Fornax Dwarf
Encyclopedia
The Fornax Dwarf Spheroidal is an elliptical dwarf galaxy
in the constellation
Fornax
that was discovered in 1938 by Harlow Shapley
. He discovered it while he was in South Africa
on photographic plates taken by a 24 inch reflecting telescope
at Boyden Observatory
, shortly after he discovered the Sculptor Dwarf galaxy.
The galaxy
is a satellite of the Milky Way
and contains six globular clusters; the largest, NGC 1049
, was discovered before the galaxy itself. The galaxy is also receding from the Milky Way
at 53 km/s. It mostly contains population II stars.
, in 1999, Buonanno et al. derived a color-magnitude diagram for Fornax 4, a globular cluster within this galaxy. Unlike the globular cluster
s Fornax 1, 2, 3, and 5, which have horizontal branch
es across a wide range of colors and include RR Lyrae variable
s, Fornax 4 is found to have only red in its horizontal branch. Fornax 4 is also ~3 Gyr younger than the other globular clusters. Buonanno et al. note that the color-magnitude diagram of Fornax 4 has a strong similarity to "young" galactic globular Ruprecht 106. This leads to two open questions: Why do dwarf spheroidals allow the formation of globular clusters like Fornax 4 and Terzan 7
(of Sagittarius dwarf
) long after globular clusters ceased to form in the main body of the Galactic halo? Is it possible that "young" globular clusters of the outer halo like Ruprecht 106 were originally formed in now defunct dwarf spheroidals?
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Fornax
Fornax
Fornax is a constellation in the southern sky. Its name is Latin for furnace. It was created in the 18th century and is now one of the 88 modern constellations.-History:Fornax was formed by Nicolas Louis de Lacaille in 1756...
that was discovered in 1938 by Harlow Shapley
Harlow Shapley
Harlow Shapley was an American astronomer.-Career:He was born on a farm in Nashville, Missouri, and dropped out of school with only the equivalent of a fifth-grade education...
. He discovered it while he was in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
on photographic plates taken by a 24 inch reflecting telescope
Reflecting telescope
A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
at Boyden Observatory
Boyden Observatory
Boyden Observatory is a South African astronomical research observatory and science education centre.-History:The observatory was originally founded in 1889 by the Harvard University at Mount Hardvard near Lima, Peru, but relocated to Arequipa, Peru in October 1890.Significant work done at Arequipa...
, shortly after he discovered the Sculptor Dwarf galaxy.
The galaxy
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
is a satellite of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
and contains six globular clusters; the largest, NGC 1049
NGC 1049
NGC 1049 is a globular cluster located in the constellation of Fornax, in the nearby Local Group galaxy of Fornax Dwarf. At a distance of 630,000 light years, it is still visible in moderate sized telescopes but the parent galaxy is nearly invisible...
, was discovered before the galaxy itself. The galaxy is also receding from the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
at 53 km/s. It mostly contains population II stars.
Globular clusters
Using the Hubble Space TelescopeHubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
, in 1999, Buonanno et al. derived a color-magnitude diagram for Fornax 4, a globular cluster within this galaxy. Unlike the globular cluster
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
s Fornax 1, 2, 3, and 5, which have horizontal branch
Horizontal branch
The horizontal branch is a stage of stellar evolution which immediately follows the red giant branch in stars whose masses are similar to the Sun's...
es across a wide range of colors and include RR Lyrae variable
RR Lyrae variable
RR Lyrae variables are periodic variable stars, commonly found in globular clusters, and often used as standard candles to measure galactic distances.This type of variable is named after the prototype, the variable star RR Lyrae in the constellation Lyra....
s, Fornax 4 is found to have only red in its horizontal branch. Fornax 4 is also ~3 Gyr younger than the other globular clusters. Buonanno et al. note that the color-magnitude diagram of Fornax 4 has a strong similarity to "young" galactic globular Ruprecht 106. This leads to two open questions: Why do dwarf spheroidals allow the formation of globular clusters like Fornax 4 and Terzan 7
Terzan 7
Terzan 7 is a sparse and young globular cluster that is believed to have originated in the Sagittarius Dwarf Elliptical Galaxy and is physically associated with it. It is relatively metal rich with Fe/H] = -0.6 and an estimated age of 7.5 Gyr...
(of Sagittarius dwarf
Sagittarius Dwarf Elliptical Galaxy
The Sagittarius Dwarf Elliptical Galaxy is an elliptical loop-shaped satellite galaxy of the Milky Way Galaxy. It consists of four globular clusters, the main cluster being discovered in 1994...
) long after globular clusters ceased to form in the main body of the Galactic halo? Is it possible that "young" globular clusters of the outer halo like Ruprecht 106 were originally formed in now defunct dwarf spheroidals?