Black Hole Scaling Relations in the Dwarf-galaxy Regime with Gaia-Sausage/Enceladus and ωCentauri

Abstract The discovery of fast moving stars in Milky Way’s most massive globular cluster, ω Centauri ( ω Cen), has provided strong evidence for an intermediate-mass black hole (IMBH). However, ω 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 ω Cen is the tidally disrupted dwarf Gaia-Sausage/Enceladus (GSE), a former Milky Way satellite as massive as the Large Magellanic Cloud. I compare ω Cen/GSE with other central BH hosts and place it within the broader context of BH–galaxy (co)evolution. The IMBH of ω Cen/GSE follows the scaling relation between central BH mass and host stellar mass ( M BH – M ⋆ ) extrapolated from local massive galaxies ( M ⋆ ≳ 10 10 M ⊙ ). Therefore, the IMBH of ω Cen/GSE suggests that this relation extends to the dwarf-galaxy regime. I verify that ω Cen (GSE), as well as other NSCs with candidate IMBHs and ultracompact galaxies also follow the M BH – σ ⋆ relation with stellar velocity dispersion. Under the assumption of direct collapse BH, ω Cen/GSE’s IMBH would require a low initial mass (≲10,000 M ⊙ ) and almost no accretion over ∼3 Gyr, which could be the extreme opposite of high- z galaxies with overmassive BHs such as GN-z11. If ω 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 M BH – M ⋆ and M BH – σ ⋆ relations in the low-mass regime and constrain IMBH demographics and their formation channels.