IC 2184 in Camelopardalis

March 2019 - Galaxy of the Month

This interactive image of the IC 2184 was provided by the Pan-STARRS1 Surveys using Aladin Sky Atlas.

This peculiar V shaped galaxy pair in Camelopardalis was first discovered in 1900 by Bigourdan using the 12.4” refractor in Paris.

Originally thought to be a single galaxy it was added into Vorontsov-Velyaminov’s catalogue of interacting galaxies as VV 644. Due to its bright emission in the UV/Blue bands it was also classified as Markarian 8.

There seemed to be a lot of confusion as to the nature of this object with some observers claiming there were four galaxies present. This mystery was cleared up when Hubble imaged the pair. The Hubble image shows distinct tidal tails as well as the massive star forming regions formed when the gas from the galaxies crashed into one another.

The presence of these star forming regions and the existence of many Wolf-Rayet stars has also led to IC 2184 being classified as a Wolf-Rayet galaxy. Wolf-Rayet (WR) galaxies are a subset of emission-line and HII galaxies, whose integrated spectra show broad emission features attributed to the presence of WR stars.

Images taken in H-Alpha show the existence of a number of bright knots, which are the starburst sites. These knots would appear to be immersed in a diffuse envelope. The rapid rate of star formation is indicated by the fact that one of the knots may have up to 850 WR stars in it. Given this the knots cannot be that old and their age has been estimated of to be of the order of 4-6 million years. The existence of these knots may be the reason that earlier observers thought there were more than two galaxies here.

From the Hubble image it would appear that we are pretty much seeing the galaxies edge on. The galaxies are perhaps 165 million light-years away and at this distance would be perhaps 45 and 40 thousand light-years across. The whole system is perhaps 65 thousand light-years across, so quite small galaxies. The pair will merge into a single galaxy and given their distance will have probably done so by now.

Visually this galaxy pair will be a challenge, not so much for their faintness as they are around 13th magnitude, but because of their size. They are quite small so you are going to need high power to separate the pair.

Perhaps not surprisingly IC 2184 does not make the standard references. Steve Gottlieb has quite an old observation in his IC notes which suggests that it was fairly faint with a 24” reflector and even at 375x he could not split the pair. I guess it has not made it onto the list for Jimi Lowery’s 48”. Uwe Glahn does have a nice drawing of the pair however with his 27” in the Interstellarum Field Guide.

Owen Brazell - Galaxy Section Director