MRI: Development of the Next Generation 211-373 GHz Receiver for the Arizona Radio Observatory’s Sub-mm Telescope

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Our atmosphere is transparent to some radio frequencies through which astronomers can collect important astrophysical information. Through these radio windows we can observe the earliest stages of star formation, the creation of dust and complex molecules that seed stars, planets, and possibly even life itself, and make the sharpest pictures of black holes. The Sub-millimeter Telescope (SMT) of the Arizona Radio Observatory, located on Mt. Graham, AZ, is an extremely capable radio telescope at a good site, but its ability to observe is limited by its aging systems. This project will develop a new receiving system for the SMT. The improvements will both increase the observing speed of the SMT and use cutting edge commercial signal processing technology to broaden by a factor 16 the range of frequencies recorded. This project is a collaboration between a national research organization and a university group to enhance the technical and scientific capabilities of both, and of the nation, by advancing submillimeter technology. It will provide new opportunities for research and education to students from high school through graduate school, as well as postdoctoral fellows. It will fund new outreach tools and educational opportunities at Eastern Arizona College, which serves rural Graham County and the San Carlos Apache Reservation. The new SMT receiver will incorporate new, state-of-the-art sideband-separating mixers for the 0.8mm (275-373 GHz) band. These will be developed by a long-running collaboration between the University of Arizona and the National Radio Astronomy Observatory (NRAO) Central Development Lab, and will be fabricated at the University of Virginia’s Multifunctional Microfabrication and Scalable Biomanufacturing Facility (IFAB). The mixers will be coupled in a “sideband-separating” configuration, allowing for 15 dB rejection of the image sideband, greatly reducing the noise temperatures and removing unwanted image line contamination. The new 0.8 mm and current 1.3 mm mixers will be mounted in a common dewar, enabling simultaneous observations in the two bands. The receiver dewar will feed a new spectrometer backend built using novel, commercial radio frequency system on chip (RFSoC) devices, that will digitize up to 32 GHz of instantaneous spectral bandwidth (8 GHz per sideband/polarization). Compared to the existing system, the improvements in receiver noise and spectrometer bandwidth will increase the survey speed of the SMT by a factor of ~50 in the 0.8mm band. This will enable new measurements in many areas of astrophysics, including the structure of cold cores on the verge of collapse, the late stages of massive stars and the outflows of planetary nebulae, and the processing of elements critical to life. The new receiver will provide enhanced observational capabilities for a large number of astronomers at many US and foreign institutions, as well as to the EHT consortium. In addition, a substantial number of graduate students will be involved in the construction of the instrument.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.