Work

The Fornax Cluster VLT Spectroscopic Survey

Year: 2026

Type: article

Abstract: NGC 1399, the bright central galaxy of the Fornax cluster, contains an extensive population of globular clusters (GCs) extending beyond 200 kpc into its outer halo, approximately 6.5 effective radii (R e ). We conducted dynamical mass modelling of NGC 1399 out to 5 R e (∼150 kpc) using the most comprehensive radial velocity catalogue of GCs to date, which includes data from the Fornax cluster VLT Spectroscopic Survey (FVSS) and previous velocity measurements from the literature. Applying spherical Jeans equations, we performed dispersion-kurtosis modelling of NGC 1399’s GC kinematics to derive its mass profile and the orbital anisotropy of its GCs. We also investigated the impact of including intra-cluster GCs in the mass modelling, which were selected based on spatial segregation and a velocity σ -clipping method. Our findings indicate that both cusp-like (NFW) and core-like (Burkert) halos can reproduce the observed kinematics of GCs. Including the intra-cluster GCs in the mass modelling yields broadly consistent mass profiles for the two halo types, with the full GC sample giving a virial mass of log M vir = 13.81 ± 0.09 M ⊙ for the NFW halo, slightly higher than the value inferred for the Burkert halo. Regardless of the dark matter halo profile adopted, we observe that the intra-cluster GCs exhibit radial anisotropy in the outskirts, especially the blue, metal-poor GCs. These results suggest that GCs in NGC 1399’s outer halo are influenced by an additional halo component associated with the galaxy cluster potential. The radial anisotropy observed in these outer-halo GCs provides strong dynamical evidence that they were accreted from external sources, which is consistent with prior photometric and spectroscopic studies of GCs. This study highlights the importance of including intra-cluster GCs in dynamical mass modelling to fully account for the contribution of dark matter to the cluster gravitational potential.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202555529