A SLUGGS and Gemini/GMOS combined study of the elliptical galaxy M60:
  wide-field photometry and kinematics of the globular cluster system
  We present new wide-field photometry and spectroscopy of the globular
clusters (GCs) around NGC 4649 (M60), the third brightest galaxy in the Virgo
cluster. Imaging of NGC 4649 was assembled from a recently-obtained HST/ACS
mosaic, and new Subaru/Suprime-Cam and archival CFHT/MegaCam data. About 1200
sources were followed up spectroscopically using combined observations from
three multi-object spectrographs: Keck/DEIMOS, Gemini/GMOS and MMT/Hectospec.
We confirm 431 unique GCs belonging to NGC 4649, a factor of 3.5 larger than
previous datasets and with a factor of 3 improvement in velocity precision. We
confirm significant GC colour bimodality and find that the red GCs are more
centrally concentrated, while the blue GCs are more spatially extended. We
infer negative GC colour gradients in the innermost 20 kpc and flat gradients
out to large radii. Rotation is detected along the galaxy major axis for all
tracers: blue GCs, red GCs, galaxy stars and planetary nebulae. We compare the
observed properties of NGC 4649 with galaxy formation models. We find that
formation via a major merger between two gas-poor galaxies, followed by
satellite accretion, can consistently reproduce the observations of NGC 4649 at
different radii. We find no strong evidence to support an interaction between
NGC 4649 and the neighbouring spiral galaxy NGC 4647. We identify interesting
GC kinematic features in our data, such as counter-rotating subgroups and bumpy
kinematic profiles, which encode more clues about the formation history of NGC
4649.
