PhD Proposal: Lizbeth Joy Tan
Location
Physics : 401
Date & Time
August 27, 2024, 1:30 pm – 3:00 pm
Description
ADVISOR: Dr. Eileen Meyer
TITLE: On the physical origin of significant quasar position differences in radio and optical astrometric surveys
ABSTRACT: Quasars are extreme examples of active galactic nuclei (AGN), which are bright, compact regions in the center of galaxies. Active galaxies are powered by accretion of material onto a supermassive black hole, producing emission that can span the whole electromagnetic spectrum from radio to gamma-rays. For decades, very long baseline interferometry (VLBI) techniques have been used to image and measure positions of compact radio sources such as quasars to incredibly high (sub-milliarcsecond) precision. With the launch of Gaia in 2013, this can now be matched in the optical. Astrometric studies of quasar positions have revealed offsets between VLBI and Gaia measurements. VLBI coordinates correspond to the most compact feature, while Gaia coordinates correspond to the optical centroid position of the source which is more affected by extended AGN properties such as optical jets, dust obscuration by the host galaxy, or strong nuclear line emission. The offsets could also be caused by a number of astrophysical phenomena such as black hole mergers, gravitational recoil resulting in offset AGN, or gravitationally-lensed systems. This research project aims to find the causes for these positional offsets, and their ultimate physical origin, using a suite of multiwavelength data from observatories like the Hubble Space Telescope (HST), Very Large Array (VLA), Very Long Baseline Array (VLBA), Atacama Large Millimeter/submillimeter Array (ALMA), and Multi-Element Radio Linked Interferometer Network (e-MERLIN).
TITLE: On the physical origin of significant quasar position differences in radio and optical astrometric surveys
ABSTRACT: Quasars are extreme examples of active galactic nuclei (AGN), which are bright, compact regions in the center of galaxies. Active galaxies are powered by accretion of material onto a supermassive black hole, producing emission that can span the whole electromagnetic spectrum from radio to gamma-rays. For decades, very long baseline interferometry (VLBI) techniques have been used to image and measure positions of compact radio sources such as quasars to incredibly high (sub-milliarcsecond) precision. With the launch of Gaia in 2013, this can now be matched in the optical. Astrometric studies of quasar positions have revealed offsets between VLBI and Gaia measurements. VLBI coordinates correspond to the most compact feature, while Gaia coordinates correspond to the optical centroid position of the source which is more affected by extended AGN properties such as optical jets, dust obscuration by the host galaxy, or strong nuclear line emission. The offsets could also be caused by a number of astrophysical phenomena such as black hole mergers, gravitational recoil resulting in offset AGN, or gravitationally-lensed systems. This research project aims to find the causes for these positional offsets, and their ultimate physical origin, using a suite of multiwavelength data from observatories like the Hubble Space Telescope (HST), Very Large Array (VLA), Very Long Baseline Array (VLBA), Atacama Large Millimeter/submillimeter Array (ALMA), and Multi-Element Radio Linked Interferometer Network (e-MERLIN).
