The effect of early dark matter halos on reionization Aravind - PowerPoint PPT Presentation

The effect of early dark matter halos on reionization Aravind Natarajan and Dominik J. Schwarz arXiv: 0805.3945 [astro-ph] (2008) Aravind Natarajan (Universität Bielefeld) Cosmo ’08 Madison, Aug 25 ’08

Outline - 1. Dark matter in the Universe. Luminosity of halos. 2. Effect on the IGM. can they reionize the Universe? (Furlanetto et al. ’06; Mapelli et al. ’06; Ripamonti et al. ’07; Chuzhoy ’08) 3. Contribution to the optical depth. constraints on particle and halo parameters.

Ordinary matter Dark Matter Dark Matter Non-thermal relic Thermal relic Hot Dark Energy Cold Warm Most of the matter in our galaxy is dark Dark matter searches : ADMX, DAMA, CDMS, Xenon, Edelweiss, Zeplin, EGRET, ......

Particle annihilation in clumps - Probability of annihilation = � σ a v � n χ δ t � σ a v � n χ δ t 1 Number of pairs = 2 n χ δ V dN γ Energy released per ann. = � dE γ E γ dE γ � ρ 2 χ ( r ) dN γ dE γ = � σ a v � dL � dE γ E γ dV 2 m 2 χ

Energy spectrum of photons - a = 0 . 9 dx = ae − bx dN γ b = 9 . 56 Let x = E γ /m χ x 1 . 5 (Bergström et al. ’98; Feng et al. ’01) dr r 2 ρ 2 ( r ) = ae − bx a e − bx dx = � σ a v � dL � L 0 4 π √ x √ x 2 m χ NFW ρ ( r ) = ρ s ( r/r s )(1+ r/r s ) 2 NFW like ρ ( r ) = ρ s ( r/r s ) α (1+ r/r s ) β Isothermal + core ρ s ρ ( r ) = ( r/r s ) 2 + K

ρ ( r ) = ρ s ( r/r s )(1+ r/r s ) 2 ρ ( z f ) = 200 ρ c Ω m (1 + z f ) 3 ¯ = r 200 : 4 π r 3 ρ ( z f ) = M ( r 200 ) ¯ 200 3 c 200 = r 200 /r s � c 200 � M dm ( r 200 ) = 4 πρ s r 3 ln(1 + c 200 ) − s 1 + c 200 = f dm M = 4 π f dm = Ω dm / Ω m 3 r 3 200 f dm ¯ ρ ( z f ) c 3 ρ s = f dm ¯ ρ ( z f ) 200 3 ln(1 + c 200 ) − c 200 1+ c 200 L 0 = L 0 ( M, c 200 )

= dE/dt n b = s + δ s s σ L = → t → d δ s − / − ′ s E → − d = L p ( s ) = n b ( s ) σδ s 4 π s 2 δ s � s n γ ( s ) = n γ ( s ′ ) × κ ( s ′ ; s ) κ ( s ′ ; s ) = exp � � − s ′ ds n ( s ) σ � �

How many halos ? z = 50 10 14 z = 10 10 10 dM (Mpc − 3 ) 10 6 dN M 10 2 10 − 2 10 − 6 10 − 4 10 − 2 10 2 10 4 10 6 10 8 1 M ( M ⊙ )

Num. ionizations per vol. per time at z = � � ) × c σ T n b 1 µ η [1 − x ion ( z )] √ Ω m √ 1+ z H 0 � � � � � � ∞ � z � 1 z F − dz ′ (1 + z ′ ) − 1 / 2 0 dx ae − bx σ ( x ) dN σ T κ ( z ′ ; z, x ) M min dM dM L 0 ( M ) √ x � µ = 0 . 76 13 . 6 eV + 0 . 06 1 1 x = E γ /m χ 0 . 82 0 . 82 24 . 6 eV � �

Recombination: n max 1 � Φ ( T K ) ≈ n α H = 2 . 076 × 10 − 11 cm 3 s − 1 2 Φ ( T K ) √ T K � 1 . 58 × 10 5 n max = T K (L. Spitzer ’48; H.Zanstra ’54) He ≈ × α H ≈ 3 . 746 × 10 − 13 ( T/ eV) − 0 . 724 ing T ≈ 8 × 10 − 4 [(1 + z ) / 61] 2 eV, ionizing photon. The Helium recombination ] α He ≈ 3 . 925 × 10 − 13 ( T/ eV) − 0 . 6353 . � 0 . 76 � 0 . 82 α H + 0 . 06 R ( z ) = n 2 b x 2 ion (1 + z ) 6 0 . 82 α He

I ( z ) − R ( z ) = n b (1 + z ) 3 dx ion dt dx ion � (1 + z ) 11 / 2 = − n b H 0 Ω m dz � σ a v � = 3 × 10 − 26 cm 3 s − 1 x depends on - ion 1. Particle mass - MeV range. 2. Minimum halo mass. 3. Halo concentration parameter.

m dm M min c 200

Optical depth � τ = ds n e ( s ) σ T • No Gunn-Peterson trough in the spectrum of quasars at z < 6. • H fully ionized at z = 6. • He doubly ionized at z = 3. • � He singly ionized at z = 6. τ ( z < 6) = 0 . 04 • But WMAP inferred τ = 0 . 087 !

Conclusions: 1. Predicts a gradual reionization history. 2. H21 signal = 10’s of mK at z=15 (L. Chuzhoy ’08) 3. Places an upper limit on the DM mass. Soft gamma ray background (K. Ahn, E. Komatsu, ’05) Positron production (J.F. Beacom, N.F. Bell, G. Bertone, ’05) m χ ∼ 20 MeV May conflict with upper limit set by optical depth. 4. Pop. III star formation. 5. DM and stars. (Spolyar et al. ’08; Freese et al. ’08; Iocco et al. ’08; Fairbairn et al. ’08; Taoso et al. ’08; Natarajan et al. ’08)