Using Subaru/Suprime-Cam wide-field imaging and both Keck/ESI and LBT/MODS spectroscopy , we identify and characterize a compact star cluster , which we term NGC 3628-UCD1 , embedded in a stellar stream around the spiral galaxy NGC 3628 .
The size and luminosity of UCD1 are similar to \omega Cen , the most luminous Milky Way globular cluster , which has long been suspected to be the stripped remnant of an accreted dwarf galaxy .
The object has a magnitude of i = 19.3 mag ( { L } _ { i } = 1.4 \times 10 ^ { 6 } L _ { \odot } ) .
UCD1 is marginally resolved in our ground-based imaging , with a half-light radius of \sim 10 pc .
We measure an integrated brightness for the stellar stream of i = 13.1 mag , with ( g - i ) = 1.0 .
This would correspond to an accreted dwarf galaxy with an approximate luminosity of { L } _ { i } \sim 4.1 \times 10 ^ { 8 } L _ { \odot } .
Spectral analysis reveals that UCD1 has an age of 6.6 Gyr , [ Z / H ] = -0.75 , and [ { \alpha } / Fe ] = -0.10 .
We propose that UCD1 is an example of an \omega Cen-like star cluster possibly forming from the nucleus of an infalling dwarf galaxy , demonstrating that at least some of the massive star cluster population may be created through tidal stripping .