Astronomers from the University of Cambridge, U.K., have detected a number of narrow streams and diffuse debris clouds around 2 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.
“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. Belokurov, together with 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 as these stars suffer little contamination from other stellar populations.
“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.
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. 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 halo substructures led the scientists to ponder on the possible revision of our current knowledge about LMC’s mass. ie it could 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.
The researchers also noted that a combination of the deep imaging and spectroscopic follow-up of the tidal debris could provide more information about the orbital history of the Magellanic Clouds. This could be crucial to our understanding of the Clouds’ future as they are in the process of merging with our Milky Way galaxy. They are currently on their way to join the already crowded Milky Way halo.
http://phys.org/news/2015-11-scientists-stellar-streams-magellanic-clouds.htmljCp
Seen from the southern skies, the Large and Small Magellanic Clouds (the LMC and SMC, respectively) are bright patches in the sky. Image credit: ESO/S. Brunier
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