Ultracompact Dwarf Candidates in the Hydra Cluster

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 ultracompact dwarfs (UCDs). We identify 29 UCD candidates with estimated masses >6 × 106 M☉ 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.