Isophotal shapes of early-type galaxies to very faint levels

TL;DR

This study examines the faint isophotal shapes of early-type galaxies using deep imaging, revealing that their inner and outer regions have statistically different shapes, indicating independent evolution.

Contribution

It provides detailed measurements of isophotal shapes at very faint levels and analyzes their radial variation, a novel approach in galaxy shape studies.

Findings

Inner and outer isophotal shapes differ statistically

Outer regions show signs of independent evolution

Empirical models for shape parameter distributions are developed

Abstract

We report on a study of the isophotal shapes of early-type galaxies, to very faint levels reaching ~ 0.1% of the sky brightness. The galaxies are from the Large Format Camera (LFC) fields obtained using the Palomar 5 m Hale telescope, with integrated exposures ranging from 1 to 4 hours in the SDSS r, i and z bands. The shapes of isophotes of early-type galaxies are important as they are correlated with the physical properties of the galaxies and are influenced by galaxy formation processes. In this paper we report on a sample of 132 E and SO galaxies in one LFC field. We have redshifts for 53 of these, obtained using AAOmega on the Anglo-Australian Telescope. The shapes of early-type galaxies often vary with radius. We derive average values of isophotal shape parameters in four different radial bins along the semi-major axis in each galaxy. We obtain empirical fitting formulae for the probability distribution of the sophotal parameters in each bin and investigate for possible correlations with other global properties of the galaxies. Our main finding is that the isophotal shapes of the inner regions are statistically different from those in the outer regions. This suggests that the outer and inner parts of early-type galaxies have evolved somewhat independently.