NGC 4912
DSS image of NGC 4912
Overlaid DSS image of NGC 4912, 60' x 60' with north at top and west to the right

Aladin viewer for the region around NGC 4912
GC 5705

Type  Unknown
Magnitude  
Right Ascension  13h 0' 46.6"  (2000)
Declination  37° 22' 40" N
Constellation  Canes Venatici
Description  neb n of and in line with 4914
Observing Notes

Harold Corwin

NGC 4912, 4913, 4914, 4916, of these galaxies, only one -- NGC 4914 -- can now be identified. That one was found by William Herschel and re-observed by John Herschel; neither found any other nebulae in the area.

The other three were seen only once by Lord Rosse, on 24 April 1865. He has a sketch showing their relationship with the surrounding star field, so it ought to be easy to identify them. His sketch, however, bears no relationship to the sky around NGC 4914, so it seems likely that he misidentified the main galaxy. Dreyer took this possibility into account by questioning the identification of the main galaxy in the descriptions of N4912, NGC 4913, and NGC 4916.

A search of the four POSS1 fields around NGC 4914 also turned up nothing that matches the sketch. Another possibility is that Lord Rosse made a 10 deg error in his position, and actually observed several galaxies in the Coma Cluster. But that is about 10 deg 25+- arcmin south, and there are no galaxies/stars in the cluster area that match his sketch. One hour errors are also possible, but I've not yet looked closely at those.

The next thing to do will be to look into the lists of nebulae that Lord Rosse had at his disposal at the time (e.g. John Herschel's 1833 observations, the GC, d'Arrest, Auwers) to see if any objects listed near NGC 4914 might be the one that he observed. Since the pattern in his sketch is clear (3 of the objects in a north-south line with a 4th following the southern most), it should jump out at us when we see it. I hope.

Wolf claimed to have found and measured NGC 4912 and NGC 4916 on his plate with the IC objects from his fifth list. The object he took as NGC 4912, however, is a star, and his N4916 is a defect (which he did not mark) on the plate. There is nothing in its position on POSS1.

[I added the following in December 2008 after some email discussion with Sue French.]

In November 2008, Sue French, Ron Buta, and I all bought originals of Lord Rosse's lists of nebulae from the 7th earl (our thanks to Andy Stephens for his kind assistance as Lord Rosse's agent). A correspondence between Sue and me followed in which I pointed out the usefulness of the lists in tracking down lost nebulae. I brought up the case of NGC 4914 and its missing companions as an example, and it was not long before Sue suggested that the quartet of galaxies formed by NGC 4922, IC 843, IC 4088, and CGCG 160-107 -- roughly eight degrees south of the nominal positions -- might be the correct objects. This would require IC 4088, the third brightest of the four, to have been mistaken for NGC 4914.

There is, in fact, a pretty good match between Lord Rosse's diagram and the field around NGC 4922. The four galaxies are shown in their correct relative positions, and Lord Rosse's description of their situation is accurate: "4 neb, 3 nearly in a line n s and one f ... A line through the 3 p nebulae is a little concave on the p side." Two of the field stars are also shown in their correct places and in the correct orientation between two of the galaxies.

A third "star" (α in the diagram), however, around which Lord Rosse suspected nebulosity, is well off its sketched position. Sue suggests that this "star" is the compact galaxy 2MASX J13002111+2920135. This matches the description, but the object is quite faint compared to field stars not diagrammed and closer to the galaxies. There are also a couple of other galaxies in the field which Lord Rosse might have been able to see, including IC 842.

Lord Rosse's relative brightnesses for the galaxies are also jumbled. He says "β brightest and lE np sf, γ and δ next and ε vF". If the field is indeed the one he saw, NGC 4922 is δ, γ is IC 843, ε is CGCG 160-107, and β is IC 4088. This last galaxy is actually quite extended, but directly east-west. NGC 4922, the brightest of the group, is a close double interacting system, with the two objects oriented southwest-northeast, just opposite Lord Rosse's note for the brightest object that he saw.

So, while the general layout of the sketch matches what we see on the sky pretty well, some of the details are wrong. And there is that 8-degree declination error, too ...

In the end, I like Sue's suggestion, but I'm only reasonably sure that it points us at the right field. Consequently, I feel compelled to put question marks on the identifications of Lord Rosse's three novae, NGC 4912, 4913, and 4916.
NGC Notes by Harold Corwin
Other Data Sources for NGC 4912
Associated objects for NGC 4912
Nearby objects for NGC 4912
Credits...

Drawings, descriptions, and CCD photos are copyright Andrew Cooper unless otherwise noted, no usage without permission.

A complete list of credits and sources can be found on the about page

NGC 4912