Astronomers from the United States and South Korea have made the first high-resolution radio telescope observations of molecular clouds in a massive star formation area of the outer Milky Way galaxy.
"This region lies behind a nearby cloud of dust and gas," said Charles Kerton, a professor of physics and astronomy at Iowa State University and a member of the study team. "The cloud blocks the light and therefore we have to use infrared or radio observations to study it."
The Milky Way region is called CTB 102. It is about 14,000 light-years from Earth. It is classified as a HII region, ie it contains clouds of ionized, charged hydrogen atoms. And because of its distance from the earth and the dust and gas in between, it was difficult to study.
And "this region has been badly hit," Kerton said.
Astronomers describe their first draft of a new higher resolution map for the region in a paper recently adopted for publication in the Astrophysical Journal (19459015). Main authors include Sung-ju Kang, a research associate at the Korea Astronomy and Space Science Institute and a former student at Iowa State University; and Brandon Marshall, a former student in Iowa State, who has accepted an apprenticeship at the University of Nebraska in Kearney. Other co-authors include Kerton and Youngsik Kim, Minho Choi and Miju Kang, all from the Korea Astronomy and Space Science Institute. Kim is also at the Daejeon Observatory in South Korea.
Kerton said astronomers used a newly commissioned radio telescope at Taeduk Radio Astronomy Observatory in South Korea to make high-resolution carbon monoxide observations of the galactic region's molecular clouds.
"That said, the mass and structure of the materials in the interstellar medium" said Kerton
Astronomers also compared their radio observations with existing infrared data from the Wide-Field Infrared Survey Explorer and the Two Micron All Sky Survey. Infrared data allowed them to classify young stars within the region's molecular clouds.
The data provide three important observations, astronomers report in their article.
First, astronomers used radiodata to describe the physical structure and properties of the newly mapped molecular clouds of the region – they are quite large, about 180 light-years long, with a mass equivalent to about 100,000 solar masses. Next, they used infrared data to determine the young star content in the clouds. Finally, they combined the two data streams to investigate the efficiency of star formation in the galactic region.
They report that the star formation efficiency of the entire CTB 102 region is about 5 to 10%, similar to other giant molecular clouds within the galaxy. However, they found a subset of the clouds with a star formation efficiency of 17% to 37% (depending on how the mass of the subarea is calculated). This is much higher than would be expected for a portion of its size. They speculate that the subregion is the site of a massive accumulation of young, evolving stars embedded in the molecular cloud.
Why all star formation in this one subregion? Kerton says that's a question for further study. Perhaps, he says, the interstellar material in this subregion has something special, besides the massive HII region.
"This is our first look at it all," Kerton said. "The older data was just a few dots, a few pixels, so we could not isolate this relatively small region of the galaxy."
But now they could – with the help of the new South Korean radio observatory.
The study's high-resolution observations, Kerton said, "also show that the telescope is ideal for studying similar regions in our galaxy – there are many other potential targets."
Multiple-wavelength observations of star formation areas reveal dozens of new celestial objects
High resolution observations of molecular clouds associated with the giant HII region CTB 102, arXiv: 1904.00529 [astro-ph.GA] arxiv.org/abs/1904.00529
Astronomers take a first, high-resolution view of the huge star-forming region of the Milky Way (2019, April 15)
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