S. F. Edgington

Current status of Bolocam: a large-format millimeter-wave bolometer camera

We describe the design and performance of Bolocam, a 144-element, bolometric, millimeter-wave camera. Bolocam is currently in its commissioning stage at the Caltech Submillimeter Observatory. We compare the instrument performance measured at the telescope with a detailed sensitivity model, discuss the factors limiting the current sensitivity, and describe our plans for future improvements intended to increase the mapping speed.

A fluctuation analysis of the Bolocam 1.1 mm Lockman Hole Survey

We perform a fluctuation analysis of the 1.1 mm Bolocam Lockman Hole Survey, which covers 324 arcmin2 to a very uniform point-source-filtered rms noise level of σ 1.4 mJy beam-1. The fluctuation analysis has the significant advantage of using all of the available data, since no extraction of sources is performed: direct comparison is made between the observed pixel flux density distribution [P(D)] and the theoretical distributions for a broad range of power-law number count models, n(S) = n0S-δ. We constrain the number counts in the 1-10 mJy range and derive significantly tighter constraints than in previous work: the power-law index δ = 2.7, while the amplitude is n0 = 1595 mJy-1 , or N(> 1 mJy) = 940 (95% confidence). At flux densities above 4 mJy, where a valid comparison can be made, our results agree extremely well with those derived from the extracted source number counts by Laurent et al.: the best-fitting differential slope is somewhat shallower (δ = 2.7 vs. 3.2), but well within the 68% confidence limit, and the amplitudes (number of sources per square degree) agree to 10%. At 1 mJy, however [the limit of the P(D) analysis], the shallower slope derived here implies a substantially smaller amplitude for the integral number counts than extrapolation from above 4 mJy would predict. Our derived normalization is about 2.5 times smaller than that determined by the Max-Planck Millimeter Bolometer (MAMBO) at 1.2 mm (Greve et al.). However, the uncertainty in the normalization for both data sets is dominated by the systematic (i.e., absolute flux calibration) rather than statistical errors; within these uncertainties, our results are in agreement. Our best-fit amplitude at 1 mJy is also about a factor of 3 below the prediction of Blain et al., but we are in agreement above a few millijanskys. We estimate that about 7% of the 1.1 mm background has been resolved at 1 mJy.

A three-stage helium sorption refrigerator for cooling of infrared detectors to 280 mK

Abstract We review some of the applications of submillimetre instruments for astronomy and Earth atmospheric sciences where helium sorption refrigerators have been used. We describe a three-stage helium refrigerator which uses a 4He–3He double-stage refrigerator to precool and intercept the parasitic heatload on a final 3He single-stage refrigerator. This multi-stage configuration permits operation of the refrigerator system without externally pumping on a 4He bath. This results in simpler integration with the instrument and allows scientific observations to be more easily made. We have achieved a base temperature of 234 mK for a hold time of 20.4 h. The heat lift at 280 mK is 15 μW.

Numerical optimization of integrating cavities for diffraction-limited millimeter-wave bolometer arrays

Far-infrared to millimeter-wave bolometers designed to make astronomical observations are typically encased in integrating cavities at the termination of feedhorns or Winston cones. This photometer combination maximizes absorption of radiation, enables the absorber area to be minimized, and controls the directivity of absorption, thereby reducing susceptibility to stray light. In the next decade, arrays of hundreds of silicon nitride micromesh bolometers with planar architectures will be used in ground-based, suborbital, and orbital platforms for astronomy. The optimization of integrating cavity designs is required for achieving the highest possible sensitivity for these arrays. We report numerical simulations of the electromagnetic fields in integrating cavities with an infinite plane-parallel geometry formed by a solid reflecting backshort and the back surface of a feedhorn array block. Performance of this architecture for the bolometer array camera (Bolocam) for cosmology at a frequency of 214 GHz is investigated. We explore the sensitivity of absorption efficiency to absorber impedance and backshort location and the magnitude of leakage from cavities. The simulations are compared with experimental data from a room-temperature scale model and with the performance of Bolocam at a temperature of 300 mK. The main results of the simulations for Bolocam-type cavities are that (1) monochromatic absorptions as high as 95% are achievable with <1% cross talk between neighboring cavities, (2) the optimum absorber impedances are 400 ohms/sq, but with a broad maximum from approximately 150 to approximately 700 ohms/sq, and (3) maximum absorption is achieved with absorber diameters > or = 1.5 lambda. Good general agreement between the simulations and the experiments was found.

Studies of atmospheric noise on Mauna Kea at 143 GHz with Bolocam

We report measurements of the fluctuations in atmospheric emission (atmospheric noise) above Mauna Kea recorded with Bolocam at 143 GHz. These data were collected in November and December of 2003 with Bolocam mounted on the Caltech Submillimeter Observatory (CSO), and span approximately 40 nights. Below ≃ 0.5 Hz, the data time-streams are dominated by the f-δ atmospheric noise in all observing conditions. We were able to successfully model the atmospheric fluctuations using a Kolmogorov-Taylor turbulence model for a thin wind-driven screen in approximately half of our data. Based on this modeling, we developed several algorithms to remove the atmospheric noise, and the best results were achieved when we described the fluctuations using a low-order polynomial in detector position over the 8 arcminute focal plane. However, even with these algorithms, we were not able to reach photon-background-limited instrument photometer (BLIP) performance at frequencies below ≃ 0.5 Hz in any observing conditions. Therefore, we conclude that BLIP performance is not possible from the CSO below ≃ 0.5 Hz for broadband 150 GHz receivers with subtraction of a spatial atmospheric template on scales of several arcminutes.

ERRATUM: “A SEARCH FOR COSMIC MICROWAVE BACKGROUND ANISOTROPIES ON ARCMINUTE SCALES WITH BOLOCAM” (2009, ApJ, 690, 1597)

J. Sayers1, S. R. Golwala1, P. Rossinot1, P. A. R. Ade2, J. E. Aguirre3, J. J. Bock4, S. F. Edgington1, J. Glenn3, A. Goldin4, D. Haig2, A. E. Lange1, G. T. Laurent3, P. D. Mauskopf2, and H. T. Nguyen4 1 Division of Physics, Mathematics, & Astronomy, California Institute of Technology, Mail Code 59-33, Pasadena, CA 91125, USA; jack@caltech.edu 2 Physics and Astronomy, Cardiff University, 5 The Parade, P.O. Box 913, Cardiff CF24 3YB, Wales, UK 3 Center for Astrophysics and Space Astronomy & Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309, USA 4 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

Erratum: A search for cosmic microwave background anisotropies on arcminute scales with bolocam (Astrophysical Journal, (2009) 690 (1597))

J. Sayers1, S. R. Golwala1, P. Rossinot1, P. A. R. Ade2, J. E. Aguirre3, J. J. Bock4, S. F. Edgington1, J. Glenn3, A. Goldin4, D. Haig2, A. E. Lange1, G. T. Laurent3, P. D. Mauskopf2, and H. T. Nguyen4 1 Division of Physics, Mathematics, & Astronomy, California Institute of Technology, Mail Code 59-33, Pasadena, CA 91125, USA; jack@caltech.edu 2 Physics and Astronomy, Cardiff University, 5 The Parade, P.O. Box 913, Cardiff CF24 3YB, Wales, UK 3 Center for Astrophysics and Space Astronomy & Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309, USA 4 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

A search for cosmic microwave background anisotropies on arcminute scales with bolocam (2009, ApJ, 690, 1597)[Erratum]

J. Sayers1, S. R. Golwala1, P. Rossinot1, P. A. R. Ade2, J. E. Aguirre3, J. J. Bock4, S. F. Edgington1, J. Glenn3, A. Goldin4, D. Haig2, A. E. Lange1, G. T. Laurent3, P. D. Mauskopf2, and H. T. Nguyen4 1 Division of Physics, Mathematics, & Astronomy, California Institute of Technology, Mail Code 59-33, Pasadena, CA 91125, USA; jack@caltech.edu 2 Physics and Astronomy, Cardiff University, 5 The Parade, P.O. Box 913, Cardiff CF24 3YB, Wales, UK 3 Center for Astrophysics and Space Astronomy & Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309, USA 4 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA