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Formation of the first galaxies and
reionization of the Universe:
current status and problems
A. Doroshkevich
Astro-Space Center, FIAN, Moscow.
What we know about early Universe
• z~25 – 10 - formation of the first galaxies
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and ionizing bubbles
Bubble model, UV-background,
non homogeneities in xH and Tg
z~ 10 WMAP: τT~0.1, xH=nH/nb << 1
z~6.5 – 5 - high ionization, xH~10-3
z< 3
- xH~10-5
• 1. We do not see any manifestations of the first stars
• 2. We do not know the main sources of ionizing UV
radiation
Universe Today 12.12.2012
Possible sources of ionizing UV
background
1. exotic sources – antimatter, unstable particles,
etc…
It is not popular,
but there is new publication - e+.
2. First stars Pop III with Zmet<10-5 Z¤ or
3. non thermal sources - AGNs and Black Holes
4. Quasars at z < 3.5, He III - observed
Reionisation
• Θ(z)=α(T)n(z)H(z)~3T4-0.7z103/2, T4~2. For z10>1
• Restrctions for the UV background
Thermal sources: E~7MeV/baryon, Nγ< 5 105 /baryon
Non thermal sources - AGNs and Black Hole
E~ 50MeV/baryon, Nγ~3.5 106 /baryon
b N b
b
7 N b 5 10

 0.8 10
f esc N
f esc N 0.04
5
 rei
• fesc~ 0.1 - 0.02, Nbγ~1 - 2
Ωmet~2 10-6Ωbar~8 10-8, Ωbh~3 10-7Ωbar~ 10-8
In all the cases very small baryon fraction is used
Universe Today 1211.6804
Ellis et al. arXiv1211.6804
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Behroosi et al. 1209.3013 – This
is important!
Labbe I., 2010,ApJ.,708,L26, 1209.3037
• Spitzer photometry
• Z~8, 63 candidats,
• 20 actually detected
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SMD for M<-18
ρ*(z=8)~106Ms/Mpc3
Ω*(z=8)~0.4 10-5
Ωmet(z=8)~0.4 10-7
Ωreio~10-7 – 10-8
z~2.5,
Ωmet~2.3 10-6 for IGM,
Ωmet~3 10-5 for galaxies
Three steps of galaxy formation
• 1. Formation of the virialized relaxed massive DM
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cloud (perhaps, anisotropic) at z<zrec~103 with
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nb~44zf10M91/2cm-3, Tb~14zf10/3 M95/6eV, zf=(1+z)/10
• 2. Cooling and dissipative compression of the baryonic
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component, thermal instability
• 3. Formation of stars – luminous matter with M>MJ
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Main Problem of the star formation
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MJ/M¤~2·107T43/2nb-1/2,
• For stars: T4~10-2, nb>102cm-3 , MJ/M¤<103
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z=zrec,T4~0.3, nb~250 cm-3, MJ/M¤ ~2·105
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Parameters of baryonic components
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<ρbar>~4·10-28z103g/cm3, <ρgal>~10-24g/cm3,
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<ρstar>~1 g/cm3, ρBH~2 M8-2g/cm3
• Cooling factors: H2 molecules and metals (dust, C I etc.)
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First galaxies and POP III stars
Two processes of the H2 formation
H+e=H-+γ, H-+H=H2+e, γ~1.6eV
H+p=H2+ +γ, H2++H=H2+p
Epar=128K, Eort=512K
The reaction rate and the H2 concentrations are
proportional to <ne>=<np>
At 1000>z>zrei xe=ne/<n>~10-3 what is very small value.
Feedback of LW radiation 912A<λ<1216A
H2+γLW =2H
Feedback of the IR radiation ~8000 A
Key problem - star formation
Three factors: xe, LW & IR
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Cooling factors: H2 and atomic for T4>1,
Three regimes of the gas evolution –
slack, rapid and isothermal
Thermal instability and the core formation
Stars are formed for Tbar<100K and
nbar>100cm-3
• with Mstar > MJ ~5 107T43/2/nbar1/2Ms
Formation of the first stars
with Mcl/M0 = 5 105 and 9 105, zf=24 (left)
and Mcl/M0=109 and 0.4 109, zf=11 (right)
Influence of the LW & IR backgrounds
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Actual limit is JLW21~1 – 0.1 for various redshifts
For the period of full ionization z~10 we get
JLW 21~4 Nbγ
This means that at 10>z>8.5
the H2 molecules are practically destroyed and
star formation is strongly suppressed
• This background is mainly disappeared at z~8.5
Safranek-Shrader, 1205.3835
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Corrections
for both limits
~10 times
J21~4Nbγ
Alternatives for the star radiation
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Hard UV and X-rays from the BH
In the case Tb~104K and thermal ionization
but we get the high entropy of baryonic
component and increasing of minimal mass,
Mgal>MJ≈5 109T43/2zf-3/2 Mo
It is not catastrophic !
What is the best way?
Low mass limit for the rapid-lazy
formation of the first galaies
Simulations (2001)
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The box ~1Mpc, 128 -256 cells,
Ndm~107, mdm~30M0, Mgal~106 – 107 M0
Very useful general presentation
(the galaxy and star formation are possible)
Restrictions:
a. small box → random regions (void or wall) &
unknown small representativity
• b. low massive halos, weak interaction of halos
• c. stars are outer model parameters
• d. large mass DM particles in comparison with
the mass of halos.
What is mostly interesting
• a. realization – it is possible!
• b. wide statistics of objects -- what is possible
for various redshifts
• c. rough characteristics of internal structure of
the first galaxies
• d. general quantitative analysis of main physical
processes
Density – temperature 2001
ρ, T & Z, Wise 1011.2632
• Formation of massive galaxies owing to the merging of low mass
galaxies.
Machacek et el. 2001, ApJ, 548, 509
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M~5 105Ms
T4~0.3
nb~10cm-3
fH2~3 10-5
j21~1
MJ(25)~104Ms
MJ(20)~500Ms
• Lazy evolution,
• Monolitic object
• Monotonic growth
ρ(z)??? Instabilities!
Conclusions
• We do not see any manifestations of the first stars
• We do not know the main sources of ionizing
UV radiation
• A. It seems that first stars Pop II & III , SNs, GRBs
are approximately effective (~20 – 40%)
• B. non thermal sources - BHs remnants and/or
AGNs - are more effective (~50% + ?)
• C. We can semi analytically describe the formation
and evolution of the first galaxies
• Observations: galaxies ↔ background
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10 000 – 20 000A – James Webb
The
Theend
end
Comments
• Importance – instead of the experiment
• Complexity, representativity and precision
(WMAP).
• Modern facilities
• Our attempts – simulations versus analysis
New semi analytical approach
We know the process of the DM halo formation
and can use this information
• Assumptions:
• a. what is the moment of halo formation
• b. baryons follow to DM and have the same
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pressure and kinetic temperature
• c. what is the cooling of the baryonic
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components
• d. thermal instability leads to formation of
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stars with masses Mst > MJeans
Bradley L., 1204.3641,
UV luminosity function for z~8
• Low massive
objects dominate
• Why?
• Is this selection
effect?
• What about object
collections?
suppression of object
formation ?
• What is at z=9? 10?
Behroozi et al., 1209.3013 - SFR(Mh)
• SMF~Mh-4/3, M>Mch; SMF~Mh2/3, M<Mch (left panel)
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Ms/Mh<2 – 3% at all z! ?continual evolution?
Analytical characteristics for DM component
• For the NFW halo with mass M=109 M9 Ms
• formed at zf=(1+z)/10
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Within central core with r< rs we have
ρDM~10-23g/cm3M91/2zf10, TDM~40eV M95/6zf10/3mDM/mb
Cooling factors: H2 and atomic for T4>1,
Three regimes of the gas evolution –
slack, rapid and isothermal
Thermal instability and the core formation
Stars are formed for Tbar<100K and nbar>100cm-3
• with Mstar > MJ ~5 107T43/2/nbar1/2Ms
Behroozi et al., 1207.6105 Stellar mass vs. host halo
Similarity of the curves
Gonzalez V., 2011, ApJ, 735, L34
UV luminosity density
Oesch P., 2012, ApJ.745, 110