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Aquarius 2 is a Difficult to Detect Dwarf Galaxy

20 May 2016, 22:00 UTC
Aquarius 2 is a Difficult to Detect Dwarf Galaxy
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Torrealba et al. (2016) present the discovery of Aquarius 2, a dwarf galaxy that is a distant satellite galaxy of the Milky Way. Aquarius 2 was identified based on an overdensity of Red Giant Branch (RGB) stars and an overpopulation of Blue Horizontal Branch (BHB) stars. RGB and BHB stars are stars that have evolved off the main sequence and they are many times more luminous than their main sequence progenitors. These luminous evolved stars can indicate the position of what would otherwise be an invisible galaxy.The estimated distance of Aquarius 2 from the Milky Way is ~360,000 light years and its estimated half-light radius is ~500 light years. The half-light radius of a galaxy is the size of the volume around the center of the galaxy which accounts for half the galaxy's brightness. The half-light radius of Aquarius 2 is estimated to enclose ~3 million times the Sun's mass.Aquarius 2 has a low surface brightness of only 30.4 mag/arcsec², and the total luminosity of this dwarf galaxy is only ~4000 times the Sun's luminosity. Aquarius 2 has a large mass-to-light ratio of ~1300, indicating it is a dark matter dominated galaxy. The low surface brightness and low overall luminosity ...

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