ProfessorScott Croom

I have PhD projects available in two broad areas:

1. Resolving Galaxy Evolution

We aim to answer some of the outstanding questions in the physics of galaxy formation by using integral field spectroscopic instrumentation, such as the Sydney-AAO Multi-object Integral field spectrograph (SAMI), Hector and MUSE.   We will obtain spatially resolved spectroscopy of thousands of galaxies and then carry out detailed comparisons to the latest and most detailed numerical models for galaxy formation.

The overwhelming difficulty in understanding galaxy formation is the complexity of baryonic physics, with multi-phase gas, star formation, dust, supernovae, super-massive black holes etc. all influencing the outcome of the galaxy formation process.  It is critical to gain spatially resolved spectroscopic data for large numbers of galaxies, in order to understand this complexity.

In this project, we will address many of the most pressing current issues in galaxy evolution, by carrying out large-scale studies providing resolved maps of galaxy emission. Such samples have the potential to profoundly impact the field of galaxy formation by addressing the physical processes at work. These lie in three key areas:

• How does a galaxy’s environment influence its evolution?  Galaxies have very different properties, depending on whether they lie in high-density clusters or more rarified void regions.  By studying the internal motions of gas and stars, as well as the spatial distribution of star formation within galaxies, we can directly tackle the question of how environment modulates galaxy formation.
• How does gas get into and out of galaxies?  The formation of stars depends critically on the supply of gas (the fuel for star formation) within a galaxy.  By studying the distribution, motion, chemical composition and ionization state of the gas we will be able to find when galaxies are most efficiently fuelled and when feedback from supernovae or black holes drives gas out of galaxies.
• How is mass and angular momentum built up in galaxies?  By measuring internal galaxy motions we can estimate galaxy masses and determine which galaxies form from mergers (typically dispersion dominated) or smoother accretion (typically rotation dominated).  The distribution of galaxy spins in voids, filaments and clusters is a powerful probe of how galaxies acquire their angular momentum as a consequence of early tidal torques.
  
  

2. The Cosmic Growth of Super-Massive Black Holes

In the heart of every massive galaxy is a super-massive black hole (a million to a billion times the mass of the Sun) that is built up in mass over cosmic time by gas accretion. Using recently completed observations of thousands of accreting black holes over most of the age of the Universe; this project aims to measure the evolution of accretion in a number of different modes.

The black holes at the centre of each galaxy have a profound impact on galaxy evolution. As gas accretes onto these black holes, it radiates energy, and may power relativistic jets. The energy from the radiation or jets can be deposited into the inter-stellar medium of the galaxy in question, heating the gas, and suppressing star formation. When the accretion is radiatively efficient, the accreting black holes can be seen over most of the observable Universe as quasars. When only the jets are visible, we observe the systems as radio galaxies, as the relativistic jets emit via the synchrotron process.

We are building large data-sets containing thousands of quasars and radio galaxies with the express aim of measuring how they evolve and what the physical processes are which drive the evolution. We can do this by studying how individual sub-populations evolve, what their environments are and the how the black holes interact with their host galaxy. We will build on this with a broad range of multi-wavelength observations (from X-ray to radio) using state-of-the-art astronomical facilities in Australia and overseas.

There are a number of projects available in this field including: detailed comparison of the evolution of accretion to current galaxy formation models; measuring the age of radio galaxies with multi-wavelength radio data; addressing how much accretion is obscured from our direct view by gas and dust; measuring the environments of quasars and radio-galaxies; understanding how accretion changes through time-domain observations and many more.