Unveiling the nature of the unidentified gamma-ray sources I: a new method for the association of gamma-ray blazars

TL;DR

This paper introduces a refined 3D color space method using PCA for identifying gamma-ray blazar candidates with high efficiency and completeness, improving association accuracy in gamma-ray source catalogs.

Contribution

A new PCA-based 3D color locus method for gamma-ray blazar identification, enhancing previous 2D approaches with higher completeness and efficiency.

Findings

Achieved ~81% completeness in blazar candidate identification.

Attained ~97% efficiency in the new association method.

Produced a catalog of gamma-ray blazar candidates with multi-frequency data.

Abstract

We present a new method for identifying blazar candidates by examining the locus, i.e. the region occupied by the Fermi gamma-ray blazars in the three-dimensional color space defined by the WISE infrared colors. This method is a refinement of our previous approach that made use of the two-dimensional projection of the distribution of WISE gamma-ray emitting blazars (the Strip) in the three WISE color-color planes (Massaro et al. 2012a). In this paper, we define the three-dimensional locus by means of a Principal Component (PCs) analysis of the colors distribution of a large sample of blazars composed by all the ROMA-BZCAT sources with counterparts in the WISE All-Sky Catalog and associated to gamma-ray source in the second Fermi LAT catalog (the WISE Fermi Blazars sample, WFB). Our new procedure yields a total completeness of c~81% and total efficiency of e~97%. We also obtain local estimates of the efficiency and completeness as functions of the WISE colors and galactic coordinates of the candidate blazars. The catalog of all WISE candidate blazars associated to the WFB sample is also presented, complemented by archival multi-frequency information for the alternative associations. Finally, we apply the new association procedure to all gamma-ray blazars in the 2FGL and provide a catalog containing all the gamma-ray candidates blazars selected according to our procedure.