The first sources of The first sources of light light in the in the Early Universe Early Universe and the and the highest plausible redshift highest plausible redshift of of luminous luminous Quasars Quasars Andreas Müller Landessternwarte Heidelberg Oberseminar 2001 „Entstehung von Quasaren“
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Andreas Müller Landessternwarte Heidelberg Oberseminar 2001 „Entstehung von Quasaren “
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The first sources of The first sources of lightlight in the in the Early UniverseEarly Universe and the and the highest plausible redshifthighest plausible redshiftof of luminousluminous QuasarsQuasars
The Hierarchical The Hierarchical StructureStructure
z ~ 30: 11stst generation generation of stars and quasars ReionizationReionization of most H in the universe at z ~ 7 Current observations at threshold for probing
H reionization epoch! Tool: observational study of HZ sources CMB anisotropiesCMB anisotropies: small density fluctuations large-scale structure of the universe (LSS) Gravitational collapsesGravitational collapses in dense regions clumpy structure Constraint by observations: evolution of galaxies at z < 6 Elementary building blocks: 1st gaseous objects with Jeans Jeans
massmass (~ 104 M) formed in SCDM models at z ~ 15-30 Evolution of the Universe:
Simple setupi) primordial power spectrum of Gaussian density fluctuationsii) DM mean densityiii) initial temperature and density of cosmic gasiv) primordial composition by Big Bang nucleosynthesisv) lack of dynamically-significant magnetic fields
Analytics: early evolution of seed density fluctuations Numerics: collapse and fragmentation of nonlinear structure Tools: HD simulations, SPH, N-Body, Radiative Transfer 11stst light light from stars and quasars ended the “dark ages” (Rees)
of the universe renaissance of enlightenmentrenaissance of enlightenment Reionization epochReionization epoch
The Cosmological The Cosmological IngredientsIngredients and Numerics and Numerics
c = 912 Aabsorption by photoionization of H and He
lookback time
= 1216 A = 1026 A
Optical spectrum of Quasar with z = 5.8Optical spectrum of Quasar with z = 5.8
Fan et al. 2000
observational diagnosis:
Universe is fully ionizedfully ionized at z = 5.8!
When and how was the IGM ionized?When and how was the IGM ionized?
Key ingredients Key ingredients for Reionizationfor Reionization
Need: intergalactic ionizing radiation field Radiative FeedbackRadiative Feedback
Sources/Ionisators: escape radiation of
first stars & Quasarsfirst stars & Quasars current reionization models with isotropic point
sources (Gnedin 2000, Miralda-Escudé et al. 1999) Sources embedded in densest regions (haloshalos) Constraint: reionization simulation resolution Simplification: point sources in large-scale IGM! Challenges:
clumpinessclumpiness (radiation affected strongly by inhomogeneous effects)
HD feedbackHD feedback (winds, SN)
Ionization fronts Ionization fronts in the IGMin the IGM
radiation of first ionisators HII bubbles HII bubbles (Strömgren spheres)H ionization threshold: 13.6 eV
Stellar ionizing spectrum: most photons above threshold;CS high thin HI layerthin HI layer suffices to absorb all photons!
no He contributions! Model assumptions: sphericalspherical ionized volume RecombinationRecombination very high in high-density clumps MaximumMaximum comoving radiuscomoving radius (neglect recombination,
SCDM: B ~ 0.045, M ~ 0.3, ~ 0.7; N: ionizing photons
per baryon, Nion: ionizations per baryon, M: halo mass,
n0H: present number density of H) :
Loeb et al. 2000
Reionization of Hydrogen Reionization of Hydrogen in the IGMin the IGM
I I initial pre-overlap stageinitial pre-overlap stage
individual sources
escape photons find their way through high-density regions (high recombination rate!)
IGM is two-phase medium
highly ionized regions
neutral regions
ionization intensity very inhomogeneous
Reionization of Hydrogen Reionization of Hydrogen in the IGMin the IGM
II II rapid overlap phase of rapid overlap phase of reionizationreionization
higher exposition by ionizing photons!
ionization intensity increases rapidly
expansion into high-density gas
several unobscured sources
ionization intensity more homogeneous
Reionization of Hydrogen Reionization of Hydrogen in the IGMin the IGM
II II moment of reionizationmoment of reionization
ionization radiation does NOT reach self-shielded, high-density clouds
end of overlap phase
IIIIII post-overlap phasepost-overlap phase
This continues indefinitely, since collapsed objects retain neutral gas even in present universe.
Milestone at zbr = 1.6
““breakthrough redshift”breakthrough redshift”
Below zbr all ionizing sources are visible!
Above zbr absorption by Ly forest clouds
Only sources in small redshift range are visible!
Reionization of Hydrogen Reionization of Hydrogen in the IGMin the IGM
Reionization of Hydrogen Reionization of Hydrogen in the IGMin the IGM
Expanding HII region around an isolated source
Scalo et al. (1998)
Vmax = 4/3rmax3
solid: source switch-on @ z = 10
dashed: source switch-on @ z = 15
C = 0
C = 1
C = 10
Evolution of Evolution of filling factorfilling factor
Nion = 40
clumping factor C = const
dashed: collapsefraction Fcol
dotted: obs. lower limit for zreion (Fan et al. 2000)
C = 0
C = 10
C = 30
C = 1
z ~15 Recombination
less important at HZ!
Loeb et al. 2000
ConsequencesConsequences
Star-forming galaxies in CDM hierarchical models can explain reionization of the universeat z ~ 6 – 15
Further contributes for ionization by mini-quasarsmini-quasars is possible
uncertain parameters for determining zdetermining zreionreion:
Source parametersSource parameters
formation efficiency of stars and quasars escape fraction of ionizing sources Clumping factor C depends on the density
and clustering of the sources source halos form in overdense regions C depends on sources and IGM density
CDMCDM with m = 0.3 radiative transfer code periodic boundary conditions 1283 DM, 1283 baryonic particles (mb = 5x105 M) thin slices through a Mpc box with 4 h-1 per side J21: mean ionization intensity at Lyman limit
(in units of 10-21 erg cm-2 s-1 sr-1 Hz-1) J21 inside HII regions depends on absorption and RT
through IGM includes local optical depth effects does notdoes not include shadowing
ionized bubbles emanate from main concentrations of sources
sources located in highest density regions (C ~100) bubbles expand in low density regions in IGM finally bubbles overlap complex topology of ionized regions neutral islands remain in highest density regions But: rough approximations in RT have to be treated