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[0801.1491] High resolution CMB power spectrum from the complete ACBAR data set
 
Authors:C. L. Reichardt, P. A. R. Ade, J. J. Bock, J. R. Bond, J. A. Brevik, C. R. Contaldi, M. D. Daub, J. T. Dempsey, J. H. Goldstein, W. L. Holzapfel, C. L. Kuo, A. E. Lange, M. Lueker, M. Newcomb, J. B. Peterson, J. Ruhl, M. C. Runyan, Z. Sta
Abstract:In this paper, we present results from the complete set of cosmic microwave background (CMB) radiation temperature anisotropy observations made with the Arcminute Cosmology Bolometer Array Receiver (ACBAR) operating at 150 GHz. We include new data from the final 2005 observing season, expanding the number of detector-hours by 210% and the sky coverage by 490% over that used for the previous ACBAR release. As a result, the band-power uncertainties have been reduced by more than a factor of two on angular scales encompassing the third to fifth acoustic peaks as well as the damping tail of the CMB power spectrum. The calibration uncertainty has been reduced from 6% to 2.2% in temperature through a direct comparison of the CMB anisotropy measured by ACBAR with that of the dipole-calibrated WMAP3 experiment. The measured power spectrum is consistent with a spatially flat, LambdaCDM cosmological model. We see evidence for weak gravitational lensing of the CMB at >3-sigma significance by comparing the likelihood for the best-fit lensed/unlensed models to the ACBAR+WMAP3 data. On fine angular scales, there is weak evidence (1.7 sigma) for excess power above the level expected from primary anisotropies. The source of this power cannot be constrained by the ACBAR 150 GHz observations alone; however, if it is the same signal seen at 30 GHz by the CBI and BIMA experiments, then it has a spectrum consistent with the Sunyaev-Zel'dovich effect.
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Alessandro Melchiorri



Joined: 24 Sep 2004
Posts: 123
Affiliation: University of Rome

PostPosted: January 11 2008  Reply with quote

Hi all,

The new results from ACBAR are impressive.
However I have some doubts on the following sentence:
"We see evidence for weak gravitational lensing of the CMB at >3-sigma significance by comparing the likelihood for the best-fit lensed/unlensed models to the ACBAR+WMAP3 data.".
How you can claim any evidence for weak lensing by just comparing the best fits ?
The "true" model can be 2 sigma away from the best fit in both cases...
I don't understand...

cheers
Alessandro
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1272
Affiliation: University of Sussex

PostPosted: January 12 2008  Reply with quote

I agree. What I would do is introduce a new parameter AL that scales the lensing potential, and plot the posterior constraint on AL. So AL=0 correspond to unlensed, AL=1 is the expected lensed result. The ratio of the marginalized posterior curve at 1 and 0 gives you the posterior odds for lensing. But you can also look at the curve, and if it peaks at AL=10 then you should be a bit worried. [I did this with old WMAP3+ data, the peak was away from zero, but consistent with both zero and one - great ACBAR is now giving something interesting!]
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