The Fornax Cluster VLT Spectroscopic Survey IV -- Cold kinematical substructures in the Fornax core from COSTA

TL;DR

The paper introduces COSTA, a new algorithm for detecting cold kinematic substructures in galaxy clusters, and applies it to the Fornax Cluster, revealing multiple streams and their potential origins.

Contribution

COSTA is a novel algorithm that identifies cold streams in phase space, applied here to the Fornax Cluster to uncover new substructures and analyze their properties.

Findings

Detected 13 cold substructures with velocity dispersions of 20-100 km/s.

Identified streams associated with large galaxies and ultra-compact dwarf galaxies.

Evidence supports that many streams are remnants of disrupted dwarf systems.

Abstract

The COld STream finder Algorithm (COSTA) is a novel algorithm to find streams in the phase space of planetary nebulae (PNe) and globular cluster (GCs) populations. COSTA isolates groups of particles with small velocity dispersion, using an iterative sigma-clipping over a defined number of neighbor particles. We have applied COSTA to a catalog of about 2000 PNe and GCs from the Fornax Cluster VLT Spectroscopic Survey (FVSS), within 200 kpc from the cluster core, to detect cold substructures and characterize their kinematics. We have found 13 cold substructures, with velocity dispersion ranging from 20 to 100 kms^{-1}, which are likely associated either to large galaxies or to ultra-compact dwarf (UCD) galaxies in the Fornax core. These streams show a clear correlation of their luminosity with the internal velocity dispersion, and their surface brightness with size and distance from the cluster center that are compatible with dissipative processes producing them. However, we cannot exclude that some of these substructures have formed by violent relaxation of massive satellites finally merged into the central galaxy. Among these substructures we have: a stream connecting NGC1387 to the central galaxy, NGC1399, previously reported in literature; a new giant stream produced by the interaction of NGC1382 with NGC1380 and possibly NGC1381; a series of streams kinematically connected to nearby ultra compact dwarf galaxies; clumps of tracers with no clear kinematical association to close cluster members. We show evidence for a variety of cold substructure predicted in simulations. Most of the streams are kinematically connected to UCDs, supporting the scenario that they can be remnants of disrupted dwarf systems. [abridged]