Characterization of a sample of $γ$-ray active galactic nuclei

Abstract: We analyse 77 \textit{Fermi} sources and their potential low-energy counterparts previously proposed in the literature. These sources were classified as active galactic nuclei, mainly blazars, based on optical spectroscopy. The main goals of this work are to examine these associations, classify the blazars based on their multi-wavelength spectral energy distributions (SEDs), and identify potential masquerading BL Lac objects. Through SED analysis, we assess whether the multi-wavelength emission follows the characteristic double-peaked curve of blazars. Additionally, we propose the region of origin of the emission at different wavelengths, investigate the correlation between $\gamma$-ray and lower-energy emission, and classify objects as low-, intermediate-, high- or extreme high synchrotron peaked (LSP, ISP, HSP, E-HSP) blazars. We search for masquerading BL Lacs, a class of flat-spectrum radio quasars where broad emission lines are swamped by non-thermal jet emission. The multi-wavelength analysis revealed that the 64 radio-loud sources in our sample exhibit an SED with a double-peak structure, typically ascribed to jet activity. Based on the synchrotron peak, 46 are HSP, 11 as ISP, and 7 as LSP. We also found 9--18 masquerading BL Lac candidates ($\approx$15--30\% of the radio-loud sample). For the 13 radio-quiet UGSs, the SEDs do not exhibit the double-peak structure typical of jetted AGN. Further analysis ruled out star formation as the origin of the observed $\gamma$-ray emission, making its reconciliation with lower-energy emission challenging. We explored alternative counterparts, identifying low-energy matches for 7 sources, with no plausible counterparts found for the others.