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Nearly one-third of the gamma-ray sources detected by Fermi are stillunidentified, despite significant recent progress in this effort. On the otherhand, all the gamma-ray extragalactic sources associated in the secondFermi-LAT catalog have a radio counterpart. Motivated by this observationalevidence we investigate all the radio sources of the major radio surveys thatlie within the positional uncertainty region of the unidentified gamma-raysources (UGSs) at 95% level of confidence. First we search for their infraredcounterparts in the all-sky survey performed by the Wide-field Infrared SurveyExplorer (WISE) and then we analyze their IR colors in comparison with those ofthe known gamma-ray blazars. We propose a new approach, based on a2-dimensional kernel density estimation (KDE) technique in the single[3.4]-[4.6]-[12] micron WISE color-color plot, replacing the constraint imposedin our previous investigations on the detection at 22 micron of each potentialIR counterpart of the UGSs with associated radio emission. The main goal ofthis analysis is to find distant gamma-ray blazar candidates that, being toofaint at 22 micron, are not detected by WISE and thus are not selected by ourpurely IR based methods. We find fifty-five UGS's likely correspond to radiosources with blazar-like IR signatures. Additional eleven UGSs having,blazar-like IR colors, have been found within the sample of sources found withdeep recent ATCA observations.

Unveiling the nature of the unidentified gamma-ray sources V: analysis of the radio candidates with the kernel density estimation