arXiv subjects

G. F. Smoot

Publications and source records attributed to G. F. Smoot.

At least 55 records · Page 3Linked to original sources

arXiv2001

A High Spatial Resolution Analysis of the MAXIMA-1 Cosmic Microwave Background Anisotropy Data

We extend the analysis of the MAXIMA-1 cosmic microwave background (CMB) data to smaller angular scales. MAXIMA, a bolometric balloon experiment, mapped a 124 deg$^2$ region of the sky with 10\arcmin resolution at frequencies of 150, 240 and 410 GHz during its first flight. The original analysis, which covered the multipole range $36 \leq \ell \leq 785$, is extended to $\ell = 1235$ using data from three 150 GHz photometers in the fully cross-linked central 60 deg$^2$ of the map. The main improvement over the original analysis is the use of 3\arcmin square pixels in the calculation of the map. The new analysis is consistent with the original for $\ell < 785$. For $\ell > 785$, where inflationary models predict a third acoustic peak, the new analysis shows power with an amplitude of $56 \pm 7$ \microk at $\ell \simeq 850$ in excess to the average power of $42 \pm 3$ \microk in the range $441 < \ell < 785$.

astro-ph↗

arXiv2001

Cosmology from Maxima-1, Boomerang and COBE/DMR CMB Observations

Recent results from BOOMERANG-98 and MAXIMA-1, taken together with COBE-DMR, provide consistent and high signal-to-noise measurements of the CMB power spectrum at spherical harmonic multipole bands over $2<\ell\lta800$. Analysis of the combined data yields 68% (95%) confidence limits on the total density, $Ω_{\rm {tot}}\simeq 1.11 \pm 0.07 (^{+0.13}_{-0.12})$, the baryon density, $Ω_b h^2\simeq 0.032^{+0.005}_{-0.004} (^{+0.009}_{-0.008})$, and the scalar spectral tilt, $n_s\simeq1.01^{+0.09}_{-0.07} (^{+0.17}_{-0.14})$. These data are consistent with inflationary initial conditions for structure formation. Taken together with other cosmological observations, they imply the existence of both non-baryonic dark matter and dark energy in the universe.

astro-ph↗

arXiv2001

Tests for Gaussianity of the MAXIMA-1 CMB Map

Gaussianity of the cosmological perturbations in the universe is one of the key predictions of standard inflation, but it is violated by other models of structure formation such as topological defects. We present the first test of the Gaussianity of the cosmic microwave background (CMB) on sub-degree angular scales, where deviations from Gaussianity are most likely to occur. We apply the methods of moments, cumulants, the Kolmogorov test, the $χ^2$ test, and Minkowski functionals in eigen, real, Wiener-filtered and signal-whitened spaces, to the MAXIMA-1 CMB anisotropy data. We conclude that the data, which probe angular scales between 10 arcminutes and 5 degrees, are consistent with Gaussianity.

astro-ph↗

arXiv2000

A New Radio Continuum Survey of the Sky at 1465 MHz between declinations -52 degrees and +68 degrees

We have mapped the total sky brightness at 1465 MHz in two adjacent 60-degree declination bands with the portable 5.5-m parabolic reflector of the Galactic Emission Mapping (GEM) project, an on-going international collaboration to survey the radio continuum of the sky in decimeter and centimeter wavelengths. The observations were conducted from two locations, one in the USA and the other in Brazil, using a novel instrumental approach to overcome the well-known shortcomings of survey experiments. Our strategy consists of a 1-rpm rotating dish to circularly scan the sky at 30 degrees from zenith. The dish uses a rim-halo to re-direct the spillover sidelobes of its backfire helical feed toward the sky and the entire assembly has been enclosed inside a wire mesh ground shield in order to minimize and level out the contamination from the ground. The diffraction characteristics of this set-up have been succesfully modelled and undesired systematic striping across the observed bands has been carefully removed by a baseline propagation method which exploits the time-forward and time-backward intersections of the circular scans. The map displays nearly 300 hours of our best quality data taken with a HPBW of 5.4 degrees at a sensitivity of 20 mK.

astro-ph↗

arXiv2000

MAXIMA-1: A Measurement of the Cosmic Microwave Background Anisotropy on angular scales of 10 arcminutes to 5 degrees

We present a map and an angular power spectrum of the anisotropy of the cosmic microwave background (CMB) from the first flight of MAXIMA. MAXIMA is a balloon-borne experiment with an array of 16 bolometric photometers operated at 100 mK. MAXIMA observed a 124 square degrees region of the sky with 10 arcminute resolution at frequencies of 150, 240 and 410 GHz. The data were calibrated using in-flight measurements of the CMB dipole anisotropy. A map of the CMB anisotropy was produced from three 150 and one 240 GHz photometer without need for foreground subtractions. Analysis of this CMB map yields a power spectrum for the CMB anisotropy over the range 36 < l < 785. The spectrum shows a peak with an amplitude of 78 +/- 6 micro-Kelvin at l ~ 220 and an amplitude varying between ~40 micro-Kelvin and ~50 micro-Kelvin for 400 < l < 785.

astro-ph↗

arXiv2000

Asymmetric Beams in Cosmic Microwave Background Anisotropy Experiments

We propose a new formalism to handle asymmetric beams in the data analysis of cosmic microwave background anisotropy experiments. For any beam shape, the formalism finds the optimal circularly symmetric equivalent and is thus easily adaptable to existing data analysis methods. We demonstrate certain key points by using a simulated highly elliptic beam, and the beams and data of the MAXIMA-1 experiment, where the asymmetry is mild. In particular, we show that in both cases the formalism does not bias the angular power spectrum estimates. We analyze the limitations of the formalism and find that it is well suited for most practical situations.

astro-ph↗

arXiv2000

Spillover and diffraction sidelobe contamination in a double-shielded experiment for mapping Galactic synchrotron emission

We have analyzed observations from a radioastronomical experiment to survey the sky at decimetric wavelengths along with feed pattern measurements in order to account for the level of ground contamination entering the sidelobes. A major asset of the experiment is the use of a wire mesh fence around the rim-halo shielded antenna with the purpose of levelling out and reducing this source of stray radiation for zenith-centered 1-rpm circular scans. We investigate the shielding performance of the experiment by means of a geometric diffraction model in order to predict the level of the spillover and diffraction sidelobes in the direction of the ground. Using 408 MHz and 1465 MHz feed measurements, the model shows how a weakly-diffracting and unshielded antenna configuration becomes strongly-diffracting and double-shielded as far-field diffraction effects give way to near-field ones. Due to the asymmetric response of the feeds, the orientation of their radiation fields with respect to the secondary must be known a priori before comparing model predictions with observational data. By adjusting the attenuation coefficient of the wire mesh the model is able to reproduce the amount of differential ground pick-up observed during test measurements at 1465 MHz.

astro-ph↗

arXiv1999

The Planck Surveyor mission: astrophysical prospects

Although the Planck Surveyor mission is optimized to map the cosmic microwave background anisotropies, it will also provide extremely valuable information on astrophysical phenomena. We review our present understanding of Galactic and extragalactic foregrounds relevant to the mission and discuss on one side, Planck's impact on the study of their properties and, on the other side, to what extent foreground contamination may affect Planck's ability to accurately determine cosmological parameters. Planck's multifrequency surveys will be unique in their coverage of large areas of the sky (actually, of the full sky); this will extend by two or more orders of magnitude the flux density interval over which mm/sub-mm counts of extragalactic sources can be determined by instruments already available (like SCUBA) or planned for the next decade (like the LSA-MMA or the space mission FIRST), which go much deeper but over very limited areas. Planck will thus provide essential complementary information on the epoch-dependent luminosity functions. Bright radio sources will be studied over a poorly explored frequency range where spectral signatures, essential to understand the physical processes that are going on, show up. The Sunyaev-Zeldovich effect, with its extremely rich information content, will be observed in the direction of a large number of rich clusters of Galaxies. Thanks again to its all sky coverage, Planck will provide unique information on the structure and on the emission properties of the interstellar medium in the Galaxy. At the same time, the foregrounds are unlikely to substantially limit Planck's ability to measure the cosmological signals. Even measurements of polarization of the primordial Cosmic Microwave background fluctuations appear to be feasible.

astro-ph↗

arXiv1999

MAXIMA: an experiment to measure temperature anisotropy in the cosmic microwave background

We describe the MAXIMA experiment, a balloon-borne measurement designed to map temperature anisotropy in the Cosmic Microwave Background (CMB) over a wide range of angular scales (multipole range 80 < l < 800). The experiment consists of a 1.3 m diameter off-axis Gregorian telescope and a receiver with a 16 element array of bolometers cooled to 100 mK. The frequency bands are centered at 150, 240, and 410 GHz. The 10' FWHM beam sizes are well matched to the scale of acoustic peaks expected in the angular power spectrum of the CMB. The first flight of the experiment in its full configuration was launched in August 1998. A 122 sq-deg map of the sky was made near the Draco constellation during the 7 hour flight in a region of extremely low galactic dust contamination. This map covers 0.3% of the sky and has 3200 independent beamsize pixels. We describe the MAXIMA instrument and its performance during the recent flight.

astro-ph↗

arXiv1998

The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background: I. Limits and Detections

The DIRBE on the COBE spacecraft was designed primarily to conduct systematic search for an isotropic CIB in ten photometric bands from 1.25 to 240 microns. The results of that search are presented here. Conservative limits on the CIB are obtained from the minimum observed brightness in all-sky maps at each wavelength, with the faintest limits in the DIRBE spectral range being at 3.5 microns (νI_ν< 64 nW/m^2/sr, 95% CL) and at 240 microns (νI_ν< 28 nW/m^2/sr, 95% CL). The bright foregrounds from interplanetary dust scattering and emission, stars, and interstellar dust emission are the principal impediments to the DIRBE measurements of the CIB. These foregrounds have been modeled and removed from the sky maps. Assessment of the random and systematic uncertainties in the residuals and tests for isotropy show that only the 140 and 240 microns data provide candidate detections of the CIB. The residuals and their uncertainties provide CIB upper limits more restrictive than the dark sky limits at wavelengths from 1.25 to 100 microns. No plausible solar system or Galactic source of the observed 140 and 240 microns residuals can be identified, leading to the conclusion that the CIB has been detected at levels of νI_ν= 25+-7 and 14+-3 nW/m^2/sr at 140 and 240 microns respectively. The integrated energy from 140 to 240 microns, 10.3 nW/m^2/sr, is about twice the integrated optical light from the galaxies in the Hubble Deep Field, suggesting that star formation might have been heavily enshrouded by dust at high redshift. The detections and upper limits reported here provide new constraints on models of the history of energy-releasing processes and dust production since the decoupling of the cosmic microwave background from matter.

astro-ph↗

arXiv1997

A Determination of the Spectral Index of Galactic Synchrotron Emission in the 1-10 GHz range

We present an analysis of simultaneous multifrequency measurements of the Galactic emission in the 1-10 GHz range with 18 degrees, angular resolution taken from a high altitude site. Our data yield a determination of the synchrotron spectral index between 1.4 GHz and 7.5 GHz of 2.81 +/- 0.16. Combining our data with the maps from Haslam et al. (1982) and Reich & Reich (1986) we find 2.76 +/- 0.11 in the 0.4 - 7.5 GHz range. These results are in agreement with the few previously published measurements. The variation of spectral index with frequency based on our results and compared with other data found in the literature suggests a steepening of the synchrotron spectrum towards high frequencies as expected from theory, because of the steepening of the parent cosmic ray electron energy spectrum. Comparison between the Haslam data and the 19 GHz map (Cottingham 1987) also indicates a significant spectral index variation on large angular scale. Addition quality data are necessary to provide a serious study of these effects.

astro-ph↗

arXiv1996

The Dipole Observed in the COBE DMR Four-Year Data

The largest anisotropy in the cosmic microwave background (CMB) is the $\approx 3$ mK dipole assumed to be due to our velocity with respect to the CMB. Using the four year data set from all six channels of the COBE Differential Microwave Radiometers (DMR), we obtain a best-fit dipole amplitude $3.358 \pm 0.001 \pm 0.023$ mK in the direction $(l,b)=(264°.31 \pm 0°.04 \pm 0°.16, +48°.05 \pm 0°.02 \pm 0°.09)$, where the first uncertainties are statistical and the second include calibration and combined systematic uncertainties. This measurement is consistent with previous DMR and FIRAS results

astro-ph↗

arXiv1996

Small Angular Scale Simulations of the Microwave Sky

We describe and compare two types of microwave sky simulations which are good for small angular scales. The first type uses expansions in spherical harmonics, and the second one is based on plane waves and the Fast Fourier Transform. The angular power spectrum is extracted from maps corresponding to both types of simulations, and the resulting spectra are appropriately compared. In this way, the features and usefulness of Fourier simulations are pointed out. For $\ell \geq 100$, all the simulations lead to similar accuracies; however, the CPU cost of Fourier simulations is $\sim 10$ times smaller than that for spherical harmonic simulations. For $\ell \leq 100$, the simulations based on spherical harmonics seem to be preferable.

astro-ph↗

arXiv1996

The Second Measurement of Anisotropy in the Cosmic Microwave Background Radiation at 0\fdg5 Scales near the Star Mu Pegasi

During the fifth flight of the Microwave Anisotropy Experiment (MAX5), we revisited a region with significant dust emission near the star Mu Pegasi. A 3.5 cm$^{-1}$ low frequency channel has been added since the previous measurement (\cite{mei93a}). The data in each channel clearly show structure correlated with IRAS 100 \micron\ dust emission. The spectrum of the structure in the 6, 9 and 14 cm$^{-1}$ channels is described by $I_ν\proptoν^βB_ν(T_{dust})$, where $β$ = 1.3 and $T_{dust}$ = 19~K and $B_ν$ is the Planck function. However, this model predicts a smaller amplitude in the 3.5 cm$^{-1}$ band than is observed. Considering only linear combinations of the data independent of the best fit foreground spectrum for the three lower channels, we find an upper limit to CMBR fluctuations of $ΔT/T = \langle \frac{C_l~l(l+1)}{2π}\rangle^{\frac{1}{2}} \leq 1.3\times 10^{-5}$ at the 95\% confidence level. The result is for a flat band power spectrum and does not include a 10\% uncertainty in calibration. It is consistent with our previous observation in the region.

astro-ph↗

arXiv1996

The Cosmic Background Radiation

We review the current status of experimental data for spectral distortions and angular anisotropies of the cosmic microwave background, as well as discussing the relevant physical processes. This is one of a number of new articles in astrophysics and cosmology which will appear in the 1996 Review of Particle Properties (Phys. Rev. D. in press). Other relevant reviews include: "Big-Bang Cosmology" by K.A. Olive; "Big-Bang Nucleosynthesis" by K.A. Olive & D.N. Schramm; "The Hubble Constant" by C.J. Hogan; "Dark Matter" by M. Srednicki; "Cosmic Rays" by T.K. Gaisser & T. Stanev; "Solar Neutrinos" by K. Nakamura. Additional information is also available, such as astrophysical and cosmological constraints on particles such as axions and neutrinos, as well as tables of physical constants and astrophysical constants. These articles are part of a new initiative to widen the scope of the RPP by providing a regular review of some important topics and parameters in astrophysics.

astro-ph↗

arXiv1996

Calibration and Systematic Error Analysis For the COBE-DMR Four-Year Sky Maps

The Differential Microwave Radiometers (DMR) instrument aboard the Cosmic Background Explorer (COBE) has mapped the full microwave sky to mean sensitivity 26 uK per 7 deg field of view. The absolute calibration is determined to 0.7% with drifts smaller than 0.2% per year. We have analyzed both the raw differential data and the pixelized sky maps for evidence of contaminating sources such as solar system foregrounds, instrumental susceptibilities, and artifacts from data recovery and processing. Most systematic effects couple only weakly to the sky maps. The largest uncertainties in the maps result from the instrument susceptibility to the Earth's magnetic field, microwave emission from the Earth, and upper limits to potential effects at the spacecraft spin period. Systematic effects in the maps are small compared to either the noise or the celestial signal: the 95% confidence upper limit for the pixel-pixel rms from all identified systematics is less than 6 uK in the worst channel. A power spectrum analysis of the (A-B)/2 difference maps shows no evidence for additional undetected systematic effects.

astro-ph↗

arXiv1996

RMS Anisotropy in the COBE-DMR Four-Year Sky Maps

The sky-RMS is the simplest model-independent characterization of a cosmological anisotropy signal. The RMS temperature fluctuations determined from the $COBE$-DMR four-year sky maps are frequency independent, consistent with the hypothesis that they are cosmological in origin, with a typical amplitude at 7 degrees of ~ 35 \pm\ 2 uK and at 10 degrees of ~29 \pm\ 1 uK. A joint analysis of the 7 deg and 10 deg "cross"-RMS derived from the data in both Galactic and Ecliptic coordinates is used to determine the RMS quadrupole normalization, $Q_{rms-PS}$, for a scale-invariant Harrison-Zel'dovich power law model. The difference in the inferred normalizations either including or excluding the quadrupole is a consequence of the sensitivity of the method to the Galaxy contaminated observed sky quadrupole. Whilst there are variations depending on the data selection, all results are consistent with an inferred \qrms\ normalization of ~18 \pm\ 2 uK.

astro-ph↗

arXiv1996

Microwave Emission at High Galactic Latitudes

We use the COBE Differential Microwave Radiometers (DMR) 4-year sky maps to model Galactic microwave emission at high latitudes (|b| > 20 deg). Cross-correlation of the DMR maps with Galactic template maps detects fluctuations in the high-latitude microwave sky brightness with the angular variation of the DIRBE far-infrared dust maps and a frequency dependence consistent with a superposition of dust and free-free emission. We find no significant correlations between the DMR maps and various synchrotron templates. On the largest angular scales (e.g., quadrupole), Galactic emission is comparable in amplitude to the anisotropy in the cosmic microwave background (CMB). The CMB quadrupole amplitude, after correction for Galactic emission, has amplitude $Q_{rms}$ = 10.7 uK with random uncertainty 3.6 uK and systematic uncertainty 7.1 uK from uncertainty in our knowledge of Galactic microwave emission.

astro-ph↗