Astronomers report that the active galactic nucleus in galaxy VV 340a is producing a strikingly wobbling outflow jet, a discovery that challenges current ideas on star-formation.
The recent work, which reveals highly unusual conditions for a young, star-forming galaxy, relied on data from the James Webb Space Telescope (JWST), Keck-II telescope, the Jansky Very Large Array (VLA), and the Atacama Large Millimeter/submillimeter Array.
The researchers reported their findings in a recent paper published in Science, explaining how they developed a mathematical model of the gas outflow and discovered the anomalous behavior.
Active Active Nuclei
Astronomers have conventionally ascribed to a two-mode paradigm for the way in which an active galactic nucleus (AGN) affects star formation in its host galaxy. In a mode known as the “radiative” or “ejective” mode, extremely hot material from the accretion disk funnels into the black hole, which combines with star-forming gas in the galaxy to produce a tremendous outflow through radiative pressure.
This wide, typically hourglass-shaped outflow can eject important star-forming gas from the galaxy, quickly depleting the fuel required for star formation, and normally occurs in younger galaxies in their active star-forming phase.
The other mode is preventive, in which the accretion disk is channeled into plasma jets that stream past the edges of the galaxy. These jets then heat gas beyond the galaxy’s edge, which should eventually fall into the galaxy at some later time. In this mode, an AGN doesn’t just deplete the fuel; it removes a future fuel source for subsequent rounds of star formation. This tends to occur in older galaxies.
Challenging Current Paradigms
However, recent observations are starting to show cracks in this two-mode paradigm. The researchers behind the new study set out not to study galaxy VV 340, but also to investigate AGN-powered outflows in infrared-luminous galaxies on a broader scale.
“To our knowledge, this is possibly the clearest case of a ‘misfit’—a disk galaxy where a low-power jet is doing the heavy lifting of feedback,” lead author Justin A. Kader told The Debrief. “VV 340 is a merging pair of disk galaxies, and VV 340a (the subject of the paper) is enormously bright in the infrared.”
“Initially, my plan was to work on a paper that included all of the more than 30 LIRGs in our sample, studying population-level trends between feedback and host galaxy properties,” Kader explained, adding that “when I looked at the VV 340a data we had collected with JWST, I was immediately struck by the very large and strangely collimated appearance of the highly ionized coronal gas surrounding the AGN.”
“This was a serendipitous discovery,” Kader said. “[W]e did not expect to find such anomalous outflow activity.”
Discovery of a Strange Galactic Jet
The researchers discovered extended coronal gas in the outflow by accident while reviewing data from the James Webb Space Telescope. From that data, they calculated the gas’s motion, which was found to be outward from the galactic center.
“We happened to have radio wave imagery of this galaxy from VLA, and when we overlaid it, we saw a bent beam of synchrotron emission that matched up very closely with the coronal gas,” Kader explained. “We quickly realized there was a radio jet coming from the AGN, and based on the energy budget of the jet, it is sufficiently powerful to be the driving engine for this coronal gas outflow.”
“One of the most interesting facets of this system is that the radio wave emission forms not only a jet, but an S-shaped one — the telltale signature of a ‘precessing’ or wobbling jet, which changes direction over time like a lighthouse beam,” Kader continued.
Modeling an Active Galactic Nucleus
Arriving at the team’s result was a lengthy process and involved sorting through many issues. Using the James Webb Space Telescope data, the researchers iterated numerous input combinations into a mathematical model of the jets. Each combination produced a 3D model, which the team then used to generate a 2D image. The team validated the model by comparing its 2D images with VLA observations, confirming that the ionized gas was outflowing.
“This model of a wobbling jet ejecting material from the galaxy is really the end result of a long process of trying to understand how all of the individually odd pieces of this puzzle fit together—it definitely kept me awake at night,” Kader said. “There was not a clear precedent for this sort of mix of phenomena, but given the favorable edge-on orientation of the galaxy, and the sheer number of quality observations brought to bear on this question, a clear picture of what was going on started to emerge.”
“We came up with a quantitative model of our wobbling jet-driven outflow idea, and tested it against the real data to find that it could simultaneously explain the appearance of the Chandra X-ray image, JWST mid-infrared data, Keck optical data, and the VLA radio wave imagery,” Kader added. “It was quite the thrill. While we can’t conclusively rule out one or two alternative scenarios, the precessing jet-driven outflow model seems to most satisfactorily explain the data.”
Unexpected Results
“The result was certainly a surprise, on several counts. For one, to our knowledge, the coronal gas nebulae extend from the AGN farther than in any other galaxy in the local Universe,” Kader said. “Secondly, there are precious few potential discoveries of a precessing jet in a disk galaxy, but this is very likely the clearest case, given that VV 340a is seen edge-on, and we get to see the jet against a clear background rather than being confused against the galaxy itself.”
But most surprising, according to Kader, was that all of this was occurring in a relatively young galaxy, with the jet not just preventing infall, but actively pushing material away from the galaxy. The outflow will not abruptly end the galaxy’s star formation, but it will significantly shorten the period during which formation will occur. Intrigued by their discovery, the team plans to continue its investigation.
“The plan going forward is to look for similar, previously missed, activity in the other 30 local universe luminous infrared galaxies in our sample,” Kader concluded. “It will be meticulous work (but now we understand it to be necessary) to combine observations of each galaxy from across the electromagnetic spectrum and from observatories around the world to identify this kind of non-conforming feedback mechanism.”
The paper, “A Precessing Jet from an Active Galactic Nucleus Drives Gas Outflow from a Disk Galaxy,” appeared in Science on January 8, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.