NGC 4754 in Virgo

May 2022 - Galaxy of the Month

With the skies from northern latitudes starting to brighten at this time of year making galaxy observing more difficult I have to start choosing brighter objects for the GOM.

Our galaxy this month is the nice pair in Virgo of NGC 4754 and NGC 4762. They were both discovered by William Herschel on the same night in March 1784. They are also known as Holmberg 478. NGC 4754 is also classified as an interacting system as VV 1573 in the extended Vorontsov-Velyaminov catalogue. Although Virgo is now starting to slip away from the observing season, and the nights are getting bright now in May, it should still be possible to pick up this pair.

Both are suggested to be lenticular galaxies with a classification of SB0 which suggests a barred form. They present quite different projections on the sky however with NGC 4762 being practically edge on and NGC 4754 being more open.

The galaxies are suggested to be a non-interacting pair, although both galaxies do show some signs of interaction, particularly NGC 4762 which shows tidal distortions at both ends of the galaxy in deep images. The problems come in that the distance measurements to each galaxy would suggest they are not close together in space, however the distance measurements by differing methods are wildly discordant. They are both however believed to be members of the Virgo cluster. There are suggestions that NGC 4762’s extensions may have come from a merger with a smaller galaxy a few billion years ago. NGC 4762 also appears to have a form of AGN, classified as a LINER. If the distances are correct these are both very large galaxies, slightly larger than our Milky Way.

Stephen O’Meara in his book The Secret Deep suggests that Allan Sandage noted that NGC 4762 is one of the flattest galaxies, as seen from the earth, in the universe. He also nicknames it the Paper Kite galaxy based on a description in Smyth’s Bedford catalogue. Both galaxies appear in the Astronomical League’s H400 program and, indeed, in many other lists. There is a stunning amateur image of the pair at the Capella Observatory website. NGC 4762 was also imaged by the Hubble Space Telescope (HST).

One of Lord Rosse’s assistants, Samuel Hunter, suggested that he could see that NGC 4762 was warped with the 72” at Birr. It is probable that with the larger aperture telescopes now in amateur hands that these may also be visible today. Night Sky Observer's Guide (NSOG) Vol.2 suggests that 20-25cm telescopes will be needed to see both galaxies and that 40-45cm should start showing some detail. I suspect that given the usual skies from the UK then perhaps 30cm maybe better for seeing them, although there are observations of NGC 4754 at least with a 25cm scope from less than ideal skies in the UK. There are also observations of NGC 4762 in the Webb Deep-Sky Society Observer's Handbook (WSDSOH) Vol 4, but perhaps surprisingly not NGC 4754. Luginbuhl and Skiff (L&S) suggests both galaxies are visible in 15cm, but remember their observations were done from high and dry altitude sites. They do suggest however larger apertures to see any detail.

Owen Brazell - Galaxy Section Director