M. C. Shepherd

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.

The Anisotropy of the microwave background to l = 3500: Mosaic observations with the Cosmic Background Imager

We report measurements of anisotropy in the cosmic microwave background radiation over the multipole range l 200 3500 with the Cosmic Background Imager based on deep observations of three fields. These results confirm the drop in power with increasing l first reported in earlier measurements with this instrument and extend the observations of this decline in power out to l 2000. The decline in power is consistent with the predicted damping of primary anisotropies. At larger multipoles, l 1⁄4 2000 3500, the power is 3.1 greater than standard models for intrinsic microwave background anisotropy in this multipole range and 3.5 greater than zero. This excess power is not consistent with expected levels of residual radio source contamination but, for 8e1, is consistent with predicted levels of a secondary Sunyaev-Zeldovich anisotropy. Further observations are necessary to confirm the level of this excess and, if confirmed, determine its origin. Subject headings: cosmic microwave background — cosmology: observations

Extended mosaic observations with the Cosmic Background Imager

Two years of microwave background observations with the Cosmic Background Imager (CBI) have been combined to give a sensitive, high-resolution angular power spectrum over the range 400 2000 power previously seen with the CBI is reduced. Under the assumption that any signal in excess of the primary anisotropy is due to a secondary Sunyaev-Zeldovich anisotropy in distant galaxy clusters, we use CBI, Arcminute Cosmology Bolometer Array Receiver, and Berkeley-Illinois-Maryland Association array data to place a constraint on the present-day rms mass fluctuation on 8 h-1 Mpc scales, σ8. We present the results of a cosmological parameter analysis on the l < 2000 primary anisotropy data that show significant improvements in the parameters as compared to WMAP alone, and we explore the role of the small-scale cosmic microwave background data in breaking parameter degeneracies.

The Cosmic Lens All-Sky Survey - I. Source selection and observations

The Cosmic Lens All-Sky Survey (CLASS) is an international collaborative program which has obtained high-resolution radio images of over 10000 flat-spectrum radio sources in order to create the largest and best studied statistical sample of radioloud gravitationally lensed systems. With this survey, combined with detailed studies of the lenses found therein, constraints can be placed on the expansion rate, matter density, and dark energy (e.g. cosmological constant, quintessence) content of the Universe that are complementary to and independent of those obtained through other methods. CLASS is aimed at identifying lenses where multiple images are formed from compact flat-spectrum radio sources, which should be easily identifiable in the radio maps. Because CLASS is radio-based, dust obscuration in lensing galaxies is not a factor, and the relative insensitivity of the instrument to environmental conditions (e.g. weather, “seeing”) leads to nearly uniform sensitivity and resolution over the entire survey. In four observing “seasons” from 1994–1999, CLASS has observed 13783 radio sources with the VLA at 8.4 GHz in its largest “A” configuration (0. ′′ 2 resolution). When combined with the JVAS survey, the CLASS sample contains over 16,000 images. A complete sample of 11685 sources was observed, selected to have a flux density of at least 30 mJy in the GB6 catalogue at 4.85 GHz (spanning the declination range 0 ◦ 6 � 6 75 ◦ and |b| > 10 ◦ , excluding the galactic plane) and a spectral index � > 0.5 between the NVSS at 1.4 GHz and the GB6. A typical 30second CLASS snapshot reached an rms noise level of 0.4 mJy. So far, CLASS has found 16 new gravitational lens systems, and the JVAS/CLASS survey contains a total of 22 lenses. The follow-up of a small number of candidates using the VLA, MERLIN, the VLBA, and optical telescopes is still underway. In this paper, we present a summary of the CLASS observations, the JVAS/CLASS sample, and statistics on sub-samples of the survey. A companion paper presents the lens candidate selection and in a third paper the implications for cosmology are discussed. The source catalogues from the JVAS/CLASS project described in this paper are available from http://www.jb.man.ac.uk/research/gravlens/ .

BLAZARS IN THE FERMI ERA: THE OVRO 40 m TELESCOPE MONITORING PROGRAM

The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope provides an unprecedented opportunity to study gamma-ray blazars. To capitalize on this opportunity, beginning in late 2007, about a year before the start of LAT science operations, we began a large-scale, fast-cadence 15 GHz radio monitoring program with the 40 m telescope at the Owens Valley Radio Observatory. This program began with the 1158 northern (δ > –20°) sources from the Candidate Gamma-ray Blazar Survey and now encompasses over 1500 sources, each observed twice per week with about 4 mJy (minimum) and 3% (typical) uncertainty. Here, we describe this monitoring program and our methods, and present radio light curves from the first two years (2008 and 2009). As a first application, we combine these data with a novel measure of light curve variability amplitude, the intrinsic modulation index, through a likelihood analysis to examine the variability properties of subpopulations of our sample. We demonstrate that, with high significance (6σ), gamma-ray-loud blazars detected by the LAT during its first 11 months of operation vary with almost a factor of two greater amplitude than do the gamma-ray-quiet blazars in our sample. We also find a significant (3σ) difference between variability amplitude in BL Lacertae objects and flat-spectrum radio quasars (FSRQs), with the former exhibiting larger variability amplitudes. Finally, low-redshift (z < 1) FSRQs are found to vary more strongly than high-redshift FSRQs, with 3σ significance. These findings represent an important step toward understanding why some blazars emit gamma-rays while others, with apparently similar properties, remain silent.

Cosmological Parameters from Cosmic Background Imager Observations and Comparisons with BOOMERANG, DASI, and MAXIMA

We report on the cosmological parameters derived from observations with the Cosmic Background Imager (CBI), covering 40 deg2 and the multipole range 300 l 3500. The angular scales probed by the CBI correspond to structures that cover the mass range from 1014 to 1017 M?, and the observations reveal, for the first time, the seeds that gave rise to clusters of galaxies. These unique, high-resolution observations also show damping in the power spectrum to l ~ 2000, which we interpret as being due to the finite width of the photon-baryon decoupling region and the viscosity operating at decoupling. Because the observations extend to much higher l, the CBI results provide information complementary to that probed by the BOOMERANG, DASI, MAXIMA, and VSA experiments. When the CBI observations are used in combination with those from COBE-DMR, we find evidence for a flat universe, ?tot = 1.00 (1 ?), a power-law index of primordial fluctuations, ns = 1.08, and densities in cold dark matter, ?cdmh2 = 0.16, and baryons, ?bh2 = 0.023. With the addition of large-scale structure priors the ?cdmh2 value is sharpened to 0.10, and we find ?? = 0.67. In the l < 1000 overlap region with the BOOMERANG, DASI, MAXIMA, and VSA experiments, the agreement between these four experiments is excellent, and we construct optimal power spectra in the CBI bands that demonstrate this agreement. We derive cosmological parameters for the combined cosmic microwave background (CMB) experiments and show that these parameter determinations are stable as we progress from the weak priors using only CMB observations and very broad restrictions on cosmic parameters, through the addition of information from large-scale structure surveys, Hubble parameter determinations, and Type Ia supernova results. The combination of these with CMB observations gives a vacuum energy estimate of ?? = 0.70, a Hubble parameter of h = 0.69 ? 0.04, and a cosmological age of 13.7 ? 0.2 Gyr. As the observations are pushed to higher multipoles, no anomalies relative to standard models appear, and extremely good consistency is found between the cosmological parameters derived for the CBI observations over the range 610 < l < 2000 and observations at lower l.

Polarization Observations with the Cosmic Background Imager

Polarization observations of the cosmic microwave background with the Cosmic Background Imager from September 2002 to May 2004 provide a significant detection of the E-mode polarization and reveal an angular power spectrum of polarized emission showing peaks and valleys that are shifted in phase by half a cycle relative to those of the total intensity spectrum. This key agreement between the phase of the observed polarization spectrum and that predicted on the basis of the total intensity spectrum provides support for the standard model of cosmology, in which dark matter and dark energy are the dominant constituents, the geometry is close to flat, and primordial density fluctuations are predominantly adiabatic with a matter power spectrum commensurate with inflationary cosmological models.

FIRST INTRINSIC ANISOTROPY OBSERVATIONS WITH THE COSMIC BACKGROUND IMAGER

We present the first results of observations of the intrinsic anisotropy of the cosmic microwave background radiation with the Cosmic Background Imager from a site at 5080 m altitude in northern Chile. Our observations show a sharp decrease in Cl in the range l = 400-1500. The broadband amplitudes we have measured are δTband = 58.7 μK for l = 603 and δTband = 29.7 μK for l = 1190, where these are half-power widths in l. Such a decrease in power at high l is one of the fundamental predictions of the standard cosmological model, and these are the first observations which cover a broad enough l range to show this decrease in a single experiment. The Cl we have measured enables us to place limits on the density parameter, Ωtot ≤ 0.4 or Ωtot ≥ 0.7 (90% confidence).

The Cosmic Background Imager

Design and performance details are given for the Cosmic Background Imager (CBI), an interferometer array that is measuring the power spectrum of fluctuations in the cosmic microwave background radiation (CMBR) for multipoles in the range 400<l< 3500. The CBI is located at an altitude of 5000 m in the Atacama Desert in northern Chile. It is a planar synthesis array with 13 0.9 m diameter antennas on a 6 m diameter tracking platform. Each antenna has a cooled, low-noise receiver operating in the 26-36 GHz band. Signals are cross-correlated in an analog filterbank correlator with 10 1 GHz bands. This allows spectral index measurements that can be used to distinguish CMBR signals from diffuse galactic foregrounds. A 1.2 kHz 180° phase-switching scheme is used to reject cross talk and low-frequency pick-up in the signal processing system. The CBI has a three-axis mount that allows the tracking platform to be rotated about the optical axis, providing improved (u, v) coverage and a powerful discriminant against false signals generated in the receiving electronics. Rotating the tracking platform also permits polarization measurements when some of the antennas are configured for the orthogonal polarization.

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.