131 research outputs found
Book Reviews
Reviews of the following books: University of Maine 1971 Seminar in MARITIME AND REGIONAL STUDIES, Clark G. Reynolds, William J. McAndrew, editors; Ride the Sandy River by L.P. Cornwall and Jack W. Farrell; The Canadian Frontier, 1834-1760 by William J. Eccles; The Red Schoolhouse Neighborhood by Ben and Natalie Butler; Pokey and Timothy of Stonehouse Farm by Marion Jaques Smit
Evidence for dark energy from the cosmic microwave background alone using the Atacama Cosmology Telescope lensing measurements
For the first time, measurements of the cosmic microwave background radiation
(CMB) alone favor cosmologies with dark energy over models without dark
energy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing
deflection power spectrum from the Atacama Cosmology Telescope with temperature
and polarization power spectra from the Wilkinson Microwave Anisotropy Probe.
The lensing data break the geometric degeneracy of different cosmological
models with similar CMB temperature power spectra. Our CMB-only measurement of
the dark energy density confirms other measurements from
supernovae, galaxy clusters and baryon acoustic oscillations, and demonstrates
the power of CMB lensing as a new cosmological tool.Comment: 4 pages, 3 figures; replaced with version accepted by Physical Review
Letters, added sentence on models with non-standard primordial power spectr
The Atacama Cosmology Telescope: A Measurement of the Thermal Sunyaev-Zel'dovich Effect Using the Skewness of the CMB Temperature Distribution
We present a detection of the unnormalized skewness induced by the
thermal Sunyaev-Zel'dovich (tSZ) effect in filtered Atacama Cosmology Telescope
(ACT) 148 GHz cosmic microwave background temperature maps. Contamination due
to infrared and radio sources is minimized by template subtraction of resolved
sources and by constructing a mask using outlying values in the 218 GHz
(tSZ-null) ACT maps. We measure = -31 +- 6 \mu K^3 (measurement error
only) or +- 14 \mu K^3 (including cosmic variance error) in the filtered ACT
data, a 5-sigma detection. We show that the skewness is a sensitive probe of
sigma_8, and use analytic calculations and tSZ simulations to obtain
cosmological constraints from this measurement. From this signal alone we infer
a value of sigma_8= 0.79 +0.03 -0.03 (68 % C.L.) +0.06 -0.06 (95 % C.L.). Our
results demonstrate that measurements of non-Gaussianity can be a useful method
for characterizing the tSZ effect and extracting the underlying cosmological
information.Comment: 9 pages, 5 figures. Replaced with version accepted by Phys. Rev. D,
with improvements to the likelihood function and the IR source treatment;
only minor changes in the result
Detection of the Power Spectrum of Cosmic Microwave Background Lensing by the Atacama Cosmology Telescope
We report the first detection of the gravitational lensing of the cosmic
microwave background through a measurement of the four-point correlation
function in the temperature maps made by the Atacama Cosmology Telescope. We
verify our detection by calculating the levels of potential contaminants and
performing a number of null tests. The resulting convergence power spectrum at
2-degree angular scales measures the amplitude of matter density fluctuations
on comoving length scales of around 100 Mpc at redshifts around 0.5 to 3. The
measured amplitude of the signal agrees with Lambda Cold Dark Matter cosmology
predictions. Since the amplitude of the convergence power spectrum scales as
the square of the amplitude of the density fluctuations, the 4-sigma detection
of the lensing signal measures the amplitude of density fluctuations to 12%.Comment: 4 pages, 4 figures, replaced title and author list with version
accepted by Physical Review Letters. Likelihood code can be downloaded from
http://bccp.lbl.gov/~sudeep/ACTLensLike.htm
The Atacama Cosmology Telescope: Data Characterization and Map Making
We present a description of the data reduction and mapmaking pipeline used
for the 2008 observing season of the Atacama Cosmology Telescope (ACT). The
data presented here at 148 GHz represent 12% of the 90 TB collected by ACT from
2007 to 2010. In 2008 we observed for 136 days, producing a total of 1423 hours
of data (11 TB for the 148 GHz band only), with a daily average of 10.5 hours
of observation. From these, 1085 hours were devoted to a 850 deg^2 stripe (11.2
hours by 9.1 deg) centered on a declination of -52.7 deg, while 175 hours were
devoted to a 280 deg^2 stripe (4.5 hours by 4.8 deg) centered at the celestial
equator. We discuss sources of statistical and systematic noise, calibration,
telescope pointing, and data selection. Out of 1260 survey hours and 1024
detectors per array, 816 hours and 593 effective detectors remain after data
selection for this frequency band, yielding a 38% survey efficiency. The total
sensitivity in 2008, determined from the noise level between 5 Hz and 20 Hz in
the time-ordered data stream (TOD), is 32 micro-Kelvin sqrt{s} in CMB units.
Atmospheric brightness fluctuations constitute the main contaminant in the data
and dominate the detector noise covariance at low frequencies in the TOD. The
maps were made by solving the least-squares problem using the Preconditioned
Conjugate Gradient method, incorporating the details of the detector and noise
correlations. Cross-correlation with WMAP sky maps, as well as analysis from
simulations, reveal that our maps are unbiased at multipoles ell > 300. This
paper accompanies the public release of the 148 GHz southern stripe maps from
2008. The techniques described here will be applied to future maps and data
releases.Comment: 20 pages, 18 figures, 6 tables, an ACT Collaboration pape
The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data
[Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new
discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the
Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial
equator. A subsample of 48 clusters within the 270 square degree region
overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14
Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters,
the sample is studied further through a "Profile Based Amplitude Analysis"
using a single filter at a fixed \theta_500 = 5.9' angular scale. This new
approach takes advantage of the "Universal Pressure Profile" (UPP) to fix the
relationship between the cluster characteristic size (R_500) and the integrated
Compton parameter (Y_500). The UPP scalings are found to be nearly identical to
an adiabatic model, while a model incorporating non-thermal pressure better
matches dynamical mass measurements and masses from the South Pole Telescope. A
high signal to noise ratio subsample of 15 ACT clusters is used to obtain
cosmological constraints. We first confirm that constraints from SZ data are
limited by uncertainty in the scaling relation parameters rather than sample
size or measurement uncertainty. We next add in seven clusters from the ACT
Southern survey, including their dynamical mass measurements based on galaxy
velocity dispersions. In combination with WMAP7 these data simultaneously
constrain the scaling relation and cosmological parameters, yielding \sigma_8 =
0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results include
marginalization over a 15% bias in dynamical mass relative to the true halo
mass. In an extension to LCDM that incorporates non-zero neutrino mass density,
we combine our data with WMAP7+BAO+Hubble constant measurements to constrain
\Sigma m_\nu < 0.29 eV (95% C. L.).Comment: 32 pages, 21 figures To appear in J. Cosmology and Astroparticle
Physic
The Atacama Cosmology Telescope: Temperature and Gravitational Lensing Power Spectrum Measurements from Three Seasons of Data
We present the temperature power spectra of the cosmic microwave background
(CMB) derived from the three seasons of data from the Atacama Cosmology
Telescope (ACT) at 148 GHz and 218 GHz, as well as the cross-frequency spectrum
between the two channels. We detect and correct for contamination due to the
Galactic cirrus in our equatorial maps. We present the results of a number of
tests for possible systematic error and conclude that any effects are not
significant compared to the statistical errors we quote. Where they overlap, we
cross-correlate the ACT and the South Pole Telescope (SPT) maps and show they
are consistent. The measurements of higher-order peaks in the CMB power
spectrum provide an additional test of the Lambda CDM cosmological model, and
help constrain extensions beyond the standard model. The small angular scale
power spectrum also provides constraining power on the Sunyaev-Zel'dovich
effects and extragalactic foregrounds. We also present a measurement of the CMB
gravitational lensing convergence power spectrum at 4.6-sigma detection
significance.Comment: 21 pages; 20 figures, Submitted to JCAP, some typos correcte
The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectrum at 148 and 218 GHz from the 2008 Southern Survey
We present measurements of the cosmic microwave background (CMB) power
spectrum made by the Atacama Cosmology Telescope at 148 GHz and 218 GHz, as
well as the cross-frequency spectrum between the two channels. Our results
clearly show the second through the seventh acoustic peaks in the CMB power
spectrum. The measurements of these higher-order peaks provide an additional
test of the {\Lambda}CDM cosmological model. At l > 3000, we detect power in
excess of the primary anisotropy spectrum of the CMB. At lower multipoles 500 <
l < 3000, we find evidence for gravitational lensing of the CMB in the power
spectrum at the 2.8{\sigma} level. We also detect a low level of Galactic dust
in our maps, which demonstrates that we can recover known faint, diffuse
signals.Comment: 19 pages, 13 figures. Submitted to ApJ. This paper is a companion to
Hajian et al. (2010) and Dunkley et al. (2010
The Atacama Cosmology Telescope: Cosmological parameters from three seasons of data
We present constraints on cosmological and astrophysical parameters from
high-resolution microwave background maps at 148 GHz and 218 GHz made by the
Atacama Cosmology Telescope (ACT) in three seasons of observations from 2008 to
2010. A model of primary cosmological and secondary foreground parameters is
fit to the map power spectra and lensing deflection power spectrum, including
contributions from both the thermal Sunyaev-Zeldovich (tSZ) effect and the
kinematic Sunyaev-Zeldovich (kSZ) effect, Poisson and correlated anisotropy
from unresolved infrared sources, radio sources, and the correlation between
the tSZ effect and infrared sources. The power ell^2 C_ell/2pi of the thermal
SZ power spectrum at 148 GHz is measured to be 3.4 +\- 1.4 muK^2 at ell=3000,
while the corresponding amplitude of the kinematic SZ power spectrum has a 95%
confidence level upper limit of 8.6 muK^2. Combining ACT power spectra with the
WMAP 7-year temperature and polarization power spectra, we find excellent
consistency with the LCDM model. We constrain the number of effective
relativistic degrees of freedom in the early universe to be Neff=2.79 +\- 0.56,
in agreement with the canonical value of Neff=3.046 for three massless
neutrinos. We constrain the sum of the neutrino masses to be Sigma m_nu < 0.39
eV at 95% confidence when combining ACT and WMAP 7-year data with BAO and
Hubble constant measurements. We constrain the amount of primordial helium to
be Yp = 0.225 +\- 0.034, and measure no variation in the fine structure
constant alpha since recombination, with alpha/alpha0 = 1.004 +/- 0.005. We
also find no evidence for any running of the scalar spectral index, dns/dlnk =
-0.004 +\- 0.012.Comment: 26 pages, 22 figures. This paper is a companion to Das et al. (2013)
and Dunkley et al. (2013). Matches published JCAP versio
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