Photometric Properties and Scaling Relations of Early Type Brightest Cluster Galaxies

TL;DR

This study analyzes the photometric properties and scaling relations of Brightest Cluster Galaxies (BCGs), revealing their extended stellar envelopes, steeper size-luminosity and Faber-Jackson relations, and suggesting dry mergers as a key formation process.

Contribution

It provides detailed photometric analysis of BCGs, compares them with elliptical galaxies, and highlights their distinct scaling relations and potential formation mechanisms.

Findings

BCGs have more extended stellar halos with increasing luminosity.

BCGs exhibit steeper size-luminosity and Faber-Jackson relations than typical ellipticals.

Approximately 49% of BCGs have disky isophotal shapes.

Abstract

We investigate the photometric properties of the early type Brightest Cluster Galaxies (BCGs) using a carefully selected sample of 85 BCGs from the C4 cluster catalogue with redshift less than 0.1. We perform accurate background subtractions, and surface photometry for these BCGs to 25 $\magsec$ in the Sloan $r$-band. By quantitatively analysing the gradient of the Petrosian profiles of BCGs, we find that a large fraction of BCGs have extended stellar envelopes in their outskirts; more luminous BCGs tend to have more extended stellar halos that are likely connected with mergers. A comparison sample of elliptical galaxies was chosen with similar apparent magnitude and redshift ranges, for which the same photometric analysis procedure is applied. We find that BCGs have steeper size-luminosity ($R \propto L^\alpha$) and Faber-Jackson ($L \propto \sigma^\beta$) relations than the bulk of early type galaxies. Furthermore, the power-law indices ($\alpha$ and $\beta$) in these relations increase as the isophotal limits become deeper. For isophotal limits from 22 to 25 $\magsec$, BCGs are usually larger than the bulk of early type galaxies, and a large fraction ($\sim 49%$) of BCGs have disky isophotal shapes. The differences in the scaling relations are consistent with a scenario where the dynamical structure and formation route of BCGs may be different from the bulk of early type galaxies, in particular dry (dissipationless) mergers may play a more important role in their formation; we highlight several possible dry merger candidates in our sample.