Using angular momentum maps to detect kinematically distinct galactic components

TL;DR

This paper introduces a physically motivated angular momentum map method for decomposing simulated galaxies into disc and spheroid components, effectively classifying galaxy morphology and properties.

Contribution

The paper presents a novel angular momentum map technique for galaxy decomposition, improving classification accuracy and identifying counter-rotating discs in simulations.

Findings

Surface density profiles match exponential and Sersic profiles.

Discs are faster rotating, younger, and more metal-rich.

Method detects counter-rotating discs effectively.

Abstract

In this work we introduce a physically motivated method of performing disc/spheroid decomposition of simulated galaxies, which we apply to the Eagle sample. We make use of the HEALPix package to create Mollweide projections of the angular momentum map of each galaxy's stellar particles. A number of features arise on the angular momentum space which allows us to decompose galaxies and classify them into different morphological types. We assign stellar particles with angular separation of less/greater than 30 degrees from the densest grid cell on the angular momentum sphere to the disc/spheroid components, respectively. We analyse the spatial distribution for a subsample of galaxies and show that the surface density profiles of the disc and spheroid closely follow an exponential and a Sersic profile, respectively. In addition discs rotate faster, have smaller velocity dispersions, are younger and are more metal rich than spheroids. Thus our morphological classification reproduces the observed properties of such systems. Finally, we demonstrate that our method is able to identify a significant population of galaxies with counter-rotating discs and provide a more realistic classification of such systems compared to previous methods.