Degree Angular Scale Interferometer Research Articles

Optimizing interferometer experiments for cosmic microwave background B-mode measurements

The sensitivity of interferometers with linear polarizers to the cosmic microwave background (CMB) E and B modes is variant under the rotation of the polarizer frame, while interferometers with circular polarizers are equally sensitive to E and B modes. We show analytically and numerically that the diagonal elements of window functions for CMB E/B power spectra are maximized in interferometric measurements of linear polarization, when the polarizer frame is in certain rotation from the associated baseline. We also present a simulated observation to show that the 1σ errors on E/B-mode power spectrum estimation are variant under the polarizer frame rotation in the case of linear polarizers, while they are invariant in the case of circular polarizers. A simulation of a configuration similar to the Degree Angular Scale Interferometer (DASI) shows that the minimum 1σ error on the B mode in interferometer measurements with linear polarizers is 26 per cent of that in interferometric measurements with circular polarizers. The simulation also shows that the E/B mixing in interferometer measurements with linear polarizers can be as low as 23 per cent of that in interferometric measurements with circular polarizers. It is not always possible to physically align the polarizer frame with all the associated baselines in the case of an interferometer array (N > 2). There exist certain linear combinations of visibilities, which are equivalent to visibilities of the optimal polarizer frame rotation. We present the linear combinations that enable B-mode optimization for an interferometer array (N > 2).

Degree Angular Scale Interferometer 3 Year Cosmic Microwave Background Polarization Results

We present the analysis of the complete 3 yr data set obtained with the Degree Angular Scale Interferometer (DASI) polarization experiment, operating from the Amundsen-Scott South Pole research station. New data obtained at the end of the 2002 austral winter and throughout the 2003 season were added to the data from which the first detection of polarization of the cosmic microwave background (CMB) radiation was reported. The analysis of the combined data supports, with increased statistical power, all of the conclusions drawn from the initial data set. In particular, the detection of E-mode polarization is increased to the 6.3 ? confidence level, TE cross-polarization is detected at 2.9 ?, and B-mode polarization is consistent with zero, with an upper limit well below the level of the detected E-mode polarization. The results are in excellent agreement with the predictions of the cosmological model that has emerged from CMB temperature measurements. The analysis also demonstrates that contamination of the data by known sources of foreground emission is insignificant.

DASI: The Degree Angular Scale Interferometer

We describe the design and current status of the Degree Angular Scale Interferometer (DASI), a compact cm-wave interferometer operating at the Amundsen-Scott South Pole research station. With 20-cm diameter primary antenna elements operating over the frequency range 26 − 36 GHz, DASI is optimized to measure the power spectrum of the cosmic microwave background radiation (CMBR) over the multipole range 140 − 920, (corresponding to scales of 25′ − 2°.6), as well as make high-sensitivity maps of the microwave sky. The telescope was built at the University of Chicago and deployed at the South Pole during the 1999-2000 austral summer.

Scientific optimization of a ground-based CMB polarization experiment

We investigate the science goals achievable with the upcoming generation of ground-based cosmic microwave background polarization experiments, focusing on one particular experiment, QUaD [QUEST (Q and U Extragalactic Submillimetre Telescope) and DASI (Degree Angular Scale Interferometer)], a proposed bolometric polarimeter operating from the South Pole. We calculate the optimal sky coverage for this experiment, including the effects of foregrounds and gravitational lensing. We find that an E-mode measurement will be sample-limited, whereas a B-mode measurement will be detector-noise-limited. We conclude that a 300 deg2 survey is an optimal compromise for a 2-yr experiment to measure both E and B modes, and that a ground-based polarization experiment can make an important contribution to B-mode surveys. QUaD can make a high significance measurement of the acoustic peaks in the E-mode spectrum, over a multipole range of 25 < ? < 2500, and will be able to detect the gravitational lensing signal in the B-mode spectrum. Such an experiment could also directly detect the gravitational wave component of the B-mode spectrum if the amplitude of the signal is close to current upper limits. We also investigate how QUaD can improve constraints on the cosmological parameters. We estimate that combining two years of QUaD data with the 4-yr Wilkinson Microwave Anisotropy Probe (WMAP) data can improve constraints on ?bh2, ?mh2, h, r and ns by a factor of 2. If the foreground contamination can be reduced, the measurement of r can be improved by up to a factor of 6 over that obtainable from WMAP alone. These improved accuracies will place strong constraints on the potential of the inflaton field.

Small-scale cosmic microwave background polarization anisotropies due to tangled primordial magnetic fields

Tangled, primordial cosmic magnetic fields create small rotational velocity perturbations on the last scattering surface (LSS) of the cosmic microwave background radiation (CMBR). Such perturbations can contribute significantly to the CMBR temperature and polarization anisotropies at large l > 1000 or so, like the excess power detected by the Cosmic Background Imager (CBI) experiment. The magnetic contribution can be distinguished from most conventional signals, as they lead to CMBR polarization dominated by the odd-parity, B-type signal. Experiments like the Degree Angular Scale Interferometer (DASI) and the Wilkinson Microwave Anisotropy Probe (WMAP) have detected evidence for CMBR polarization at low l. Many experiments will also probe the large l regime. Therefore we calculate the polarization signals due to primordial magnetic fields for different spectra and different cosmological parameters. A scale-invariant spectrum of tangled fields which redshifts to a present value of B0= 3 × 10−9 G produces B-type polarization anisotropies of ∼0.3–0.4 μK between l∼ 1000 and 5000. Larger signals result if the spectral index of magnetic tangles is steeper, n > −3. The peak of the signal shifts to larger l for a Λ-dominated universe or if the baryon density is larger. The signal will also have non-Gaussian statistics. We also predict the much smaller E-type polarization and T–E cross-correlations for these models.

Detection of polarization in the cosmic microwave background using DASI. Degree Angular Scale Interferometer.

The past several years have seen the emergence of a standard cosmological model, in which small temperature differences in the cosmic microwave background (CMB) radiation on angular scales of the order of a degree are understood to arise from acoustic oscillations in the hot plasma of the early Universe, arising from primordial density fluctuations. Within the context of this model, recent measurements of the temperature fluctuations have led to profound conclusions about the origin, evolution and composition of the Universe. Using the measured temperature fluctuations, the theoretical framework predicts the level of polarization of the CMB with essentially no free parameters. Therefore, a measurement of the polarization is a critical test of the theory and thus of the validity of the cosmological parameters derived from the CMB measurements. Here we report the detection of polarization of the CMB with the Degree Angular Scale Interferometer (DASI). The polarization is deteced with high confidence, and its level and spatial distribution are in excellent agreement with the predictions of the standard theory.

Measurement of polarization with the Degree Angular Scale Interferometer.

Measurements of the cosmic microwave background (CMB) radiation can reveal with remarkable precision the conditions of the Universe when it was approximately 400,000 years old. The three most fundamental properties of the CMB are its frequency spectrum (which determines the temperature), and the fluctuations in both the temperature and polarization across a range of angular scales. The frequency spectrum has been well determined, and considerable progress has been made in measuring the power spectrum of the temperature fluctuations. But despite many efforts to measure the polarization, detection of this property of the CMB has hitherto been beyond the reach of even the most sensitive observations. Here we describe the Degree Angular Scale Interferometer (DASI), an array of radio telescopes, which for the past two years has conducted polarization-sensitive observations of the CMB from the Amundsen-Scott South Pole research station.

Experiment Design and First Season Observations with the Degree Angular Scale Interferometer

We describe the instrumentation, experiment design, and data reduction for the first season of observations with the Degree Angular Scale Interferometer (DASI), a compact microwave interferometer designed to measure anisotropy of the cosmic microwave background (CMB) on degree and subdegree scales (l 100-900). The telescope was deployed at the Amundsen-Scott South Pole Research Station during the 1999-2000 austral summer, and we conducted observations of the CMB throughout the following austral winter. In its first season of observations, DASI has mapped CMB fluctuations in 32 fields, each 34 across, with high sensitivity.

Degree Angular Scale Interferometer First Results: A Measurement of the Cosmic Microwave Background Angular Power Spectrum

We present measurements of anisotropy in the cosmic microwave background (CMB) from the first season of observations with the Degree Angular Scale Interferometer (DASI). The instrument was deployed at the South Pole in the austral summer 1999-2000, and we made observations throughout the following austral winter. We present a measurement of the CMB angular power spectrum in the range 100 < l < 900 in nine bands with fractional uncertainties in the range 10%-20% and dominated by sample variance. In this paper, we review the formalism used in the analysis, in particular the use of constraint matrices to project out contaminants such as ground and point source signals and to test for correlations with diffuse foreground templates. We find no evidence of foregrounds other than point sources in the data, and we find a maximum likelihood temperature spectral index β = -0.1 ± 0.2 (1 σ), consistent with CMB. We detect a first peak in the power spectrum at l ~ 200, in agreement with previous experiments. In addition, we detect a peak in the power spectrum at l ~ 550 and power of similar magnitude at l ~ 800, which are consistent with the second and third harmonic peaks predicted by adiabatic inflationary cosmological models.

Microwave surfing - which came first: big bang or big crunch?

Microwave radio astronomy has been one of the driving forces behind the spectacular success of the "standard" account of the origin of our universe, popularly known as the inflationary "Big Bang" theory. This article briefly reviews a few concepts in the field including the discovery of the cosmic microwave background, the cosmic background imager, the degree angular scale interferometer, the grafting of "dark energy" onto the prevailing inflationary Big Bang model, and the conception of the cyclic universe paradigm.

Cosmological Parameter Extraction from the First Season of Observations with the Degree Angular Scale Interferometer

The Degree Angular Scale Interferometer (DASI) has measured the power spectrum of the cosmic microwave background anisotropy over the range of spherical harmonic multipoles 100 0.45 and 0.0 ≤ τc ≤ 0.4, we find that the total density of the universe Ωtot = 1.04 ± 0.06 and the spectral index of the initial scalar fluctuations ns = 1.01 in accordance with the predictions of inflationary theory. In addition, we find that the physical density of baryons Ωbh2 = 0.022, and the physical density of cold dark matter Ωcdmh2 = 0.14 ± 0.04. This value of Ωbh2 is consistent with that derived from measurements of the primeval deuterium abundance combined with big bang nucleosynthesis theory. Using the result of the Hubble Space Telescope (HST) Key Project, h = 0.72 ± 0.08, we find that Ωtot = 1.00 ± 0.04, the matter density Ωm = 0.40 ± 0.15, and the vacuum energy density ΩΛ = 0.60 ± 0.15. (All 68% confidence limits.)

Interferometric Observation of Cosmic Microwave Background Anisotropies

We present a formalism for analyzing interferometric observations of the cosmic microwave background anisotropy and polarization. The formalism is based on the l-space expansion of the angular power spectrum favored in recent years. Explicit discussions of maximum likelihood analysis, power spectrum reconstruction, parameter estimation, imaging, and polarization are given. As an example, several calculations for the Degree Angular Scale Interferometer and Cosmic Background Interferometer experiments are presented.