UCD Candidates in the Hydra Cluster

TL;DR

This study identifies 29 ultra-compact dwarf candidates in the Hydra cluster, demonstrating a smooth transition from globular clusters to UCDs and supporting the idea of a continuous sequence linking these objects to elliptical galaxy structures.

Contribution

The paper provides new photometric data revealing a well-defined UCD sequence merging with globular clusters, enhancing understanding of galaxy and star cluster evolution.

Findings

29 UCD candidates identified with masses > 6x10^6 solar masses

UCD sequence extends smoothly from globular clusters

Supports continuous transition from globular clusters to UCDs and elliptical galaxies

Abstract

NGC 3311, the giant cD galaxy in the Hydra cluster (A1060), has one of the largest globular cluster systems known. We describe new Gemini GMOS (g',i') photometry of the NGC 3311 field which reveals that the red, metal-rich side of its globular cluster population extends smoothly upward into the mass range associated with the new class of Ultra-Compact Dwarfs (UCDs). We identify 29 UCD candidates with estimated masses > 6x10^6 solar masses and discuss their characteristics. This UCD-like sequence is the most well defined one yet seen, and reinforces current ideas that the high-mass end of the globular cluster sequence merges continuously into the UCD sequence, which connects in turn to the E galaxy structural sequence.