1. Fu Jian Max Planck Institute for Astrophysics, Garching 18/12/2012 1

2. Millennium Simulation: Springel et al. 2005 Millennium II Simulation: Boylan-Kolchin et al. 2009 The mass resolution of MS-II is 125 larger than MS: use to study dwarf galaxies and small galaxies at high z Millennium I (MS)Millennium II (MS-II) Particle number2160 3 Particle Mass8.6×10 8 M h -1 6.8×10 6 M h -1 Box size500 h -1 Mpc100 h -1 Mpc Output snapshots64 snapshots Between z=0 and 127 68 snapshots Between z=0 and 127 Minimum halo mass 1.7×10 10 M h -1 1.4×10 8 M h -1 2

3. Galaxy formation models including only cold gas phase in ISM (e.g DLB07, Guo11, Bower et al. 2006) Post-Processing models including molecular and atomic phase based on the outputs of models without two-phase gas (Obreschkow et al. 2009; Power et al. 2010) not self-consistent Models including the atomic-molecular transition and star formation processes throughout the calculation (Cook et al. 2010; Fu et al. 2010; Lagos et al. 2011) Trace the atomic and molecular gas radial profiles throughout the history 3

4. Multiple concentric ring for each disk The H 2 formation recipes H 2 prescription 1: Krumholz et al. 2009; Mckee & Krumholz 2010 H 2 prescription 2: Pressure related H 2 fraction recipe H 2 proportional star formation law Based on Munich L-Galaxies model by Guo et al. 2011 models with similar methods in Fu et al. 2010 (based on DLB07) 4

5. Leroy et al. 2008 Schruba et al. 2011 Genzel et al. 2010 for high z 5

6. Solution: Include the radial gas inflow Too much gas in outer disks flows inward to compensate too fast gas consumption in inner disk Too fast gas consumption in inner disk because of star formation and SN feedback Improper gas surface density profiles compared to the observations 6

7. Galaxy chemical evolution models with radial gas inflow: Lacey & Fall (1985), Portinari & Chiosi (2000), Spitoni & Matteucci (2011), Schönrich & Binney (2009) etc. Physical Mechanisms: The mixing of cooling gas with existant disk gas causes the change of specific angular momentum of gas disk Suppress the increase of specific angular momentum of gas disk caused by the difference of the gas consumption at different radius Assumption: 7

8. Bigiel et al. 2012 8

9. DLB07 & Guo11: all metal from star formation mix with cold gas, supernova reheat cold gas and metal into halo hot gas too high gas metallicity in inner disk region too shallow gas metallicity radial gradients compared to observations (e.g Moran et al. 2012) New model: metal from SN directly mix with halo hot gas; metal from AGB star mix with disk cold gas flatter gas metallicity gradients 9

10. 10

11. Moran et al. 2012 :174 galaxies with M * >10 10 M from GASS survey: Galaxies with larger M * tends to have flatter metallicity gradients Models give similar trends 11

12. Larger gas metallicity gradients in the unit of kpc: smaller galaxy has smaller disk size larger value for dZ/kpc Larger gas metallicity radial slope in dZ/r 90 : galaxy with larger M * larger bulge to disk fraction more galaxy merger history decreases the gas metallicity difference between inner and outer disk 12

13. Larger galaxies have larger size of (Leroy et al. 2008; Moran et al. 2012) 13

14. In the unit of r/r d, the size of and r d tend to be similar l SFR ~ l * ~l H2 (similar to results in Leroy et al. 2008) 14

15. 15 The inner disk has almost constant average HI surface density because of the transition between HI and H 2 Broeils & Rhee 1997; Swaters et al. 2002

16. Radial gas inflow can solve the problem of too fast gas consumption in inner disk and give proper gas surface density profiles when adopting H 2 proportional star formation law. The fraction of metal element directly mix with cold/hot gas components can affect the results of gas metallicity radial gradients. Smaller galaxies tend to have larger gas metallicity gradients Larger galaxies tend to have larger size of star formation rate surface density profiles, because all have similar tends. The HI disk size and HI mass: 16

17. 17