Why Spiral Galaxies Show Asymmetric Radio Lobes?

The RAD@home project discovered two spiral galaxies with gigantic radio lobes, ranging from 30 to 220 kiloparsecs. The galaxies, NGC 3898 and WISEA J221656.57‑132042434.1, are young and star‑rich. Their disks are distorted, as if being pulled by an invisible force. This force is ram pressure, which pushes gas out of the disk when the galaxy moves through a dense medium. The pressure is uneven: in some areas the gas is denser, in others less so. This creates radio lobes that are not symmetric but curved and lopsided. The result looks like FR‑II or wide‑angle‑tailed galaxies. These observations help explain why many active galaxies, such as Seyferts, show odd radio shapes. With new telescopes uGMRT, MeerKAT, LOFAR and the future SKAO, we will find more galaxies with lobes of this kind. RAD@home’s work shows that citizens can help scientific research, using machine‑learning and AI algorithms to analyze complex data. Collaboration between professionals and enthusiasts is key to uncovering the universe’s secrets.

The radio lobes of the studied spiral galaxies span 30–220 kpc, far exceeding typical scales of classical radio galaxies. Multi‑spectral analysis, combining 1.4 GHz data from uGMRT, 1.4 GHz from MeerKAT, and optical images from the Sloan Digital Sky Survey, shows that the stellar disks are distorted and exhibit gas protrusions indicative of a ram‑pressure stripping process. In this phenomenon, the galaxy moves through a dense intergalactic medium, and the external gas flow pressure pushes interstellar gas outward, creating a gas “tail” and an asymmetric disk shape. Ram pressure is not uniform: in some regions the surrounding gas is denser, in others less, leading to lobes with differentiated shapes and brightness. The studied galaxies display features similar to FR‑II and wide‑angle‑tailed (WAT) galaxies, where radio lobes are bent due to interactions with the surrounding environment. The analysis suggests that the non‑uniform external gas density can explain the observed lobe asymmetry. These findings have implications for understanding active galaxies, particularly Seyferts, and for emerging populations of galaxies with galaxy‑scale radio jets. With the advancement of telescopes such as uGMRT, MeerKAT, LOFAR, and the future SKAO, more galaxies with lobes of this nature can be examined. Moreover, the citizen‑science approach, combined with machine‑learning and AI algorithms, demonstrates the potential to analyze complex radio data, helping to identify new galaxy classes and better understand galaxy‑environment interactions.