NGC 3430 in Leo Minor
January 2018 - Galaxy of the Month
For the first time in the GOM column we head into the constellation of Leo Minor and the nice group of galaxies around NGC 3430. All of the NGC galaxies in the group (NGC 3430, NGC 3425, NGC 3413, NGC 3395 and NGC 3396) were discovered by William Herschel in 1785.
The area is also littered with IC objects that were discovered by Bigourdan, although almost none of them are real, he was obviously having a bad night!
The group is listed as LGG 218 which apparently contains 10 galaxies including the main core around NGC 3430. However, it appears from its radial velocity that NGC 3413 is not part of the physical group, just a line of sight addition.
NGC 3395/6 are also known as Arp 270 and it maybe that Bigourdan saw a knot in the spiral arm of NGC 3395 part of this galaxy pair when he reported the object that became IC 2605. This pair were also noted in the VV catalogue of interacting systems that preceded Arp’s work. Arp 270 has also featured in the DSF OOTW column.
NGC 3430 itself is classified as a Wolf-Rayet (WR) galaxy, a relatively rare type of galaxy undergoing a strong burst of star formation and showing emission lines in its spectra. The WR phenomena in galaxies are normally triggered by interactions between galaxies and it is thought that NGC 3430 is interacting with NGC 3424 and indeed deep images and radio observations suggest that both NGC 3430 and NGC 3424 do show signs of tidal interaction.
NGC 3430 was also one of the galaxies that the Rosse team at Birr thought were spiral in nature, and it appears that they were correct in that call in this case. With the exception of NGC 3413 which is a lenticular galaxy all of the others in the field are spiral in nature.
The group is probably of the order of 90 million light years away, although I have seen distances as close as 76 million light years quoted.
Arp 270 is a merging galaxy system, probably in the early stages of the merger and there is a lot of star formation going on. There is a sixth NGC galaxy which is also part of the LGG 218 group in NGC 3442 but this is almost a degree north of the main core around NGC 3430.
The main galaxies are bright enough to be seen in medium aperture telescopes, of the order of 30cm, and the group around NGC 3430 is a nice triple system when using high power. All five galaxies may appear on the same field when using a modern hyperwide eyepiece with a medium power of say 180x.
Also in the same area is IC 2604, a 14th magnitude galaxy that was discovered by Javelle in 1896. It is also thought to be part of the group and will be a challenge for owners of larger telescopes. So overall an interesting group which appears to have two independent interaction events going on in it.
Owen Brazell - Galaxy Section Director