Finding the Missing Link: Host Galaxies of Intermediate-Mass Black Holes in Illustris

Authors

• Michael J. Pinto II, Belmont UniversityFollow

Publication Date

Fall 11-23-2026

College

College of Sciences & Mathematics

Department

Chemistry and Physics, Department of

SURS Faculty Advisor

Dr. Christina Davis

Presentation Type

Poster Presentation

Abstract

Black holes are significant cosmological objects that challenge the fundamentals of physics and our understanding of black hole evolution. Moreover, formation pathways and lifetimes for intermediate-mass black holes (IMBHs) remain poorly constrained. This raises the question of whether these bodies persist as stable remnants or represent transient stages in supermassive black hole (SMBH) evolution. This study utilizes the Illustris Project’s Illustris-3, a cosmological hydrodynamical simulation, to build and characterize different galactic environments that host IMBHs across four distinct environmental samples: dwarf galaxies, Milky Way-mass galaxies, massive galaxies, and cluster-mass halos at redshifts z ≈ 4.9, 0.6, and 0. We then compare the stellar mass, halo mass, gas fraction, gas metallicity, and star formation rate of IMBH hosts to those of SMBH hosts. IMBHs tend to make up most of the black holes in dwarf galaxies at every timescale we examined, rising from 86% at z ≈ 4.9 to over 99% at z = 0. In massive galaxies, they are almost absent, with their population below 1%. IMBH hosts are systematically poor in metals but rich in gas. This is the opposite of SMBHs. Within Milky Way-mass halos, around 96% of IMBHs live in a satellite galaxy, while most SMBHs occupy the center of the galaxy. For example, Sagittarius A* the SMBH at the center of our own galaxy. These results show that low-mass, chemically young environments preserve black holes near their initial seed mass, whereas rapid growth to SMBH scales happens in environmentally favored central massive hosts.

Recommended Citation

Pinto, Michael J. II, "Finding the Missing Link: Host Galaxies of Intermediate-Mass Black Holes in Illustris" (2026). Science University Research Symposium (SURS). 394.
https://repository.belmont.edu/surs/394