April 2017 - Galaxy of the Month

NGC 2964 in Leo

Having put out some very challenging galaxies of the month for the last couple we return to a galaxy grouping that that will be somewhat easier to see without a large telescope (Ed: it's actually on the Herschel 400 list for beginners like me).

Sometimes known as the Leo triplet 2, or the forgotten Leo triplet, the three galaxies NGC 2964, 2988 and 2970 ride high above the head of Leo. NGC 2964 and NGC 2968 were both discovered in 1785 by William Herschel but NGC 2970 was not discovered until 1828 by John Herschel whilst revisiting his father’s observations.

The group is an interesting mix of types with NGC 2964 being a spiral (SAB(r)bc), NGC 2968 being classified as I0 and NGC 2970 as E1. The WBL catalogue suggests they are a group and it is numbered WBL 235 and, although the distances are perhaps a bit discordant, it appears to be a true physical group about 80 million light years away or so.

NGC 2964 is listed as a strong radio source, although does not appear to be an AGN. It is also classified as Markarian 404. In general Markarian galaxies are classified as those with nuclei which emit large amounts of UV light compared to normal galaxies. In the case of NGC 2964 and Mrk 404 it is not actually the nucleus that provides the UV excess that made Markarian classify it but a giant HII region in the spiral arms.

There is some suggestion of an interaction and light bridge between NGC 2968 and NGC 2970 in deep images and certainly in this linked image by Bernhard Hubl you can see that NGC 2968 is very distorted and appears to have shells around it. Another deep image by Adam Block can be seen at Mount Lemmon SkyCenter (University of Arizona).

NGC 2970 itself is also listed in the Markarian catalogue as number 405 and is linked with 2968 as an interacting pair. Some of the fainter galaxies in the field also seem to have similar redshifts and may be dwarf galaxies in the system.

In terms of visibility Harrington in his book Cosmic Challenge suggests all three galaxies may be the range of a 20cm (8”) telescope. I do wonder about this, particularly with reference to NGC 2970 and I think a larger telescope will be needed from typical UK skies at least. Certainly, they were all easily visible with direct vision in less than ideal skies with my 55cm telescope, although NGC 2970 is just a faint dot. All three galaxies should fit in the field of a medium power (x265) modern hyperwide field (100) degree eyepiece, although perhaps lower powers around 180x might be better. I find that with fainter galaxies sometimes pushing the power which darkens the sky background will bring them into view.

Owen Brazell - Galaxy Section Director