The Coma Cluster Luminosity Function from Ultraviolet to Near–infrared

The Coma cluster luminosity function (LF) from ultraviolet (2000Å) to the near–infrared (H band) is summarized. In the U V the LF is very steep, much steeper than in the optical. The steep Coma U V LF implies that faint and bright galaxies give similar contributions to the total U V flux and to the total metal production rate. The Coma U V LF is dominated in number and luminosity by blue galaxies, which are often faint in the optical. Therefore the Coma U V LF is dominated by star forming galaxies, not by massive and large galaxies. The optical Coma LF is relatively steep (α = −1.4) over the 11 magnitudes sampled, but its slope and shape depend on considered filter and magnitude. We found a clear steeping of the FL going from B to R bands, indicative of the presence of a large number of red dwarfs, as faint as three bright globular clusters. Furthermore, using Hubble Space Telescope images, we discover 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. The existence of these fake extended sources increases the steepness of the LF at faint magnitudes, if not deal on. This concern affects previous deep probing of the luminosity function, but not the present work. The near–infrared LF was computed on a near–infrared selected sample of galaxies which photometry is complete down to the typical dwarf (M * + 5) luminosity. The Coma LF can be described by a Schechter function with intermediate slope (α ∼ −1.3), plus a dip at MH ∼ −22 mag. The shape of the Coma LF in H band is quite similar to the one found in the B band. The similarity of the LF in the optical and H bands implies that in the central region of Coma there is no new population of galaxies which is too faint to be observed in the optical band (because dust enshrouded, for instance), down to the magnitudes of dwarfs. The exponential cut of the LF at the bright end is in good agreement with the one derived from shallower near–infrared samples of galaxies, both in clusters and in the field. The faint end of the LF, reaching MH ∼ −19 mag (roughly MB ∼ −15), is steep, but less than previously suggested from shallower near–infrared …