Title: JWST Discovery of Warm Dust in the Circumgalactic Medium of the Makani Galaxy
Authors: Sylvain Veilleux, Steven D. Shockley, Marcio Melendez, David S. N. Rupke, Alison L. Coil, Aleksandar M. Diamond-Stanic, James E. Geach, Ryan C. Hickox, John Moustakas, Gregory H. Rudnick, Paul H. Sell, Christy A. Tremonti, and Hojoon Cha
First Author’s Institution: Department of Astronomy, University of Maryland, College Park, MD 20742, USA
Status: Published in The Astrophysical Journal (2025 July 10) [open access]
The Windy Galaxy
Billions of light years away lies Makani, as seen in Figure 1, a record breaking galaxy discovered in 2019 by researchers at the Keck Observatory atop Mauna Kea, Hawaii. The galaxy shows evidence of a large merger event, where two galaxies collided to form a larger galaxy. This event triggered starburst activity or several waves of intense star formation that changed the makeup of not just Makani, but the region around it.
There are several processes that can create galactic winds. An active supermassive black hole at the center of the galaxy can slingshot particles close to the speed of light out of the galaxy, or supernovae leftover from previous starburst activity can help to expel material for the galaxy. Makani, whose name in Hawaiian just so happens to mean wind, has both factors contributing to its galactic winds: massive amounts of star formation, and a very active black hole in its center.
This contributes to some of the strongest galactic winds discovered to date, stretching approximately 100 kiloparsecs beyond the galaxy, roughly ten times the typical galactic wind. These galactic winds help to enrich the circumgalactic medium (CGM) around the galaxy, and remove gas from the galaxy themselves. There is still much to discover about how galactic winds change the makeup of such galaxies, and what exactly they take with them on their way out.
Earth’s Favorite Carcinogen: Polycyclic Aromatic Hydrocarbons
Polycyclic Aromatic Hydrocarbons (PAHs, pronounced P-A-Hs or “paws”) are small flat dust grains scattered into every corner of the universe. From the atmosphere of Earth in the form of exhaust and wildfire smoke, to the circumgalactic medium, the mostly empty space between galaxies, Polycyclic Aromatic Hydrocarbons, are scattered into every corner of the universe. These PAHs are small flat dust grains that contribute to regulating the temperature of the interstellar medium (ISM), but astronomers have long wondered how they migrate across galaxies.
Even though they are smaller than a human hair, they are still easily observable even in very distant galaxies. These dust grains emit infrared light, and if there are enough PAHs in a region, they are bright enough to be observed with modern telescopes, such as the James Webb Space Telescope (JWST). By combining multiple observations across multiple filters, astronomers can create ratios that reveal information about the PAHs’ size, temperature, and charge, allowing them to further discern properties about the regions in which they reside.
With redshifted galaxies like Makani, the light from PAHs is stretched beyond its usual wavelength, but fortunately for today’s authors, it was just enough to land known PAH features well within JWST filters, as seen in Figure 2. They were then able to use this information to track the distribution of these PAHs across Makani.
PAHs Gone Extragalactic
Using the James Webb Space Telescope (JWST), the authors scrutinized Makani for any signs of PAHs. They found that not only did PAHs exist within the galaxy, but up to thirty kiloparsecs outside the galaxy. Makani’s strong galactic winds were ejecting the dust grains from the galaxy, over an estimated timescale of a billion years.
Previously, astronomers had not expected to find high quantities of dust grains outside the protection of a galaxy. The journey across a galaxy is long and hot, with temperatures in the millions of degrees. A dust grain would likely not survive the trip, as it would be destroyed by high energy photons. This suggests that the PAHs were somehow shielded from the hotter parts of the ISM and CGM, in large enough volumes to make it beyond the edge of Makani.
This answered questions about how galaxies enrich the CGM, but also added several more. Since today’s authors were limited by the sensitivity and range of their instruments, they were unable to confirm if there were PAHs along Makani’s entire wind structure, just the first thirty-five kiloparsecs of it. They also would like to turn their sights towards the intergalactic medium (IGM) to see if PAHs could make it even further beyond the reach of their host galaxy.
Astrobite edited by Chloe Klare
Featured image credit: Jim Geach, David Tree, Peter Richardson (University of Hertfordshire)
