arXiv subjects

M. Halpern

Publications and source records attributed to M. Halpern.

At least 181 records · Page 10Linked to original sources

arXiv2010

The far-infrared/radio correlation as probed by Herschel

We set out to determine the ratio, q(IR), of rest-frame 8-1000um flux, S(IR), to monochromatic radio flux, S(1.4GHz), for galaxies selected at far-IR and radio wavelengths, to search for signs that the ratio evolves with redshift, luminosity or dust temperature, and to identify any far-IR-bright outliers - useful laboratories for exploring why the far-IR/radio correlation is generally so tight when the prevailing theory suggests variations are almost inevitable. We use flux-limited 250-um and 1.4-GHz samples, obtained in GOODS-N using Herschel (HerMES; PEP) and the VLA. We determine bolometric IR output using ten bands spanning 24-1250um, exploiting data from PACS and SPIRE, as well as Spitzer, SCUBA, AzTEC and MAMBO. We also explore the properties of an L(IR)-matched sample, designed to reveal evolution of q(IR) with z, spanning log L(IR) = 11-12 L(sun) and z=0-2, by stacking into the radio and far-IR images. For 1.4-GHz-selected galaxies, we see tentative evidence of a break in the flux ratio, q(IR), at L(1.4GHz) ~ 10^22.7 W/Hz, where AGN are starting to dominate the radio power density, and of weaker correlations with z and T(d). From our 250-um-selected sample we identify a small number of far-IR-bright outliers, and see trends of q(IR) with L(1.4GHz), L(IR), T(d) and z, noting that some of these are inter-related. For our L(IR)-matched sample, there is no evidence that q(IR) changes significantly as we move back into the epoch of galaxy formation: we find q(IR) goes as (1+z)^gamma, where gamma = -0.04 +/- 0.03 at z=0-2; however, discounting the least reliable data at z<0.5 we find gamma = -0.26 +/- 0.07, modest evolution which may be related to the radio background seen by ARCADE2, perhaps driven by <10uJy radio activity amongst ordinary star-forming galaxies at z>1.

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arXiv2010

Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Sky Maps, Systematic Errors, and Basic Results

(Abridged) New full sky temperature and polarization maps based on seven years of data from WMAP are presented. The new results are consistent with previous results, but have improved due to reduced noise from the additional integration time, improved knowledge of the instrument performance, and improved data analysis procedures. The improvements are described in detail. The seven year data set is well fit by a minimal six-parameter flat Lambda-CDM model. The parameters for this model, using the WMAP data in conjunction with baryon acoustic oscillation data from the Sloan Digital Sky Survey and priors on H_0 from Hubble Space Telescope observations, are: Omega_bh^2 = 0.02260 +-0.00053, Omega_ch^2 = 0.1123 +-0.0035, Omega_Lambda = 0.728 +0.015 -0.016, n_s = 0.963 +-0.012, tau = 0.087 +-0.014 and sigma_8 = 0.809 +-0.024 (68 % CL uncertainties). The temperature power spectrum signal-to-noise ratio per multipole is greater that unity for multipoles < 919, allowing a robust measurement of the third acoustic peak. This measurement results in improved constraints on the matter density, Omega_mh^2 = 0.1334 +0.0056 -0.0055, and the epoch of matter- radiation equality, z_eq = 3196 +134 -133, using WMAP data alone. The new WMAP data, when combined with smaller angular scale microwave background anisotropy data, results in a 3 sigma detection of the abundance of primordial Helium, Y_He = 0.326 +-0.075.The power-law index of the primordial power spectrum is now determined to be n_s = 0.963 +-0.012, excluding the Harrison-Zel'dovich-Peebles spectrum by >3 sigma. These new WMAP measurements provide important tests of Big Bang cosmology.

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arXiv2009

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Bayesian Estimation of CMB Polarization Maps

We describe a sampling method to estimate the polarized CMB signal from observed maps of the sky. We use a Metropolis-within-Gibbs algorithm to estimate the polarized CMB map, containing Q and U Stokes parameters at each pixel, and its covariance matrix. These can be used as inputs for cosmological analyses. The polarized sky signal is parameterized as the sum of three components: CMB, synchrotron emission, and thermal dust emission. The polarized Galactic components are modeled with spatially varying power law spectral indices for the synchrotron, and a fixed power law for the dust, and their component maps are estimated as by-products. We apply the method to simulated low resolution maps with pixels of side 7.2 degrees, using diagonal and full noise realizations drawn from the WMAP noise matrices. The CMB maps are recovered with goodness of fit consistent with errors. Computing the likelihood of the E-mode power in the maps as a function of optical depth to reionization, tau, for fixed temperature anisotropy power, we recover tau=0.091+-0.019 for a simulation with input tau=0.1, and mean tau=0.098 averaged over 10 simulations. A `null' simulation with no polarized CMB signal has maximum likelihood consistent with tau=0. The method is applied to the five-year WMAP data, using the K, Ka, Q and V channels. We find tau=0.090+-0.019, compared to tau=0.086+-0.016 from the template-cleaned maps used in the primary WMAP analysis. The synchrotron spectral index, beta, averaged over high signal-to-noise pixels with standard deviation sigma(beta)<0.25, but excluding ~6% of the sky masked in the Galactic plane, is -3.03+-0.04. This estimate does not vary significantly with Galactic latitude, although includes an informative prior.

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arXiv2009

AzTEC Half Square Degree Survey of the SHADES Fields -- I. Maps, Catalogues, and Source Counts

We present the first results from the largest deep extragalactic millimetre-wavelength survey undertaken to date. These results are derived from maps covering over 0.7 deg^2, made at 1.1mm, using the AzTEC continuum camera mounted on the James Clerk Maxwell Telescope. The maps were made in the two fields originally targeted at 0.85mm with SCUBA in the SHADES project, namely the Lockman Hole East (mapped to a depth of 0.9-1.3 mJy rms) and the Subaru XMM Deep Field (1.0-1.7 mJy rms). The wealth of existing and forthcoming deep multi-frequency data in these two fields will allow the bright mm source population revealed by these images to be explored in detail in subsequent papers. Here we present the maps themselves, a catalogue of 114 high-significance sub-millimetre galaxy detections, and a thorough statistical analysis leading to the most robust determination to date of the 1.1mm source number counts. Through careful comparison, we find that both the COSMOS and GOODS North fields, also imaged with AzTEC, contain an excess of mm sources over the new 1.1mm source-count baseline established here. In particular, our new AzTEC/SHADES results indicate that very luminous high-redshift dust enshrouded starbursts (S_{1.1} > 3 mJy) are 25-50% less common than would have been inferred from these smaller surveys, thus highlighting the potential roles of cosmic variance and clustering in such measurements. We compare number count predictions from recent models of the evolving mm/sub-mm source population to these SMG surveys, which provide important constraints for the ongoing refinement of semi-analytic and hydrodynamical models of galaxy formation, and find that all recent models over-predict the number of bright sub-millimetre galaxies found in this survey.

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arXiv2009

An AzTEC 1.1 mm survey of the GOODS-N field -- II. Multi-wavelength identifications and redshift distribution

We present results from a multi-wavelength study of 29 sources (false detection probabilities <5%) from a survey of the Great Observatories Origins Deep Survey-North field at 1.1mm using the AzTEC camera. Comparing with existing 850um SCUBA studies in the field, we examine differences in the source populations selected at the two wavelengths. The AzTEC observations uniformly cover the entire survey field to a 1-sigma depth of ~1mJy. Searching deep 1.4GHz VLA, and Spitzer 3--24um catalogues, we identify robust counterparts for 21 1.1mm sources, and tentative associations for the remaining objects. The redshift distribution of AzTEC sources is inferred from available spectroscopic and photometric redshifts. We find a median redshift of z=2.7, somewhat higher than z=2.0 for 850um-selected sources in the same field, and our lowest redshift identification lies at a spectroscopic redshift z=1.1460. We measure the 850um to 1.1mm colour of our sources and do not find evidence for `850um dropouts', which can be explained by the low-SNR of the observations. We also combine these observed colours with spectroscopic redshifts to derive the range of dust temperatures T, and dust emissivity indices $β$ for the sample, concluding that existing estimates T~30K and $β$~1.75 are consistent with these new data.

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arXiv2008

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Galactic Foreground Emission

We present a new estimate of foreground emission in the WMAP data, using a Markov chain Monte Carlo (MCMC) method. The new technique delivers maps of each foreground component for a variety of foreground models, error estimates of the uncertainty of each foreground component, and provides an overall goodness-of-fit measurement. The resulting foreground maps are in broad agreement with those from previous techniques used both within the collaboration and by other authors. We find that for WMAP data, a simple model with power-law synchrotron, free-free, and thermal dust components fits 90% of the sky with a reduced chi-squared of 1.14. However, the model does not work well inside the Galactic plane. The addition of either synchrotron steepening or a modified spinning dust model improves the fit. This component may account for up to 14% of the total flux at Ka-band (33 GHz). We find no evidence for foreground contamination of the CMB temperature map in the 85% of the sky used for cosmological analysis.

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arXiv2008

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Likelihoods and Parameters from the WMAP data

This paper focuses on cosmological constraints derived from analysis of WMAP data alone. A simple LCDM cosmological model fits the five-year WMAP temperature and polarization data. The basic parameters of the model are consistent with the three-year data and now better constrained: Omega_b h^2 = 0.02273+-0.00062, Omega_c h^2 = 0.1099+-0.0062, Omega_L = 0.742+-0.030, n_s = 0.963+0.014- 0.015, tau = 0.087+-0.017, sigma_8 = 0.796+-0.036. With five years of polarization data, we have measured the optical depth to reionization, tau>0, at 5 sigma significance. The redshift of an instantaneous reionization is constrained to be z_reion = 11.0+-1.4 with 68% confidence. This excludes a sudden reionization of the universe at z=6 at more than 3.5 sigma significance, suggesting that reionization was an extended process. Using two methods for polarized foreground cleaning we get consistent estimates for the optical depth, indicating an error due to foreground treatment of tau~0.01. This cosmological model also fits small-scale CMB data, and a range of astronomical data measuring the expansion rate and clustering of matter in the universe. We find evidence for the first time in the CMB power spectrum for a non-zero cosmic neutrino background, or a background of relativistic species, with the standard three light neutrino species preferred over the best-fit LCDM model with N_eff=0 at >99.5% confidence, and N_eff > 2.3 (95% CL) when varied. The five-year WMAP data improve the upper limit on the tensor-to-scalar ratio to r < 0.43 (95% CL), for power-law models. With longer integration we find no evidence for a running spectral index, with dn_s/dlnk = -0.037+-0.028.

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arXiv2008

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results

We present new full-sky temperature and polarization maps in five frequency bands from 23 to 94 GHz, based on data from the first five years of the WMAP sky survey. The five-year maps incorporate several improvements in data processing made possible by the additional years of data and by a more complete analysis of the instrument calibration and in-flight beam response. We present several new tests for systematic errors in the polarization data and conclude that Ka band data (33 GHz) is suitable for use in cosmological analysis, after foreground cleaning. This significantly reduces the overall polarization uncertainty. With the 5 year WMAP data, we detect no convincing deviations from the minimal 6-parameter LCDM model: a flat universe dominated by a cosmological constant, with adiabatic and nearly scale-invariant Gaussian fluctuations. Using WMAP data combined with measurements of Type Ia supernovae and Baryon Acoustic Oscillations, we find (68% CL uncertainties): Omega_bh^2 = 0.02267 \pm 0.00059, Omega_ch^2 = 0.1131 \pm 0.0034, Omega_Lambda = 0.726 \pm 0.015, n_s = 0.960 \pm 0.013, tau = 0.084 \pm 0.016, and Delta_R^2 = (2.445 \pm 0.096) x 10^-9. From these we derive: sigma_8 = 0.812 \pm 0.026, H_0 = 70.5 \pm 1.3 km/s/Mpc, z_{reion} = 10.9 \pm 1.4, and t_0 = 13.72 \pm 0.12 Gyr. The new limit on the tensor-to-scalar ratio is r < 0.22 (95% CL). We obtain tight, simultaneous limits on the (constant) dark energy equation of state and spatial curvature: -0.14 < 1+w < 0.12 and -0.0179 < Omega_k < 0.0081 (both 95% CL). The number of relativistic degrees of freedom (e.g. neutrinos) is found to be N_{eff} = 4.4 \pm 1.5, consistent with the standard value of 3.04. Models with N_{eff} = 0 are disfavored at >99.5% confidence.

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arXiv2008

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP)Observations: Beam Maps and Window Functions

Cosmology and other scientific results from the WMAP mission require an accurate knowledge of the beam patterns in flight. While the degree of beam knowledge for the WMAP one-year and three-year results was unprecedented for a CMB experiment, we have significantly improved the beam determination as part of the five-year data release. Physical optics fits are done on both the A and the B sides for the first time. The cutoff scale of the fitted distortions on the primary mirror is reduced by a factor of ~2 from previous analyses. These changes enable an improvement in the hybridization of Jupiter data with beam models, which is optimized with respect to error in the main beam solid angle. An increase in main-beam solid angle of ~1% is found for the V2 and W1-W4 differencing assemblies. Although the five-year results are statistically consistent with previous ones, the errors in the five-year beam transfer functions are reduced by a factor of ~2 as compared to the three-year analysis. We present radiometry of the planet Jupiter as a test of the beam consistency and as a calibration standard; for an individual differencing assembly, errors in the measured disk temperature are ~0.5%.

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arXiv2008

The Wilkinson Microwave Anisotropy Probe (WMAP) Source Catalog

We present the list of point sources found in the WMAP 5-year maps. The technique used in the first-year and three-year analysis now finds 390 point sources, and the five-year source catalog is complete for regions of the sky away from the galactic plane to a 2 Jy limit, with SNR > 4.7 in all bands in the least covered parts of the sky. The noise at high frequencies is still mainly radiometer noise, but at low frequencies the CMB anisotropy is the largest uncertainty. A separate search of CMB-free V-W maps finds 99 sources of which all but one can be identified with known radio sources. The sources seen by WMAP are not strongly polarized. Many of the WMAP sources show significant variability from year to year, with more than a 2:1 range between the minimum and maximum fluxes.

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arXiv2008

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Angular Power Spectra

We present the temperature and polarization angular power spectra of the cosmic microwave background (CMB) derived from the first 5 years of WMAP data. The 5-year temperature (TT) spectrum is cosmic variance limited up to multipole l=530, and individual l-modes have S/N>1 for l<920. The best fitting six-parameter LambdaCDM model has a reduced chi^2 for l=33-1000 of chi^2/nu=1.06, with a probability to exceed of 9.3%. There is now significantly improved data near the third peak which leads to improved cosmological constraints. The temperature-polarization correlation (TE) is seen with high significance. After accounting for foreground emission, the low-l reionization feature in the EE power spectrum is preferred by Δχ^2=19.6 for optical depth tau=0.089 by the EE data alone, and is now largely cosmic variance limited for l=2-6. There is no evidence for cosmic signal in the BB, TB, or EB spectra after accounting for foreground emission. We find that, when averaged over l=2-6, l(l+1)C^{BB}_l/2π< 0.15 uK^2 (95% CL).

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arXiv2008

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation

(Abridged) The WMAP 5-year data strongly limit deviations from the minimal LCDM model. We constrain the physics of inflation via Gaussianity, adiabaticity, the power spectrum shape, gravitational waves, and spatial curvature. We also constrain the properties of dark energy, parity-violation, and neutrinos. We detect no convincing deviations from the minimal model. The parameters of the LCDM model, derived from WMAP combined with the distance measurements from the Type Ia supernovae (SN) and the Baryon Acoustic Oscillations (BAO), are: Omega_b=0.0456+-0.0015, Omega_c=0.228+-0.013, Omega_Lambda=0.726+-0.015, H_0=70.5+-1.3 km/s/Mpc, n_s=0.960+-0.013, tau=0.084+-0.016, and sigma_8=0.812+-0.026. With WMAP+BAO+SN, we find the tensor-to-scalar ratio r<0.22 (95% CL), and n_s>1 is disfavored regardless of r. We obtain tight, simultaneous limits on the (constant) equation of state of dark energy and curvature. We provide a set of "WMAP distance priors," to test a variety of dark energy models. We test a time-dependent w with a present value constrained as -0.33<1+w_0<0.21 (95% CL). Temperature and matter fluctuations obey the adiabatic relation to within 8.9% and 2.1% for the axion and curvaton-type dark matter, respectively. The TE and EB spectra constrain cosmic parity-violation. We find the limit on the total mass of neutrinos, sum(m_nu)<0.67 eV (95% CL), which is free from the uncertainty in the normalization of the large-scale structure data. The effective number of neutrino species is constrained as N_{eff} = 4.4+-1.5 (68%), consistent with the standard value of 3.04. Finally, limits on primordial non-Gaussianity are -9<f_{NL}^{local}<111 and -151<f_{NL}^{equil}<253 (95% CL) for the local and equilateral models, respectively.

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arXiv2008

The Balloon-borne Large-Aperture Submillimeter Telescope for Polarization: BLAST-pol

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a sub-orbital experiment designed to study the process of star formation in local galaxies (including the Milky Way) and in galaxies at cosmological distances. Using a 2-m Cassegrain telescope, BLAST images the sky onto a focal plane, which consists of 270 bolometric detectors split between three arrays, observing simultaneously in 30% wide bands, centered at 250, 350, and 500 microns. The diffraction-limited optical system provides a resolution of 30" at 250 microns. The pointing system enables raster-like scans with a positional accuracy of ~30", reconstructed to better than 5" rms in post-flight analysis. BLAST had two successful flights, from the Arctic in 2005, and from Antarctica in 2006, which provided the first high-resolution and large-area (~0.8-200 deg^2) submillimeter surveys at these wavelengths. As a pathfinder for the SPIRE instrument on Herschel, BLAST shares with the ESA satellite similar focal plane technology and scientific motivation. A third flight in 2009 will see the instrument modified to be polarization-sensitive (BLAST-Pol). With its unprecedented mapping speed and resolution, BLAST-Pol will provide insights into Galactic star-forming nurseries, and give the necessary link between the larger, coarse resolution surveys and the narrow, resolved observations of star-forming structures from space and ground based instruments being commissioned in the next 5 years.

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arXiv2008

SPIDER: A Balloon-borne Large-scale CMB Polarimeter

Spider is a balloon-borne experiment that will measure the polarization of the Cosmic Microwave Background over a large fraction of a sky at 1 degree resolution. Six monochromatic refracting millimeter-wave telescopes with large arrays of antenna-coupled transition-edge superconducting bolometers will provide system sensitivities of 4.2 and 3.1 micro K_cmb rt s at 100 and 150 GHz, respectively. A rotating half-wave plate will modulate the polarization sensitivity of each telescope, controlling systematics. Bolometer arrays operating at 225 GHz and 275 GHz will allow removal of polarized galactic foregrounds. In a 2-6 day first flight from Alice Springs, Australia in 2010, Spider will map 50% of the sky to a depth necessary to improve our knowledge of the reionization optical depth by a large factor.

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arXiv2008

An AzTEC 1.1 mm Survey of the GOODS-N Field I: Maps, Catalogue, and Source Statistics

We have conducted a deep and uniform 1.1 mm survey of the GOODS-N field with AzTEC on the James Clerk Maxwell Telescope (JCMT). Here we present the first results from this survey including maps, the source catalogue, and 1.1 mm number-counts. The results presented here were obtained from a 245 sq-arcmin region with near uniform coverage to a depth of 0.96-1.16 mJy/beam. Our robust catalogue contains 28 source candidates detected with S/N >= 3.75, only 1-2 of which are expected to be spurious detections. Of these source candidates, 8 are also detected by SCUBA at 850 um in regions where there is good overlap between the two surveys. The major advantage of our survey over that with SCUBA is the uniformity of coverage. We calculate number counts using two different techniques: the first using a frequentist parameter estimation, and the second using a Bayesian method. The two sets of results are in good agreement. We find that the 1.1 mm differential number counts are well described in the 2-6 mJy range by the functional form dN/dS = N' (S'/S) exp(-S/S') with fitted parameters S' = 1.25 +/-0.38 mJy and dN/dS = 300 +/- 90 per mJy per sq-deg at 3 mJy.

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arXiv2008

Detecting the B-mode Polarisation of the CMB with Clover

We describe the objectives, design and predicted performance of Clover, which is a ground-based experiment to measure the faint ``B-mode'' polarisation pattern in the cosmic microwave background (CMB). To achieve this goal, clover will make polarimetric observations of approximately 1000 deg^2 of the sky in spectral bands centred on 97, 150 and 225 GHz. The observations will be made with a two-mirror compact range antenna fed by profiled corrugated horns. The telescope beam sizes for each band are 7.5, 5.5 and 5.5 arcmin, respectively. The polarisation of the sky will be measured with a rotating half-wave plate and stationary analyser, which will be an orthomode transducer. The sky coverage combined with the angular resolution will allow us to measure the angular power spectra between 20 < l < 1000. Each frequency band will employ 192 single polarisation, photon noise limited TES bolometers cooled to 100 mK. The background-limited sensitivity of these detector arrays will allow us to constrain the tensor-to-scalar ratio to 0.026 at 3sigma, assuming any polarised foreground signals can be subtracted with minimal degradation to the 150 GHz sensitivity. Systematic errors will be mitigated by modulating the polarisation of the sky signals with the rotating half-wave plate, fast azimuth scans and periodic telescope rotations about its boresight. The three spectral bands will be divided into two separate but nearly identical instruments - one for 97 GHz and another for 150 and 225 GHz. The two instruments will be sited on identical three-axis mounts in the Atacama Desert in Chile near Pampa la Bola. Observations are expected to begin in late 2009.

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arXiv2008

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) 2005: Calibration and Targeted Sources

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) operated successfully during a 100-hour flight from northern Sweden in June 2005 (BLAST05). As part of the calibration and pointing procedures, several compact sources were mapped, including solar system, Galactic, and extragalactic targets, specifically Pallas, CRL 2688, LDN 1014, IRAS 20126+4104, IRAS 21078+5211, IRAS 21307+5049, IRAS 22134+5834, IRAS 23011+6126, K3-50, W 75N, and Mrk 231. One additional source, Arp 220, was observed and used as our primary calibrator. Details of the overall BLAST05 calibration procedure are discussed here. The BLAST observations of each compact source are described, flux densities and spectral energy distributions are reported, and these are compared with previous measurements at other wavelengths. The 250, 350, and 500 um BLAST data can provide useful constraints to the amplitude and slope of the submillimeter continuum, which in turn may be useful for the improved calibration of other submillimeter instruments.

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arXiv2008

The Balloon-borne Large Aperture Submillimeter Telescope: BLAST

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a sub-orbital surveying experiment designed to study the evolutionary history and processes of star formation in local galaxies (including the Milky Way) and galaxies at cosmological distances. The BLAST continuum camera, which consists of 270 detectors distributed between 3 arrays, observes simultaneously in broad-band (30%) spectral-windows at 250, 350, and 500 microns. The optical design is based on a 2m diameter telescope, providing a diffraction-limited resolution of 30" at 250 microns. The gondola pointing system enables raster mapping of arbitrary geometry, with a repeatable positional accuracy of ~30"; post-flight pointing reconstruction to ~5" rms is achieved. The on-board telescope control software permits autonomous execution of a pre-selected set of maps, with the option of manual override. In this paper we describe the primary characteristics and measured in-flight performance of BLAST. BLAST performed a test-flight in 2003 and has since made two scientifically productive long-duration balloon flights: a 100-hour flight from ESRANGE (Kiruna), Sweden to Victoria Island, northern Canada in June 2005; and a 250-hour, circumpolar-flight from McMurdo Station, Antarctica, in December 2006.

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