111 research outputs found
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Sky Maps, Systematic Errors, and Basic Results
(Abridged) New full sky temperature and polarization maps based on seven
years of data from WMAP are presented. The new results are consistent with
previous results, but have improved due to reduced noise from the additional
integration time, improved knowledge of the instrument performance, and
improved data analysis procedures. The improvements are described in detail.
The seven year data set is well fit by a minimal six-parameter flat Lambda-CDM
model. The parameters for this model, using the WMAP data in conjunction with
baryon acoustic oscillation data from the Sloan Digital Sky Survey and priors
on H_0 from Hubble Space Telescope observations, are: Omega_bh^2 = 0.02260
+-0.00053, Omega_ch^2 = 0.1123 +-0.0035, Omega_Lambda = 0.728 +0.015 -0.016,
n_s = 0.963 +-0.012, tau = 0.087 +-0.014 and sigma_8 = 0.809 +-0.024 (68 % CL
uncertainties). The temperature power spectrum signal-to-noise ratio per
multipole is greater that unity for multipoles < 919, allowing a robust
measurement of the third acoustic peak. This measurement results in improved
constraints on the matter density, Omega_mh^2 = 0.1334 +0.0056 -0.0055, and the
epoch of matter- radiation equality, z_eq = 3196 +134 -133, using WMAP data
alone. The new WMAP data, when combined with smaller angular scale microwave
background anisotropy data, results in a 3 sigma detection of the abundance of
primordial Helium, Y_He = 0.326 +-0.075.The power-law index of the primordial
power spectrum is now determined to be n_s = 0.963 +-0.012, excluding the
Harrison-Zel'dovich-Peebles spectrum by >3 sigma. These new WMAP measurements
provide important tests of Big Bang cosmology.Comment: 42 pages, 9 figures, Submitted to Astrophysical Journal Supplement
Serie
First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Implications for Inflation
We confront predictions of inflationary scenarios with the WMAP data, in
combination with complementary small-scale CMB measurements and large-scale
structure data. The WMAP detection of a large-angle anti-correlation in the
temperature--polarization cross-power spectrum is the signature of adiabatic
superhorizon fluctuations at the time of decoupling. The WMAP data are
described by pure adiabatic fluctuations: we place an upper limit on a
correlated CDM isocurvature component. Using WMAP constraints on the shape of
the scalar power spectrum and the amplitude of gravity waves, we explore the
parameter space of inflationary models that is consistent with the data. We
place limits on inflationary models; for example, a minimally-coupled lambda
phi^4 is disfavored at more than 3-sigma using WMAP data in combination with
smaller scale CMB and large scale structure survey data. The limits on the
primordial parameters using WMAP data alone are: n_s(k_0=0.002
Mpc^{-1})=1.20_{-0.11}^{+0.12}, dn/dlnk=-0.077^{+0.050}_{- 0.052}, A(k_0=0.002
Mpc}^{-1})=0.71^{+0.10}_{-0.11} (68% CL), and r(k_0=0.002 Mpc^{-1})<1.28 (95%
CL).Comment: Accepted by ApJ; 49 pages, 9 figures. V2: Gives constraints from WMAP
data alone. Corrected approximation which made the constraints in Table 1 to
shift slightly. Corrected the Inflation Flow following the revision to
Kinney, astro-ph/0206032. No conclusions have been changed. For a detailed
list of changes see http://www.astro.princeton.edu/~hiranya/README.ERRATA.tx
First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Angular Power Spectrum
We present the angular power spectrum derived from the first-year Wilkinson
Microwave Anisotropy Probe (WMAP) sky maps. We study a variety of power
spectrum estimation methods and data combinations and demonstrate that the
results are robust. The data are modestly contaminated by diffuse Galactic
foreground emission, but we show that a simple Galactic template model is
sufficient to remove the signal. Point sources produce a modest contamination
in the low frequency data. After masking ~700 known bright sources from the
maps, we estimate residual sources contribute ~3500 uK^2 at 41 GHz, and ~130
uK^2 at 94 GHz, to the power spectrum l*(l+1)*C_l/(2*pi) at l=1000. Systematic
errors are negligible compared to the (modest) level of foreground emission.
Our best estimate of the power spectrum is derived from 28 cross-power spectra
of statistically independent channels. The final spectrum is essentially
independent of the noise properties of an individual radiometer. The resulting
spectrum provides a definitive measurement of the CMB power spectrum, with
uncertainties limited by cosmic variance, up to l~350. The spectrum clearly
exhibits a first acoustic peak at l=220 and a second acoustic peak at l~540 and
it provides strong support for adiabatic initial conditions. Kogut et al.
(2003) analyze the C_l^TE power spectrum, and present evidence for a relatively
high optical depth, and an early period of cosmic reionization. Among other
things, this implies that the temperature power spectrum has been suppressed by
\~30% on degree angular scales, due to secondary scattering.Comment: One of thirteen companion papers on first-year WMAP results submitted
to ApJ; 44 pages, 14 figures; a version with higher quality figures is also
available at http://lambda.gsfc.nasa.gov/product/map/map_bibliography.htm
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Are There Cosmic Microwave Background Anomalies?
(Abridged) A simple six-parameter LCDM model provides a successful fit to
WMAP data, both when the data are analyzed alone and in combination with other
cosmological data. Even so, it is appropriate to search for any hints of
deviations from the now standard model of cosmology, which includes inflation,
dark energy, dark matter, baryons, and neutrinos. The cosmological community
has subjected the WMAP data to extensive and varied analyses. While there is
widespread agreement as to the overall success of the six-parameter LCDM model,
various "anomalies" have been reported relative to that model. In this paper we
examine potential anomalies and present analyses and assessments of their
significance. In most cases we find that claimed anomalies depend on posterior
selection of some aspect or subset of the data. Compared with sky simulations
based on the best fit model, one can select for low probability features of the
WMAP data. Low probability features are expected, but it is not usually
straightforward to determine whether any particular low probability feature is
the result of the a posteriori selection or of non-standard cosmology. We
examine in detail the properties of the power spectrum with respect to the LCDM
model. We examine several potential or previously claimed anomalies in the sky
maps and power spectra, including cold spots, low quadrupole power,
quadropole-octupole alignment, hemispherical or dipole power asymmetry, and
quadrupole power asymmetry. We conclude that there is no compelling evidence
for deviations from the LCDM model, which is generally an acceptable
statistical fit to WMAP and other cosmological data.Comment: 19 pages, 17 figures, also available with higher-res figures on
http://lambda.gsfc.nasa.gov; accepted by ApJS; (v2) text as accepte
The MAP Satellite Feed Horns
We present the design, manufacturing methods, and characterization of 20
microwave feed horns currently in use on the Microwave Anisotropy Probe (MAP)
satellite. The nature of the cosmic microwave background (CMB) anisotropy
requires a detailed understanding of the properties of every optical component
of a microwave telescope. In particular, the properties of the feeds must be
known so that the forward gain and sidelobe response of the telescope can be
modeled and so that potential systematic effects may be computed. MAP requires
low emissivity, azimuthally symmetric, low-sidelobe feeds in five microwave
bands (K, Ka, Q, V, and W) that fit within a constrained geometry. The beam
pattern of each feed is modeled and compared with measurements; the agreement
is generally excellent to the -60 dB level (80 degrees from the beam peak).
This agreement verifies the beam-predicting software and the manufacturing
process. The feeds also affect the properties and modeling of the microwave
receivers. To this end, we show that the reflection from the feeds is less than
-25 dB over most of each band and that their emissivity is acceptable. The
feeds meet their multiple requirements.Comment: 9 pages with 7 figures, of which 2 are in low-resolution versions;
paper is available with higher quality figures at
http://map.gsfc.nasa.gov/m_mm/tp_links.htm
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Planets and Celestial Calibration Sources
(Abridged) We present WMAP seven-year observations of bright sources which
are often used as calibrators at microwave frequencies. Ten objects are studied
in five frequency bands (23 - 94 GHz): the outer planets (Mars, Jupiter,
Saturn, Uranus and Neptune) and five fixed celestial sources (Cas A, Tau A, Cyg
A, 3C274 and 3C58). The seven-year analysis of Jupiter provides temperatures
which are within 1-sigma of the previously published WMAP five-year values,
with slightly tighter constraints on variability with orbital phase, and limits
(but no detections) on linear polarization. Scaling factors are provided which,
when multiplied by the Wright Mars thermal model predictions at 350 micron,
reproduce WMAP seasonally averaged observations of Mars within ~2%. An
empirical model is described which fits brightness variations of Saturn due to
geometrical effects and can be used to predict the WMAP observations to within
3%. Seven-year mean temperatures for Uranus and Neptune are also tabulated.
Uncertainties in Uranus temperatures are 3%-4% in the 41, 61 and 94 GHz bands;
the smallest uncertainty for Neptune is ~8% for the 94 GHz band. Intriguingly,
the spectrum of Uranus appears to show a dip at ~30 GHz of unidentified origin,
although the feature is not of high statistical significance. Flux densities
for the five selected fixed celestial sources are derived from the seven-year
WMAP sky maps, and are tabulated for Stokes I, Q and U, along with polarization
fraction and position angle. Fractional uncertainties for the Stokes I fluxes
are typically 1% to 3%. Source variability over the seven-year baseline is also
estimated. Significant secular decrease is seen for Cas A and Tau A: our
results are consistent with a frequency independent decrease of about 0.53% per
year for Cas A and 0.22% per year for Tau A.Comment: 72 pages, 21 figures; accepted to ApJS; (v2) corrected Mars model
scaling factors, added figure 21, added text to Mars, Saturn and celestial
sources section
Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results
We present new full-sky temperature and polarization maps in five frequency
bands from 23 to 94 GHz, based on data from the first five years of the WMAP
sky survey. The five-year maps incorporate several improvements in data
processing made possible by the additional years of data and by a more complete
analysis of the instrument calibration and in-flight beam response. We present
several new tests for systematic errors in the polarization data and conclude
that Ka band data (33 GHz) is suitable for use in cosmological analysis, after
foreground cleaning. This significantly reduces the overall polarization
uncertainty. With the 5 year WMAP data, we detect no convincing deviations from
the minimal 6-parameter LCDM model: a flat universe dominated by a cosmological
constant, with adiabatic and nearly scale-invariant Gaussian fluctuations.
Using WMAP data combined with measurements of Type Ia supernovae and Baryon
Acoustic Oscillations, we find (68% CL uncertainties): Omega_bh^2 = 0.02267 \pm
0.00059, Omega_ch^2 = 0.1131 \pm 0.0034, Omega_Lambda = 0.726 \pm 0.015, n_s =
0.960 \pm 0.013, tau = 0.084 \pm 0.016, and Delta_R^2 = (2.445 \pm 0.096) x
10^-9. From these we derive: sigma_8 = 0.812 \pm 0.026, H_0 = 70.5 \pm 1.3
km/s/Mpc, z_{reion} = 10.9 \pm 1.4, and t_0 = 13.72 \pm 0.12 Gyr. The new limit
on the tensor-to-scalar ratio is r < 0.22 (95% CL). We obtain tight,
simultaneous limits on the (constant) dark energy equation of state and spatial
curvature: -0.14 < 1+w < 0.12 and -0.0179 < Omega_k < 0.0081 (both 95% CL). The
number of relativistic degrees of freedom (e.g. neutrinos) is found to be
N_{eff} = 4.4 \pm 1.5, consistent with the standard value of 3.04. Models with
N_{eff} = 0 are disfavored at >99.5% confidence.Comment: 46 pages, 13 figures, and 7 tables. Version accepted for publication,
ApJS, Feb-2009. Includes 5-year dipole results and additional references.
Also available at
http://lambda.gsfc.nasa.gov/product/map/dr3/map_bibliography.cf
Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Angular Power Spectra
We present the temperature and polarization angular power spectra of the
cosmic microwave background (CMB) derived from the first 5 years of WMAP data.
The 5-year temperature (TT) spectrum is cosmic variance limited up to multipole
l=530, and individual l-modes have S/N>1 for l<920. The best fitting
six-parameter LambdaCDM model has a reduced chi^2 for l=33-1000 of
chi^2/nu=1.06, with a probability to exceed of 9.3%. There is now significantly
improved data near the third peak which leads to improved cosmological
constraints. The temperature-polarization correlation (TE) is seen with high
significance. After accounting for foreground emission, the low-l reionization
feature in the EE power spectrum is preferred by \Delta\chi^2=19.6 for optical
depth tau=0.089 by the EE data alone, and is now largely cosmic variance
limited for l=2-6. There is no evidence for cosmic signal in the BB, TB, or EB
spectra after accounting for foreground emission. We find that, when averaged
over l=2-6, l(l+1)C^{BB}_l/2\pi < 0.15 uK^2 (95% CL).Comment: 29 pages, 13 figures, accepted by ApJ
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