Astronomers Take Starburst Galaxy Census
December 4, 2012

Starburst Galaxies Are Powerful Star-making Machines

Lee Rannals for - Your Universe Online

Astronomers have taken a census of hundreds of previously unseen starburst galaxies, revealing high star-formation rates across the Universe.

The team used the European Space Agency's Herschel space observatory and ground-based W. M. Keck Observatory to make the observation.

Starburst galaxies give birth to hundreds of solar masses' worth of stars every year, while galaxies like our Milky Way produce only one Sun-like star per year.

According to the ESA, starburst galaxies generate so much starlight that they outshine our galaxy hundreds to thousands of times over, but the large quantities of gas fueling them contains so much dust it makes them harder to see.

The dust absorbs much of the visible light, making them look quite insignificant in that part of the spectrum. The dust is warmed by the surrounding hot stars, and re-emits the energy at infrared wavelengths.

ESA's Herschel helped astronomers measure the temperature and brightness of thousands of dusty galaxies using the infrared spectrum.

“Starburst galaxies are the brightest galaxies in the Universe and contribute significantly to cosmic star formation, so it´s important to study them in detail and understand their properties,” said Dr Caitlin Casey of the University of Hawaii, lead author of the papers discussing the results in the Astrophysical Journal.

“Some of the galaxies found in this new survey have star-formation rates equivalent to the birth of several thousand solar-mass stars per year, constituting some of the brightest infrared galaxies yet discovered.”

The team had to calculate the distances to the galaxies in order to provide context to the observations and understand how star formation has changed throughout the Universe's history.

Astronomers used spectrum on the twin W.M. Keck telescopes on Mauna Kea, Hawaii, and obtained the redshifts of 767 of the starburst galaxies. These redshifts helped the team measure how long the light from each galaxy has traveled across the Universe.

For most of the galaxies, the team found that the light has been traveling towards Earth for 10 billion years or less. About 5 percent of the galaxies are at even greater redshifts, taking just 1 to 3 billion years to travel.

“The Herschel data tell us how fiercely and prolifically these galaxies are producing stars,” said Seb Oliver from University of Sussex and Principal Investigator for the HerMES Key Program.

“Combining this information with the distances provided by the Keck data, we can uncover the contribution of the starburst galaxies to the total amount of stars produced across the history of the Universe.”

How the numbers of starburst galaxies formed during the first few billions of years of the Universe's existence matters when trying to understand galaxy formation and evolution.

One theory believes that a collision between two young galaxies could have sparked an intense short-lived phase of star formation.

Another theory proposes that when the Universe was young, individual galaxies had more gas available to them to feed from, which enabled higher rates of star formation without the need of collisions.

“It´s a hotly debated topic that requires details on the shape and rotation of the galaxies before it can be resolved,” Dr Casey concluded.