Judd D. Bowman

Judd D. Bowman
Associate Professor

Cosmology Initiative
School of Earth and Space Exploration (SESE)
Arizona State University (ASU)

ISTB4
781 E Terrace Mall
P.O. Box 876004
Tempe, AZ 85287-6004, USA

(480) 965-8880 (office)
judd.bowman at asu.edu

Research

Hydrogen gas is the one of the unifying topics throughout astrophysics. From its production following the Big Bang during recombination to its central role in star formation and galaxy evolution, its history encompasses both the fundamental themes of cosmology -- played out on the largest scales as the universe unfolds -- and the rich details of astrophysical processes set within that global framework. Now, for the first time, modern digital signal processing technology and statistical observational-cosmology techniques are poised to exploit the unique ubiquity of hydrogren gas and to literally chart the entire history of structure formation in the universe. In so doing, we are embarking along a new field that promises to reveal the secrets of reionization (when the first stars and galaxies exerted their influence on the intergalactic medium), probe new facets of galaxy evolution, provide the first indications of the nascent universe during the Dark Ages, and offer new and unique tests of inflationary cosmology and dark energy.

My research activities are aimed at unlocking the full potential of this promising resource. I am engaged in a vigorous research program focused on developing and deploying the technologies and techniques to enable observational probes of hydrogen throughout cosmological time. The critical advance in the ability to measure hydrogen gas from z=0 to z=30 comes from new approaches for targeting the 21 cm hyperfine transition line of neutral hydrogen atoms. This line appears in radio frequencies at or below 1420 MHz, depending on the redshift and velocity of the hydrogen gas under observation. Traditional radio telescopes are generally able to detect this faint line only in localized objects such as nearby galaxies and damped Lyman-alpha systems, or broadly within our own Milky Way Galaxy. Along with a number of collaborators around the world in both theory and instrumentation, we are creating a new generation of radio experiments that are optimized to detect and characterize the 21 cm line of the pervasive, diffuse hydrogen gas at high redshifts (z>6) during and before the epoch of reionization (EoR), as well as in the local universe. These experiments are remarkable for both the scope of their objectives and the range of their designs -- from an interferometer with 125,000 baselines (each dependent on real-time correlation and calibration) that will measure sub-degree-scale spatial fluctuations in the neutral hydrogen background during reionzation, to a small, portable, single-dipole experiment with a high-precision wide-band spectrometer that will characterize the global evolution of the intergalactic medium and has already yielded the first direct constraints on the duration of reionization [Bowman & Rogers 2010, Nature]. More...


Current Projects

Experiment to Detect the Global EoR Signature (EDGES): This project seeks to implement a high-dynamic-range, standalone radio spectrometer and compact broadband antenna with carefully controlled systematic errors. The portable system will enable high-precision measurements of the smoothness of the all-sky radio spectrum between 45 and 200 MHz (6<z<30) and will demonstrate scientifically stringent limits on the derivative (with respect to redshift) of the global 21 cm contribution to the all-sky spectrum. This approach yields powerful tests of the radiative histories of the first luminous sources and overcomes the inherent challenges of separating the 21 cm signal from foreground Galactic synchrotron and extragalactic emission. Astrophysical observations with of proof-of-concept system developed in 2006-2007 yielded the first empirical limits on 21 cm emission during reionization. Observations with the first full system from August through November, 2009, yielded a lower limit on the duration of reionziation--the first-ever measurement of its kind using redshifted 21 cm emission to probe the early Universe [Bowman & Rogers 2010, Nature]. Over the last few year, a second generation experiment has been underway. It recently began observing in early 2015. Stay tuned for the latest results!

Murchison Widefield Array (MWA): The MWA is designed to characterize spatial fluctuations in the redshifted 21 cm HI emission from the cosmological epoch of reionization through CMB-style statistical measurements of the fluctuation power spectrum and other diagonistics. It will also survey the sky for astronomical radio transient sources and investigate the heliosphere through scintillation and Faraday rotation effects to improve the prediction of space weather. I serve as the Project Scientist for the MWA and coordinate the implementation of the EoR software analysis pipeline.

The array design features a large number of small, phased-array antenna tiles with 10-30 degree fields-of-view. The full array will consist of 500 such antenna tiles spread over an area 1.5 km in diameter and will have a total collecting area of order 8000 square meters per polarization. Nearly every aspect of the planned experiment with this array is novel. During the design and development phase of this project, my research interests have been directed at investigating foreground subtraction and scientific analysis techniques, developing the tools to characterize and assess the performance of critical new technologies, including the core array configuration, the phased-array antennas, and most recently calibration requirements, and constraining the unknown properties of the low-frequency astrophysical sky.