An article published in the journal “Nature Astronomy” reports the results of a study of the Hyper Luminous Infrared Galaxy (HyLIRG) cataloged as PJ0116-24 which offers some surprises about this type of galaxy. A team of researchers combined observations conducted with the ALMA radio telescope and the Enhanced Resolution Imager and Spectrograph (ERIS) instrument mounted on ESO’s VLT to obtain details of PJ0116-24.
The complication in the study comes from the fact that it’s about 10 billion light-years away from Earth and is visible thanks to a gravitational lensing effect that makes it appear like a so-called Einstein ring, a name due to the fact that it’s a result predicted by the theory of general relativity. The surprise is due to the fact that the researchers expected to find traces of a galaxy merger while the details indicate that it’s an orderly galaxy although very active in star formation.
Astronomical surveys conducted in recent years made it possible to discover rare Hyper Luminous Infrared Galaxies. Astronomers believe that their abnormal brightness is due to intense star formation triggered by galaxy merger processes. However, a second possibility was proposed that sees them as very young galaxies that are going through the period of maximum star formation.
About 10 billion light-years away from Earth, PJ0116-24 is about 10,000 times brighter than the Milky Way in infrared light. This makes it ideal for in-depth, high-resolution observations. An elliptical galaxy between PJ0116-24 and the Earth generates a gravitational lensing effect that distorts its shape into what is called an Einstein ring.
The image of PJ0116-24 visible from Earth is 17 times brighter and offers 10 times more detail than if it weren’t magnified by gravitational lensing. However, the distortion makes it more difficult to study, and capturing its details helps reconstruct its true form.
The ALMA radio telescope and the ERIS instrument mounted on the VLT offer excellent performance in capturing infrared images and allowed excellent images of the PJ0116-24 galaxy to be obtained. ALMA captured the cold gas signatures, visible in blue in the image, while ERIS captured the warm gas signatures, visible in red. Mapping the gas made it possible to understand that it rotates in the galaxy in an orderly way and not in the chaotic way that was expected from a galaxy merger. In short, PJ0116-24 is an isolated galaxy in which there is unusual star formation activity due to internal processes.
This study is part of the branch of astronomy that deals with the evolution of galaxies. The fact that a hyperluminous infrared galaxy shows intense star formation activity due to internal processes and not a galactic merger may not be an exception but these galaxies are rare so it is difficult to obtain meaningful statistics. The case of PJ0116-24 confirms the idea that a galaxy can have periods in which enormous quantities of gas lead to very intense star formation and then have long periods of relative calm.
