WMAP observations: Foreground Emission Adric Riedel

Overview What it is The Cosmic Background Removing the foreground Sources of Contamination –Free-Free emission –Synchrotron emission –Thermal Dust emission –Spinning/Magnetic Dust emission –Extragalactic sources –Sunyaev-Zeldovich effect

What it is W M P A ilkinson icrowave nisotropy robe Designed to measure minute CMB variations Follow up to COBE Launched 2001 Located at the L2 Lagrange Point Still in operation

The Cosmic Microwave Background Predicted by Gamow as a consequence of the Big Bang theory Predicted to be observable by Dicke Discovered accidentally by Penzias & Wilson at Bell Labs in 1965 Isotropic (so they thought) Non-polarized (so they thought) Constant (non-seasonal) Traces a blackbody curve (Weymann, 1967)

COBE The Big Bang model predicted the CMB should not be isotropic The COBE satellite was the first to measure the anisotropy of the CMB (variations of out of K)

How the CMB is observed WMAP is outfitted with sensors for a variety of frequencies: 23, 33, 41, 61, 94 Ghz The CMB dominates all other emission between GHz Other spacecraft (including COBE) have made detailed maps of the sky at various relevant frequencies Use other data sets to find the extent of contamination

Removing the foreground The Cosmic Microwave background is in the background, hidden behind everything else in the universe. To get the CMB, the foreground must be removed. Masks based on K-band (23 GHz)

A note on notation All the spectra are characterized as power law spectra T A ~ υ β, and T A is the antenna temperature. Spectra also characterized by flux S~ υ  where we assume β =  -2 So, for a given wavelength υ and varying fluxes S, we can convert flux to temperature given the value of β (or  ) The intent is to separate out just the CMB around T=2.725 K by filtering out the microwave emissions of other processes

Sources of Contamination: Earth Cars, antennas, radios WMAP is situated at Earth’s L2 point, thus removing it from Earthbound interference

Sources of Contamination: Galactic Four major processes: Free-Free emission Synchrotron Emission Thermal emission Spinning dust (Magnetic)

Sources of Contamination: Galactic Free-Free emission T A ~ υ β where β =-2.15 for Microwave frequencies (S~ υ ) Found in hydrogen clouds. Not mapped in radio waves- emission is not dominant at any radio frequency γ

Sources of Contamination: Galactic Free-Free emission Fortunately, H  has been mapped H  corresponds to the same thing (Hydrogen) Not a perfect correspondence especially due to dust, helium presence, rates...

Sources of Contamination: Galactic Synchrotron Emission Produced by acceleration of electrons to cosmic ray levels. (Type Ib and II supernovae) Found: SNR, diffuse Propagate via scattering off random B fields (diffusion) or systematic motion (convection) Diffuse component more common than SNR (90%) SNR component more powerful due to B fields

Sources of Contamination: Galactic Synchrotron Emission Various ways for cosmic rays to lose energy- Synchrotron emission, inverse Compton scattering, adiabatic loss, free-free loss. Most cosmic rays do not leave the galaxy, especially the most powerful- they lose energy faster.

Sources of Contamination: Galactic Synchrotron Emission N(E)~E - γ, flux density  =-( γ -1)/2 γ (and  ) vary greatly; the resulting flux is very frequency-dependent For the CMB frequencies, β =-2.6 (plane) to -3.1 (halo); average is This is common. The sky at 408 MhZ (Synchrotron Emission )

Sources of Contamination: Galactic Thermal Dust Characteristic dust emission has been mapped in IR (IRAS, COBE) and representative temperatures Seems to be correlated with the synchrotron emission; probably due to the fact that both are centred around star-forming regions.

Sources of Contamination: Galactic Thermal Dust β is generally 1.5 to 2; below 20 K the slope is between 1.6 and 2.5 W band (94 GHz)

Sources of Contamination: Galactic Magnetic Dust Electric dipole emission from spinning dust Magnetic dipole emission from thermally fluctuating dust. β ~-2 Though predicted, there doesn’t seem to be very much- out of 10 examined (Finkbeiner et al. 2002), 2 ‘tentative’ detections, 8 failures.

Results from other galaxies Klein & Emerson (1981) and a few others report that the power spectra of galaxies is synchrotron & free-free only. Few observations have been carried out above 10 GHz, where spinning dust is predicted to become apparent

Sources of Contamination: Extragalactic Point sources The galactic removal methods generally clean up extragalactic sources as well Use galaxy catalogue of sources observed at Radio and Microwave frequencies where the CMB doesn’t dominate 208 sources were removed, statistically five are spurious

Sources of Contamination: Extragalactic Sunyaev-Zeldovich Effect Hot Gas excites CMB photons, shifting the peak but not increasing the amplitude to match, effectively making the CMB look cooler. ( bonn.mpg.de/staff/mthierbach/s z.html) Most prominently due to the gas in the Coma Cluster Removed like the point sources

WMAP mapping Combine the five frequencies linearly, properly scaled so that the foreground cancels itself out and leaves only the background Model the absorption by combining properly- scaled maps of the particular emission contaminants, and subtract

WMAP map error Note that the maximum difference 70 μ K (errors confined to 5 μ K, the CMB anisotropy is on the order of 200 μ K) Result Error images/Hinshaw.ppt

Works Cited Bennett, C.L. et al. 2003, ApJS, 148, 97 Hinshaw,G. 2003, 5 th Boston University Astrophysical Conference notes. Weymann, R.J. 1967, ASPL, 10, 81 Theirbach, M. “Sunyaev-Zeldovich Effect” 1997, bonn.mpg.de/staff/mthierbach/sz.html. January 28, September 27,