NGC 6340 in Draco

July 2020 - Galaxy of the Month

July comes and we are back to lengthening nights, although still no astronomical dark until August here in the UK.

My choice for this month’s GOM is the strange galaxy NGC 6340 in Draco. Discovered by William Herschel in 1788, NGC 6348 has an anomalous appearance. It appears to be like a lenticular galaxy and the shape suggests that it was the result of a major merger between an elliptical and a spiral galaxy about 12 billion years ago.

The bulge and inner part of the disk appear to be rotating in a different direction to the stellar disk. It also shows some signs of being a polar ring galaxy with material at right angles to the main disk.

The distance is also somewhat uncertain but may be of the order of 62 million light-years.

SIMBAD says it is part of a pair of galaxies but does not suggest what the other galaxy is. It could be one (or both) of the two IC objects in the field, IC 1251 and IC 1254, both galaxies, discovered by Edward Swift using a 16” refractor in 1890. It has been suggested that both IC 1251 and IC 1254 may be part of an interacting group with NGC 6340 as both of them show some signs of gravitational distortion. IC 1251 in particular appears to be furiously forming stars from its image in the UV from the GALEX satellite. If they are at the same distance as NGC 6340 then they are both quite small galaxies.

NGC 6340 itself also shows some signs of an interaction/merger event perhaps within the last few hundred million years. NGC 6340 also appears to have a low activity AGN at its centre. The disk contains a ring of counter-rotating stars which is part of the reason that it has been suggested that it was involved in a major merger event. Currently NGC 6340 is classified as an S0-a galaxy. One of the best images of the group including NGC 6340 can be found on Adam Block's website.

Although NGC 6340 is quite bright in terms of its total magnitude it is also quite large so may be a challenge to see in twilight skies. It has certainly been seen in a 25cm telescope from the UK but was not an easy catch. For those with larger telescopes the companions are the objects of interest. If these prove to be too easy then there are a number of other fainter galaxies in the field at around 16th magnitude to try for. These are almost certainly unrelated to NGC 6340 and are much further away.

The NGC 6340 group is also well covered in the Cambridge Photographic Atlas of Galaxies, available from the Society.

Owen Brazell - Galaxy Section Director