Galaxy ‘census’ reveals young galaxies were surprisingly advanced for their age

MEASURING the pulse of 70,000 galaxies has revealed many were alive and kicking — and even dancing — as little as three billion years after the Big Bang.

A survey of galaxies has revealed they were forming their complex cosmic structures earlier than previously thought. Picture: Dr Lee Spitler / Macquarie University

MEASURING the pulse of 70,000 galaxies has revealed many were alive and kicking — and even dancing — as little as three billion years after the Big Bang.

Macquarie University and an international team of researchers have mapped a three-dimensional view of the deep universe, tracking distances and energy outputs of a swath of galaxies over more than 12 billion years

The FourStar Galaxy Evolution Survey, named ZFOURGE, watched the life cycle of galaxies over a period equivalent to 90 per cent of cosmic history.

The idea was to identify which galaxies were dead or alive.

To achieve this, researchers including Dr Lee Spitler from Macquarie University’s Department of Physics and Astronomy created a multicoloured set of telescope filters — each sensitive to a particular narrow section of light in the near infra-red.

Over 45 nights at the Carnegie 6.5m Baade Telescope at Las Campanas Observatory, Chile, the researchers compiled a photo album of 2000 snapshots covering a patch of sky containing 70,000 galaxies.

Sifting through the images for the presence or otherwise of those specific types of light revealed whether or not a galaxy was ‘alive’ and actively engaged in star formation. It also shows how far they were from our own galaxy, the Milky Way.

The resulting 3D map reveals that even in the very early universe, some galaxies had all but ‘died’ — failing to generate any new stars.

Others, however, proved to be startlingly active.

New light ... the ZFOURGE lenses allowed researchers to discover more about the galaxies in the telescope’s field of view. Source: FourStar Galaxy Evolution Survey

‘BABY BOOM’

It would appear that, in the cosmic scheme of things, our Sun is something of a GenX’er. Or perhaps even Generation Y.

It was a simpler time. 10 billion years ago. Galaxies were smaller. There was more gas to go around. And galaxies — such as our own Milky Way — were popping out new stars some 30 times faster than today.

It was an interstellar baby boom.

“This showed that our Sun was late to the party, not forming until roughly five billion years ago,” says Michael Cowley, also from Macquarie University’s Department of Physics and Astronomy.

“Perhaps the most surprising result from the survey is that galaxies in the young universe appear as diverse as they are today,” said Caroline Straatman from Leiden University and lead author of the paper. “The fact that we see young galaxies in the distant universe that have already shut down star formation is remarkable.”

Massive ‘dead’ or ‘quiescent’ galaxies — which are not generating new stars — identified by the ZFOURGE survey.

ANCIENT ‘GALAXY CITY’

Where some galaxies died young, others appear to have been quick in forming communities.

Some appear to have formed as long as 12.5 billion years ago. Only a handful of similarly old galaxies had previously been identified.

“One of our discoveries in the survey was the earliest example of a galaxy cluster, a ‘galaxy city’ made up of a dense concentration of galaxies, when the universe was only three billion years old,” Dr Spitler says. “This finding is much like discovering an ancient city that existed earlier than any other known city.”

Somehow these particular galaxies had managed to devise a complex ‘social’ structure when the universe was only three billion years old. It’s now going on 14 billion years.

Smart kids.

The ZFOURGE study sought to provide a ‘census’ of the evolution of galaxies to help answer questions such as how do they evolve over time, when do they form stars and when did they settle into the enormous and spectacular intergalactic structures we see in our current universe.

The results of the now completed ZFOURGE survey have been published in the Astrophysical Journal.