Dissecting the luminosity function of the Coma cluster of galaxies using CFHT wide field images

We determined the relative spatial density of the Coma cluster galaxies selected by luminosity, and the contribution of the galaxies of each central brightness to the luminosity function (i.e. the luminosity function bi–variate in central brightness). The Coma cluster and control fields were imaged using the CFH12K (42 × 28 arcmin) and UH8K (28 × 28 arcmin) wide–field cameras at the Canada–France–Hawaii Telescope. Selected Hubble Space Telescope images were used for testing. Quantities were derived from measurements in at least two colors, which have the following features: (1) Galaxies as faint as three times the luminosity of the brightest globular clusters are in the completeness region of our data. (2) We have a complete census (in the explored region) of low surface brightness galaxies with central surface brightness galaxies almost as low as the faintest so far cataloged ones. (3) The explored area is among the largest ever sampled with CCDs at comparable depth for any cluster of galaxies. (4) The error budget includes all sources of errors known to date. Using Hubble Space Telescope images we also discovered that blends of globular clusters, not resolved in individual components due to seeing, look like dwarf galaxies when observed from the ground and are numerous and bright. When mistaken as extended sources, they increase the steepness of luminosity function at faint magnitudes. The derived Coma luminosity function is relatively steep (α = −1.4) over the 11 magnitudes sampled, but the slope and shape depend on color. A large population of faint low surface brightness galaxies was discovered, representing the largest contributor (in number) to the luminosity function at faint magnitudes. We found a clear progression Based on observations obtained at the Canada–France–Hawaii Telescope and in part at theHubble Space Telescope