# The parallelism between galaxy clusters and early-type galaxies: I. The light and mass profiles

## TL;DR

This study compares the light and mass profiles of galaxy clusters and early-type galaxies, finding strong similarities in their structures and testing simulation models against observations to understand their evolution.

## Contribution

It demonstrates the parallelism between galaxy clusters and early-type galaxies' profiles and evaluates the accuracy of the Illustris simulation in reproducing these properties.

## Key findings

- Luminosity profiles fit by Sersic's law with small scatter.
- Simulations reproduce ETG profiles well except in inner and outer regions.
- Mass profiles, when normalized, also follow Sersic's law.

## Abstract

We have analyzed the parallelism between the properties of galaxy clusters and early-type galaxies (ETGs) by looking at the similarity between their light profiles. We find that the equivalent luminosity profiles of all these systems in the \vfilt\ band, once normalized to the effective radius \re\ and shifted in surface brightness, can be fitted by the S\'ersic's law \Sers\ and superposed with a small scatter ($\le0.3$ mag). By grouping objects in different classes of luminosity, the average profile of each class slightly deviates from the other only in the inner and outer regions (outside $0.1\leq r/R_e\leq 3$), but the range of values of $n$ remains ample for the members of each class, indicating that objects with similar luminosity have quite different shapes. The "Illustris" simulation reproduces quite well the luminosity profiles of ETGs, with the exception of in the inner and outer regions where feedback from supernovae and active galactic nuclei, wet and dry mergers, are at work. The total mass and luminosity of galaxy clusters as well as their light profiles are not well reproduced. By exploiting simulations we have followed the variation of the effective half-light and half-mass radius of ETGs up to $z=0.8$, noting that progenitors are not necessarily smaller in size than current objects. We have also analyzed the projected dark+baryonic and dark-only mass profiles discovering that after a normalization to the half-mass radius, they can be well superposed and fitted by the S\'ersic's law.