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Shimako Yamada 1 Takuma Suda 2 Yutaka Komiya 2 Masayuki, Y. Fujimoto 1 , 3

Two modes of star formation in the Galaxy derived by the Galactic archaeology. Shimako Yamada 1 Takuma Suda 2 Yutaka Komiya 2 Masayuki, Y. Fujimoto 1 , 3 1: Hokkaido Uni., 2: NROJ, 3: Hokkaigakuen Univ. Galactic Archeology Near Field Cosmology. Most iron-poor star [Fe/H]=-5.6.

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Shimako Yamada 1 Takuma Suda 2 Yutaka Komiya 2 Masayuki, Y. Fujimoto 1 , 3

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  1. 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.

  2. GalacticArcheologyNear Field Cosmology Most iron-poor star [Fe/H]=-5.6 ? • Formation and evolution of stars in the early universe • Nature of first stars and first supernovae • Galaxy formation process ⇔ IMF WMAP SUBARU • 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.

  3. 星形成率 IMF 星の組成比から何がわかるのか？ [X/Fe]平均値の変動差: 超新星のFe依存性 (Type Iaの寿命より短い) low-[Fe/H] の場合 Fe生成小・寿命短い x ~100 星形成率  Type II SNeが多い 星形成率高い  Type IaSNeが多い 星形成率低い Low- High- 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

  4. 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

  5. [C/Fe] Enrichment history of Carbon 0.3 dex [Fe/H] bin • 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 0.4 dex [Fe/H] bin 0.25 dex [Fe/H] bin 平均値[X/Fe]mの差 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 平均値の差の誤差 t-value 3σ 2σ [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 [Fe/H]

  6. 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 • 種族 主な支配領域 [X/Fe]ave ~ 0.1-0.2 dexの有意な平均値の差

  7. Δ[X/Fe]ave at [Fe/H] ⋍-1.8 有意な平均値の差：Δ[X/Fe]ave 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

  8. 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

  9. [Zn/Fe]の空間分布 [Fe/H]=-2.2 [Fe/H]=-2.2 |Z|<500 pc |Z|>500 pc Pop IId [Zn/Fe]=0 0.1 dex UP 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 IIb [Zn/Fe]=0.2 Pop IIc [Zn/Fe]=0.1 Pop IIc [Fe/H] [Fe/H]

  10. Hierarchical Galaxy Formation 1) ハローの衝突・合体プロセスによる銀河形成 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~106M☉ Pre-Galaxy 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 trappedin Pre-Galaxy HERMES program (Hierarchical Evolution Researcher by MEtal-poor Stars) To realize the formation and evolution history of EMP stars

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

  12. 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~0.1dex  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 主な支配領域

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