Feedback by relativistic jets, Gigahertz Peak Spectrum and Compact Steep Spectrum radio galaxies
In previous work (Bicknell et al. 2018) we have shown how the properties of Gigahertz Peak Spectrum (GPS) and Compact Steep Spectrum (CSS) radio galaxies may be explained in terms of free-free absorption of the radio emission by dense, warm clouds in the interstellar medium. It is feasible that these sources represent feedback in general in elliptical galaxies and this is an avenue of research that we are following at the present time. The aim of this project is to significantly extend this work in the following directions:
- Improve the model for the galactic potential and the warm ISM.
- Include the dynamical effects of magnetic fields both in the jet and ISM.
- So far the simulations we have carried out have not driven the outflows to escape velocity. Is there a combination of jet power and warm ISM density that is compatible with the constraints provided by GPS and CSS sources and in which the ISM is driven to escape velocity.
- On the other hand it may be the effects of a photoionizing source, warming clouds and making them more tenuous, that makes the jets more effective in dispersing them.
- Incorporate models of synchrotron and inverse Compton cooling in the non-thermal plasma in order to calculate the radio and X-ray spectra of the modelled sources.
- Calculate the rotation measure of the radio spectrum.
Not all of these topics would be attempted in one PHD thesis but a selection of the above would be feasible.
The impact of ultrafast outflows in evolving galaxies
The discovery of ultrafast outflows (see e.g. Tombesi et al. 2010; Tombesi 2016) in galaxies with an active nucleus has laid open the possibility of important feedback being powered by winds from accretion disks. We have published one paper on this subject (Wagner et al. 2013) but there is much more work to be done in this field, including:
- Incorporation of the dynamical effect of magnetic fields
- Driving of fast atomic and molecular outflows by ultrafast outflows.
- Are outflows driven to escape velocity?
Positive vs negative feedback
To a large extent our research has concentrated on negative feedback – the termination of star formation via AGN-induced outflows. However, at redshifts z > 2, jet stimulated star formation (i.e. positive feedback) may be important and the aim of this project would be to distinguish between the two. This would involve:
- Collaborating on a computational module to incorporate self-gravity into the PLUTO MHD code
- Running simulations of jet/wind interactions, including self-gravity in order to assess the relative importance of negative and positive feedback.