The SLUGGS Survey: Globular cluster kinematics in a "double sigma" galaxy - NGC 4473

TL;DR

This study analyzes the globular cluster kinematics in the double sigma galaxy NGC 4473, revealing complex, multi-component dynamics and a transition in kinematic behavior at around 4 effective radii, shedding light on its formation history.

Contribution

It provides the first detailed kinematic analysis of globular clusters in NGC 4473, demonstrating persistent double sigma features and complex rotational patterns extending to large radii.

Findings

Double sigma feature persists up to 3 R_e

Kinematic transition at ~4 R_e with distinct inner and outer components

Presence of a kinematically distinct, very red GC population

Abstract

NGC 4473 is a so--called double sigma (2$\sigma$) galaxy, i.e. a galaxy with rare, double peaks in its 2D stellar velocity dispersion. Here, we present the globular cluster (GC) kinematics in NGC 4473 out to $\sim10\,R_e$ (effective radii) using data from combined HST/ACS and Subaru/Suprime--Cam imaging and Keck/DEIMOS spectroscopy. We find that the 2$\sigma$ nature of NGC 4473 persists up to 3 $R_e$, 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 counter--rotating stars producing little net stellar rotation. We identify a sharp radial transition in the GC kinematics at $\sim4\,R_e$ suggesting a well defined kinematically distinct halo. In the inner region ($<4\,R_e$), 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 ($>4\,R_e$), 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 2$\sigma$ galaxy, as well as a distinct transition between the inner and outer components.