We report an optical/UV jet and counterjet in M84 , previously unreported in archival HST imaging .
With archival VLA , ALMA , and Chandra imaging , we examine the first well-sampled spectral energy distribution of the inner jet of M84 , where we find that multiple co-spatial spectral components are required .
In particular , the ALMA data reveal that the radio spectrum of all four knots in the jet turns over at approximately 100 GHz , which requires a second component for the bright optical/UV emission .
Further , the optical/UV has a soft spectrum and is inconsistent with the relatively flat X-ray spectrum , which indicates a third component at higher energies .
Using archival VLA imaging , we have measured the proper motion of the innermost knots at 0.9 \pm 0.6 and 1.1 \pm 0.4 c , which when combined with the low jet-to-counterjet flux ratio yields an orientation angle for the system of 74 ^ { +9 } _ { -18 } ^ { \circ } .
In the radio , we find high fractional polarization of the inner jet of up to 30 % while in the optical no polarization is detected ( < 8 % ) .
We investigate different scenarios for explaining the particular multi-component SED of the knots .
Inverse Compton models are ruled out due to the extreme departure from equipartition and the unrealistically high total jet power required .
The multi-component SED can be naturally explained within a leptohadronic scenario , but at the cost of very high power in relativistic protons .
A two-component synchrotron model remains a viable explanation , but more theoretical work is needed to explain the origin and properties of the electron populations .