The Parallelism between Galaxy Clusters and Early-type Galaxies. I. The Light and Mass Profiles

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 V band, once normalized to the effective radius R _e and shifted in surface brightness, can be fitted by the Sérsic law {r}^1/n and superposed with a small scatter (≤0.3 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 ≤ r/R _e ≤ 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 the luminosity profiles of ETGs quite well, with the exception of in the inner and outer regions, where feedback from supernovae, active galactic nuclei, and wet and dry mergers is 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 Sérsic law.