1: Hokkaido Uni., 2: NROJ, 3: Hokkaigakuen Univ. Two modes of star formation in the Galaxy derived by the Galactic archaeology Shimako Yamada1 Takuma Suda2 Yutaka Komiya2 Masayuki, Y. Fujimoto1, 3 1: Hokkaido Uni., 2: NROJ, 3: Hokkaigakuen Univ.

Galactic Archeology Near Field Cosmology Extremely Metal-Poor (EMP) stars ([Fe/H] ≲ -2.5) = “Messengers from the early universe” Stars formed in the proto-galaxy in the early universe. and low-mass stars are still alive near to us. Most iron-poor star [Fe/H]=-5.6 ? I also would like to talk about extremely metal-poor stars and the cosmology with these stars as a probe. These EMP stars were formed in the proto-galaxy in the early universe, and low mass stars still survive and are alive in the Milky Way. So, we can call them “messengers from the early universe”. From them, we can investigate the Formation and evolution of stars in the early universe, Nature of first stars and first supernovae, & Galaxy formation process. Formation and evolution of stars in the early universe Nature of first stars and first supernovae Galaxy formation process ⇔ IMF WMAP SUBARU 2

星の組成比から何がわかるのか？ IMF IMF 星形成率 星形成率 High-  Type II SNe が多い  星形成率高い [X/Fe]平均値の変動差: 星形成率 IMF 超新星のFe依存性 星形成率 (Type Iaの寿命より短い) low-[Fe/H] の場合 Fe生成小・寿命短い  Type II SNe が多い  星形成率高い High-  Type Ia SNe が多い  星形成率低い Low- x ~100 Fe生成大・寿命長い 全ての元素に対して平均値の変動差が等しい ② Supernova(SN) yields with metallicity dependence IMF 超新星のFe依存性 必ずしも全ての元素に対して平均値の変動差は等しくない

本研究 Milky WayのEnrichment history (鉄の増加に伴う星の組成比の変動) を調べる 星の元素組成の空間分布を調べた SAGA database (http://saga.sci.hokudai.ac.jp) のデータ(星の元素組成,　位置,　速度)を使った 解析で得られた、星形成率, IMF, の情報から銀河形成過程を考える

Enrichment history of Carbon Welch’s t-test: 2つの母集団の平均値の有意差を 検出する統計テスト 2σ [C/Fe] t-value 平均値[X/Fe]m の差 平均値の差の誤差 平均値 [Fe/H] ⋍ -2.2 :有意水準2σを越える変動 at and -1.8 (which we call “break”) at which [C/Fe]m changes statistically significantly Welch’s test is the statistical test of difference between two population means. I perform the Welch’s test to see the statistical difference of mean [X/Fe] between adjacent metallicity bins of 0.3dex. Welch's t-test defines the statistic t-value by this equation; This upper figure shows the enrichment history of C as a function of metallictiy, And lower panel shows the t-value as a function of metallicity. Mean values of [C/Fe] between adjacent metalictiy bins show significant differences, we call ‘break’, over 3σ at [Fe/H]=-2.2 and -1.8. And also in the case of high-resolution data measured by R>20000m the similar breaks also appear. 3σ [Fe/H] ⋍ -1.8, -2.2 において有意水準2-3σを越える平均値の変動を検出 0.3 dex [Fe/H] bin 0.4 dex [Fe/H] bin 0.25 dex [Fe/H] bin [Fe/H]

異なる[X/Fe]aveで特徴づけられた4つの種族 [Fe/H] ⋍ -1.8,-2.2,-3.2 で有意な平均値の差を検出 [X/Fe]ave (dex) Mg Si Ca Ti II Ni Co Zn Pop IIa 0.34 0.43 0.29 0.32 0.00 0.45 0.44 UMP [Fe/H] <-3.2 Pop IIb 0.38 0.36 0.33 0.28 0.21 EMP -3.2<[Fe/H] <-2.2 Pop IIc 0.42 0.39 0.31 0.01 0.12 0.09 VMP -2.2<[Fe/H] <-1.8 Pop IId 0.30 0.26 -0.05 - MP -1.8<[Fe/H] <-1 種族 主な支配領域 Next element is Ni. [X/Fe]ave ~ 0.1-0.2 dex の有意な平均値の差

有意な平均値の差：Δ[X/Fe]ave 星形成率低い  IMFの変化 or 超新星のFe依存性 Δ[X/Fe]ave at [Fe/H] ⋍ -1.8 Δ[X/Fe]ave at [Fe/H] ⋍ -1.8 (Pop IIc  Pop IId) - C, Mg, Si, Ca, TiII, Ni, Zn(ALL元素) - Δ[X/Fe]ave ⋍ - 0.1 (同程度) Δ[X/Fe]ave at [Fe/H] ⋍ -2.2 全ての元素に対して平均値の変動差が等しい 星形成率低い Δ[X/Fe]ave at [Fe/H] ⋍ -3.2, -2.2 (Pop IIa  Pop IIb  Pop IIc) - C, Co, Zn ([Fe/H] ⋍ -2.2;特定の元素) - Co, Zn ([Fe/H] ⋍ -3.2; 特定の元素) Δ[X/Fe]ave at [Fe/H] ⋍ -3.2 特定の元素に対して平均値の変動差が見られる  IMFの変化 or 　　 　 超新星のFe依存性

VMP:-1.8>[Fe/H]>-2.2 EMP:-2.2>[Fe/H]>-3.2 Distributions of stars along vertical distance from the Galactic disk (Z) MP MP:-1>[Fe/H]>-1.8 VMP:-1.8>[Fe/H]>-2.2 EMP:-2.2>[Fe/H]>-3.2 UMP:-3.2>[Fe/H] Concentrated VMP EMP Extended VMP, MP  Disk面に集中した成分 小　　　　　　　　[Fe/H]　 　　　　　　　大 EMP UMP, EMP Disk面から広がった成分 が現れる UMP

Δ[X/Fe]ave at [Fe/H] ⋍ -2.2 (Pop IIb  Pop IIc) [Zn/Fe]の空間分布 [Fe/H]=-2.2 [Fe/H]=-2.2 |Z|<500 pc |Z|>500 pc 0.1 dex UP Pop IId [Zn/Fe]=0 Pop IIb [Zn/Fe]=0.2 Δ[X/Fe]ave at [Fe/H] ⋍ -2.2 (Pop IIb  Pop IIc)  IMFの変化 　or　超新星のFe依存性  Disk面からの高さ(空間)に依存 Pop IIc [Zn/Fe]=0.1 Pop IIc [Fe/H] [Fe/H]

Hierarchical Galaxy Formation 1) ハローの衝突・合体プロセスによる銀河形成 Pre-Galaxy 中心ポテンシャル大 Early chemical evolution with Structure formation Top heavy IMF Binary Accretion of ISM First star Mini-halos ~106 M☉ With these effects peculiar to the early universe taken into account, now, we are trying to realize the total formation & evolution history of EMP stars, based on the current theory of structure formation, that the galaxies are formed through the merging of the smaller scaled cloud, We calculate the MDF of the EMP stars and our ingredients are early chemical evolution with Effect of structure formation Top heavy IMF Binarity, Change of element abundance by surface pollution. First stars were produces from out of the primordial gas and hence should be totally lack of the C and heavier elements. 2）Gas clouds moving in the gravitational fields of pre-Galaxy to be flattened & form disk-like structure. Gas, stripped off their host halos and trapped in Pre-Galaxy HERMES program (Hierarchical Evolution Researcher by MEtal-poor Stars) To realize the formation and evolution history of EMP stars 10

Two mode of star formation Pre-Galaxy Host-halo Pop IIc,Pop IId Pop IIa, Pop IIb Disk形成 High-mass/top-heavy Disk面から広がった成分 星形成サイト： Low-mass Disk面に集中した成分 星形成サイト： Low-mass or no top-heavy High-mass/top-heavy IMF IMF Host-halos Host-halos Pre-Galaxy Pre-Galaxy flattened & disk-like structures

Summary C, Mg, Si, Ca, Ti II, Co, Ni, Znの Enrichment histories を調べた [Fe/H] ⋍ -1.8,-2.2,-3.2 で有意な平均値の差(Δ[X/Fe]m)を検出 異なる[X/Fe]aveで特徴づけられた4つの種族 を同定 Δ[X/Fe]ave at [Fe/H] ⋍ -1.8 (Pop IIc  Pop IId) 全ての元素で同程度のΔ[X/Fe]ave~0.1 dex  星形成率低い Δ[X/Fe]ave at [Fe/H] ⋍ -2.2 (Pop IIb  Pop IIc) 特定の元素で変動が見られる　& 空間分布に依存  IMFの変化 種族 Pop IIa Pop IIb Pop IIc Pop IId UMP [Fe/H] <-3.2 EMP -3.2<[Fe/H] <-2.2 VMP -2.2<[Fe/H] <-1.8 MP -1.8<[Fe/H] <-1 IMF Top-heavy /High-mass Low-mass 空間分布 Disk面から広がった成分 Disk面に集中した成分 主な支配領域