NGC 6308 in Hercules

August 2024 - Galaxy of the Month

With the month of August we now get true dark skies again from the UK, and I am going to continue in this GOM with the objects discovered by Albert Marth theme from last month, and for this we have a nice line of galaxies discovered by him in Hercules. These are the galaxies NGC 6308, NGC 6314 and NGC 6315. They hold pride of place in Marth’s listing as they were the first galaxies that he discovered using William Lassell’s 48” speculum metal mirror telescope from Malta. All of these objects appear to be spiral galaxies with NGC 6308 and NGC 6315 being almost face on and NGC 6314 edge on.

NGC 6308 has a bright core and is listed as a Seyfert Type II, a form of AGN. Type II Seyfert galaxies have very narrow emission lines in their spectrum compared to those of type I. It may be that the classification into Type I or type II depends on the angle at which we view the nuclear region. NGC 6308 does not appear to be related to the other two, which may form a physical pair, but is purely a line-of-sight coincidence. NGC 6308 lies about 130 Mpc from us.

It is suggested that NGC 6314 and NGC 6315 may form a pair at about 71 Mpc from us, however a more recent observation suggests they too are a line-of-sight pair and may be separated by as much as 6 Mpc. It appears that NGC 6314 also contains an AGN of the LINER type. Although NGC 6315 does not appear to contain an AGN it is classified as an emission line galaxy and the GALEX UV image is very strong so it is likely that a lot of star formation is going on here. This would be consistent with its blue colours. Not much research appears to have been done on these galaxies.

Perhaps as expected with the galaxies that Marth found there are no observations of this group of galaxies in any of the standard references. The group is tight enough that all the galaxies will fit in the field of view of a medium power (260x) hyperwide eyepiece. Steve Gottlieb describes them as fairly faint in a 17.5” telescope so I suspect that 50cm may be required to find them from the UK, although 45cm may do. The galaxies pass very high up as seen from UK latitudes so it should be easy to track the field down.

Owen Brazell - Galaxy Section Director