Intro to Research Resources
Global Signal Interferometer
Measuring 21-cm hyperfine emission from neutral hydrogen at cosmological distances is one of the most promising techniques for probing our early universe. A positive detection would provide direct observations of key unexplored epochs of our cosmic history, including the cosmic dark ages before the universe’s first stars formed, and the reionization of the bulk of the hydrogen in the universe by starlight once star formation became widespread. Measuring the spherically averaged 21 cm brightness temperature as a function of redshift (the "global signal") provides unique information about our universe that cannot be accessed any other way.
Several experiments are attempting to measure the global signal with a single antenna, reasoning that for a globally present signal, directionality is not a critical aspect of the experiment. I believe that this is incorrect, and have begun investigating how the directionality of an interferometer could be leveraged to improve such experiments. The conventional wisdom is that interferometers are not sensitive to a global signal, owing to the differential nature of their measurements. However, in Presley, Liu, and Parsons (2015), we demonstrate that this is incorrect. We are now working to design and build a radio interferometer capable of carrying out this experiment and measuring the cosmic dawn of our universe.
There are many ways for students to get involved in this project, ranging from physically assembling and testing analog electronics. to designing the digital correlator using supercomputing hardware, to programming in Python to calibrate and analyze data, to applying sophisticated linear algebra techniques to extract the cosmological signal. A good way to get started on the science is to read “21-cm cosmology in the 21st Century” by Pritchard & Loeb (2011). For understanding the principles of the analog system, “SARAS measurement of the Radio Background at long wavelengths” by Patra et al. (2015) is an good reference. For the digital signal processing, I recommend “A Scalable Correlator Architecture Based on Modular FPGA Hardware, Reuseable Gateware, and Data Packetization” by Parsons et al. (2008).
This work is supported by an NSF CAREER award (#1352519) and is designed to be a student-led project in order to help train our next generation of instrument builders in radio astronomy.