A cluster of galaxies, as captured by VIMOS on the Very Large Telescope of the European Southern Observatory. An international team using the instrument recently found that a galaxy's neighbors can be used to predict its luminosity and colour.

Credit: European Southern Observatory

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SYDNEY: A galaxy's neighbourhood exerts strong influence on the way it forms and evolves, according to a team of French and Italian astronomers.

Charting remote parts of the universe revealed that the distribution of galaxies has considerably evolved with time, depending on an individual galaxy's immediate surroundings. This surprising discovery has implications for theories of the formation and evolution of galaxies.

The findings, reported in the current issue of Astronomy & Astrophysics, suggest that being located in a cluster quenches a galaxy's ability to form stars more quickly than those in isolation. Luminous galaxies also run out of star-forming material at an earlier time than fainter ones.

Astronomers have long grappled with the question: are the galaxies we see today simply the product of the primordial conditions in which they formed, or did experiences in the past change the path of their evolution?

"Our results indicate that environment is a key player in galaxy evolution," said Olivier Le Fèvre from the Laboratoire d'Astrophysique de Marseille, France, who coordinated the Deep Survey team that made the discovery. "They suggest that galaxies as we see them today are the product of their inherent genetic information, evolved over time, as well as complex interactions with their environments, such as mergers."

Scientists have known for several decades that galaxies in the Universe's past look different to those in the present-day Universe, local to the Milky Way. Today, galaxies can be roughly classified as red, when few or no new stars are being born, or blue, where star formation is still ongoing. Moreover, a strong correlation exists between a galaxy's colour and the environment it resides in: the more 'sociable' types found in dense clusters are more likely to be red than the more isolated ones.

By looking back at a wide range of galaxies of a variety of ages, the astronomers were aiming to study how this peculiar correlation has evolved over time.

In a three year survey carried out with VIMOS - the Visible Imager and Multi-Object Spectrograph on the European Southern Observatory's Very Large Telescope - the team studied more than 6,500 galaxies over a wide range of distances to investigate how their properties vary over different timescales, in different environments and for varying galaxy luminosities. They were able to build an atlas of the Universe in three dimensions, going back more than 9 billion years.

"Using VIMOS, we were able to use the largest sample of galaxies currently available for this type of study, and because of the instrument's ability to study many objects at a time we obtained many more measurements than previously possible," said co-author Angela Iovino, from the Brera Astronomical Observatory, Italy.

They conclude that the connection between galaxies' colour, luminosity and their local environment is not merely a result of primordial conditions 'imprinted' during their formation - rather, just as for humans, galaxies' relationship and interactions can have a profound impact on their evolution.

"There's no simple answer to the 'nature versus nurture' problem in galaxy evolution," said Le Fèvre.