Andrew Lange, California Institute of Technology
Paolo de Bernardis, Università de Sapienza, Rome
Phillip Mauskopf, University of Massachusetts
Julian Borrill, NERSC, Lawrence Berkeley National Laboratory

Research Objectives

In December 1998 and January 1999, the BOOMERANG (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics) Long Duration flight spent 10.5 days in the Antarctic stratosphere measuring the temperature of the cosmic microwave background (CMB). The resulting data set is the most significant measurement of the tiny fluctuations in the microwave sky temperature since they were first detected by the COBE satellite. The data covers 2000 square degrees of the sky at 10 arcminute resolution and high signal-to-noise. This research project is devoted to analyzing the BOOMERANG LDB data set, first to produce a map of the CMB anisotropies and then to extract their angular power spectrum.

Computational Approach

The analysis of a massive CMB data set can be recast as a problem in numerical linear algebra, and, in particular, in the solution of linear systems involving very large, dense, symmetric matrices. First we convert the time-ordered CMB data to a pixelized map, triangular-solving a linear system with a single right hand side to obtain the maximum of the map likelihood function. Then we apply a Newton-Raphson iterative method to locate the peak of the CMB power spectrum likelihood function (which has no closed-form solution) given this map. Each iteration requires triangular-solving many linear systems, each with as many right hand sides as there are pixel-pixel correlation matrix rows and columns. The entire analysis algorithm has been implemented in parallel on the T3E at NERSC as the Microwave Anisotropy Dataset Computational Analysis Package (MADCAP).

Accomplishments

Over the past year we have used MADCAP to analyze the data from the 1997 BOOMERANG North America flight. Although this was primarily a test flight in preparation for the Long Duration/Antarctic flight, the data obtained was still one of the best measurements of the CMB to date. The results of this analysis, which are about to be submitted for publication, provide the first single-experiment measurement of the CMB angular power spectrum over a wide enough range of angular scales to place a significant constraint on cosmological models. Based on this work we can be confidant that (i) BOOMERANG LDB will be an extraordinarily powerful data set, capable of providing the tightest constraints yet on cosmological parameters; (ii) our current data analysis approach is capable of extracting a significant fraction of the information content of BOOMERANG LDB, whilst the promise of the full data content will be a compelling driver for further CMB data analysis research.

BOOMERANG was launched on December 29, 1998. For the next 10.5 days it made its way slowly around Antarctica at an altitude of 120,000 feet, collecting CMB temperature data. Finally, after a complete circle, the payload was dropped by parachute to a spot about 50 km from the launch pad for an easy recovery.

Significance

Publications

J. Borrill, "MADCAP: The Microwave Anisotropy Dataset Computational Analysis Package," in Proceeedings of the 5th European SGI/Cray MPP Workshop (Bologna, Italy, 1999). astro-ph/9911389

P. D. Mauskopf et al., "Measurement of a peak in the cosmic microwave background power spectrum from the North American test flight of BOOMERANG," Astrophys. J. (submitted, 1999). astro-ph/9911444

A. Melchiorri et al., "A measurement of Omega from the North American test flight of BOOMERANG," Astrophys. J. (submitted, 1999). astro-ph/9911445

http://www.astro.caltech.edu/~lgg/boomerang_front.htm
http://crd.lbl.gov/~borrill/cmb/madcap/