The optical morphology of galaxies is strongly related to the galactic environment, with the fraction of early-type galaxies increasing with the local density of galaxies. A new study led by astronomers at the International Center for Radio Astronomy Research (ICRAR) presented the first analysis of the morphology of galaxies. Scientists have discovered the reason behind differences in the shape of the galaxy.

Lead author Dr. Joel Pfeffer from the University of Western Australia node of ICRAR said the research explains the “morphology-density relationship” – where clustered galaxies appear smoother and less characteristic than their solo counterparts.

“We’ve discovered a few different things that happen when we get a lot of galaxies together,” said Dr. Pfeffer.

“The spiral arms of galaxies are so fragile, and as you get to higher densities in the galaxy clusters, spiral galaxies start to lose their gas.

“This loss of gas causes them to ‘drop’ their spiral arms and transform into a lenticular shape.”

“Another cause is galaxy mergers, where two or more spiral galaxies can collide together to form one large elliptical galaxy in the aftermath.”

For the study, scientists used the powerful EAGLE simulations to analyze a group of galaxies in detail. They used an AI to classify galaxies based on their shape.

Scientists can confidently use the simulation results to understand observations of galaxy clusters, as the simulations closely mimic what has been observed in the Universe.

In addition, the study found several lenticular galaxies outside of the high-density regions where they are commonly found, and the modeling indicates that these galaxies formed from the merger of two other galaxies.

said Dr. Pfeffer the work brings together several studies in galactic evolution to understand the relationship between morphology and density for the first time.

“There have been many suggestions over time. But this is the first work to put all the pieces of the puzzle together.”

Magazine reference:

  1. Joel Pfeffer et al. The relationship between morphology and density of galaxies in the EAGLE simulation. Monthly communications from the Royal Astronomical Society. DOI: 10.1093/mnras/stac3466