Application of the MST clustering to the high energy gamma-ray sky. IV - Blazar candidates found as possible counterparts of photon clusters

TL;DR

This paper uses the MST clustering algorithm on Fermi-LAT gamma-ray data to identify potential blazar candidates as counterparts to photon clusters, revealing new sources without prior associations.

Contribution

It introduces a novel application of MST clustering to high-energy gamma-ray data for identifying unassociated blazar candidates.

Findings

Identified 30 gamma-ray cluster candidates.

Verified candidates with Maximum Likelihood analysis.

Most candidates lack optical spectroscopic data.

Abstract

We present the results of a cluster search in the Fermi-LAT Pass 8 gamma-ray sky by means of the Minimum Spanning Tree algorithm, at energies higher than 10 GeV and at Galactic latitudes higher than 25 degrees. The selected clusters have a minimum number of photons higher than or equal to 5, a high degree of concentration, and are without a clear corresponding counterpart in blazar catalogues. A sample of 30 possible gamma-ray sources was obtained. These objects were verified by applying the standard Maximum Likelihood analysis on the Fermi-LAT data. A search for possible radio counterparts in a circle having a radius of 6 arcmin was performed, finding several interesting objects, the majority of them without optical spectroscopical data. These can be considered as new blazar candidates. Some of them were already noticed as possible blazars or Active Galactic Nuclei in previous surveys, but never associated with high energy emission. These possible counterparts are reported and their properties are discussed.