The Sizes of Early-type Galaxies

TL;DR

This study investigates the size-luminosity relation of early-type galaxies in the Virgo Cluster, revealing a dichotomy between dwarf and giant galaxies that challenges the idea of a single continuous sequence.

Contribution

It provides the first homogeneous, model-independent analysis showing a clear size-luminosity dichotomy in early-type galaxies, supported by comparison with semi-analytic models.

Findings

Dwarfs show weak or no dependence on luminosity.

Giants and dwarfs do not form a single sequence.

The observed dichotomy supports a physical origin.

Abstract

In this letter we present a study of the size luminosity relation of 475 early-type galaxies in the Virgo Cluster with Sloan Digital Sky Survey imaging data. The analysis of our homogeneous, model-independent data set reveals that giant and dwarf early-type galaxies do not form one common sequence in this relation. The dwarfs seem to show weak or no dependence on luminosity, and do not fall on the extension of the rather steep relation of the giants. Under the assumption that the light profile shape varies continuously with magnitude, a curved relation of size and magnitude would be expected. While the galaxies do roughly follow this trend overall, we find that the dwarf galaxies are significantly larger and the low-luminosity giants are significantly smaller than what is predicted. We come to the conclusion that in this scaling relation there is not one common sequence from dwarfs to giants, but a dichotomy which can not be resolved by varying profile shapes. The comparison of our data to a semi-analytic model supports the idea of a physical origin of this dichotomy.