Gemini Spectroscopy of Ultra-Compact Dwarfs in the Fossil Group NGC 1132

TL;DR

This study confirms the presence of six ultra-compact dwarf galaxies in the fossil group NGC 1132 using Gemini spectroscopy, demonstrating their potential as tracers for galaxy group dynamics and formation across different environments.

Contribution

First spectroscopic confirmation of UCDs in the fossil group NGC 1132, showing their properties and potential as dynamical probes in diverse galaxy environments.

Findings

Six UCDs confirmed at ~100 Mpc distance

UCDs have velocity dispersion similar to poor galaxy groups

The brightest UCD is an M32 analog with specific size and magnitude

Abstract

A spectroscopic follow up of Ultra-Compact Dwarf (UCD) candidates in the fossil group NGC 1132 is undertaken with the Gemini Multi Object Spectrograph (GMOS). These new Gemini spectra prove the presence of six UCDs in the fossil group NGC 1132 at a distance of D~100 Mpc and a recessional velocity of v_r = 6935 +/- 11 km/s. The brightest and largest member of the UCD population is an M32 analog with a size of 77.1 pc and a magnitude of M_V=-14.8 mag with the characteristics in between those of the brightest UCDs and compact elliptical galaxies. The ensemble of UCDs have an average radial velocity of <v_r> = 6966 +/- 208 km/s and a velocity dispersion of sigma_v = 169 +/-18 km/s similar to the one of poor galaxy groups. This work shows that UCDs can be used as test particles to determine the dynamical properties of galaxy groups. The presence of UCDs in the fossil group environment is confirmed and thus the fact that UCDs can form across diverse evolutionary conditions.