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 Cosmo ’08 Madison, Aug 25 ’08

(Universität Bielefeld)

Outline -

• 1. Dark matter in the Universe.

Luminosity of halos.

• 2. Effect on the IGM.

can they reionize the Universe?

• 3. Contribution to the optical depth.

constraints on particle and halo parameters.

(Furlanetto et al. ’06; Mapelli et al. ’06; Ripamonti et al. ’07; Chuzhoy ’08)

Dark Energy Dark Matter Ordinary matter

Most of the matter in our galaxy is dark Dark matter searches : ADMX, DAMA, CDMS, Xenon, Edelweiss, Zeplin, EGRET, ......

Dark Matter Non-thermal relic Thermal relic Hot Warm Cold

Particle annihilation in clumps -

Probability of annihilation = Number of pairs = Energy released per ann. =

σav nχ δt

σav nχ δt

1 2 nχ δV

• dEγ Eγ

dNγ dEγ

• dL

dEγ = σav 2 dNγ dEγ Eγ

• dV

ρ2

χ(r)

m2

χ

Energy spectrum of photons -

Let x = Eγ/mχ

dNγ dx = ae−bx x1.5

a = 0.9

b = 9.56

NFW NFW like Isothermal + core

ρ(r) =

ρs (r/rs)(1+r/rs)2

ρ(r) =

ρs (r/rs)α(1+r/rs)β

ρ(r) =

ρs (r/rs)2+K

dL dx = σav 2mχ a e−bx √x

4π

• dr r2ρ2(r) = ae−bx

√x

L0

(Bergström et al. ’98; Feng et al. ’01)

ρ(r) =

ρs (r/rs)(1+r/rs)2

¯ ρ(zf) = 200 ρc Ωm (1 + zf)3

= r200 :

c200 = r200/rs

L0 = L0(M, c200) Mdm(r200) = 4πρsr3

s

• ln(1 + c200) −

c200 1 + c200

• = fdm M

= 4π 3 r3

200 fdm ¯

ρ(zf) ρs = fdm ¯ ρ(zf) 3 c3

200

ln(1 + c200) −

c200 1+c200

fdm = Ωdm/Ωm

4πr3

200

3

¯ ρ(zf) = M(r200)

L = − →

L = d E / d t − →

= dE/dt − →

s

s + δs

s

′

σ δs

nb =

p(s) = nb(s)σδs

4πs2δs

nγ(s) = nγ(s′) × κ(s′; s)

• κ(s′; s) = exp
• −

s

s′ ds n(s)σ

How many halos ?

10−2 102 106 1010 1014 10−6 10−4 10−2 1 102 104 106 108 M

dN dM (Mpc−3)

M(M⊙) z = 50 z = 10

• Num. ionizations per vol. per time at z =
• cσTnb

H0 √Ωm

• µ η [1 − xion(z)]

1 √1+z

• ) ×
• z

zF −dz′ (1 + z′)−1/2

1

0 dx ae−bx √x σ(x) σT κ(z′; z, x)

• ∞

Mmin dM dN dM L0(M)

x = Eγ/mχ

µ = 0.76

0.82 1 13.6 eV + 0.06 0.82 1 24.6 eV

Recombination:

αH = 2.076 × 10−11cm3s−1 √TK Φ(TK)

Φ(TK) ≈

nmax

• 2

1 n nmax =

• 1.58 × 105

TK

ionizing photon. The Helium recombination ] αHe ≈ 3.925 × 10−13 (T/eV)−0.6353.

R(z) = n2

b x2 ion(1 + z)6

0.76 0.82 αH + 0.06 0.82 αHe

• He ≈

× ing T ≈ 8 × 10−4[(1 + z)/61]2 eV,

(L. Spitzer ’48; H.Zanstra ’54)

αH ≈ 3.746 × 10−13(T/eV)−0.724

I(z) − R(z) = nb(1 + z)3dxion dt = −nbH0

• Ωm

dxion dz (1 + z)11/2

• 1. Particle mass - MeV range.
• 2. Minimum halo mass.
• 3. Halo concentration parameter.

x depends on -

ion

σav = 3 × 10−26 cm3 s−1

mdm Mmin c200

• 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.
• But WMAP inferred

τ =

• ds ne(s) σT
• τ(z < 6) = 0.04

τ = 0.087 !

Optical depth

• 1. Predicts a gradual reionization history.

Conclusions:

• 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)

mχ ∼ 20 MeV

• 4. Pop. III star formation.

(Spolyar et al. ’08; Freese et al. ’08; Iocco et al. ’08; Fairbairn et al. ’08; Taoso et al. ’08; Natarajan et al. ’08)

• 5. DM and stars.

May conflict with upper limit set by optical depth.