The central region of the Fornax cluster -- II. Spectroscopy and radial velocities of member and background galaxies

TL;DR

This study measures radial velocities of galaxies in the Fornax cluster, identifying cluster members, background galaxies, and a background galaxy cluster, providing insights into galaxy properties and cluster composition.

Contribution

It presents new spectroscopic data for 94 galaxies in the Fornax region, including the discovery of a background galaxy cluster and analysis of compact objects' nature.

Findings

Identified 8 Fornax cluster members among 94 galaxies.

Discovered a background galaxy cluster at z=0.11 near Fornax.

Characterized properties of compact objects, ambiguous between GCs and nuclei.

Abstract

Radial velocities of 94 galaxies brighter than about V_tot = 20 mag in the direction of the central Fornax cluster have been measured. Except for 8 Fornax members, all galaxies lie in the background. Among the 8 members, there are 5 nucleated dwarf ellipticals that are already listed in the FCC (Ferguson 1989, AJ 98, 367). Two of the 3 ``new'' members are very compact and have surface brightnesses comparable to globular clusters, however their luminosities are in the range of dwarf elliptical nuclei. The measured line indices (especially Mg2, H beta, and iron) of the brighter of the compact objects suggest a solar metallicity, whereas the fainter compact object as well as the dE,Ns have line indices that are similar to those of old metal-poor globular clusters (GCs). However, with these data it is not possible to clearly classify the compact objects either as very bright globular clusters, isolated nuclei of dE,Ns, or even compact ellipticals. A background galaxy cluster at z = 0.11 has been found just behind the center of the Fornax cluster. This explains the excess population of galaxies reported in Paper I. The brightest galaxy of the background cluster lies only 1.1 arcmin south of NGC 1399 and is comparable in absolute luminosity with the central Fornax galaxy itself.