AsianScientist (Mar. 29, 2016) – Using the Atacama Large Millimeter/submillimeter Array (ALMA), researchers from Japan have detected the faintest millimeter-wave source ever observed.
By accumulating millimeter-waves from such faint sources, the team has confirmed that the faint objects are the origins of the enigmatic infrared background light filling the Universe. Their findings have been published in The Astrophysical Journal.
The Universe looks dark in the parts between stars and galaxies. However, astronomers have found that there is faint but uniform light, called the cosmic background emission, coming from all directions. This background emission consists of three main components; cosmic optical background (COB), cosmic microwave background (CMB), and cosmic infrared background (CIB).
The origins of the first two have already been revealed. The COB comes from a huge number of stars, and the CMB comes from hot gas just after the Big Bang. However, the origin of the CIB was yet to be discovered. Various research projects, including past ALMA observations, have been conducted, but they could only explain half of the CIB.
A research team led by graduate student Mr. Seiji Fujimoto and Associate Professor Masami Ouchi at the University of Tokyo, tackled this mysterious infrared background by examining the ALMA data archive.
They went through the vast amount of ALMA data taken during about 900 days in total, looking for faint objects. They also searched the datasets extensively for lensed sources, where huge gravity has magnified the source, making even fainter objects visible.
“The origin of the CIB is a long-standing missing piece in the energy coming from the Universe,” said Fujimoto. “We devoted ourselves to analyzing the gigantic ALMA data in order to find the missing piece.”
Finally, the team discovered 133 faint objects, including an object five times fainter than any other ever detected. The researchers found that the entire CIB can be explained by summing up the emissions from such objects.
By comparing the ALMA data with the data taken by the Hubble Space Telescope and the Subaru Telescope, the team found that 60 percent of the obejects are galaxies which can also be seen in the optical/infrared images. Dust in galaxies absorbs optical and infrared light and re-emits the energy in longer millimeter waves which can be detected with ALMA.
“However, we have no idea what the rest of them are. I speculate that they are galaxies obscured by dust. Considering their darkness, they would be very low-mass galaxies,” Ouchi explained.
“This means that such small galaxies contain great amounts of dust. That conflicts with our current understanding: small galaxies should contain small amounts of dust. Our results might indicate the existence of many unexpected objects in the distant Universe. We are eager to unmask these new enigmatic sources with future ALMA observations.”
The article can be found at: Fujimoto et al. (2016) ALMA Census of Faint 1.2 mm Sources Down to ~0.02 mJy: Extragalactic Background Light And Dust-Poor High-z Galaxies.
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Source: National Institutes of Natural Sciences; Photo: Shutterstock.
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