Using evolutionary algorithms to model relativistic jets

Abstract

Context. High-resolution Very-Long-Baseline Interferometry (VLBI) observations of NGC 1052 show a two sided jet with several regions of enhanced emission and a clear emission gap between the two jets. This gap shrinks with increasing frequency and vanishes around ν ∼ 43 GHz. The observed structures are due to both the macroscopic fluid dynamics interacting with the surrounding ambient medium including an obscuring torus and the radiation microphysics. In order to model the observations of NGC 1052 via state-of-the art numerical simulations both the macro-and micro-physics have to be taken into account. Aims. In this paper we investigate the possible physical conditions in relativistic jets of NGC 1052 by directly modelling the observed emission and spectra via state-of-the-art special-relativistic hydrodynamic (SRHD) simulations and radiative transfer calculations. Methods. We performed SRHD simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code Ratpenat. To investigate the physical conditions in the relativistic jet we coupled our radiative transfer code to evolutionary algorithms and performed simultaneous modelling of the observed jet structure and the broadband radio spectrum. During the calculation of the radiation we consider both thermal and non-thermal emission. In order to compare our model to VLBI observations we take into account the sparse sampling of the u-v plane, the array properties and the imaging algorithm. Results. We present for the first time an end-to-end pipeline for fitting numerical simulations to VLBI observations of relativistic jets taking into account the macrophysics including fluid dynamics and ambient medium configurations together with thermal/non-thermal emission and the properties of the observing array. The detailed analysis of our simulations shows that the structure and properties of the observed relativistic jets in NGC 1052 can be reconstructed by a slightly over-pressured jet (d k ∼ 1.5) embedded in a decreasing pressure ambient medium

Polarimetric Properties of Event Horizon Telescope Targets from ALMA

“…The cold gas in the torus can be photoionized by UV photons from the inner accretion disk and the mixture of thermal and non-thermal material could be responsible for the strong depolarization of the inner regions via Faraday rotation-and one speaks of Faraday depolarization. In the case of NGC 1052, Fromm et al (2018Fromm et al ( , 2019 created synthetic radio maps of the jets using special-relativistic hydrodynamic simulations and suggested that an obscuring torus can explain some of the observed properties of these jets. In fact, the presence of a massive (∼10 7 M e ) and dense (> 10 7 cm −3 ) molecular torus has been recently demonstrated with ALMA observations (Kameno et al 2020).…”

THEZA: TeraHertz Exploration and Zooming-in for Astrophysics

“…To illustrate the jet imaging possibilities with Space VLBI, we consider the jet model by [29][30][31]. VLBI observations of radio galaxies reveal highly collimated jets surrounded by obscuring dusty tori.…”

Ambilateral collimation study of the twin-jets in NGC 1052

“…This is consistent with a globally averaged column density of (1−2) × 10 23 cm −2 estimated from X-ray observations (Baloković et al 2021). This results in an emission gap between both jet cores at frequencies below 43 GHz; see modelling by Fromm et al (2018Fromm et al ( , 2019. At centimetre(cm)-wavelengths the mean speeds of features in both jets have been derived as β ≤ 0.39 (Vermeulen et al 2003;Böck 2012;Lister et al 2019).…”