Brilliant Starburst Galaxy is the Best Evidence Yet for Merging Galaxies

More than 12.5 billion light-years away is a galactic powerhouse, a galaxy that is producing stars at nearly 1,000 times fasters than our own Milky Way. Now, scientists have found that this starburst galaxy, known as AzTEC-3, together with its gang of calmer galaxies may just represent the best evidence yet that large galaxies grow from the merger of smaller ones in the early universe.

"The ALMA data reveal that AzTEC-3 is a very compact, highly disturbed galaxy that is bursting with new stars at close to its theoretically predicted maximum limit and is surrounded by a population of more normal, but also actively star-forming galaxies," said Dominik Riechers, one of the researchers, in a news release. "This particular grouping of galaxies represents an important milestone in the evolution of our universe: the formation of a galaxy cluster and early assemblage of large, mature galaxies."

AzTEC-3 is what astronomers refer to as a submillimeter galaxy, since it shines brightly in that portion of the spectrum, but is remarkably dim at optical and infrared wavelengths. This is partly due to the fact that light from its stars is absorbed by dust in the star-forming environments of the galaxy and then re-emitted by the dust at far-infrared wavelengths. As this light travels toward Earth, it becomes stretched due to the expansion of the universe and shifts from far-infrared light to the submillimeter/millimeter portion of the spectrum.

In the early universe, starburst galaxies like this one were forming new stars at a monstrous pace fueled by enormous quantities of star-forming materials that they devoured and acquired by merging with other galaxies. Over billions of years, these mergers continued and eventually produced the large galaxies that we see today.

Now, scientists have evidence for this type of merging in the form of AzTEC-3. The scientists found evidence that this galaxy has recently merged with another one, which may explain its rapid star formation.

"AzTEC-3 is currently undergoing an extreme, but short-lived event," said Riechers. "This is perhaps the most violent phase in its evolution, leading to a star formation activity level that is very rare at its cosmic epoch."

The findings are published in The Astrophysical Journal.