Harold Corwin

NGC 4912, NGC 4913, NGC 4914, and NGC 4916. Of these, only NGC 4914 appears on the sky in the place that the Herschel's found it. The other three, seen only by LdR, are not in the field around NGC 4914.

The missing three were seen by LdR on 24 April 1865. He sketched a field, nominally around NGC 4914 = GC 3365 = h 1514 = H II 645, with three additional galaxies, but that sketch does not match what we now see on the sky near the Herschel's galaxy. Courtney Seligman points out that Dreyer must have had a suspicion that LdR's identification was incorrect as he (Dreyer) made two more observations of GC 3365, one on 5 April 1877, and a third on 1 April 1878. This third observation yeilded three other nebulae in the area of NGC 4914 (NGC 4868, 4870, and 4893), but none matched LdR's sketch of April 1865.

I want to break here for a short biographical note. I've called the observer above "LdR", but he was in fact, Lawrence Parsons, Lord Oxmantown, the eldest son of the the third Earl of Rosse (he was soon to be the fourth earl as his father died in 1867). At the time of the observation in 1865, Lawrence was 25 years old and perhaps a relatively inexperienced observer with the 72-inch. (More knowledge of his life is clearly going to be needed here to clear up my speculation in that previous sentence! Here's some more speculation: the third earl may have given up observing by the time his son went to the eyepiece.)

Back to the galaxies. The only other observations of the "nebulae" here were claimed by Max Wolf in his fifth list of new nebulae. Wolf measured objects he called NGC 4912 and NGC 4916. However, the object he took as N4912 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.

At this point, the field was still a mystery to me, so that is where I left it in the early 2000s.

However, 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 with Sue 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 4088, CGCG 160-107, and the galaxy then called IC 843 -- roughly eight degrees south of the nominal positions -- might be the correct objects. Her original suggestion had IC 4088, the third brightest of the four, being mistaken for NGC 4914 by Lawrence Parsons.

There is, in fact, a pretty good match between the diagram and the field south of NGC 4922. The four galaxies are shown in their correct relative positions, and LdR's description of their situation is accurate: "4 neb, 3 nearly in a line n s and one f. Suspected neby round the * [alpha]. A line through the 3 p nebulae is a little concave on the p side. [beta] brightest and lE np sf, [gamma] and [delta] next and [epsilon] vF." Two of the nearby field stars are also shown in their correct places and in the correct orientation between two of the galaxies.

A third "star" ([alpha] in the diagram), however, around which LdR suspected nebulosity, is west of its sketched position. I can't put too much emphasis on this, however, as many of the sketches in LdR's 1880 monograph are pretty free representations of what's actually on the sky. 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. I suspect that LdR included this "star" only because he suspected it to be nebulous. There are also a couple of other galaxies in the field which LdR might have been able to see, including IC 842 (which has no identification problems), that are not in his sketch.

LdR's relative brightnesses for the galaxies are also jumbled. He says "[beta] brightest and lE np sf, [gamma] and [delta] next and [epsilon] vF". If the field is indeed the one he saw, NGC 4922 is [delta], [gamma] is the nominal IC 843, [epsilon] is CGCG 160-107, and [beta] is IC 4088. This last galaxy is actually quite extended, but directly east-west, so I wonder if he hasn't confused [beta] and [gamma]. This galaxy is indeed extended northwest to southeast. The brightest of the group, NGC 4922, is a close double interacting system, with the two objects oriented southwest-northeast, just opposite LdR's note for the brightest object that he picked up. This reinforces my notion that this set of descriptions is rather confused, not corresponding to the galaxies we see today.

In May/June 2021, Courtney Seligman took a look at this field and came to a somewhat different conclusion about LdR's diagram. He suggests that the future LdR got the north/south directions in the sketch flipped. This would have led him (LdR) to have believed that NGC 4922 was GC 3365 = h 1514, and that the three "novae" in the field were north of JH's object, not south as they appear on the sky. This would explain Dreyer's positions given in the NGC where all three are north of "GC 3365" rather than south. Courtney again notes Dreyer's uncertainty about these three by calling attention to the queries in the NGC descriptions.

So, Courtney suggests the following identifications (J2000 positions):

  [delta]   = NGC 4922                    at 13 01 24.9, +29 18 40
  [gamma]   = NGC 4912                    at 13 01 33.6, +29 07 50
  [beta]    = NGC 4913 = IC 4088 = IC 843 at 13 01 43.4, +29 02 41
  [epsilon] = NGC 4916 = CGCG 160-107     at 13 02 04.2, +29 15 12 = PGC 44973
  [alpha]   = 2MASX J13002111+2920135     at 13 00 21.1, +29 20 14

These have the benefit of preserving the relative orientations of the galaxies in the sketch, as well as preserving Sue's suggestion that the compact 2MASS galaxy is the nebulous star [alpha] noted by LdR. Note, however, that -- based on work by Courtney -- I now think IC 843 to be identical with IC 4088, both of which see for further discussion.

After some email correspondence with Courtney, it now seems to me to be entirely likely that this north-south flip is a second mistake that LdR made in his April 1865 observation, the first of course being the 8-degree error in his reading the setting the telescope. This does give us a hypothesis that matches much of the information in the observation, if not the relative brightnesses.

This has led me to be pretty liberal with colons on these suggested identifications, but I think this is about the best we can do with this field. My thanks to Sue and Courtney for their diligence in helping to sort it all out.

― NGC Notes by Harold Corwin

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

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