Internal structure and dynamics of the kiloparsec-scale jet in M87

Abstract

Detailed analysis of HST and VLA observations enables quantitative modeling of the internal structure of the kiloparsec-scale jet in M87. The jet transverse profiles can be modeled by double-Gaussian profiles. The jet structure is dominated by two threads resembling closely a double helix visible until about 20″ distance. It is produced by a combination of the helical mode and of the elliptical mode of Kelvin-Helmholtz instability. The elliptical mode dominates the pre-knot A jet, while the helical mode becomes prominent at larger distances. Modeling the jet structure constrains well the instability pattern speed, β_w=0.5 c and jet viewing angle, θ_j=40°. The estimated bulk Lorentz factor of the jet is 3.4. The model reproduces the jet structure on scales of up to 50″ (accounting for the jet curvature).