Milky Way Strips Away Star-Forming Gas from Nearby Dwarf Galaxies

It turns out that our Milky Way Galaxy may be stripping away star-forming materials. Astronomers have taken a look at our closest galactic neighbors, the dwarf spheroidal galaxies, and have found that they're devoid of star-forming gas--and our Milky Way may be to blame.

The Milky Way Galaxy is the largest member of a compact clutch of galaxies that are bound together by gravity. The smallest galaxies in this cluster are the relatively nearby dwarf spheroidals, which may actually be leftover building blocks of galaxy formation. Further out are a number of similarly sized and slightly misshaped dwarf irregular galaxies.

"Astronomers wondered if, after billions of years of interaction, the nearby dwarf spheroidal galaxies have all the same star-forming 'stuff' that we find in more distant dwarf galaxies," said Kristine Spekkens, lead author of the new paper, in a news release.

In order to better understand these spheroidal galaxies, the researchers used the Green Bank Telescope (GBT) and other giant telescopes from around the world to examine the dwarf galaxies. Using these instruments, the researchers then searched for tiny amounts of atomic hydrogen in these galaxies.

"What we found is that there is a clear break, a point near our home Galaxy where dwarf galaxies are completely devoid of any traces of neutral atomic hydrogen," said Spekkens.

Beyond this point, which extends about 1,000 light-years from the edge of the Milky Way's star-filled disk to a point that is thought to coincide with the edge of its dark matter distribution, dwarf spheroidals become vanishingly rare while gas-rich, dwarf irregular galaxies flourish.

So how do these galaxies lose their star-forming material? They're susceptible to the influences of the Milky Way, which resides within an extended, diffuse halo of hot hydrogen plasma. It's likely that this halo is dense enough to impact the composition of dwarf galaxies. The pressure created by the velocities of the dwarf spheroidals can actually strip away any detectable traces of hydrogen. In other words, the Milky Way shuts down star formation in neighboring galaxies.

The findings reveal a bit more about how the Milky Way interacts with other galaxies. This, in turn, shows astronomers a great deal about the size of the hot halo around our home Galaxy.

The findings are published in The Astrophysical Journal.