SPH Simulations of the Galaxy Evolution NAKASATO, Naohito University of Tokyo

No.2 GENSO (Galaxy EvolutioN with the SPH methOd) Our code for modeling the galaxy evolution GRAPE SPH Chemical Evolution Stellar feedback Cooling function

No.3 Star formation scheme SF : converting a SPH particle to a star particle SF model SPH particle creating a star (SSP) (SSP: single stellar population) decreasing mass of SPH particle ｔ t ＋ dt SF rate strongly depends on gas density! Dependence on temperature is weaker.

No.4 The Galactic Model (2) Starburst due to sub-clump merging Summary of NN2003 –Our model well fits the galactic bulge –the galactic bulge composed of two components –(a) merger component & (b) non-merger component dashed line : t form < 0.5 Gyr dotted line : t form >= 0.5 Gyr

No.5 Initial Model Catalog(1) Public database for researchers – –Program (modified version of GRAFIC), results, and parameter files etc. are all available for public use. 150 full chemo-dynamical models –LCDM cosmology with h = 0.65 –3 sigma sphere –M ~ 5 – Mo (R ~ 1.5 Mpc) –e gas = e star = 0.5 kpc, e dark = 1.0 kpc –spin parameter ~ 0.1 –z start ~ 24 to z end ~ 1.3 (5 Gyr)

No.6 Initial Model Catalog (2)

No.7 Initial Model Catalog (2) Well fitted : 100 galaxies

No.8 Initial Model Catalog (5) Global star formation history

No.9 Initial Model Catalog (4) Global supernova explosion rate

No.10 Summary for the first half –Analysis is underway. –Initial model dependence is strong. –Bulges seem good. –Disks tend to be smaller than the real ones. –We select 5 models for higher density re- simulations. –Global SFR has a peak at z~ 6-7. –Global SN Ia rate has a peak at z~3.

No.11 Face on view VB - V (red-yellow-blue) Initially: N sph ~ 60000, N dark ~ 60000

No.12 Several problems Too much star formation at early phase –Simple criteria for SF (1) cooling time < dynamical time (2) dynamical time < sound crossing time (3) flow is convergent –Poor numerical resolution (~ a few kpc) Supernova explosions are not effective –Poor numerical resolution

No.13 New model: chain reaction model SN explosions induce star formation –A SN explosion produce a shell –The shell contains ejecta mass –The shell is the site for next star formation Supernova explosion ISM Mixture of ISM and ejecta Tsujimoto, Shigeyama & Yoshii 1999

No.14 Chain reaction model details Gas cloud ~ 10 6 Mo (1)First stars formation 0.04% of the could mass (2)Next stars form in the shell 0.8% of the shell mass (3) Repeated Star formation

No.15 Further details of our model Star formation rates by this process Gas mass, stellar mass etc. evolve similarly

No.16 CD evolution with CR SF model What we newly have are multiple stellar population star particles!!

No.17 Results (1) Initial model : selected from our catalog –Seems to become a disk galaxy (ID 143) N sph ~ N dark ~ (M sph ~ 10 6 Mo) Evolve upto t = 0.9 Gyr (z~5.5) Chemical evolution for Fe & O –SN explosions heat up the gas particle –Break up when the reaction stops namely separation of “star particle” Resulted in effectively better resolution in mass and time.

No.18 Results (2) Obtained metallicity distribution function New model Old model

No.19 For disk galaxy formation models –Pop III star formation? (currently not modeled) –SN induced star formation Good for halo formation phase (early phase) Mechanism : shell fragmentation –Conventional SF Good for bulge & disk formation (late phase) Mechanism : cloud collapse Transition, connection, or relation? Star formation modes

No.20 Summary for the last-half Introducing sub-grid physics (chain reaction model) in our chemical and dynamical SPH code. Better time resolution in CE. Our new model shows better star formation history in the early universe. Future : we will have precise galaxy evolution models with the detailed chemical and kinematical information.