20 research outputs found
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
The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters
We present the temperature and polarization angular power spectra measured by
the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time
data collected during 2013-14 using two detector arrays at 149 GHz, from 548
deg of sky on the celestial equator. We use these spectra, and the spectra
measured with the MBAC camera on ACT from 2008-10, in combination with Planck
and WMAP data to estimate cosmological parameters from the temperature,
polarization, and temperature-polarization cross-correlations. We find the new
ACTPol data to be consistent with the LCDM model. The ACTPol
temperature-polarization cross-spectrum now provides stronger constraints on
multiple parameters than the ACTPol temperature spectrum, including the baryon
density, the acoustic peak angular scale, and the derived Hubble constant.
Adding the new data to planck temperature data tightens the limits on damping
tail parameters, for example reducing the joint uncertainty on the number of
neutrino species and the primordial helium fraction by 20%.Comment: 23 pages, 25 figure
The Atacama Cosmology Telescope: CMB Polarization at
We report on measurements of the cosmic microwave background (CMB) and
celestial polarization at 146 GHz made with the Atacama Cosmology Telescope
Polarimeter (ACTPol) in its first three months of observing. Four regions of
sky covering a total of 270 square degrees were mapped with an angular
resolution of . The map noise levels in the four regions are between 11
and 17 K-arcmin. We present TT, TE, EE, TB, EB, and BB power spectra from
three of these regions. The observed E-mode polarization power spectrum,
displaying six acoustic peaks in the range , is an excellent fit
to the prediction of the best-fit cosmological models from WMAP9+ACT and Planck
data. The polarization power spectrum, which mainly reflects primordial plasma
velocity perturbations, provides an independent determination of cosmological
parameters consistent with those based on the temperature power spectrum, which
results mostly from primordial density perturbations. We find that without
masking any point sources in the EE data at , the Poisson tail of
the EE power spectrum due to polarized point sources has an amplitude less than
K at at 95\% confidence. Finally, we report that
the Crab Nebula, an important polarization calibration source at microwave
frequencies, has 8.7\% polarization with an angle of when smoothed with a Gaussian beam.Comment: 16 pages, 15 figures, 5 table
The Atacama Cosmology Telescope: delensed power spectra and parameters
International audienceWe present ΛCDM cosmological parameter constraints obtained from delensed microwave background power spectra. Lensing maps from a subset of DR4 data from the Atacama Cosmology Telescope (ACT) are used to undo the lensing effect in ACT spectra observed at 150 and 98 GHz. At 150 GHz, we remove the lensing distortion with an effective efficiency of 30% (TT), 30% (EE), 26% (TE) and 20% (BB); this results in detections of the delensing effect at 8.7σ (TT), 5.1σ (EE), 2.6σ (TE), and 2.4σ (BB) significance. The combination of 150 and 98 GHz TT, EE, and TE delensed spectra is well fit by a standard ΛCDM model. We also measure the shift in best-fit parameters when fitting delensed versus lensed spectra; while this shift does not inform our ability to measure cosmological parameters, it does provide a three-way consistency check among the lensing inferred from the best-fit parameters, the lensing in the CMB power spectrum, and the reconstructed lensing map. This shift is predicted to be zero when fitting with the correct model since both lensed and delensed spectra originate from the same region of sky. Fitting with a ΛCDM model and marginalizing over foregrounds, we find that the shift in cosmological parameters is consistent with zero. Our results show that gravitational lensing of the microwave background is internally consistent within the framework of the standard cosmological model
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The Atacama Cosmology Telescope: delensed power spectra and parameters
We present ΛCDM cosmological parameter constraints obtained from delensed
microwave background power spectra. Lensing maps from a subset of DR4 data from the
Atacama Cosmology Telescope (ACT) are used to undo the lensing effect in ACT spectra
observed at 150 and 98 GHz. At 150 GHz, we remove the lensing distortion with an effective
efficiency of 30% (T T ), 30% (EE), 26% (T E) and 20% (BB); this results in detections of
the delensing effect at 8.7σ (T T ), 5.1σ (EE), 2.6σ (T E), and 2.4σ (BB) significance. The
combination of 150 and 98 GHz T T, EE, and T E delensed spectra is well fit by a standard
ΛCDM model. We also measure the shift in best-fit parameters when fitting delensed versus
lensed spectra; while this shift does not inform our ability to measure cosmological param-
eters, it does provide a three-way consistency check among the lensing inferred from the
best-fit parameters, the lensing in the CMB power spectrum, and the reconstructed lensing
map. This shift is predicted to be zero when fitting with the correct model since both lensed
and delensed spectra originate from the same region of sky. Fitting with a ΛCDM model and
marginalizing over foregrounds, we find that the shift in cosmological parameters is consis-
tent with zero. Our results show that gravitational lensing of the microwave background is
internally consistent within the framework of the standard cosmological model
Atacama Cosmology Telescope: Constraints on cosmic birefringence
International audienceWe present new constraints on anisotropic birefringence of the cosmic microwave background polarization using two seasons of data from the Atacama Cosmology Telescope covering 456 square degrees of sky. The birefringence power spectrum, measured using a curved-sky quadratic estimator, is consistent with zero. Our results provide the tightest current constraint on birefringence over a range of angular scales between 5 arc minutes and 9°. We improve previous upper limits on the amplitude of a scale-invariant birefringence power spectrum by a factor of between 2 and 3. Assuming a nearly massless axion field during inflation, our result is equivalent to a 2σ upper limit on the Chern-Simons coupling constant between axions and photons of gαγ<4.0×10-2/HI, where HI is the inflationary Hubble scale
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The Atacama Cosmology Telescope: a CMB lensing mass map over 2100 square degrees of sky and its cross-correlation with BOSS-CMASS galaxies
We construct cosmic microwave background lensing mass maps using data from
the 2014 and 2015 seasons of observations with the Atacama Cosmology Telescope
(ACT). These maps cover 2100 square degrees of sky and overlap with a wide variety
of optical surveys. The maps are signal dominated on large scales and have fidelity
such that their correlation with the cosmic infrared background is clearly visible by
eye. We also create lensing maps with thermal Sunyaev-Zel’dovich contamination
removed using a novel cleaning procedure that only slightly degrades the lensing
signal-to-noise ratio. The cross-spectrum between the cleaned lensing map and the
BOSS CMASS galaxy sample is detected at 10-σ significance, with an amplitude of
A = 1.02 ± 0.10 relative to the Planck best-fit LCDM cosmological model with fiducial
linear galaxy bias. Our measurement lays the foundation for lensing cross-correlation
science with current ACT data and beyon
The Atacama Cosmology Telescope: A CMB lensing mass map over 2100 square degrees of sky and its cross-correlation with BOSS-CMASS galaxies
International audienceWe construct cosmic microwave background lensing mass maps using data from the 2014 and 2015 seasons of observations with the Atacama Cosmology Telescope (ACT). These maps cover 2100 square degrees of sky and overlap with a wide variety of optical surveys. The maps are signal dominated on large scales and have fidelity such that their correlation with the cosmic infrared background is clearly visible by eye. We also create lensing maps with thermal Sunyaev−Zel’dovich contamination removed using a novel cleaning procedure that only slightly degrades the lensing signal-to-noise ratio. The cross-spectrum between the cleaned lensing map and the BOSS CMASS galaxy sample is detected at 10σ significance, with an amplitude of A = 1.02 ± 0.10 relative to the Planck best-fitting Lambda cold dark matter cosmological model with fiducial linear galaxy bias. Our measurement lays the foundation for lensing cross-correlation science with current ACT data and beyond
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The Atacama Cosmology Telescope: Summary of DR4 and DR5 Data Products and Data Access
Two recent large data releases for the Atacama Cosmology Telescope (ACT), called DR4 and DR5,
are available for public access. These data include temperature and polarization maps that cover
nearly half the sky at arcminute resolution in three frequency bands; lensing maps and component-
separated maps covering ∼ 2,100 deg2 of sky; derived power spectra and cosmological likelihoods; a
catalog of over 4,000 galaxy clusters; and supporting ancillary products including beam functions and
masks. The data and products are described in a suite of ACT papers; here we provide a summary.
In order to facilitate ease of access to these data we present a set of Jupyter IPython notebooks
developed to introduce users to DR4, DR5, and the tools needed to analyze these data. The data
products (excluding simulations) and the set of notebooks are publicly available on the NASA Legacy
Archive for Microwave Background Data Analysis (LAMBDA); simulation products are available on
the National Energy Research Scientific Computing Center (NERSC