An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277

TL;DR

This paper reports the discovery of an extremely massive black hole in galaxy NGC1277, which contains a black hole mass that is a significant fraction of its bulge mass, challenging existing scaling relations.

Contribution

It provides the first detailed stellar kinematic measurements indicating an over-massive black hole in NGC1277, suggesting some compact galaxies may deviate from established black hole-bulge mass relations.

Findings

Black hole mass in NGC1277 is 1.7 x 10^10 Msun, 59% of its bulge mass.

NGC1277's black hole is over 100 times larger than typical for its bulge.

Several similar compact galaxies may also host over-massive black holes.

Abstract

All massive galaxies likely have supermassive black holes at their centers, and the masses of the black holes are known to correlate with properties of the host galaxy bulge component. Several explanations have been proposed for the existence of these locally-established empirical relationships; they include the non-causal, statistical process of galaxy-galaxy merging, direct feedback between the black hole and its host galaxy, or galaxy-galaxy merging and the subsequent violent relaxation and dissipation. The empirical scaling relations are thus important for distinguishing between various theoretical models of galaxy evolution, and they further form the basis for all black hole mass measurements at large distances. In particular, observations have shown that the mass of the black hole is typically 0.1% of the stellar bulge mass of the galaxy. The small galaxy NGC4486B currently has the largest published fraction of its mass in a black hole at 11%. Here we report observations of the stellar kinematics of NGC 1277, which is a compact, disky galaxy with a mass of 1.2 x 10^11 Msun. From the data, we determine that the mass of the central black hole is 1.7 x 10^10 Msun, or 59% its bulge mass. Five other compact galaxies have properties similar to NGC 1277 and therefore may also contain over-sized black holes. It is not yet known if these galaxies represent a tail of a distribution, or if disk-dominated galaxies fail to follow the normal black hole mass scaling relations.