Brought to Light. I. Quantification of Disk Substructure in Dwarf Early-type Galaxies

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, that 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% and 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, as well as 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., in which we investigate the origins of the substructure in such dwarf systems.

Brought to Light. II. Revealing the Origins of Cloaked Spiral Features in Cluster Passive Dwarf Galaxies

“…We aim to have a stellar distribution with an effective radius R eff = 1.5 kpc in all our models. This is consistent with the sizes of early-type galaxies with this stellar mass from Janz et al (2012) and is typical for our sample of dwarfs (see Table 2 of our companion paper, Michea et al 2021). We try to keep this value fixed between all our models because the ease with which tidal stripping of stellar disks occurs is known to be a strong function of the ratio of the stellar disk size to the halo size (Smith et al 2016), and we are more interested in the effects of varying stellar disk dynamics in this study, as described below.…”

“…These could perhaps represent the Lagrangian points due to the nonaxisymmetric shape of the potential arising from the bar. In our companion paper (Michea et al 2021), we quantitatively classify these spiral features and their bars using a Fourier analysis.…”

“…A full description of our methodology for producing residual maps and associated testing is presented in our companion paper (Michea et al 2021). Here we provide a short, concise description of the method for completeness.…”

“…In this study, we focus on the nine Virgo cluster passive dwarfs in our companion paper (Brought to Light I: Michea et al 2021). These are VCC 0216, 0308, 0490, 0523, 0856, 0940, 1010, 1695, and 1896.…”

“…The actual depth reached for individual different targets is given in the third column of Table 1. For a more detailed description of the data and how they were processed, please see our companion paper (Michea et al 2021).…”