Portion of the spectrum around the [Fe XXI] λ1354.1, with velocities relative to it in the rest frame of M87. A linear estimate of the local background is indicated with the black dotted line, and the overall model is shown with the red solid line. Our best-fit model for this line has , and , and the 2σ upper limit on the velocity dispersion is σ_r < 229 km s⁻¹. Unlike the other lines presented in this paper, [Fe XXI] traces T ~ 10⁷ K plasma, and it appears to be slightly blueshifted while all the other FUV lines are redshifted. We discuss the implications of this blueshift, and potential geometries which can explain it, in Sect. 7.1.