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Written in the Gas: Jet Feedback in a Voorwerp Galaxy

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NGC 5972
The looping green object in this Hubble Space Telescope image of NGC 5972 is a relic of a more active phase in the galaxy's past. [NASA, ESA, and W. Keel (University of Alabama, Tuscaloosa)]

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Title: Jet-Mode Feedback in NGC 5972: Insights from Resolved MUSE, GMRT, and VLA Observations
Authors: Arshi Ali et al.
First Author’s Institution: Savitribai Phule Pune University
Status: Published in ApJ

Voorwerp Galaxies as Laboratories for Active Galactic Nuclei

Supermassive black holes are believed to reside at the centers of nearly all massive galaxies. As supermassive black holes accrete matter, they can release enormous amounts of energy in the form of radiation, winds, and relativistic jets — powering active galactic nuclei and influencing their host galaxies. This process, known as active galactic nucleus feedback, can regulate star formation and the properties of the gas in the interstellar medium, making it a key mechanism for shaping how galaxies form and evolve over cosmic time.

Of the many diverse manifestations of active galactic nuclei, radio “loud” galaxies stand out as powerful laboratories for studying feedback in action. Not only do these galaxies have characteristic [O III] emission lines, but they also host intense radio-emitting lobes of gas that extend well beyond the structure of the galaxy, indicative of jets. (Today’s article refers to these lobes as the extended emission-line region or EELR.)

Originally discovered by a schoolteacher, Voorwerp galaxies are a special category of radio galaxies that are candidate sites of active galactic nucleus activity in terms of their emission-line signatures. Moreover, they exhibit intriguing clouds of ionized gas that may have originated from jets. Figure 1 shows some examples of Voorwerp galaxies. Exploring these galaxies can shed light on how jets interact with the interstellar medium, a major player in active galactic nucleus feedback.

trio of Voorwerp galaxies

Figure 1: Voorwerp galaxies are compelling laboratories for exploring the interaction between jets and the interstellar medium. Examples are Hanny’s Voorwerp (left), NGC 5972 (middle), and the Teacup Quasar (right). [NASA, ESA, W. Keel (University of Alabama), and the Galaxy Zoo Team; NASA, ESA, and W. Keel (University of Alabama, Tuscaloosa); NASA, ESA, and W. Keel (University of Alabama, Tuscaloosa)]

Today’s article focuses on the physical and kinematic properties of one particular Voorwerp galaxy, NGC 5972. This galaxy is interesting for its bizarre, helical structure of ionized gas, as well as hints of a rich history of active galactic nucleus activity. Could jet feedback have played a significant role in the evolution of this galaxy?

Evidence for Relativistic Jets in NGC 5972

To study the interstellar medium of the Voorwerp galaxy, the authors combined observations from multiple instruments that probe different phases of the galaxy’s gas. Specifically, they used data from the Very Large Telescope (VLT), the Giant Metrewave Radio Telescope (GMRT), and the Very Large Array (VLA) to create maps of the ionized gas emission, allowing them to trace the structures and movement of the gas and jet material. Together, these datasets offer a comprehensive, multi-wavelength view of how the radio jet shaped the surrounding interstellar medium. The maps of NGC 5972, shown in Figure 2, display an impressive spiraling structure that could be the result of prolonged active galactic nucleus activity.

radio emission of NGC 5972

Figure 2: The radio emission of NGC 5972 reveals the extended helical, spiral structure of the ionized gas, where the inner jets are connected to the outer lobes (top: VLA, bottom: GMRT). This suggests that the intriguing shape of NGC 5972 could have originated from active galactic nucleus jets. [Ali et al. 2025]

When the authors examined the extended emission-line region, they found that the velocity profiles (shown in Figure 3) are closely aligned with the direction of where we would expect to find a radio jet. The enhanced velocities around the jet region likely represent gas that is outflowing due to feedback. The expected amount of energy from a radio jet would have been capable of driving outflows at these velocities.

velocity profiles of the OIII emission lines

Figure 3: The velocity profiles of NGC 5972’s [O III] emission lines, a characteristic signature of the active galactic nucleus’s extended emission-line region. The velocities are aligned and enhanced along the jet axis, indicating that active galactic nucleus feedback influenced the gas by powering jets and outflows. [Adapted from Ali et al. 2025]

While the structure and movement of the ionized gas give promising hints of jet feedback, astronomers use a tool called Baldwin–Phillips–Terlevich (BPT) analysis to figure out what exactly is ionizing the gas. By comparing the ratio of different emission lines, we can categorize whether the galaxy’s gas was primarily ionized by radiation from an active galactic nucleus, stars, or other processes. The results of the BPT analysis are shown in the left panel of Figure 4.

sources of ionized gas in NGC 5972

Figure 4: The left panel shows the ionizing sources of the gas in NGC 5972. While the gas along the jet axis is ionized by radiation from the active galactic nucleus (orange in the diagram), the regions transverse to the jet are ionized by shock waves (blue). Moreover, the gas in the jet regions is more turbulent, as shown in the right panel. [Adapted from Ali et al. 2025]

In the case of NGC 5972, the radio jet is mostly ionized by radiation from the active galactic nucleus! However, the gas perpendicular to the jet shows a different signature — one that matches shock waves rather than strong radiation. In addition, the gas in the shock region is more turbulent (right panel of Figure 4). This suggests that the radio jet is not just a byproduct of the active galactic nucleus — it actively disturbs and heats the surrounding gas by way of shocks. This dual process of jet-induced shocks creates a richer picture of how supermassive black holes interact with the interstellar medium.

Putting the Story of NGC 5972 Together

These findings suggest that jet-driven feedback plays a crucial role in shaping the extended emission-line region of NGC 5972 (see Figure 5 for a summary). The interaction between the radio jet and the surrounding gas not only sustains ionization but also influences the gas structure. To further unravel the jet’s impact, future high-resolution radio observations will be essential, providing deeper insights into how active galactic nucleus–driven jets function.

cartoon diagram of NGC 5972

Figure 5: Cartoon schematic diagram showing various mechanisms at play in NGC 5972, including the active galactic nucleus jets, shocks, and outflows. [Ali et al. 2025]

NGC 5972 is more than just a bizarre-looking galaxy — it’s a time capsule, preserving the memory of a powerful supermassive black hole and revealing how its energy continues to shape the galaxy.

Original astrobite edited by Alexandra Masegian.

About the author, Shalini Kurinchi-Vendhan:

After studying astrophysics and literature at Caltech, I moved onto a Fulbright Fellowship in Heidelberg, Germany. I’m passionate about using computer simulations to explore supermassive black holes and galaxy evolution—but I also love poetry and traveling.