4. SUMMARY AND FUTURE WORK

We have reviewed the current observational status of the M87 jet, as well as several models and problems suggested by the data. To briefly summarize:

1. High resolution observations show the jet is well collimated on scales from about 1 to 1000 pc, with evidence collimation extending down to scales ~ 0.01 pc. Beyond 1 kpc the jet passes through "shock-like" structures, becomes unstable and poorly collimated, but yet continues to scales ~ 35 kpc.

2. The optical and X-ray morphology of the 25" (2 kpc) jet, except for a few systematic trends, is nearly identical to the radio morphology. Knots along the inner jet have similar radio-to-optical spectra, thus creating the "particle lifetime" problem.

3. Comparison of radio images from different epochs give evidence for proper motions with typical apparent speeds between 0.5c and 1.0c. Speeds up to 3c are seen for the inner jet.

4. The recent discovery of an optical continuum hot spot opposite the jet strongly suggests a counter-jet is present.

5. The emission regions within the jet appear to be out of pressure balance with the surrounding interstellar medium. It is possible that some of these regions are freely expanding, while others may be shocks. The most serious confinement problems appear in knot B, and magnetic effects may be able to provide confinement.

6. It is difficult to produce the observed radio-to-X-ray spectrum with existing models.

7. We have outlined a kinematic model wherein the first kpc of the jet moves with a relativistic velocity ( 3). The jet is then slowed at several shocks, and finally proceeds outward to distances ~ 35 kpc at sub-relativistic speeds. In this model the inner jet is aligned about 40° from the line of sight.

Future VLA observations, as well as monitoring with HST, are needed to confirm the observed motions. As speeds are measured for more regions, it may be possible to assemble and observed flow diagram, and hence perform detailed tests of numerical models. VLBI monitoring may clarify the situation at pc-scales, where low velocities have been seen. Combined radio, infrared, optical, UV, and X-ray observations at similar resolution ( 1") are needed to assemble a detailed spectrum of the jet, both in the knots and inter-knot regions. This may elucidate the cause of the optical spectral break and the process responsible for the X-rays. Theoretical and numerical models are needed which address the possibility of relativistic flow for the inner jet, and the consequences this may have for M87 and other FR-I sources.