Dynamical modelling of the twisted galaxy PGC 046832

Abstract

We analyse VLT/MUSE observations of PGC 046832, the brightest cluster galaxy of Abell 3556. The velocity structure of this galaxy is startling and shows two reversals in sign along the minor axis, and one along the major axis. We use triaxial Schwarzschild models to infer the intrinsic shape, central black hole mass and orbit distribution of this galaxy. The shape determination suggests that the galaxy is highly triaxial in the centre (almost prolate) but has a low triaxiality (almost oblate) in the outer parts. The orbit distribution of the best-fit Schwarzschild model shows that the kinematic reversal along the projected minor axis is driven by a slight asymmetry in the distribution and amount of long axis tubes in the inner parts. The kinematic reversals along the projected major axis are driven by a high fraction of counter-rotating orbits at intermediate radii in the galaxy. Using chemical tagging of orbits in the Schwarzschild model, we do not find evidence for any association of these orbits with specific stellar population parameters. Although the inner part of the galaxy almost certainty formed through one or more dry mergers producing the prolate shape, the outer parts are consistent with both accretion and in situ formation. While axisymmetric models suggests the presence of a supermassive black hole with mass ∼6 × 109M⊙and ∼1010M⊙(with Schwarzschild and Jeans modelling, resp), triaxial Schwarzschild models provide only an upper limit of ∼2 × 109M⊙.

Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass

“…This work is one of only a small number of studies that have produced constraints on all three intrinsic shape parameters for individual galaxies (Jin et al 2020;Santucci et al 2022). Even fewer galaxies have been observed with sufficient angular resolution, field of view, spectral coverage, and S/N for a simultaneous determination of the intrinsic shape, supermassive black hole mass, and galaxy mass (van den Bosch & de Zeeuw 2010; Walsh et al 2012;den Brok et al 2021;Quenneville et al 2022;Pilawa et al 2022). As demonstrated in this work, further advancements have only been made possible by the installations of wide-field and highly sensitive IFUs on large groundbased telescopes.…”

The Isotropic Center of NGC 5419—A Core in Formation?

“…Other studies from the literature that analyzed KDCs with Schwarzschild models (Cappellari et al 2002;Van den Bosch et al 2008;Krajnović et al 2015;den Brok et al 2021) suggested that their examined KDCs are not actually decoupled in the sense that counter-rotating orbits are not exclusively localized in the central region but present everywhere. This is in agreement with our analysis from Section 4.5, where we show that NGC 5419ʼs KDC results from an excess of tube orbits rotating in the contrary direction compared to the outskirts.…”