The Black Hole Mass and Extreme Orbital Structure in NGC1399

TL;DR

This study uses Hubble Space Telescope data to measure the black hole mass in NGC1399, revealing an unusually high tangential orbital bias and providing insights into black hole growth mechanisms in central cluster galaxies.

Contribution

It presents the first detailed orbital structure and black hole mass measurement for NGC1399, highlighting a unique tangential anisotropy and a black hole mass below established correlations.

Findings

Black hole mass of 5.1 ± 0.7 x 10^8 Msun

Largest tangential to radial velocity dispersion ratio observed

Evidence of strong central tangential anisotropy

Abstract

The largest galaxies, and in particular central galaxies in clusters, offer unique insight into understanding the mechanism for the growth of nuclear black holes. We present Hubble Space Telescope kinematics for NGC1399, the central galaxy in Fornax. We find the best-fit model contains a black hole of 5.1 +-0.7 x 10^8 Msun (at a distance of 21.1 Mpc), a factor of over 2 below the correlation of black hole mass and velocity dispersion. We also find a dramatic signature for central tangential anisotropy. The velocity profiles on adjacent sides 0.5" away from the nucleus show strong bimodality, and the central spectrum shows a large drop in the dispersion. Both of these observations point to an orbital distribution that is tangentially biased. The best-fit orbital model suggests a ratio of the tangential to radial internal velocity dispersions of three. This ratio is the largest seen in any galaxy to date and will provide an important measure for the mode by which the central black hole has grown.