Most of you are probably familiar with the Andromeda Galaxy (M31). You might also know that it has two prominent satellite galaxies – M32 and NGC 205 – nestled close by. However, M31 has more than just these companions. In fact, astronomers have identified a total of 35 satellite galaxies orbiting the Andromeda Galaxy, many of which are smaller and spread across various constellations. Interestingly, only four of them were discovered before the photographic era: the well-known M32 and NGC 205, as well as NGC 185 and NGC 147, these latter two located in the constellation Cassiopeia. NGC185 was found by William Herschel in 1787, and a larger and fainter NGC185 by his son Jon in 1829. All other M31 satellite galaxies were discovered during the last 50 years.
NGC 185 and 147 are only one degree apart in the sky. Both are dwarf elliptical galaxies in the M31’s outer halo. Past studies of them indicated they are about at the same distance from us as the Andromeda Galaxy and that they form a gravitationally bound pair. However, a recent 2020 study published in The Astrophysical Journal presented new measurements. NGC147 distance was calculated for 2.36 million light-years, and NGC185 distance is 2.07 million light-years, which places them both on the near side of M31.
NGC 147 is also catalogued as Caldwell 17. It is visually fainter and apparently larger than NGC 185, making it more difficult to observe visually with a telescope. In the Webb Society Deep-Sky Observer’s Handbook, the visual appearance of NGC 147 is described as follows: Large, quite faint, irregularly round; it brightens in the middle to a stellar nucleus.
NGC 185 (aka Caldwell 18), unlike most dwarf elliptical galaxies, contains young stellar clusters, and star formation proceeded until the recent past. It has an active galactic nucleus (AGN) and is classified as a type 2 Seyfert galaxy – the closest known Seyfert galaxy.
When you image a galaxy or galaxy group, there are often very many faint, distant objects present in the same field of view. This frame, however, presents a sky area close to the Milky Way plane – there are many stars of our Galaxy, and also, the interstellar matter concentration in this area is significant. That is why some distant galaxies can be spotted among the stars in the picture, but the extinction hides most of them.
The comparison below shows the NGC147 galaxy center. The image in the insert was made by the Hubble Space Telescope. Some key elements are visible in my image, and that is good news 🙂
Image technical data: Date: December 2024 Location: Nieborowice, Poland Telescope: TS Photoline 130/910 Corrector: TS FF/FR 0.8x Camera: QHY268M Mount: EQ6 Guiding: ASI290MM + Evoguide ED50 Exposures: LRGB 480:90:60:80 minutes Conditions: Bortle 6, transparency and seeing medium-good
