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24 February 2012

MaGICC Disks: Matching Observed Galaxy Relationships Over a Wide Stellar Mass Range

In this paper (link) the authors demonstrate that using their feedback model (note this is just stellar feedback : supernovae + heating from massive stars) in cosmological zoom simulations results in galaxies that match observed relations between a wide range of properties. A key aspect of this result is that the simulations also reproduce the way these relations scale with stellar mass, suggesting that their feedback model has a realistic efficiency over 2 orders of magnitude in stellar mass. The authors claim that it is the amount of outflow they get in their models that allows them to get the correct mass dependence. They also show that this level of outflow is supported by OVI absorption line observations (which can indicate the radial extent of metal rich gas that has been ejected from a galaxy).

1 comment:

  1. The main difference with a ‘typical’ SN feedback recipe that the paper outlines seems to be the addition of a model to mimic the effect of radiation pressure from massive stars (10^52 ergs are added as thermal energy over periods of ~1Myr). However, one must refer to other papers by the same authors, to see specifically how this model differs from their previous ones, so it is hard to immediately appreciate what changes in the model have produced the dramatic improvements in matching to observations. In fact, it seems there are 3 additional changes: to the IMF, the star formation density threshold and the SN energy.

    The idea that the outflows are the key to matching properties is central to the paper, but it is somewhat unclear which aspects of their updated model actually result in these stronger outflows.
    For example, what role in boosting the outflows, if any, is played by the addition of heating by massive stars (which at first glance seems to be the main difference with typical models)?
    Could changing just one parameter e.g. the IMF (which I believe is Chabrier) have boosted the outflows to the required level, or are all the changes required in combination to get this result?
    In summary, are all the changes required together to get the strong outflows or do some aid the outflows and others ‘fix’ the other galaxy properties?
    Perhaps this is covered by a more detailed parameter study in an earlier paper?