Synthetic synchrotron emission maps from MHD models for the jet of M87

TL;DR

This paper develops self-consistent MHD models and synthetic synchrotron emission maps for the M87 jet, successfully reproducing observed morphological features and brightness profiles, and providing insights into jet collimation and shock structures.

Contribution

It introduces a two-zone MHD model of the M87 jet that explains its collimation, morphology, and brightness features, aligning well with observations.

Findings

The model reproduces the jet's opening angle over large scales.

Synthetic maps show center-bright and limb-bright profiles matching observations.

Recollimation shock location coincides with the HST-1 knot.

Abstract

We present self-consistent global, steady-state MHD models and synthetic optically thin synchrotron emission maps for the jet of M87. The model consist of two distinct zones: an inner relativistic outflow, which we identify with the observed jet, and an outer cold disk-wind. While the former does not self-collimate efficiently due to its high effective inertia, the latter fulfills all the conditions for efficient collimation by the magneto-centrifugal mechanism. Given the right balance between the effective inertia of the inner flow and the collimation efficiency of the outer disk wind, the relativistic flow is magnetically confined into a well collimated beam and matches the measurements of the opening angle of M87 over several orders of magnitude in spatial extent. The synthetic synchrotron maps reproduce the morphological structure of the jet of M87, i.e. center-bright profiles near the core and limb-bright profiles away from the core. At the same time, they also show a local increase of brightness at some distance along the axis associated to a recollimation shock in the MHD model. Its location coincides with the position of the optical knot HST-1. In addition our best fitting model is consistent with a number of observational constraints such as the magnetic field in the knot HST-1, and the jet-to-counterjet brightness ratio.