Galaxy of the Month Archive 2022
In this series of articles we draw your attention to galaxies particularly worthly of an observer's time.
NGC 3202 in Ursa Major
January 2022 - Galaxy of the Month
The small triplet of galaxies in the hind feet of UMa, comprising NGC 3202, NGC 3205 and NGC 3207, were all discovered by William Herschel and must be amongst the faintest of his discoveries. They were all found in February 1788 using the large 20ft which had the 18.7” speculum mirror.
The group is also included as Holmberg 179, although strictly speaking that is only NGC 3205 and NGC 3207, and WBL 264 which includes just the three galaxies in the trio.
All of the galaxies in the trio are spirals and NGC 3205 and NGC 3207 show some signs of distortion. The Pan-STARRS image shows NGC 3205 wrapped in shells which suggests a recent merger. It is also suggested that NGC 3205 contains a weak AGN known as a LINER. NGC 3207 it also reported to have an AGN of the same form but is also a low power radio galaxy. It is possible that there is much more activity going on but it is obscured by dust surrounding the nucleus. Perhaps unsurprisingly then NGC 3202 is also thought to contain a weak AGN, also classified as a LINER.
All three are face on spiral galaxies classified as red and dead, which means there is no star formation going on in them at this time. The group appears to be at a distance of about 330 million light-years from us, which suggests that NGC 3205 at least is quite a large galaxy, comparable in size to the Milky Way. The distances here come from the redshifts so there may be some variation in the actual distances to the group members. Otherwise not much research seems to have been done on the group.
Perhaps unsurpingly the trio does not make it into the Night Sky Observer's Guide (NSOG) Vol. 2 but is included in Alvin Huey’s booklet on galaxy trios. The group is very tight and will probably require a high power to bring out all the galaxies as they are relatively faint. The group is very compact so will fit in the field of a modern high power wide field eyepiece. It lies only about 41’ from the 4th magnitude star lambda UMa so a high power will be required to keep the glow from this out of the field.
If you find the main galaxies in the group too easy then try for the edge on spiral UGC 5578, which will also appear in the same medium power field as the rest of the trio. I had half expected the trio to be listed in Wolfgang’s book on Galaxies and How to Observe Them as they appear as a precanned list in Eye and Telescope but they are not there.
Owen Brazell - Galaxy Section Director