Collaborative Research: Detecting First Light and Reionization of the Universe using Advanced Radio Instrumentation

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

In the Big Bang model, the universe started in a very hot state in which the material was ionized. This is now seen as the Cosmic Microwave Background (CMB) radiation. As the universe expanded, it cooled. At later stages, the first stars formed. These caused the neutral material to be ionized again, in the Epoch of Reionization (EoR). At later times, the limit is set by the ionization caused by the first stars. After the first stars, the first galaxies formed. This is a theoretical scenario, so measurements are needed to provide important details needed. The goal of this project is the first measurement of neutral hydrogen from the EoR. Such a measurement is extremely difficult because of instrumental effects. In addition, this project includes the mentoring of undergraduate, graduate and postdoctoral students. The hands-on training provides a unique introduction to ultra-precise measurements, so this will be an unequaled experience involving instrumentation and data analysis. The goal of this project is the measurement of the hyperfine transition of neutral hydrogen. The history of the universe is traced by redshifts, so higher redshifts correspond to earlier times. The CMB arose at a redshift of about 1000. At redshifts of about 30, the most abundant constituent is neutral atomic hydrogen. The highest measured redshift for a galaxy is about 8. Presumably, at redshifts higher than 8, this material was reionized by stars, during the Epoch of Recombination (EoR). Thus the EoR should be bounded by redshifts 8 and 30. At earlier times the limit to the EoR is set by the recombination of ions caused by the CMB. The EoR allows a look back to a time before the first stars and galaxies formed. Depending on the local physical conditions, the spectral line can be either in absorption against the CMB or in emission. Though a measurement of this line, the state of the universe during the EoR can be determined in more detail. This complements the extensive, ongoing studies of the CMB. The proposers will lower the instrumental effects caused by the large linewidth and the high intensity of foreground radiation. They will accomplish this by constructing an improved receiver with a more uniform response over the range of redshifts studied. In addition they will investigate a dipole design that has a more uniform response. These advances are at the forefront of electronics design, and so require a large number of laboratory tests, each of which is very time-consuming. In addition, the proposers are improving their data reductions to further reduce the effect of systematic errors. The detection of the EoR spectrum will serve to expand our knowledge of the evolution of the universe in a very significant, perhaps transformational, fashion. This will provide an important link between the early stages of the universe, before stars formed, and the present stage. The training of students in the techniques of ultra-precise measurements is unique. The interaction with commercial firms may have wide-ranging implications for the design of much improved test equipment.