NGC 533 in Cetus
December 2022 - Galaxy of the Month
This month’s challenge is the galaxy pair in Cetus including NGC 533 and NGC 521. There is also a third galaxy in the field in IC 1694. NGC 521 and NGC 533 were discovered by William Herschel in 1785. IC 1694 was discovered in 1891 by Bigourdan using a 12.4” refractor. The group will best be seen in the early evening this month.
The RC 1 suggested that NGC 521 and NGC 533 form a physical pair, however they do not appear to be interacting and their distances do appear to be somewhat different. NGC 533 is described as an elliptical galaxy with a classification of E3. It is also classified as a cD galaxy, which would be the brightest and largest galaxy in a cluster. NGC 521 is a face on low surface brightness spiral, classified as SB(r)bc. The GALEX images in the UV indicate the NGC 521 is undergoing a lot of star formation in its spiral arms.
Interestingly NGC 533 is suggested to be part of the galaxy cluster Abell 189 although NGC 521 which is in a pair with it is not, although they are very much brighter than the other galaxies in the cluster and somewhat offset from it. The distances for NGC 521 and 533 are also very different so it may be that they are just an optical pair. NGC 533 Is also surrounded by many faint galaxies. The cluster ACO 189 is also much further away than either of the NGC galaxies. NGC 521 lies at a distance of perhaps 34 Mpc whilst NGC 533 would appear to be almost twice as far away at perhaps 70Mpc.
NGC 521 has produced 3 supernovae since 1966.
IC 1684 is also suggested to be part of Abell 189 and thus associated with the NGC 533/521 pair, however although it is not well studied its distance lies at around 50 Mpc so in these terms at least it would not be associated with either ACO 189 or the other two galaxies. All in all this is quite a confused field and it may be that none of the galaxies are associated.
Perhaps surprisingly Night Sky Observer's Guide (NSOG) Vol.1 suggests that much can be seen of this pair with telescopes in the 20-25cm aperture. However, to see IC 1694 will require telescopes in the 45-50cm range. I suspect that many of the observations used in the NSOG may have been from high altitude, and from the poorer skies of the UK 30cm may be required to see much. All three galaxies are close enough together that they will fit in the field of view of a medium power hyperwide eyepiece. To find IC 1694 however is likely to require a high power. The much fainter galaxies around NGC 533 are probably out of visual range but should be picked up by EAA systems.
Owen Brazell - Galaxy Section Director