# The SLUGGS Survey: Trails of SLUGGS galaxies in a modified spin-ellipticity diagram

## TL;DR

This paper introduces radial spin-ellipticity tracks for early-type galaxies, revealing their transition from fast to slow rotation and providing a new diagnostic tool for galaxy classification beyond single aperture measures.

## Contribution

It presents a novel method of plotting radial spin and ellipticity profiles as tracks, offering deeper insights into galaxy structure and morphology.

## Key findings

- Radial tracks show galaxies transition from fast to slow rotation.
- Discy elliptical galaxies exhibit downturns in spin and ellipticity at large radii.
- Tracks differentiate between elliptical, lenticular, and hybrid ES galaxies.

## Abstract

We present radial tracks for four early-type galaxies with embedded intermediate-scale discs in a modified spin-ellipticity diagram. Here, each galaxy's spin and ellipticity profiles are shown as a radial track, as opposed to a single, flux-weighted aperture-dependent value as is common in the literature. The use of a single ellipticity and spin parameter is inadequate to capture the basic nature of these galaxies, which transition from fast to slow rotation as one moves to larger radii where the disc ceases to dominate. After peaking, the four galaxy's radial tracks feature a downturn in both ellipticity and spin with increasing radius, differentiating them from elliptical galaxies, and from lenticular galaxies whose discs dominate at large radii. These galaxies are examples of so-called discy elliptical galaxies, which are a morphological hybrid between elliptical (E) and lenticular (S0) galaxies, and have been designated ES galaxies. The use of spin-ellipticity tracks provides extra structural information about individual galaxies over a single aperture measure. Such tracks provide a key diagnostic for classifying early-type galaxies, particularly in the era of 2D kinematic (and photometric) data beyond one effective radius.