Semi-analytic Models based on Millennium II Haloes 1

Introduction to Millennium II Simulation Michael Boylan-Kolchin et al The comparison between Millennium I and Millennium II: higher resolution Mini-Millennium II: same resolution as Millennium I but same box size as Millennium II sql queries for Millennium II halo tree data Millennium IMillennium IIMini-Millennium II Particle number Particle Mass8.6×10 8 M h ×10 6 M h ×10 8 M h -1 Box size500 h -1 Mpc100 h -1 Mpc Output snapshots64 snapshots Between z=0 and snapshots Between z=0 and 127 Minimum halo mass1.7×10 10 M h ×10 8 M h ×10 10 M h -1 2

The halo mass functions between MI and MII simulations 3

The semi-analytic models The L-Galaxies models based on Millennium I haloes by De Lucia et al The inconsistency for the merger history of haloes smaller than M halo ~10 11 M at z=0 Resolution effect for galaxies smaller than M * ~ M Both the results based on Millennium I and II haloes predict too much small galaxies Stellar mass function from L-Galaxies at z=0 4

5 hot gas Cooling &Infall Star formation and evolution Feedback (reheating) Feedback (ejection) ejected gas reincorporation

The models by Guo Qi et al aims to solve the problem of too much small galaxies from the model results The changes to L-Galaxies model: 1.supernova feedback recipes The semi-analytic models 6

The changes to L-Galaxies model: 2. reincorporation recipe 3. other changes gas stripping, satellite disruption disk size recipes The semi-analytic models 7 Trace the change of angular momentum in gas infall, star formation, bulge formation, galaxy merger etc…

The mass functions at z=0 from Guo Qios model compared to the observational results 8

H 2 formation and star formation processes in Millennium II haloes Migrate my previous codes based on Millennium I haloes to Millennium II haloes Include the multiple ring Include the H 2 formation processes to get HI and H 2 components in Millennium II simulation Star formation rate Get the redshift evolution of gas (neutral and molecular), i.e. MZ relation as a function of z 9

Inconsistency for the results from different halo resolutions 10

The reason for the inconsistency from different halo resolutions 11

The reason for the inconsistency from different halo resolutions No gas consumption or metal production in small haloes based on Millennium simulation The H 2 proportional star formation law is more sensitive to the gas metallicity than Guo Qi and De Lucias recipe Inconsistency: earlier star formation processes in Millennium II scenario metallicity H 2 star formation gas consumption Possible solution: decrease the H 2 formation rate in small galaxies/haloes change the supernova feedback …. 12

Thank you! 13