Planetary nebula kinematics in NGC 1316: a young Sombrero

TL;DR

This study analyzes planetary nebulae in NGC 1316 to understand its rotation and dark matter content, revealing significant outer rotation likely due to past merger activity, and positioning it as a transitional galaxy.

Contribution

It provides the largest sample of planetary nebulae velocities for NGC 1316 and models its kinematics, highlighting rotation and dark matter distribution in a merger remnant.

Findings

NGC 1316 shows significant outer rotation.

High dark matter content in outer regions.

Transition phase from merger to bulge-dominated galaxy.

Abstract

Aims. We present positions and velocities for 796 planetary nebulae (PNe) in the Fornax Brightest Cluster Galaxy NGC 1316 (Fornax A). The planetary nebulae and existing kinematics are used to explore the rotation of this merger remnant and constrain dynamical models. Methods. Using FORS2 on the VLT, the PN velocities were measured using a counter-dispersed slitless-spectroscopy technique that produced the largest-to-date sample outside of the Local Group. Spherical, non-rotating, constant-anisotropy Jeans models were con- strained by observations of the planetary nebulae and existing integrated light spectra. Results. The two-dimensional velocity field indicates dynamically-important rotation that rises in the outer parts, possibly due to the outward transfer of angular momentum during the merger. The modeling indicates a high dark matter content, particularly in the outer parts, that is consistent with previous estimates from dynamical models, lensing and stellar population models. Conclusions. The exceptionally large sample of PN velocities makes it possible to explore the kinematics of NGC 1316 in detail. Comparing the results to other early-type galaxies like NGC 1399 and NGC 4594 (M104, Sombrero), NGC 1316 represents a transi- tion phase from a major-merger event to a bulge-dominated galaxy like NGC 4594.