364 research outputs found
Measurement of electron screening in muonic lead
Energies of the transitions between high-lying (n≥6) states of muonic lead were accurately determined. The results are interpreted as a ∼2% test of the electron screening. The agreement between experiment and theory is good if it is assumed that the refilling of the electron K shell is fast. The present results furthermore severely restrict possible ionization of the electron L shell
The Atacama Cosmology Telescope: The LABOCA/ACT Survey of Clusters at All Redshifts
We present a multi-wavelength analysis of eleven Sunyaev Zel'dovich effect
(SZE)-selected galaxy clusters (ten with new data) from the Atacama Cosmology
Telescope (ACT) southern survey. We have obtained new imaging from the Large
APEX Bolometer Camera (345GHz; LABOCA) on the Atacama Pathfinder EXperiment
(APEX) telescope, the Australia Telescope Compact Array (2.1GHz; ATCA), and the
Spectral and Photometric Imaging Receiver (250, 350, and ;
SPIRE) on the Herschel Space Observatory. Spatially-resolved 345GHz SZE
increments with integrated S/N > 5 are found in six clusters. We compute 2.1GHz
number counts as a function of cluster-centric radius and find significant
enhancements in the counts of bright sources at projected radii . By extrapolating in frequency, we predict that the combined
signals from 2.1GHz-selected radio sources and 345GHz-selected SMGs contaminate
the 148GHz SZE decrement signal by ~5% and the 345GHz SZE increment by ~18%.
After removing radio source and SMG emission from the SZE signals, we use ACT,
LABOCA, and (in some cases) new Herschel SPIRE imaging to place constraints on
the clusters' peculiar velocities. The sample's average peculiar velocity
relative to the cosmic microwave background is .Comment: 19 pages, 11 figures, Accepted for Publication in The Astrophysical
Journa
The Atacama Cosmology Telescope: The polarization-sensitive ACTPol instrument
The Atacama Cosmology Telescope (ACT) is designed to make high angular
resolution measurements of anisotropies in the Cosmic Microwave Background
(CMB) at millimeter wavelengths. We describe ACTPol, an upgraded receiver for
ACT, which uses feedhorn-coupled, polarization-sensitive detector arrays, a 3
degree field of view, 100 mK cryogenics with continuous cooling, and meta
material anti-reflection coatings. ACTPol comprises three arrays with separate
cryogenic optics: two arrays at a central frequency of 148 GHz and one array
operating simultaneously at both 97 GHz and 148 GHz. The combined instrument
sensitivity, angular resolution, and sky coverage are optimized for measuring
angular power spectra, clusters via the thermal Sunyaev-Zel'dovich and kinetic
Sunyaev-Zel'dovich signals, and CMB lensing due to large scale structure. The
receiver was commissioned with its first 148 GHz array in 2013, observed with
both 148 GHz arrays in 2014, and has recently completed its first full season
of operations with the full suite of three arrays. This paper provides an
overview of the design and initial performance of the receiver and related
systems
The Atacama Cosmology Telescope: A Measurement of the 600< ell <8000 Cosmic Microwave Background Power Spectrum at 148 GHz
We present a measurement of the angular power spectrum of the cosmic
microwave background (CMB) radiation observed at 148 GHz. The measurement uses
maps with 1.4' angular resolution made with data from the Atacama Cosmology
Telescope (ACT). The observations cover 228 square degrees of the southern sky,
in a 4.2-degree-wide strip centered on declination 53 degrees South. The CMB at
arcminute angular scales is particularly sensitive to the Silk damping scale,
to the Sunyaev-Zel'dovich (SZ) effect from galaxy clusters, and to emission by
radio sources and dusty galaxies. After masking the 108 brightest point sources
in our maps, we estimate the power spectrum between 600 < \ell < 8000 using the
adaptive multi-taper method to minimize spectral leakage and maximize use of
the full data set. Our absolute calibration is based on observations of Uranus.
To verify the calibration and test the fidelity of our map at large angular
scales, we cross-correlate the ACT map to the WMAP map and recover the WMAP
power spectrum from 250 < ell < 1150. The power beyond the Silk damping tail of
the CMB is consistent with models of the emission from point sources. We
quantify the contribution of SZ clusters to the power spectrum by fitting to a
model normalized at sigma8 = 0.8. We constrain the model's amplitude ASZ < 1.63
(95% CL). If interpreted as a measurement of sigma8, this implies sigma8^SZ <
0.86 (95% CL) given our SZ model. A fit of ACT and WMAP five-year data jointly
to a 6-parameter LCDM model plus terms for point sources and the SZ effect is
consistent with these results.Comment: 15 pages, 8 figures. Accepted for publication in Ap
The Atacama Cosmology Telescope: Physical Properties of Sunyaev-Zel'dovich Effect Clusters on the Celestial Equator
We present the optical and X-ray properties of 68 galaxy clusters selected
via the Sunyaev-Zel'dovich Effect at 148 GHz by the Atacama Cosmology Telescope
(ACT). Our sample, from an area of 504 square degrees centered on the celestial
equator, is divided into two regions. The main region uses 270 square degrees
of the ACT survey that overlaps with the co-added ugriz imaging from the Sloan
Digital Sky Survey (SDSS) over Stripe 82 plus additional near-infrared pointed
observations with the Apache Point Observatory 3.5-meter telescope. We confirm
a total of 49 clusters to z~1.3, of which 22 (all at z>0.55) are new
discoveries. For the second region the regular-depth SDSS imaging allows us to
confirm 19 more clusters up to z~0.7, of which 10 systems are new. We present
the optical richness, photometric redshifts, and separation between the SZ
position and the brightest cluster galaxy (BCG). We find no significant offset
between the cluster SZ centroid and BCG location and a weak correlation between
optical richness and SZ-derived mass. We also present X-ray fluxes and
luminosities from the ROSAT All Sky Survey which confirm that this is a massive
sample. One of the newly discovered clusters, ACT-CL J0044.4+0113 at z=1.1
(photometric), has an integrated XMM-Newton X-ray temperature of kT_x=7.9+/-1.0
keV and combined mass of M_200a=8.2(-2.5,+3.3)x10^14 M_sun/h70 placing it among
the most massive and X-ray-hot clusters known at redshifts beyond z=1. We also
highlight the optically-rich cluster ACT-CL J2327.4-0204 (RCS2 2327) at z=0.705
(spectroscopic) as the most significant detection of the whole equatorial
sample with a Chandra-derived mass of M_200a=1.9(-0.4,+0.6)x10^15 M_sun/h70,
comparable to some of the most massive known clusters like "El Gordo" and the
Bullet Cluster.Comment: 18 pages, 12 figures. Accepted to the Astrophysical Journal. New
version includes minor changes in the accepted pape
Single-field inflation constraints from CMB and SDSS data
We present constraints on canonical single-field inflation derived from WMAP
five year, ACBAR, QUAD, BICEP data combined with the halo power spectrum from
SDSS LRG7. Models with a non-scale-invariant spectrum and a red tilt n_s < 1
are now preferred over the Harrison-Zel'dovich model (n_s = 1, tensor-to-scalar
ratio r = 0) at high significance. Assuming no running of the spectral indices,
we derive constraints on the parameters (n_s, r) and compare our results with
the predictions of simple inflationary models. The marginalised credible
intervals read n_s = 0.962^{+0.028}_{-0.026} and r < 0.17 (at 95% confidence
level). Interestingly, the 68% c.l. contours favour mainly models with a convex
potential in the observable region, but the quadratic potential model remains
inside the 95% c.l. contours. We demonstrate that these results are robust to
changes in the datasets considered and in the theoretical assumptions made. We
then consider a non-vanishing running of the spectral indices by employing
different methods, non-parametric but approximate, or parametric but exact.
With our combination of CMB and LSS data, running models are preferred over
power-law models only by a Delta chi^2 ~ 5.8, allowing inflationary stages
producing a sizable negative running -0.063^{+0.061}_{-0.049} and larger
tensor-scalar ratio r < 0.33 at the 95% c.l. This requires large values of the
third derivative of the inflaton potential within the observable range. We
derive bounds on this derivative under the assumption that the inflaton
potential can be approximated as a third order polynomial within the observable
range.Comment: 32 pages, 7 figures. v2: additional references, some typos corrected,
passed to JCAP style. v3: minor changes, matches published versio
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
The Atacama Cosmology Telescope: the stellar content of galaxy clusters selected using the Sunyaev-Zel'dovich effect
We present a first measurement of the stellar mass component of galaxy
clusters selected via the Sunyaev-Zel'dovich (SZ) effect, using 3.6 um and 4.5
um photometry from the Spitzer Space Telescope. Our sample consists of 14
clusters detected by the Atacama Cosmology Telescope (ACT), which span the
redshift range 0.27 < z < 1.07 (median z = 0.50), and have dynamical mass
measurements, accurate to about 30 per cent, with median M500 = 6.9 x 10^{14}
MSun. We measure the 3.6 um and 4.5 um galaxy luminosity functions, finding the
characteristic magnitude (m*) and faint-end slope (alpha) to be similar to
those for IR-selected cluster samples. We perform the first measurements of the
scaling of SZ-observables (Y500 and y0) with both brightest cluster galaxy
(BCG) stellar mass and total cluster stellar mass (M500star). We find a
significant correlation between BCG stellar mass and Y500 (E(z)^{-2/3} DA^2
Y500 ~ M*^{1.2 +/- 0.6}), although we are not able to obtain a strong
constraint on the slope of the relation due to the small sample size.
Additionally, we obtain E(z)^{-2/3} DA^2 Y500 ~ M500star^{1.0 +/- 0.6} for the
scaling with total stellar mass. The mass fraction in stars spans the range
0.006-0.034, with the second ranked cluster in terms of dynamical mass (ACT-CL
J0237-4939) having an unusually low total stellar mass and the lowest stellar
mass fraction. For the five clusters with gas mass measurements available in
the literature, we see no evidence for a shortfall of baryons relative to the
cosmic mean value.Comment: Accepted for publication in MNRAS; 12 pages, 10 figure
The Atacama Cosmology Telescope: Cosmological Parameters from the 2008 Power Spectra
We present cosmological parameters derived from the angular power spectrum of
the cosmic microwave background (CMB) radiation observed at 148 GHz and 218 GHz
over 296 deg^2 with the Atacama Cosmology Telescope (ACT) during its 2008
season. ACT measures fluctuations at scales 500<l<10000. We fit a model for the
lensed CMB, Sunyaev-Zel'dovich (SZ), and foreground contribution to the 148 GHz
and 218 GHz power spectra, including thermal and kinetic SZ, Poisson power from
radio and infrared point sources, and clustered power from infrared point
sources. The power from thermal and kinetic SZ at 148 GHz is estimated to be
B_3000 = 6.8+-2.9 uK^2, where B_l=l(l+1)C_l/2pi. We estimate primary
cosmological parameters from the 148 GHz spectrum, marginalizing over SZ and
source power. The LCDM cosmological model is a good fit to the data, and LCDM
parameters estimated from ACT+WMAP are consistent with the 7-year WMAP limits,
with scale invariant n_s = 1 excluded at 99.7% CL (3sigma). A model with no CMB
lensing is disfavored at 2.8sigma. By measuring the third to seventh acoustic
peaks, and probing the Silk damping regime, the ACT data improve limits on
cosmological parameters that affect the small-scale CMB power. The ACT data
combined with WMAP give a 6sigma detection of primordial helium, with Y_P =
0.313+-0.044, and a 4sigma detection of relativistic species, assumed to be
neutrinos, with Neff = 5.3+-1.3 (4.6+-0.8 with BAO+H0 data). From the CMB alone
the running of the spectral index is constrained to be dn/dlnk = -0.034 +-
0.018, the limit on the tensor-to-scalar ratio is r<0.25 (95% CL), and the
possible contribution of Nambu cosmic strings to the power spectrum is
constrained to string tension Gmu<1.6 \times 10^-7 (95% CL).Comment: 20 pages, 13 figures. Submitted to ApJ. This paper is a companion to
Hajian et al. (2010) and Das et al. (2010
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