stelle e galassie primordiali

Transcription

1 stelle e galassie primordiali Raffaella Schneider INAF/Osservatorio Astronomico di Roma

2 Matteo de Bennassuti, PhD INAF/OAR Stefania Marassi, Pdoc INAF/OAR Luca Graziani, Pdoc INAF/OAR Rosa Valiante, Pdoc INAF/OAR Stefania Salvadori, Kapteyn, Groningen Marco Limongi, INAF/OARoma Alessandro Chieffi, INAF/IAPS Kazuyuki Omukai, Tohoku University Gen Chiaki, Tokyo University Takaya Nozawa, NAOJ Naoki Yoshida, Tokyo University Daisuke Kawata, University College, UK

3 FIRST Scientific background CMB radiation z = yr An early universe experiment Minihalo 300pc theoretical studies: numerical simulations semi-analytical models Resolving planetary scale structures in a cosmological volume! Molecular cloud New-born protostar 5pc A complete picture of how a protostar is formed from tiny density fluctuations. most distant galaxies & quasars z 25 7solar-radii NY, Omukai, Hernquist 2008, Myr Science Milky Way and its satellites z Gyr

4 FIRST Scientific background CMB radiation z = yr first supernovae explode gas is enriched with metals and dust z = Pop III stars form [10 300] Msun cosmic reionization Pop II stars < 1 Msun is started fossils in the local Universe first Black Holes are formed most distant galaxies & quasars grow to power the first QSOs z Myr Milky Way and its satellites z Gyr

5 from the first stars to the local universe CMB radiation z = yr An early universe experiment first supernovae explode Minihalo theoretical studies: z = numerical simulations Pop III stars form semi-analytical models [30 100] Msun is enriched with metals and dust Resolving planetary scale structures cosmic reionization in a cosmological volume! is started Pop II stars < 1 Msun Molecular cloud New-born protostar 5pc A complete picture of how a protostar is formed from tiny density fluctuations. most distant galaxies & quasars grow to power the first QSOs z 25 7solar-radii NY, Omukai, Hernquist 2008, Myr Science Milky Way and its satellites z Gyr fossils in the local Universe first Black Holes are formed gas 300pc

6 stellar archaeology with the most metal poor stars [Fe/H] < -3 [Fe/H] < Nature, 506, 463 [Fe/H] < -7.1

7 the metallicity distribution function of the Galactic halo SMSS J Schörck et al Christlieb 2013

8 the C to Zn abundances of metal poor stars Cayrel et al. 2004; Spite et al. 2005; François et al. 2007

9 carbon-enhanced metal poor stars ~ 20 % of stars with [Fe/H] < -2 are C-enhanced: [C/Fe] > 0.7 CEMP r/s mass transfer from an AGB companion in binary systems 80% CEMP no metal yields from faint SNe with mixing/fallback [C/Fe] > 0.7 Yong et al. 2013; Norris et al. 2013

10 C-normal and C-rich stars: different formation patways? D trans = Log(10 [C/H] [O/H] ) Norris+07 Caffau+11 forbidden zone for CII and OI cooling Frebel et al. (2009) C-normal stars with [Fe/H] < -3.5 can not form through metal line-cooling Dust-driven fragmentation if the D > D cr = (4.4 ± 2.0) x 10-9 Schneider & Omukai (2010) Schneider et al. (2012)

11 Questions that we want to address: What are the formation pathways of C-normal and C-rich stars? What are the physical processes that shape the low-[fe/h] tail of the MDF? Why is the relative fraction of C-normal and C-rich stars varying with [Fe/H]?

12 simulating the birth environment of C-normal and C-rich stars SDSS J [Fe/H] = SMSS J [Fe/H] < Caffau et al 11 Keller et al 14 C NO Mg Si Ca Ti Fe Ni Sr Pop III core-collapse SNe M star = 20, 35 M sun Pop III faint SNe M star = 13, 15, 50, 80 M sun C NO Mg Si Ca Ti Fe Ni Sr Schneider et al Marassi et al. 2014

13 simulating the birth environment of C-normal and C-rich stars SDSS J [Fe/H] = SMSS J [Fe/H] < Caffau et al 11 Keller et al 14 Silicate dust M dust ~ 0.4 M sun 0.2 < f sil < 0.6 Carbon dust M dust ~ M sun 0.01 < f carb < 0.84 Marassi et al Schneider et al. 2012

14 simulating the birth environment of C-normal and C-rich stars Marassi et al minimum Si - abundance SDSS J [Fe/H] = x minimum C - abundance critical dust-to-gas ratio a single formation pathway based on dust-driven fragmentation Thermal Pathway molecular cooling fragmentamon metal cooling fragmentamon [Si/H], D > D cr dust cooling FragmentaMon

15 GAMETE GAlaxy MErger Tree and Evolution GAMETE Salvadori et al. 2007, 2008, 2009; Valiante et al. 2011, 2014; de Bennassuti et al dark matter halo merger tree star formation and chemical evolution time redshift M MW = M sun

16 The MW and its dusty progenitors global properties of the MW 2-phase structure of the ISM Pop III and Pop II SFRs average over 50 independent merger trees 1 σ de Bennassuti et al 2014

17 The MW and its dusty progenitors gas and dust scaling relations de Bennassuti et al 2014 data points: sample of local Virgo galaxies Corbelli et al. (2012) dust-to-gas ratio vs metallicity data points: sample of GRB hosts 0.1 < z < 6.3 Zafar & Watson (2013) Local dwarfs Galametz et al. (2011) Madden et al. (2013), Remy-Ruyer et al. (2014)

18 The low-[fe/h] tail of the MDF Pop III stars [10 300] M sun ordinary ccsn pair instability SN Pop III stars [10 300] M sun faint ccsn pair instability SN Pop III stars [10 140] M sun faint ccsn Pop III/II dust-driven transition D cr =4.4 x 10-9 Pop III/II metal-driven transition D trans > -3.5 Pop III stars IMF à [10-140] M sun and explode as faint ccsn Pop III/II transition criterium à degenerate with the Pop III IMF Change of slope in the low-[fe/h] tail à radiative feedback effects? de Bennassuti et al 2014

19 Metallicity distribution of C-rich stars Pop III/II dust-driven transition D cr =4.4 x 10-9 Pop III/II metal-driven transition D trans > -3.5 de Bennassuti et al 2014

20 Relative fraction of C-rich and C-normal stars data points from Yong et al. (2013) de Bennassuti et al 2014

21 Conclusions: Stellar Archaeology of the most metal-poor stars is a powerful way to constrain the first stellar generations What are the formation pathways of C-normal and C-rich stars? Ordinary vs faint SN: a single thermal pathway with dust- driven fragmentamon What are the physical processes that shape the low-[fe/h] tail of the MDF? very sensimve to the adopted Pop III IMF and SN yields interplay between chemical and radiamve feedback effects Why is the relative fraction of C-normal and C-rich stars varying with [Fe/H]? sensimve to the Pop III/II transimon observed CEMP fracmon at [Fe/H] > - 4 may require that a fracmon of Pop II SN is faint