The Evolution of Massive Star-forming Galaxies: Energetics and the Interstellar Medium

Abstract

Over the last ~20 years, the importance of dusty star-forming galaxies in contributing approximately half the energy density of the Universe has been realised. Much research in this field has focused on the subset of submillimetre bright galaxies (SMGs). Submillimetre
Astronomy has recently seen major advances due largely to huge developments in the available instrumentation. In this thesis I present the first spectroscopic redshift distribution of unambiguously-identified SMGs, targeted with ALMA. The redshift distribution is shown to peak at z~2.4. The next step to understanding the SMG population is to use their redshifts to facilitate high-resolution follow-up observations, probing the conditions and physical structure within the interstellar medium (ISM) of these systems. I present the detailed observations of the ISM within the gravitationally lensed SMG, SMMJ2135. In particular, the spectral line energy distributions of 12CO,
13CO and C18O are measured and used to infer the temperature, densities and chemical abundances within this
intrinsically representative SMG, with strong variation found between the multiple kinematic components in the galaxy. Furthermore, an unusually high abundance of C18O is measured, implying the presence of preferentially massive stars, perhaps highlighting some differences between star formation locally and at high-redshift. The cosmic star-formation rate density has rapidly declined since
z~2 and there is much evidence to suggest that massive
star-forming galaxies at z~2 may evolve into massive passive
elliptical galaxies at z=0. I investigate the potential influence of active galactic nuclei (AGN) on the suppression of star formation within massive elliptical galaxies over z=0.1-1.2. I determine that the hot gas within these evolved systems does not cool as rapidly as
expected and demonstrate that heating due to mechanical feedback from radio AGN is more than sufficient to balance the X-ray cooling of hot gas, thus suppressing further star formation.