GALACTIC SATELLITE GALAXIES

In this thesis, we investigate the luminosity functions (LFs) and projected number density profiles of galactic satellites around isolated primaries of differing luminosity. To this end, we develop a new method to select isolated galactic satellite systems using the Sloan Digital Sky Survey (SDSS) spectroscopic and photometric galaxy samples. For specific luminosity primaries, we are able to stack as many as ~ 50,000 galaxy systems to obtain robust statisitcal results. Based on these samples, we derive accurate satellite luminosity functions extending almost 8 magnitudes fainter than their primaries and accurate projected number densities profiles of satellites down to 4 magnitudes fainter than their primaries. Then, we determine how the satellite luminosity functions and projected number density profiles vary with both the properties of their satellites and their primaries. In addition, we find that the normalized profiles can be well fitted by the NFW profiles in most cases. The dependence of the NFW concentration parameters on the luminosity of the satellites and their primaries are explored. Inspired by the similar independent study, we also explore the dependence of estimates of satellite luminosity functions on two different background subtraction methods. We then measure these quantities for model satellites placed into the Millennium and Millennium II dark matter simulations by the GALFORM semi-analytic galaxy formation model for different bins of primary galaxy magnitude. We compare our model predictions to the data that we previously measured. The generally successful comparison of the GALFORM model with the SDSS data performed here provides a non-trivial validation of the assumptions and framework of this kind of modelling.