> Can somebody who knows about this tell me how much of the novelty in this is CS and how much physics?
It's a little bit of both. Over the past 5–8 years, some new numerical techniques ("moving mesh") have been developed (or at least first applied in astronomy) for hydrodynamic simulations[0,1]. These new techniques do a much better job of handling fluid instabilities, which can be important for properly simulating the gas in galaxies (which can have a huge range in densities and temperatures).
Also, people have developed what they call "cosmological zoom" simulations. In these simulations, you run a low-resolution (sometimes dark-matter only) simulation of a fairly large volume of the universe. Then you identify a particular dark matter halo at the end, that you think matches the type of galaxy you're interested in (say, a Milky Way type galaxy). Then you go back to the initial conditions, re-initialize it at very high resolution and include "normal matter" (baryons) and re-simulate the whole thing to study the formation of that particular dark matter halo and its associated galaxy.
Finally, the general increase in computing speed has allowed people to add in more physics to the simulations and run higher-resolution simulations. In this case, it is the addition of a physically-motivated model for energy injection into the gas in galaxies, from the ongoing star formation. This means energy from supernovae explosions and associated shocks, stellar winds, and momentum from scattering/absorption of photons by dust grains[2,3]. This more realistic set of models manages to reproduce the overall efficiency of star formation (what fraction of the gas gets turned into stars over some period of time) _and_ create a realistic temperature-density structure for the gas.
Now that people seem confident that these models can reproduce the overall star formation properties in galaxies, they are starting to see what this type of star formation / feedback model implies for the properties of galaxies. Of course, there's still lots of work to be done in making detailed tests of these models. While they reproduce the overall efficiency of star formation, we aren't yet sure if they can reproduce the shapes and sizes of galaxies. But people are working on that and we should know before too long...
It's a little bit of both. Over the past 5–8 years, some new numerical techniques ("moving mesh") have been developed (or at least first applied in astronomy) for hydrodynamic simulations[0,1]. These new techniques do a much better job of handling fluid instabilities, which can be important for properly simulating the gas in galaxies (which can have a huge range in densities and temperatures).
Also, people have developed what they call "cosmological zoom" simulations. In these simulations, you run a low-resolution (sometimes dark-matter only) simulation of a fairly large volume of the universe. Then you identify a particular dark matter halo at the end, that you think matches the type of galaxy you're interested in (say, a Milky Way type galaxy). Then you go back to the initial conditions, re-initialize it at very high resolution and include "normal matter" (baryons) and re-simulate the whole thing to study the formation of that particular dark matter halo and its associated galaxy.
Finally, the general increase in computing speed has allowed people to add in more physics to the simulations and run higher-resolution simulations. In this case, it is the addition of a physically-motivated model for energy injection into the gas in galaxies, from the ongoing star formation. This means energy from supernovae explosions and associated shocks, stellar winds, and momentum from scattering/absorption of photons by dust grains[2,3]. This more realistic set of models manages to reproduce the overall efficiency of star formation (what fraction of the gas gets turned into stars over some period of time) _and_ create a realistic temperature-density structure for the gas.
Now that people seem confident that these models can reproduce the overall star formation properties in galaxies, they are starting to see what this type of star formation / feedback model implies for the properties of galaxies. Of course, there's still lots of work to be done in making detailed tests of these models. While they reproduce the overall efficiency of star formation, we aren't yet sure if they can reproduce the shapes and sizes of galaxies. But people are working on that and we should know before too long...
[0] https://arxiv.org/abs/0901.4107
[1] https://arxiv.org/abs/1409.7395
[2] https://arxiv.org/abs/1311.2073
[3] https://arxiv.org/abs/1307.5639