21cm constraints on reionization benedetta ciardi mpa t. di matteo (cmu), a. ferrara (sissa), i....
TRANSCRIPT
21cm Constraints on
Reionization
Benedetta CiardiMPA
T. Di Matteo (CMU), A. Ferrara (SISSA), I. Iliev (CITA), P. Madau (UCSC), A. Maselli (MPA), F. Miniati (ETH), R. Salvaterra (UInsubria), E. Scannapieco (UCSB),
P. Shapiro (UAustin), F. Stoehr (IAU), M. Valdes (SISSA), S. White (MPA)
The gas needs to cool to beavailable for star formation
The first sites of ionizing radiation
KTvir410
KTvir410
Atomic hydrogen cooling
Molecular hydrogen cooling
DM halos virial temperature Cooling function (no metals!)
Temperature [K]
Λ/n
² [e
rg c
m³/
s]
H2 cooling
Atomic H cooling
HD coolingTem
pera
ture
[K
]
1-σ
2-σ
3-σ
(Barka
na &
Loeb
20
01
)
Redshift
H2 is a key species in the early universe
Feedback effects on primordial objects
The first generation of stars affects the subsequent star formation process
Radiative feedback
Mechanical feedback
Chemical feedback
H2 photodissociation(L-W photons, 11.2-13.6 eV)
Radiative feedback
Photoheating
(Gn
ed
in 2
00
0)
Photoevaporation
(Sh
ap
iro e
t al. 2
00
3)
Feedback effects on primordial objects
Blowout/blowaway
Blow-awayBlow-out
(Mac Lo
w &
Ferra
ra 9
9)
Radiative feedback
Mechanical feedback
Chemical feedback
Mechanical feedback
Feedback effects on primordial objects
Change in fragmentation mode due to ZRadiative feedback
Mechanical feedback
Chemical feedbackChemical feedback~ 100 Msun
~ 1 Msun
~ 0.1 Msun
F rac t
ion
of
meta
ls d
ep
lete
d o
nto
du
s t g
r ain
s
Metallicity / Solar Metallicity
(Sch
neid
er e
t al)
(Bromm et al, Schneider et al)
Feedback effects on primordial objects
Radiative feedback
Mechanical feedback
Chemical feedback
IGM reionization
See Ciardi & Ferrara 2005 for a review
Constraints on the epoch of reionization
High-z QSOs latest stages of reionization at z~6
CMB global amount of electrons
Which are the first sources of ionizing radiation?How did the reionization process evolve?
Which is its interplay with the galaxy formation process?
21 cm line diagnostic
21 cm
T S CMBT
Ideal probe of neutral H at high-zdifferent observed frqs. different z
(ν~150,120,80 MHz z~8,11,18)
DECOUPLING
HI ground state
)s0.07K/T3exp(l/nun
• CMB photons are absorbed by HI thermal equilibrium
u
l
Scattering with Lyalpha photons emitted by the same stars that reionize
Absorption or emission?
Differential brightness temperature:
)/TT-(1z1
T-TT sCMB
CMBsb
CMBs TT
sCMB TT absorption
emission
30<z<200 absorption
z_ion<z<30 emission
Heating by Lyalpha or X-ray photons, shock heating (Madau, Meiksin & Rees 1997; Giroux & Shull 2001; Glover & Brand 2002; Chen & Miralda-Escude’ 2003; Gnedin & Shaver 2004)
(1+z)
(Loeb
& Z
ald
arria
ga 2
00
4)
1 10 100 1000
IGM
CMB
Simulations of galaxy formation (feedback effects)
Galaxies Quasars
Properties of the sources of ionizing radiation
Radiative transfer of ionizing radiation
Modeling of cosmic reionization: ingredients
computationallydemanding
Tsu3: cosmological radiative transfer codes comparison
(Iliev, BC et al. 2006)
Stromgren sphere Dense clump Cosmological field
ww
w.m
pa-g
arch
ing.m
pg.d
e/tsu
3
Simulations of galaxy formation (feedback effects)
Galaxies Quasars
Properties of the sources of ionizing radiation
Radiative transfer of ionizing radiation
Modeling of cosmic reionization: ingredients
computationallydemanding
Spectral Energy Distribution
? Source emission properties:
? Escape Fraction:
Modeling of cosmic reionization: parameters
Zero or higher metallicity?
Salpeter or Larson IMF?
Fesc <20% but there is a big variation in the number both theoretically & observationally
? IMF and spectrum:
Simulations of reionization
M~M 910
Simulation properties Source properties
- - metal-free stars - L=20/h Mpc com. - Salpeter/Larson IMF - Fesc=5-20%
Simulations of galaxy formation gas & galaxy properties (Springel et al. ‘00; Stoehr ‘04)
Stellar type sources emission properties
propagation of ionizing photons (BC et al. ’01; Maselli, Ferrara & BC ’03)
(BC
, Sto
ehr &
White
20
03
) Redshift Evolution of HI density
‘Proto-Cluster’: 10/h Mpc‘Field’: 20/h Mpc
z=18
z=16
z=14
z=12
z=10
z=8
0.0
0.015 0.5
0.0
The environment affects the reionization process
S5: Salpeter IMF+fesc=5% (late reion.
case)
S20: Salpeter IMF+fesc=20%
L20: Larson IMF+fesc=20% (early reion.
case)
Early/Late Reionization
0.040.16e 68% CL (Kogut et al. 2003)
(BC
, Ferra
ra &
White
20
03
)
The simulations are consistentwith the WMAP results
Source properties:
- MHs are sinks of UV photons
- MHs photoevaporation has been studied in hydro-simulation
and implemented in semi-analytic models (e.g. Shapiro, Iliev & Raga
2004;
Iliev, Scannapieco & Shapiro
2005)
Effect of mini-halos
cell
sub-gridphysics
• Fraction of gas collapsed in MHs • UV photons needed to photoevaporate the MHs
1. No MHs re-formation allowed once they are evaporated
2. MHs are allowed to form again
Effect of mini-halosIonization fraction
no MHs
MHs, re-formation
MHs, no re-formation
With no MHs re-formation there is nosubstantial difference form the no-MHs caseIf MHs are allowed to re-form, reionization
can be delayed by Δz~2
(BC
et a
l 20
06
)
-6
0
-4
-2
/k)Tlog( b
21 cm line diagnostic
(BC & Madau 2003)
The 21cm line is observed in emission if:
HIsCMBCMBs
b n)/TT-(1z1
T-TT
CMBs TT
Fluctuations of brightness temp.The fluctuations are due to variations in HI distribution (density distrib. + ionized regions)
Late/Early reionization show similar behaviour
The peak of the emission is ~10 mK
Early reion. peaks @ 90MHz, late reion. peaks @ 115MHz
S5 L20
Future radio telescopes should be able to detect such signal
LOw Frequency ARray
(Valdes, BC et al. , 2006)
• Instrument sampling
• Instrument sensitivity
• Convolution with a Gaussian beam (=3 arcmin)
LOFAR will be able to map the reionization history,
especially its latest stages
LOFAR expected response (late reion.)
/k)Tlog( b
Simulated Synthetic
z=10.6, ν=122 MHz
z=9.89, ν=130 MHz
z=9.26, ν=138 MHz
-1
-1
-2
-2
-2
-3
-3
-3
-4
-4
-4
-5
-5
-5
-1-1.4
-1.6
-1.8
-2.0
-2.2-1.6
-1.8
-2.0
-2.2
-2.4
-1.6
-1.8
-2.0
-2.2
-2.4
-2.6
-2.8
S5 L20
T/T)(
1
040 ),(ˆ),()ˆ(
xvxd
T
THII
CMB
CMB anisotropies are produced by free electrons 21cm line is emitted by neutral hydrogen
The power spectrum is dominated by the secondary anis. at l > 4000 (θ < 3’). They reach a peak of ~
which could be detected by e.g. ALMA, ACT
2K][ 1
CMB secondary anisotropies CMB/21cm line correlation(Salvaterra, BC, Ferrara & Baccigalupi 2005)
S5 L20
Characteristic angular scale of the cross-correlation function
S5
L20
Mpc/h
The characteristic angular scale of the cross-correlation function gives an estimate
of the typical dimension of the HII regions at redshift of the 21cm emission line.
CMB/21cm line correlation
We find an anti-correlation below a characteristic angular scale, θ0, when the correlation function becomes < 0.
Extra-galactic foreground contamination (Di Matteo, BC & Miniati 2004)
Point Sources:
- Free-free emission from IS HII regions
- Low-z radio galaxies
Extended Sources:
- Free-free emission from IG HII regions
- Syncrotron emission from cluster radio halos
& relics
Late reionization case @115 MHz
F>0.1 mJy
Extra-galactic foreground contamination
Radio galaxies
Radio halos
After removal of bright sources (F>0.1 mJy), at scales >1 arcmin 21cm emission line is free from
extra-galactic foreground contamination
Conclusions
• Simulations of cosmic reionization
• 21cm line emission from neutral IGM (from reionization simulations)
• CMB/21cm line cross-correlation
• Extra-galactic foreground contamination calculated self-consistently with emission signal
LOFAR should be able to map the reionization process, at least its latest stages
More detailed information will be acquired implementing the above observations with CMB anisotropies measurements
Observations of 21cm line at angles > 1 arcmin could be free from extra-galactic foreground contamination