Galaxies and the Universe - Cosmic Microwave Background

Galaxies and the Universe - Cosmic Microwave Background -...

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1/15/12 Gala[ieV and Whe UniYeuVe - CoVmic MicuoZaYe BackguoXnd 1/5 ZZZ.aVWu.Xa.edX/keel/gala[ieV/cmbu.hWml The Cosmic Microwave Background Detailed analysis of the microwave background radiation gives practically our only direct evidence of conditions before galaxy formation. The spectral shape and departures from perfect isotropies give (temporal and angular) evidence on the existence of structures at the epoch of recombination, which is the last view we currently have until galaxies and AGN begin to take shape at some epoch like ] =10 (or whatever it is. ..). Two very useful references for much of the material in these final lectures are Peacock's Cosmological Ph\sics (Cambridge 1999) and Gala[\ Formation by Longair (Springer 1998). The existence of a recombination epoch happens because the densities of matter and radiation have different dependences on the cosmic scale factor (1/ R ñ versus 1/ R 4 ). The best-known maps of fluctuations in the background are from the COBE Differential Microwave Radiometer (DMR). These images illustrate the four-year data products as measured at 53 GHz, in galactic coordinates with the galactic center in the middle. At the top is the overall background temperature (blank to an excellent approximation), then in the middle we see the result at a magnified stretch with the mean value removed. This shows the dipole interpreted as a Doppler shift due to motion of the Milky Way with respect to the sphere of matter now seen radiating in the background, and some of the residual contamination from the Galactic foreground. Finally at the bottom we see the all-sky fluctuations with the dipole removed (note, by the way, that we cannot separate any intrinsic dipole structure in the CMBR from effects of our relative motion). The individual fluctuations at high galactic latitudes are now significant (which was an improvement over the initial announcements based on 2-year maps from the data). The Tenerife and South Pole experiments also confirmed individual structures. A further advance and unification of structures on various scales came with the first maps from the Wilkinson Microwave Anisotropy Probe (WMAP) , shown below the COBE results.
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Galaxies and the Universe - Cosmic Microwave Background -...

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