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Title: You Shall Not Pass! The Propagation of Low-/Moderate-Powered Jets Through a Turbulent Interstellar Medium
Authors: Olga Borodina et al.
First Author’s Institution: Center for Astrophysics | Harvard & Smithsonian
Status: Published in ApJ
The central black holes of some galaxies are surrounded by accretion disks of hot infalling gas. In cases when the accretion disk is massive and highly energetic, this central system forms an active galactic nucleus that outshines the rest of the galaxy. Active galactic nucleus feedback is the process of energetic interactions between the central supermassive black hole and its surroundings. Active galactic nuclei are essential for galaxy quenching, and correctly modeling their contribution is important for accurate cosmological simulations.
Active galactic nuclei release the energy from their accretion via winds, which are widespread outflows, and jets. Jets are collimated, fast outflows of baryonic matter that can spread out from hundreds to tens of thousands of parsecs from their origin. There’s a big range in power for jets, ranging from a low end of around 1038 erg/s to a high end of 1046 erg/s. For context, our Sun emits at about 1033 erg/s.
As jets pass through their host galaxy, they interact with the gas and dust of the interstellar medium. There isn’t a lot of observational evidence for what goes on in that interaction, as the scale of resolution needed is so small — on the order of parsecs within the galaxy. Cosmological simulations don’t model scales small enough to accurately simulate these interactions, and they instead rely on feedback models that implement the macroscale effects. This means we could be missing part of the picture. Today’s article considers galaxy-scale numeric models for jets passing through a turbulent interstellar medium to study how the jet is affected by the gas and dust.
To do this, the authors used the Arepo code, which has an adaptive mesh setup that improves the resolution in areas that need it. They set up a 2-kiloparsec-cubed box full of gas with properties based on real galaxies’ interstellar media. This study is unique compared to other works because the authors use a filamentary structure for the interstellar medium, while previous studies used a clumpy structure. This filamentary structure reflects our actual Milky Way’s interstellar medium and creates more low-density cavities for the jet to interact with. The authors studied three jet powers on the low to intermediate end, of 1038, 1040, and 1043 erg/s. This is also unique to the study, as many works look at higher-powered jets, which produce large-scale radio galaxies, despite lower powers being more common. The jets were launched along the x-axis and had a tracer set up to track their positions through time.
Figure 1: From top to bottom, the high to low power jets, which are traced in color against the background interstellar medium density in grayscale. The lower power jets are stalled by the interstellar medium and do not make it as far out in the simulation space. [Adapted from Borodina et al. 2025]
The highest-power jets, 1043 erg/s, were easily able to pass through the turbulent environment and reach the outer boundary of the simulation. They mostly traveled along the axis that the jet was launched along, with some lateral expansion.
The intermediate-power jets, 1040 erg/s, were highly disrupted and redirected from the axis they were launched along. The jets bent, filled the low-density cavities between the filaments, and produced bubble-like shapes. These jets did make it all the way to the simulation boundary, but at later times and not along the axis they were initialized on. These intermediate-power jets don’t have enough ram pressure — the pressure against the gas due to the jet’s motion — to push through the turbulent structure of the interstellar medium, and they have to fill pre-existing cavities rather than plowing their own. The authors developed an analytic model for the minimum energy needed for jets to be able to plow through the interstellar medium, at approximately 1041 erg/s.
The jets in the lowest-power case, 1038 erg/s, were stalled out by the interstellar medium within the first kiloparsec of travel. They couldn’t penetrate the higher-density regions of the interstellar medium the way the 1040 erg/s case could, and they couldn’t make it to lower-density cavities to expand into.
All three of these cases were slower and shorter than the same power of jets run in a non-turbulent simulation, with the most significant disruption in the lowest-powered jets. This work demonstrates that a turbulent interstellar medium–jet interaction can be the sole cause of observed asymmetric and bent active galactic nucleus jets. By improving our understanding of this small-scale interaction, the authors are contributing to making better active galactic nucleus feedback models in cosmological simulations.
Original astrobite edited by Ansh Gupta.
About the author, Lindsey Gordon:
Lindsey Gordon is a fourth-year PhD candidate at the University of Minnesota. She works on active galactic nucleus jets, radio relics, magnetohydrodynamics simulations, and how to use AI to study all those things better.