Draco Dwarf Galaxy

The Draco Dwarf is a spheroidal galaxy. It is part of the Local Group and a satellite galaxy of the Milky Way galaxy. The Draco Dwarf is situated at 34.6° above the galactic plane.

Characteristics

The ellipticity of the galaxy is 0.29 ± 0.04. Studies have indicated that the galaxy may potentially hold large amounts of dark matter. Having an absolute magnitude of -8.6, it is one of the faintest companions to our Milky Way.

Draco Dwarf contains many red giant branch (RGB) stars; five carbon stars have been identified in Draco Dwarf and four likely asymptotic giant branch (AGB) stars have also been detected.

The Draco Dwarf is estimated to span a distance of 830 ± 100 × 570 ± 70 pc.

Metallicity

The Draco Dwarf contains primarily an old population of stars and insignificant amounts of interstellar matter (being basically dust free). From 75% to 90% of its stars formed more than ~10 Gyr ago followed by a low rate of formation with a small burst of star formation around 2-3 Gyr ago. It has a single Gaussian distribution with average metallicity of [Fe/H] = −1.74 dex with a standard deviation (sigma/σ) of 0.24 dex and a small tail of metal-rich stars. The central region of Draco Dwarf exhibits a concentration of more metal-rich stars there being more centrally concentrated red horizontal branch stars than blue horizontal branch stars.

Dark matter

Radial velocity computations of Draco have revealed a large internal velocity dispersion giving a mass to luminosity ratio that suggests large amounts of dark matter. It has been hypothesized that large velocity dispersions could be explained as tidal dwarfs (virtually unbound stellar streams from dwarf galaxies tidally disrupted in the Milky Way potential). However, Draco Dwarf's narrow horizontal branch width does not support this model. This only leaves the dark matter explanation and makes Draco Dwarf one of the most dark matter dominated objects known. The dark matter distribution within Draco Dwarf is at least nearly isothermal.