Starburst & Active Galaxies
Star-burst and Seyfert galaxies (AGN) represent two inter-related facets of activity in galaxies. Star-burst galaxies are so-called because their current star-formation rates (SFR) are so high that the available gas would all be consumed in a time much shorter than the age of the galaxy. Seyfert galaxies, and their more extreme cousins the quasars, are galaxies in which accretion on to the central black hole liberates huge amounts of gravitational energy, leading to the production of their characteristic strong, broad, and highly ionised emission lines. It is widely believed that star-formation provides the gas that fuels the accretion. At any one time around 10% of AGN are "radio loud" and produce twin, oppositely directed, relativistic jets carrying mechanical energy into the galaxy and its environment. This feedback to the environment, especially at redshifts of ~1-2 when the bulk of galaxy building happened, may even control their properties and explain, for example, why there is a tight relationship between black hole mass and velocity dispersion of stars in every galaxy. In the local universe there are plenty of examples of both star-bursts, AGN and even hybrid objects but this pales compared to the situation pertaining at high redshifts where the activity levels may be up to a factor 100 higher.
Our research covers nearby and distant star-burst galaxies, Seyfert galaxies and radio galaxies/quasars. The kinds of questions we are trying to answer are:
- How can the star-formation rates of galaxies be measured reliably?
- To what extent is star-formation triggered and regulated by AGN activity?
- Stellar feedback in star-burst dwarf galaxies: what drives the gas out of the disk into the halo and possibly into the intergalactic medium? what is the final fate of the gas?
- The physics of non-thermal AGN jets: what controls the maximum energy that electron can be accelerate? What is the velocity structure in the jet? How are jet properties related to the accretion history of the system?