The Role of Environment in Galaxy Formation

Abstract

In this thesis we investigate the influence that environment has on the formation and evolution of galaxies in the Galaxy And Mass Assembly (GAMA) survey. The highly complete equatorial regions of GAMA cover 180 square degrees of the sky, providing spectroscopic redshifts for 180,000 galaxies brighter than m_r = 19.8. GAMA is the largest multi-wavelength spectroscopic survey of its kind to date, designed to study aspects of galaxy formation on scales of <1 Mpc.
The dependence of the galaxy luminosity function (LF) on local environment is well described by linear relations with overdensity. The faint end slope of the LF is largely independent of environment but steepens in void regions. The environmental dependence shows little evolution over the last 3 Gyrs, and can again be parameterised by a linear relation when split by colour. The dependence of the LF on the cosmic web classification can be predicted from its dependence on overdensity and the distribution of overdensities within each cosmic web structure.
Observations from the GAMA survey can be theoretically interpreted by comparing to predictions made by the semi-analytic galaxy formation model of GALFORM through lightcone mock catalogues, which exhibit the same selection criteria as GAMA. Galaxy groups trace the underlying distribution of dark matter haloes in the Universe, and the use of galaxy group properties to infer the properties of dark matter, such as halo mass, is explored. Measurements of the galaxy density profile in galaxy groups in the GAMA survey and in the lightcone mocks suggest that the GALFORM model predicts the galaxy density profile to be too centrally concentrated. Comparisons to galaxy surveys such as GAMA lead to a bright future for the studies of galaxy formation.