We present the combined Luminosity Function of five nearby Hickson Compact Groups. We identify at the faint end the dwarf galaxy group members using the red sequence of the Color Magnitude Diagram from our deep 2.2 m WFI photometry of Hickson Compact Groups 16, 19, 30, 31 and 42. We find that the Luminosity Function of compact groups shows a bimodal distribution of bright galaxies and a dwarf galaxy population as it is known for galaxy clusters, but not for field galaxies. From measuring the field to field variance of background galaxies fulfilling the red sequence criterion coincidentally, a lower limit for the significance of the dwarf galaxy peak in the Luminosity Function was derived. With this method we determined the dwarf galaxy peak to have a significance of more than 2.6σ. Thus, compact groups can be classified as bound systems like galaxy clusters, which also accommodate two galaxy populations. Hence, it seems less unlikely that compact groups are chance configurations of individual galaxies. Our result shows that compact groups are building blocks of galaxy clusters underlining a hierarchical model of structure formation and galaxy evolution. Further we note that the existence of a significant number of satellites in bound systems like compact groups is predicted by Λ Cold Dark Matter theory.

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The formation and evolution scenarios that led to the existence of Low Surface Brightness (LSB) galaxies are not well understood yet. Although LSBs have HI components with low surface densities (systematically below the Kennicutt criterion), they can be regarded as gas-rich in general. Hence, the key in understanding LSBs lies in the answer to the question what prevented them from sufficient star formation. Using the public data releases of the Sloan Digital Sky Survey (SDSS), we investigated the galaxy density around LSBs in comparison to High Surface Brightness (HSB) galaxies. We performed a number counting analysis in three dimensions within spheres of several radii on a sample of HSBs and LSBs with well measured SDSS redshifts. On scales between 2 and 5 Mpc our results show significantly lower galaxy densities in the vicinity of LSBs compared to HSBs. At larger scales than 5 Mpc LSBs and HSBs share the same clustering properties but on scales below 2 Mpc the galaxy densities in the neighbourhood of LSBs lie systematically (but only with a slight significance) below that of HSBs. In the pie slice diagrams LSBs favour the outer rims of the filaments of the Large Scale Structure and some LSBs are even found in voids. These results give strong evidence to a formation and evolution scenario where LSBs were formed in low density environments. Hence, the lack of tidal interactions with companions must have caused the absence of an effective trigger for a sufficient starburst. Baryons in Dark Matter PoS(BDMH2004)025The enviroment of Low Surface Brightness Galaxies Stefan Dominik Rosenbaum • (right) are plotted containing a total of ∼800 LSB galaxies (black dots) and ∼16000 HSB galaxies (green/grey dots).