Dwarf Spheroidal Galaxy NGC 147

The dwarf spheroidal galaxy NGC 147 is a dSph galaxy located in the constellation Cassiopeia at a distance of about 2.2 million light-years from Earth. It was discovered in 1790 by astronomer Wilhelm Herschel.

NGC 147 has a spheroidal shape and a diameter of about 3.5 thousand light-years. It contains few stars and belongs to the group of dwarf satellites of the Andromeda Galaxy. Despite its small mass and size, NGC 147 may be of great importance for the study of the structure and evolution of galaxies.

This galaxy has been studied by many telescopes, including the Hubble Space Telescope, which allowed scientists to obtain detailed images of its stars and structure. Studying NGC 147 can help scientists better understand the processes of galaxy formation and the interactions between them. It may also be an important target for dark matter research, as observations suggest that it contains significant amounts of this mysterious constituent of the Universe.

NGC 147 (also known as DDO3 or Caldwell 17) is a dwarf spheroidal galaxy located approximately 2.58 million light-years away in the constellation Cassiopeia. NGC 147 is a member of the Local Group of galaxies and a satellite galaxy of Andromeda (M31). It forms a physical pair with nearby NGC 185, another distant companion of M31. The galaxy was discovered by John Herschel in September 1829. It is visually dimmer and slightly larger than NGC 185, and thus has a significantly lower surface brightness. This means that NGC 147 is harder to see than NGC 185, which is visible in smaller telescopes. The Webb Society Deep-Sky Observer's Handbook describes NGC 147 visually as follows:

"Large, rather faint, irregularly round; brighter at center, with star-like nucleus."

NGC 147's membership in the Local Group was confirmed by Walter Bade in 1944, when he resolved the galaxy into individual stars using the 100-inch (2.5 m) telescope on Mount Wilson near Los Angeles.

Characteristics

A survey of the brightest asymptotic giant branch (AGB) stars within 2′ of the center of NGC 147 shows that the last significant star formation activity in NGC 147 occurred about 3 billion years ago. NGC 147 contains a large population of old stars that show a range of metallicities and ages. The range of metallicities suggests that NGC 147 has undergone chemical enrichment. However, H I is not observed, and the upper limit on the mass of the interstellar medium (ISM) is significantly lower than expected if material emitted by developing stars remained in the galaxy. This indicates an ISM deficiency.

Distance Measurements

At least two techniques have been used to measure the distance to NGC 147. The surface brightness variation method estimates the distances to spiral galaxies based on the grainy appearance of their cores. The distance to NGC 147 measured using this method is 2.67 ± 0.18 million light-years (870 ± 60 kpc). However, since NGC 147 is close enough, the end-of-red giant branch (TRGB) distance estimation method can be used. The distance estimate to NGC 147 using this method is 2.21 ± 0.09 million light-years (680 ± 30 kpc). The average of these measurements is 2.53 ± 0.11 million light-years (780 ± 30 kpc).

NGC 147 is an elliptical galaxy in the constellation Cassiopeia. It is located north of the celestial equator and as such is more easily visible from the northern hemisphere. With a visual magnitude of 9.5, NGC 147 can be seen with 80 mm aperture binoculars or a small telescope.