Supermassive Black Hole Assembly from Heavy Seeds with Dynamical Friction in the BRAHMA Simulations: Implications for JWST, LISA, and the Local Universe. Bhowmick, A. K., Blecha, L., Torrey, P., Kelley, L. Z., Somerville, R. S., Weinberger, R., Natarajan, P., Matteo, T. D., Hernquist, L., Vogelsberger, M., & Garcia, A. M. June, 2026. arXiv:2606.12851 [astro-ph.GA]
Supermassive Black Hole Assembly from Heavy Seeds with Dynamical Friction in the BRAHMA Simulations: Implications for JWST, LISA, and the Local Universe [link]Paper  doi  abstract   bibtex   
The JWST discoveries of supermassive black holes (BHs) at z ≳ 5 may provide key insights into their seeding origins. Using new [18−72 Mpc]3 BRAHMA cosmological simulations, we investigate how variations in heavy-seed prescriptions, coupled with a subgrid dynamical friction model, shape BH populations at z ∼ 5 and z ∼ 0. We consider two “lenient” seed models, in which all halos containing sufficient dense & metal-poor gas form ∼ 104 and ∼ 105 M⊙ seeds, and a “strict” seed model, in which ∼ 105 M⊙ seeds form only under additional constraints motivated by direct collapse black hole formation. By z ∼ 5, all models produce M∗ −MBH relations broadly consistent with the observed local Universe for M∗ ≳ 109 M⊙ galaxies, but only the lenient scenarios generate systems near the upper envelope of the observed local scatter. In galaxies hosting MBH ∼ 108–109 M⊙ BHs, lenient production of ∼ 105 M⊙ seeds also produces multiple overmassive systems with MBH/M∗ ≳ 0.01. Although their growth is dominated by seeding and mergers, these systems reach luminosities of ∼ 1043–1045 erg s−1, comparable to those inferred for JWST -detected BHs. As a key observational signature, the lenient seed models yield merger rates of ≳ 100 yr−1 and near-unity local BH occupation fractions even in galaxies with M∗ ≲ 107 M⊙. In contrast, the strict seed model produces merger rates of only ∼ 1 yr−1 and local occupation fractions of ≲ 10% for galaxies with M∗ ≲ 108 M⊙. Future gravitational-wave event rates and measurements of local BH occupation fractions will therefore provide strong constraints on the dominant pathways responsible for high-redshift BH assembly.
@misc{bhowmick_supermassive_2026,
	title = {Supermassive {Black} {Hole} {Assembly} from {Heavy} {Seeds} with {Dynamical} {Friction} in the {BRAHMA} {Simulations}: {Implications} for {JWST}, {LISA}, and the {Local} {Universe}},
	shorttitle = {Supermassive {Black} {Hole} {Assembly} from {Heavy} {Seeds} with {Dynamical} {Friction} in the {BRAHMA} {Simulations}},
	url = {http://arxiv.org/abs/2606.12851},
	doi = {10.48550/arXiv.2606.12851},
	abstract = {The JWST discoveries of supermassive black holes (BHs) at z ≳ 5 may provide key insights into their seeding origins. Using new [18−72 Mpc]3 BRAHMA cosmological simulations, we investigate how variations in heavy-seed prescriptions, coupled with a subgrid dynamical friction model, shape BH populations at z ∼ 5 and z ∼ 0. We consider two “lenient” seed models, in which all halos containing sufficient dense \& metal-poor gas form ∼ 104 and ∼ 105 M⊙ seeds, and a “strict” seed model, in which ∼ 105 M⊙ seeds form only under additional constraints motivated by direct collapse black hole formation. By z ∼ 5, all models produce M∗ −MBH relations broadly consistent with the observed local Universe for M∗ ≳ 109 M⊙ galaxies, but only the lenient scenarios generate systems near the upper envelope of the observed local scatter. In galaxies hosting MBH ∼ 108–109 M⊙ BHs, lenient production of ∼ 105 M⊙ seeds also produces multiple overmassive systems with MBH/M∗ ≳ 0.01. Although their growth is dominated by seeding and mergers, these systems reach luminosities of ∼ 1043–1045 erg s−1, comparable to those inferred for JWST -detected BHs. As a key observational signature, the lenient seed models yield merger rates of ≳ 100 yr−1 and near-unity local BH occupation fractions even in galaxies with M∗ ≲ 107 M⊙. In contrast, the strict seed model produces merger rates of only ∼ 1 yr−1 and local occupation fractions of ≲ 10\% for galaxies with M∗ ≲ 108 M⊙. Future gravitational-wave event rates and measurements of local BH occupation fractions will therefore provide strong constraints on the dominant pathways responsible for high-redshift BH assembly.},
	language = {en},
	urldate = {2026-06-15},
	publisher = {arXiv},
	author = {Bhowmick, Aklant K. and Blecha, Laura and Torrey, Paul and Kelley, Luke Zoltan and Somerville, Rachel S. and Weinberger, Rainer and Natarajan, Priyamvada and Matteo, Tiziana Di and Hernquist, Lars and Vogelsberger, Mark and Garcia, Alex M.},
	month = jun,
	year = {2026},
	note = {arXiv:2606.12851 [astro-ph.GA]},
	keywords = {Astrophysics - Astrophysics of Galaxies, WG: Explainable},
}
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