The Large Aperture Experiment to Detect the Dark Ages (LEDA) project seeks to detect hyperfine emission from neutral Hydrogen (21 cm rest wavelength) in the intergalactic medium about 100 million years after the Big Bang (redshifts 16-40). A detection would deliver the first observational constraints on models of structure formation and on the formation of the first stars and black holes in the Universe. LEDA will develop and integrate signal processing instrumentation into the new first station of the Long Wavelength Array (LWA). This comprises a large-N correlator serving all 512 dipole antennas of the LWA-1, leveraging a packetized CASPER architecture and combining FPGAs and GPUs for the F and X stages. Iterative calibration and imaging will rely on warped snapshot imaging and be drawn from a GPU-enabled library (CUWARP) that is designed specifically to support wide-field full polarization imaging with fixed dipole arrays. Calibration techniques will include correction for ionospheric refraction and direction dependent dipole gains, and exploration of pulsar data analysis to improve performance. Accurate calibration and imaging will be crucial requirements for LEDA, necessary to subtract the bright foreground sky and detect the faint neutral Hydrogen signal. From the computational standpoint, LEDA is a O(100) TeraFlop per second challenge that enables a scalable architecture looking toward development of radio arrays requiring power efficient 10 PetaFlop per second performance. Stage two of the Hydrogen Epoch of Reionization Array (HERA2) is one example.
Lay Abstract When did the first stars form? These stars are expected to be much more massive than the stars that are around us today. Did supermassive black holes form at the same time, earlier, or later? One of the great challenges of cosmology today is the study of these first generation objects. Their formation is widely hypothesized to have begun about 100 million years after the Big Bang, but no data are available to test this theory. The only available means to study the Universe at so young an age (just 1% of what it is today) is via electromagnetic radiation from the intergalactic medium between the stars and black holes. Today, this is hot and ionized plasma, but in the early Universe it was a vast reservoir of cold neutral Hydrogen gas that fed the formation of the first stars and black holes and radiated long wavelength radiation copiously.
The LEDA project seeks to apply frontier radio astronomical techniques to make the first detection of this signal. LEDA will build a "radio camera" for deployment to the Long Wavelength Array, a radio telescope in New Mexico whose first 100m-diameter aperture was recently completed. The LEDA camera will combine several innovative technologies and data analysis techniques, giving students and young scientists the opportunity to join in cutting-edge science and development of the most advanced tools. In particular, LEDA will harness the massive computing power and flexibility of Graphics Processing Units (GPUs) - the engines that power video games - to make instantaneous images of nearly the whole sky at up to 10 meters wavelength (10 million times longer than visible radiation).
From these images the light of our and other galaxies will be subtracted with high accuracy, enabling a search for signals from the dawn of the Universe. LEDA will push the frontiers of cosmology while contributing groundwork for future radio astronomical facilities where massive computing and signal processing systems will be lynchpins. Cross-disciplinary outgrowths of the LEDA effort will benefit astronomical, computational and solar sciences.
project targets a frontier challenge in observational cosmology: Characterization of physical conditions in the intergalactic medium (IGM) during the transition from the Dark Age to the Epoch of Reionization, when the first generations of stars lit up the Universe. The LEDA instrument consists of calibrated dipoles which measure the spectrum of the cosmic microwave background, and an imaging antenna array which is used to deduce the Galactic "foreground" emission which may then be calibrated out of the dipole measurements, nominally leaving the spectral feature of interest. LEDA is a collaborative research project in which Harvard U. is the lead institution and U. New Mexico, U. California at Berkeley, and Virginia Tech are partners. Please consult the report of Harvard U. for project-level perspectives. Virginia Tech's role was antenna & instrument modeling and consulting on radio frequency interference and various other technical aspects of the project. Virginia Tech's principal contributions to the project included analysis leading to the selection of designs for the antenna and front end electronics used for the dipoles, and electromagnetic analysis of the antennas, antenna array, and surrounding structures to assess potential for deleterious interactions and to determine strategies to manage these effects.
