Cosmological Simulation of EllipticalsCosmological 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 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 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 Monolithic Collapse

Kobayashi (2004) MNRAS 347, 740

The star formation rate [log SFR (Mo/yr)] as a functions of time t (Gyr) inpresent day galaxies (r<20kpc, |z|<100kpc).

Metallicity Gradients Metallicity Gradients

Kobayashi (2004) MNRAS 347, 740

The metallicity gradients : [O/H] (thick line) and [Fe/H] (thin line)

Evolution of Metallicity Gradients Evolution of Metallicity Gradients

Kobayashi (2004) MNRAS 347, 740

monolithic collapse

major merger

[Fe/H]

[O/Fe]

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。

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。

Metallicity Gradients Metallicity Gradients

Kobayashi (2004) MNRAS 347, 740

(a)

(b)

(c)

a) Observation (Kobayashi & Arimoto 1999)b) Non-major mergersc) Major mergers

Non-major merger : Major merger = 1 : 1

Merger History IndicatorMerger 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 observedmetallicity 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 Scaling Relations

Kobayashi (2005) MNRAS 361, 1216

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

high SFR low SFR low SFR

Scaling Relations Scaling Relations

Kobayashi (2005) MNRAS 361, 1216

FJ

K

Z-M* Relations Z-M* Relations

Kobayashi (2005) MNRAS 361, 1216

Compared with observations, the mass-metallicity relations are weak, with

shallower sloe and larger scatter in thesimulations, although the average isconsistent. These are because the

thermal feedback of supernovae is notenough to stop star formation in the

SPH simulation.

Yamada et al. (2006)

Takagi et al. (2004)

Mass-to-Light RatioMass-to-Light Ratio

Kobayashi (2005) MNRAS 361, 1216

Fundamental PlaneFundamental Plane

Kobayashi (2005) MNRAS 361, 1216

Bender et al. (1993)

Face-on-View: No correlation between the masses and surface brightness.

Edge-on-View : Simulated galaxies follow the observed relation with shallow slope.

Obs: Pahre(1999)

large scatter !

Scatter along the FPScatter along the FP

Kobayashi (2005) MNRAS 361, 1216

major merger galaxiesnon-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

Origin of the Fundamental Plane

Kobayashi (2005) MNRAS 361, 1216

力学的質量

光度 /力学的質量

観測monolithic & assembly

merger & multiple mergerdwarf ellipticals

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。 κ １＞ 3.5 にある巨大楕円銀河の

年齢は１０ Gyr 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 κ ３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。