NGC 7778 in Pisces

October 2019 - Galaxy of the Month

My thanks to Mark Stuart for recommending this rather nice group of galaxies in Pisces. Three of these galaxies, NGC 7778, NGC 7779 and NGC 7782 were discovered by William Herschel in November 1784 and the fourth galaxy NGC 7781 was discovered by his son, John, in 1830 whilst reobserving his father’s objects. Also in this field, but very much fainter is the edge on galaxy, RFGC 4209.

All of the NGC galaxies are included as a group WBL 727 which contains just the four NGC galaxies. The group is often called the NGC 7782 group after its brightest member. It also seems to be classified as cluster Zwicky 2350.6+0758.

NGC 7778 and NGC 7779 are regarded as a physical pair, despite this they do not seem to show any signs of gravitational interaction. NGC 7778 is an elliptical whereas NGC 7779 appears to be a face on spiral with a very bright core, although it has also been classified as a lenticular galaxy. Both of these galaxies were digitised as stars in the GSC catalogue due to their bright cores.

The group lies at a distance of perhaps 70 Mpc. The group is classified as a triple system in Alvin Huey’s guide to Galaxy Trios. Interestingly he does not include NGC 7782 as part of the triple but adds NGC 7781.

Whilst NGC 7778 and NGC 7779 should be visible in relatively small instruments NGC 7781 will be far more of challenge with a listed blue magnitude of 15. It may be much brighter however in the visual, perhaps at 14th magnitude, nevertheless I would expect that from UK skies at least 40-cm will be needed to see it.

The Night Sky Observer's Guide (NSOG) also includes a fifth galaxy, NGC 7780, in this group. Although probably not physically associated with the NGC 7782 group, NGC 7780 was discovered by Stephan in 1881 and independently by Swift in 1886. Both NGC 7780 and NCG 7781 are likely to be challenges for 45-cm telescopes according to the NSOG. NGC 7780 was host to sn 2001da. If these prove too easy then near NGC 7780 is MCG+1-60-44 for large telescopes.

All five NGC galaxies should fit in the field of view of a medium power (240x) modern hyperwide (100 degree) eyepiece.

If these galaxies are all too easy then try for RFGC 4209. I am not sure if RFGC 4209 will be visible in normal amateur class instruments however, perhaps some of the giant Dobsonians that seem to be around could give it a go. Here RFGC stands for the Revised Flat Galaxy Catalogue by Karachentsev et al. There are 4236 galaxies in this catalogue with axial ratios (a/b)B ≥ 7. Within this group RFGC 4209 would be classified as an Ultra thin. It is also known as LEDA 091829 but has no listed magnitude. It is not part of the group being much more distant. There is some interesting information and an image of this group at ManTrapSkies.

Owen Brazell - Galaxy Section Director