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Despite the large number of discoveries made recently by Fermi, the originsof the so called unidentified gamma-ray sources remain unknown. The largenumber of these sources suggests that among them there could be a populationthat significantly contributes to the isotropic gamma-ray background and istherefore crucial to understand their nature. The first step toward a completecomprehension of the unidentified gamma-ray source population is to identifythose that can be associated with blazars, the most numerous class ofextragalactic sources in the gamma-ray sky. Recently, we discovered thatblazars can be recognized and separated from other extragalactic sources usingthe infrared (IR) WISE satellite colors. The blazar population delineates aremarkable and distinctive region of the IR color-color space, the WISE blazarstrip. In particular, the subregion delineated by the gamma-ray emittingblazars is even narrower and we named it as the WISE Gamma-ray Strip (WGS). Inthis paper we parametrize the WGS on the basis of a single parameter s that wethen use to determine if gamma-ray Active Galactic Nuclei of the uncertain type(AGUs) detected by Fermi are consistent with the WGS and so can be consideredblazar candidates. We find that 54 AGUs out of a set 60 analyzed have IR colorsconsistent with the WGS; only 6 AGUs are outliers. This result implies that avery high percentage (i.e., in this sample about 90%) of the AGUs detected byFermi are indeed blazar candidates.

The WISE gamma-ray strip parametrization: the nature of the gamma-ray Active Galactic Nuclei of Uncertain type