A Short Review on the Multi-Wavelength Spectral Energy Distribution of Low-Luminosity Active Galactic Nuclei

Black hole accretion and jet formation are very fundamental and important physical processes in astrophysics. Despite the great progress made in the last decades, our knowledge of the physics of BHs remains highly incomplete. The compact radio cores and/or weak jets are usually observed in nearby LLAGNs, which can help us to better understand and explore the jet and accretion physics due to their proximity and fruitful multi-waveband observations. In this short review, we studied the recent multi-waveband observations of the SMBH activities in LLAGNs and found that the high-resolution millimeter/submillimeter observations are very important for the nearby LLAGNs. The centers of LLAGNs are believed to be powered by hot accretion flow and jets. The aim of this review is to model the multi-wavelength spectral energy distribution (SED) of LLAGNs, and all the data we used here in the literature correspond to the core emission. We found these important features in LLAGNs are hard to fit by pure ADAF or jet models, which implies that they may come from different regions around the SMBH. We usually use the coupled ADAF and jet model to fit the multi-wavelength SED of LLAGNs and found that the submillimeter bump can be naturally modeled by the synchrotron emission of the thermal electrons in ADAF, which is very useful for us to constrain the physical parameters in the accretion disk and jet.