low frequency background and cosmology
DESCRIPTION
Low Frequency Background and Cosmology. Xuelei Chen National Astronomical Observatories. Kashigar, September 10th 2005. Outline. The angular power spectrum of the galactic synchrotron radiation (based on Chen, astro-ph/0409733) - PowerPoint PPT PresentationTRANSCRIPT
Low Frequency Background and
CosmologyXuelei Chen
National Astronomical Observatories
Kashigar, September 10th 2005
Outline
• The angular power spectrum of the galactic synchrotron radiation (based on Chen, astro-ph/0409733)
• The evolution of 21cm signal during the dark age and the epoch of reionzation (based on Chen & Miralda-Escude, ApJ 602, 1 (2004)),
• The 21cm signature of the first starsThe 21cm signature of the first stars (based on Chen & Miralda-Escude, in preparation)
408 MHz skymap
Foreground for CMB and 21cm observation: galactic synchrotron
Tgal ~ 280 (/150MHz)-2.5 K @ NCP
(MHz) Tgal (K) z
200 140 6.1150 280 8.5151 770 1370 1900 1950 4400 27
Foreground Removal
Wang et al astro-ph/0501081
Synchrotron foreground is removable as long as it is smooth. Still, can we understand it physically?
A spherical cow model
Understand the synchrotron radiation at • high galactic latitude • small scale • random field • Fourier space
galactic synchrotron
power law distribution of cosmic ray electron
synchrotron emissivity
Total intensity along a line of sight
Angular power spectrum
Separable spatial and frequency variation
power spectrum
angular power spectrum (Limber approximation)
cosmic ray electron
B ~ microgauss, for 70-200 MHz, radiation from electron 0.1 GeV < E < 10 GeV
CR electron spectrum
Local measurement (Casadei & Bindi 2004):
Model
• B ~ 4 microG
• scale height ~ 1 kpc
• brightness temperature ~ 20 K at 408 MHz
Magnetic Field Variation
large scale magnetic field on the galactic plane (Beurmann, Kanbach, Bekhuijsen 1985)
small scale, out-of-galactic plane magnetic field
Magnetic Field in Turbulent ISM
Komolgorov turbulence
E(k)~k-5/3
Observation (Faraday Rotation): on small scale(0.01-100pc),
E(k)~k-5/3
on larger scale
E(k)~k-2/3
Han, Ferriere, Manchester (2004)
Cosmic Ray Variation
Injection-Diffusion model: cosmic ray electrons are injected at some points (SNR), propagate in random magnetic field, and diffuse out.
(Kobayashi et al 2004)
(Casadei & Binsi 2004)
scale height:
Solution of the Diffusion Equation
Fourier transformed
Steady State solution
power spectrum
Injection Rate
If SNe is Poisson,
V: effective volume where SNe occur, tSN: average interval for SNe within V
Result
WMAP
magnetic field induced
Field strength ~ OK
cosmic ray induced
WMAP:
Discussion
• Geometry
• Gaussianity
• Large scale field
• Variation of spectral index
• Correlation between magnetic field and cosmic ray
Theoretical simplification
Discussion
Observation:
• some observations with steeper angular spectrum
• extragalactic (unresolved point source) contribution
What to do next
• realistic geometry
• variation of spectral index
• include large scale field
• polarization
• multiwavelength cross correlation
• connection with dynamo and CR model
The Epoch of Reionization (EOR)
21cm probe of EOR
VLBI
21CMA
LOFAR
MWA
Related processes
• spontanous transition
F=1
F=0
• Lyman series scattering (Wouthousian-Field mechanism) Ly
• collision induced transition
• CMB induced transition
CMB
n=0
n=1
21cm
The spin temperature
Ly
collision
Thermal systems:
spin
atomic motion
CMBLy
photons
Chen & Miralda-Escude 2004
Simulation by Furlanetto, Sokasian, Hernquist, astro-ph/0305065
Modulation: density ionization fraction spin temperature
21cm tomography
Adiabatic Evolution of Temperatures
CMB
gas
spin
star formation
Star Formation and X-ray Heating of gas
spin temperature evolution
21cm brightness temperature
Chen & Miralda-Escude 2004
Heating of IGM:
• Shock• ionizing radiation (limited to HII)• Lyman alpha? (Madau, Meiksen, Rees
1997)• X-ray
X
possibility of absorption signal
Formation of first stars
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Frenk 2005• primodial density fluctuation grow to form dark matter halos, small halos form first
• gas fall in for sufficiently large halos (Jeans mass)
• gas cool by molecule or atomic H radiation to form first stars
• first stars may be very massive ~ a few hundred solar masses
Property of first stars
• pop I: disk stars Z~Zo
• pop II: halo stars Z~0.01 Zo
• pop III: ? Z<0.001 Zo
Tumlinson & Shull 2000 Bromm et al 2000
Comoving density
The Evolution of Lyman alpha background
Evolution of gas temperature
21cm signature of high-z objects: a quasar
Tozzi et al 2000
Lyman alpha photons emitted by the quasar couples spin temperature to the kinetic temperature
Ly alpha sphere around a first star
Heating function
Lyman alpha sphere
The 21cm signature of the first star
The 21cm brightness temperature around a first star
Typical size: a few arcsec
Typical width: 10 kHz
Typical dT: 20mK/2000K
Challenge for the future generation of radio astronomers!
The End