Showing papers by "Peter A. R. Ade published in 2008"

The AzTEC mm-wavelength camera

Abstract: AzTEC is a mm-wavelength bolometric camera utilizing 144 silicon nitride micromesh detectors. Here, we describe the AzTEC instrument architecture and its use as an astronomical instrument. We report on several performance metrics measured during a three-month observing campaign at the James Clerk Maxwell Telescope and conclude with our plans for AzTEC as a facility instrument on the Large Millimetre Telescope.

The Balloon-borne Large Aperture Submillimeter Telescope: BLAST

Abstract: The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a suborbital 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 three arrays, observes simultaneously in broadband (30%) spectral windows at 250, 350, and 500 μm. The optical design is based on a 2 m diameter telescope, providing a diffraction-limited resolution of 30'' at 250 μm. The gondola pointing system enables raster mapping of arbitrary geometry, with a repeatable positional accuracy of ~30''; postflight pointing reconstruction to lesssim5'' rms is achieved. The onboard telescope control software permits autonomous execution of a preselected 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 hr flight from ESRANGE (Kiruna), Sweden to Victoria Island, northern Canada in 2005 June; and a 250 hr, circumpolar flight from McMurdo Station, Antarctica, in 2006 December.

Sanepic: a mapmaking method for time stream data from large arrays

Abstract: We describe a mapmaking method that we have developed for the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) experiment, but which should have general application to data from other submillimeter arrays. Our method uses a maximum likelihood-based approach, with several approximations, which allows images to be constructed using large amounts of data with fairly modest computer memory and processing requirements. This new approach, Signal and Noise Estimation Procedure Including Correlations (SANEPIC), builds on several previous methods but focuses specifically on the regime where there are a large number of detectors sampling the same map of the sky, and explicitly allowing for the possibility of strong correlations between the detector time streams. We provide real and simulated examples of how well this method performs compared with more simplistic mapmakers based on filtering. We discuss two separate implementations of SANEPIC: a brute-force approach, in which the inverse pixel-pixel covariance matrix is computed, and an iterative approach, which is much more efficient for large maps. SANEPIC has been successfully used to produce maps using data from the 2005 BLAST flight.

First season QUaD CMB temperature and polarization power spectra

Abstract: 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 deg2. 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.

High resolution CMB power spectrum from the complete ACBAR data set

Abstract: In this paper, we present results from the complete set of cosmic microwave background (CMB) radiation temperature anisotropy observations made with the Arcminute Cosmology Bolometer Array Receiver (ACBAR) operating at 150 GHz. We include new data from the final 2005 observing season, expanding the number of detector-hours by 210% and the sky coverage by 490% over that used for the previous ACBAR release. As a result, the band-power uncertainties have been reduced by more than a factor of two on angular scales encompassing the third to fifth acoustic peaks as well as the damping tail of the CMB power spectrum. The calibration uncertainty has been reduced from 6% to 2.1% in temperature through a direct comparison of the CMB anisotropy measured by ACBAR with that of the dipole-calibrated WMAP5 experiment. The measured power spectrum is consistent with a spatially flat, LambdaCDM cosmological model. We include the effects of weak lensing in the power spectrum model computations and find that this significantly improves the fits of the models to the combined ACBAR+WMAP5 power spectrum. The preferred strength of the lensing is consistent with theoretical expectations. On fine angular scales, there is weak evidence (1.1 sigma) for excess power above the level expected from primary anisotropies. We expect any excess power to be dominated by the combination of emission from dusty protogalaxies and the Sunyaev-Zel'dovich effect (SZE). However, the excess observed by ACBAR is significantly smaller than the excess power at ell > 2000 reported by the CBI experiment operating at 30 GHz. Therefore, while it is unlikely that the CBI excess has a primordial origin; the combined ACBAR and CBI results are consistent with the source of the CBI excess being either the SZE or radio source contamination.

South Pole Telescope optics

Abstract: The South Pole Telescope is a 10 m diameter, wide-field, offset Gregorian telescope with a 966-pixel, millimeter-wave, bolometer array receiver. The telescope has an unusual optical system with a cold stop around the secondary. The design emphasizes low scattering and low background loading. All the optical components except the primary are cold, and the entire beam from prime focus to the detectors is surrounded by cold absorber.

SPIDER: A Balloon-borne Large-scale CMB Polarimeter

Abstract: Spider is a balloon-borne experiment that will measure the polarization of the Cosmic Microwave Backgroundover a large fraction of a sky at 1 resolution. Six monochromatic refracting millimeter-wave telescopes withlarge arrays of antenna-coupled transition-edge superconducting bolometers will provide system sensitivities of4.2 and 3.1 µ K cmb s at 100 and 150 GHz, respectively. A rotating half-wave plate will modulate the polarizationsensitivity of each telescope, controlling systematics. Bolometer arrays operating at 225 GHz and 275 GHz willallow removal of polarized galactic foregrounds. In a 2- 6 day “rst ”ight 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 depthby a large factor. 1. INTRODUCTION Rapid progressin millimeter-wave receiver technology enabled major advances in cosmologyover the past decade.Extremely sensitive receivers measur ed the very faint anisotro pies and polarization of the Cosmic MicrowaveBackground (CMB), which are a mere part in 10

Sunyaev-Zel'dovich Effect Observations of the Bullet Cluster (1E 0657-56) with APEX-SZ

Abstract: We present observations of the Sunyaev-Zel'dovich effect (SZE) in the Bullet cluster (1E 0657--56) using the APEX-SZ instrument at 150 GHz with a resolution of 1 arcmin. The main results are maps of the SZE in this massive, merging galaxy cluster. The cluster is detected with 23 sigma significance within the central 1 arcmin radius of the source position. The SZE map has a broadly similar morphology to that in existing X-ray maps of this system, and we find no evidence for significant contamination of the SZE emission by radio or IR sources. In order to make simple quantitative comparisons with cluster gas models derived from X-ray observations, we fit our data to an isothermal elliptical beta model, despite the inadequacy of such a model for this complex merging system. With an X-ray derived prior on the power-law index, beta = 1.04 +0.16 -0.10, we find a core radius r_c =142 +/- 18 arcsec, an axial ratio of 0.889 +/- 0.072, and a central temperature decrement of -771 +/- 71 micro-K_CMB, including a +/-5.5% flux calibration uncertainty. Combining the APEX-SZ map with a map of projected electron surface density from Chandra X-ray observations, we determine the mass-weighted temperature of the cluster gas to be T_mg=10.8 +/- 0.9 keV, significantly lower than some previously reported X-ray spectroscopic temperatures. Under the assumption of an isothermal cluster gas distribution in hydrostatic equilibrium, we compute the gas mass fraction for prolate and oblate spheroidal geometries and find it to be consistent with previous results from X-ray and weak lensing observations. This work is the first result from the APEX-SZ experiment, and represents the first reported scientific result from observations with a large array of multiplexed superconducting transition-edge sensor bolometers.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) 2005: A 4 deg2 Galactic Plane Survey in Vulpecula (ℓ = 59°)

Abstract: We present the first results from a new 250, 350, and 500 μm Galactic plane survey taken with the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST) in 2005. This survey's primary goal is to identify and characterize high-mass protostellar objects (HMPOs). The region studied here covers 4 deg2 near the open cluster NGC 6823 in the constellation Vulpecula ( = 59°). We find 60 compact sources (<60'' diameter) detected simultaneously in all three bands. Their SEDs are constrained through BLAST, IRAS, Spitzer MIPS, and MSX photometry, with inferred dust temperatures spanning ~12-40 K assuming a dust emissivity index β = 1.5. The luminosity-to-mass ratio, a distance-independent quantity, spans ~0.2-130 L M−1. Distances are estimated from coincident 13CO(1→ 0) velocities combined with a variety of other velocity and morphological data in the literature. In total, 49 sources are associated with a molecular cloud complex encompassing NGC 6823 (distance ~2.3 kpc), 10 objects with the Perseus arm (~8.5 kpc), and one object is probably in the outer Galaxy (~14 kpc). Near NGC 6823, the inferred luminosities and masses of BLAST sources span ~40-104 L and ~15-700 M, respectively. The mass spectrum is compatible with molecular gas masses in other high-mass star-forming regions. Several luminous sources appear to be ultracompact H II regions powered by early B stars. However, many of the objects are cool, massive gravitationally bound clumps with no obvious internal radiation from a protostar, and hence excellent HMPO candidates.

Metal-mesh achromatic half-wave plate for use at submillimeter wavelengths

Abstract: A metal-mesh achromatic half-wave plate (HWP) has been designed, manufactured, and tested for potential use in millimeter and submillimeter astronomical instruments. The prototype device presented here is based on a 12-grid Shatrow [ IEEE Trans. Antennas Propag. 43, 109 (1995)] recipe to operate over the frequency range of 120–180 GHz . Transmission line modeling and finite-element analysis [Ansoft HFSS website: http://www.ansoft.com/hfss/ ] were used to optimize the design geometrical parameters in terms of the device transmission, reflection, absorption, phase-shift, and cross-polarization as a function of frequency. The resulting prototype device was constructed and characterized using incoherent radiation from a polarizing Fourier transform spectrometer to explore its frequency and polarization behavior. These measurements are shown to be in excellent agreement with the models. Lists of the achieved HWP performance characteristics are reported.

QUaD: A High-Resolution Cosmic Microwave Background Polarimeter

Abstract: We describe the QUaD experiment, a millimeter-wavelength polarimeter designed to observe the Cosmic Microwave Background (CMB) from a site at the South Pole. The experiment comprises a 2.64 m Cassegrain telescope equipped with a cryogenically cooled receiver containing an array of 62 polarization-sensitive bolometers. The focal plane contains pixels at two different frequency bands, 100 GHz and 150 GHz, with angular resolutions of 5 arcmin and 3.5 arcmin, respectively. The high angular resolution allows observation of CMB temperature and polarization anisotropies over a wide range of scales. The instrument commenced operation in early 2005 and collected science data during three successive Austral winter seasons of observation.

Spider optimization : probing the systematics of a large-scale b-mode experiment

Abstract: Spider is a long-duration, balloon-borne polarimeter designed to measure large-scale cosmic microwave background (CMB) polarization with very high sensitivity and control of systematics. The instrument will map over half the sky with degree angular resolution in the I, Q, and U Stokes parameters in four frequency bands from 96 to 275 GHz. Spider's ultimate goal is to detect the primordial gravity-wave signal imprinted on the CMB B-mode polarization. One of the challenges in achieving this goal is the minimization of the contamination of B-modes by systematic effects. This paper explores a number of instrument systematics and observing strategies in order to optimize B-mode sensitivity. This is done by injecting realistic-amplitude, time-varying systematics into a set of simulated time streams. Tests of the impact of detector noise characteristics, pointing jitter, payload pendulations, polarization angle offsets, beam systematics, and receiver gain drifts are shown. Spider's default observing strategy is to spin continuously in azimuth, with polarization modulation achieved by either a rapidly spinning half-wave plate or a rapidly spinning gondola and a slowly stepped half-wave plate. Although the latter is more susceptible to systematics, the results shown here indicate that either mode of operation can be used by Spider.

Detection of the 13CO J = 6→ 5 transition in the Starburst Galaxy NGC 253

Abstract: We report the detection of 13CO J = 6→ 5 emission from the nucleus of the starburst galaxy NGC 253 with the redshift (z) and Early Universe Spectrometer (ZEUS), a new submillimeter grating spectrometer. This is the first extragalactic detection of the 13CO J = 6→ 5 transition, which traces warm, dense molecular gas. We employ a multiline LVG analysis and find 35%-60% of the molecular interstellar medium is both warm (T ~ 110 K) and dense (nH2 ~ 104 cm−3). We analyze the potential heat sources and conclude that ultraviolet and X-ray photons are unlikely to be energetically important. Instead, the molecular gas is most likely heated by an elevated density of cosmic rays or by the decay of supersonic turbulence through shocks. If the cosmic rays and turbulence are created by stellar feedback within the starburst, then our analysis suggests the starburst may be self-limiting.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) 2005: calibration and targeted Sources

Abstract: The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) operated successfully during a 100 hr flight from northern Sweden in 2005 June (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, W75N, 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 μm 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.

Herschel-SPIRE: design, ground test results, and predicted performance

Abstract: SPIRE, the Spectral and Photometric Imaging Receiver, is a submillimetre camera and spectrometer for Herschel. It comprises a three-band camera operating at 250, 350 and 500 µm, and an imaging Fourier Transform Spectrometer covering 194-672 µm. The photometer field of view is 4×8 arcmin., viewed simultaneously in the three bands. The FTS has an approximately circular field of view of 2.6 arcmin. diameter and spectral resolution adjustable between 0.04 and 2 cm?1 (?/??. =20-1000 at 250 µm). Following successful testing in a dedicated facility designed to simulate the in-flight operational conditions, SPIRE has been integrated in the Herschel spacecraft and is now undergoing system-level testing prior to launch. The main design features of SPIRE are reviewed, the key results of instrument testing are outlined, and a summary of the predicted in-flight performance is given.

MUSTANG: 90 GHz science with the Green Bank telescope

Abstract: MUSTANG is a 90 GHz bolometer camera built for use as a facility instrument on the 100 m Robert C. ByrdGreen Bank radio telescope (GBT). MUSTANG has an 8 by 8 focal plane array of transition edge sensorbolometers read out using time-domain multiplexed SQUID electronics. As a continuum instrument on a largesingle dish MUSTANG has a combination of high resolution (8) and good sensitivity to extended emissionwhich make it very competitive for a wide range of galactic and extragalactic science. Commissioning finishedin January 2008 and some of the first science data have been collected.

POLARBEAR: Ultra‐high Energy Physics with Measurements of CMB Polarization

Abstract: POLARBEAR is a ground‐based experiment to measure polarization anisotropy in the Cosmic Microwave Background. It is designed to have a combination of sensitivity, foreground mitigation, and rejection of systematic errors to search for the B‐mode signature of Inflationary gravity waves over much of the parameter range suggested by simple power‐law Inflation models. POLARBEAR is designed to detect a gravitational‐wave signature with a tensor‐to‐scalar ratio r as low as 0.025 (95% confidence). POLARBEAR will also measure polarized lensing of the Cosmic Microwave Background which will give valuable information on large‐scale structure at z>1 and bound the total mass of the neutrinos. POLARBEAR will have a 3.5 meter primary meter giving it an angular resolution of 3.0′ at its main observation frequency band centered at 150 GHz. The 250 mK focal plane design contains 637 dual‐polarization pixels (1274 bolometers) that are coupled to the telescope using microlithographed planar antennas. The experiment will be sited in the Atacama Desert in Chile at 5000 meter (16,500 ft) altitude starting in 2009 after a prototype testing stage at Cedar Flats California. The first configuration of the experiment will observe at only one frequency band with the first season at 150 GHz and the second at 220 GHz. The optics will be upgraded to have simultaneous observations in those two bands in the third season of observations. POLARBEAR and QUIET will observe the same sky patches, and together they will have frequency bands at 30, 40, 90, 150, and 220 GHz giving broad coverage of galactic foregrounds and a valuable cross‐check by comparison of polarization maps. In POLARBEAR, polarization systematic errors are mitigated by a continuously rotating 50 K half‐wave plate and an observation strategy that takes advantage of parallactic angle rotation to rotate the experiment relative to polarization patterns on the sky.

TES Bolometer Array for the APEX-SZ Camera

Abstract: We will report on the APEX-SZ bolometer camera which houses a 320 element Transition-Edge Sensor (TES) bolometer array designed to survey for galaxy clusters using the 12-meter diameter APEX telescope sited in Chile. Design and fabrication of the TES bolometer array will be discussed, as well as its integration with a frequency-domain SQUID multiplexed readout system. The full configuration of the APEX-SZ camera was deployed in April 2007. A preliminary galaxy cluster map from this deployment will be presented.

Instrument design and characterization of the Millimeter Bolometer Array Camera on the Atacama Cosmology Telescope

Abstract: The Millimeter Bolometer Array Camera (MBAC) was commissioned in the fall of 2007 on the new 6-meterAtacama Cosmology Telescope (ACT). The MBAC on the ACT will map the temperature anisotropies of theCosmic Microwave Background (CMB) with arc-minute resolution. For this first observing season, the MBACcontained a diffraction-limited, 32 by 32 element, focal plane array of Transition Edge Sensor (TES) bolometersfor observations at 145 GHz. This array was coupled to the telescope with a series of cold, refractive, reimagingoptics. To meet the performance specifications, the MBAC employs four stages of cooling using closed-cycle3He/4He sorption fridge systems in combination with pulse tube coolers. In this paper we present the design ofthe instrument and discuss its performance during the first observing season. Finally, we report on the statusof the MBAC for the 2008 observing season, when the instrument will be upgraded to a total of three separate1024-element arrays at 145 GHz, 220 GHz and 280 GHz.

CMB polarimetry with BICEP: instrument characterization, calibration, and performance

Abstract: Bicep is a ground-based millimeter-wave bolometric array designed to target the primordial gravity wave signature on the B-mode polarization of the cosmic microwave background (CMB) at degree angular scales. Currently in its third year of operation at the South Pole, Bicep is measuring the CMB polarization with unprecedented sensitivity at 100 and 150 GHz in the cleanest available 2% of the sky, as well as deriving independent constraints on the diffuse polarized foregrounds with select observations on and off the Galactic plane. Instrument calibrations are discussed in the context of rigorous control of systematic errors, and the performance during the first two years of the experiment is reviewed.

EBEX: the E and B Experiment

Abstract: The E and B Experiment, EBEX, is a Cosmic Microwave Background polarization experiment designed to detector set upper limits on the signature of primordial gravity waves. Primordial gravity waves are predicted to beproduced by inflation, and a measurement of the power spectrum of these gravity waves is a measurement ofthe energy scale of inflation. EBEX has sufficient sensitivity to detect or set an upper limit at 95% confidenceon the energy scale of inflation of < 1.4 × 1016 GeV. This article reviews our strategy for achieving our sciencegoals and discusses the implementation of the instrument.

A Multi-Band Dual-Polarized Antenna-Coupled TES Bolometer

Abstract: We are developing multi-band dual-polarized antenna-coupled transition edge sensor (TES) bolometers for observing Cosmic Microwave Background (CMB) polarization anisotropies. We have designed a prototype pixel that uses a dual-polarized log-periodic antenna on a silicon hemispherical lens. Each polarization is coupled onto a separate microstrip transmission line. Microstrip filters are used to divide the broadband output of this antenna into a set of narrow frequency bands centered at 90, 150, and 220 GHz with bandwidths of 20%. We report on the fabrication of these devices as well as the initial optical testing.

Antenna-Coupled Bolometer Arrays for Measurement of the Cosmic Microwave Background Polarization

Abstract: We are building antenna-coupled Transition Edge Sensor bolometer arrays to measure the polarization of the cosmic microwave background. 217 GHz prototype pixels have previously been characterized and showed promising performance (Myers et al. in Appl. Phys. Lett. 86:114103, [2005]). Our design uses a double slot dipole antenna and an integrated microstrip band defining filter. New devices have been tested which include on-chip test structures to improve our understanding of detector performance and guide future development. In parallel with this, large arrays of bolometers based on the prototype pixel design have also been constructed. The array pixels are a heterogeneous mixture of single band pixels at 90 GHz, 150 GHz, and 220 GHz and now incorporate dual-polarization antennas (Chattopadhyay and Zmuidzinas in IEEE Trans. Antennas Propag. 46:736, [1998]). Preliminary results from optical testing of array pixels are presented. These bolometer arrays will be used in the upcoming CMB polarization experiment Polarbear.

BICEP2/SPUD: searching for inflation with degree scale polarimetry from the South Pole

Abstract: BICEP2/SPUD is the new powerful upgrade of the existing BICEP1 experiment, a bolometric receiver to study the polarization of the cosmic microwave background radiation, which has been in operation at the South Pole since January 2006. BICEP2 will provide an improvement up to 10 times mapping speed at 150 GHz compared to BICEP1, using the same BICEP telescope mount. SPUD, a series of compact, mechanically-cooled receivers deployed on the DASI mount at the Pole, will provide similar mapping speed in to BICEP2 in three bands, 100, 150, and 220 GHz. The new system will use large TES focal plane arrays to provide unprecedented sensitivity and excellent control of foreground contamination.

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

Abstract: The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLAST-Pol) is a suborbital mapping experiment designed to study the role played by magnetic fields in the star formation process. BLAST-Pol is the reconstructed BLAST telescope, with the addition of linear polarization capability. Using a 1.8m Cassegrain telescope, BLAST-Pol images the sky onto a focal plane that consists of 280 bolometric detectors in three arrays, observing simultaneously at 250, 350, and 500μm. The diffraction-limited optical system provides a resolution of 30"at 250μm. The polarimeter consists of photolithographic polarizing grids mounted in front of each bolometer/ detector array. A rotating 4K achromatic half-wave plate provides additional polarization modulation. With its unprecedented mapping speed and resolution, BLAST-Pol will produce three-color polarization maps for a large number of molecular clouds. The instrument provides a much needed bridge in spatial coverage between larger-scale, coarse resolution surveys and narrow field of view, and high resolution observations of substructure within molecular cloud cores. The first science flight will be from McMurdo Station, Antarctica in December 2010.

The effects of the mechanical performance and alignment of the Atacama Cosmology Telescope on the sensitivity of microwave observations

Abstract: The Atacama Cosmology Telescope is a six meter, off-axis Gregorian telescope for measuring the cosmic microwave background at arcminute resolutions. The Millimeter Bolometer Array Camera (MBAC) is its current science instrument. Erected in the Atacama Desert of Chile in early 2007, it saw first light with the MBAC on 22 October 2007. In this paper we review its performance after one month of observing, focusing in particular on issues surrounding the alignment of the optical system that impact the sensitivity of the experiment. We discuss the telescope motion, pointing, and susceptibility to thermal distortions. We describe the mirror alignment procedure, which has yielded surface deviations of 31 μm rms on the primary and 10 μm rms on the secondary. Observations of planets show that the optical performance is consistent with the telescope design parameters. Preliminary analysis measures a solid angle of about 215 nanosteradians with a full width at half maximum of 1.44 arcminutes at 145 GHz.

SPIDER: A Balloon-borne Large-scale CMB Polarimeter

Abstract: 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.

Galaxy clusters discovered with a Sunyaev-Zel'dovich effect survey

Abstract: The South Pole Telescope (SPT) is conducting a Sunyaev-Zel'dovich (SZ) effect survey over large areas of the southern sky, searching for massive galaxy clusters to high redshift. In this preliminary study, we focus on a 40 square-degree area targeted by the Blanco Cosmology Survey (BCS), which is centered roughly at right ascension 5h30m, declination -53 degrees. Over two seasons of observations, this entire region has been mapped by the SPT at 95 GHz, 150 GHz, and 225 GHz. We report the four most significant SPT detections of SZ clusters in this field, three of which were previously unknown and, therefore, represent the first galaxy clusters discovered with an SZ survey. The SZ clusters are detected as decrements with greater than 5-sigma significance in the high-sensitivity 150 GHz SPT map. The SZ spectrum of these sources is confirmed by detections of decrements at the corresponding locations in the 95 GHz SPT map and non-detections at those locations in the 225 GHz SPT map. Multiband optical images from the BCS survey demonstrate significant concentrations of similarly colored galaxies at the positions of the SZ detections. Photometric redshift estimates from the BCS data indicate that two of the clusters lie at moderate redshift (z ~ 0.4) and two at high redshift (z >~ 0.8). One of the SZ detections was previously identified as a galaxy cluster using X-ray data from the ROSAT All-Sky Survey (RASS). Potential RASS counterparts (not previously identified as clusters) are also found for two of the new discoveries. These first four galaxy clusters are the most significant SZ detections from a subset of the ongoing SPT survey. As such, they serve as a demonstration that SZ surveys, and the SPT in particular, can be an effective means for finding galaxy clusters.

Opto-mechanical design and performance of a compact three-frequency camera for the Millimeter Bolometer Array Camera on the Atacama Cosmology Telescope.

Abstract: The 6-meter Atacama Cosmology Telescope will map the cosmic microwave background at millimeter wavelengths.The commissioning instrument for the telescope, the Millimeter Bolometer Array Camera, is based on arefractive optical system which simultaneously images three separate fields of view at three different frequencies:145, 220, and 280 GHz. Each frequency band contains around twelve individual optical elements at five differenttemperature stages ranging from 300 K to 300 mK and a 32 x 32 array of Transition Edge Sensor bolometers at300 mK. We discuss the design of the close-packed on-axis optical design of the three frequencies. The thermaldesign and performance of the system are presented in the context of the scientific requirements and observingschedule. A major part of the design was the incorporation of multiple layers of magnetic shielding. We discussthe performance of the 145 GHz optical system in 2007 and the implementation of the additional two frequencychannels in 2008.

Detecting the B-mode Polarisation of the CMB with Clover

Abstract: 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.