Primeval galaxies Spitzer Daniel Schaerer Geneva Observatory OMP
Primeval galaxies Spitzer Daniel Schaerer (Geneva Observatory, OMP Toulouse) VLT, Keck 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 13. 7 solar system or universe) billion years c) earliest formed in the growth of an individual or organ Cosmic renaissance
Primeval galaxies Daniel Schaerer (Geneva Observatory, OMP Toulouse) Spitzer VLT, Keck 13. 7 billion years Cosmic renaissance
Quasars & galaxies Galaxies + several « candidates/objects » at z~7 to 9 with photometric redshifts Chemical elements… Tracers of cosmic history
HST Keck Spitzer also Chandra VLT and soon GTC…
Outline of the lectures 1 a. 1 b. Introduction Pop. III stars and galaxies --> « top down » theoretical approach 2. , 3 a. 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.
dark ages cosmic renaissance CMB: z=1100 (~300’ 000 yr) age redshift End of reionisation: z~6 (~1 Gyr) Low mass halos Massive halos
The global picture
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)
Outline of Part 1 Pop. III 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, 36 th Saas-Fee course, Springer)
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 H 2 molecules can form General result: At Z<~Zcrit=10 -5± 1 Z --> H 2 and HD main coolants
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)
Fragmentation/SF inside DM halos PRIMORDIAL STAR FORMATION Subsequent « fate » of framents strongly dependent on feedback processes (radiative, mechanical). Schematically: - gaseous galaxy - naked star cluster - dark object Ciardi et al. (2000) MH: min. mass for H cooling Msh: min. mass for self shielding(against H 2 destruction) Mby: max. mass for blow-away
SF within galaxies PRIMORDIAL STAR FORMATION 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± 1 Z for IMF transition determined by fragmentation physics Schneider et al. (2002)
SF within galaxies Critical metallicity Zcrit=10 -5± 1 Z for IMF transition determined by fragmentation physics Schneider et al. (2002, 2004) PRIMORDIAL STAR FORMATION
PRIMORDIAL STAR FORMATION Population III: hydrodynamic simulations Abel et al. (1999, 2002)
PRIMORDIAL STARS: PROPERTIES Properties of Pop. III 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) enables 3 -α reaction 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)
PRIMORDIAL STARS: PROPERTIES Properties of Pop. III 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) àstars may reach critical (break-up) velocity àMechanical mass loss! Fig ekstroem… Rotation alters evolution: - detailed chemical yields - evolution at hotter Teff, even WR stars - may alter final fate of Pop. III/very metal-poor stars --> avoidance of pair instability SN (PISN) ? ? ! Meynet, Ekstroem et al. (2005)
PRIMORDIAL STARS: PROPERTIES Properties of Pop. III 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)
ionising photon flux [photon/s/cm^2] blackbody spectral hardness
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 !?
PRIMORDIAL STARS & GALAXIES: PROPERTIES Pop. III synthetic spectrum Nebular continuum dominates ! Unique signatures: * strong He. II lines (He. II 1640, 3203, 4686, …) * also: strong Ly-a emission stellar + nebular stellar
PRIMORDIAL STARS & GALAXIES: PROPERTIES Lyman-alpha emission Z=0 Z=10 -7 Z=10 -5 Z=1/50 - 2 Zsun Schaerer (2003)
PRIMORDIAL STARS & GALAXIES: PROPERTIES Predicted UV spectra Lowest Z: Mup variations (100, 500) Pop. III Zsun Pop. III Metallicities Z=0, 10 -7, 10 -5, …, 0. 02=Zsun Most metal-poor objects ==> Not necessarily bluest UV spectra! Caution: interpretation of UV slope
PRIMORDIAL STARS: FINAL FATE (Very) low metallicity - Pop. III: 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)
PRIMORDIAL STARS: FINAL FATE metallicity Remnants initial mass PISN SN types Heger & Woosley (2003)
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
PRIMORDIAL SN: NUCLEOSYNTHESIS PISN elemental ratios Pair instability SNe Type II SNe with/without PISNe 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
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 (SN 1987 A) - 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!
PRIMORDIAL SN: DUST PRODUCTION Evidence for PISN dust: • peculiar extinction curve in BAL QSO SDSS 1048+46, redshift=6. 2 • good agreement with SN dust models àFirst dust produced by SNe !? àGeneral feature? Dust common in high-z galaxies? Aλ= -2. 5 log (Fobs/Fintr) Maiolino et al. (2004)
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, …
Summary Part 1 Pop. III stars and galaxies -- « top down » theoretical approach Primordial star formation H 2, 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, He. II 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)
Outline of the lectures 1 a. 1 b. Introduction Pop. III stars and galaxies --> « top down » theoretical approach 2. , 3 a. 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.
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