Galactic Evolution Both “Nature” and “Nurture”
 

A team of astronomers has found that galaxies “evolve” as a result of influences from their surroundings.

The scientists said their work showed that the distribution of galaxies has considerably changed over time, depending on the galaxies’ surroundings. The surprising finding challenges existing theories on galactic formation and evolution, they added.

In biology, researchers have debated for centuries whether human development is primarily a result of “nature” or “nurture”—that is, genes or experience.

Astronomers face similar conundrums, said Olivier Le Fevre of the Astrophysics Laboratory in Marseille, France, who coordinated the new research. Are galaxies today simply the products of primordial conditions in which they formed, or did experiences change their evolution?

His team conducted a three-year survey using an instrument on the Very Large Telescope array at the European Southern Observatory’s Paranal Observatory.

The astronomers studied more than 6,500 galaxies at widely varying distances to see how their properties vary in different environments and for varying galaxy luminosities. The furthest galaxies were seen as they were when the universe was a third its present age, more than 9 billion years ago. This is because that time frame is how long their light takes to reach us.

This census found what the researchers called a surprising trend in the “colour-density relation,” a description of the relationship between the properties of a galaxy and its environment. This relationship was markedly different 7 billion years ago, the researchers said.

The astronomers concluded that the galaxies’ luminosity, their initial “genetic” properties, and their environments profoundly affect their evolution.

“There’s no simple answer to the ‘nature versus nurture’ problem,” said Le Fevre. The results “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 decades that galaxies in ancient times, which we see far off, look different to those of today, which we see nearby.

Today, galaxies can be roughly classified as “red,” where few or no new stars are being born, or “blue,” where star formation is ongoing. There is a strong link between a galaxy’s colour and its environment. The sociable types found in dense clusters of galaxies are likelier to be red than more isolated ones.

The astronomers aimed to study how this correlation has evolved using a device called the Visible Multi-Object Spectrograph on the telescope, in northern Chile.

The finding of marked variation in the colour-density relationship, depending on whether a galaxy is found in a cluster or alone, and on its luminosity, has many potential implications, the researchers said. The findings suggest, for example, that a cluster environment quenches a galaxy’s ability to form stars quickly compared with those in isolation. And bright galaxies run out of star-forming material earlier than fainter ones.

“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 Angela Iovino of the Brera Astronomical Observatory in Italy, another member of the team.

The findings were published in the October IV issue of the research journal Astronomy and Astrophysics.


- Courtesy European Southern Observatory
and World Science staff