Boötes II (dwarf galaxy)

Boat II ( briefly also Boo II) is a spheroidal dwarf galaxy ( dSph ) in the constellation of the bear trap. It was discovered in 2007 in imaging survey of the Sloan Digital Sky Survey. The galaxy is located at a distance of about 42 kpc from the solar system and is moving at 120 km / s for the sun to. As a spheroidal dwarf galaxy, it has a nearly round shape with a half-light radius of only 51 pc ( other sources mention even just 36 pc).

Properties

Luminosity

Boat II is one of the smallest and faintest satellite galaxies of our Milky Way (only Segue 2 and Willman 1 are fainter ). The integral luminosity is MV = -2.7 m only about 1000 times as strong as that of the sun, the luminosity is thus lower than that of the majority of globular clusters. The mass of the dwarf galaxy, however, is clearly significant because of the high mass-luminosity ratio of more than 100, which suggests a high density of dark matter.

Metallicity

The stellar population of the boat II consists mainly of older stars, which arose prior to 10 to 12 billion years ago. The metallicity of these old stars with [Fe / H] = -1.8 low. You have 80 times less heavy elements than our Sun. At present, it must be held no star formation in the boat II. Even now was to no neutral hydrogen gas can be measured in the dwarf galaxy (upper limit of which is only 86 M ☉ ).

Affiliation

Boat II is only 1.5 ° (corresponding to 1.6 kpc ) away from the boat I. However, it is unlikely that the two galaxies are physically coupled, as they move with respect to the Milky Way in opposite directions, and this with the still high relative velocity of 200 km / s However, it seems more likely that the boat II is part of the Sagittarius stream and thus is more of a satellite galaxy or even just one of seized 4 -7 billion years ago globular clusters of the Sagittarius dwarf galaxy.

More

• Dwarf galaxy
• Local Group