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

TL;DR

This study uses a novel kernel density estimation method on WISE infrared colors to identify potential distant gamma-ray blazar candidates among unidentified Fermi sources by analyzing radio and IR data.

Contribution

It introduces a new 2D KDE approach in IR color space to find gamma-ray blazar candidates missed by previous IR-only methods.

Findings

Identified 55 UGSs likely linked to blazar-like radio sources.

Discovered 11 additional UGSs with blazar-like IR colors from recent observations.

Enhanced the identification process of distant gamma-ray blazar candidates.

Abstract

Nearly one-third of the gamma-ray sources detected by Fermi are still unidentified, despite significant recent progress in this effort. On the other hand, all the gamma-ray extragalactic sources associated in the second Fermi-LAT catalog have a radio counterpart. Motivated by this observational evidence we investigate all the radio sources of the major radio surveys that lie within the positional uncertainty region of the unidentified gamma-ray sources (UGSs) at 95% level of confidence. First we search for their infrared counterparts in the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) and then we analyze their IR colors in comparison with those of the known gamma-ray blazars. We propose a new approach, based on a 2-dimensional kernel density estimation (KDE) technique in the single [3.4]-[4.6]-[12] micron WISE color-color plot, replacing the constraint imposed in our previous investigations on the detection at 22 micron of each potential IR counterpart of the UGSs with associated radio emission. The main goal of this analysis is to find distant gamma-ray blazar candidates that, being too faint at 22 micron, are not detected by WISE and thus are not selected by our purely IR based methods. We find fifty-five UGS's likely correspond to radio sources with blazar-like IR signatures. Additional eleven UGSs having, blazar-like IR colors, have been found within the sample of sources found with deep recent ATCA observations.