Post on 31-Dec-2015
transcript
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
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