C-BASS

Abstract:

We present 12CO J = 3→2 maps of NGC 2976 and NGC 3351 obtained with the James Clerk Maxwell Telescope (JCMT), both early targets of the JCMT Nearby Galaxy Legacy Survey (NGLS). We combine the present observations with 12CO J = 1→0 data and find that the computed 12CO J = 3→2 to 12CO J = 1→0 line ratio (R31) agrees with values measured in other NGLS field galaxies. We compute the MH2 value and find that it is robust against the value of R31 used. Using HI data from The HI Nearby Galaxy Survey, we find a tight correlation between the surface density of H2 and star formation rate density for NGC 3351 when 12CO J = 3→2 data are used. Finally, we compare the 12CO J = 3→2 intensity with the polycyclic aromatic hydrocarbon (PAH) 8 μm surface brightness and find a good correlation in the high surface brightness regions. We extend this study to include all 25 Spitzer Infrared Nearby Galaxies Survey galaxies within the NGLS sample and find a tight correlation at large spatial scales. We suggest that both PAH 8 μm and 12CO J = 3→2 are likely to originate in regions of active star formation. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

Modern ground-based radio-telescopes have stringent requirements on the receiver's feed-horn performance. These include a bandwidth covering a full atmospheric window from good sites (∼ 30%), low cross polarization and high beam circularity. In addition the unprecedented sensitivity required by recent proposed experiments requires large format focal plane arrays consisting of a large number of high performance feeds. While these feeds are straightforward to fabricate at microwave frequencies, the tight tolerances required in the THz region makes the realization of a large format array both expensive and time consuming. In this paper we describe feed designs that can be fabricated cheaply and rapidly without compromising the science requirements within the operating bandwidth. We present simulated and measured far-field beam patterns showing low sidelobe levels, good beam circularity and low cross-polarization levels over a fractional bandwidth of 20%. Having demonstrated the efficacy of our horn designs and fabricating technique experimentally, we have designed, fabricated and tested a prototype focal plane array of 37 hexagonally close packed horns milled in a single block of aluminum. Experimental testing of the radiation patterns of the array feeds demonstrated that they were essentially identical to the patterns of the feeds fabricated individually and that cross coupling between adjacent feeds was negligible. © 2013 IEEE.

Abstract:

The Q/U Imaging ExperimenT (QUIET) is designed to measure polarization in the cosmic microwave background, targeting the imprint of inflationary gravitational waves at large angular scales(~1°). Between 2008 October and 2010 December, two independent receiver arrays were deployed sequentially on a 1.4 m side-fed Dragonian telescope. The polarimeters that form the focal planes use a compact design based on high electron mobility transistors (HEMTs) that provides simultaneous measurements of the Stokes parameters Q, U, and I in a single module. The 17-element Q-band polarimeter array, with a central frequency of 43.1 GHz, has the best sensitivity (69 μKs1/2) and the lowest instrumental systematic errors ever achieved in this band, contributing to the tensor-to-scalar ratio at r < 0.1. The 84-element W-band polarimeter array has a sensitivity of 87 μKs1/2 at a central frequency of 94.5 GHz. It has the lowest systematic errors to date, contributing at r < 0.01. The two arrays together cover multipoles in the range ℓ ~ 25-975. These are the largest HEMT-based arrays deployed to date. This article describes the design, calibration, performance, and sources of systematic error of the instrument.