HANG-ES. XXIV. First Detection of A Radio Nuclear Ring and Potential LLAGN in NGC 5792

We report the discoveries of a nuclear ring of diameter 10$\arcsec$($\sim$1.5 kpc) and a potential low luminosity active galactic nucleus (LLAGN)in the radio continuum emission map of the edge-on barred spiral galaxyNGC~5792. These discoveries are based on the Continuum Halos in Nearby Galaxies- an Expanded Very Large Array (VLA) Survey, as well as subsequent VLAobservations of sub-arcsecond resolution. Using a mixture of H$\alpha$ and 24$\mu$m calibration, we disentangle the thermal and non-thermal radio emissionof the nuclear region, and derive a star formation rate (SFR) of $\sim0.4~M_{\sun}$ yr$^{-1}$. We find that the nuclear ring is dominated bynon-thermal synchrotron emission. The synchrotron-based SFR is about threetimes of the mixture-based SFR. This result indicates that the nuclear ringunderwent more intense star-forming activity in the past, and now its starformation is in the low state. The sub-arcsecond VLA images resolve sixindividual knots on the nuclear ring. The equipartition magnetic field strength$B_{\rm eq}$ of the knots varies from 77 to 88 $\mu$G. The radio ring surroundsa point-like faint radio core of $S_{\rm 6GHz}=(16\pm4)$ $\mu$Jy with polarizedlobes at the center of NGC~5792, which suggests an LLAGN with an Eddingtonratio $\sim10^{-5}$. This radio nuclear ring is reminiscent of the CentralMolecular Zone (CMZ) of the Galaxy. Both of them consist of a nuclear ring andLLAGN.