Radio Active Galactic Nuclei (Agns)

Extragalactic radio source population is a mixture of both AGNs and normal galaxies. In the former, the radio emission arises from the gas accretion onto super massive black holes (SMBH), i.e., from jets and lobes, or accretion flows, whereas in the later, the radio emission is related to relativistic plasma ejected by supernovae associated with massive formed stars, and to free-free emission from H11regions ionized by the same massive stars. The observed spectral energy distributions (SEDs) were found to be different from one source to another, even among AGNs, indicating that the structure and the geometry of the emitting regions also play important role. For these reasons, we aim at investigating how efficient are different selection criteria mostly used in radio-quiet AGNs when they are applied to radio sources. In order to identify clearly the main emission mechanism at each wavelength, and hence, deduce the object radio type, multi-wavelength selection criteria have been used in the classification processes, we have, thereby, used WISE color-color diagram, X-ray-to-optical flux ratios and MIR/radio ratios defined by L22μm/L1.4GHz or S22μum/S1.4GHz as selection criteria. The X-ray-to-optical flux ratios together with the MIR-to-radio ratios are proven to be more powerful in classification tasks. In fact, while the log(fx/fR)>-1selects efficiently pure AGNs, the ratio S22μm/S1.4AGHz is powerful for sources defined by log(fx/fR)<-1.Even if the presence of a supermassive black hole (SMBH) fueled by an accretion disk at centers of all Active galactic Nuclei (AGNs) is proven to be evident, the observed characteristics of the derived spectra are often different from source to another, which can be attributed to either different viewing angles, and intrinsic different structures.In the second work, we have employed low frequency radio variability as tool to select a large sample of face-on radio quasars in the SDSS DR7and SDSS DR10and compared to the sample of non-variable radio sources that are viewed at larger inclination angle with a goal to examene the anisotropy of quasars properties. The very high brightness temperature of radio variable sources indicates that the relativistic jet is beamed strongly toward the observer, consistent with a face-on view of these sources. We have made a comparison of the composite spectra of the variable and non-variable sources, and found significant difference among the two. Our result suggest that optical and near-UV continuum emission, as well as gas kinematics of the broad and narrow emission lines are anisotropic, although some further works are need to exclude possibility that variable sources are intrinsically different from radio non variable sources.