Maps reveal massive clouds in star-forming region

Astronomers have made the first high-resolution, radio telescope observations of the molecular clouds within a huge star-forming region of the outer Milky Way.

“This region is behind a nearby cloud of dust and gas,” says Charles Kerton, an associate professor of physics and astronomy at Iowa State University and a member of the study team.

“The cloud blocks the light and so we have to use infrared or radio observations to study it.”

The Milky Way region, called CTB 102, is about 14,000 light years from Earth. It’s classified as an HII region, meaning it contains clouds of ionized—charged—hydrogen atoms. And, because of its distance from Earth and the dust and gas in between, it has been difficult to study.

And so, “this region has been very poorly mapped out,” Kerton says.

star-forming region image
This image from a radio telescope shows a huge star-forming region of the outer Milky Way galaxy. The ovals identify the main subdivisions of the region’s molecular cloud, including the smaller 1a, which is very efficient at producing stars. (Credit: Charles Kerton)

The astronomers used a newly commissioned radio telescope at the Taeduk Radio Astronomy Observatory in South Korea to take high resolution, carbon monoxide observations of the galactic region’s molecular clouds, Kerton says. “That tells us the mass and structure of the material in the interstellar medium there.”

The astronomers also compared their radio observations with existing infrared data from the Wide-field Infrared Survey Explorer and the Two Micron All Sky Survey. The infrared data allowed them to classify young stars forming within the region’s molecular clouds.

The data yield three major observations, the astronomers report in their paper, which will appear in Astrophysical Journal.

First, the astronomers used radio data to describe the physical structure and characteristics of the region’s newly mapped molecular clouds—they’re fairly large, about 180 light years across with a mass equal to about 100,000 masses of our sun. Next, they used infrared data to determine the young stellar content within the clouds. And finally, they combined the two data streams to study the efficiency of star formation within the galactic region.

The researchers report the star formation efficiency of the entire CTB 102 region is about 5 to 10 percent, similar to other giant molecular clouds within the galaxy. But, they found one subregion of the clouds with a star formation efficiency of 17 to 37 percent (depending on how they calculate the mass of the subregion). That’s much higher than astronomers would expect for a subregion of its size. The researchers speculate the subregion is the site of a massive cluster of young, developing stars embedded in the molecular cloud.

Why all the star formation in that one subregion? Kerton says that’s a question for further study. Maybe, he says, there’s something special about the interstellar material in that subregion, which is next to the massive HII region.

“This is our first look at all of this,” Kerton says. “The older data were just a few dots, a few pixels. We couldn’t isolate this relatively small region of the galaxy.”

But now they can—with the help of the new South Korean radio observatory.

The study’s high-resolution observations, Kerton says, “are also a demonstration that the telescope is ideal for studying similar regions in our galaxy—there are many other potential targets.”

Additional researchers from Korea Astronomy and Space Science Institute and the University of Nebraska contributed to the work.

Source: Iowa State University