International study charts the rise and fall of galaxies

31 August 2016

In what is the most precise study of the distant universe ever conducted, Macquarie University and an international team of astronomers measured the distances and energy output of more than 70,000 galaxies over the past 12 billion years.

The FourStar Galaxy Evolution Survey (ZFOURGE) spied galaxies over 90 per cent of cosmic history, seeing them as they rapidly build up their stellar mass and shut down the formation of new stars at later times.

The survey, published in the Astrophysical Journal, provided a three-dimensional view of the deep universe and in order to determine whether the galaxies were dead or alive, the researchers fabricated a new set of filters, each one sensitive to narrow sections of wavelengths of light in the near-infrared part of the spectrum.

With this approach, the research team was able to collect light from 70,000 galaxies and measure accurate distances, ranging from the nearby universe out to 12 billion light years away.

“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. This finding is much like discovering an ancient city that existed earlier than any other known city,” said survey researcher Dr Lee Spitler from the Department of Physics and Astronomy.

By combining the results with observations from many of the world’s most powerful telescopes it could then be determined that even in the very early universe some galaxies had all but ceased star formation.

“Another finding was that today’s more typical galaxies, like the Milky Way, underwent a stellar ‘baby boom’ 10 billion years ago, churning out stars at a prodigious rate, about 30 times faster than today. This showed that our Sun was late to the party, not forming until roughly five billion years ago,” said Michael Cowley, also from the 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.”

The ZFOURGE survey is now complete.

Filed under: Uncategorized