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arXiv · 2605.16501

Co-evolution of Supermassive Black Holes and their Host L* galaxies: implications for Milky Way and M31

Salvador E. Grimozzi·Maria Emilia De Rossi·Andreea S. Font
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Abstract

We investigate the origin of the scatter in supermassive black hole (BH) masses among L* galaxies, using the ARTEMIS and EAGLE simulations. We classify galaxies by their central BH-to-stellar mass ratios and track systems with the lowest and highest ratios (LBH and HBH, respectively). Although these populations have similar properties at z~ 2, they diverge significantly towards lower redshifts. LBH galaxies maintain higher gas fractions and sustain star formation, while HBHs form stars earlier, experience faster BH growth, more efficient feedback, and subsequent quenching. The simulations broadly match the observed scatter in the BH masses and galaxy morphologies in the L* regime, linking it to differences in merger histories. Galaxies with more active merger histories host more massive BHs at present and are predominantly elliptical, whereas those with quieter histories host lower-mass BHs and tend to be disc-like. Mergers induce BH growth through enhanced gas accretion and direct BH-BH coalescences. However, these channels operate differently: in HBH galaxies, BHs grow primarily (~90%) through gas accretion, whereas in LBHs they grow through both gas accretion and BH--BH mergers, in comparable fractions. These results suggest that the contrasting BH masses in the Milky Way and M31 may arise from differences in their merger histories. We also investigate the role of feedback from supernovae (SN) versus active galactic nuclei (AGN) on these scales. AGN feedback appears to be the primary mechanism responsible for quenching MW-mass systems, although SN feedback remains the dominant regulator of their overall evolution.

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Salvador E. Grimozzi, Maria Emilia De Rossi, Andreea S. Font. 2026-05-15. Co-evolution of Supermassive Black Holes and their Host L* galaxies: implications for Milky Way and M31. https://arxiv.org/abs/2605.16501

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