NGC 147
Large, quite faint, irregularly round; it brightens in the middle to a stellar nucleus.
The membership of NGC 147 in the Local Group was confirmed by Walter Baade in 1944 when he was able to resolve the galaxy into individual stars with the 100-inch (2.5 m) telescope at Mount Wilson near Los Angeles.
Characteristics
A survey of the brightest asymptotic giant branch (AGB) stars in the area of radius 2′ from the center of NGC 147 shows that the last significant star-forming activity in NGC 147 occurred around 3 Gyr ago. NGC 147 contains a large population of older stars which show a spread in metallicity and age. The metallicity spread suggests that NGC 147 has had chemical enrichment. However, H I has not been observed and the interstellar medium (ISM) mass upper limit is much lower than expected had the material which is emitted from evolving stars been kept in the galaxy. This implies depletion of the ISM.
Distance measurements
At least two techniques have been used to measure distances to NGC 147. The surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to NGC 147 using this technique is 2.67 ± 0.18 Mly (870 ± 60 kpc). However, NGC 147 is close enough that the tip of the red giant branch (TRGB) method may be used to estimate its distance. The estimated distance to NGC 147 using this technique is 2.21 ± 0.09 Mly (680 ± 30 kpc). Averaged together, these distance measurements give a distance estimate of 2.53 ± 0.11 Mly (780 ± 30 kpc).