# The Isophotal Structure of Early-Type Galaxies in the SDSS: Dependence on AGN Activity and Environment

## TL;DR

This study analyzes how the isophotal shapes of early-type galaxies relate to their luminosity, mass, nuclear activity, and environment, finding that luminosity and mass primarily determine their isophotal structure.

## Contribution

It provides a large, statistically robust analysis showing that galaxy luminosity and mass are the main factors influencing isophotal shape, independent of activity or environment.

## Key findings

- Disky galaxy fraction decreases with increasing luminosity.
- Correlations with activity and environment are explained by luminosity or mass.
- Isophotal shape depends mainly on galaxy luminosity and mass.

## Abstract

We study the dependence of the isophotal shape of early-type galaxies on their absolute B-band magnitude, their dynamical mass, and their nuclear activity and environment, using an unprecedented large sample of 847 early-type galaxies identified in the SDSS by Hao et al (2006). We find that the fraction of disky galaxies smoothly decreases with increasing luminosity. The large sample allows us to describe these trends accurately with tight linear relations that are statistically robust against the uncertainty in the isophotal shape measurements. There is also a host of significant correlations between the disky fraction and indicators of nuclear activity (both in the optical and in the radio) and environment (soft X-rays, group mass, group hierarchy). Our analysis shows however that these correlations can be accurately matched by assuming that the disky fraction depends only on galaxy luminosity or mass. We therefore conclude that neither the level of activity, nor group mass or group hierarchy help in better predicting the isophotal shape of early-type galaxies.