Friday, 27 November 2009
Friday, 20 November 2009
March), Moster et al. use (something like) an abundance-matching
technique to match galaxies to halos. The paper focuses mostly on
z=0, but they also show results for higher redshifts, where they use
stellar mass functions from Drory and from Fontana.
This figure shows the average stellar mass as a function of halo mass
at different redshifts. I've drawn a line that shows the what a
constant ratio would look like. The highest ratio (which means the
highest efficiency for putting baryons in stars) for the z=0 curve
appears at a stellar mass of log(M)~10.5, and increases with
redshift. Another thing to notice is that the curves evolve strongly
at lower masses, and cross at higher masses. This means that, at
lower masses, galaxies grow in mass much faster than their halos. But
at higher masses halos grow faster than galaxies.
Friday, 6 November 2009
In astro-ph/0911.0891, Marie Martig and Frederic Bournaud report on the growth of bulges in disk like galaxies in a cosmological environment. The zoom in on a Milky-Way like halo in cosmological box that had a quiet merger history, to make it prone to disk formation. They include baryonic physics, including star formation, but excluding supernova feedback. In one simulation they add the mass loss of older stellar populations in a relatively simple way. They let the stars loose an amount of mass that is typical for a Salpeter IMF (~45% of the SSP mass is returned in total). This lost gas mass adds to the disk and makes disk survival (and a smaller bulge fraction) a lot easier. The disk becomes more stable to both internal instabilities and to minor mergers.