The Association of Faint Radio Sources with Fluctuations in the X-Ray Background

We have examined edited, flat-fielded images from two of the Einstein Deep Survey pointings for X-ray fluctuations down to the 2 σ level. Deep VLA images at 20 cm were obtained for both fields, and a comparison of the positions of radio sources brighter than 150 microjanskys with the X-ray fluctuations reveals 21 coincidences; only seven are expected for uncorrelated samples, yielding a chance occurrence probability of 10^-5. In addition, we find that the correlation of X-ray sources with radio source positions has a higher amplitude than the autocorrelation function for the sources alone; i.e., X-ray emitting objects are found preferentially in areas of high submillijansky radio source density. While our results are consistent with the notion that the majority of the 0.3-3.5 keV X-ray sources at a flux threshold of ∼10¹⁴ ergs cm^-2 s^-1 are the active galactic nuclei seen at brighter fluxes, they reveal a potentially new population of X-ray and radio luminous galaxies which could contribute substantially to the cosmic X-ray background.