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/ ) 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 T gal ~ 280 ( /150MHz) -2.5 NCP (MHz) T gal (K) z

Foreground Removal Wang et al astro-ph/ 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 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( pc), 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, t SN : 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 VL BI 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 CMB Ly  photons Chen & Miralda-Escude 2004

Simulation by Furlanetto, Sokasian, Hernquist, astro- ph/ 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 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~Z o pop II: halo stars Z~0.01 Z o pop III: ? Z<0.001 Z o 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