261 research outputs found
Visualizing probabilistic models: Intensive Principal Component Analysis
Unsupervised learning makes manifest the underlying structure of data without
curated training and specific problem definitions. However, the inference of
relationships between data points is frustrated by the `curse of
dimensionality' in high-dimensions. Inspired by replica theory from statistical
mechanics, we consider replicas of the system to tune the dimensionality and
take the limit as the number of replicas goes to zero. The result is the
intensive embedding, which is not only isometric (preserving local distances)
but allows global structure to be more transparently visualized. We develop the
Intensive Principal Component Analysis (InPCA) and demonstrate clear
improvements in visualizations of the Ising model of magnetic spins, a neural
network, and the dark energy cold dark matter ({\Lambda}CDM) model as applied
to the Cosmic Microwave Background.Comment: 6 pages, 5 figure
Southern Cosmology Survey III: QSO's from Combined GALEX and Optical Photometry
We present catalogs of QSO candidates selected using photometry from GALEX
combined with SDSS in the Stripe 82 region and Blanco Cosmology Survey (BCS)
near declination -55 degrees. The SDSS region contains ~700 objects with
magnitude i < 20 and ~3600 objects with i < 21.5 in a ~60 square degree sky
region, while the BCS region contains ~280 objects with magnitude i < 20 and
~2000 objects with i < 21.5 for a 11 square degree sky region that is being
observed by three current microwave Sunyaev-Zeldovich surveys. Our QSO catalog
is the first one in the BCS region. Deep GALEX exposures (~2000 seconds in FUV
and NUV, except in three fields) provide high signal-to-noise photometry in the
GALEX bands (FUV, NUV < 24.5 mag). From this data, we select QSO candidates
using only GALEX and optical r-band photometry, using the method given by Atlee
and Gould (2008). In the Stripe 82 field, 60% (30%) of the GALEX selected QSO's
with optical magnitude i<20 (i<21.5) also appear in the Richards et al. (2008)
QSO catalog constructed using 5-band optical SDSS photometry. Comparison with
the same catalog by Richards et al. shows that the completeness of the sample
is approximately 40%(25%). However, for regions of the sky with very low dust
extinction, like the BCS 23hr field and the Stripe 82 between 0 and 10 degrees
in RA, our completeness is close to 95%, demonstrating that deep GALEX
observations are almost as efficient as multi-wavelength observations at
finding QSO's. GALEX observations thus provide a viable alternate route to QSO
catalogs in sky regions where u-band optical photometry is not available. The
full catalog is available at http://www.ice.csic.es/personal/jimenez/PHOTOZComment: Submitted to ApJ
Improving Photometric Redshifts using GALEX Observations for the SDSS Stripe 82 and the Next Generation of SZ Cluster Surveys
Four large-area Sunyaev-Zeldovich (SZ) experiments -- APEX-SZ, SPT, ACT, and
Planck -- promise to detect clusters of galaxies through the distortion of
Cosmic Microwave Background photons by hot (> 10^6 K) cluster gas (the SZ
effect) over thousands of square degrees. A large observational follow-up
effort to obtain redshifts for these SZ-detected clusters is under way. Given
the large area covered by these surveys, most of the redshifts will be obtained
via the photometric redshift (photo-z) technique. Here we demonstrate, in an
application using ~3000 SDSS stripe 82 galaxies with r<20, how the addition of
GALEX photometry (FUV, NUV) greatly improves the photometric redshifts of
galaxies obtained with optical griz or ugriz photometry. In the case where
large spectroscopic training sets are available, empirical neural-network-based
techniques (e.g., ANNz) can yield a photo-z scatter of . If large spectroscopic training sets are not available, the addition of
GALEX data makes possible the use simple maximum likelihood techniques, without
resorting to Bayesian priors, and obtains , accuracy that
approaches the accuracy obtained using spectroscopic training of neural
networks on ugriz observations. This improvement is especially notable for blue
galaxies. To achieve these results, we have developed a new set of high
resolution spectral templates based on physical information about the star
formation history of galaxies. We envision these templates to be useful for the
next generation of photo-z applications. We make our spectral templates and new
photo-z catalogs available to the community at
http://www.ice.csic.es/personal/jimenez/PHOTOZ .Comment: 10 pages, 8 figure
Corrugated Silicon Platelet Feed Horn Array for CMB Polarimetry at 150 GHz
Next generation cosmic microwave background (CMB) polarization anisotropy
measurements will feature focal plane arrays with more than 600 millimeter-wave
detectors. We make use of high-resolution photolithography and wafer-scale etch
tools to build planar arrays of corrugated platelet feeds in silicon with
highly symmetric beams, low cross-polarization and low side lobes. A compact
Au-plated corrugated Si feed designed for 150 GHz operation exhibited
performance equivalent to that of electroformed feeds: ~-0.2 dB insertion loss,
<-20 dB return loss from 120 GHz to 170 GHz, <-25 dB side lobes and <-23 dB
cross-polarization. We are currently fabricating a 50 mm diameter array with 84
horns consisting of 33 Si platelets as a prototype for the SPTpol and ACTpol
telescopes. Our fabrication facilities permit arrays up to 150 mm in diameter.Comment: 12 pages; SPIE proceedings for Millimeter, Submillimeter, and
Far-Infrared Detectors and Instrumentation for Astronomy V (Conference 7741,
June 2010, San Diego, CA, USA
Infrared Dielectric Properties of Low-stress Silicon Nitride
Silicon nitride thin films play an important role in the realization of sensors, filters, and high-performance circuits. Estimates of the dielectric function in the far- and mid-IR regime are derived from the observed transmittance spectra for a commonly employed low-stress silicon nitride formulation. The experimental, modeling, and numerical methods used to extract the dielectric parameters with an accuracy of approximately 4% are presented
BFORE: The B-mode Foreground Experiment
The B-mode Foreground Experiment (BFORE) is a proposed NASA balloon project
designed to make optimal use of the sub-orbital platform by concentrating on
three dust foreground bands (270, 350, and 600 GHz) that complement
ground-based cosmic microwave background (CMB) programs. BFORE will survey ~1/4
of the sky with 1.7 - 3.7 arcminute resolution, enabling precise
characterization of the Galactic dust that now limits constraints on inflation
from CMB B-mode polarization measurements. In addition, BFORE's combination of
frequency coverage, large survey area, and angular resolution enables science
far beyond the critical goal of measuring foregrounds. BFORE will constrain the
velocities of thousands of galaxy clusters, provide a new window on the cosmic
infrared background, and probe magnetic fields in the interstellar medium. We
review the BFORE science case, timeline, and instrument design, which is based
on a compact off-axis telescope coupled to >10,000 superconducting detectors.Comment: 7 pages, 4 figures, conference proceedings published in Journal of
Low Temperature Physic
The Atacama Cosmology Telescope: Cross Correlation with Planck maps
We present the temperature power spectrum of the Cosmic Microwave Background
obtained by cross-correlating maps from the Atacama Cosmology Telescope (ACT)
at 148 and 218 GHz with maps from the Planck satellite at 143 and 217 GHz, in
two overlapping regions covering 592 square degrees. We find excellent
agreement between the two datasets at both frequencies, quantified using the
variance of the residuals between the ACT power spectra and the ACTxPlanck
cross-spectra. We use these cross-correlations to calibrate the ACT data at 148
and 218 GHz, to 0.7% and 2% precision respectively. We find no evidence for
anisotropy in the calibration parameter. We compare the Planck 353 GHz power
spectrum with the measured amplitudes of dust and cosmic infrared background
(CIB) of ACT data at 148 and 218 GHz. We also compare planet and point source
measurements from the two experiments.Comment: 9 pages, 8 figure
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