The SLUGGS Survey: Kinematics for over 2500 Globular Clusters in Twelve Early-type Galaxies

TL;DR

This survey of over 2500 globular clusters across twelve early-type galaxies reveals distinct kinematic behaviors between metal-rich and metal-poor subpopulations, highlighting their different dynamical states and relationships with host galaxy properties.

Contribution

It provides the first extensive kinematic analysis of globular cluster subpopulations in multiple galaxies using high-precision spectroscopy and combines new data with literature for comprehensive insights.

Findings

Red GCs are kinematically coupled with host galaxy stars.

Blue GCs exhibit more random motions and are often decoupled from red GCs.

Kinematic differences between subpopulations correlate with galaxy mass.

Abstract

We present a spectro-photometric survey of 2522 extragalactic globular clusters (GCs) around twelve early-type galaxies, nine of which have not been published previously. Combining space-based and multi-colour wide field ground-based imaging, with spectra from the Keck DEIMOS instrument, we obtain an average of 160 GC radial velocities per galaxy, with a high velocity precision of 15 km/s per GC. After studying the photometric properties of the GC systems, such as their spatial and colour distributions, we focus on the kinematics of metal-poor (blue) and metal-rich (red) GC subpopulations to an average distance of ~8 effective radii from the galaxy centre. Our results show that for some systems the bimodality in GC colour is also present in GC kinematics. The kinematics of the red GC subpopulations are strongly coupled with the host galaxy stellar kinematics. The blue GC subpopulations are more dominated by random motions, especially in the outer regions, and decoupled from the red GCs. Peculiar GC kinematic profiles are seen in some galaxies: the blue GCs in NGC 821 rotate along the galaxy minor axis, whereas the GC system of the lenticular galaxy NGC 7457 appears to be strongly rotation supported in the outer region. We supplement our galaxy sample with data from the literature and carry out a number of tests to study the kinematic differences between the two GC subpopulations. We confirm that the GC kinematics are coupled with the host galaxy properties and find that the velocity kurtosis and the slope of their velocity dispersion profiles is different between the two GC subpopulations in more massive galaxies.