EVIDENCE FOR ANOMALOUS DUST-CORRELATED EMISSION AT 8 GHz

Abstract

In 1969 Edward Conklin measured the anisotropy in celestial emission at 8 GHz with a resolution of 16.degrees 2 and used the data to report a detection of the cosmic microwave background 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 the Wilkinson Microwave Anisotropy Probe (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 alpha nu(beta). Free-free emission has beta approximate to -2.15 and synchrotron emission has beta approximate to -2.7 to -3. Thermal dust emission (beta approximate to 1.7) 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 chi(2) = 31). However, the source of the new component cannot be determined uniquely.