Tuesday, July 2, 2013

Wagner, A. Y.; Bicknell, G. V.; Umemura, M.; Driving Outflows with Relativistic Jets and the Dependence of Active Galactic Nucleus Feedback Efficiency on Interstellar Medium Inhomogeneity

Driving Outflows with Relativistic Jets and the Dependence of Active Galactic Nucleus Feedback Efficiency on Interstellar Medium Inhomogeneity
by: Wagner, A. Y.; Bicknell, G. V.; Umemura, M.
[arXiv:1205.0542, pdf, First author, second, third]
I noticed this paper because the second author on it has also written several papers with Jackie Cooper, whose research forms the jumping off point for my own work. There are many things about the set up to this problem that mirror what was already done by Cooper and Bicknell in previous papers. So they drew upon years of previous work to create this set of simulations that form the foundation of this paper. Having taken all the tools and mechanics that were developed previously all they had to do was modify it for this specific problem and let it run. No need to reinvent the wheel. If you take a glance at this paper you may not realize the large amount of work that went into setting up this problem by many other people before this problem was solved. This is the way almost all science works and this is how I have done a lot of my work. As one of my former professors would say, "A lazy physicist is a good physicist!"

They use the code FLASH in its relativistic hydrodynamics configuration to do a series of simulations of relativistic jets streaming off of an AGN and into the local ISM. They use a fractal distribution to create the initial density of the warm phase ISM (~104K). The rest is hot gas (~107K). Their study consists of 29 different simulations, where 15 of those were done for this paper and the rest were included in a previous paper. In their different simulations they tested different parameters such as the jet pressure, the density of the hot phase medium, average density of warm phase, volume filling factor of warm phase, maximum cloud size, total mass in warm phase, and other parameters that depend of the sampling wavenumber (effectively a measure of the fractal scale relative to the overall size of the fractal cube).

In this paper they are looking at the potential for galactic feedback, effectively a measure of how much of the energy in the AGN gets transferred into the warm ISM, thereby dispersing the clouds. They find that the feedback is sensitive to the maximum cloud size but not so much the filling factor. In order to determine the veracity of their findings they compare the velocity dispersion of the ablated clouds with observations of galaxies with radio lobes (i.e. those that have powerful AGN jets).

I thought that this paper was interesting since it deals with something close to what I am doing, with similar problems, methods and solutions. I will definitely use it as a reference for references, ideas and ways of organizing my own simulations. There are some questions that they explored here and things that they calculated or measured that I will definitely consider including in my own work.