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The Chemistry of the Early Universe

The Chemistry of the Early Universe. Francesco Palla & Daniele Galli, Raffaella Schneider INAF-Osservatorio Astrofisico di Arcetri, Firenze. Outline The early years of the early chemistry Cosmology, nucleosynthesis & chemistry Molecules & the CMB The first stars.

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The Chemistry of the Early Universe

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  1. The Chemistry of theEarly Universe Francesco Palla & Daniele Galli, Raffaella Schneider INAF-Osservatorio Astrofisico di Arcetri, Firenze Outline The early years of the early chemistry Cosmology, nucleosynthesis & chemistry Molecules & the CMB The first stars Södertuna, June 11, 2006

  2. The early years:the quest for coolants • Saslaw & Zipoy (1967) suggest H2 formation through H2+ • at z~1000: [H2]~10-6 & cooling function (Takayanagi & Nishimura 1960) • Peebles & Dicke (1968) propose H2 formation through H- at • lower redshifts: formation of globular clusters •  suggestions by Dalgarno (1958), McDowell (ISM, 1961), Pagel (Sun, 1959) • Hirasawa, Takeda, Hutchins, Silk, Carlberg (1970s) calculate • chemical and dynamical evolution of collapsing primordial clouds •  Jeans mass: poor cooling & high minimum mass • unlike now, IMF of first stars shifted • towards massive stars

  3. The early years • Palla, Salpeter & Stahler (1983) introduce 3-body reactions:

  4. The early years • Palla, Salpeter & Stahler (1983) introduce 3-body reactions: •  full conversion to H2 during collapse •  almost isothermal cooling at T~1000 K •  minimum Jeans mass ~0.1 M0 : normal IMF…

  5. The early years • Palla, Salpeter & Stahler (1983) introduce 3-body reactions: •  full conversion to H2 during collapse •  almost isothermal cooling at T~1000 K •  minimum Jeans mass ~0.1 M0 : normal IMF… • Lepp & Shull (1984), Dalgarno & Lepp (1987), Latter & • Black (1991) follow the formation of several other molecules (HD, LiH, HeH+…) •  beginning of the chemistry of the early universe: • H2~10-6 - HD~10-10 - LiH~10-12 - HeH+<10-13 •  need for cosmological model & reaction rates!

  6. The chemistry of theEarly Universe • …a recipe with 3 ingredients: • Cosmological model Ω0Ωb H0η … • Big Bang nucleosynthesis initial abundances • of atoms & ions • Reaction rates chemical network & evolution

  7. Most recent constraints on their values from CMB observations (WMAP-3: Spergel et al. 2006) Best Fit Model Full sky temperature map +0.013 -0.017 Power spectrum of T fluctuations 0 =1.003  =0.758 +0.035 -0.058 excellent agreement with independent data based on high-z SNIa and galaxy cluster evolution +0.030 -0.041 m = 0.238 +0.028 -0.038 h = 0.734 100 bh2 = 2.233 +0.072 -0.091 8 = 0.774 +0.050 -0.060 WMAP satellite launched 30 June 2001 3-years data release on 16 March 2006 n = 0.951 +0.015 -0.019 Hinshaw, et.al., 2006 Knop et al 2003 The Cosmological Model At present, the most popular model is a CDM model in which dark matter is composed of cold, weakly interacting, massive particles. Fully specified by the following parameters: 0 =m +adimensional density of the universe (matter and vacuum) H0 = 100hkm s-1 Mpc-1Hubble constant badimensional baryon density 8rms mass fluctuations on 8 h-1 Mpc scale nspectral index of the primordial densityfluctuations

  8. Concordance Model +0.013 -0.017 0 =1.003  =0.758 +0.035 -0.058 +0.030 -0.041 m = 0.238 +0.028 -0.038 h = 0.734 100 bh2 = 2.233 +0.072 -0.091 8 = 0.774 +0.050 -0.060 n = 0.951 +0.015 -0.019 The Cosmological Model At present, the most popular model is a CDM model in which dark matter is composed of cold, weakly interacting, massive particles. Fully specified by the following parameters: 0 =m + adimensional density of the universe (matter and vacuum) H0 = 100hkm s-1 Mpc-1Hubble constant badimensional baryon density 8rms mass fluctuations on 8 h-1 Mpc scale nspectral index of the primordial densityfluctuations WMAP-3 main results: 1- Reionization occurred at high z 2- Large Thompson scattering τe=0.09 ↓ Star Formation at high z is needed ↓ H2 & HD formation is critical

  9. Standard Big Bang Nucleosynthesis • Baryon density is independently measured by CBR anisotropies: • Theory of BBN is parameter free  observed vs. predicted light element abundances constrains theory • Accuracy of BBN: Weak reactions for n/p equilibrium (<1%) + neutrino decoupling • 4He mass fraction uncertain at 0.1% (due to neutron lifetime) • Nuclear reaction rates: NACRE collaboration (Angulo et al. 99+) EXFOR-CSISRS database Table of Isotopes 8th ed. Review by Serpico et al astro-ph06 WMAP-3 New cross sections of 2H(d,p)3H & 2H(d,n)3He at BBN energies (110-650 keV) ~7% > NACRE-values  [D/H]=-7% - [Li/H]=+5% (Leonard et al. nucl-ex/0601035) Burles et al. (2001+): BBN code+analytic results for light element abubdaces

  10. H2 andD abundances at high z D/H=N(DI)/N(HI) in QSO absorption line systems due to ~ identical ionization Since D/H is low, D seen only in systems with high N(H) which are rare… Observations D/H=(1.6±0.5-4±0.6)x10-5 dispersion > expectations sources of errors… Best fit value: D/H=2.78±0.40 x 10-5 =5.9±0.5 x 10-10 Ωbh2=0.0214±0.020…good

  11. The chemistry of theEarly Universe… • …a recipe with 3 ingredients: • Cosmological model  Ω0Ωb H0η … • Big Bang nucleosynthesis  initial abundances • atoms & ions • Reaction rates  chemical network & evolution

  12. The chemistry of the early Universe p,e H He p,e D H2 HD He++ -5 D+ n -10 Li+ -15 -20 SBBN + Chemistry

  13. The The chemical evolution • ~20 atomic & molecular species • ~200 gas-phase reactions • among 3 elements H,He,Li • 3-body reactions are inefficient, • due to low density after recomb • First molecules & molecular ions • formed via radiative processes • He  H  Li • Models: • Stancil, Lepp & Dalgarno (1998, 2002…) • Galli & Palla (1998, 2002…) • Puy; Shapiro & Kang; Flower; Abel…

  14. The chemical evolution: Stancil, Lepp & Dalgarno 1998, 2002

  15. HD H2 HeH+ LiH+

  16. Hydrogen chemistry H recombination Peebles & Dicke 1968 Jones & Wyse 1991 Sasaki & Takahara 1998 Seager et al. 1999, 2000 … more refinements 2005, 2006 Minor routes: H2 , H2+ formation through H-excited stated; H- form through stimulated CBR

  17. CDM concordance model Recombination H-recombination at z1100 makes the universe transparent to CBR photons Time and duration of recombination influence CBR anisotropies and the formation of molecules (z<300) RECFAST(Seager, Sasselov & Scott 1999): fast computation of recombination history for arbitrary cosmology, retaining accuracy of complete (multilevel atoms) model (Seager et al. 2000) Comparison GP98 vs RECFAST Comparison RECFAST ..... MULTILEV --- Difference: 25% 50%

  18. Hydrogen chemistry H2 formation: z~1000 H+ + He  HeH+ + ν HeH+ + H  H2+ + He H2+ + H  H2 + H Abundance: ~10-7 H2 formation: z~100 H + e  H- + ν H- + H  H2 + e Abundance: ~10-6 H2+ formation: z~1000 H + H+  H2+ + ν Abundance: ~10-12 H3+ formation: z~300 H* + H2  H3+ + e H+ + H2  H3+ + ν Minor routes: H2 , H2+ formation through H-excited stated; H- form through stimulated CBR

  19. Deuterium chemistry Deuteraded molecules have dipole moments  cooling (HD), CMB (H2D+) HD formation: Same routes as H2: (D,D+)+ H2 Abundance ~ 10-9 HD/H2~10-3 fractionation due to H + D  HD + ν faster D-swapping with H: H+ + D  H + D+ H2 + D+  HD + H+ (main source in ISM) D, D+ conversion: H+ + D  H + D+ and reverse (threshold at 43 K  rates…) HD+, H2D+ formation: Abundance <~10-18  irrelevant… Minor routes: D + H-  HD + e, D- + H  HD + e, H + D  HD + ν

  20. Helium chemistry First atom to recombine and to form a molecule He2+ formation: He + He+ He2+ + ν Abundance: ~10-22 irrelevant HeH+ formation: He + H+ HeH+ + ν(RD82) He+ + H  HeH+ + ν (Zyg98) Abundance: ~10-13 …but rates… Influence on H2+ production HeD+ formation: Same as HeH+ - mass scaled Abundance: ~10-18  irrelevant He Minor route: HeH+ formation through CBR stimulated radiative association

  21. Lithium chemistry Potentially important for CMB  recombination history Uncertain due to unkwon rate coefficients  Dalgarno, Gianturco Li+ recombination: Li+ + e  Li + ν Abundance: ~Li LiH formation: z<300 Li + H  LiH + ν (LS84) (uncertain rate, but…) Li- + H  LiH + e (SLD96,98) Li + H-  LiH + e LiH + H  Li + H2 Abundance: ~10-19 (±20…) LiH+ formation: z<40 Li+ + H  LiH+ + ν (DL87) Li + H +  LiH+ + ν Abundance: ~10-17 +

  22. Abundance variations as function of cosmology: η10=1−10 H2,LiH+: poor diagnostics e,HD,HeH+: sensitive diagnostics

  23. H-chemistry Rates for critical reactions main uncertainty on H2+ formation/ photodissociation at z~1000 Revised rates for: H2 + H+(X 1Σg+,v=0,J=0) H2+ + H(1s) dominant reaction for halos with Tvir>104 K (Savin et al. 2004)

  24. The role of H2+ photodissociation: v=0 vs. v=9 H2 abundance enhanced by a factor ~200! V=0 LTE LTE conditions marginally satisfied: how is H2+ formed? …lack of RV state-to-state data V=9 good question…

  25. He-chemistry: rates for critical reactions rate by Jurek (1995) lowers [HeH+]~10 wrt Roberge & Dalgarno (1982) HeH+ + H  H2+ + He reduced [H2+]~10

  26. D-chemistry: rates for critical reactions Langevin Main route for HD formation revised rate Savin et al. (2002): below Langevin value  reduce [HD] proportionally (+ D-sensitivity to cosmology) D vs D+ relative abundance Savin et al. (2002) vs Watson et al. (1978, empty circles)

  27. The chemistry of theEarly Universe:Molecules &the CBR

  28. The chemistry of theEarly Universe:Molecules & the CBR • Spectral distorsions in the CBR: • ΔJ\J ~ (1−Trad/Tex) τ , Tgas≤ Tex ≤ Trad • molecules trasnsfer energy from the radiation to the gas when Tgas < Trad • (Varshalovich & Khersonski 1977) small effect due to low abundance • Spatial fluctuations in the CBR: • ΔJ\J ~ 4 V/c τ , σmol~1Å2~10-18 cm2>>σel ~ re2 ~ 10-25 cm2 • Thomson scattering of CBR on molecules in protoclouds moving with • velocity V induces CBR spatial anisotropies(Zeldovich et al. 1968, • Dubrovich 1993, Maoli 1994)  several candidates…

  29. The chemistry of theEarly Universe:Molecules & the CBR • H2D+ & LiH: promising due to large dipole moments, • (Dubrovich; Maoli) but tiny abundance ~10-19 yield small τ • τ(LiH)~10-10 @ 30 GHz • τ(H2D+)~10-13 @ 40 GHz • HeH+: exciting due to higher abundance ~10-13 • (GPS 2006)τ(LiH)~10-5 @ 50 GHz (rotational transitions) • for V=300 km/sΔT/T~10-8 too small • …but all angular scales smaller than angular • diameter of the horizon affected by an amount(1−e-τ)~10-5 • high sensitivity ~1μHz search of CBR anisotrpy @10-50 GHz

  30. The chemistry of theEarly Universe:Molecules & the CBR • Li I (6708 Å): resonant formation of Li I modifies anisotropy maps of CBR through absorption and reemission at resonance from ground state (Loeb 2001, Stancil et al. 2002)  • τ(Li I)~0.4 (fLi /3.8x10-10) @ z~400 if Li~Li+ • suppression of anisotropies by e-τ(Li) + T- & polar’n anisotropies on • subdegree scales through Doppler effect (far-IR bkgr contamination…) 0.5 z~400 Li-Li+ histories z< 500: Li+ + e  Li + ν Li + ν  Li+ + e Li + H+ Li+ + H + ν Suppression of T-power spectrum @268μm

  31. The chemistry of theEarly Universe:The First Stars,where and when?

  32. Projected gas distribution atz = 17 Mini-halosM  106 Msun z = 20 – 30 Tvir << 104 K H2 cooling positive feedback from X-rays, shocks, relic HII regions … negative feedback from UV background DwarfsM  108 Msun z = 10-20 Tvir ≥ 104 K H cooling (Lyα) Yoshida et al 2003 End of dark ages & Onset of star formation if tcool<<tHubble  The role of H2 and HD within first structures H + e- H- +  H- + H  H2 + e-

  33. Adaptive Mesh Refinement Smooth Particle Hydrodynamics Mclump ~ 103 Msun 550 AU 6.6 kpc Mclump~ 103 Msun 0.5 pc 30 pc Abel, Bryan & Norman (2000-2002) Bromm, Coppi & Larson (2000-2002) Convergence toward a regime with Tcr 200 K and ncr  104 cm-3 H2 properties Fragmentation into protostellar clouds with Mclump Mjeans(ncr,Tcr) = 700 Msun(n/ncr)-1/2(T/Tcr)3/2 Final stellar mass 30 Msun < M* < 100 Msun ? Radiative feedback during accretion ? PopIII star formation in mini-halos 3D simulations: from cosmological initial conditions to molecular clouds

  34. H2+HD Efficient formation of H2 and HD during non-equilibrium cooling: large abundance of e-  enhanced HD & H2 formation H2 TCMB Fragmentation into protostellar clouds with Mclump Mjeans(ndisk,Tcmb)=30Msun(M/108Msun)-1/3 nearly present-day conditions & IMF ! Johnson & Bromm 2006 PopIII star formation in dwarfs Lya cooling  nearly isothermal collapse at T 8000 K H H2 HD cools the gas to the CBR floor in less than a hubble time

  35. The future: From precision cosmology to precision chemistry and cooling Detection of H2,HD  JSWT, SPICA Effects of HeH+, LiI on CBR  Planck… Detection of HI  LOFAR Surprises in chemistry!

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