Cosmological Simulation of Ellipticals Kobayashi (2004) MNRAS 347, 740 Chemodynamical GRAPE-SPH Model (Nakasato 2000) Hydrodynamics (Navarro & White 1993) Radiative Cooling (H0, He0, He+, He++, Z) Star Formation (converging, rapid cooling, Jeans unstable) Thermal Feedback (stellar wind, SNeIa, SNeII) Chemical Enrichment (stellar wind, SNeIa, SNeII) Cosmological Parameters (H0=50km/s/Mpc, Ωm=1.0, σ8=1.0)

ゴキブリ飼育中

Monolithic Collapse Kobayashi (2004) MNRAS 347, 740 The evolution in ±100kpc of dark matter (1st ), gas (2nd), stars (3rd ), V-luminosity (4th), And stellar metallicity (5th ) of the galaxy that forms monolithically. logZ/Zo=-1 to 0.4.

Major Merger @ z=2.0 Kobayashi (2004) MNRAS 347, 740 The evolution in ±100kpc of dark matter (1st ), gas (2nd), stars (3rd ), V-luminosity (4th), And stellar metallicity (5th ) of the galaxy that undergoes a major merger at z=2.0..

Monolithic Collapse Kobayashi (2004) MNRAS 347, 740 The star formation rate [log SFR (Mo/yr)] as a functions of time t (Gyr) in present day galaxies (r<20kpc, |z|<100kpc).

Metallicity Gradients Kobayashi (2004) MNRAS 347, 740 The metallicity gradients : [O/H] (thick line) and [Fe/H] (thin line)

Evolution of Metallicity Gradients Kobayashi (2004) MNRAS 347, 740 大規模な銀河の合体が発生する 場合には金属量の勾配は消滅し、 その後の星形成に伴って再度形成 される。初期の勾配よりも緩やかになる。 [O/Fe] [Fe/H] monolithic collapse 重力収縮に近い場合には初期に 金属量勾配が形成された後 ほぼ一定で推移する。 major merger

Metallicity Gradients Kobayashi (2004) MNRAS 347, 740 Observation (Kobayashi & Arimoto 1999) Non-major mergers Major mergers (b) (c) (a) Non-major merger : Major merger = 1 : 1

Merger History Indicator Kobayashi (2004) MNRAS 347, 740 The global properties of elliptical galaxies depend mainly on their masses, while their metallicity gradients are greatly affected by their merging history. A major merger makes the gradient shallower. Therefore, merging histories can be inferred from the observed metallicity gradients of present-day galaxies. Available observations for nearby galaxies suggest that there exist non-major merger galaxies and major merger galaxies half and half. The observed variation in the metallicity gradients cannot be explained by either monolithic collapse or by major merger alone. Instead, it is reproduced well in the present model in which both formation processes arise under the CDM scheme.

Scaling Relations Kobayashi (2005) MNRAS 361, 1216 high SFR low SFR 有効半径、星の金属量の光度平均と銀河の絶対光度の関係

Scaling Relations Kobayashi (2005) MNRAS 361, 1216 FJ K

Z-M* Relations Kobayashi (2005) MNRAS 361, 1216 Compared with observations, the mass- metallicity relations are weak, with shallower sloe and larger scatter in the simulations, although the average is consistent. These are because the thermal feedback of supernovae is not enough to stop star formation in the SPH simulation. Takagi et al. (2004) Yamada et al. (2006)

Mass-to-Light Ratio Kobayashi (2005) MNRAS 361, 1216

Fundamental Plane large scatter ! Bender et al. (1993) Kobayashi (2005) MNRAS 361, 1216 Face-on-View: No correlation between the masses and surface brightness. large scatter ! Obs: Pahre(1999) Bender et al. (1993) Edge-on-View : Simulated galaxies follow the observed relation with shallow slope.

Scatter along the FP major merger galaxies non-major merger galaxies Kobayashi (2005) MNRAS 361, 1216 major merger galaxies non-major merger galaxies 基準平面の分散はマージングの 歴史を反映している。 大規模な合体を経験した銀河は 大きな有効半径と暗い表面輝度 を持つ傾向にある。けれども、 速度分散と光度はあまり変化しない。

Origin of the Fundamental Plane Kobayashi (2005) MNRAS 361, 1216 光度/力学的質量 merger & multiple merger dwarf ellipticals 観測 monolithic & assembly 力学的質量 基準平面の傾きは金属量、年齢、ダークマターの量によって決まっている。 もっとも大きなファクターは金属量である。κ１＞3.5にある巨大楕円銀河の 年齢は１０Gyrでほぼ一定であるが、小さな銀河には金属量が高く 同時に年齢が若いのでκ３が小さいものもある。力学的な光度/質量比は 大質量の銀河程小さい、これはFPとは逆センスである。