A blind detection of a large, complex, Sunyaev–Zel’dovich structure

We present an interesting Sunyaev–Zel’dovich (SZ) detection in the first of the Arcminute Microkelvin Imager (AMI) ‘blind’, degree-square fields to have been observed down to our target sensitivity of 100µJy beam^(-1). In follow-up deep pointed observations the SZ effect is detected with a maximum peak decrement greater than eight times the thermal noise. No corresponding emission is visible in the ROSAT all-sky X-ray survey and no cluster is evident in the Palomar all-sky optical survey. Compared with existing SZ images of distant clusters, the extent is large (≈10 arcmin) and complex; our analysis favours a model containing two clusters rather than a single cluster. Our Bayesian analysis is currently limited to modelling each cluster with an ellipsoidal or spherical β model, which does not do justice to this decrement. Fitting an ellipsoid to the deeper candidate we find the following. (a) Assuming that the Evrard et al. approximation to Press & Schechter correctly gives the number density of clusters as a function of mass and redshift, then, in the search area, the formal Bayesian probability ratio of the AMI detection of this cluster is 7.9 × 10^4:1; alternatively assuming Jenkins et al. as the true prior, the formal Bayesian probability ratio of detection is 2.1 × 10^5:1. (b) The cluster mass is M_(T,200) = 5.5_(-1.3)^(+1.2) x 10^(14)h^(-1)_(70) M_☉. (c) Abandoning a physical model with number density prior and instead simply modelling the SZ decrement using a phenomenological β model of temperature decrement as a function of angular distance, we find a central SZ temperature decrement of -295_(-15)^(+36) µK – this allows for cosmic microwave background primary anisotropies, receiver noise and radio sources. We are unsure if the cluster system we observe is a merging system or two separate clusters

A Millimeter-wave Galactic Plane Survey with the BICEP Polarimeter

In order to study inflationary cosmology and the Milky Way Galaxy's composition and magnetic field structure, Stokes I, Q, and U maps of the Galactic plane covering the Galactic longitude range 260° < ℓ < 340° in three atmospheric transmission windows centered on 100, 150, and 220 GHz are presented. The maps sample an optical depth 1 ≾ AV ≾ 30, and are consistent with previous characterizations of the Galactic millimeter-wave frequency spectrum and the large-scale magnetic field structure permeating the interstellar medium. The polarization angles in all three bands are generally perpendicular to those measured by starlight polarimetry as expected and show changes in the structure of the Galactic magnetic field on the scale of 60°. The frequency spectrum of degree-scale Galactic emission is plotted between 23 and 220 GHz (including WMAP data) and is fit to a two-component (synchrotron and dust) model showing that the higher frequency BICEP data are necessary to tightly constrain the amplitude and spectral index of Galactic dust. Polarized emission is detected over the entire region within two degrees of the Galactic plane, indicating the large-scale magnetic field is oriented parallel to the plane of the Galaxy. A trend of decreasing polarization fraction with increasing total intensity is observed, ruling out the simplest model of a constant Galactic magnetic field orientation along the line of sight in the Galactic plane. A generally increasing trend of polarization fraction with electromagnetic frequency is found, varying from 0.5%-1.5% at frequencies below 50 GHz to 2.5%-3.5% above 90 GHz. The effort to extend the capabilities of BICEP by installing 220 GHz band hardware is described along with analysis of the new band

Application of a Self-Similar Pressure Profile to Sunyaev-Zel'dovich Effect Data from Galaxy Clusters

We investigate the utility of a new, self-similar pressure profile for fitting Sunyaev-Zel'dovich (SZ) effect observations of galaxy clusters. Current SZ imaging instruments - such as the Sunyaev-Zel'dovich Array (SZA) - are capable of probing clusters over a large range in physical scale. A model is therefore required that can accurately describe a cluster's pressure profile over a broad range of radii, from the core of the cluster out to a significant fraction of the virial radius. In the analysis presented here, we fit a radial pressure profile derived from simulations and detailed X-ray analysis of relaxed clusters to SZA observations of three clusters with exceptionally high quality X-ray data: A1835, A1914, and CL J1226.9+3332. From the joint analysis of the SZ and X-ray data, we derive physical properties such as gas mass, total mass, gas fraction and the intrinsic, integrated Compton y-parameter. We find that parameters derived from the joint fit to the SZ and X-ray data agree well with a detailed, independent X-ray-only analysis of the same clusters. In particular, we find that, when combined with X-ray imaging data, this new pressure profile yields an independent electron radial temperature profile that is in good agreement with spectroscopic X-ray measurements.Comment: 28 pages, 6 figures, accepted by ApJ for publication (probably April 2009

The Genetic Analysis Workshop 16 Problem 3: simulation of heritable longitudinal cardiovascular phenotypes based on actual genome-wide single-nucleotide polymorphisms in the Framingham Heart Study

The Genetic Analysis Workshop (GAW) 16 Problem 3 comprises simulated phenotypes emulating the lipid domain and its contribution to cardiovascular disease risk. For each replication there were 6,476 subjects in families from the Framingham Heart Study (FHS), with their actual genotypes for Affymetrix 550 k single-nucleotide polymorphisms (SNPs) and simulated phenotypes. Phenotypes are simulated at three visits, 10 years apart. There are up to 6 "major" genes influencing variation in high- and low-density lipoprotein cholesterol (HDL, LDL), and triglycerides (TG), and 1,000 "polygenes" simulated for each trait. Some polygenes have pleiotropic effects. The locus-specific heritabilities of the major genes range from 0.1 to 1.0%, under additive, dominant, or overdominant modes of inheritance. The locus-specific effects of the polygenes ranged from 0.002 to 0.15%, with effect sizes selected from negative exponential distributions. All polygenes act independently and have additive effects. Individuals in the LDL upper tail were designated medicated. Subjects medicated increased across visits at 2%, 5%, and 15%. Coronary artery calcification (CAC) was simulated using age, lipid levels, and CAC-specific polymorphisms. The risk of myocardial infarction before each visit was determined by CAC and its interactions with smoking and two genetic loci. Smoking was simulated to be commensurate with rates reported by the Centers for Disease Control. Two hundred replications were simulated

Automatic classification of field-collected dinoflagellates by artificial neural network

Automatic taxonomic categorisation of 23 species of dinoflagellates was demonstrated using field-collected specimens. These dinoflagellates have been responsible for the majority of toxic and noxious phytoplankton blooms which have occurred in the coastal waters of the European Union in recent years and make severe impact on the aquaculture industry. The performance by human 'expert' ecologists/taxonomists in identifying these species was compared to that achieved by 2 artificial neural network classifiers (multilayer perceptron and radial basis function networks) and 2 other statistical techniques, k-Nearest Neighbour and Quadratic Discriminant Analysis. The neural network classifiers outperform the classical statistical techniques. Over extended trials, the human experts averaged 85% while the radial basis network achieved a best performance of 83%, the multilayer perceptron 66%, k-Nearest Neighbour 60%, and the Quadratic Discriminant Analysis 56%

A Millimeter-Wave Galactic Plane Survey With The BICEP Polarimeter

In addition to its potential to probe the Inflationary cosmological paradigm, millimeter-wave polarimetry is a powerful tool for studying the Milky Way galaxy's composition and magnetic field structure. Towards this end, presented here are Stokes I, Q, and U maps of the Galactic plane from the millimeter-wave polarimeter BICEP covering the Galactic longitude range 260 - 340 degrees in three atmospheric transmission windows centered on 100, 150, and 220 GHz. The maps sample an optical depth 1 < AV < 30, and are consistent with previous characterizations of the Galactic millimeter-wave frequency spectrum and the large-scale magnetic field structure permeating the interstellar medium. Polarized emission is detected over the entire region within two degrees of the Galactic plane and indicates that the large-scale magnetic field is oriented parallel to the plane of the Galaxy. An observed trend of decreasing polarization fraction with increasing total intensity rules out the simplest model of a constant Galactic magnetic field throughout the Galaxy. Including WMAP data in the analysis, the degree-scale frequency spectrum of Galactic polarization fraction is plotted between 23 and 220 GHz for the first time. A generally increasing trend of polarization fraction with electromagnetic frequency is found, which varies from 0.5%-1.5%at frequencies below 50 GHz to 2.5%-3.5%above 90 GHz. The BICEP and WMAP data are fit to a two-component (synchrotron and dust) model showing that the higher frequency BICEP data are necessary to tightly constrain the amplitude and spectral index of Galactic dust. Furthermore, the dust amplitude predicted by this two-component fit is consistent with model predictions of dust emission in the BICEP bands

The QUaD galactic plane survey. I. Maps and analysis of diffuse emission

We present a survey of ~800 deg^2 of the galactic plane observed with the QUaD telescope. The primary products of the survey are maps of Stokes I, Q, and U parameters at 100 and 150 GHz, with spatial resolution of 5' and 3'.5, respectively. Two regions are covered, spanning approximately 245°–295° and 315°–5° in the galactic longitude l and −4° < b < +4° in the galactic latitude b. At 0°.02 square pixel size, the median sensitivity is 74 and 107 kJy sr^(−1) at 100 GHz and 150 GHz respectively in I, and 98 and 120 kJy sr^(−1) for Q and U. In total intensity, we find an average spectral index of α = 2.35 ± 0.01 (stat) ± 0.02 (sys) for |b| ≤ 1°, indicative of emission components other than thermal dust. A comparison to published dust, synchrotron, and free–free models implies an excess of emission in the 100 GHz QUaD band, while better agreement is found at 150 GHz. A smaller excess is observed when comparing QUaD 100 GHz data to the WMAP five-year W band; in this case, the excess is likely due to the wider bandwidth of QUaD. Combining the QUaD and WMAP data, a two-component spectral fit to the inner galactic plane (|b| ≤ 1°) yields mean spectral indices of α_s = −0.32 ± 0.03 and α_d = 2.84 ± 0.03; the former is interpreted as a combination of the spectral indices of synchrotron, free–free, and dust, while the second is largely attributed to the thermal dust continuum. In the same galactic latitude range, the polarization data show a high degree of alignment perpendicular to the expected galactic magnetic field direction, and exhibit mean polarization fraction 1.38 ± 0.08 (stat) ± 0.1 (sys)% at 100 GHz and 1.70 ± 0.06 (stat) ± 0.1 (sys)% at 150 GHz. We find agreement in polarization fraction between QUaD 100 GHz and the WMAP W band, the latter giving 1.1% ± 0.4%

First season QUaD CMB temperature and polarization power spectra

QUaD is a bolometric CMB polarimeter sited at the South Pole, operating at frequencies of 100 and 150 GHz. In this paper we report preliminary results from the first season of operation (austral winter 2005). All six CMB power spectra are presented derived as cross spectra between the 100 and 150 GHz maps using 67 days of observation in a low foreground region of approximately 60 deg^2. These data are a small fraction of the data acquired to date. The measured spectra are consistent with the ΛCDM cosmological model. We perform jackknife tests that indicate that the observed signal has negligible contamination from instrumental systematics. In addition, by using a frequency jackknife we find no evidence for foreground contamination

Characterization of the Millimeter-Wave Polarization of Centaurus A with QUaD

Centaurus (Cen) A represents one of the best candidates for an isolated, compact, highly polarized source that is bright at typical cosmic microwave background (CMB) experiment frequencies. We present measurements of the 4 degree by 2 degree region centered on Cen A with QUaD, a CMB polarimeter whose absolute polarization angle is known to 0.5 degrees. Simulations are performed to assess the effect of misestimation of the instrumental parameters on the final measurement and systematic errors due to the field's background structure and temporal variability from Cen A's nuclear region are determined. The total (Q, U) of the inner lobe region is (1.00 +/- 0.07 (stat.) +/- 0.04 (sys.), -1.72 +/- 0.06 +/- 0.05) Jy at 100 GHz and (0.80 +/- 0.06 +/- 0.06, -1.40 +/- 0.07 +/- 0.08) Jy at 150 GHz, leading to polarization angles and total errors of -30.0 +/- 1.1 degrees and -29.1 +/- 1.7 degrees. These measurements will allow the use of Cen A as a polarized calibration source for future millimeter experiments.Comment: 9 pages, 8 figures, v2 matches version published in Ap