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ALMA’s highest frequency receiver produces its first scientific result on massive star formation

(22 November 2018 - ALMA) The Atacama Large Millimeter/submillimeter Array (ALMA) has opened another new window to the Universe.

Using its highest frequency receivers yet, researchers obtained 695 radio signals from various molecules, including simple sugar, in the direction of a massive star forming region, and revealed a pair of water vapor fountains erupting from the region. These first scientific results from the ALMA Band 10 receivers developed in Japan ensure a promising future for high frequency observations.

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Photo of the star forming region NGC 6334I, also known as the Cat’s Paw Nebula, taken by the NASA/ESA Hubble Space Telescope (top) and the high frequency radio spectra (bottom). The blue line shows the spectral lines detected by ALMA and the gray line shows the lines detected by the European Space Agency’s Herschel Space Observatory. The ALMA observations detected more than ten times as many spectral lines. Note that the Herschel data have been inverted for comparison. Two molecular lines are labeled for reference. (courtesy: S. Lipinski/NASA & ESA, NAOJ, NRAO/AUI/NSF, B. McGuire et al.)

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ALMA Band 10 receiver (courtesy: ALMA (ESO/NAOJ/NRAO))

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Composite ALMA image of NGC 6334I, a star-forming region in the Cat’s Paw Nebula, taken with the Band 10 receivers, ALMA’s highest-frequency vision. The blue component is heavy water (HDO) streaming away from either a single protostar or a small cluster of protostars. The orange region is the “continuum emission” in the same region, which scientists found is extraordinarily rich in molecular fingerprints, including glycoaldehyde, the simplest sugar-related molecule. (courtesy: ALMA (ESO/NAOJ/NRAO): NRAO/AUI/NSF, B. Saxton)

The institutes participating in ALMA have shared responsibility for developing dedicated radio receivers for each of ALMA’s 10 frequency bands. The National Astronomical Observatory of Japan (NAOJ) developed receivers for three bands; Band 4 (125-163 GHz), Band 8 (385-500 GHz), and Band 10 (787 to 950 GHz). The Band 10 receiver covers the highest frequency range in ALMA, which has not yet been extensively observed with other ground-based telescopes.

“High-frequency radio observations like in Band 10 are normally not possible from the ground,” said Brett McGuire, a chemist at the National Radio Astronomy Observatory in Charlottesville, Virginia, and lead author on a paper in the Astrophysical Journal Letters. “They require the extreme precision and sensitivity of ALMA, along with some of the driest and most stable atmospheric conditions that can be found on Earth.”

ALMA is a supremely sensitive cosmic chemical sensor. As molecules tumble and vibrate in space, they naturally emit electromagnetic radiation at specific frequencies, which appear as spikes on a spectrum. Each of ALMA’s receiver bands can detect a different selection of these unique spectral fingerprints. The highest frequencies offer unique insight into lighter, important chemicals, like heavy water (HDO), as well as complex, warm molecules.

McGuire and his team observed NGC 6634I, a nursery cloud of massive stars, with ALMA in 880 GHz. NGC 6334I is part of the Cat’s Paw Nebula located 4,300 light-years away from Earth. “We detected a wealth of complex organic molecules surrounding this massive star-forming region,” said McGuire. “These results have been received with excitement by the astronomical community and show once again how ALMA will reshape our understanding of the universe.”

The European Space Agency’s Herschel Space Observatory has observed NGC 6334I in the same frequency range and detected 65 molecular emission lines. On the other hand, ALMA detected 695, 10 times as many spectral lines as Herschel. ALMA’s prominent sensitivity and resolution offers a new level of astrochemistry research.

The molecules detected in the direction of NGC 6334I include methanol, ethanol, methylamine, and glycolaldehyde, the simplest sugar-related molecule. Glycolaldehyde has already been detected around small baby stars in the IRAS 16293-2422 system with ALMA at a lower frequency. The difference in frequency reflects a difference in the environment. With Band 10 receivers, astronomers obtained a new tool to investigate warmer, denser regions.

The other Band 10 result was also one of the most challenging, the direct observation of jets of water vapor streaming away from one of the massive protostars in NGC 6334I. ALMA was able to detect the high frequency radio waves naturally emitted by heavy water (water molecules made up of oxygen, hydrogen, and deuterium atoms, which are hydrogen atoms with a proton and a neutron in their nuclei).

As a star begins to form out of massive clouds of dust and gas, the material surrounding the star falls onto the mass at the center. A portion of this material, however, is propelled away from the growing protostar as a pair of jets, which carry away gas and molecules, including water.

The heavy water the researchers observed is flowing away from either a single protostar or a small cluster of protostars. These jets are oriented differently from what appear to be much larger and potentially more-mature jets emanating from the same region. The astronomers speculate that the heavy-water jets seen by ALMA are relatively recent features just beginning to move out into the surrounding nebula.

“It is with much pleasure that we see the first scientific result from the ALMA Band 10 receiver,” said Yoshinori Uzawa, the Director of the NAOJ Advanced Technology Center. He is an engineering researcher specializing in superconducting devices and led the Band 10 receiver development. “I have devoted myself to the research of superconducting devices for more than two decades, and the Band 10 receiver is one of the fruits of my work and the efforts of many staffs, including the Band 10 development team and the commissioning team in Chile. I’d like to express my appreciation to all, and I am looking forward to seeing yet more new insights into the Universe.”

Development of the ALMA receivers was not easy, especially for Band 10. Due to its extreme high frequency, researchers could not use the conventional superconducting devices made of Niobium. The development team made a high quality film from the compound superconductive material NbTiN (niobium-titanium nitrides) in cooperation with the National Institute of Information and Communication Technology to achieve the world’s highest performance in the frequency of Band 10 in 2009. The team finished manufacturing and shipping the 73 receiver cartridges in 2014. After extensive commissioning and test observation on site, the Band 10 receivers have been used in ALMA’s normal science operation since October 2015.

Publication

These observation results were published as B. A. McGuire et al. “First Results of an ALMA Band 10 Spectral Line Survey of NGC 6334I: Detections of Glycolaldehyde (HC(O)CH2OH) and a New Compact Bipolar Outflow in HDO and CS” in Astrophysical Journal Letters in August 2018.

ALMA

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.