning and operational strategies, and the results of initial testing and
observations.Comment: 18 pages, 11 figures. To appear in Millimeter and Submillimeter
Detectors and Instrumentation for Astronomy III, Proceedings of SPIE, 6275,
200
Consistency of cosmic microwave background temperature measurements in three frequency bands in the 2500-square-degree SPT-SZ survey
We present an internal consistency test of South Pole Telescope (SPT)
measurements of the cosmic microwave background (CMB) temperature anisotropy
using three-band data from the SPT-SZ survey. These measurements are made from
observations of ~2500 deg^2 of sky in three frequency bands centered at 95,
150, and 220 GHz. We combine the information from these three bands into six
semi-independent estimates of the CMB power spectrum (three single-frequency
power spectra and three cross-frequency spectra) over the multipole range 650 <
l < 3000. We subtract an estimate of foreground power from each power spectrum
and evaluate the consistency among the resulting CMB-only spectra. We determine
that the six foreground-cleaned power spectra are consistent with the null
hypothesis, in which the six cleaned spectra contain only CMB power and noise.
A fit of the data to this model results in a chi-squared value of 236.3 for 235
degrees of freedom, and the probability to exceed this chi-squared value is
46%.Comment: 21 pages, 4 figures, current version matches version published in
JCA
SPIDER: a new balloon-borne experiment to measure CMB polarization on large angular scales
We describe SPIDER, a novel balloon-borne experiment designed to measure the polarization of the Cosmic Microwave Background (CMB) on large angular scales. The primary goal of SPIDER is to detect the faint signature of inflationary gravitational waves in the CMB polarization. The payload consists of six telescopes, each operating in a single frequency band and cooled to 4 K by a common LN/LHe cryostat. The primary optic for each telescope is a 25 cm diameter lens cooled to 4 K. Each telescope feeds an array of antenna coupled, polarization sensitive sub-Kelvin bolometers that covers a 20 degree diameter FOV with diffraction limited resolution. The six focal planes span 70 to 300 GHz in a manner optimized to separate polarized galactic emission from CMB polarization, and together contain over 2300 detectors. Polarization modulation is achieved by rotating a cryogenic half-wave plate in front of the primary optic of each telescope. The cryogenic system is designed for 30 days of operation. Observations will be conducted during the night portions of a mid-latitude, long duration balloon flight which will circumnavigate the globe from Australia. By spinning the payload at 1 rpm with the six telescopes fixed in elevation, SPIDER will map approximately half of the sky at each frequency on each night of the flight
Embodied imitation-enhanced reinforcement learning in multi-agent systems
Imitation is an example of social learning in which an individual observes and copies another's actions. This paper presents a new method for using imitation as a way of enhancing the learning speed of individual agents that employ a well-known reinforcement learning algorithm, namely Q-learning. Compared with other research that uses imitation with reinforcement learning, our method uses imitation of purely observed behaviours to enhance learning, with no internal state access or sharing of experiences between agents. The paper evaluates our imitation-enhanced reinforcement learning approach in both simulation and with real robots in continuous space. Both simulation and real robot experimental results show that the learning speed of the group is improved. © The Author(s) 2013
A Comparison of Maps and Power Spectra Determined from South Pole Telescope and Planck Data
We study the consistency of 150 GHz data from the South Pole Telescope (SPT)
and 143 GHz data from the Planck satellite over the patch of sky covered by the
SPT-SZ survey. We first visually compare the maps and find that the residuals
appear consistent with noise after accounting for differences in angular
resolution and filtering. We then calculate (1) the cross-spectrum between two
independent halves of SPT data, (2) the cross-spectrum between two independent
halves of Planck data, and (3) the cross-spectrum between SPT and Planck data.
We find the three cross-spectra are well-fit (PTE = 0.30) by the null
hypothesis in which both experiments have measured the same sky map up to a
single free calibration parameter---i.e., we find no evidence for systematic
errors in either data set. As a by-product, we improve the precision of the SPT
calibration by nearly an order of magnitude, from 2.6% to 0.3% in power.
Finally, we compare all three cross-spectra to the full-sky Planck power
spectrum and find marginal evidence for differences between the power spectra
from the SPT-SZ footprint and the full sky. We model these differences as a
power law in spherical harmonic multipole number. The best-fit value of this
tilt is consistent among the three cross-spectra in the SPT-SZ footprint,
implying that the source of this tilt is a sample variance fluctuation in the
SPT-SZ region relative to the full sky. The consistency of cosmological
parameters derived from these datasets is discussed in a companion paper.Comment: 15 pages, 9 figures. Published in The Astrophysical Journal. Current
arxiv version matches published versio
A Comparison of Cosmological Parameters Determined from CMB Temperature Power Spectra from the South Pole Telescope and the Planck Satellite
The Planck cosmic microwave background (CMB) temperature data are best fit
with a LCDM model that is in mild tension with constraints from other
cosmological probes. The South Pole Telescope (SPT) 2540 SPT-SZ
survey offers measurements on sub-degree angular scales (multipoles ) with sufficient precision to use as an independent check of
the Planck data. Here we build on the recent joint analysis of the SPT-SZ and
Planck data in \citet{hou17} by comparing LCDM parameter estimates using the
temperature power spectrum from both data sets in the SPT-SZ survey region. We
also restrict the multipole range used in parameter fitting to focus on modes
measured well by both SPT and Planck, thereby greatly reducing sample variance
as a driver of parameter differences and creating a stringent test for
systematic errors. We find no evidence of systematic errors from such tests.
When we expand the maximum multipole of SPT data used, we see low-significance
shifts in the angular scale of the sound horizon and the physical baryon and
cold dark matter densities, with a resulting trend to higher Hubble constant.
When we compare SPT and Planck data on the SPT-SZ sky patch to Planck full-sky
data but keep the multipole range restricted, we find differences in the
parameters and . We perform further checks, investigating
instrumental effects and modeling assumptions, and we find no evidence that the
effects investigated are responsible for any of the parameter shifts. Taken
together, these tests reveal no evidence for systematic errors in SPT or Planck
data in the overlapping sky coverage and multipole range and, at most, weak
evidence for a breakdown of LCDM or systematic errors influencing either the
Planck data outside the SPT-SZ survey area or the SPT data at .Comment: 14 pages, 7 figures. Updated 1 figure and expanded on the reasoning
for fixing the affect of lensing on the power spectrum instead of varying
Alen
A Measurement of the Cosmic Microwave Background Damping Tail from the 2500-square-degree SPT-SZ survey
We present a measurement of the cosmic microwave background (CMB) temperature
power spectrum using data from the recently completed South Pole Telescope
Sunyaev-Zel'dovich (SPT-SZ) survey. This measurement is made from observations
of 2540 deg of sky with arcminute resolution at GHz, and improves
upon previous measurements using the SPT by tripling the sky area. We report
CMB temperature anisotropy power over the multipole range . We
fit the SPT bandpowers, combined with the seven-year Wilkinson Microwave
Anisotropy Probe (WMAP7) data, with a six-parameter LCDM cosmological model and
find that the two datasets are consistent and well fit by the model. Adding SPT
measurements significantly improves LCDM parameter constraints; in particular,
the constraint on tightens by a factor of 2.7. The impact of
gravitational lensing is detected at , the most significant
detection to date. This sensitivity of the SPT+WMAP7 data to lensing by
large-scale structure at low redshifts allows us to constrain the mean
curvature of the observable universe with CMB data alone to be
. Using the SPT+WMAP7 data, we measure the
spectral index of scalar fluctuations to be in the LCDM
model, a preference for a scale-dependent spectrum with .
The SPT measurement of the CMB damping tail helps break the degeneracy that
exists between the tensor-to-scalar ratio and in large-scale CMB
measurements, leading to an upper limit of (95%,C.L.) in the LCDM+
model. Adding low-redshift measurements of the Hubble constant () and the
baryon acoustic oscillation (BAO) feature to the SPT+WMAP7 data leads to
further improvements. The combination of SPT+WMAP7++BAO constrains
in the LCDM model, a detection of , ... [abridged]Comment: 21 pages, 10 figures. Replaced with version accepted by ApJ. Data
products are available at http://pole.uchicago.edu/public/data/story12
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