The SLUGGS survey: Globular cluster kinematics in a 'double sigma' galaxy - NGC 4473

Abstract

NGC4473 is a so-called double sigma (2σ) galaxy, i.e. a galaxy with rare, double peaks in its2D stellar velocity dispersion. Here, we present the globular cluster (GC) kinematics in NGC 4473 out to ~10Re (effective radii) using data from combined Hubble Space Telescope/Advanced Camera for Surveys and Subaru/Suprime-Cam imaging and Keck/Deep Imaging Multi-Object Spectrograph. We find that the 2σ nature of NGC 4473 persists up to 3Re, though it becomes misaligned to the photometric major axis. We also observe a significant offset between the stellar and GC rotation amplitudes. This offset can be understood as a co-addition of counterrotating stars producing little net stellar rotation.We identify a sharp radial transition in the GC kinematics at ~4Re suggesting a well defined kinematically distinct halo. In the inner region (<4Re), the blue GCs rotate along the photometric major axis, but in an opposite direction to the galaxy stars and red GCs. In the outer region (>4Re), the red GCs rotate in an opposite direction compared to the inner region red GCs, along the photometric major axis, while the blue GCs rotate along an axis intermediate between the major and minor photometric axes. We also find a kinematically distinct population of very red GCs in the inner region with elevated rotation amplitude and velocity dispersion. The multiple kinematic components in NGC 4473 highlight the complex formation and evolutionary history of this 2σ galaxy, as well as a distinct transition between the inner and outer components.