Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have found eight molecular clouds in the heart of NGC 253, an active starburst (star-forming) galaxy approximately 11 million light-years away in the constellation Sculptor.
The starburst galaxy NGC 253 and the radio spectra obtained with ALMA. Image credit: ESO / J. Emerson / VISTA / ALMA / NAOJ / NRAO / Ando et al / Cambridge Astronomical Survey Unit.
University of Tokyo astronomer Ryo Ando and co-authors observed NGC 253 and resolved the locations of star formation in the galaxy down to the scale of a molecular cloud — a site of star formation about 30 light-years across.
As a result, the researchers identified eight massive, dusty clouds aligned along NGC 253’s center.
“With its unprecedented resolution and sensitivity, ALMA showed us the detailed structure of the clouds,” Ando said.
“To our surprise, the gas clouds have a strong chemical individuality despite their similarity in size and mass.”
Different molecules emit radio waves at different frequencies.
Using this feature, Ando and colleagues investigated the chemical composition of the distant clouds by analyzing the radio signals precisely.
They identified signals from various molecules including formaldehyde (H2CO), hydrogen cyanide (HCN), and many organic molecules.
One of the clumps, dubbed Clump 1, exhibits very complex chemical composition.
The astronomers identified footprints of 19 different molecules in this cloud, such as thioformaldehyde (H2CS), propyne (CH3CCH), and complex organic molecules including methanol (CH3OH) and acetic acid (CH3COOH).
“The data are filled with the signals of various molecules. It is like a forest of molecules,” Ando said.
Many ‘molecular forests’ have been found in our Milky Way Galaxy, but this is the first example outside the Milky Way.
The research is published in the Astrophysical Journal (arXiv.org preprint).
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Ryo Ando et al. 2017. Diverse Nuclear Star-forming Activities in the Heart of NGC 253 Resolved with 10-pc-scale ALMA Images. ApJ 849, 81; doi: 10.3847/1538-4357/aa8fd4
