Ultracompact dwarfs in the Perseus Cluster: UCD formation via tidal stripping

TLDR: In this paper, the authors present the results of a Keck/DEIMOS survey of UCDs in the Perseus Cluster core, and confirm cluster membership for 14 UCD with radial velocities ∼ 5300 km s −1.

Abstract: We present the results of a Keck/DEIMOS survey of Ultra Compact Dwarfs (UCDs) in the Perseus Cluster core. We confirm cluster membership for 14 UCDs, with radial velocities ∼ 5300 km s −1 . Two of these confirmed Perseus UCDs have extremely blue colours ( B−R < 0.6 mag), reside in star forming filaments surrounding NGC 1275, and have likely formed as massive star clusters in the last ∼ 100 Myr. We also measure a central velocity dispersion of a third, UCD13 (σ0 = 38 ± 8 km s −1 ), the most extended UCD in our sample. We determine it to have radius Re = 85 ± 1.1 pc, a dynamical mass of (2.3 ± 0.8) × 10 8 M⊙, and a −0.52 +0.33 metallicity [Z/H]= dex. UCD13 and the cluster’s central galaxy, NGC 1275, −0.29 have a projected separation of 30 kpc and a radial velocity difference of ∼ 20 km s −1 . Based on its size, red colour, internal velocity dispersion, dynamical mass, metallicity and proximity to NGC 1275, we argue that UCD13 is likely the remnant nucleus of a tidally stripped dE, with this progenitor dE having MB ≈ −16 mag and mass ∼ 10 9 M⊙.