Current Signatures and Search for Pop. III stars in the Local Universe

1. Current Signatures andSearch for Pop. III stars inthe Local Universe Yutaka Komiya (National Astronomical Observatory of Japan) Takuma Suda (NAOJ), Masayuki Y. Fujimoto (Hokkai Gakuen Univ.)

2. Introduction • Extremely metal-poor (EMP) stars = “living fossils” in the local group • Observation : • ~ 1,000 stars with [Fe/H]<-2.5 is identified in the Milky Way (MW) halo • Database: SAGA (Stellar Abundance for Galactic Archaeology, see Suda-san’s poater) • 2nd generation stars chemical signature of Pop. III supernovae (SN) • Were low mass Pop. III stars formed ? • Pop. III star cluster : Clark+ (2008, 2011), Greif+ (2011), Susa+ (2012) • Pop. III binary : Machida+ (2008), Turk+ (2009), Stacy+ (2010) ⇒Pop. III survivors • Pop. III survivors • Where are they ? • What they looks like ? • How can we observe them ?

3. Contents Method • Hierarchical chemical evolution model based on the concordance cosmology • Merging history of the Milky Way (semi-analytic) • Gas outflow, circumgalactic matter • Surface pollution of stars by the accretion of interstellar matter. • Pop. III survivors • In the MW halo • Surface abundance • Outside the MW • Escape fraction • Spatial distribution, Detection probability • （2nd generation stars） • Metallicity distribution • Chemical signature of Pop. III stars (PISN) Mini-halo go out from mini-halo.

4. Computation method • Merger tree: Somerville & K (1999) MMW=1012 M☉, Mmin=M(Tvir=103K) • Gas infall (merger tree), outflow (SN) • All the individual EMP stars are registered in computations • Constant star formation efficiency : 1×10-10/yr • Instantaneous mixing inside mini-halos. • Yield : Kobayashi et al.(2006, Type II SN) Nomoto et al. (1984, Type Ia SN) Umeda & Nomoto (2002, PISN) First star First supernova Mini-halo~106M☉ Milky Way Proto-galaxy mass redshift

5. Assumptions: Initial mass function (IMF) • Lognormal IMF • ξ(log m) = exp( -log(m/Mmd)2/σ２) • Mmd=10Mʘ, σ=0.4 (Pop. II) (Komiya et al. 2007) • Binary • Binary fraction: 50% • Mass ratiodistribution: n(q) = 1 • Pop. III IMF • Fiducial model: Mmd = 200Mʘ (Pop. III.1), Mmd = 40Mʘ (Pop. III.2), Zcr = 10-6Zʘ • A little low mass Pop. III stars are formed. • Parameter dependence Primary Secondary

6. Computation method: Surface pollution by ISM accretion EMP star

7. Basic results of the hierarchical chemical evolution model 「 [Mg/Fe] [Ba/Fe] Gray histogram: HES survey (Schöerck+ 2009) Black line : SAGA sample Data from SAGA(Suda et al. 2008, 2010) Rp-rpcess source: 8 – 10 Mʘ http://saga.sci.hokudai.ac.jp

8. Pop. III survivors ~ 800 Poop. III survivors • In the Milky Way halo • Their surface abundance is changed by the accretion of interstellar medium (ISM)⇒Observed as Z ≠ 0 • How muchare they polluted ? • Outside the Milky Way • Some Pop. III stars are escaped from mini-halo • when their primary companion explode • (3 body interaction in star cluster ) binary SN explosion Secondary star go away • Remains with Z=0

9. Pop. III survivors • In the Milky Way halo • Metallicity, chemical abundance object [Fe/H] [C/Fe] HE0107-5240: -5.4 +3.7 HE1327-2326: -5.7 +4.16 HE0557-4840: -4.8 +1.65 SDSSJ102915+172927: -4.89 <0.93 [Fe/H] ~－５ ⇒ Observed as Hyper Metal Poor stars. （C, N, s-process: binary mass transfer）

10. Pop. III survivors ~ 800 Poop. III survivors. • In the Milky Way halo • Their surface is polluted by the accretion of interstellar medium (ISM)⇒Observed as Z ≠ 0 • How muchare they polluted ? • Outside the Milky Way • Some Pop. III stars are escaped from mini-halo • when their primary companion explode • (3 body interaction in star cluster ) binary SN explosion Secondary star go away • Remains with Z=0

11. Pop. III survivors Preliminary • Outside the Milky Way • Escape frequency • (We assume that the distribution of the orbital parameters of Pop. III binaries is the same as the solar vicinity ) • From mini-halos with 106Mʘ, 20 % of low-mass Pop. III stars go out.

12. Pop. III survivors Preliminary • Outside the Milky Way • Spatial distribution 10 merger trees 100 – 170 Pop. III stars 1000 – 1800 EMP stars ([Fe/H]< -2.5) 2 – 3 Mpc 300kpc 1Mpc 3Mpc

13. Pop. III, EMP survivors Outside the Milky Way Preliminary • Detection probability • Giant • V ~ 26 mag @ 1Mpc • (Subaru Strategic Program, i<26 mag, u,g,r,I,z band, 1,400 deg^2 by 5 yrs, ) • Discrimination • Narrow band filter ? • Spectroscopic follow-up • Main sequence, Turn-off star ⇒　very difficult • Evidence of the Hierarchical Galaxy Formation • Constrain the Dark-halo Mass of the First Galaxy

14. Summary • Hierarchical chemical evolution model • Surface pollution • Metal enrichment of circum-galactic matter • Pop. III survivors • In the Milky Way halo⇒　observed as HMP starsby the surface pollution • Outside the Milky Way halo remained with Z=0 • ~100 Pop. III survivors, 2 – 3 Mpc • can be observed by Subaru Hyper Suprime-Cam (?)

15. Pop. III survivorsoutside the Milky Way IMF of Pop.IIIMmd=10Mʘ Minimum halo mass Tvir > 104 K

16. 2nd generation stars • MDF

17. 2nd generation stars • Chemical signature

18. 2nd generation stars • Parameter dependence Mmd(Pop.III.1) = 40Mʘ Mmd(Pop.III.1) = 10Mʘ Zcr = 10-4Zʘ

19. Pop. III survivors Greif+ (2011) • Low mass Pop. III stars • Cluster : • Clark+ (2008, 2011) • Greif+ (2011) • Susa+ (2012) • … • Binary (multiple system)： • Machida+ (2008) • Turk+ (2009) • Stacy+ (2010) • … • How and where can we observe Pop. III survivors ? Machida+ (2008)

20. Assumption: Gas blowout, Circumgalactic matter Mini halo First SN • Gas blowout (SN driven wind) • Energy injection : • Mass loading : • Metal loading : • Evolution of galactic wind in the CGM • momentum conservation snowplow of th spherical shell Ek: SN kinetic energy = 0.1*EexpEbin: Binding energy of a proto-glaxy ε(=0.1): minimum outflow energy rate Msw: mass swept up by a SN shell SN ejecta Pre-enriched mini halo

21. Computation method:Escape fraction • IMF: • Lognrmal IMF, Mmd=200Mʘ (Pop. III.1), Mmd=40Mʘ (Pop.III.2) • Binary fraction: 50% • Mass ratio distribution: n(q)=1 • Binary orbit • Period: Duquennoy & Mayer (1991) • Eccentricity: e=1 • Remnant mass of massive stars • Woosley (2002) • Mini-halo • NFW density profile • Stars are formed at the center of mini-halo • Escape criterion

22. Computation method: distribution of Pop.III stars outside MW Merger tree tmerge Main halo Mass:Mmh(t) Initial distance: estimated from merger tree. We assume that, distance of mini-halo which accrete to main halo with mass M at tmerge= radius of a spherical shell with M which collapse at tmerge We computed distance and radial velocity of mini-halos as a function of tmerge and Mmh(tmerge). Where tmerge is a age when the mini-halo accrete to the main halo and Mmh(tmerge) is the mass of main halo at the merger. d2r/dt2 = -GM/r2 + Λc2r/3

23. Universe d2r/dt2 = -GM/r2 + Λc2r/3 time

24. Computation method:motion of stars outside MW Angle Θ(random) vinit d2r/dt2 = -G(Mmain(t)+4πρavr(t)3/3)/r2 + Λc2r/3 + l2/r3 rinit Mini halo Main halo l = r(tform)vescsinθ

25. Pop. III binary formation

26. Pop. III survivors • In the Milky Way halo Hyper metal poor stars = Pop. III survivors ? object [Fe/H] [C/Fe] HE0107-5240: -5.4 +3.7 HE1327-2326: -5.7 +4.16 HE0557-4840: -4.8 +1.65 SDSSJ102915+172927: -4.7 <0.93 Fe: accretion of ISM C, N. Mg.. : binary mass transfer

27. Pop.III Supernova Umeda & Nomoto (2002) • PISN ? (~200 Mʘ) • Low [Zn/Fe] • High [Si/Fe], [Ca/Fe] • Odd even effect • Type II ? (10 – 50 Mʘ) • (typical abundance of the halo stars) • Hypernovae ? ( 20 – 50 Mʘ) • Large [Zn/Fe] • (Fast rotating star ?) • (Supermassive star ?)

28. Mass ratio • Sana & Evans 2010

29. Mass ratio Raghavan et al. 2010

30. Mass ratio

31. Pop. III survivors • In the Milky Way halo • Formation epoch

32. Chemical evolution, star formation history Formation redshift of low mass EMP stars (red) and Pop.III stars (green) .

33. Circumgalactic matter Metal enrichment history of the CGM