93 research outputs found
Testing CMB Anomalies in E-mode Polarization with Current and Future Data
In this paper, we explore the power of the cosmic microwave background (CMB)
polarization (E-mode) data to corroborate four potential anomalies in CMB
temperature data: the lack of large angular-scale correlations, the alignment
of the quadrupole and octupole (Q-O), the point-parity asymmetry, and the
hemispherical power asymmetry. We use CMB simulations with noise representative
of three experiments -- the Planck satellite, the Cosmology Large Angular Scale
Surveyor (CLASS), and the LiteBIRD satellite -- to test how current and future
data constrain the anomalies. We find the correlation coefficients
between temperature and E-mode estimators to be less than , except for the
point-parity asymmetry ( for cosmic-variance-limited simulations),
confirming that E-modes provide a check on the anomalies that is largely
independent of temperature data. Compared to Planck component-separated CMB
data (SMICA), the putative LiteBIRD survey would reduce errors on E-mode
anomaly estimators by factors of for hemispherical power asymmetry and
point-parity asymmetry, and by for lack of large-scale correlation.
The improvement in Q-O alignment is not obvious due to large cosmic variance,
but we found the ability to pin down the estimator value will be improved by a
factor . Improvements with CLASS are intermediate to these.Comment: 23 pages, 15 figures, 6 table
Microwave Observations of Venus with CLASS
We report on the disk-averaged absolute brightness temperatures of Venus
measured at four microwave frequency bands with the Cosmology Large Angular
Scale Surveyor (CLASS). We measure temperatures of 432.3 2.8 K, 355.6
1.3 K, 317.9 1.7 K, and 294.7 1.9 K for frequency bands
centered at 38.8, 93.7, 147.9, and 217.5 GHz, respectively. We do not observe
any dependence of the measured brightness temperatures on solar illumination
for all four frequency bands. A joint analysis of our measurements with lower
frequency Very Large Array (VLA) observations suggests relatively warmer
( 7 K higher) mean atmospheric temperatures and lower abundances of
microwave continuum absorbers than those inferred from prior radio occultation
measurements.Comment: 10 pages, 3 figures, published in PS
Venus Observations at 40 and 90 GHz with CLASS
Using the Cosmology Large Angular Scale Surveyor, we measure the
disk-averaged absolute Venus brightness temperature to be 432.3 2.8 K and
355.6 1.3 K in the Q and W frequency bands centered at 38.8 and 93.7 GHz,
respectively. At both frequency bands, these are the most precise measurements
to date. Furthermore, we observe no phase dependence of the measured
temperature in either band. Our measurements are consistent with a
CO-dominant atmospheric model that includes trace amounts of additional
absorbers like SO and HSO.Comment: 7 pages, 3 figures, published in PS
CLASS Observations of Atmospheric Cloud Polarization at Millimeter Wavelengths
The dynamic atmosphere imposes challenges to ground-based cosmic microwave
background observation, especially for measurements on large angular scales.
The hydrometeors in the atmosphere, mostly in the form of clouds, scatter the
ambient thermal radiation and are known to be the main linearly polarized
source in the atmosphere. This scattering-induced polarization is significantly
enhanced for ice clouds due to the alignment of ice crystals under gravity,
which are also the most common clouds seen at the millimeter-astronomy sites at
high altitudes. This work presents a multifrequency study of cloud polarization
observed by the Cosmology Large Angular Scale Surveyor (CLASS) experiment on
Cerro Toco in the Atacama Desert of northern Chile, from 2016 to 2022, at the
frequency bands centered around 40, 90, 150, and 220 GHz. Using a
machine-learning-assisted cloud classifier, we made connections between the
transient polarized emission found in all four frequencies with the clouds
imaged by monitoring cameras at the observing site. The polarization angles of
the cloud events are found to be mostly from the local meridian,
which is consistent with the presence of horizontally aligned ice crystals. The
90 and 150 GHz polarization data are consistent with a power law with a
spectral index of , while an excess/deficit of polarization
amplitude is found at 40/220 GHz compared with a Rayleigh scattering spectrum.
These results are consistent with Rayleigh-scattering-dominated cloud
polarization, with possible effects from supercooled water absorption and/or
Mie scattering from a population of large cloud particles that contribute to
the 220 GHz polarization.Comment: 16 pages, 14 figures, submitted to Ap
CLASS Angular Power Spectra and Map-Component Analysis for 40 GHz Observations through 2022
Measurement of the largest angular scale () features of the cosmic
microwave background (CMB) polarization is a powerful way to constrain the
optical depth to reionization, , and search for the signature of
inflation through the detection of primordial -modes. We present an analysis
of maps covering nearly 75% of the sky made from the ground-based
channel of the Cosmology Large Angular Scale Surveyor
(CLASS) from August 2016 to May 2022. Using fast front-end polarization
modulation from the Atacama Desert in Chile, we show this channel achieves
higher sensitivity than the analogous frequencies from satellite measurements
in the range . After a final calibration adjustment, noise
simulations show the CLASS linear (circular) polarization maps have a white
noise level of . We measure the
Galaxy-masked and spectra of diffuse synchrotron radiation and
compare to space-based measurements at similar frequencies. In combination with
external data, we expand measurements of the spatial variations of the
synchrotron spectral energy density (SED) to include new regions of the sky and
measure the faint diffuse SED in the harmonic domain. We place a new upper
limit on a background of circular polarization in the range
with the first bin showing at 95%
confidence. These results establish a new standard for recovery of the
largest-scale CMB polarization from the ground and signal exciting
possibilities when the higher sensitivity and higher frequency CLASS channels
are included in the analysis.Comment: 36 pages, 24 figures, 6 tables. Submitted to The Astrophysical
Journa
Two Year Cosmology Large Angular Scale Surveyor (CLASS) Observations: Long Timescale Stability Achieved with a Front-End Variable-delay Polarization Modulator at 40 GHz
The Cosmology Large Angular Scale Surveyor (CLASS) is a four-telescope array
observing the largest angular scales () of the
cosmic microwave background (CMB) polarization. These scales encode information
about reionization and inflation during the early universe. The instrument
stability necessary to observe these angular scales from the ground is achieved
through the use of a variable-delay polarization modulator (VPM) as the first
optical element in each of the CLASS telescopes. Here we develop a demodulation
scheme used to extract the polarization timestreams from the CLASS data and
apply this method to selected data from the first two years of observations by
the 40 GHz CLASS telescope. These timestreams are used to measure the
noise and temperature-to-polarization () leakage present in the
CLASS data. We find a median knee frequency for the pair-differenced
demodulated linear polarization of 15.12 mHz and a leakage of
(95\% confidence) across the focal plane. We examine the
sources of noise present in the data and find the component of due
to atmospheric precipitable water vapor (PWV) has an amplitude of for 1 mm of PWV when evaluated at 10 mHz;
accounting for of the noise in the central pixels of the focal
plane. The low level of leakage and noise achieved
through the use of a front-end polarization modulator enables the observation
of the largest scales of the CMB polarization from the ground by the CLASS
telescopes.Comment: Submitted to Ap
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