A collaborative survey involving the Australian National University (ANU), the University of Queensland, and others, has provided a more detailed look into a cosmic merger between two spiral galaxies, NGC5713 and NGC5719. According to the research, this event appears to be the first clear example of an equal-mass disk galaxy merger where a kinematically coherent satellite system is still in the process of forming. This finding is particularly significant because the NGC5713/19 pair is approximately 3 billion years ahead of our own Milky Way and Andromeda galaxies in their merging process, offering a potential glimpse into our own galactic future.

 

 

Published in Monthly Notices of the Royal Astronomical Society, the paper was led by Professor Helmut Jerjen from the Australian National University’s Research School of Astronomy and Astrophysics. The research analysed the interacting galaxy pair, NGC5713 and NGC5719, which is separated by 94 kiloparsecs and linked by a straight, elongated neutral hydrogen structure that stretches over 200 kiloparsecs.

 

The research focused on the 14 smaller satellite galaxies that surround the two larger ones. The scientists found that these smaller galaxies weren't moving randomly. Instead, they appeared to be organised, splitting into two distinct groups based on their movement and location in the sky. This suggested a "coherent kinematic structure," meaning their spatial motions are coordinated, with a clear and consistent speed difference of 67 ± 12 kilometers per second. 

 

 

To explain this unusual observation, the researchers tested four different scenarios, from random movements to various satellite planes. The most consistent explanation, considering the geometry and dynamic state of the galaxies, is that two satellite systems are in the process of falling in, following their host galaxies along a vast cosmic filament. This finding reinforces the idea that major mergers are a crucial mechanism for producing co-rotating satellite systems. The observations from this research challenge current cosmological simulations and suggest that these models need to be updated to better understand how structures like the Milky Way's satellite system form and evolve.

 

The research was published in Monthly Notices of the Royal Astronomical Society.