Molecular zoo found in Sculptor Galaxy

Hubble image of NGC 253

A group of research scientists led by Ryo Ando from the University of Tokyo have peered into the starburst galaxy, NGC 253 – also known as the Sculptor Galaxy – to reveal a collection of diverse molecules in never-seen-before resolution.

Starburst galaxies like NGC 253 are active star-forming galaxies, and have been major players in galaxy evolution over the long history of the Universe.

Using data from the Atacama Large Millimeter/submillimeter Array (ALMA), situated in a cold, dry desert, high in the Chilean Andes, Ryo and his collaborators have managed to identify complex molecular structure inside eight dusty, star-forming clumps known as giant molecular clouds (GMCs). And all this in a galaxy far, far away – 11.42 million lightyears to be precise.

ALMA Radio Observatory
Antennas of the Atacama Large Millimeter/submillimeter Array (ALMA), on the Chajnantor Plateau in the Chilean Andes. The Large and Small Magellanic Clouds, two companion galaxies to our own Milky Way galaxy, can be seen as bright smudges in the night sky, in the centre of the photograph. Credit: ESO/C.Malin

The GMCs in question, each of which contain gas and dust many thousands of times the mass of the Sun, seem to be aligned in two massive ridges near to the galaxy’s centre.

Lots of molecular clouds have been found in our own galaxy, but this is the first time these exotic objects have been seen in a distant galaxy, far from the Milky Way.

“With its unprecedented resolution and sensitivity, ALMA showed us the detailed structure of the clouds,” said Ryo, the lead author of a new research paper published in the Astrophysical Journal in November 2017. “To my surprise, the gas clouds have a strong chemical individuality despite their similarity in size and mass.”

Although all eight star-forming clumps are similar in size, only one appears to contain a wide assortment of molecules – 19 have so far been detected – while the other seven clumps show a lack of fragile species, such as complex organic molecules. The variety of chemistry seen in these star-forming regions has never been seen before. It will surely spur us on to make sense of starburst processes nearer to home, within the Milky Way.

It appears that the molecule-rich GMC, known as Clump 1, is composed of predominantly hot molecular gas. The gas itself contains hot core clusters – sites of high-mass star formation, taking place around 11 million years ago!

This research, carried out by Ryo and his team and supported by the Japan Society for the Promotion of Science, demonstrates the superior capabilities of ALMA. In particular, the ability to see through the fog of dust associated with molecular clouds to reveal the structure of individual molecules and chemical diversity.

Molecules found in NGC 253
The starburst galaxy NGC 253 and the radio spectra obtained with ALMA. ALMA detected radio signals from 19 different molecules at the center of this galaxy. Credit: ESO/J.Emerson/VISTA, ALMA (ESO/NAOJ/NRAO), Ando et al. Acknowledgment: Cambridge Astronomical Survey Unit

© Melanie Davies 2017

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