16 results on '"Spectrum analysis"'
Search Results
2. CAN EFFECTS OF QUANTUM GRAVITY BE OBSERVED IN THE COSMIC MICROWAVE BACKGROUND?
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KIEFER, CLAUS and KRÄMER, MANUEL
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QUANTUM gravity , *ASTRONOMICAL observations , *COSMIC background radiation , *INFLATIONARY universe , *ANISOTROPY , *SPECTRUM analysis , *GRAVITATIONAL fields - Abstract
We investigate the question whether small quantum-gravitational effects can be observed in the anisotropy spectrum of the cosmic microwave background radiation. An observation of such an effect is needed in order to discriminate between different approaches to quantum gravity. Using canonical quantum gravity with the Wheeler-DeWitt equation, we find a suppression of power at large scales. Current observations only lead to an upper bound on the energy scale of inflation, but the framework is general enough to study other situations in which such effects might indeed be seen. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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3. Can relic superhorizon inhomogeneities be responsible for large-scale CMB anomalies?
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Gao, Xian
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COSMIC background radiation , *FLUCTUATIONS (Physics) , *QUADRUPOLES , *ANISOTROPY , *SPECTRUM analysis , *QUANTUM perturbations - Abstract
Abstract: We investigate the effects of the presence of relic classical superhorizon inhomogeneities during inflation. This superhorizon inhomogeneity appears as a gradient locally and picks out a preferred direction. Quantum fluctuations on this slightly inhomogeneous background are generally statistical anisotropic. We find a quadrupole modification to the ordinary isotropic spectrum. Moreover, this deviation from statistical isotropy is scale-dependent, with a factor. This result implies that the statistical anisotropy mainly appears on large scales, while the spectrum on small scales remains highly isotropic. Moreover, due to this factor, the power on large scales is suppressed. Thus, our model can simultaneously explain the observed anisotropic alignments of the low-ℓ multipoles and their low power. [Copyright &y& Elsevier]
- Published
- 2011
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4. No large-angle correlations on the non-Galactic microwave sky.
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Copi, Craig J., Huterer, Dragan, Schwarz, Dominik J., and Starkman, Glenn D.
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ASTRONOMY , *ANISOTROPY , *PROPERTIES of matter , *GALAXIES , *SPECTRUM analysis - Abstract
We investigate the angular two-point correlation function of temperature in the Wilkinson Microwave Anisotropy Probe (WMAP) maps. Updating and extending earlier results, we confirm the lack of correlations outside the Galaxy on angular scales greater than about 60° at a level that would occur in 0.025 per cent of realizations of the concordance model. This represents a dramatic increase in significance from the original observations by the Cosmic Background Explorer Differential Microwave Radiometer (COBE-DMR) and a marked increase in significance from the first-year WMAP maps. Given the rest of the reported angular power spectrum , the lack of large-angle correlations that one infers outside the plane of the Galaxy requires covariance among the up to . Alternately, it requires both the unusually small (5 per cent of realizations) full-sky large-angle correlations and an unusual coincidence of alignment of the Galaxy with the pattern of cosmological fluctuations (less than 2 per cent of those 5 per cent). We argue that unless there is some undiscovered systematic error in their collection or reduction, the data point towards a violation of statistical isotropy. The near-vanishing of the large-angle correlations in the cut-sky maps, together with their disagreement with results inferred from full-sky maps, remains open problems, and are very difficult to understand within the concordance model. [ABSTRACT FROM AUTHOR]
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- 2009
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5. Bianchi model CMB polarization and its implications for CMB anomalies.
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Pontzen, Andrew and Challinor, Anthony
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COSMIC background radiation , *GIANT multipole resonance , *ANISOTROPY , *SPECTRUM analysis , *HEAT radiation & absorption , *POLARIZATION (Nuclear physics) - Abstract
We derive the cosmic microwave background (CMB) radiative transfer equation in the form of a multipole hierarchy in the nearly Friedmann–Robertson–Walker limit of homogeneous, but anisotropic, universes classified via their Bianchi type. Compared with previous calculations, this allows a more sophisticated treatment of recombination, produces predictions for the polarization of the radiation and allows for reionization. Our derivation is independent of any assumptions about the dynamical behaviour of the field equations, except that it requires anisotropies to be small back to recombination; this is already demanded by observations. We calculate the polarization signal in the Bianchi VII h case, with the parameters recently advocated to mimic the several large-angle anomalous features observed in the CMB. We find that the peak polarization signal is for the best-fitting model to the temperature anisotropies, and is mostly confined to multipoles . Remarkably, the predicted large-angle EE and TE power spectra in the Bianchi model are consistent with Wilkinson Microwave Anisotropy Probe ( WMAP) observations that are usually interpreted as evidence of early reionization. However, the power in B-mode polarization is predicted to be similar to the E-mode power and parity-violating correlations are also predicted by the model; the WMAP non-detection of either of these signals casts further strong doubts on the veracity of attempts to explain the large-angle anomalies with global anisotropy. On the other hand, given that there exist further dynamical degrees of freedom in the VII h universes that are yet to be compared with CMB observations, we cannot at this time definitively reject the anisotropy explanation. [ABSTRACT FROM AUTHOR]
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- 2007
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6. Applications of Bayesian model selection to cosmological parameters.
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Trotta, Roberto
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BAYESIAN analysis , *METAPHYSICAL cosmology , *ANISOTROPY , *SPECTRUM analysis , *DATA analysis , *ASTROPHYSICS , *DARK matter - Abstract
Bayesian model selection is a tool for deciding whether the introduction of a new parameter is warranted by the data. I argue that the usual sampling statistic significance tests for a null hypothesis can be misleading, since they do not take into account the information gained through the data, when updating the prior distribution to the posterior. In contrast, Bayesian model selection offers a quantitative implementation of Occam's razor. I introduce the Savage–Dickey density ratio, a computationally quick method to determine the Bayes factor of two nested models and hence perform model selection. As an illustration, I consider three key parameters for our understanding of the cosmological concordance model. By using Wilkinson Microwave Anisotropy Probe ( WMAP) 3-year data complemented by other cosmological measurements, I show that a non-scale-invariant spectral index of perturbations is favoured for any sensible choice of prior. It is also found that a flat universe is favoured with odds of 29:1 over non-flat models, and that there is strong evidence against a cold dark matter isocurvature component to the initial conditions which is totally (anti)correlated with the adiabatic mode (odds of about 2000:1), but that this is strongly dependent on the prior adopted. These results are contrasted with the analysis of WMAP 1-year data, which were not informative enough to allow a conclusion as to the status of the spectral index. In a companion paper, a new technique to forecast the Bayes factor of a future observation is presented. [ABSTRACT FROM AUTHOR]
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- 2007
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7. Cosmic microwave background signal in Wilkinson Microwave Anisotropy Probe three-year data withfastica.
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Maino, D., Donzelli, S., Banday, A. J., Stivoli, F., and Baccigalupi, C.
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COSMIC background radiation , *MONTE Carlo method , *ANISOTROPY , *SPECTRUM analysis , *ASTROPHYSICAL radiation - Abstract
We present an application of the fast Independent Component Analysis (fastica) to the Wilkinson Microwave Anisotropy Probe ( WMAP) three-year data with the goal of extracting the cosmic microwave background (CMB) signal. We evaluate the confidence of our results by means of Monte Carlo simulations including the CMB, foreground contaminations and instrumental noise specific to each WMAP frequency band. We perform a complete analysis involving all or a subset of the WMAP channels in order to select the optimal combination for CMB extraction, using the frequency scaling of the reconstructed component as a figure of merit. We find that the combination KQVW provides the best CMB frequency scaling, indicating that the low-frequency foreground contamination in Q, V and W bands is better traced by the emission in the K band. The CMB angular power spectrum is recovered up to the degree scale; it is consistent within errors for all WMAP channel combinations considered, and in close agreement with the WMAP three-year results. A power spectrum analysis is made of the sky map divided into two hemispheres that have been previously reported as showing evidence of an asymmetric ratio of power on large angular scales. We then confirm the findings of several previous works with independent techniques. [ABSTRACT FROM AUTHOR]
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- 2007
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8. A determination of the spectra of Galactic components observed by the Wilkinson Microwave Anisotropy Probe.
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Davies, R. D., Dickinson, C., Banday, A. J., Jaffe, T. R., Górski, K. M., and Davis, R. J.
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COSMIC background radiation , *METAPHYSICAL cosmology , *SYNCHROTRONS , *GALAXIES , *ANISOTROPY , *SPECTRUM analysis - Abstract
Wilkinson Microwave Anisotropy Probe ( WMAP) data when combined with ancillary data on free–free, synchrotron and dust allow an improved understanding of the spectrum of emission from each of these components. Here, we examine the sky variation at intermediate latitudes using a cross-correlation technique. In particular, we compare the observed emission in 15 selected sky regions to three ‘standard’ templates. The free–free emission of the diffuse ionized gas is fitted by a well-known spectrum at K and Ka band, but the derived emissivity corresponds to a mean electron temperature of ∼4000–5000 K. This is inconsistent with estimates from Galactic H ii regions although a variation in the derived ratio of Hα to free–free intensity by a factor of ∼2 is also found from region to region. The origin of the discrepancy is unclear. The anomalous emission associated with dust is clearly detected in most of the 15 fields studied. The anomalous emission correlates well with the Finkbeiner, Davis & Schlegel model 8 predictions (FDS8) at 94 GHz, with an effective spectral index between 20 and 60 GHz, of . Furthermore, the emissivity varies by a factor of ∼2 from cloud to cloud. A modestly improved fit to the anomalous dust at K band is provided by modulating the template by an estimate of the dust colour temperature, specifically . We find a preferred value , although there is a scatter from region to region. Nevertheless, the preferred index drops to zero at higher frequencies where the thermal dust emission dominates. The synchrotron emission steepens between GHz frequencies and the WMAP bands. There are indications of spectral index variations across the sky but the current data are not precise enough to accurately quantify this from region to region. Our analysis of the WMAP data indicates strongly that the dust-correlated emission at the low WMAP frequencies has a spectrum which is compatible with spinning dust; we find no evidence for a synchrotron component correlated with dust. The importance of these results for the correction of cosmic microwave background data for Galactic foreground emission is discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2006
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9. Template fitting and the large-angle cosmic microwave background anomalies.
- Author
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Land, Kate and Magueijo, João
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COSMIC background radiation , *ANISOTROPY , *GALAXIES , *ASTROPHYSICS , *WAVELENGTHS , *SPECTRUM analysis - Abstract
We investigate two possible explanations for the large-angle anomalies in the cosmic microwave background (CMB): an intrinsically anisotropic model and an inhomogeneous model. We take as an example of the former a Bianchi model (which leaves a spiral pattern in the sky) and of the latter a background model that already contains a non-linear long-wavelength plane wave (leaving a stripy pattern in the sky). We make use of an adaptation of the ‘template’ formalism, previously designed to detect galactic foregrounds, to recognize these patterns and produce confidence levels for their detection. The ‘corrected’ maps, from which these patterns have been removed, are free of anomalies, in particular their quadrupole and octopole are not planar and their intensities are not low. We stress that although the ‘template’ detections are not found to be statistically significant they do correct statistically significant anomalies. [ABSTRACT FROM AUTHOR]
- Published
- 2006
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10. The kinetic Sunyaev–Zel’dovich effect from reionization
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McQuinn, Matthew, Furlanetto, Steven R., Hernquist, Lars, Zahn, Oliver, and Zaldarriaga, Matias
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ANISOTROPY , *CRYSTALLOGRAPHY , *PROPERTIES of matter , *SPECTRUM analysis , *COSMIC background radiation - Abstract
Abstract: During the epoch of reionization, local variations in the ionized fraction (patchiness) imprint arcminute-scale temperature anisotropies in the cosmic microwave background through the kinetic Sunyaev–Zel’dovich (kSZ) effect. We employ an analytic model of reionization devised by Furlanetto and coworkers to calculate the kSZ anisotropies for patchy reionization. We find that the angular power spectrum of the kSZ anisotropies depends strongly on the size distribution of the HII bubbles and on the duration of reionization. In addition, we show that upcoming measurements of the kSZ effect should be able to distinguish between several popular reionization scenarios. In particular, the amplitude of the patchy power spectrum for reionization scenarios in which the IGM is significantly ionized by Population III stars (or by mini-quasars/decaying particles) can be larger (or smaller) by over a factor of 3 than the amplitude in more traditional reionization histories (with temperature anisotropies that range between 0.5 and 3μK at l =5000). [Copyright &y& Elsevier]
- Published
- 2006
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11. Cosmic microwave background and foregrounds in Wilkinson Microwave Anisotropy Probe first-year data.
- Author
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Patanchon, G., Cardoso, J.-F., Delabrouille, J., and Vielva, P.
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COSMIC background radiation , *ASTROPHYSICAL radiation , *ANISOTROPY , *METAPHYSICAL cosmology , *SPECTRUM analysis , *ASTRONOMY - Abstract
We perform a blind multicomponent analysis of the Wilkinson Microwave Anisotropy Probe ( WMAP) 1-yr foreground-cleaned maps using Spectral Matching Independent Component Analysis ( smica). We provide a new estimate of the cosmic microwave background (CMB) power spectrum as well as the amplitude of the CMB anisotropies across frequency channels. We show that the CMB anisotropies are compatible with temperature fluctuations as expected from the standard paradigm. The analysis also allows us to identify and separate a weak residual Galactic emission, present significantly in the Q band outside of the Kp2 1 mask limits, and mainly concentrated at low Galactic latitudes. We produce a map of this residual component by Wiener filtering using estimated parameters. The level of contamination of CMB data by this component is compatible with the WMAP-team estimation of foreground residual contamination. In addition, the multicomponent analysis allows us to estimate jointly the power spectrum of unresolved point-source emission. [ABSTRACT FROM AUTHOR]
- Published
- 2005
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12. A very extended reionization epoch?
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Melchiorri, A., Choudhury, T. Roy, Serra, P., and Ferrara, A.
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COSMIC background radiation , *ASTROPHYSICAL radiation , *ANISOTROPY , *POWER spectra , *SPECTRUM analysis , *THOMSON scattering , *ELECTROMAGNETIC wave scattering - Abstract
The recent observations of cross temperature–polarization power spectra of the cosmic microwave background (CMB) made by the Wilkinson Microwave Anisotropy Probe ( WMAP) satellite are in better agreement with a high value of the Thomson scattering optical depth τ≈ 0.17. This value is close to τ= 0.3, which is taken as the upper limit in the parameter extraction analysis made by the WMAP team. However, models with τ∼ 0.3 provide a good fit to current CMB data and are not significantly excluded when combined with large-scale structure data. By making use of a self-consistent reionization model, we verify the astrophysical feasibility of models with τ∼ 0.3. It turns out that current data on various observations related to the thermal and ionization history of the intergalactic medium are not able to rule out τ∼ 0.3. The possibility of a very extended reionization epoch can significantly undermine the WMAP constraints on crucial cosmological parameters such as the Hubble constant, the spectral index of primordial fluctuations and the amplitude of dark matter clustering. [ABSTRACT FROM AUTHOR]
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- 2005
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13. Error analysis of quadratic power spectrum estimates for cosmic microwave background polarization: sampling covariance.
- Author
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Challinor, Anthony and Chon, Gayoung
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COSMIC background radiation , *SPECTRUM analysis , *ERROR analysis in mathematics , *ASTROPHYSICAL radiation , *POLARIZATION (Nuclear physics) , *ANISOTROPY , *COSMIC ripples - Abstract
Quadratic methods with heuristic weighting (e.g. pseudo-or correlation function methods) represent an efficient way to estimate power spectra of the cosmic microwave background (CMB) anisotropies and their polarization. We construct the sample covariance properties of such estimators for CMB polarization, and develop semi-analytic techniques to approximate the pseudo-sample covariance matrices at high Legendre multipoles, taking account of the geometric effects of mode coupling and the mixing between the electric (E) and magnetic (B) polarization that arise for observations covering only part of the sky. TheE– Bmixing ultimately limits the applicability of heuristically weighted quadratic methods to searches for the gravitational-wave signal in the large-angleB-mode polarization, even for methods that can recover (exactly) unbiased estimates of theB-mode power. We show that for surveys covering 1 or 2 per cent of the sky, the contribution ofE-mode power to the covariance of the recoveredB-mode power spectrum typically limits the tensor-to-scalar ratio that can be probed with such methods to∼0.05. [ABSTRACT FROM AUTHOR]
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- 2005
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14. Effects of destriping errors on estimates of the CMB power spectrum.
- Author
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Efstathiou, G.
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COSMIC background radiation , *ASTROPHYSICAL radiation , *ANISOTROPY , *SPECTRUM analysis , *GEOMETRY , *ASTRONOMY - Abstract
Destriping methods for constructing maps of the cosmic microwave background (CMB) anisotropies have been investigated extensively in the literature. However, their error properties have been studied in less detail. Here we present an analysis of the effects of destriping errors on CMB power spectrum estimates forPlanck-like scanning strategies. Analytic formulae are derived for certain simple scanning geometries that can be rescaled to account for different detector noise. AssumingPlanck-like low-frequency noise, the noise power spectrum is accurately white at high multipoles. Destriping errors, though dominant at lower multipoles, are small in comparison to the cosmic variance. These results show that simple destriping map-making methods should be perfectly adequate for the analysis ofPlanckdata and support the arguments given in an earlier paper in favour of applying a fast hybrid power spectrum estimator to CMB data with realistic‘1/ f’ noise. [ABSTRACT FROM AUTHOR]
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- 2005
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15. The WMAP data and results
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Wright, E.L.
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ANISOTROPY , *EARTH (Planet) , *SUN , *SPECTRUM analysis , *ELECTRON scattering - Abstract
The Wilkinson Microwave Anisotropy Probe (WMAP) science team has released results from the first year of operation at the Earth–Sun L
2 Lagrange point. The maps are consistent with previous observations but have much better sensitivity and angular resolution than the COBE DMR maps, and much better calibration accuracy and sky coverage than ground-based and balloon-borne experiments. The angular power spectra from these ground-based and balloon-borne experiments are consistent within their systematic and statistical uncertainties with the WMAP results. WMAP detected the large angular-scale correlation between the temperature and polarization anisotropies of the CMB caused by electron scattering since the Universe became reionized after the “Dark Ages”, giving a value for the electron scattering optical depth of 0.17 ± 0.04. The simplest ΛCDM model withn=1 andΩtot=1 fixed provides an adequate fit to the WMAP data and gives parameters which are consistent with determinations of the Hubble constant and observations of the accelerating Universe using supernovae. The time-ordered data, maps, and power spectra from WMAP can be found at http://lambda.gsfc.nasa.gov along with 13 papers by the WMAP science team describing the results in detail. [Copyright &y& Elsevier]- Published
- 2003
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16. MAXIMA: A balloon-borne cosmic microwave background anisotropy experiment
- Author
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J. Borrill, M. E. Abroe, Jiun-Huei Proty Wu, Calvin B. Netterfield, Shaul Hanany, G. F. Smoot, C. D. Winant, Paul L. Richards, V. V. Hristov, Bahman Rabii, Andrew H. Jaffe, Amedeo Balbi, R. Stompor, Andrew E. Lange, J. J. Bock, A. Boscaleri, B. Johnson, Enzo Pascale, J. Collins, Peter A. R. Ade, P. de Bernardis, Pedro G. Ferreira, A. T. Lee, AstroParticule et Cosmologie (APC (UMR_7164)), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3), Computational Research Division [LBNL Berkeley] (CRD), Lawrence Berkeley National Laboratory [Berkeley] (LBNL), Space Sciences Laboratory [Berkeley] (SSL), University of California [Berkeley], University of California-University of California, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), University of California [Berkeley] (UC Berkeley), University of California (UC)-University of California (UC), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, and PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)
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Correlation matrices ,media_common.quotation_subject ,Cosmic microwave background ,Millimeter waves ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Matrix algebra ,Microwave devices ,Spectral line ,Planck Surveyor Satellite ,law.invention ,[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO] ,Wilkinson Microwave Anisotropy ,Settore FIS/05 - Astronomia e Astrofisica ,law ,0103 physical sciences ,95.55.Jz, 95.55.Rg, 07.57.Kp, 98.70.Vc ,010306 general physics ,Anisotropy ,GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries) ,010303 astronomy & astrophysics ,Instrumentation ,Magnetic anisotropy ,media_common ,Physics ,Bolometers ,Correlation methods ,Detector circuits ,Spectrum analysis ,Cosmic microwave background (CMB) ,Astrophysics (astro-ph) ,Bolometer ,Astrophysics::Instrumentation and Methods for Astrophysics ,Spectral bands ,Sky ,Extremely high frequency ,Maxima - Abstract
We describe the Millimeter wave Anisotropy eXperiment IMaging Array (MAXIMA), a balloon-borne experiment designed to measure the temperature anisotropy of the Cosmic Microwave Background (CMB) on angular scales of 10' to 5 degrees . MAXIMA mapped the CMB using 16 bolometric detectors in spectral bands centered at 150 GHz, 240 GHz, and 410 GHz, with 10' resolution at all frequencies. The combined receiver sensitivity to CMB anisotropy was ~40 microK/rt(sec). Systematic parasitic contributions were minimized by using four uncorrelated spatial modulations, thorough crosslinking, multiple independent CMB observations, heavily baffled optics, and strong spectral discrimination. Pointing reconstruction was accurate to 1', and absolute calibration was better than 4%. Two MAXIMA flights with more than 8.5 hours of CMB observations have mapped a total of 300 deg^2 of the sky in regions of negligible known foreground emission. MAXIMA results have been released in previous publications. MAXIMA maps, power spectra and correlation matrices are publicly available at http://cosmology.berkeley.edu/maxima, 22 pages, 22 figures, 13 tables. Submitted to ApJ. More information and figures are available for download at http://cosmology.berkeley.edu/maxima/
- Published
- 2006
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