The Luminosity Function in Groups of Galaxis

With targeted imaging of groups in the local volume, the regions of collapse around bright galaxies can be clearly identified by the distribution of dwarfs and luminosity functions can be established to very faint levels. In the case of the M81 Group there is completion to M_R ~ -9. In all well studied cases, the faint end slopes are in the range -1.35 < alpha < -1.2, much flatter than the slope for the bottom end of the halo mass spectrum anticipated by LambdaCDM hierarchical clustering theory. Small but significant variations are found with environment. Interestingly, the populations of dwarf galaxies are roughly constant per unit halo mass. With the numbers of dwarfs as an anchor point, evolved environments (dominated by early morphological types) have relatively fewer intermediate luminosity systems and at least one relatively more important galaxy at the core. The variations with environment are consistent with a scenario of galaxy merging. However it is questionable if the universal dearth of visible dwarf systems is a consequence of an astrophysical process like reionization.Comment: 4 pages, 4 figures. `A Universe of Dwarf Galaxies', 14-18 June, Lyon, Franc

Environmental Dependencies in the Luminosity Function of Galaxies

The evidence is becoming strong that the luminosity function of galaxies varies with environment. Higher density, more dynamically evolved regions appear to have more dwarfs per giant. The situation is becoming clearer as a result of wide field imaging surveys with the Canada-France-Hawaii and Subaru telescopes and spectroscopy of faint dwarfs with the Keck telescope. We report here on extensive observations of the small but dense NGC 5846 Group. The faint end of the luminosity function rises relatively steeply in this case.Comment: Proceedings IAU Colloq. 198 "Near-Field Cosmology with Dwarf Elliptical Galaxies" 6 pages, 4 figure