Magnetically Driven Relativistic Jet in the High-Redshift Blazar OH~471

TL;DR

This paper investigates the magnetic and accretion processes powering a high-redshift blazar's relativistic jet, providing evidence for magnetically arrested disk (MAD) states influencing jet launching in the early universe.

Contribution

It presents the first detailed analysis of magnetic flux and jet launching mechanisms in a high-redshift blazar, supporting the role of MAD accretion in early cosmic jet formation.

Findings

Magnetic flux in the jet exceeds theoretical predictions for spin-powered jets.

OH 471's jet is consistent with being in a MAD state.

Magnetic fields are strong within the compact core, influencing jet dynamics.

Abstract

Context : Understanding the mechanisms that launch and shape powerful relativistic jets from supermassive black holes (SMBHs) in high-redshift active galactic nuclei (AGN) is crucial for probing the co-evolution of SMBHs and galaxies over cosmic time. Aims :We study the high-redshift ($z=3.396$) blazar OH~471 to explore the jet launching mechanism in the early Universe. Methods : Using multi-frequency radio monitoring observations and high-resolution Very Long Baseline Interferometry imaging over three decades, we study the milliarcsecond structure and long-term variability of OH~471. Results : Spectral modelling of the radio flux densities reveals a synchrotron self-absorbed spectrum indicating strong magnetic fields within the compact core. By applying the flux freezing approximation, we estimate the magnetic flux carried by the jet and find that it reaches or exceeds theoretical predictions for jets powered by black hole spin energy via the Blandford-Znajek mechanism. This implies that OH~471 was in a magnetically arrested disk (MAD) state where the magnetic flux accumulated near the horizon regulates the accretion flow, allowing efficient extraction of black hole rotational energy. Conclusions : Our study demonstrates the dominance of MAD accretion in powering the prominent radio flares and relativistic jets observed in the radio-loud AGN OH~471 and statistical studies of large samples of high-redshift AGN will shed light on the role of MAD accretion in launching and accelerating the earliest relativistic jets.