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Evidence for anomalous dust-correlated emission at 8 GHz

In 1969 Edward Conklin measured the anisotropy in celestial emission at 8 GHz with a resolution of 16.2 degrees and used the data to report a detection of the CMB dipole. Given the paucity of 8 GHz observations over large angular scales and the clear evidence for non-power law Galactic emission near 8 GHz, a new analysis of Conklin's data is informative. In this paper we compare Conklin's data to that from Haslam et al. (0.4 GHz), Reich and Reich (1.4 GHz), and WMAP (23-94 GHz). We show that the spectral index between Conklin's data and the 23 GHz WMAP data is beta=-1.7+-0.1, where we model the emission temperature as T \propto nu^beta. Free-free emission has beta \approx -2.15, synchrotron emission has beta \approx -2.7 to -3. Thermal dust emission (beta \approx1.7) is negligible at 8 GHz. We conclude that there must be another distinct non-power law component of diffuse foreground emission that emits near 10 GHz, consistent with other observations in this frequency range. By comparing to the full complement of data sets, we show that a model with an anomalous emission component, assumed to be spinning dust, is preferred over a model without spinning dust at 5 sigma (Delta chi2= 31). However, the source of the new component cannot be determined uniquely.