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| Artist’s impression of the Milky Way. Its hot halo appears to be stripping away the star-forming atomic hydrogen from its companion dwarf spheroidal galaxies. Image credit: NRAO/AUI/NSF |
Excerpt from
earthsky.org
Astronomers have discovered that our nearest galactic neighbors are devoid of star-forming gas, and that our Milky Way is to blame.
New observations by large radio telescopes reveal that within a well-defined boundary around our galaxy, dwarf galaxies are completely devoid of hydrogen gas. Beyond this point, dwarf galaxies are teeming with star-forming material.
The Milky Way galaxy is actually the largest member of a compact clutch of galaxies that are bound together by gravity. Swarming around our home galaxy is a menagerie of smaller dwarf galaxies, the smallest of which are the relatively nearby dwarf spheroidals, which may be the leftover building blocks of galaxy formation.
Further out are a number of similarly sized and slightly misshaped dwarf irregular galaxies, which are not gravitationally bound to the Milky Way and may be relative newcomers to our galactic neighborhood.
Kristine Spekkens is an assistant professor at the Royal Military College of Canada and lead author on a paper published in the Astrophysical Journal Letters. She said:
“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.”
Previous studies have shown that the more distant dwarf irregular galaxies have large reservoirs of neutral hydrogen gas, the fuel for star formation. These past observations, however, were not sensitive enough to rule out the presence of this gas in the smallest dwarf spheroidal galaxies.
Spekkens said:
“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.”
Bottom line: New observations by large radio telescopes reveal that within a well-defined boundary around our galaxy, dwarf galaxies are completely devoid of star-making hydrogen gas. Astronomers say our Milky Way is to blame.
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| Neighboring galaxies to our own Milky Way (Descriptions below) |
| NAME | DISTANCE (kpc) | DISCOVERY PAPER |
|---|---|---|
| Canes Major | 7.2 | Martin et al. 2004, A dwarf galaxy remnant in Canis Major: the fossil of an in-plane accretion on to the Milky Way |
| Segue 3 | 17 | Belokurov et al. 2010, Big Fish, Little Fish: Two New Ultra-Faint Satellites of the Milky Way |
| Segue 1 | 23 | Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions |
| Sagittarius | 24 | Ibata, Gilmore & Irwin, 1994, A dwarf satellite galaxy in Sagittarius 1995, Sagittarius: the nearest dwarf galaxy |
| Segue 2 | 34.7 | Belokurov et al. 2009, The discovery of Segue 2: a prototype of the population of satellitesof satellites |
| Bootes II | 43 | Walsh, Jerjen & Willman, 2007, A Pair of Bootes: A New Milky Way Satellite |
| Coma | 44 | Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions |
| Willman 1 (SDSSJ1049+5103) | 45 | Willman et al. 2005, A New Milky Way Companion: Unusual Globular Cluster or Extreme Dwarf Satellite? |
| Bootes III | 46 | Grillmair 2009, Four New Stellar Debris Streams in the Galactic Halo |
| LMC | 50.8 | – |
| SMC | 59.7 | – |
| Bootes | 60 | Belokurov et al. 2006, A Faint New Milky Way Satellite in Bootes |
| Ursa Minor | 66 | A.G. Wilson of the Lowell Observatory in 1955, Sculptor-Type Systems in the Local Group of Galaxies |
| Sculptor (Scl) | 79 | discovered in 1938 by Harlow Shapley, A Stellar System of a New Type |
| Draco | 82 | A.G. Wilson of the Lowell Observatory in 1955, Sculptor-Type Systems in the Local Group of Galaxies |
| Sextans | 89 | Mike Irwin, M.T. Bridgeland, P.S. Bunclark and R.G. McMahon, 1990 A new satellite galaxy of the Milky Way in the constellation of Sextans |
| Ursa Major (UMa) | 100 | Willman et al. 2005, A New Milky Way Dwarf Galaxy in Ursa Major |
| Carina | 103 | Cannon, R. D., Hawarden, T. G., & Tritton, S. B., 1977, A new Sculptor-type dwarf elliptical galaxy in Carina |
| Hercules | 140 | Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions |
| Fornax | 140 | discovered in 1938 by Harlow Shapley, described in “Two Stellar Systems of a New Kind”, Nature, Vol. 142, p. 715 |
| Canes Venatici II | 150 | Sakamoto & Hasegawa 2006, Discovery of a Faint Old Stellar System at 150 kpc |
| Leo IV | 160 | Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions |
| Pisces II | 182 | Belokurov et al. 2010, Big Fish, Little Fish: Two New Ultra-Faint Satellites of The Milky Way |
| Leo II (Leo B) | 208 | Robert G. Harrington and Albert George Wilson, 1950, Two New Stellar Systems in Leo |
| Canes Venatici | 220 | Zucker et al. 2006 A New Milky Way Dwarf Satellite in Canes Venatici |
| Leo I | 254 | Robert G. Harrington and Albert George Wilson, 1950, Two New Stellar Systems in Leo |
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