Jet Collimation Profile of Low-Luminosity AGN M84: Insight into the Jet Formation in the Low Accretion Regime

TL;DR

This study uses high-resolution radio observations to analyze the jet structure of the low-luminosity AGN M84, revealing a transition from semi-parabolic to conical shape and offering insights into jet formation in low-accretion environments.

Contribution

First detailed measurement of jet collimation profile in a low-luminosity AGN, linking jet shape transition to accretion rate in M84.

Findings

Jet transitions from semi-parabolic to conical at ~1.67 x 10^4 Schwarzschild radii.

M84 jet is less collimated compared to other LLAGNs.

Provides constraints for jet formation models in low-accretion regimes.

Abstract

Recent advancements in high-resolution Very Long Baseline Interferometry (VLBI) have significantly improved our understanding of jet collimation near supermassive black holes in active galactic nuclei (AGNs), particularly in high-power systems. However, the collimation properties of jets in low-luminosity AGNs (LLAGNs) remain poorly explored. In this study, we investigate the jet structure of M84, a nearby radio galaxy and a representative LLAGN, to probe jet collimation properties in a low-accretion regime. Utilizing astrometric phase-referencing observations from the Very Long Baseline Array (VLBA), supplemented by archival Very Large Array (VLA) data, we trace the jet geometry of M84 over a broad range of scales, from approximately 10^2 to 10^7 Schwarzschild radii (rs). Our analysis reveals a well-defined transition from a semi-parabolic profile, W(r) proportional to r^0.71, to a conical shape, W(r) proportional to r^1.16, occurring at approximately 1.67 x 10^4 rs. This indicates that the M84 jet is notably less collimated than those in other known LLAGN sources. Our findings provide new insights into the relationship between jet collimation and accretion rate, offering crucial constraints for jet formation models in LLAGNs.