"All stars form in dense clouds of dust and gas," said Adam Leroy, an astronomer with Ohio State University in Columbus. "Until now, however, scientists struggled to see exactly what was going on inside starburst galaxies that distinguished them from other star-forming regions."
ALMA changes that by offering the power to resolve individual star-forming structures, even in distant systems. Leroy and his colleagues mapped the distributions and motions of multiple molecules in clouds at the core of the Sculptor Galaxy.
"There is a class of galaxies and parts of galaxies, we call them starbursts, where we know that gas is just plain better at forming stars," noted Leroy. "To understand why, we took one of the nearest such regions and pulled it apart - layer by layer - to see what makes the gas in these places so much more efficient at star formation."
ALMA's exceptional resolution and sensitivity allowed the researchers to first identify ten distinct stellar nurseries inside the heart of Sculptor, something that was remarkably hard to accomplish with earlier telescopes, which blurred the different regions together.
The team then mapped the distribution of "signatures" from different molecules inside the center of the galaxy. By comparing the concentration, distribution, and motion of these molecules, the researchers were able to peel apart the layers and peer into the very heart of these violent star nurseries.
They found that it's not just the number of stellar nurseries that sets the throttle for a galaxy to create new stars, but also what kind of stellar nurseries are present. Because the star-forming clouds in Sculptor pack so much material into such a small space, they are simply better at forming stars than the clouds in a galaxy like the Milky Way.
Starburst galaxies, therefore, show real physical changes in the star-formation process, not just a one-to-one scaling of star formation with the available reservoir of material.
These results are accepted for publication in the Astrophysical Journal and were presented February 15, 2015, at a news conference at the American Association for the Advancement of Science (AAAS) meeting in San Jose, California.
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