Unveiling blazar candidates within unassociated Fermi sources through radio and near-infrared observations

¹ Observatorio Astronómico Félix Aguilar, Universidad Nacional de San Juan, Av. Benavidez Oeste, 8175 San Juan, Argentina
² Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Godoy Cruz 2290 Ciudad Autónoma de Buenos Aires, Argentina
³ Instituto de Ciencias Astronómicas de la Tierra y el Espacio (CONICET-UNSJ), Av. España, 1512 sur, San Juan, Argentina
⁴ Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque, B1900FWA, La Plata, Buenos Aires, Argentina
⁵ Instituto de Astrofísica de La Plata (CONICET-UNLP), Paseo del Bosque, B1900FWA, La Plata, Buenos Aires, Argentina
⁶ Departamento de Física, Universidade Federal de Santa Catarina, Trindade, 88040-900 Florianópolis, Brazil
⁷ Instituto de Astrofísica, Departamento de Física y Astronomía, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. Fernandez Concha 700 Las Condes, Santiago, Chile
⁸ Vatican Observatory, Specola Vaticana, V00120 Vatican City State, Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 November 2025
Accepted: 23 February 2026

Abstract

Context. The Fermi Large Area Telescope (LAT) detected 7195 γ-ray sources within the first 12 years of scientific observations, spanning an energy range from 50 MeV to 1 TeV. The fourth source catalog 4FGL-DR4 (Fermi Gamma-ray LAT Data Release 4), contains 2423 unassociated γ-ray sources (UGSs). This catalog provides an excellent opportunity to explore the scientific potential of these high-energy targets and to identify their counterparts at different wavelengths.

Aims. We identified blazar candidates as counterparts to UGSs in the Galactic plane through a multiwavelength analysis of near-infrared and radio observations.

Methods. We compiled an initial list of 318 non-extended Fermi sources located in the Galactic plane. After filtering the list based on interstellar extinction and the 95% confidence Fermi error ellipse, we selected 22 UGS for evaluation. We searched the Very Large Array Sky Survey (VLASS) catalog for sources of continuum radio emission near each target on the sample list. We identified a total of 34 radio sources as potential counterparts to the 22 UGSs within the Fermi error ellipses. We confirmed these radio sources as blazar candidates by analyzing their associated near-infrared sources using the color-magnitude diagram (CMD), color-color diagram (CCD), and K_s-band variability from the VISTA Variables in the Via Lactea (VVV) catalog. Additionally, we examined the radio spectral energy distribution (SED) using observations from the Rapid ASKAP Continuum Survey (RACS).

Results. We found evidence for the association of five UGSs: four with blazar candidates and one with an elliptical galaxy. Additionally, we estimated its SED using RACS bands.