Galaxies and their evolution

Stellar populations

Vivienne Wild, Rita Tojeiro

Knowledge of the star formation histories of galaxies is required in order to accurately determine their physical properties, such as stellar mass, and to help us understand the physical processes that cause galaxies to evolve over time. Examples of past projects include the accurate determination of star formation histories from spectra (e.g. with the VESPA code) and identification and characterisation of rare objects such as post-starburst galaxies.

Interstellar medium

Kenny Wood, Ian Bonnell

The interstellar medium or ISM is the vast reservoir of gas and dust that fills the galaxy and, as it coalesces, provides material for the next round of star formation. The properties of the ISM are determined by physical processes over a range of scales. St Andrews researchers have show how the densest phases of the ISM, star forming clouds, are born in the interactions of gas with a galaxy’s spiral arms. Stars themselves produce feedback such as radiation pressure, stellar winds, and supernovae events, which influence the physical conditions (density, temperature, chemistry, metallicity) in nearby clouds. Magnetohydrodynamic and radiative transfer simulations show how this can affect later star formation and alter the structure of the host galaxy over kiloparsec scales.

Shown is a simulation of a supernova detonation taking place within a star forming cloud. The supernova originated from a star of almost 96 solar masses located in a cluster forming within a dense filament of gas. This snapshot shows how, 86,000 years after the explosion, the cloud has been torn apart and formed low density escape channels. As a result, the stars in the main cluster, seen as the white points near the centre, are no longer accreting, while a nearby cluster to the upper right has remained embedded. Comparison with similar simulations in which earlier feedback in the form of ionization and stellar winds shows that in these cases the supernova’s effect may be greatly reduced.

Galaxy dynamics

Anne-Marie Weijmans, Vivienne Wild, Ian Bonnell

The dynamics of stars and gas in galaxies tells us about how they formed and evolved with time. With integral field surveys such as CALIFA and MaNGA, the kinematics of both the stars and gas in large numbers of galaxies can now be studied. Complementary to this are hydrodynamic simulations, that help us to interpret the observations. We post-process simulations to make mock observations, to compare directly with our survey datasets.

Active Galactic Nuclei

Keith Horne, Vivienne Wild

Many galaxies harbour active nuclei (AGN), where matter accreting onto a super massive black hole emits significant amounts of radiation. The group has a long standing interest in the technique of reverberation mapping, which beats resolution limitations of conventional observations to allow us to “see” into the central engine of the AGN. The group also works on the links between AGN and their host galaxies, to understand the impact of AGN on galaxy evolution.