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VLT, Keck

Primeval galaxies. Daniel Schaerer (Geneva Observatory, OMP Toulouse). VLT, Keck. Cosmic renaissance. Spitzer. Primeval : adj. [primaevus, from: primus first + aevum age] of or relating to the earliest ages (as of the world or human history) Primordial : adj.

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VLT, Keck

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  1. Primeval galaxies Daniel Schaerer (Geneva Observatory, OMP Toulouse) VLT, Keck Cosmic renaissance Spitzer Primeval: adj. [primaevus, from: primus first + aevum age] of or relating to the earliest ages (as of the world or human history) Primordial: adj. [primordialis, from primordium origin, from primus first + ordiri to begin] a) first created or developed b) existing in or persisting from the beginning (as of a solar system or universe) c) earliest formed in the growth of an individual or organ 13.7 billion years

  2. Primeval galaxies Daniel Schaerer (Geneva Observatory, OMP Toulouse) VLT, Keck Cosmic renaissance Spitzer 13.7 billion years

  3. Quasars & galaxies + several « candidates/objects » at z~7 to 9 with photometric redshifts Galaxies Chemical elements… Tracers of cosmic history

  4. HST Keck VLT Spitzer also Chandra and soon GTC…

  5. Outline of the lectures 1a. Introduction 1b. PopIII stars and galaxies --> « top down » theoretical approach 2.,3a. Ly physics and astrophysics 3.b,4. Distant/primeval galaxies: - observational searches - current knowledge about high-z galaxies --> « bottom up » observational approach and confrontation with theory 1.

  6. Low mass halos Massive halos CMB:z=1100 (~300’000 yr) dark ages age cosmic renaissance redshift End of re-ionisation:z ~ 6 (~1 Gyr)

  7. The global picture

  8. The global picture Following the growth of quantum fluctuations we have in parallel: --> Structure formation (hierarchical) --> Star formation in sufficiently massive halos --> Local and global chemical evolution (including dust formation) --> Local and global reionisation Processes coupled via several feedback mechanisms (radiation, hydrodynamics, …) Local: within DM halo, with proto-cluster,within galaxies,… IGM, ICM, ISM Global: on larger scales… (IGM)

  9. Outline of Part 1 PopIII stars and galaxies -- « top down » theoretical approach Primordial star formation Primordial stars: properties Primordial stars & galaxies: observable properties Final fate Nucleosynthesis & abundance pattern Dust at high-z Cf. reviews by: Loeb & Barkana (2001, Physics Report) Bromm & Larson (2004, ARA&A) Ciardi & Ferrara (2005, Space Science Reviews) Ferrara (2006, 36th Saas-Fee course, Springer)

  10. PRIMORDIAL STAR FORMATION • Present-day gas • Heavy element mass fraction < 2% • C+, O, CO, dust grains excellent radiators • Thermal eq. timescale « dynamical timescale • Typical cloud temperature ≈10 K • Primordial gas • No heavy elements • H, He poor radiators for T < 104 K • Cloud evolves almost adiabatically.. • ..unless H2 molecules can form • General result: • At Z<~Zcrit=10-5±1Z--> H2 and HD main coolants

  11. PRIMORDIAL STAR FORMATION Fragmentation/SF inside DM halos Necessary condition for fragmentation (SF): t_cool << t_ff Implies minimum mass Mcrit of DM halo (equivalent Tvir…) for SF at each redshift Tegmark et al. (1997)

  12. PRIMORDIAL STAR FORMATION • Fragmentation/SF inside DM halos • Subsequent « fate » of framents strongly dependent on feedback processes (radiative, mechanical). • Schematically: • gaseous galaxy • naked star cluster • dark object MH: min.mass for H cooling Msh: min.mass for self shielding(against H2 destruction) Mby: max.mass for blow-away Ciardi et al. (2000)

  13. PRIMORDIAL STAR FORMATION SF within galaxies Mass of « final » star depends on: fragment mass, accretion rate, radiation pressure, (+rotation, outflow, competitive accretion…) At Z<~Zcrit: * massive fragments Subsequently: * runaway collapse * + high accretion rate ==> (very) massive stars Critical metallicity Zcrit=10-5±1Z for IMF transition determined by fragmentation physics Schneider et al. (2002)

  14. PRIMORDIAL STAR FORMATION SF within galaxies Critical metallicity Zcrit=10-5±1Z for IMF transition determined by fragmentation physics Schneider et al. (2002, 2004)

  15. PRIMORDIAL STAR FORMATION Population III: hydrodynamic simulations Abel et al. (1999, 2002)

  16. PRIMORDIAL STARS: PROPERTIES • Properties of PopIII stars - Interior and stellar evolution • (very?) massive (10 - 100 –1000 M) after formation • • Metal free • •Nuclear burning: initially p-p chain • (inefficient, high T required); high T (10 8.1 K) enables3-αreaction producing the first heavy elements. Start of CNO cycle, convective interior, radiative envelope • •Only effective source of opacity: • electron scattering • High Tc and low opacity --> • compact (small R) and high Teff • « Normal » lifetimes • (minimum ~3 Myr) since L ~ M Schaerer (2002)

  17. PRIMORDIAL STARS: PROPERTIES • Properties of PopIII stars - Interior and stellar evolution • Mass loss ? • radiation pressure low --> negligible • pulsational instability: short phase • during MS evolution • - fast rotation (initial and inefficient • transport of angular momentum) • stars may reach critical (break-up) velocity • Mechanical mass loss! Rotation alters evolution: • detailed chemical yields • evolution at hotter Teff, even WR stars - may alter final fate of PopIII/very metal-poor stars --> avoidance of pair instability SN (PISN) ??! Fig ekstroem… Meynet, Ekstroem et al. (2005)

  18. PRIMORDIAL STARS: PROPERTIES • Properties of PopIII stars - Atmospheres and emerging spectra • • High mass, high T→radiation pressure dominates →stars radiate close to Eddington limit LEdd≈1038(M/M) erg s-1 • • High T implies important non-LTE effects in the atmospheres • Very hot: ZAMS up to ~ 100'000 K, 5 Msun star still ionising source ! Strong He+ ionising flux: unique feature ! Hard spectrum comparable to QSO ? ==> High ionisation efficiency (per unit stellar mass formed) and hard spectrum Schaerer (2002)

  19. ionising photon flux [photon/s/cm^2] blackbody spectral hardness

  20. PRIMORDIAL STARS: PROPERTIES Schaerer & Fall (2006) Hardness of He+/H ionising spectra of starbursts for all metalliticies Schaerer (2003) Strong increase of ionising / UV flux with decreasing metallicity! * Very hard spectra restricted to very low Z (<~ 10-7) ! * Possible perturbation: hot « WR-like » stars due to rapid rotation !?

  21. PopIII synthetic spectrum stellar + nebular stellar PRIMORDIAL STARS & GALAXIES: PROPERTIES Nebular continuum dominates ! Unique signatures: * strong HeII lines (HeII 1640, 3203, 4686, …) * also:strong Ly-a emission

  22. PRIMORDIAL STARS & GALAXIES: PROPERTIES Lyman-alpha emission Schaerer (2003) Z=0 Z=10-7 Z=10-5 Z=1/50 - 2 Zsun

  23. PRIMORDIAL STARS & GALAXIES: PROPERTIES Predicted UV spectra Lowest Z: Mup variations (100, 500) PopIII Zsun Zsun PopIII Metallicities Z=0, 10-7, 10-5, …,0.02=Zsun Most metal-poor objects ==> Not necessarily bluest UV spectra! Caution: interpretation of UV slope 

  24. PRIMORDIAL STARS: FINAL FATE • (Very) low metallicity - PopIII: • New type of SN expected--> • pair instability supernovae (PISN) • Complete disruption of star • Very energetic --> detectable out to high-z • Large mass ejected • Peculiar nucleosynthesis • Also: dust production • … • But: no PISN seen/known so far… PISN… Yields… Heger & Woosley (2003)

  25. PRIMORDIAL STARS: FINAL FATE Remnants metallicity initial mass PISN SN types Heger & Woosley (2003)

  26. PRIMORDIAL SN: NUCLEOSYNTHESIS Heger & Woosley (2003) • PISN: • high energy • large gas quantities ejected • large quantities of O and Si • --> e.g. large O/C, Si/C ratios predicted

  27. PRIMORDIAL SN: NUCLEOSYNTHESIS PISN elemental ratios Type II SNe with/without PISNe Pair instability SNe Key features •Roughly solar abundance of even nuclear charge nuclei (Si, S, Ar..) • Very deficient in odd nuclei (Na, Al, P, V..) --> strong odd/even effect • No elements heavier than Zn,due to lack of s-and r-processes

  28. PRIMORDIAL SN: DUST PRODUCTION • Dust at high redshift • Evidence: • dust in DLA • sub-mm emission from z~6 Quasars • SED of some galaxies at z~6?! • Also: dust known in metal-poor galaxies (e.g. SBS 0335-052, 1/50 Zsun) • Possible short-lived dust producers: • SNII, PISN • Wolf-Rayet stars ? massive AGB stars ? • Dust production in SN: • SNII known dust producers (SN1987A) - but enough ? • Efficient dust production found in explosions of SNII and PISN • Todini & Ferrara (2001), Schneider et al. (2003) • E.g.: 7-20% of PISN mass converted into dust. Very efficient mechanism at Z=0!

  29. PRIMORDIAL SN: DUST PRODUCTION • Evidence for PISN dust: • peculiar extinction curve in BAL QSO SDSS1048+46, redshift=6.2 • good agreement with SN dust models • First dust produced by SNe !? • General feature?Dust common in high-z galaxies? Aλ= -2.5 log (Fobs/Fintr) Maiolino et al. (2004)

  30. Possible direct observations of high-z Population III objects With ground-based facilities and the future JWST • rest-frame UV emission • individual SN (rest optical-near-IR) • mid-IR molecular hydrogen in supernova cooling shells • high energy neutrinos from GRB (fast X-ray transients) • … Haiman & Loeb 1997, Miralda-Escude & Rees 1997, Oh 1999, Tumlinson etal. 2001, Ciardi & Ferrara 2001, Bromm et al. 2001, Schneider et al. 2002, …

  31. Summary Part 1 PopIII stars and galaxies -- « top down » theoretical approach Primordial star formation H2, HD main coolants --> massive fragments Galaxy type dependent on feedback Primordial stars: properties Massive stars favoured at Z< Zcrit=10 -5±1 Zsun€ Primordial stars & galaxies: observable properties Strong ionising output, hard spectrum. Strong Lya, HeII lines! Final fate 130-260 Msun --> PISN Nucleosynthesis & abundance pattern Peculiar abundance pattern from PISN Dust at high-z Dust formation on short timescales possible in SNII or PISN Peculiar dust properties (--> extinction law)

  32. Outline of the lectures 1a. Introduction 1b. PopIII stars and galaxies --> « top down » theoretical approach 2.,3a. Ly physics and astrophysics 3.b,4. Distant/primeval galaxies: - observational searches - current knowledge about high-z galaxies --> « bottom up » observational approach and confrontation with theory 1.

  33. THE END

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