Where M87 Dilutes into Virgo: The Power-Law Halo, Its Integral, and Its Merging Radius

M87's stellar halo is the place where a galaxy's light and a cluster's light become the same thing, and its profile states the terms of the merger. Adopting the published description of the halo as a power law of intensity slope -1.8 passing through 27.0 magnitudes per square arcsecond in V at 100 kpc, this paper integrates it from 15 to 300 kpc. The intensity at 100 kpc is 0.577 solar luminosities per square parsec; the profile stands at 24.65 magnitudes per square arcsecond at 30 kpc, 25.65 at 50 kpc, and 28.35 at 200 kpc. It reaches 28.5, the level at which it merges indistinguishably into the general intracluster background, at 215 kpc. The integrated halo luminosity over the range is 1.02e+11 solar luminosities, 3.05e+11 solar masses of stars, and a fraction 0.437 of that light lies beyond 100 kpc, in the region where ownership by galaxy or cluster is a convention rather than a fact. M87 does not end at any radius its photometry can find; it dilutes into Virgo, and this paper quantifies the dilution.