The distribution of dwarf galaxies and black holes in the local cosmic density field
In the first chapter, which was the most independent work of all the thesis, a method was presented that allows the extraction of information about the luminosity function of a deep survey without redshift information. The method relies on the hypothesis that faint galaxies are clustered around bright ones, therefore two surveys were combined in order to extract a sample of galaxies with faint magnitudes and distance indicators. The 2dFGRS survey galaxies were used as centre galaxies, whereas the galaxies of the MGC catalogue were used as the satellite galaxies that exist around the bright centers.Eventhough the method proved accurate for luminosities in the M* range, the uncertainty at the faint end did not allow an accurate determination of a faint end slope for the luminosity function. An upper limit was given of a = —1.7 to the Schechter function fit at the faint end. This is an important result, since it provides an observational restriction to models of galaxy formation. Models that predict very steep slopes for the faint end and advocate the creation of a large number of low mass dark matter haloes are in contrast to this observation. In order to reduce the number of low mass haloes the models have to be altered in order to incorporate feedback processes that will restrict the creation of small galaxies.The faint end of the luminosity function is a very important part of any galaxy formation model. If calculated accurately, it will allow CDM theory to finally settle one of the biggest challenges that are facing it; namely the missing dwarf galaxies problem. Sufficiently deep and wide redshift surveys,that will allow the calculation of the LF directly in the faint end, have yet to become available. The method proposed in this thesis is a viable alternative if its accuracy is improved. In order to do so, a bigger number of objects is needed, which translates in to the need for larger survey but without any redshift information, something that is more than viable. Furthermore, some criteria can be imposed on the centre galaxies themselves. It would be interesting to separate the galaxies according to their type or their local environment and proceed to calculate the LF taking into account only certain types. The accuracy of the calculated LF should increase when galaxies in clusters are used as centres, thus ensuring that the galaxies observed in projection around them have a higher chance of being satellite galaxies in reality.Of farther interest would be to investigate the population of dwarf galaxies themselves according to their galaxy types. Further results from the MGC survey are expected and it will allow the separations in different populations. Different slopes of the faint end of the LF for different dwarf galaxy populations would allow better restrictions to galaxy formation models.The second chapter introduced the 2dFGRS bj and 7 7 colours extracted from the SCSS survey. It also provided a new formula for calculating the k-corrections for the ‘2dFGRS survey. The colours were shown to be very accurate and a good statistical indicator of galaxy type. This enhances the quality and information of the final 2dFGRS results and provides a powerful tool to the astronomical community.Using the Maggorian relation between the bulge luminosity and the black hole mass, the survey mass function was calculated and compared to similar work done using the more difficult to obtain relation between stellar velocity dispersions and black hole mass. The results were compatible in accuracy, which is further proof that the Maggorian relation is very accurate and can be used without introducing any bias.On the next chapter, the radio galaxies of the 2dFGRS survey were identified by cross matching the 2dFGRS with the NVSS radio survey. The final sample of ^ 3000 radio galaxies with colour and redshift information is one of the largest available and it allowed the calculation of the radio luminosity function with great accuracy. Investigation on the relation between black hole mass and radio output of galaxies did not reveal any direct relation. There was an indication of a relation of the form L Radl0 ~ MgJ, as was previously reported from workers in the field, but it was shown that this is probably due to selection effects and not any real relationship. The bivariate luminosity function calculated using the black hole mass and the radio luminosity of the galaxies indicated that the radio emission is independent of black home mass size, farther proof that the quoted relation between radio output and black hole mass is not real.There is a lot to be investigated in this chapter, especially regarding the origin of the radio emission. An effort was made to link H a luminosity to radio emission from star forming galaxies but the scatter in the relation made it difficult to have any solid conclusion. Identification of SF galaxies using only one feature of their spectra is not possible. It would be interesting to do a similar investigation taking into account more spectral lines or using galaxies with information on the IR spectrum. Isolating radio emission from AGN galaxies accurately could settle the question whether the radio emission is linked to the black hole or not.The final chapter introduced a local numerical density estimator based on Smooth Particle Hydrodynamics principles. The local density at each galaxy was calculated and separation of the 2dFGRS survey in different density areas became possible. The radio galaxy population was found to be similar to the normal galaxy population, regarding their placement in the local density field. This is strong indication that radio galaxies are not a product of a special process but simply a fraction of normal galaxies. There is indication of a small differentiation142 ill higher black hole masses and this should be investigated further. Examining the larger galaxies requires a deeper redshift survey. A next generation survey would allow a density estimator of real space density to be calculated instead of a redshift space. Using the 2dFGRS spectra does not allow for the calculation of peculiar velocities in order to eliminate redshift space effects but this should be made possible with more advanced surveys..