PhD Defense: Agniva Roy Chowdhury
Location
Physics : 401
Date & Time
August 22, 2023, 1:00 pm – 3:00 pm
Description
ADVISOR: Dr. Eileen Meyer
TITLE: Investigating the Dynamics of Extragalactic Jets from Parsec to Kiloparsec Scales: Novel Constraints on Jet Acceleration and Emission
ABSTRACT: Actively accreting supermassive black holes, known as 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 to distances of a megaparsec or more, 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. Studies of motions of bright compact inhomogeneities at different positions in these jets ("proper motions") can, in principle, be used to produce model-independent constraints on the Lorentz factor of the bulk motion at different spatial scales in the jet. This inferred velocity profile of the jet, in addition to constraining theories of jet acceleration-deceleration, is vital in understanding the origin of high-energy emission (X-rays and beyond) from extragalactic jets. Combining the large time baseline (40 years) and richness of the well-known radio telescope Very Large Array's archive with continually proposed observations, this thesis develops radio interferometric techniques to measure velocities for the first time beyond the few hundred parsec scales in extragalactic jets, throwing new light on their physical nature by studying proper motions in several radio galaxies.
TITLE: Investigating the Dynamics of Extragalactic Jets from Parsec to Kiloparsec Scales: Novel Constraints on Jet Acceleration and Emission
ABSTRACT: Actively accreting supermassive black holes, known as 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 to distances of a megaparsec or more, 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. Studies of motions of bright compact inhomogeneities at different positions in these jets ("proper motions") can, in principle, be used to produce model-independent constraints on the Lorentz factor of the bulk motion at different spatial scales in the jet. This inferred velocity profile of the jet, in addition to constraining theories of jet acceleration-deceleration, is vital in understanding the origin of high-energy emission (X-rays and beyond) from extragalactic jets. Combining the large time baseline (40 years) and richness of the well-known radio telescope Very Large Array's archive with continually proposed observations, this thesis develops radio interferometric techniques to measure velocities for the first time beyond the few hundred parsec scales in extragalactic jets, throwing new light on their physical nature by studying proper motions in several radio galaxies.
