Evidence for anomalous dust-correlated emission at 8 GHz

In 1969 Edward Conklin measured the anisotropy in celestial emission at 8GHz with a resolution of 16°.2 and used the data to report a detection of the cosmic microwave background dipole. Given the paucity of 8GHz observations over large angular scales and the clear evidence for non-power-law Galactic emission near 8GHz, a new analysis of Conklin's data is informative. In this paper, we compare Conklin's data to that from Haslam et al. (0.4GHz), Reich and Reich (1.4GHz), and the Wilkinson Microwave Anisotropy Probe (WMAP; 23-94GHz). We show that the spectral index between Conklin's data and the 23GHz WMAP data is β = -1.7 ± 0.1, where we model the emission temperature as Tν^β. Free-free emission has β ≈ - 2.15 and synchrotron emission has β ≈ - 2.7 to -3. Thermal dust emission (β ≈ 1.7) is negligible at 8GHz. We conclude that there must be another distinct non-power-law component of diffuse foreground emission that emits near 10GHz, 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 5σ (Δχ² = 31). However, the source of the new component cannot be determined uniquely.