MHD models and synthetic synchrotron maps for the jet of M87

TL;DR

This paper develops a self-consistent MHD model of the M87 jet with a two-zone structure, successfully reproducing observed collimation and morphology, and generates synthetic synchrotron maps to compare with observations.

Contribution

It introduces a novel two-zone MHD model for the M87 jet, combining an inner relativistic outflow with an outer cold disk-wind, and produces synthetic emission maps for observational comparison.

Findings

The outer disk wind efficiently collimates the jet via magneto-centrifugal mechanism.

The model matches the observed opening angle of M87's jet over large spatial scales.

Synthetic synchrotron maps can reproduce key morphological features of the jet.

Abstract

We present a self-consistent MHD model 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 for a wide range of parameters and matches the measurements of the opening angle of M87 over several orders of magnitude in spatial extent. In the second part of this work, we present synthetic synchrotron emission maps for our MHD models. In principle the two-zone model can reproduce the morphological structure seen in radio observations, as central-peaked profiles across the jet close the the source, limb-bright further down the jet, and a bright knot close to the position of HST-1. However it is difficult to reconcile all features into a single set of parameters.