Kinematic properties of early-type galaxy haloes using planetary nebulae

TL;DR

This study uses planetary nebulae to analyze the kinematic properties of early-type galaxy haloes, revealing diverse velocity profiles, complex angular momentum structures, and correlations with galaxy characteristics, extending understanding to outer regions up to about 8 effective radii.

Contribution

It provides a comprehensive kinematic analysis of early-type galaxy haloes using planetary nebulae, extending previous stellar kinematic studies to larger radii and revealing new dynamical features.

Findings

Velocity profiles fall into two groups: slowly decreasing and steeply falling.

Outer haloes show more complex angular momentum profiles than inner regions.

Many galaxies are more rotationally dominated at large radii.

Abstract

We present new planetary nebulae (PNe) positions, radial velocities, and magnitudes for 6 early-type galaxies obtained with the Planetary Nebulae Spectrograph, their two-dimensional velocity and velocity dispersion fields. We extend this study to include an additional 10 early-type galaxies with PNe radial velocity measurements available from the literature, to obtain a broader description of the outer-halo kinematics in early-type galaxies. These data extend the information derived from stellar kinematics to typically up to ~8 Re. The combination of photometry, stellar and PNe kinematics shows: i) good agreement between the PNe number density and the stellar surface brightness in the region where the two data sets overlap; ii) good agreement between PNe and stellar kinematics; iii) that the mean rms velocity profiles fall into two groups: with of the galaxies characterized by slowly decreasing profiles and the remainder having steeply falling profiles; iv) a larger variety of velocity dispersion profiles; v) that twists and misalignments in the velocity fields are more frequent at large radii, including some fast rotators; vi) that outer haloes are characterised by more complex radial profiles of the specific angular momentum-related lambda_R parameter than observed within 1Re; vii) that many objects are more rotationally dominated at large radii than in their central parts; and viii) that the halo kinematics are correlated with other galaxy properties, such as total luminosity, isophotal shape, total stellar mass, V/sigma, and alpha parameter, with a clear separation between fast and slow rotators.