1,604 research outputs found
Mapping the CMB I: the first flight of the QMAP experiment
We report on the first flight of the balloon-borne QMAP experiment. The
experiment is designed to make a map of the cosmic microwave background
anisotropy on angular scales from 0.7 to several degrees. Using the map we
determine the angular power spectrum of the anisotropy in multipole bands from
l~40 to l~140. The results are consistent with the Saskatoon (SK) measurements.
The frequency spectral index (measured at low l) is consistent with that of CMB
and inconsistent with either Galactic synchrotron or free-free emission. The
instrument, measurement, analysis of the angular power spectrum, and possible
systematic errors are discussed.Comment: 4 pages, with 5 figures included. Submitted to ApJL. Window functions
and color figures are available at
http://pupgg.princeton.edu/~cmb/welcome.htm
Mapping the CMB II: the second flight of the QMAP experiment
We report the results from the second flight of QMAP, an experiment to map
the cosmic microwave background near the North Celestial Pole. We present maps
of the sky at 31 and 42 GHz as well as a measurement of the angular power
spectrum covering the l-range 40-200. Anisotropy is detected at about 20 sigma
and is in agreement with previous results at these angular scales. We also
report details of the data reduction and analysis techniques which were used
for both flights of QMAP.Comment: 4 pages, with 5 figures included. Submitted to ApJL. Window functions
and color figures are available at
http://pupgg.princeton.edu/~cmb/welcome.htm
Galactic contamination in the QMAP experiment
We quantify the level of foreground contamination in the QMAP Cosmic
Microwave Background (CMB) data with two objectives: (a) measuring the level to
which the QMAP power spectrum measurements need to be corrected for foregrounds
and (b) using this data set to further refine current foreground models. We
cross-correlate the QMAP data with a variety of foreground templates. The 30
GHz Ka-band data is found to be significantly correlated with the Haslam 408
MHz and Reich and Reich 1420 MHz synchrotron maps, but not with the Diffuse
Infrared Background Experiment (DIRBE) 240, 140 and 100 micron maps or the
Wisconsin H-Alpha Mapper (WHAM) survey. The 40 GHz Q-band has no significant
template correlations. We discuss the constraints that this places on
synchrotron, free-free and dust emission. We also reanalyze the
foreground-cleaned Ka-band data and find that the two band power measurements
are lowered by 2.3% and 1.3%, respectively.Comment: 4 ApJL pages, including 4 figs. Color figures and data at
http://www.hep.upenn.edu/~angelica/foreground.html#qmap or from
[email protected]
A New Spin on Galactic Dust
We present a new puzzle involving Galactic microwave emission and attempt to
resolve it. On one hand, a cross-correlation analysis of the WHAM H-alpha map
with the Tenerife 10 and 15 GHz maps shows that the well-known DIRBE correlated
microwave emission cannot be dominated by free-free emission. On the other
hand, recent high resolution observations in the 8-10 GHz range with the Green
Bank 140 ft telescope by Finkbeiner et al. failed to find the corresponding 8
sigma signal that would be expected in the simplest spinning dust models. So
what physical mechanism is causing this ubiquitous dust-correlated emission? We
argue for a model predicting that spinning dust is the culprit after all, but
that the corresponding small grains are well correlated with the larger grains
seen at 100 micron only on large angular scales. In support of this grain
segregation model, we find the best spinning dust template to involve higher
frequency maps in the range 12-60 micron, where emission from transiently
heated small grains is important. Upcoming CMB experiments such as ground-based
interferometers, MAP and Planck LFI with high resolution at low frequencies
should allow a definitive test of this model.Comment: Minor revisions to match accepted ApJ version. 6 pages, 4 figs. Color
figures and more foreground information at
http://www.hep.upenn.edu/~angelica/foreground.html#spin or from
[email protected]
The Quest for Microwave Foreground X
The WMAP team has produced a foreground map that can account for most of the
low-frequency Galactic microwave emission in the WMAP maps, tentatively
interpreting it as synchrotron emission. Finkbeiner and collaborators have
challenged these conclusions, arguing that the WMAP team "synchrotron" template
is in fact not dominated by synchrotron radiation, but by some dust-related
Galactic emission process, perhaps spinning dust grains, making dramatically
different predictions for its behavior at lower frequencies. By
cross-correlating this "synchrotron" template with 10 and 15 GHz CMB
observations, we find that its spectrum turns over in a manner consistent with
spinning dust emission, falling about an order of magnitude below what the
synchrotron interpretation would predict.Comment: 4 pages, 1 fig. Submitted to ApJ. Color figures and more foreground
information at http://www.hep.upenn.edu/~angelica/foreground.html or from
[email protected]
Mapping the Cosmic Microwave Background Anisotropy:The First Flight of the QMAP Experiment
We report on the first flight of the balloon-borne QMAP experiment. The experiment is designed to make a map of the cosmic microwave background (CMB) anisotropy on angular scales from 0fdg70 to several degrees. Using the map, we determine the angular power spectrum of the anisotropy in multipole bands from l~40 to l~140. The results are consistent with the SK (from Saskatoon, Saskatchewan, Canada) measurements. The frequency spectral index (measured at low l) is consistent with that of CMB and inconsistent with either Galactic synchrotron or free-free emission. The instrument, measurement, analysis of the angular power spectrum, and possible systematic errors are discussed
What does inflation really predict?
If the inflaton potential has multiple minima, as may be expected in, e.g.,
the string theory "landscape", inflation predicts a probability distribution
for the cosmological parameters describing spatial curvature (Omega_tot), dark
energy (rho_Lambda, w, etc.), the primordial density fluctuations (Omega_tot,
dark energy (rho_Lambda, w, etc.). We compute this multivariate probability
distribution for various classes of single-field slow-roll models, exploring
its dependence on the characteristic inflationary energy scales, the shape of
the potential V and and the choice of measure underlying the calculation. We
find that unless the characteristic scale Delta-phi on which V varies happens
to be near the Planck scale, the only aspect of V that matters observationally
is the statistical distribution of its peaks and troughs. For all energy scales
and plausible measures considered, we obtain the predictions Omega_tot ~
1+-0.00001, w=-1 and rho_Lambda in the observed ballpark but uncomfortably
high. The high energy limit predicts n_s ~ 0.96, dn_s/dlnk ~ -0.0006, r ~ 0.15
and n_t ~ -0.02, consistent with observational data and indistinguishable from
eternal phi^2-inflation. The low-energy limit predicts 5 parameters but prefers
larger Q and redder n_s than observed. We discuss the coolness problem, the
smoothness problem and the pothole paradox, which severely limit the viable
class of models and measures. Our findings bode well for detecting an
inflationary gravitational wave signature with future CMB polarization
experiments, with the arguably best-motivated single-field models favoring the
detectable level r ~ 0.03. (Abridged)Comment: Replaced to match accepted JCAP version. Improved discussion,
references. 42 pages, 17 fig
Is cosmology consistent?
We perform a detailed analysis of the latest CMB measurements (including
BOOMERaNG, DASI, Maxima and CBI), both alone and jointly with other
cosmological data sets involving, e.g., galaxy clustering and the Lyman Alpha
Forest. We first address the question of whether the CMB data are internally
consistent once calibration and beam uncertainties are taken into account,
performing a series of statistical tests. With a few minor caveats, our answer
is yes, and we compress all data into a single set of 24 bandpowers with
associated covariance matrix and window functions. We then compute joint
constraints on the 11 parameters of the ``standard'' adiabatic inflationary
cosmological model. Out best fit model passes a series of physical consistency
checks and agrees with essentially all currently available cosmological data.
In addition to sharp constraints on the cosmic matter budget in good agreement
with those of the BOOMERaNG, DASI and Maxima teams, we obtain a heaviest
neutrino mass range 0.04-4.2 eV and the sharpest constraints to date on gravity
waves which (together with preference for a slight red-tilt) favors
``small-field'' inflation models.Comment: Replaced to match accepted PRD version. 14 pages, 12 figs. Tiny
changes due to smaller DASI & Maxima calibration errors. Expanded neutrino
and tensor discussion, added refs, typos fixed. Combined CMB data, window and
covariance matrix at http://www.hep.upenn.edu/~max/consistent.html or from
[email protected]
Comparing and combining the Saskatoon, QMAP and COBE CMB maps
We present a method for comparing and combining maps with different
resolutions and beam shapes, and apply it to the Saskatoon, QMAP and COBE/DMR
data sets. Although the Saskatoon and QMAP maps detect signal at the 21 sigma
and 40 sigma levels, respectively, their difference is consistent with pure
noise, placing strong limits on possible systematic errors. In particular, we
obtain quantitative upper limits on relative calibration and pointing errors.
Splitting the combined data by frequency shows similar consistency between the
Ka- and Q-bands, placing limits on foreground contamination. The visual
agreement between the maps is equally striking. Our combined QMAP+Saskatoon
map, nicknamed QMASK, is publicly available at
www.hep.upenn.edu/~xuyz/qmask.html together with its 6495x6495 noise covariance
matrix. This thoroughly tested data set covers a large enough area (648 square
degrees -- currently the largest degree-scale map available) to allow a
statistical comparison with COBE/DMR, showing good agreement.Comment: Replaced to match accepted PRD version. 12 pages, 11 figs. Map and
covariance matrix at http://www.hep.upenn.edu/~xuyz/qmask.html or from
[email protected]
The significance of the largest scale CMB fluctuations in WMAP
We investigate anomalies reported in the Cosmic Microwave Background maps
from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite on very large
angular scales and discuss possible interpretations. Three independent
anomalies involve the quadrupole and octopole:
1. The cosmic quadrupole on its own is anomalous at the 1-in-20 level by
being low (the cut-sky quadrupole measured by the WMAP team is more strikingly
low, apparently due to a coincidence in the orientation of our Galaxy of no
cosmological significance);
2. The cosmic octopole on its own is anomalous at the 1-in-20 level by being
very planar;
3. The alignment between the quadrupole and octopole is anomalous at the
1-in-60 level.
Although the a priori chance of all three occurring is 1 in 24000, the
multitude of alternative anomalies one could have looked for dilutes the
significance of such a posteriori statistics. The simplest small universe model
where the universe has toroidal topology with one small dimension of order half
the horizon scale, in the direction towards Virgo, could explain the three
items above. However, we rule this model out using two topological tests: the
S-statistic and the matched circle test.Comment: N.B. that our results do not rule out the recently proposed
dodecahedron model of Luminet, Weeks, Riazuelo, Lehoucq & Uzan, which has a
36 degree twist between matched circles. 12 pages, 5 figs; more info at
http://www.hep.upenn.edu/~angelica/topology.htm
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