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Astronomy, Astrophysics, Space, Stars

Astronomers complete cosmic dust census

Astronomers have completed a benchmark study of more than 300 galaxies, producing the largest census of dust in the local Universe, the Herschel Reference Survey. Astronomers observed galaxies at far-infrared and sub-millimeter wavelengths and captured the light directly emitted by dust grains.
Galaxies in the Herschel Reference Survey. The images are presented in false-colour to highlight different dust temperatures, with blue and red representing colder and warmer regions respectively. Credit: ESA/Herschel/HRS-SAG2 and HeViCS Key Programmes/L. Cortese (Swinburne University)

Galaxies in the Herschel Reference Survey. The images are presented in false-colour to highlight different dust temperatures, with blue and red representing colder and warmer regions respectively.
Credit: ESA/Herschel/HRS-SAG2 and HeViCS Key Programmes/L. Cortese (Swinburne University)

“These dust grains are believed to be fundamental ingredients for the formation of stars and planets, but until now very little was known about their abundance and physical properties in galaxies other than our own Milky Way,” said Dr Cortese.

‘Cosmic dust is heated by starlight to temperatures of only a few tens of degrees above absolute zero, and can thus be only seen at far-infrared/sub-millimetre wavelengths.”

The two cameras on board the Herschel satellite, SPIRE and PACS, allowed astronomers to probe different frequencies of dust emission, which bear imprints on the physical properties of the grains and therefore were critical for this study. Although the SPIRE data were obtained three years ago, the team had to wait for the completion of the PACS survey last year.

“The long wait was worthwhile, as the combination of the PACS and SPIRE data shows that the properties of grains vary from one galaxy to another — more than we originally expected. As dust is heated by starlight, we knew that the frequencies at which grains emit should be related to a galaxy’s star formation activity. However, our results show that galaxies’ chemical history plays an equally important role,” commented Dr Cortese.

Co-author of the work, Dr Jacopo Fritz, from Ghent University in Belgium, said: “This affects our ability to accurately estimate how much dust is in the Universe. It is particularly an issue for the most distant galaxies, which have a star formation and chemical history significantly different to the one in our own Milky Way.”

Reference: L. Cortese, J. Fritz, S. Bianchi, A. Boselli, L. Ciesla, G. J. Bendo, M. Boquien, H. Roussel, M. Baes, V. Buat, M. Clemens, A. Cooray, D. Cormier, J. I. Davies, I. De Looze, S. A. Eales, C. Fuller, L. K. Hunt, S. Madden, J. Munoz-Mateos, C. Pappalardo, D. Pierini, A. Rémy-Ruyer, M. Sauvage, S. di Serego Alighieri, M. W. L. Smith, L. Spinoglio, M. Vaccari, and C. Vlahakis. PACS photometry of the Herschel Reference Survey – far-infrared/submillimetre colours as tracers of dust properties in nearby galaxies. MNRAS, March 17, 2014 DOI: 10.1093/mnras/stu175

 

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