Coma cluster object populations down to M_R~-9.5

TL;DR

This paper investigates the distribution of very faint galaxies and globular clusters in the Coma cluster down to M_R~-9.5, revealing environmental dependence and contrasting properties in different regions.

Contribution

It provides the deepest analysis of faint galaxy populations in Coma, highlighting environmental effects and differences in luminosity functions across regions.

Findings

Western region is poorly populated with faint galaxies.

Regions near NGC 4874 and NGC 4889 have many faint blue galaxies.

Faint galaxy luminosity function slope is -2, differing from field estimates.

Abstract

This study follows a recent analysis of the galaxy luminosity functions and colour-magnitude red sequences in the Coma cluster (Adami et al. 2007). We analyze here the distribution of very faint galaxies and globular clusters in an east-west strip of $\sim 42 \times 7$ arcmin$^2$ crossing the Coma cluster center (hereafter the CS strip) down to the unprecedented faint absolute magnitude of M$_R \sim -9.5$. This work is based on deep images obtained at the CFHT with the CFH12K camera in the B, R, and I bands. The analysis shows that the observed properties strongly depend on the environment, and thus on the cluster history. When the CS is divided into four regions, the westernmost region appears poorly populated, while the regions around the brightest galaxies NGC 4874 and NGC 4889 (NGC 4874 and NGC 4889 being masked) are dominated by faint blue galaxies. They show a faint luminosity function slope of -2, very significantly different from the field estimates. Results are discussed in the framework of galaxy destruction (which can explain part of the very faint galaxy population) and of structures infalling on to Coma.