Cosmic reionization and the history of the neutral intergalactic medium MAGPOP Summer School, Kloster Seeon Chris Carilli, NRAO, August 10, 2007 Introduction: What is Cosmic Reionization? Current constraints on the IGM neutral fraction with cosmic epoch Neutral Intergalactic Medium (IGM) – HI 21cm signals Low frequency telescopes and observational challenges
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Cosmic reionization and the history of the neutral intergalactic medium MAGPOP Summer School, Kloster Seeon Chris Carilli, NRAO, August 10, 2007 Introduction:
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Cosmic reionization and the history of the neutral intergalactic medium
MAGPOP Summer School, Kloster Seeon
Chris Carilli, NRAO, August 10, 2007
Introduction: What is Cosmic Reionization?
Current constraints on the IGM neutral fraction with cosmic epoch
Neutral Intergalactic Medium (IGM) – HI 21cm signals
Low frequency telescopes and observational challenges
References
Reionization and HI 21cm studies of the neutral IGM
CSS: Constraints on neutral fraction at z~6 Nine z~6 QSOs with CO or MgII redshifts: <R> = 4.4 Mpc (Wyithe et al. 05; Fan et al. 06; Kurk et al. 07)
GP => f(HI) > 0.001
If f(HI) ~ 0.001, then <tqso> ~ 1e4 yrs – implausibly short given QSO fiducial lifetimes (~1e7 years)?
Probability arguments + size evolution suggest: f(HI) > 0.05
Wyithe et al. 2005
=tqso/4e7 yrs
90% probability x(HI) > curve
P(>xHI)
Fan et al 2005
Difficulties for Cosmic Stromgren Spheres
(Lidz + 07, Maselli + 07)
Requires sensitive spectra in difficult near-IR band
Sensitive to R: f(HI) R^-3
Clumpy IGM => ragged edges
Pre-QSO reionization due to star forming galaxies, early AGN activity
ESO
OI
Not ‘event’ but complex process, large variance: zreion ~ 14 to 6
Good evidence for qualitative change in nature of IGM at z~6
ESO
OI
Saturates, HI distribution function, pre-ionization?
Abundance?
3, integral measure?
Local ionization?
Geometry, pre-reionization?
Current probes are all fundamentally limited in diagnostic power
Need more direct probe of process of reionization = HI 21cm line
Local ioniz.?
Low frequency radio astronomy: Most direct probe of the neutral IGM during, and prior to, cosmic reionization, using the redshifted HI 21cm line: z>6 => 100 – 200 MHz
Square Kilometer Array
1e13 Mo
1e9 Mo
HI mass limits => large scale structure
Reionization
HI 21cm radiative transfer: large scale structure of the IGM
LSS: Neutral fraction / Cosmic density / Temperature: Spin, CMB
Dark Ages HI 21cm signal
•z > 200: T = TK = Ts due to collisions + Thomson scattering => No signal
•z ~ 30 to 200: TK decouples from T, but collisions keep Ts ~ TK => absorption signal
•z ~ 20 to 30: Density drops Ts~ T => No signal
Barkana & Loeb: “Richest of all cosmological data sets”
• Three dimensional in linear regime
• Probe to k ~ 10^3 /Mpc vs. CMB limit set by photon diffusion ~ 0.2/Mpc
•Alcock-Pascinsky effect
•Kaiser effect + peculiar velocites
TK = 0.026(1+z)^2
T = 2.73(1+z)
Furlanetto et al. 2006
Enlightenment and Cosmic Reionization -- first luminous sources
•z ~ 15 to 20: TS couples to TK via Lya scattering, but TK < T => absorption
•z ~ 6 to 15: IGM is heated (Xrays, Lya, shocks), partially ionized => emission
•z < 6: IGM is fully ionized
TK
T
Signal I: Global (‘all sky’) reionization signature
Signal ~ 20mK < 1e-4 sky
Possible higher z absorption signal via Lya coupling of Ts -- TK due to first luminous objects
Feedback in Galaxy formation
No Feedback
Furlanetto, Oh, Briggs 06
Signal II: HI 21cm Tomography of IGM Zaldarriaga + 2003
All sky reionization HI experiment. Single broadband dipole experiment with (very) carefully controlled systematics + polynomial baseline subtraction (7th order)
Treion < 450mK at z = 6.5 to 10 (DNR ~ 2700)
(expect ~ 20mK)
Sky > 150 K rms = 75 mK
VaTech Dipole Ellingson
GMRT 230 MHz – HI 21cm abs toward highest z (~5.2) radio AGN
0924-220 z=5.2
S230MHz = 0.5 Jy
1”
8GHz Van Breugel et al.
GMRT at 230 MHz = z21cm
RFI = 20 kiloJy !
CO Klamer +
M(H2) ~ 3e10 Mo
GMRT 230 MHz – HI 21cm abs toward highest z radio AGN (z~5.2)
rms(20km/s) = 5 mJy
229Mhz 0.5 Jy232MHz 30mJy
rms(40km/s) = 3mJy
N(HI) ~ 2e20TS cm^-2 ?
Limits:
Few mJy/channel
Few percent in optical depth
Focus: Reionization (power spec,CSS,abs)
PAPER: Staged Engineering Approach
• Broad band sleeve dipole => 2x2 tile
• 8 dipole test array in GB (06/07) => 32 station array in WA (12/07)