Study on the potential and limitations of numerical simulations of galaxy formation, by developing a novel method for scanning their parameter space
Final Report Abstract
In this project we have shown that both hydrodynamical simulations (HYDs) and semi-analytic models of galaxy formation (SAMs) can be united into one formalism. This hybrid method is able to include the physics from both methods, and could help in develop new models that better fit the observational data. We have proved that the problem of galaxy formation could be handled at various scales, where the simplest models (i.e. SAMs with only one phase of gas) deal with only a couple of numbers per a galaxy, and could be easily tuned against observations. Nonetheless, these simple models could also be tuned to agree with very complex models (i.e. HYDs). Matching models of very different complexity could be useful to extend our knowledge of galaxy formation. For example, it is possible to adopt one physical ingredient from one method (e.g. cooling rates from a HYD), and incorporate it within the other method. It also allows us to use the simplicity of SAMs in order to find the set of models that could match observations, and apply these models within a HYD. Interestingly, the current physical implementations within HYDs are different from the assumptions used within SAMs, and could already by adopted from our current study. In a different project, we have explored the constraints on the dark-matter content around galaxies, by using a combination of various observations including weak gravitational lensing, stellar mass function, and the twopoint auto-correlation function. We have shown that our method is able to find a large range of models that fit the same constraints, with a large range in the relation between the mass of galaxies and their host haloes. Unlike previous studies, we have shown that weak lensing provides a poor constraint on the dark-matter content around galaxies, mainly because of the degeneracy between satellite and central galaxies. This is also true for the number-fraction of satellite galaxies out of all galaxies of a given stellar mass. In addition, the population of black-holes (BHs) and active galactic nuclei (AGNs) was studied. Here we have used a state-of-the-art SAM, with a population of galaxies that matches the recent observational constraints in terms of stellar mass, star-formation rates, clustering, and evolution with redshift. Assuming that galaxies are the backbone for growing BHs, we have tested which scenario for BH accretion allows the model to match the luminosity function of AGNs, the mass function of BHs, and the relation between star-formation rates (within galaxies) and AGN luminosity. We have found that the simple merger scenario is able to simultaneously explain all these observational constraints. This finding was used to interpret the duration of BH accretion events, their relation with bursts of starformation, and their evolution with redshift. Our model is showing several predictions for the relation between BH mass, AGN luminosity, and the star-formation rate of the host galaxy.
Publications
- 2012, MNRAS, 421, 3579
Neistein, E., Khochfar, S., Dalla Vecchia, C., Schaye, J.
- 2012, MNRAS, 425, 2854
Agarwal, B., Khochfar, S., Johnson, J. L., Neistein, E., Dalla Vecchia, C., & Livio, M.
- 2013, MNRAS
Neistein, E., Khochfar, S.
- 2013, MNRAS
Neistein, E., Netzer, H.
