Dongjin Kim

PhD Project: A search for molecular absorption in AGNs

Defende on December 8, 2021

October 24, 2019

PhD Advisor: Dr. Thomas P. Krichbaum

Collaborators: T.P. Krichbaum, R. Mauersberger, C. Henkel, B. Boccardi, A. L. Roy, J.A. Zensus, M. Bremer, C.M.V. Impellizzeri, F. Combes

Dongjin Kim in Pico Veleta, Granada, September 2019

© Dongjin Kim (MPIfR)

Dongjin Kim in Pico Veleta, Granada, September 2019

© Dongjin Kim (MPIfR)

The PhD project: Molecular gas in the vicinity of the active galactic nuclei (AGN), likely to be confined in a torus around the central engine, has been supposed to be a key element, which determines the observational properties of AGN. In the Unified Scheme model (Antonucci 1993; Urry & Padovani 1995), different types of AGN appear depending on viewing angle and geometry of the toroidal gaseous structure (thickness, inner and outer radius). However, despite its importance in understanding AGN classification and evolution, the physical properties of molecular torus are still mysterious. In this project we want to test the idea of a molecular torus, and aim to better constrain its geometry and physical properties in various types of AGN. After initial detection in a molecular absorption line survey, follow-up spectral line VLBI imaging will provide imaging with sub-pc scale resolution. This will test the Unified Scheme of AGNs and directly probe the matter reservoir around an AGN, which is essential to discriminate between accretion inflow (hot vs. cold disks; Yuan & Narayan 2014) and jet outflow (BH or disk driven; Blandford & Znajek 1977; Blandford & Payne 1982).

An illustration for the molecular absorptions in AGNs and research plans for the PhD project.

© D.J. Kim (MPIfR)

An illustration for the molecular absorptions in AGNs and research plans for the PhD project.

© D.J. Kim (MPIfR)

About me: I was born in Seoul, South Korea. I obtained my bachelor’s degree in physics at Kyung Hee University. My thesis topic was designing a space-ground VLBI system based on a cube satellite.

I was fascinated by sophisticated technologies of the VLBI system and it motivated me to pursue further study in radio astronomy. I earned my master's degree in Astronomy at Yonsei University. During my masters I studied galactic MASER (e.g., H2O and SiO) via VLBI astrometry and single-dish monitoring observations, and the main research goal was to understand the mass-loss process in evolved stars.

In June 2018 I started my PhD as an IMPRS fellow at the VLBI group of the MPIfR. I’m interested in spectral line VLBI observations toward extragalactic sources, which include not only mega-maser sources, but also molecular absorption lines against a bright background continuum sources such as radio jets.

Asymmetric distributions of H2O and SiO masers towards V627 Cas

Yang, H.; Cho, S.-H.; Yun, Y.; Yoon, D.-H.; Kim, D.-J.; Kim, H.; Yoon, S.-C.; Dodson, R.; Rioja, M. J.; Imai, J.: Monthly Notices of the Royal Astronomical Society, 495, 1284-1290 (2020)

Simultaneous VLBI Astrometry of H2O and SiO Masers toward the Semiregular Variable R Crateris

Kim, D.-J.; Cho, S.-H.; Yun, Y.; Choi, Y. K.; Yoon, D.-H.; Kim, J.; Dodson, R.; Rioja, M. J.; Yang, H.; Yoon, S.-J.: The Astrophysical Journal Letters, 866, L19 (2018)