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PhD Proposal: Agniva Roy Chowdhury

Thursday, April 8, 2021
1:00 PM – 3:00 PM
Off Campus : via WebEx
ADVISOR: Dr. Eileen Meyer

TITLE: Mapping the Velocity Profiles of Extragalactic Jets From Parsec to Kiloparsec Scales

ABSTRACT: Actively accreting super-massive black holes (active galactic nuclei, or AGN) are known to produce bipolar jets of relativistic plasma which carry matter and energy out of the central nucleus of a galaxy to scales far beyond the host galaxy -- up to a megaparsec or more in distance, close to 10 orders of magnitude in gravitational radius. However, in spite of tremendous progress over the last several decades in astronomical observations of jets, it is relatively unknown how these jets form, accelerate and maintain strong collimation through the kiloparsec scale. Jets possess characteristic uneven brightness profiles comprising compact, bright and faint, diffuse features, which have been observed to exhibit outward motions along the jet and away from the supermassive black-hole engine. Studies of these motions, primarily conducted with very long baseline interferometry (VLBI), have revealed bulk relativistic velocities that can exceed 99% the speed of light (bulk Lorentz factors up to ~ 80). The motions traced by VLBI observations are on parsec scales, very near the black hole, and often show a flow that is still accelerating. However very few velocity measurements of the jet plasma on larger (100-1000 parsecs) scales exist, where the jet structure, the environment, and the magnetic field configuration are likely very different. The Very Large Array (VLA) has now been in operation for over 40 years, and the National Radio Astronomy Observatory (NRAO) hosts a very rich archive of observations of kpc-scale extragalactic jets, spanning decades, which I propose to utilize to build the first catalogue of kilo-parsec scale proper motions in AGN jets. In compliment with multi-wavelength imaging and VLBI-scale measurements, the goal is to use these observations to constrain theoretical models of jet structure, particle acceleration mechanisms, and to determine the emission mechanism for high-energy optical and X-ray emission from kpc-scale jets. These are major open questions in the study of AGN jets, and the observational techniques and experimental results will likely have applications to studies of relativistic outflows in other contexts.

Proposal will be held using WebEx.