Brought to Light I: Quantification of Disk Substructure in Dwarf Early-Type Galaxies

TL;DR

This paper introduces a new method to identify and quantify faint disk substructures in dwarf early-type galaxies, revealing their contribution to galaxy light and analyzing their properties.

Contribution

The authors develop a robust iterative technique to extract and analyze faint disk features embedded in dwarf ETGs, improving understanding of their structural complexity.

Findings

Disk substructure contributes 2.2% to 6.4% of galaxy light within two effective radii.

The method accurately recovers faint disk features even at low light fractions.

Fourier analysis reveals properties of bars and spiral arms in the extracted substructures.

Abstract

Dwarf early-type galaxies (ETGs) display a rich diversity in their photometric, structural, and dynamical properties. In this work, we address their structural complexity by studying with deep imaging a sample of nine dwarf ETGs from the Virgo galaxy cluster, characterized by having faint disk features, such as bars and spiral arms, which lie mostly hidden within the bright diffuse light of the galaxies. We present a new, robust method that aims to identify and extract the disk substructure embedded in these dwarf ETGs. The method consists in an iterative procedure that gradually separates a galaxy image into two components; the bright, dominant diffuse component, and the much fainter, underlying disk component. By applying it to the dwarf ETG sample, we quantify their disk substructure and find that its relative contribution to the total galaxy light ranges between 2.2 to 6.4% within two effective radii. We test the reliability of the method, and prove that it is accurate in recovering the disk substructure we introduce in mock galaxy images, even at low disk-to-total light fractions of a few percent. As a potential application of the method, we perform a Fourier analysis on the extracted disk substructures and measure the orientation, length, and strength of the bars, and the pitch angle and strength of the spiral arms. We also briefly discuss a scenario based on the numerical simulations presented in our companion paper, Brought to Light II: Smith et al. 2021, in which we investigate the origins of the substructure in such dwarf systems.