Ena Choi, Astrophysicist

Publication : ADS_link

Recent Work:  Investigating the Impact of Supernova Feedback on Satellites in Elliptical Galaxies (Kim, EC et al. 2025)
We explored how supernova (SN) feedback shapes the satellites of massive elliptical galaxies using cosmological zoom-in simulations. Interestingly, the host ellipticals look almost the same regardless of SN feedback strength, but their satellites do not: weak feedback produces far too many compact, metal-rich satellites compared to observations. With mechanical SN winds, however, the simulated satellites match reality much better — showing just how crucial proper feedback modeling is for reproducing galaxy populations.

Recent Work: The Origins of Gas Accreted by Supermassive Black Holes: the Importance of Recycled Gas (Choi et al. 2024)

 What do black holes eat? We know that there are supermassive black holes (SMBHs) at the center of almost all massive galaxies. However, we don't know much about how these black holes become so massive - more than 10^9 times the mass of the Sun. To learn more about this from a simulation perspective, we used 10 cosmological zoom-in hydrodynamic simulations of massive galaxy formation with SMBHs forming at 10^9 solar masses. In these simulations, we traced the origin of each and every gas particle that was consumed by the black hole (eaten by the black hole) to study in detail where they came from. This allowed us to understand in detail how SMBHs formed in the framework of our simulations. We found that the contribution of recycled gas is very large among the external gas that came in through mergers from external galaxies, the smooth gas that slowly entered by cosmological infall, and the recycled gas that was formed through stellar evolution from nearby stars and returned to the ISM via SN and AGB winds. This is a relevant result that can explain recent observations that AGN activity is often seen in elliptical galaxies with large populations of old stars with little residual gas. For more information, please check out the paper via the ADS link above.

Scientific Interests

Unveiling the Co-evolution of Galaxies and Supermassive Black Holes in the JWST Era

My research focuses on understanding how galaxies and their central supermassive black holes co-evolve across cosmic time, with particular emphasis on the role of feedback in regulating star formation and black hole growth. Cosmological hydrodynamic simulations combined with new observations from JWST provide an unprecedented opportunity to probe these processes in the early universe.  

Building on my earlier development of a unified AGN feedback model that incorporates both mechanical (broad absorption line winds) and radiative (X-ray heating, radiation pressure) components (Choi+12, Choi+14, Choi+15), I now apply state-of-the-art cosmological zoom-in simulations to investigate the physical origin of quenching in massive galaxies (Choi+17). My recent simulation suites reveal diverse star formation histories and demonstrate that quenching timescales can vary substantially depending on the interplay between AGN and supernova feedback.  

Looking ahead, I am especially interested in connecting theory and observation more directly, for example through JWST mock imaging and spectroscopy of compact and quenched galaxies at high redshift. I am also starting to explore the formation pathways of black hole seeds and their early impact on galaxy evolution — projects that will keep me busy (and excited) for the coming years.  

If you are a student or researcher curious about these topics, please don’t hesitate to reach out. I’d be happy to chat!

This video shows the evolution of the projected gas density (in brightness) and temperature (in color) of the central galaxy in a zoom-in simulation of a  6e12 M ⊙ ​   dark matter halo. The run on the left is without AGN feedback, while the one on the right includes both mechanical and radiative feedback. In the AGN feedback case, high-velocity BAL winds hit the surrounding gas, carving out cavities around the central massive galaxy. These bubbles then expand outward, lowering the gas density across the halo’s virial radius (marked by the white circle).  Feel free to use this movie for educational or personal purposes — just please cite me or Choi et al. (2017) as the source.