The development of large-format heterodyne receiver arrays will enable a number of state-of-the-art astrophysical measurements. In particular, we are developing instruments that will conduct spectroscopic mapping of star-forming galactic regions, detection of the cosmic microwave background polarization, and measurements of the Sunyaev-Zel’dovich effect.
We are targeting spectral lines from 85-100 GHz. These frequencies are known to be good tracers of dense molecular gas (e.g. HCN). By placing large-format arrays on high resolution telescopes such as the 100m Green Bank Telescope in West Virginia (http://www.gb.nrao.edu/) we will be able to make high resolution maps of star-forming regions in the Milky Way and in other nearby galaxies that could help answer fundamental questions about the physics and chemistry of star formation.
Cosmic Microwave Background Polarization
Large-format polarization-sensitive instruments are under development for cosmic microwave background measurements, including those that search for the polarization signature from inflationary gravity waves (B-modes). Because these instruments are the only means currently available to probe the physics of inflation, their scientific value is potentially very large.
However, the expected signals are extremely tiny, requiring carefully designed experiments capable of effectively filtering out foreground signals and systematic effects. Large-format arrays operating in the 30-90 GHz are well suited to separating CMB signals from polarized synchrotron emission. They also allow the use of instrument configurations such as interferometry and correlation polarimetry. Both techniques complement those used by other Stanford-led experiments such as POLAR.
The Sunyaev Zel’dovich (SZ) Effect is an upward shift of the CMB blackbody spectrum caused by inverse Compton scattering of CMB photons off hot gas in galaxy clusters. This shift causes a decrement in the CMB spectrum at about 150 GHz and no change at 218 GHz.
We are developing 90 GHz and 150 GHz focal plane arrays that can be deployed on existing instruments such as the CARMA array, a 23-element radio interferometer located in the Inyo mountains of Southern California, or ALMA, a TKTKTKTK TELESCOPE LOCATED IN TK. The goal is to obtain wide-field, high-resolution SZ maps, which can be used to measure the distribution of cluster gas, which, in turn, can be used to probe cluster mergers. SZ data can also be combined with optical and X-ray measurements to investigate the distribution of dark matter and the properties of dark energy.
Our receiver modules are based on Monolithic Microwave Integrated Circuit (MMIC) amplifiers. These instruments offer extremely low noise and can be packaged into compact multi-chip modules that are amenable to mass-production. Solutions for scalable, high frequency signal routing and feedhorn antennas with optimized beam patterns are also under development.