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The primordial non-Gaussianity of local type (f^(local)_(NL)) in the WMAP 5-year data: the length distribution of CMB skeleton

Hou, Zhen and Banday, A. J. and Górski, Krzysztof M. and Elsner, Franz and Wandelt, Benjamin D. (2010) The primordial non-Gaussianity of local type (f^(local)_(NL)) in the WMAP 5-year data: the length distribution of CMB skeleton. Monthly Notices of the Royal Astronomical Society, 407 (4). pp. 2141-2156. ISSN 0035-8711.

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We present skeleton studies of non-Gaussianity in the cosmic microwave background temperature anisotropy observed in the 5-yr Wilkinson Microwave Anisotropy Probe (WMAP) data. The local skeleton is traced on the 2D sphere by cubic spline interpolation which leads to more accurate estimation of the intersection positions between the skeleton and the secondary pixels than conventional linear interpolation. We demonstrate that the skeleton-based estimator of non-Gaussianity of the local type (f^(local)_(NL)) – the departure of the length distribution from the corresponding Gaussian expectation – yields an unbiased and sufficiently converged likelihood function for f^(local)_(NL). We analyse the skeleton statistics in the WMAP 5-yr combined V- and W-band data outside the Galactic base-mask determined from the KQ75 sky coverage. The results are consistent with Gaussian simulations of the best-fitting cosmological model, but deviate from the previous results determined using the WMAP 1-yr data. We show that it is unlikely that the improved skeleton tracing method, the omission of Q-band data, the modification of the foreground-template fitting method or the absence of six extended regions in the new mask contribute to such a deviation. However, the application of the Kp0 base-mask in data processing does improve the consistency with the WMAP1 results. The f^(local)_(NL)-likelihood functions of the data are estimated at nine different smoothing levels. It is unexpected that the best-fitting values show positive correlation with the smoothing scales. Further investigation argues against a point source or goodness-of-fit explanation but finds that about 30 per cent of either Gaussian or f_(NL) samples having better goodness-of-fit than the WMAP 5-yr data show a similar correlation. We present the estimate f^(local)_(NL)= 47.3 ± 34.9 (1σ error) determined from the first four smoothing angles and f^(local)_(NL)= 76.8 ± 43.1 for the combination of all nine. The former result may be overestimated at the 0.21σ level because of point sources.

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Additional Information:© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 May 21. Received 2010 May 21; in original form 2010 March 17. ZH acknowledges the support by Max-Planck-Gesellschaft Chinese Academy of Sciences Joint Doctoral Promotion Programme (MPGCAS- DPP), and some useful discussions with H. K. Eriksen, Jun Pan and Xi Kang. We give special thanks to Stéphane Colombi for suggestions on improving the manuscript. The computations were performed at the Rechenzentrum Garching (RZG) of Max-Planck- Gesellschaft and the GPU cluster of the cosmology group in Purple Mountain Observatory (PMO). Some of the results in this paper have been derived using the HEALPix (Górski et al. 2005) software and analysis package. We acknowledge use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA) supported by the NASA Office of Space Science.
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Max-Planck-Gesellschaft Chinese Academy of SciencesUNSPECIFIED
NASA Office of Space ScienceUNSPECIFIED
Subject Keywords:methods: data analysis; cosmic background radiation
Issue or Number:4
Record Number:CaltechAUTHORS:20101026-083403091
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Official Citation:Hou, Z., Banday, A. J., Górski, K. M., Elsner, F. and Wandelt, B. D. (2010), The primordial non-Gaussianity of local type (flocalNL) in the WMAP 5-year data: the length distribution of CMB skeleton. Monthly Notices of the Royal Astronomical Society, 407: 2141–2156. doi: 10.1111/j.1365-2966.2010.17098.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20523
Deposited By: Tony Diaz
Deposited On:06 Dec 2010 20:19
Last Modified:03 Oct 2019 02:11

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