1 / 44

First objects and IGM reionization

First objects and IGM reionization. Benedetta Ciardi. MPA. Cosmic Microwave Background. Timeline in cosmic history. Big Bang: the Universe is filled with hot plasma. Years since the Big Bang ~350000 (z~1000) ~100 million (z~20-30) ~1 billion (z~6) ~13 billion (z=0).

nevina
Download Presentation

First objects and IGM reionization

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. First objects and IGM reionization Benedetta Ciardi MPA

  2. Cosmic Microwave Background Timeline in cosmic history • Big Bang: the Universe is filled with hot plasma Years since the Big Bang ~350000 (z~1000) ~100 million (z~20-30) ~1 billion (z~6) ~13 billion (z=0) • The gas cools and becomes neutral: recombination The Dark Ages  The first structures begin to form: reionization starts FIR/Radio?  Reionization is complete UV/Optical/IR  Today’s structures

  3. Cooling function (no metals!) 3-σ (Barkana & Loeb 2001) Atomic H cooling 2-σ Temperature [K] Λ/n² [erg cm³/s] 1-σ H2 cooling Redshift Temperature [K] The sites of the first ionizing radiation DM halos virial temperature The gas needs to cool to be available for star formation H2 is a key species in the early universe HD cooling Atomic hydrogen cooling Molecular hydrogen cooling

  4. Feedback effects H2 photodissociation (Lyman-Werner photons, 11.2-13.6 eV) Radiative feedback Mechanical feedback Chemical feedback Radiative feedback Ionization/dissociation of atoms/molecules The first generation of structures/stars affects the subsequent structure/star formation process via energy and mass deposition Object formation is delayed/halted

  5. (Gnedin 2000) Feedback effects H2 photodissociation Radiative feedback Mechanical feedback Chemical feedback Radiative feedback Photoheating To have a collapse: M(z)>MJeans; MJeans increases with T

  6. (Shapiro et al. 2003) Feedback effects H2 photodissociation Radiative feedback Mechanical feedback Chemical feedback Radiative feedback Photoheating Photoevaporation Gas in mini-halos is boiled out of the potential well

  7. Blow-out Blow-away (Mac Low & Ferrara 99) Feedback effects Blowout/blowaway Radiative feedback Mechanical feedback Chemical feedback Mechanical feedback Mechanical energy injection from winds/SN The first generation of stars affects the SF process inside the same object

  8. ~ 100 Msun ~ 1 Msun ~ 0.1 Msun Fraction of metals depleted onto dust grains (Schneider et al) Metallicity / Solar Metallicity Feedback effects Radiative feedback Mechanical feedback Chemical feedback Chemical feedback Change in fragmentation mode due to Z (Bromm et al, Schneider et al) Critical metallicity of the gas that induces the transition between massive and more standard star formation Transition between massive  standard SF mode

  9. First stars: what do they look like? • First generation of stars formed out of metal-free, non-magnetized gas: • fragmentation scale • accretion efficiency • emission properties • mass loss efficiency • are different from those of metal enriched stars. Which is the mass/IMF of the first stars?

  10. SNII PISN First stars: what do they look like? (Heger & Woosley 2002)

  11. Fragment mass Accretion properties First stars: what do they look like? (Bromm et al; Abel et al; Nakamura&Umemura) (Omukai&Nishi; Ripamonti et al) (Omukai&Palla; Tan&McKee; Bromm et al) (Nakamura&Umemura; Omukai; Uehara&Inutsuka)

  12. Feedback effects Radiative feedback Mechanical feedback Chemical feedback IGM metal enrichment IGM reionization See Ciardi & Ferrara 2005 for a review

  13. QSO HI absorption features at ν>νLyα Evidence for IGM reionization

  14. Evidence for IGM reionization optical depth τ cross-section column density The optical depth of HI at mean density is: Iin Iabs=Iin [1-exp(-τ)] τ=1  Iabs=63% Iin A tiny fraction of HI would absorb everything

  15. QSO HI Evidence for IGM reionization We observe Ly-alpha emission from high-z QSOs: this indicates that the IGM is highly ionized

  16. Expected reionization history Redshift Neutral IGM z  zi z < zi z > zi Wavelength Wavelength Wavelength Lyman Forest Absorption Gunn-Peterson trough Patchy Absorption

  17. Spectra of high-z QSOs Ly-α optical depth HI fraction (Fan et al. 2002) (Fan et al. 2006) z (Fan) Constraints on the epoch of reionization • The IGM is highly ionized @ z<6 • The HI abundance increases • with increasing redshift Spectra of high-z QSOs are sensitive to the latest stages of reionization

  18. Constraints on the epoch of reionization CMB power-spectrum (Hu webpage) e + CMB  anisotropies in the power spectrum Thomson scattering optical depth:

  19. Constraints on the epoch of reionization 1st yr WMAP TE Cross-Power Spectrum (Kogut et al. 2003) Thomson scattering optical depth:

  20. Constraints on the epoch of reionization TT TE EE BB (Page et al 2006) 3rd yr WMAP power spectra Measurements of CMB anisotropies provide an estimate of the global amount of electrons produced during reionization, but NOT the z_reion τ=0.09 ± 0.03 Thomson scattering optical depth:

  21. Constraints on the epoch of reionization ne,tot = ne,tot= ne,tot same Thomson scattering opt. depth 1 zion zion zion Redshift

  22. Ionization energies ν>13.6 eV: HI  HII ν>24.6 eV: HeI  HeII ν>54.4 eV: HeII  HeIII Recombination time-scale for HeIII is shorter than for HII/HeII  later HeII reionization

  23. He reionization: observational contraints (Shull et al, 04) HeII HI • Gunn-Peterson trough technique used to determine HeII abundance

  24. He reionization: observational contraints Reimers et al 2004 for QSOs @ 2.4 < z < 3.5 log(η) log(NHI) • Gunn-Peterson trough technique used to determine HeII abundance Dishomogeneous distribution of HeII  evidence for patchy HeII reionization • BUT it could be caused by (e.g. Miralda-Escude’ et al 00, Kriss et al 01, Telfer et al 02, Maselli&Ferrara 05) • fluctuations in the IGM density • fluctuations in the ionizing background flux • wide range in the QSOs spectral index

  25. He reionization: observational contraints • A rise in the IGM temperature is observed @ z~3 Indication for HeII reionization at z~3 BUT it is very controversial IGM heating from hard photons  HeII reionization BUT how sharp is the rise? (e.g. Schaye et al 00; Theuns et al 02)

  26. Constraints on the epoch of reionization High-z QSOs  latest stages of reionization at z~6 Which are the first sources of ionizing radiation? How did the reionization process evolve? CMB  global amount of electrons QSOs absorption spectra  HeII reion at z~3

  27. First sources of ionizing radiation Gals? QSOs? QSOs comoving space density Fan et al.(2001) Schmidt et al.(1995) (Fan et al. 2004) • QSOs space density drops @ z>3 No evidence for the existence of high-redshift QSOs

  28. Metals are observed down to very • low densities in the IGM  • far away from their production sites • Metals are relatively cold (~10 K)  • they had time to cool down 4 Metal Abundance at z=3 (Pettini 2000) First sources of ionizing radiation Existence of an early population of stars that polluted the IGM

  29. Evolution of the reionization process

  30. Ideal probe of neutral H at high-z: The population of the states can be described by Boltzmann relation: spin temperature statistical weight 21 cm line diagnostic u 21 cm l HI ground state

  31. τ,TS absorption brightness temperature emission Absorption or emission? CMB photons at TCMB For radio frequencies (Rayleigh-Jeans) I(T)=T: Lyalpha /X-ray photons heat the gas above the CMB EMISSION

  32. Next generation of radio telescopes LOFAR: Low Frequency ARray; Netherlands www.lofar.org 21cmA/PAST: Primeval Structure Telescope; China web.phys.cmu.edu/~past MWA: Mileura Widefield Array; Australia space.mit.edu/RADIO/research/mwa.html SKA: Square Kilometre Array www.skatelescope.org

  33. Modeling of IGM reionization: ingredients • Simulations of galaxy formation (feedback effects) Galaxies Quasars • Properties of the sources of ionizing radiation • Radiative transfer of ionizing radiation

  34. Properties of the sources of ionizing radiation Spectral Energy Distribution Salpeter IMF: Larson IMF: ?Source emission properties: ?Initial Mass Function and spectrum: Salpeter or Larson IMF? Zero or higher metallicity?

  35. Properties of the sources of ionizing radiation Salpeter IMF: Larson IMF: Log of ionizing photons per baryon in star

  36. Properties of the sources of ionizing radiation Clumpy (BC et al 2002) (Ricotti & Shull 2000) Gaussian Ionization rate [1/s] 1+z Fesc <20% but there is a big variation in the number both theoretically & observationally ?Escape Fraction: Observations: • Fesc < 57% Theory: • At z~0 Fesc~10% • Fesc decreases with increasing M and z (eg. Leitherer et al. 95; Hurwitz et al. 97; Bland-Hawthorn & Maloney 99; Steidel, Pettini & Adelberger 01) (eg. Dove, Shull & Ferrara 00; Ricotti & Shull 00; Wood & Loeb 00; BC, Bianchi & Ferrara 02; Fujita et al 03)

  37. Modeling of IGM reionization: ingredients • Simulations of galaxy formation (feedback effects) Galaxies Quasars • Properties of the sources of ionizing radiation • Radiative transfer of ionizing radiation computationally demanding

  38. Radiative transfer redshift emission I II III V IV absorption dilution from expansion path length change from expansion 7 dimensions, no simmetry!!! 2. III/II ~ HL/c = L/LH << 1 local approximation

  39. Radiative transfer 7 dimensions, no simmetry!!! (see Iliev, BC et al 2006 for a review of RT codes)

  40. Modeling of IGM reionization: ingredients • Simulations of galaxy formation (feedback effects) Galaxies Quasars • Properties of the sources of ionizing radiation • Radiative transfer of ionizing radiation

  41. A model of IGM reionization • Simulations of galaxy formation  gas & galaxy properties (Springel et al. ‘00; Stoehr ‘04) • Sources of ionizing radiation  stellar type sources • Radiative transfer of ionizing photons  (BC et al. ’01; Maselli, Ferrara & BC ’03) Simulation properties Source properties - - metal-free stars - L=10-20/h Mpc com. - Salpeter/Larson IMF - Fesc=5-20%

  42. A model of IGM reionization: HI distribution 0.015 0.5 z=18 z=12 0.0 0.0 z=10 z=16 z=8 z=14 (BC, Stoehr & White 2003) ‘Field’: 20/h Mpc ‘Proto-Cluster’: 10/h Mpc

  43. Simulated Synthetic -1.4 -1 -1.6 -2 -3 -1.8 -4 -2.0 z=10.6, ν=122 MHz -5 -2.2 -1 -1.6 -1.8 -2 -3 -2.0 0 -2.2 -4 z=9.89, ν=130 MHz -2.4 -5 LOFAR -1.6 -1 -2 -1.8 • Instrument sky coverage • Instrument sensitivity • Gaussian beam (s=3 arcmin) -2 -2.0 -2.2 -3 -4 -2.4 -4 -2.6 z=9.26, ν=138 MHz -5 -2.8 -6 (Valdes, BC et al 2006) (BC & Madau 2003) A model of IGM reionization: 21cm line

  44. Conclusions • The IGM is highly ionized at z<6 • The Thomson scattering optical depth produced by reionization is ~ 0.09 • Indications for a HeII reionization at z~3 • Indications for the existence of an early population of stars • Which are the properties of the first sources of ionizing radiation? • How did the feedback effects affect the first structure evolution? • How did the reionization process evolve? • Future 21cm line observation will help answering the above questions

More Related