NGC 6269 in Hercules

August 2020 - Galaxy of the Month

For the August GOM we move to the constellation of Hercules and the small faint group of galaxies around NGC 6269. NGC 6269 is part of a small group of galaxies in Hercules, including NGC 6263, NGC 6264 and NGC 6265, that were originally discovered by Albert Marth using William Lassell’s 48” speculum metal telescope from Malta. The group were independently rediscovered by Stephan in 1871 using the 30” Foucault reflector at Marseille.

NGC 6264, NGC 6265 and NGC 6269 are included as part of a 3 galaxy physical group catalogued as WBL 625. The group also appears to be known as AWM 5. NGC 6263 is not part of the group apparently.

Marth also added two more galaxies found in the field in NGC 6271 and NGC 6722 whilst Stephan added NGC 6261, bringing a total of 7 NGC galaxies within a radius of 15 arc-seconds from NGC 6269. The majority of them lie on a line from NGC 6261 to NGC 6272.

NGC 6269 itself is an elliptical with NGC 6265 being an S0 and NGC 6264 a spiral. The group around NGC 6269 appears to be embedded in a hot gas component found in X-Rays. It may be that NGC 6265 is a recent addition to the group and is having its gas stripped out by the RAM pressure interactions with the hot gas in the inter group medium as X-Ray observations done with Chandra shows a tail of material being stripped out of it. The NGC 6269 group also shows some of the characteristics of a fossil galaxy group. Fossil groups are where there is a cD galaxy, in this case NGC 6269, which has merged with most of the other galaxies in the group. Although NGC 6269 is not currently an AGN it is suggested that it does contain a billion solar mass black hole and there are suggestions that it was active in the past.

Distance measurements to the group suggest it is about 120Mpc away. Interestingly the AWM 5 group definition includes a lot more galaxies than the WBL one, including NGC 6271 and 6272. The velocity maps from there suggest that there may be two clumps of galaxies in this cluster.

Visually at 13th magnitude and fainter these galaxies are likely to be a challenge for any telescopes below 35cm, with NGC 6269 itself showing as a faint smudge. Using a modern hyperwide eyepiece at a medium power of, say 200x, will fit all the galaxies in this field in the same eyepiece FOV. Perhaps unsurprisingly the group does not appear in Night Sky Observer's Guide (NSOG) or the other observing handbooks. Owners of larger telescopes may well find other faint galaxies scattered in this field.

This will be a challenging field to work on because of the faintness of the galaxies, many being around 15th magnitude, so it will be interesting to see how many can be picked out. It is interesting to note that Steve Gottlieb in his NGC note collection describes the whole group as very faint with his 17.5” reflector. Mark Stuart from the UK reports that NGC 6269 is on the edge with a 14” but does not report any of the other galaxies to be visible.

Owen Brazell - Galaxy Section Director