Black Hole Scaling Relations in the Dwarf-galaxy Regime with $Gaia$-Sausage/Enceladus and $\omega$Centauri

TL;DR

This paper investigates the presence and scaling relations of intermediate-mass black holes in dwarf galaxies, using $ ext{omega}$Cen and GSE as case studies, and explores implications for black hole formation and galaxy evolution.

Contribution

It extends black hole scaling relations to the dwarf-galaxy regime and compares $ ext{omega}$Cen/GSE with other low-mass systems, providing insights into black hole formation mechanisms.

Findings

$ ext{omega}$Cen/GSE's IMBH follows the ${ m M}_{ m BH}{-}{ m M}_ ext{star}$ relation extrapolated from massive galaxies.

$ ext{omega}$Cen/GSE's IMBH also aligns with the ${ m M}_{ m BH}{-}\sigma_ ext{star}$ relation.

The formation of the IMBH could involve low initial mass and minimal accretion, or light seeding from Population III supernovae.

Abstract

The discovery of fast moving stars in the Milky Way's most massive globular cluster, $\omega$Centauri ($\omega$Cen), has provided strong evidence for an intermediate-mass black hole (IMBH) inside of it. However, $\omega$Cen is known to be the stripped nuclear star cluster (NSC) of an ancient, now-destroyed, dwarf galaxy. The best candidate to be the original host progenitor of $\omega$Cen is the tidally disrupted dwarf $Gaia$-Sausage/Enceladus (GSE), a former Milky Way satellite as massive as the Large Magellanic Cloud. I compare $\omega$Cen/GSE with other central BH hosts and place it within the broader context of BH-galaxy (co)evolution. The IMBH of $\omega$Cen/GSE follows the scaling relation between central BH mass and host stellar mass (${\rm M}_{\rm BH}{-}{\rm M}_\star$) extrapolated from local massive galaxies (${\rm M}_\star \gtrsim 10^{10}\,{\rm M}_\odot$). Therefore, the IMBH of $\omega$Cen/GSE suggests that this relation extends to the dwarf-galaxy regime. I verify that $\omega$Cen (GSE), as well as other NSCs with candidate IMBHs and ultracompact dwarf galaxies, also follow the ${\rm M}_{\rm BH}{-}\sigma_\star$ relation with stellar velocity dispersion. Under the assumption of a direct collapse BH, $\omega$Cen/GSE's IMBH would require a low initial mass ($\lesssim$10,000 ${\rm M}_{\odot}$) and almost no accretion over $\sim$3 Gyr, which could be the extreme opposite of high-$z$ galaxies with overmassive BHs such as GN-z11. If $\omega$Cen/GSE's IMBH formed from a Population III supernova remnant, then it could indicate that both light and heavy seeding mechanisms of central BH formation are at play. Other stripped NSCs and dwarf galaxies could help further populate the ${\rm M}_{\rm BH}{-}{\rm M}_{\star}$ and ${\rm M}_{\rm BH}{-}\sigma_\star$ relations in the low-mass regime and constraint IMBH demographics and their formation channels.