ALMA Observations of Extragalactic Optical Jets Suggest the Need for at Least Three Emission Components

The large-scale jets of plasma emitted from radio-loud active galactic nuclei (AGN) are known to interact with the intergalactic medium, impact star formation within galaxies, and play a role in galaxy evolution. Despite being very influential on their surrounding environment, many properties of AGN jets are still not well understood, including the emission mechanisms responsible for the X-rays emitted on kiloparsec scales. It was previously believed that a single continuous synchrotron spectrum extended from the radio to optical/UV frequencies. However, with recent ALMA observations, in conjunction with new and archival VLA and HST data, we have discovered multiple jets displaying a synchrotron spectrum that unexpectedly turns over at approximately 100 GHz. This turnover indicates that a single synchrotron spectrum does not account for the higher frequency radiation. As a result of this turnover, in addition to the X-ray spectral hardness, we conclude that at least three distinct emission components are required to explain the jet emission. We explore as possible explanations the presence of multiple synchrotron components, as well as leptohadronic models.