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February 9, 2004

Not So Hot

This PhysicsWeb article reports on the buzz being generated by a recent paper on astro-ph. According to the authors, the Sunyaev-Zeldovich effect (inverse Compton scattering of CMB photons off energetic electrons in the inter-galactic medium of a cluster of galaxies) may be important at angular scales as large as 1° (due to supercluster ‘haloes’ of hot gas) — much larger than previously thought.

Their method was to cross-correlated galactic surveys with decrements in the CMB temperature in the WMAP data.

We have found evidence for anti-correlation between WMAP data and the positions on the sky of galaxy clusters derived from the ACO, APM and 2MASS surveys. We interpret the signal as caused by the SZ effect, inverse Compton scattering of the CMB photons by hot gas in groups and clusters of galaxies. The signal may extend to ≈ 1deg scales around ACO clusters, implying they have extended gaseous haloes which may also constitute a diffuse gas component in superclusters.

The galactic surveys they analyze are not “deep” enough to significantly affect the first acoustic peak in the CMB power spectrum (though they may affect higher peaks). But, if the effect persists for more distant clusters of galaxies, it could potentially affect even the first acoustic peak in the CMB power spectrum, and hence the fit of WMAP data to the cosmological parameters.

We have briefly investigated how SZ contamination might affect the location and shape of the acoustic peaks in the WMAP temperature and find that although there is little effect from the temperature decrements found so far, if they persist out to z≈0.5 with the amplitude and extent seen at z<0.2, then even the first acoustic peak at the 1 deg scale could be significantly affected. Further crosscorrelation analysis of deeper catalogues of groups and clusters will be needed to judge the seriousness of this potential SZ ‘contamination’.

Posted by distler at February 9, 2004 12:30 AM

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