ANNUAL REPORT: 1997-1998

PARTICLE ASTROPHYSICS & COSMOLOGY

PRINCIPAL INVESTIGATOR: GEORGE F. SMOOT

Other Group Members:

1. COSMOLOGY with the Cosmic Background Radiation

Measurements of The Cosmic Background Radiation (CMB) provide important information about physical processes in the Universe from soon after the Big Bang until the present. In the Big Bang model, which has now become the standard model of cosmology, the CMB last interacted significantly with matter at a time roughly one third of million years after the start of the universal expansion and about 10-15 billion years before the present epoch. The CMB carries with it the information about that interaction and to a lesser degree the effects occurring during its journey to us. Its angular distribution is related to the distribution of matter and energy in the early Universe; its spectrum provides information about processes involving the release of energy.

During the past year we have continued our investigations using the cosmic microwave background (CMB) radiation as a probe of cosmology.

COBE

Analysis of the COBE satellite data sets continues to provide additional new results and acts as a test bed for new techniques and algorithms in the 8th year past its launch and 5 years since its discovery of CMB anisotropies. Its data remain in many ways the best CMB anisotropy data. During 1998 the primary new results were presented in papers about the discovery of the cosmic infrared background radiation.

With COBE we have made major advances in measuring the large angular scale distribution of the CMB. The major products from COBE include a series of maps of the full sky in the 1 micrometer to 1 centimeter wavelength range. COBE was operated for four years, providing high quality data from about half its sensors. The other half of the sensors were turned off when the liquid helium coolant was exhausted near the end of the first year.

The processing and analysis of the data from COBE has provided high quality maps of the microwave and infrared sky, and their subsequent analysis has yielded significant new cosmological and astrophysical information. Of the three instruments aboard COBE, Dr. Smoot is principal investigator of the Differential Microwave Radiometer (DMR) experiment. The announcement of the detection of anisotropies by Dr. Smoot has been followed by numerous interpretive papers by members of the COBE/DMR collaboration and by outside researchers.

The observed anisotropies have been a powerful cosmological tool providing information on the initial conditions leading to the formation of large scale structure such as galaxies and clusters of galaxies. It has also let us determine important cosmological parameters such as the dynamics, geometry and topology of the Universe.

Our group has continued the analysis of the old and new data. Public release of the resulting skymaps occurred for the first year's observations in June 1993. The first two years worth of data were released in June, 1994. The full four-year data and first results were made public in January 1996. The COBE project came to its official termination at the end of 1997; however, we can anticipate that its data and experience will continue to play an important role in cosmology for a few more years.

Full sky map of CMB anisotropies

Figure 1. Full sky map of the CMB anisotropies from the COBE DMR.

Max Planck Surveyor

We, as part of a larger collaboration, have completed the Phase A study of the third generation CMB anisotropy mission, the European Space Agency (ESA) M3 mission: Max Planck Surveyor satellite. Launch is anticipated circa 2007.

MAXIMA/BOOMERANG Balloon-borne Instruments

We - a collaboration with Professors Paul Richards at SSL, Andrew Lange (CalTech), and Paola deBernardis (Rome) - have built and tested a pair of new generation balloon-borne gondolas and instruments MAXIMA & BOOMERANG . BOOMERANG had its first and successful flight in early September 1997. MAXIMA had its first scientific utilizing an array receiver in August 1998. A long-duration flight of BOOMERANG from Antarctica is planned for in the coming season (mid-December to mid-January). We anticipate flying MAXIMA again in the summer of 1999 and preparations are underway.
 
Data processing and analysis of these data is underway and we anticipate first results being made public in early 1999 and much more later.

Foreground Emissions

We have reached the point where the emission from the galaxy is beginning to limit the interpretation of the data. Thus we have embarked on a program to improve our understanding and modeling of this emission for both the cosmological interpretations and the study of our galaxy. This involves both a project to make low frequency radio maps of the sky dubbed the Galactic Emission Mapping (GEM) project and an effort to model and find means to remove Galactic and extragalactic foregrounds from the data. The GEM instrument was shipped to Brazil from Tenerife. It has been refurbished and is now operating and taking data.

2. Ultra-High Energy Neutrino Astronomy

In collaboration with Hank Crawford (SSL), Willi Chinowsky, Dave Nygren, and Bob Stokstad we have been working on the development of a km-scale ultra-high energy neutrino detector. This work has led us to a collaboration with the AMANDA project. At this time we are deeply involved in the analysis of the 1997 AMANDA data in which a number of very high energy neutrino-induced muons have been detected. We are also busy preparing for the arrival of the 1998 AMANDA data. Work is underway on the development of a digital optical module technology and its deployment in the Antarctic ice an the 1999-2000 season.
 

6. Milestones

7. Graduate Students Supported

8. Publications

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