tokens: We acknowledge partial financial support from the Spanish Ministerio de Economía y Competitividad Project AYA2012-39475-C02-01 and Consolider-Ingenio 2010 CSD2010-00064. The authors thank Enrique Martínez-González for useful discussions and Francesco Paci for providing an apodisation code. The healp ix package (Górski et al. 2005 ) was used throughout the data analysis.
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