Benedetta CiardiMPA

Reionization

Nucl

eosy

nth

es i

s

‘Dark Ages’

Big

Ban

g

Fluctuations begin to condense into first stars

and protogalaxies

Decouplingmatter-radiation CMB fluctuations

In an ideal world we would have…

Reliable simulations of + Radiative transfer galaxy formation calculations

• Large volume: ~ 50/h Mpc com.

• High resolution: ~

• Correct treatment of SF and feedback effects

sun7M10

• Accurate

• Fast

Couple simulations and radiative transfer, including the effect of the transfer on the galaxy formation and evolution process

to avoid cosmic variance…

to resolve objects that producethe bulk of ionizing photons…

to correctly account forsmall mass objetcs

In the real world we have…

Simulations of galaxy formation

• Still don’t have enough resolution

• No complete treatment of feedback effects on formation of small-mass objects ?

Radiative transfer

III

c

tH

a

In

t

I

c

3)(ˆ1

),ˆ,,( nxtII

• Point sources• Diffuse radiation• (Background radiation)

• Accurate• Poor angular resolution• Dependent on number of sources

slower

Radiative transfer

Monte Carlo – Ray tracing Local Optical Depth Approx.

Optically Thin Variable Eddington Tensor

• Fast & independent on # of sources• Shadowing is not well reproduced• Problems with multiple sources

• Fast & independent on # of sources• It fails in the ~ 1 range• It is correct only “on average”

1 1~ 1

better!

Summary of reionization simulations

Ciardi et al. N-body+ 20 100 Monte Carlo post-process SAM Gnedin et al. hydro 4 0.1 LOD approx coupled

Razoumov et al. hydro 7 100 ray-tracing post-

process

Ricotti et al. hydro 1 0.05 OTVET coupled

Sokasian et al. hydro 10 10 ray-tracing post-process

Group Simul. L M Rad.Trans. Coupling]M[10 [Mpc/h] sun

7N-body + SAM hydrodynamics

More flexibility of SAMs if different modelsare analyzed

Small box/masses Large box/masses

Small:

• Very early stages of reionization M~Jeans mass• Study of feedback effect on formation of small-mass objs• Contribution of small-mass objects to reionization

Large:

• Global reionization process, down to z~6• Estimates for observability (e.g. 21cm line emission…)

Monte Carlo/Ray tracing LOD/OTVET

Monte Carlo/Ray tracing:

• Solve exact radiative transfer• Poor angular resolution • Slower

LOD/OTVET:

• Faster• Approximations fail in certain regimes

Source type & emission properties

Source type:

• Stars

• QSOs

• Decaying exotic particles• …

Stellar emission properties:

• Metal-free/enriched

• IMF

ZZ=0

More ionizing photons

?

Simulations of galaxy formation

CDM N-body simulation DM+gas distribution (Yoshida, Sheth & Diaferio 2001; Stoehr 2004)

Semi-analytical model for galaxy formation galaxy SFR... (Kauffmann et al. 1999; Springel et al. 2000)

M~M 910

20/h

Mpc

com

.

Salpeter IMF

Metal-free stars

Fesc=5%

We don’t have the resolutionto model the escape fraction ?

CRASH

Follow the propagation of photon packets and solvethe time-dependent ionization equation

Input

Cosmological RAdiative transfer Scheme for Hydrodynamic

Ip. Discretized radiation field Involved processes treated statistically

(BC, Ferrara, Marri & Raimondo 2001; Maselli, Ferrara & BC 2003)

128

128

(BC

, Sto

ehr &

White

20

03

) Redshift Evolution

(Springel et al. 2000)

‘Proto-Cluster’

15 Mpc

‘Field’

30 Mpc

z=16.5 z=12 z=8.5

H0

num

ber

densi

ty

Environment is important!

S5: Salpeter IMF+fesc=5%S20: Salpeter IMF+fesc=20%L20: Larson IMF+fesc=20%

Early/Late Reionization

We don’t need exotic

assumptions!!!

(BC

, Ferra

ra &

White

20

03

)

0.040.16e 68% CL

(Kogut et al. 2003)

Conclusions

• Thanks to: N. Gnedin, A. Razoumov, M. Ricotti, T. Abel

• Theory/simulations are not YET behind observations

• Higher resolution Better treatment of SF and feedback effects Deeper understanding of sources of reionization & escape fraction

• Need to compare radiative transfer codes on common tests (TSU3)

• Use results of small boxes with exact radiative transfer as guideline for big boxes with approximate radiative transfer

Volume averaged ionization fractionCRASH Coral Razoumov