Triaxial Schwarzschild Models of Brightest Cluster Galaxies with Long-Slit LBT Data

TL;DR

This study models the mass distribution of 16 Brightest Cluster Galaxies using new long-slit stellar kinematics and triaxial Schwarzschild models, revealing ultramassive black holes and diverse dark matter halo geometries.

Contribution

First application of triaxial Schwarzschild models to a large BCG sample with comprehensive multi-instrument data, discovering new ultramassive black holes and analyzing dark matter halo shapes.

Findings

Discovered 8 ultramassive black holes with masses > 10^{10} M_sun.

Revealed diverse geometries of dark matter halos.

Identified a kinematically decoupled core in one galaxy.

Abstract

We present new long-slit stellar kinematics for a sample of 21 Brightest Cluster Galaxies (BCGs) and triaxial Schwarzschild models for 16 of these objects using our orbit modelling code SMART. The new kinematics obtained with the Large Binocular Telescope (LBT) is complemented with high-resolution photometry from HST or new AO-assisted ground-based observations also obtained at LBT and combined with wide-field imaging from the Wendelstein Observatory. These data enable robust modeling from the innermost regions - where the Supermassive Black Hole dominates the potential - to larger radii, where stars and dark matter (DM) are the primary mass contributors. As already discussed in a companion paper, we discovered 8 Ultramassive Black Holes (UMBHs, with mass $> 10^{10}$ M$_\odot$) in this BCG sample, more than doubling the number of galaxies with dynamically detected UMBHs. We show that the DM halos display a wide variety of geometries. Purely kinematical results include low central velocity dispersion with increasing profiles towards the outskirts, and the discovery of one Kinematically Decoupled Core.