arXiv subjects

M. Limon

Publications and source records attributed to M. Limon.

At least 73 records · Page 4Linked to original sources

arXiv2003

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters

WMAP precision data enables accurate testing of cosmological models. We find that the emerging standard model of cosmology, a flat Lambda-dominated universe seeded by nearly scale-invariant adiabatic Gaussian fluctuations, fits the WMAP data. With parameters fixed only by WMAP data, we can fit finer scale CMB measurements and measurements of large scle structure (galaxy surveys and the Lyman alpha forest). This simple model is also consistent with a host of other astronomical measurements. We then fit the model parameters to a combination of WMAP data with other finer scale CMB experiments (ACBAR and CBI), 2dFGRS measurements and Lyman alpha forest data to find the model's best fit cosmological parameters: h=0.71+0.04-0.03, Omega_b h^2=0.0224+-0.0009, Omega_m h^2=0.135+0.008-0.009, tau=0.17+-0.06, n_s(0.05/Mpc)=0.93+-0.03, and sigma_8=0.84+-0.04. WMAP's best determination of tau=0.17+-0.04 arises directly from the TE data and not from this model fit, but they are consistent. These parameters imply that the age of the universe is 13.7+-0.2 Gyr. The data favors but does not require a slowly varying spectral index. By combining WMAP data with other astronomical data sets, we constrain the geometry of the universe, Omega_tot = 1.02 +- 0.02, the equation of state of the dark energy w < -0.78 (95% confidence limit assuming w >= -1), and the energy density in stable neutrinos, Omega_nu h^2 < 0.0076 (95% confidence limit). For 3 degenerate neutrino species, this limit implies that their mass is less than 0.23 eV (95% confidence limit). The WMAP detection of early reionization rules out warm dark matter.

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arXiv2003

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Tests of Gaussianity

We present limits to the amplitude of non-Gaussian primordial fluctuations in the WMAP 1-year cosmic microwave background sky maps. A non-linear coupling parameter, f_NL, characterizes the amplitude of a quadratic term in the primordial potential. We use two statistics: one is a cubic statistic which measures phase correlations of temperature fluctuations after combining all configurations of the angular bispectrum. The other uses the Minkowski functionals to measure the morphology of the sky maps. Both methods find the WMAP data consistent with Gaussian primordial fluctuations and establish limits, -58<f_NL<134, at 95% confidence. There is no significant frequency or scale dependence of f_NL. The WMAP limit is 30 times better than COBE, and validates that the power spectrum can fully characterize statistical properties of CMB anisotropy in the WMAP data to high degree of accuracy. Our results also validate the use of a Gaussian theory for predicting the abundance of clusters in the local universe. We detect a point-source contribution to the bispectrum at 41 GHz, b_src = (9.5+-4.4) X 1e-5 uK^3 sr^2, which gives a power spectrum from point sources of c_src = (15+-6) X 1e-3 uK^2 sr in thermodynamic temperature units. This value agrees well with independent estimates of source number counts and the power spectrum at 41 GHz, indicating that b_src directly measures residual source contributions.

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arXiv2003

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Foreground Emission

Full sky maps are made in five microwave frequency bands to separate the temperature anisotropy of the CMB from foreground emission. We define masks that excise regions of high foreground emission. The effectiveness of template fits to remove foreground emission from the WMAP data is examined. These efforts result in a CMB map with minimal contamination and a demonstration that the WMAP CMB power spectrum is insensitive to residual foreground emission. We construct a model of the Galactic emission components. We find that the Milky Way resembles other normal spiral galaxies between 408 MHz and 23 GHz, with a synchrotron spectral index that is flattest (beta ~ -2.5) near star-forming regions, especially in the plane, and steepest (beta ~ -3) in the halo. The significant synchrotron index steepening out of the plane suggests a diffusion process in which the halo electrons are trapped in the Galactic potential long enough to suffer synchrotron and inverse Compton energy losses and hence a spectral steepening. The synchrotron index is steeper in the WMAP bands than in lower frequency radio surveys, with a spectral break near 20 GHz to beta < -3. The modeled thermal dust spectral index is also steep in the WMAP bands, with beta ~ 2.2. Microwave and H alpha measurements of the ionized gas agree. Spinning dust emission is limited to < ~5% of the Ka-band foreground emission. A catalog of 208 point sources is presented. Derived source counts suggest a contribution to the anisotropy power from unresolved sources of (15.0 +- 1.4) 10^{-3} microK^2 sr at Q-band and negligible levels at V-band and W-band.

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arXiv2003

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Preliminary Maps and Basic Results

We present full sky microwave maps in five bands (23 to 94 GHz) from the WMAP first year sky survey. Calibration errors are <0.5% and the low systematic error level is well specified. The 2 1 per mode to l=658. The temperature-polarization cross-power spectrum reveals both acoustic features and a large angle correlation from reionization. The optical depth of reionization is 0.17 +/- 0.04, which implies a reionization epoch of 180+220-80 Myr (95% CL) after the Big Bang at a redshift of 20+10-9 (95% CL) for a range of ionization scenarios. This early reionization is incompatible with the presence of a significant warm dark matter density. The age of the best-fit universe is 13.7 +/- 0.2 Gyr old. Decoupling was 379+8-7 kyr after the Big Bang at a redshift of 1089 +/- 1. The thickness of the decoupling surface was dz=195 +/- 2. The matter density is Omega_m h^2 = 0.135 +0.008 -0.009, the baryon density is Omega_b h^2 = 0.0224 +/- 0.0009, and the total mass-energy of the universe is Omega_tot = 1.02 +/- 0.02. The spectral index of scalar fluctuations is fit as n_s = 0.93 +/- 0.03 at wavenumber k_0 = 0.05 Mpc^-1, with a running index slope of dn_s/d ln k = -0.031 +0.016 -0.018 in the best-fit model. This flat universe model is composed of 4.4% baryons, 22% dark matter and 73% dark energy. The dark energy equation of state is limited to w<-0.78 (95% CL). Inflation theory is supported with n_s~1, Omega_tot~1, Gaussian random phases of the CMB anisotropy, and superhorizon fluctuations. An admixture of isocurvature modes does not improve the fit. The tensor-to-scalar ratio is r(k_0=0.002 Mpc^-1)<0.90 (95% CL).

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arXiv2003

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).

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arXiv2003

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Dark Energy Induced Correlation with Radio Sources

The first-year WMAP data, in combination with any one of a number of other cosmic probes, show that we live in a flat Λ-dominated CDM universe with Ω_m ~ 0.27 and Ω_Λ~ 0.73. In this model the late-time action of the dark energy, through the integrated Sachs-Wolfe effect, should produce CMB anisotropies correlated with matter density fluctuations at z<2 (Crittenden & Turok 1996). The measurement of such a signal is an important independent check of the model. We cross-correlate the NRAO VLA Sky Survey radio source catalog (Condon et al. 1998) with the WMAP data in search of this signal, and see indications of the expected correlation. Assuming a flat Λ-CDM cosmology, we find Ω_Λ>0 (95% CL, statistical errors only) with the peak of the likelihood at Ω_Λ=0.68, consistent with the preferred WMAP value. A closed model with Ω_m=1.28, h=0.33, and no dark energy component (Ω_Λ=0), marginally consistent with the WMAP CMB TT angular power spectrum, would produce an anti-correlation between the matter distribution and the CMB. Our analysis of the cross-correlation of the WMAP data with the NVSS catalog rejects this cosmology at the 3σlevel.

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arXiv2003

Design, Implementation and Testing of the MAP Radiometers

The Microwave Anisotropy Probe (MAP) satellite, launched June 30, 2001, will produce full sky maps of the cosmic microwave background radiation in 5 frequency bands spanning 20 - 106 GHz. MAP contains 20 differential radiometers built with High Electron Mobility Transistor (HEMT) amplifiers with passively cooled input stages. The design and test techniques used to evaluate and minimize systematic errors and the pre-launch performance of the radiometers for all five bands are presented.

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arXiv2003

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: On-Orbit Radiometer Characterization

The WMAP satellite has completed one year of measurements of the Cosmic Microwave Background (CMB) radiation using 20 differential high-electron-mobility-transistor (HEMT) based radiometers. All the radiometers are functioning nominally, and characterizations of the on-orbit radiometer performance are presented, with an emphasis on properties that are required for the production of sky maps from the time ordered data. A radiometer gain model, used to smooth and interpolate the CMB dipole gain measurements is also presented. No degradation in the sensitivity of any of the radiometers has been observed during the first year of observations.

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arXiv2003

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing Methods and Systematic Errors Limits

We describe the calibration and data processing methods used to generate full-sky maps of the cosmic microwave background (CMB) from the first year of Wilkinson Microwave Anisotropy Probe (WMAP) observations. Detailed limits on residual systematic errors are assigned based largely on analyses of the flight data supplemented, where necessary, with results from ground tests. The data are calibrated in flight using the dipole modulation of the CMB due to the observatory's motion around the Sun. This constitutes a full-beam calibration source. An iterative algorithm simultaneously fits the time-ordered data to obtain calibration parameters and pixelized sky map temperatures. The noise properties are determined by analyzing the time-ordered data with this sky signal estimate subtracted. Based on this, we apply a pre-whitening filter to the time-ordered data to remove a low level of 1/f noise. We infer and correct for a small ~1% transmission imbalance between the two sky inputs to each differential radiometer, and we subtract a small sidelobe correction from the 23 GHz (K band) map prior to further analysis. No other systematic error corrections are applied to the data. Calibration and baseline artifacts, including the response to environmental perturbations, are negligible. Systematic uncertainties are comparable to statistical uncertainties in the characterization of the beam response. Both are accounted for in the covariance matrix of the window function and are propagated to uncertainties in the final power spectrum. We characterize the combined upper limits to residual systematic uncertainties through the pixel covariance matrix.

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arXiv2003

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.

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arXiv2003

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Galactic Signal Contamination from Sidelobe Pickup

Since the Galactic center is ~1000 times brighter than fluctuations in the Cosmic Microwave Background (CMB), CMB experiments must carefully account for stray Galactic pickup. We present the level of contamination due to sidelobes for the year one CMB maps produced by the WMAP observatory. For each radiometer, full 4 pi sr antenna gain patterns are determined from a combination of numerical prediction, ground-based and space-based measurements. These patterns are convolved with the WMAP year one sky maps and observatory scan pattern to generate expected sidelobe signal contamination, for both intensity and polarized microwave sky maps. Outside of the Galactic plane, we find rms values for the expected sidelobe pickup of 15, 2.1, 2.0, 0.3, 0.5 uK for K, Ka, Q, V, and W bands respectively. Except at K band, the rms polarized contamination is <<1 uK. Angular power spectra of the Galactic pickup are presented.

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arXiv2003

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.

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arXiv2003

The Microwave Anisotropy Probe (MAP) Mission

The purpose of the MAP mission is to determine the geometry, content, and evolution of the universe via a 13 arcmin full-width-half-max (FWHM) resolution full sky map of the temperature anisotropy of the cosmic microwave background radiation with uncorrelated pixel noise, minimal systematic errors, multifrequency observations, and accurate calibration. These attributes were key factors in the success of NASA's Cosmic Background Explorer (COBE) mission, which made a 7 degree FWHM resolution full sky map, discovered temperature anisotropy, and characterized the fluctuations with two parameters, a power spectral index and a primordial amplitude. Following COBE considerable progress has been made in higher resolution measurements of the temperature anisotropy. With 45 times the sensitivity and 33 times the angular resolution of the COBE mission, MAP will vastly extend our knowledge of cosmology. MAP will measure the physics of the photon-baryon fluid at recombination. From this, MAP measurements will constrain models of structure formation, the geometry of the universe, and inflation. In this paper we present a pre-launch overview of the design and characteristics of the MAP mission. This information will be necessary for a full understanding of the MAP data and results, and will also be of interest to scientists involved in the design of future cosmic microwave background experiments and/or space science missions.

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arXiv2003

The Optical Design and Characterization of the Microwave Anisotropy Probe

The primary goal of the MAP satellite, now in orbit, is to make high fidelity polarization sensitive maps of the full sky in five frequency bands between 20 and 100 GHz. From these maps we will characterize the properties of the cosmic microwave background (CMB) anisotropy and Galactic and extragalactic emission on angular scales ranging from the effective beam size, <0.23 degree, to the full sky. MAP is a differential microwave radiometer. Two back-to-back shaped offset Gregorian telescopes feed two mirror symmetric arrays of ten corrugated feeds. We describe the prelaunch design and characterization of the optical system, compare the optical models to the measurements, and consider multiple possible sources of systematic error.

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arXiv2000

Millimetric Ground Based Observation of CMBR Anisotropy at $δ=+28^{\lowercase{o}}$

Results from the third campaign of a ground-based multi-band observation of the millimeter emission of the sky from Tenerife (Canary Islands) are presented. The instrument consists of a 0.45 meter diameter off-axis telescope equipped with a 4-band multi-mode $^3He$ cooled photometer working at 1.1, 1.3, 2.1 and 3.1{\notetoeditor{These are effective wavelengths}} mm wavelengths. The beam is well approximated by a Gaussian with 1$% ^{o}$.35 Full Width Half Maximum (FWHM) at all wavelengths. The wide wavelength coverage of our instrument allows us to characterize and reduce both the atmospheric and galactic contamination in our data. The CMBR data is analyzed in 6 multipole bands whose centers span the range $\ell=39$ to $\ell =134$ at the two longest wavelengths (2.1 and 3.1 mm). A likelihood analysis indicates that we have detected fluctuations in all bands at the two wavelengths. We have evidence of a rise in the angular power spectrum from low $\ell $ to high $\ell $. Our measured spectrum is consistent with current popular theories of large scale structure formation, COBE, and other recent balloon-borne experiments with similar wavelength coverage.

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arXiv1997

The IAC-Bartol Cosmic Microwave Background Anisotropy Experiment: Results of the 1994 Campaign

We present the results of a Cosmic Microwave Background (CMB) anisotropy ground-based millimetric experiment sensitive to fluctuations on angular scales of $\sim 2\degg$. Four independent bands centered at 3.3, 2.1, 1.3 and 1.1 mm collected $\sim 550$ hours of observation during the Summer of 1994. The instrument was located on the island of Tenerife at an altitude of 2400 m. The low water-vapor content and the atmospheric stability of the site, combined with new techniques to subtract atmospheric noise, result in the reduction of atmospheric contamination in the lowest frequency channel to a level of $\sim 1.5$~times the instrument noise. Detailed estimations of Galactic foreground contamination show that this contribution is negligible at $|b| \stackrel{>}{_\sim} 12\degg$. Two different multipole bands ($\ell=53^{+22}_{-13}$ and $33^{+24}_{-13}$) are analyzed showing that our technique to subtract the atmospheric contribution is more effective in the multipole band at $\ell=53$. A likelihood analysis of these data reveals the presence of a common signal between the channels at 3.3, 2.1 and 1.3 mm corresponding to a band power estimate of $ \sqrt{\lla (\lla+1) C_{\lla}/(2 π)} = 2.0^{+1.0}_{-0.8} \cdot 10^{-5}$ and $\sqrt{\lla (\lla+1) C_{\lla}/(2 π)} = 4.1^{+2.4}_{-2.2} \cdot 10^{-5}$ for the $\ell =53$ and 33 multipole bands respectively. Calibration uncertainty has been treated as a systematic effect. The level of fluctuations in the $\ell =53$ band is in good agreement with our preliminary analysis presented in Piccirillo \et 1997, with measurements by other experiments working at similar angular scales, and with the predictions of standard Cold Dark Matter (CDM) models.

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arXiv1997

A search for millimetric emission from Gamma Ray Bursts

We have used the 2- year Differential Microwave Radiometer data from the COsmic Background Explorer (COBE) satellite to systematically search for millimetric (31 - 90 GHz) emission from the Gamma Ray Bursts (GRBs) in the Burst And Transient Source Experiment (BATSE) GRB 3B catalog. The large beamsize of the COBE instrument (7 degs FWHM) allows for an efficient search of the large GRB positional error boxes, although it also means that fluxes from (point source) GRB objects will be somewhat diluted. A likelihood analysis has been used to look for a change in the level of millimetric emission from the locations of 81 GRB events during the first two years (1990 & 1991) of the COBE mission. The likelihood analysis determined that we did not find any significant millimetric signal before or after the occurance of the GRB. We find 95% confidence level upper limits of 175, 192 and 645 Jy or, in terms of fluxes, of 9.6, 16.3 and 54.8 10^{-13} erg/cm^2/s, respectively at 31, 53 and 90 GHz. We also look separately at different classes of GRBs, including a study of the top ten (in peak flux) GRBs, the "short burst" and "long burst" subsets, finding similar upper limits. While these limits may be somewhat higher than one would like, we estimate that using this technique with future planned missions could push these limits down to \sim 1 mJy.

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arXiv1996

Millimetric Ground-based Observations of Cosmic Microwave Background Anisotropy

First results of a Cosmic Microwave Background (CMB) anisotropy experiment conducted at the Observatorio del Teide (Tenerife, Spain) are presented. The instrument is a four channel (3.1, 2.1, 1.3 and 1.1 mm) $^3$He bolometer system coupled to a 45 cm diameter telescope. The resultant configuration is sensitive to structures on angular scales ~ 1-2 degrees. We use the channels at the two highest frequencies for monitoring the atmosphere, and apply a simple method to subtract this contribution in channels 1 (3.1 mm) and 2 (2.1 mm). The most intense structure at these two frequencies is the Galactic crossing with peak amplitudes of ~ 350 micro-K. These crossings have been clearly detected with the amplitude and shape predicted. This demonstrates that our multifrequency observations allow an effective assessment and subtraction of the atmospheric contribution. In the section of data at high Galactic latitude we obtain sensitivities ~ 40 micro-K per beam. The statistical analyses show the presence of common signals between channels 1 and 2. Assuming a simple Gaussian auto-correlation model with a scale of coherence $θ_c=1.32$ degrees for the signal, a likelihood analysis of this section of data reveals the presence of fluctuations with intrinsic amplitude $C_{0}^{1/2} = 76^{+43}_{-32}$ micro -K (68 % CL including a ~ 20% calibration uncertainty). Since residual atmospheric noise might still contaminate our results, we also give our result as an upper limit of 118 micro-K at 95% c.l.

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