The Evolution Of Massive Disc Galaxies With Environment And Redshift
Creators: name: Bamford, Steven Peter
Publisher: name: Zenodo
Year: 2006

description: This thesis examines the evolution of massive disc galaxies as a function of cosmic time and environment by analysing a sample of luminous disc galaxies, located in the field and rich clusters at intermediate redshifts.  The data utilised for this study are two-dimensional optical spectra obtained with the FORS2 instrument on the VLT, along with imaging from a variety of sources.

We investigate evolution in the field using the Tully-Fisher relation (TFR) and interstellar gas properties of these galaxies.  A mild overall evolution is found, which appears to be slower than that derived bay studies of the overall field galaxy population. This suggests that the rapid evolution of the SFR density of the universe observed since z~1 is not in general driven by the evolution of the SFR in individual bright spiral galaxies.

The interstellar gas properties cover similar ranges to those observed across a large sample of local galaxies.  However, a fraction have oxygen abundances significantly lower than local galaxies with similar high luminosities.  The galaxies in this luminous, metal-poor subsample exhibit physical conditions similar to those of local faint and metal-poor star-forming galaxies. These galaxies must subsequently experience substantial evolution in luminosity and star formation rate.  The mild overall field evolution thus appears to be due to a combination of some galaxies undergoing substantial evolution, with the remainder changing little.

We find no evidence for a change in TFR slope with redshift, although this is not well constrained.  However, previous studies have used an observed correlation between TFR residuals and rotation velocity to argue that low mass galaxies have evolved significantly more than those with higher mass.  We demonstrate that such a correlation does not necessarily indicate a physical difference in the evolution of galaxies with different rotation velocity.

Matched samples of intermediate-redshift field and cluster galaxies are compared using the TFR and the properties of their interstellar gas.  While the distributions of basic properties are comparable for the two samples, we find evidence that the cluster galaxies are significantly brighter than those in the coeval field.  The cluster galaxies have specific star formation rates that are, on average, significantly lower than for the field galaxies.  However, a contrasting fraction appear to have much higher star formation activity, comparable to the highest seen in the field.  This implies a bimodality in the star formation activity of distant cluster galaxies, which is not present for our field sample.  In addition, star formation appears to be more centrally concentrated in the cluster galaxies.  We find no substantial differences in the long term star formation histories of these cluster and field galaxies, as indicated by their gas-phase metallicities.

The most likely explanation for these results is that spiral galaxies entering intermediate-redshift clusters generally experience a short-lived enhancement of their star formation rate, followed by a decline.