The formation and evolution of galaxies in a cold dark matter universe

• Main Author: Groom, W.
• Published: University of Cambridge 1997
• Subjects: 520
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599748

The field of galaxy formation is as rich and diverse as the many disciplines encompassed by it. A comprehensive theory must encapsulate structure formation and evolution on scales as small as stars, whilst simultaneously illustrating the natural occurrence of the physical conditions required, from the cosmological perspective. Whilst current analytical techniques have been highly successful in quantifying the bulk properties of a galaxy population evolving within some cosmological scenario, to trace the detailed evolution of individual objects requires the use of numerical codes. This thesis represents a study of the formation and evolution of galaxies within the context of the popular Cold Dark Matter model (Peebles 1982), and using the technique known as Smoothed Particle Hydrodynamics (SPH). I investigate the detailed history of a galaxy as it forms and evolves hierarchically from the many sub-units the cosmology prescribes, and makes direct comparisons of the results thus obtained with the wealth of data available in this field, both at high and low redshift. The series of simulations presented confirm the long suspected link between absorption phenomena in the spectra of QSO's at high redshift, and the present day population of field galaxies, a result which is insensitive to my implementation of star formation and/or feedback processes. From a series of simulations in which various physical ingredients are gradually included, I am also able to conclude that feedback from the stellar population must have been an important ingredient in the formation of field galaxies, in order to ensure that a significant portion of the stellar population is assembled towards low redshifts, reducing the bulge-to-disk ratios otherwise obtained. My models are able, when feedback is included, to qualitatively reproduce many features of the observed galaxy population, such as the Tully-Fisher relation, which I discuss in the context of a universal density profile, as well as the chemical abundances of galaxies both at high redshift (as observed in damped Lyα systems), and at low redshifts (as appropriate to local field galaxies). I furthermore present a solution to the so called <I>angular momentum</I> <I>problem</I> previously discussed by various authors, via the (necessary) inclusion of <I>both</I> star formation <I>and </I>feedback from the resulting stellar population.