ALMA sheds new light on starburst galaxies

Scientists come closer to solving cosmic riddle of very active 'starburst' galaxies

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In this ALMA image of NGC 253, dense, star-forming areas are seen in yellow, surrounded by much less dense clouds of CO (shown in red)

Credit: B. Saxton (NRAO/AUI/NSF); ALMA (NRAO/ESO/NAOJ); A. Leroy


By Russell Deeks

Why 'starburst' galaxies produce many more stars, more quickly than other galaxies is a question that has puzzled astronomers for years. However, we are now a step closer to understanding the mechanisms behind this phenomenon, thanks to high-definition data captured by the Atacama Large Millimeter/submillimenter Array (ALMA) telescope in Chile, which only became fully operational in March 2013.

At an American Association for the Advancement of Science press conference in San Jose yesterday (15 February), Adam Leroy - formerly of the National Radio Astronomy Observatory, and currently of Ohio State University - explained how he and his colleagues used ALMA to obtain data that revealed the inner workings of a 'starburst' region in unprecedented detail.

"Until now, scientists [have] struggled to see exactly what was going on inside starburst galaxies that distinguished them from other star-forming regions," explained Leroy.

Leroy and his colleagues used ALMA to map the distribution and motion of molecules in clouds at the heart of the Sculptor Galaxy, NGC 253. This disc-shaped galaxy is the nearest starburst galaxy known, lying 11.5 million lightyears from Earth. Thanks to ALMA's high resolution and sensitivity, Leroy's team were able to identify 10 separate star-forming regions withing the galaxy. They then mapped the distribution of various molecules within those regions by detecting the different molecules' millimeter-wavelength 'signatures'. This enabled them to build up a picture of the structures of these regions. Large amounts of CO (carbon monoxide), for instance, indicate large clouds of less dense gas, while large quantities of HCN (hydrogen cyanide) suggest much denser regions where star formation is taking place.

What the team discovered is that clouds inside 'starburst' regions are much more massive, 10 times denser and much more turbulent than similar clouds in other galaxies. "These differences have wide-ranging implications for how galaxies grow and evolve," said Leroy. "What we would ultimately like to know is whether a starburst like Sculptor produces not just more stars, but different types of stars than a galaxy like the Milky Way. ALMA is bringing us much closer to that goal."

Other research projects that have already been completed by ALMA include studying the composition of Comet C/2012 S1 (ISON) and imaging the protoplanetary disc around HL Tauri, a star in the constellation of Taurus. 

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