WEAVE spectrograph uncovers dual nature of galaxy shock

Using the set of first-light observations from the new William Herschel Telescope Enhanced Area Velocity Explorer (WEAVE) wide-field spectrograph, a team of more than 50 astronomers, led by Dr. Marina Arnaudova at the University of Hertfordshire, has presented the first WEAVE scientific results on Stephan’s Quintet in the Monthly Notices of the Royal Astronomical Society.

This state-of-the-art wide-field spectrograph is a 20-million Euro project that brings together leading experts from around the world. WEAVE is set to revolutionize our understanding of the universe, offering unprecedented detail, as demonstrated in this new study of Stephan’s Quintet.

Stephan’s Quintet, also known as the Hickson Compact Group 92, is a nearby galaxy group that consists of five galaxies (NGC 7317, NGC 7318a, NGC 7318b, NGC 7319 and NGC 7320c). Ever since its discovery in 1877, it has captivated astronomers, particularly because it represents a galactic crossroad where past collisions between galaxies have left behind a complex field of debris.

Dynamical activity in this galaxy group has now been reawakened by NGC 7318b, a galaxy smashing through it at an incredible speed of over 2 million miles per hour (3.2 million kilometers per hour), leading to an immensely powerful shock, much like a sonic boom from a jet fighter.

Dr. Arnaudova said, “This system thus presents an ideal laboratory to understand the chaotic and often violent relationship between galaxies, and as such was the focus of the first-light observations by the WEAVE Large Integral Field Unit (LIFU).”

Dr. Arnaudova (University of Hertfordshire, UK) and her team provide a new insight into the large-scale shock front. By combining data from WEAVE’s LIFU with other cutting-edge instruments such as the Low Frequency Array (LOFAR), the Very Large Array (VLA), and the James Webb Space Telescope (JWST), they have found a previously undiscovered dual nature of the shock.

Dr. Arnaudova explained, “As the shock moves through pockets of cold gas, it travels at hypersonic speeds—several times the speed of sound—powerful enough to rip apart electrons from atoms, leaving behind a glowing trail of charged gas, as seen with WEAVE.”

Ph.D. student Soumyadeep Das (University of Hertfordshire, U.K.) added, “However, when the shock passes through the surrounding hot gas, it becomes much weaker. Instead of causing significant disruption, the weak shock compresses the hot gas, resulting in radio waves that are picked up by radio telescopes like LOFAR.”

Dr. Marc Balcells, Director of the Isaac Newton Group of Telescopes, said, “I’m excited to see that the data gathered at the WEAVE first light already provide a high-impact result, and I’m sure this is just an early example of the types of discoveries that will be made possible with WEAVE on the William Herschel Telescope in the coming years.”

Professor Gavin Dalton, WEAVE Principal Investigator at RAL Space and the University of Oxford, said, “It’s fantastic to see the level of detail uncovered here by WEAVE. As well as the details of the shock and the unfolding collision that we see in Stephan’s Quintet, these observations provide a remarkable perspective on what may be happening in the formation and evolution of the barely resolved faint galaxies that we see at the limits of our current capabilities.”