Scientists detect stellar streams around Magellanic Clouds

November 23, 2015 by Tomasz Nowakowski, Phys.org report
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

(Phys.org)—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 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 substructures 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.

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.

Explore further: The Magellanic Clouds may be much larger than astronomers caluclated

More information: Stellar streams around the Magellanic Clouds, arXiv:1511.03667 [astro-ph.GA], arxiv.org/abs/1511.03667

Abstract
Using Blue Horizontal Branch stars identified in the Dark Energy Survey Year 1 data, we report the detection of an extended and lumpy stellar debris distribution around the Magellanic Clouds. At the heliocentric distance of the Clouds, overdensities of BHBs are seen to reach at least to ~30 degrees, and perhaps as far as ~50 degrees from the LMC. In 3D, the stellar halo is traceable to between 25 and 50 kpc from the LMC. We catalogue the most significant of the stellar sub-structures revealed, and announce the discovery of a number of narrow streams and diffuse debris clouds. Two narrow streams appear approximately aligned with the Magellanic Clouds' proper motion. Moreover, one of these overlaps with the gaseous Magellanic Stream on the sky. Curiously, two diffuse BHB agglomerations seem coincident with several of the recently discovered DES satellites. Given the enormous size and the conspicuous lumpiness of the LMC's stellar halo, we speculate that the dwarf could easily have been more massive than previously had been assumed.

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12 comments

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cantdrive85
1.4 / 5 (11) Nov 23, 2015
The gaseous and stellar streams are interstellar and intergalactic Birkeland currents, powering the stars and galaxies alike. Depending upon their scale of course.
plasmasrevenge
1 / 5 (8) Nov 23, 2015
The Magellanic clouds themselves are actually streams as well. There is a convention in the astrophysical community to over-use the word "cloud." Radio astronomer Gerrit Verschuur has spent much time analyzing these structures by hand, and he will only use the term "cloud" in quotes. He's also published a number of papers which appear to show these extensive filaments emitting critical ionization velocities -- which suggests that they are a source for ionization. However, as with electricity in space more generally, you won't see such things if you are not looking for them, as at these wavelengths, the frequencies from vastly different distances tend to overlay one another. It takes a meticulous hand analysis to see it.
Captain Stumpy
4.3 / 5 (6) Nov 23, 2015
The gaseous and stellar streams are interstellar and intergalactic Birkeland currents, powering the stars and galaxies alike. Depending upon their scale of course.


Birkeland current - "A Birkeland current is a set of currents that flow along geomagnetic field lines connecting the Earth's magnetosphere to the Earth's high latitude ionosphere."
SuperThunder
5 / 5 (4) Nov 23, 2015
The article could have said a bit more about stellar streams.
https://en.wikipe..._streams
It leaves out how cool they are.
cantdrive85
1.6 / 5 (7) Nov 23, 2015
Hmmm...

Birkeland current - "A Birkeland current is a set of currents that flow along geomagnetic field lines connecting the Earth's magnetosphere to the Earth's high latitude ionosphere."

If you say so. Electricity does work the same way every time....

Surprising someone who claims to be so familiar with plasma would be so completely ignorant of basic terminology and concepts. A little historical perspective would do you well, you might also realize the magic bowls are an expected response to a Z-pinched Birkeland current.

Captain Stumpy
5 / 5 (7) Nov 23, 2015
A little historical perspective would do you well
@cd
why? he didn't say that Birkeland didnt come up with his labeled pinches... nor is he trying to state Birkeland didn't exist
history is moot WRT proving science, unless you want to prove subject A came up with the idea before Subject B
Surprising someone who claims to be so familiar with plasma would be so completely ignorant of basic terminology and concepts
irony
considering you've completely refused to accept known PLASMA concepts proven repeatedly in various plasma labs, like this: http://www.pppl.g...nnection

or what about your ignorance regarding Diocotron Instabilities and their analogue?
isn't that " basic terminology and concepts" ???

.

thanks for the laugh

my2cts
4 / 5 (4) Nov 26, 2015
The Magellanic clouds themselves are actually streams as well. There is a convention in the astrophysical community to over-use the word "cloud."

So Magellan the astrophysicist started a 500 year old conspiracy to overuse the word "cloud".
All that to cross your attempt to enlighten us.
Evil..
plasmasrevenge
1 / 5 (2) Nov 28, 2015
There is hardly anything extraordinary about astrophysicists making a mistake. The bulk of the scientific community was, for example, dead wrong when they declared claims of radio waves from space either a mistake or a hoax ...

https://plus.goog...4Q5Ceggb

When Alfven initially proposed that galaxies could possess magnetic fields, he was ridiculed for not understanding that space was an empty vacuum. Alfven proved to be right.

What's happening with the filaments is much the same: When Alfven initially proposed that space must be filamentary if plasmas dominate in cosmology, we lacked the instruments required to actually confirm the claim. But, that's no longer the case, and anybody who actually looks at a section of an HI hydrogen survey would immediately notice that cloud is not the proper term. These structures extend to very great distances, and include knots.
my2cts
5 / 5 (2) Nov 29, 2015

anybody who actually looks at a section of an HI hydrogen survey would immediately notice that cloud is not the proper term. These structures extend to very great distances, and include knots.

Please explain how a HI region containing neutral hydrogen atoms is a plasma.
HI regions dominate in cosmology and they are not plasmas.
cantdrive85
1 / 5 (2) Nov 30, 2015
Are you suggesting there are zero free electrons or ions available in HI regions? Even a very slightly ionized "cloud" will behave as a plasma. One need look no further than results produced by IBEX and the behavior of the ENA's it discovered.
my2cts
5 / 5 (2) Nov 30, 2015
@cd
Of course I suggested no such thing. The ionisation degree of HI clouds is typically 10^-4. At finite temperature any gas has a small degree of ionisation. No gas exists at absolute zero, so by your standards _all_ gases are plasma's! I finally got to the root cause: faulty standards are why you think the whole world is wrong and only you are right.
Captain Stumpy
5 / 5 (2) Dec 03, 2015
There is hardly anything extraordinary about astrophysicists making a mistake. The bulk of the scientific community was, for example, dead wrong when they declared claims of radio waves from space either a mistake or a hoax ...
@plasma
don't forget to try to justify your beliefs by throwing out the whole "Galileo argument" too...
and flat earth
and since you are simply making unsubstantiated claims (WRT your eu crud) that are directly refuted by evidence, why not throw in a pinch of creationism too? after all, it has the same level of evidence you've provided for your beliefs (and some of the same arguments too)

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