Scientists detect stellar streams around Magellanic Clouds

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Astronomers from the University of Cambridge, U.K., have detected a number of narrow streams and diffuse debris clouds around two nearby irregular dwarf galaxies called the Magellanic Clouds. The research also implies that one of these dwarf galaxies – the Large Magellanic Cloud (LMC) could be more massive than previously thought. A paper detailing these findings was published last week on ArXiv.

“Even though a prominent gaseous stream emanating from the clouds has been known and studied for some time, no obvious stellar streams had been found until recently,” Vasily Belokurov, one of the co-authors of the paper, told Phys.org.

Belokurov, together with his colleague Sergey Koposov, used the Dark Energy Survey (DES) to track down stellar debris on the outskirts of the Magellanic Clouds. They were searching for the Magellanic stellar halo substructure using blue horizontal-branch (BHB) stars as tracers. BHBs are old and metal-poor stars powered by helium fusion that appear blue. They were chosen by Cambridge scientists as these stars suffer little contamination from other stellar populations. BHBs can be easily picked up and are one of the best stellar standard rulers available.

“Thanks to their unique properties, BHBs have proven to be a powerful tool to scrutinize the galactic halo out from the core to its far-flung fringes,” the researchers wrote in the paper.

“In the halo, not only can these old and metal-poor stars be easily identified above the foreground of other populations thanks to their peculiar color, they are also one of the best stellar distance estimators available,” they added.

DES is an astronomical survey specifically designed to measure the expansion history of the universe. It has one of the widest fields of view available for ground-based optical and infrared imaging. The scientists used DES’ Year 1 public dataset for this study.

“To study the stellar halo substructure around the Magellanic Clouds, we use the photometric catalogs obtained from the publicly released DES Year 1 imaging, in particular, the latest improved version of the reduction,” the paper reads.

Scanning many BHBs, the astronomers detected the stellar halo of the Magellanic system and its substructures. Each of these substructures is different in shape, extent and luminosity, and deserves its own detailed analysis.

The discovery of these stellar halosubstructures led the scientists to ponder on the possible revision of our current knowledge about LMC’s mass. They ask whether the LMC could, in fact, be much more massive than has been previously assumed.

“Our discoveries imply that the Large Magellanic Cloud might have been a lot more massive than we previously thought. To figure out exactly how much more massive, we need to follow these streams up with spectroscopy in order to measure their velocities,” Belokurov said.

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