Ultra-massive black hole feedback in compact galaxies

TL;DR

This paper explores how ultra-massive black holes in compact galaxies influence galaxy evolution through intense early feedback, affecting star formation, galaxy size, and surrounding environments.

Contribution

It proposes a new model linking UMBH feedback to galaxy compactness and evolution, emphasizing radiation pressure-driven outflows at high redshift.

Findings

UMBH feedback can expel gas and trigger inner star formation.

Extreme feedback may create diffuse stellar halos or eject stars into intergalactic space.

Less massive black holes produce weaker feedback, allowing galaxy growth over time.

Abstract

Recent observations confirm the existence of ultra-massive black holes (UMBH) in the nuclei of compact galaxies, with physical properties similar to NGC 1277. The nature of these objects poses a new puzzle to the `black hole-host galaxy co-evolution' scenario. We discuss the potential link between UMBH and galaxy compactness, possibly connected via extreme active galactic nucleus (AGN) feedback at early times ($z > 2$). In our picture, AGN feedback is driven by radiation pressure on dust. We suggest that early UMBH feedback blows away all the gas beyond a $\sim$kpc or so, while triggering star formation at inner radii, eventually leaving a compact galaxy remnant. Such extreme UMBH feedback can also affect the surrounding environment on larger scales, e.g. the outflowing stars may form a diffuse stellar halo around the compact galaxy, or even escape into the intergalactic or intracluster medium. On the other hand, less massive black holes will drive less powerful feedback, such that the stars formed within the AGN feedback-driven outflow remain bound to the host galaxy, and contribute to its size growth over cosmic time.