Design of 280 GHz feedhorn-coupled TES arrays for the balloon-borne polarimeter SPIDER

We describe 280 GHz bolometric detector arrays that instrument the balloon-borne polarimeter spider. A primary science goal of spider is to measure the large-scale B-mode polarization of the cosmic microwave background (cmb) in search of the cosmic-inflation, gravitational-wave signature. 280 GHz channels aid this science goal by constraining the level of B-mode contamination from galactic dust emission. We present the focal plane unit design, which consists of a 16x16 array of conical, corrugated feedhorns coupled to a monolithic detector array fabricated on a 150 mm diameter silicon wafer. Detector arrays are capable of polarimetric sensing via waveguide probe-coupling to a multiplexed array of transition-edge-sensor (TES) bolometers. The spider receiver has three focal plane units at 280 GHz, which in total contains 765 spatial pixels and 1,530 polarization sensitive bolometers. By fabrication and measurement of single feedhorns, we demonstrate 14.7° FHWM Gaussian-shaped beams with <1% ellipticity in a 30% fractional bandwidth centered at 280 GHz. We present electromagnetic simulations of the detection circuit, which show 94% band-averaged, single-polarization coupling efficiency, 3% reflection and 3% radiative loss. Lastly, we demonstrate a low thermal conductance bolometer, which is well-described by a simple TES model and exhibits an electrical noise equivalent power (NEP) = 2.6 x 10^(-17) W/√Hz, consistent with the phonon noise prediction

The EBEX Balloon-borne Experiment—Gondola, Attitude Control, and Control Software

The E and B Experiment (EBEX) was a long-duration balloon-borne instrument designed to measure the polarization of the cosmic microwave background (CMB) radiation. EBEX was the first balloon-borne instrument to implement a kilopixel array of transition edge sensor (TES) bolometric detectors and the first CMB experiment to use the digital version of the frequency domain multiplexing system for readout of the TES array. The scan strategy relied on 40 s peak-to-peak constant-velocity azimuthal scans. We discuss the unique demands on the design and operation of the payload that resulted from these new technologies and the scan strategy. We describe the solutions implemented, including the development of a power system designed to provide a total of at least 2.3 kW, a cooling system to dissipate 590 W consumed by the detectors' readout system, software to manage and handle the data of the kilopixel array, and specialized attitude reconstruction software. We present flight performance data showing faultless management of the TES array, adequate powering and cooling of the readout electronics, and constraint of attitude reconstruction errors such that the spurious B-modes they induced were less than 10% of the CMB B-mode power spectrum with r = 0.05

Balloon-Borne Submillimeter Polarimetry of the Vela C Molecular Cloud: Systematic Dependence of Polarization Fraction on Column Density and Local Polarization-Angle Dispersion

We present results for Vela C obtained during the 2012 flight of the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry. We mapped polarized intensity across almost the entire extent of this giant molecular cloud, in bands centered at 250, 350, and 500 μm. In this initial paper, we show our 500 μm data smoothed to a resolution of 2farcm5 (approximately 0.5 pc). We show that the mean level of the fractional polarization p and most of its spatial variations can be accounted for using an empirical three-parameter power-law fit, p ∝ N^(-0.45) S^(-0.60), where N is the hydrogen column density and S is the polarization-angle dispersion on 0.5 pc scales. The decrease of p with increasing S is expected because changes in the magnetic field direction within the cloud volume sampled by each measurement will lead to cancellation of polarization signals. The decrease of p with increasing N might be caused by the same effect, if magnetic field disorder increases for high column density sightlines. Alternatively, the intrinsic polarization efficiency of the dust grain population might be lower for material along higher density sightlines. We find no significant correlation between N and S. Comparison of observed submillimeter polarization maps with synthetic polarization maps derived from numerical simulations provides a promising method for testing star formation theories. Realistic simulations should allow for the possibility of variable intrinsic polarization efficiency. The measured levels of correlation among p, N, and S provide points of comparison between observations and simulations

Submillimeter Polarization Spectrum of the Carina Nebula

Linear polarization maps of the Carina Nebula were obtained at 250, 350, and 500 μm during the 2012 flight of the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol). These measurements are combined with Planck 850 μm data in order to produce a submillimeter spectrum of the polarization fraction of the dust emission, averaged over the cloud. This spectrum is flat to within ±15% (relative to the 350 μm polarization fraction). In particular, there is no evidence for a pronounced minimum of the spectrum near 350 μm, as suggested by previous ground-based measurements of other molecular clouds. This result of a flat polarization spectrum in Carina is consistent with recently published BLASTPol measurements of the Vela C molecular cloud and also agrees with a published model for an externally illuminated, dense molecular cloud by Bethell and collaborators. The shape of the spectrum in Carina does not show any dependence on the radiative environment of the dust, as quantified by the Planck-derived dust temperature or dust optical depth at 353 GHz

Comparing Submillimeter Polarized Emission with Near-infrared Polarization of Background Stars for the Vela C Molecular Cloud

We present a large-scale combination of near-infrared (near-IR) interstellar polarization data from background starlight with polarized emission data at submillimeter wavelengths for the Vela C molecular cloud. The near-IR data consist of more than 6700 detections probing a range of visual extinctions between 2 and 20 mag in and around the cloud. The submillimeter data were collected in Antarctica by the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry. This is the first direct combination of near-IR and submillimeter polarization data for a molecular cloud aimed at measuring the "polarization efficiency ratio" R_(eff), a quantity that is expected to depend only on grain-intrinsic physical properties. It is defined as p_(500)/(pt_TV), where p 500 and p I are polarization fractions at 500 µm and the I band, respectively, and t_V is the optical depth. To ensure that the same column density of material is producing both polarization from emission and from extinction, we conducted a careful selection of near-background stars using 2MASS, Herschel, and Planck data. This selection excludes objects contaminated by the Galactic diffuse background material as well as objects located in the foreground. Accounting for statistical and systematic uncertainties, we estimate an average R_(eff) value of 2.4 ± 0.8, which can be used to test the predictions of dust grain models designed for molecular clouds when such predictions become available. The ratio R_(eff) appears to be relatively flat as a function of the cloud depth for the range of visual extinctions probed

Submillimeter Polarization Spectrum in the Vela C Molecular Cloud

Polarization maps of the Vela C molecular cloud were obtained at 250, 350, and 500 μm during the 2012 flight of the balloon-borne telescope BLASTPol. These measurements are used in conjunction with 850 μm data from Planck to study the submillimeter spectrum of the polarization fraction for this cloud. The spectrum is relatively flat and does not exhibit a pronounced minimum at λ ~ 350 μm as suggested by previous measurements of other molecular clouds. The shape of the spectrum does not depend strongly on the radiative environment of the dust, as quantified by the column density or the dust temperature obtained from Herschel data. The polarization ratios observed in Vela C are consistent with a model of a porous clumpy molecular cloud being uniformly heated by the interstellar radiation field

BLAST : studying cosmic and Galactic star formation from a stratospheric balloon

Understanding the history of the formation of stars and evolution of galaxies is one of the foremost goals of astrophysics. While stars emit most of their energy at visible and ultraviolet wavelengths, during the early stages of star formation these photons are absorbed by the dusty molecular clouds that host and fuel the emerging stars, and re-emitted as thermal radiation at infrared and submillimeter wavelengths. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) was designed to study the history of obscured star forma- tion in galaxies at cosmological distances and witness the details of the star-formation processes in our own Galaxy, by conducting large- area surveys of the sky at 250, 350, and 500 �m from a long-duration stratospheric balloon platform. Its polarimetric adaptation, BLAST- Pol, will allow us to further probe the strength and morphology of magnetic fields in dust-enshrouded star-forming molecular clouds in our Galaxy. The study of these two diverse, yet highly complemen- tary, topics is the primary scientific motivation for this thesis, which is in two parts. Part One is concerned with the analysis of a combination of the extragalactic dataset collected by BLAST in the 2006 Antarctic cam- paign, which comprises maps containing hundreds of distant, highly dust-obscured, and actively star-forming galaxies, with a wealth of ancillary multi-wavelength data spanning the radio to the ultravio- let. The star-formation rates we observe in massive galaxies at high redshift support downsizing and size evolution. Part Two describes the BLAST-Pol instrument. In particular, we focus on the gondola's primary pointing sensors, the star cameras, and on the design, manufacture and characterization of a polarization IX modulation scheme, comprising a cryogenic achromatic half-wave plate and photolithographed polarizing grids, which has been effectively retrofitted on BLAST-Pol. We report on the construction and deployment of BLAST-Pol, which completed its first successful 9.5-day ight over Antarctica in January 2011 and mapped ten science targets with unprecedented combined mapping speed, sensitivity, and resolution.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

BLAST: studying cosmic and Galactic star formation from a stratospheric balloon

Understanding the history of the formation of stars and evolution of galaxies is one of the foremost goals of astrophysics. While stars emit most of their energy at visible and ultraviolet wavelengths, during the early stages of star formation these photons are absorbed by the dusty molecular clouds that host and fuel the emerging stars, and re-emitted as thermal radiation at infrared and submillimeter wavelengths. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) was designed to study the history of obscured star forma- tion in galaxies at cosmological distances and witness the details of the star-formation processes in our own Galaxy, by conducting large- area surveys of the sky at 250, 350, and 500 �m from a long-duration stratospheric balloon platform. Its polarimetric adaptation, BLAST- Pol, will allow us to further probe the strength and morphology of magnetic fields in dust-enshrouded star-forming molecular clouds in our Galaxy. The study of these two diverse, yet highly complemen- tary, topics is the primary scientific motivation for this thesis, which is in two parts. Part One is concerned with the analysis of a combination of the extragalactic dataset collected by BLAST in the 2006 Antarctic cam- paign, which comprises maps containing hundreds of distant, highly dust-obscured, and actively star-forming galaxies, with a wealth of ancillary multi-wavelength data spanning the radio to the ultravio- let. The star-formation rates we observe in massive galaxies at high redshift support downsizing and size evolution. Part Two describes the BLAST-Pol instrument. In particular, we focus on the gondola's primary pointing sensors, the star cameras, and on the design, manufacture and characterization of a polarization IX modulation scheme, comprising a cryogenic achromatic half-wave plate and photolithographed polarizing grids, which has been effectively retrofitted on BLAST-Pol. We report on the construction and deployment of BLAST-Pol, which completed its first successful 9.5-day ight over Antarctica in January 2011 and mapped ten science targets with unprecedented combined mapping speed, sensitivity, and resolution

Comparison of Prestellar Core Elongations and Large-scale Molecular Cloud Structures in the Lupus I Region

Turbulence and magnetic fields are expected to be important for regulating molecular cloud formation and evolution. However, their effects on sub-parsec to 100 parsec scales, leading to the formation of starless cores, are not well understood. We investigate the prestellar core structure morphologies obtained from analysis of the Herschel-SPIRE 350 μm maps of the Lupus I cloud. This distribution is first compared on a statistical basis to the large-scale shape of the main filament. We find the distribution of the elongation position angle of the cores to be consistent with a random distribution, which means no specific orientation of the morphology of the cores is observed with respect to the mean orientation of the large-scale filament in Lupus I, nor relative to a large-scale bent filament model. This distribution is also compared to the mean orientation of the large-scale magnetic fields probed at 350 μm with the Balloon-borne Large Aperture Telescope for Polarimetry during its 2010 campaign. Here again we do not find any correlation between the core morphology distribution and the average orientation of the magnetic fields on parsec scales. Our main conclusion is that the local filament dynamics—including secondary filaments that often run orthogonally to the primary filament—and possibly small-scale variations in the local magnetic field direction, could be the dominant factors for explaining the final orientation of each core