Title: Jet-mode feedback in NGC 5972: insights from resolved MUSE, GMRT and VLA observations
Authors: Arshi Ali, Biny Sebastian, Darshan Kakkad, Sasikumar Silpa, Preeti Kharb, Christopher P. O’Dea, Mainak Singha, K, Rubinur, Stefi A. Baum, Omkar Bait, Sravani Vaddi, Sushma Kurapati
First Author’s Institution: Department of Physics, Savitribai Phule Pune University, India
Status: Accepted to The Astrophysical Journal [open]
Voorwerp Galaxies as Laboratories for Active Galactic Nuclei
Supermassive black holes (SMBHs) are believed to reside at the centers of nearly all massive galaxies. As they accrete matter, they can release enormous amounts of energy in the form of radiation, winds, and relativistic jets—powering active galactic nuclei (AGN) and influencing their host galaxies. This process, known as AGN feedback, can regulate star formation and the properties of the gas in the interstellar medium, making it a key mechanism in shaping how galaxies form and evolve over cosmic time.
Of the many diverse manifestations of AGN, radio “loud” galaxies stand out as powerful laboratories for studying feedback in action. Not only do these galaxies have OIII emission lines that are characteristic of AGN, but they also host intense radio-emitting lobes of gas that extend well beyond the structure of the galaxy, indicative of jets. (Today’s paper refers to these lobes as the “EELR,” or the extended emission-line region.)
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). Images adapted from NASA/ESA Hubble.
Originally discovered by a schoolteacher, Voorwerp galaxies are a special category of radio galaxies that are candidate sites of AGN 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 AGN feedback.
Today’s paper 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 AGN 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 AGN activity.
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 AGN jets. Figure 3 in the original paper.
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 from the AGN. The expected amount of energy from a radio jet would have been capable of driving outflows at these velocities.
Figure 3: The velocity profiles of the OIII emission lines in NGC 5972, a characteristic signature of the AGN extended emission line region. The velocities are aligned and enhanced along the jet axis, indicating that AGN feedback influenced the gas by powering jets and outflows. Adapted from Figure 6 in the original paper.
While the structure and movement of the ionized gas give promising hints of jet feedback, astronomers use a tool called “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 AGN, stars, or other processes. The results of the BPT analysis are shown in the left panel of Figure 4.
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 AGN (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. Figure 8 in the original paper.
In the case of NGC 5972, the radio jet is mostly ionized by radiation from AGN! 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 AGN—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 SMBHs 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 AGN-driven jets function.
Figure 5: Cartoon schematic diagram showing various mechanisms at play in NGC 5972, including the AGN jets, shocks, and outflows. Figure 13 in the original paper.
NGC 5972 is more than just a bizarre-looking galaxy—it’s a time capsule, preserving the memory of a powerful SMBH and revealing how its energy continues to shape the galaxy.
Astrobite edited by Alexandra Masegian.
Featured image credit: “Hubble view of green filament in galaxy NGC 5972” by NASA/ESA.
