July 2016 - Galaxy of the Month
NGC 6906 in Aquila
This interactive image of the galaxies around NGC 6906 was provided by the Sloan Digital Sky Survey using Aladin Sky Atlas. We have a widefield finder chart should help you locate these galaxies, and a close-up chart for the image above.
Summer is never the best time for galaxies but if you do get a clear moonless night in the semi dark then this month’s galaxy is NGC 6906 in Aquila.
First discovered in 1863 by Albert Marth using William Lassells 48” speculum mirror telescope in Malta this galaxy makes a nice pair with the un-related galaxy NGC 6901 (also discovered by Marth). Interestingly both galaxies are marked as part of a pair in NED but I think this is erroneous.
NGC 6906 itself is actually part of a sparse group of galaxies as listed in the Lyon Galaxy Group catalogue (LGG). Listed as number 435 in this catalogue the group consists of 3 galaxies, NGC 6906 along with UGC 11551 and UGC 11555. Both of the latter two are actually across the border in the constellation of Delphinius. The group is perhaps 1.6 degrees across on the sky. Interestingly all the galaxies are spirals. The distance is to NGC 6906 is perhaps 60 Mpc, so probably similar to the other two galaxies in the group.
NGC 6901 is perhaps at a distance of 69 Mpc, so 9 Mpc further away than NGC 6906. NGC 6901 is also incorrectly labelled as IC 5000 due to a bad set of co-ordinates published by Marth and Bigourdan rediscovering it and thinking it was a new galaxy. It is also listed as IC 1316 in SIMBAD but this is now recognised as an error and the designation has been deleted from NED. SIMBAD also lists NGC 6901 as being part of a group of galaxies but I have been unable to determine what other galaxies might be involved. NGC 6906 has also had an IC number assigned to it in IC 5006 but this is really a double star.
Both NGC 6901 and NGC 6906 are spiral galaxies with NGC 6901 being much further away. There is also a much fainter edge on spiral in the same field but at mag 16 it only has a LEDA number and will probably require a very large telescope to spot visually. NGC 6901 was host to SN 2004da which was discovered by the UK amateur Tom Boles.
Owen Brazell - Galaxy Section Director