Asymmetry at Low Surface Brightness as an Indicator of Environmental Processes in the Fornax Cluster

TL;DR

This study investigates how dwarf galaxy asymmetries in the Fornax Cluster relate to their environment, revealing that outer and inner regions show different disturbance causes, with implications for galaxy evolution and cluster assembly history.

Contribution

It introduces isophotal CAS-parameters for outer galaxy morphology analysis and links asymmetry variations to environmental effects like ram pressure and tidal interactions.

Findings

Outer dwarf galaxies are more asymmetric, indicating environmental disturbances.

Inner dwarf galaxies show higher asymmetry due to tidal effects.

Asymmetry increases with fainter magnitudes and bluer colours.

Abstract

Dwarf galaxies play an important role in studying the effects of the environment on galaxy formation and evolution. In this study, we aim to explore the relationship between the morphology, in particular the asymmetries of galaxies, and their distances to the cluster centre. For galaxies in the Fornax Deep Survey, we quantified the morphologies of dwarf galaxies using Asymmetry (A) and Smoothness (S). Unlike previous work, we use isophotal CAS-parameters, which are sensitive to the outer parts of galaxies. We constructed the A-r and S-r diagrams to investigate the relationship between morphology and distance. Additionally, we examined the effects of asymmetry on magnitude and colour. Furthermore, to better understand the assembly history of the galaxy cluster, we performed a phase-space analysis for Fornax dwarf galaxies. We find that dwarf galaxies in the outer regions of the Fornax cluster have higher values of asymmetry compared to other dwarfs in the cluster, indicating a greater degree of morphological disturbances within dwarf galaxies in these regions. We also find that galaxies in the very inner regions are more asymmetric than those further out. The A-magnitude relation reveals a trend where asymmetry increases as galaxies become fainter, and the A-colour relation shows that galaxies with bluer colours tend to exhibit higher asymmetry. We do not find any correlations with smoothness, except that smoothness strongly decreases with stellar mass. We propose that the higher asymmetry of dwarfs in the outer regions is most likely caused by ram pressure stripping. In the very inner parts, the asymmetries most likely are caused by tidal effects. In addition, our phase-space diagram suggests that galaxies near pericentre in the Fornax cluster exhibit significantly higher asymmetry, indicating that morphological disturbances happened during their first pericentric passage.