125 research outputs found
Survey strategy optimization for the Atacama Cosmology Telescope
In recent years there have been significant improvements in the sensitivity
and the angular resolution of the instruments dedicated to the observation of
the Cosmic Microwave Background (CMB). ACTPol is the first polarization
receiver for the Atacama Cosmology Telescope (ACT) and is observing the CMB sky
with arcmin resolution over about 2000 sq. deg. Its upgrade, Advanced ACTPol
(AdvACT), will observe the CMB in five frequency bands and over a larger area
of the sky. We describe the optimization and implementation of the ACTPol and
AdvACT surveys. The selection of the observed fields is driven mainly by the
science goals, that is, small angular scale CMB measurements, B-mode
measurements and cross-correlation studies. For the ACTPol survey we have
observed patches of the southern galactic sky with low galactic foreground
emissions which were also chosen to maximize the overlap with several galaxy
surveys to allow unique cross-correlation studies. A wider field in the
northern galactic cap ensured significant additional overlap with the BOSS
spectroscopic survey. The exact shapes and footprints of the fields were
optimized to achieve uniform coverage and to obtain cross-linked maps by
observing the fields with different scan directions. We have maximized the
efficiency of the survey by implementing a close to 24 hour observing strategy,
switching between daytime and nighttime observing plans and minimizing the
telescope idle time. We describe the challenges represented by the survey
optimization for the significantly wider area observed by AdvACT, which will
observe roughly half of the low-foreground sky. The survey strategies described
here may prove useful for planning future ground-based CMB surveys, such as the
Simons Observatory and CMB Stage IV surveys.Comment: 14 Pages, 9 Figures, 4 Table
CCAT-prime: Science with an Ultra-widefield Submillimeter Observatory at Cerro Chajnantor
We present the detailed science case, and brief descriptions of the telescope
design, site, and first light instrument plans for a new ultra-wide field
submillimeter observatory, CCAT-prime, that we are constructing at a 5600 m
elevation site on Cerro Chajnantor in northern Chile. Our science goals are to
study star and galaxy formation from the epoch of reionization to the present,
investigate the growth of structure in the Universe, improve the precision of
B-mode CMB measurements, and investigate the interstellar medium and star
formation in the Galaxy and nearby galaxies through spectroscopic,
polarimetric, and broadband surveys at wavelengths from 200 um to 2 mm. These
goals are realized with our two first light instruments, a large field-of-view
(FoV) bolometer-based imager called Prime-Cam (that has both camera and an
imaging spectrometer modules), and a multi-beam submillimeter heterodyne
spectrometer, CHAI. CCAT-prime will have very high surface accuracy and very
low system emissivity, so that combined with its wide FoV at the unsurpassed
CCAT site our telescope/instrumentation combination is ideally suited to pursue
this science. The CCAT-prime telescope is being designed and built by Vertex
Antennentechnik GmbH. We expect to achieve first light in the spring of 2021.Comment: Presented at SPIE Millimeter, Submillimeter, and Far-Infrared
Detectors and Instrumentation for Astronomy IX, June 14th, 201
The Atacama Cosmology Telescope: Two-Season ACTPol Lensing Power Spectrum
We report a measurement of the power spectrum of cosmic microwave background
(CMB) lensing from two seasons of Atacama Cosmology Telescope Polarimeter
(ACTPol) CMB data. The CMB lensing power spectrum is extracted from both
temperature and polarization data using quadratic estimators. We obtain results
that are consistent with the expectation from the best-fit Planck LCDM model
over a range of multipoles L=80-2100, with an amplitude of lensing A_lens =
1.06 +/- 0.15 (stat.) +/- 0.06 (sys.) relative to Planck. Our measurement of
the CMB lensing power spectrum gives sigma_8 Omega_m^0.25 = 0.643 +/- 0.054;
including baryon acoustic oscillation scale data, we constrain the amplitude of
density fluctuations to be sigma_8 = 0.831 +/- 0.053. We also update
constraints on the neutrino mass sum. We verify our lensing measurement with a
number of null tests and systematic checks, finding no evidence of significant
systematic errors. This measurement relies on a small fraction of the ACTPol
data already taken; more precise lensing results can therefore be expected from
the full ACTPol dataset.Comment: 17 pages, 11 figures, to be submitted to Physical Review
Detection of the pairwise kinematic Sunyaev-Zel'dovich effect with BOSS DR11 and the Atacama Cosmology Telescope
We present a new measurement of the kinematic Sunyaev-Zeldovich effect using
data from the Atacama Cosmology Telescope (ACT) and the Baryon Oscillation
Spectroscopic Survey (BOSS). Using 600 square degrees of overlapping sky area,
we evaluate the mean pairwise baryon momentum associated with the positions of
50,000 bright galaxies in the BOSS DR11 Large Scale Structure catalog. A
non-zero signal arises from the large-scale motions of halos containing the
sample galaxies. The data fits an analytical signal model well, with the
optical depth to microwave photon scattering as a free parameter determining
the overall signal amplitude. We estimate the covariance matrix of the mean
pairwise momentum as a function of galaxy separation, using microwave sky
simulations, jackknife evaluation, and bootstrap estimates. The most
conservative simulation-based errors give signal-to-noise estimates between 3.6
and 4.1 for varying galaxy luminosity cuts. We discuss how the other error
determinations can lead to higher signal-to-noise values, and consider the
impact of several possible systematic errors. Estimates of the optical depth
from the average thermal Sunyaev-Zeldovich signal at the sample galaxy
positions are broadly consistent with those obtained from the mean pairwise
momentum signal.Comment: 15 pages, 8 figures, 2 table
The optical design of the six-meter CCAT-prime and Simons Observatory telescopes
A common optical design for a coma-corrected, 6-meter aperture,
crossed-Dragone telescope has been adopted for the CCAT-prime telescope of CCAT
Observatory, Inc., and for the Large Aperture Telescope of the Simons
Observatory. Both are to be built in the high altitude Atacama Desert in Chile
for submillimeter and millimeter wavelength observations, respectively. The
design delivers a high throughput, relatively flat focal plane, with a field of
view 7.8 degrees in diameter for 3 mm wavelengths, and the ability to
illuminate >100k diffraction-limited beams for < 1 mm wavelengths. The optics
consist of offset reflecting primary and secondary surfaces arranged in such a
way as to satisfy the Mizuguchi-Dragone criterion, suppressing first-order
astigmatism and maintaining high polarization purity. The surface shapes are
perturbed from their standard conic forms in order to correct coma aberrations.
We discuss the optical design, performance, and tolerancing sensitivity. More
information about CCAT-prime can be found at ccatobservatory.org and about
Simons Observatory at simonsobservatory.org.Comment: Event: SPIE Astronomical Telescopes + Instrumentation, 2018, Austin,
Texas, USA; Proceedings Volume 10700, Ground-based and Airborne Telescopes
VII; 1070041 (2018
Comparing complex impedance and bias step measurements of Simons Observatory transition edge sensors
The Simons Observatory (SO) will perform ground-based observations of the
cosmic microwave background (CMB) with several small and large aperture
telescopes, each outfitted with thousands to tens of thousands of
superconducting aluminum manganese (AlMn) transition-edge sensor bolometers
(TESs). In-situ characterization of TES responsivities and effective time
constants will be required multiple times each observing-day for calibrating
time-streams during CMB map-making. Effective time constants are typically
estimated in the field by briefly applying small amplitude square-waves on top
of the TES DC biases, and fitting exponential decays in the bolometer response.
These so-called "bias step" measurements can be rapidly implemented across
entire arrays and therefore are attractive because they take up little
observing time. However, individual detector complex impedance measurements,
while too slow to implement during observations, can provide a fuller picture
of the TES model and a better understanding of its temporal response. Here, we
present the results of dark TES characterization of many prototype SO
bolometers and compare the effective thermal time constants measured via bias
steps to those derived from complex impedance data.Comment: 10 pages, 6 figures, SPIE Astronomical Telescopes + Instrumentation
2020, Paper Number: 11453-18
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Two-season Atacama Cosmology Telescope polarimeter lensing power spectrum
© 2017 American Physical Society. We report a measurement of the power spectrum of cosmic microwave background (CMB) lensing from two seasons of Atacama Cosmology Telescope polarimeter (ACTPol) CMB data. The CMB lensing power spectrum is extracted from both temperature and polarization data using quadratic estimators. We obtain results that are consistent with the expectation from the best-fit Planck ΛCDM model over a range of multipoles L=80-2100, with an amplitude of lensing Alens=1.06±0.15(stat)±0.06(sys) relative to Planck. Our measurement of the CMB lensing power spectrum gives σ8Ωm0.25=0.643±0.054; including baryon acoustic oscillation scale data, we constrain the amplitude of density fluctuations to be σ8=0.831±0.053. We also update constraints on the neutrino mass sum. We verify our lensing measurement with a number of null tests and systematic checks, finding no evidence of significant systematic errors. This measurement relies on a small fraction of the ACTPol data already taken; more precise lensing results can therefore be expected from the full ACTPol data set.This
work was supported by the U.S. National Science Foundation
(NSF) through Grants. No. AST-1440226, No. AST-0965625
and No. AST-0408698 for the ACT project, as well as Grants
No. PHY-1214379 and No. PHY-0855887. Funding was also
provided by Princeton University, the University of
Pennsylvania, and a Canada Foundation for Innovation
(CFI) grant to U. B. C. A. C. T. operates in the Parque
Astronómico Atacama in northern Chile under the auspices
of the Comisión Nacional de Investigación Científica y
Tecnológica de Chile (CONICYT). Computations were
performed on the GPC supercomputer at the SciNet HPC
Consortium. SciNetis funded bytheCFI under the auspices of
Compute Canada, the Government of Ontario, the Ontario
Research Fund Research Excellence, and the University of
Toronto. The development of multichroic detectors and lenses
was supported by NASA Grants No. NNX13AE56G and
No. NNX14AB58G. N. S. acknowledges support from NSF
Grant No. 1513618. A. K. has been supported by NSF Grant
No. AST-1312380. R. D. and L. M. thank CONICYT for
Grants No. ALMA-CONICYT 31140004, No. FONDECYT 1141113, No. Anillo ACT-1417 and BASAL CATA. We also
thank the Mishrahi Fund and the Wilkinson Fund for their
generous support of the project
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