Arp 232 in Leo

May 2023 - Galaxy of the Month

This interactive image of the Arp 232 and was provided by the Sloan Digital Sky Survey (SDSS) using Aladin Sky Atlas. We also have a finder chart should help you locate these galaxies, as will this link for NGC 2911 on the Stellarium Web planetarium.

As the skies start to get brighter as we approach the summer season in the northern hemisphere, I have chosen the relatively bright galaxy NGC 2911, also known as Arp 232, as my galaxy of the month. The galaxy is also included in the extended Vorontsov-Velyaminov (VV) catalogue as VV 1290.

Lying in the constellation of Leo, NGC 2911 was discovered by William Herschel in 1784. It is catalogued as a lenticular galaxy, although unusually for that type of galaxy it does contain a number of dust lanes. Arp catalogued it as an example of his galaxies in fission group, but also suggested that it might have concentric rings. NASA/IPAC Extragalactic Database (NED) suggests it is part of WBL 226, a small group of three galaxies, which also contains NGC 2914 along with UGC 5093.

The nucleus of NGC 2911 appears to contain an AGN of the LINER type, which suggests there maybe, or have been interactions in the group. The AGN has also been classified as a type 3 Seyfert. There does not seem to be a lot of activity in the nucleus given that NGC 2911 is practically invisible in the UV images from GALEX.

There is also some confusion in the group as an object (PGC 27167) was found that some sources include as NGC 2912. This cannot be true as studies of the original discovery notes for NGC 2912 show it cannot be this object and the object included in the New General Catalogue of Nebulae and Clusters of Stars (NGC) as NGC 2912 is now thought to be just a star.

It is unlikely that NGC 2911 is interacting with NGC 2914. The group lies at a distance of perhaps 155 million light-years from us. Perhaps surprisingly for an Arp object there does not seem to have been a lot of research published on it. NGC 2914 was also included by Arp in his catalogue as Arp 137 so you get two Arp objects in the same field. NGC 2914 is also classified as a lenticular galaxy but this time showing what appears to be tidal tails. It may also be an example of a polar ring galaxy.

The whole group is very compact and all three objects will fall in the field of a high power ultra-wide field eyepiece. A medium power field will also include the galaxy NGC 2919. Some sources suggest that this galaxy may also be part of the NGC 2911 group but it is probably unlikely. The Night Sky Observer's Guide (NSOG) Vol. 2 suggests that this galaxy group maybe more challenging than I suggested and it is a target for 40-45cm scopes and even with those NGC 2914 is no more than a faint patch. UGC 5093 is suggested to be an AV object with that class of telescope. Observations form the UK with a 40cm telescope would fit those notes with NGC 2911 being described as a faint oval.

Owen Brazell - Galaxy Section Director