Surprising ring sheds light on galaxy formation

The as-yet-unknown question of what causes extremely rapid star formation within Hyperluminous Infrared Galaxies (HyLIRGs) is of great interest in guiding our understanding of galaxy formation and evolution in the universe. A new photo released by the European Southern Observatory shows a HyLIRG 10,000 times brighter than our own Milky Way (in infrared light) – the distant galaxy PJ0116-24 – and was published alongside a paper just published in Astronomy of Nature that sheds light on its formation.

Previous studies suggested that such extremely bright galaxies must result from galaxy mergers. These galaxy collisions are thought to create gas-dense regions in which rapid star formation is triggered. But isolated galaxies can also become HyLIRGs through internal processes alone, if star-forming gas flows rapidly towards the galactic center.

In the paper titled “Detailed Study of a Rare Hyperluminous Rotating Disk in an Einstein Ring 10 Billion Years Ago,” in which Cornell astronomer Amit Vishwas, Ph.D. is a co-author, observations from ESO’s Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA) were combined to study the motion of gas within PJ0116-24.

ALMA tracks the cold gas, pictured in blue, while the VLT, with the new Enhanced Resolution Imager and Spectrograph (ERIS), tracks the warm gas, shown in red. Thanks to these detailed observations, the international research team found that the gas in this extreme galaxy was rotating in an organized way, rather than the chaotic way expected after a galactic collision – a surprising result. This shows, the researchers said, that mergers are not always necessary for a galaxy to become a HyLIRG.

PJ0116-24 is so far away that its light took about 10 billion years to reach us. A foreground galaxy acted as a gravitational lens, bending and magnifying the light of PJ0116-24 behind it into the Einstein ring seen here. This precise cosmic alignment allows astronomers to zoom in on very distant objects and see them at a level of detail that would otherwise be very difficult to achieve.

Vishwas, a research associate at the Cornell Center for Astrophysics and Planetary Sciences (CCAPS), helped map the emission and kinematics from atomic and molecular gas in PJ0116-24 using ALMA, which provided strong support for the rotating disk scenario. He was also involved in acquiring data with the newly operated ERIS instrument on the VLT. The research was led by Daizhong Liu of the Max Planck Institute for Extraterrestrial Physics and the Purple Mountains Observatory.

The interpretation of the gas conditions and element abundances in PJ0116-24 is similar to what Vishwas and his co-authors reported last year for another galaxy at an earlier age in the universe, using data from the James Webb Space Telescope .

PJ0116-24, however, is about five times more massive and brighter than the source studied in last year’s paper, Vishwas said.

“In both cases, gravitational lensing helped us zoom in to study the details of the interstellar medium of these galaxies. I believe these new observations are helping us build a case for how galaxies evolve and build—transforming efficient gas in stars with rapid growth spurts separated by long periods of relative calm,” he explained.