An Enhanced Massive Black Hole Occupation Fraction Predicted in Cluster Dwarf Galaxies

Understand

The occupation fraction of massive black holes (MBHs) in dwarf galaxies offers interesting insights into initial black hole seeding mechanisms and their mass assembly history, though disentangling these two effects remains challenging.

• Using the {\sc Romulus} cosmological simulations we examine the impact of environment on the occupation fraction of MBHs in low mass galaxies.
• Unlike most modern cosmological simulations, {\sc Romulus} seeds MBHs based on local gas properties, selecting dense ($n>3$ cm$^{-3}$), pristine ($Z<3e-4Z_{\odot}$), and rapidly collapsing regions in the early Universe as sites to host MBHs without assuming anything about MBH occupation as a function of galaxy stellar mass, or halo mass, {\it a priori}.
• The simulations predict that dwarf galaxies with M$_{\star}<10^9$ M$_{\odot}$ in cluster environments are $\sim2$ times more likely to host a MBH compared to those in the field.