A remarkably fine 2MASX in Abell 2634

[Ivan Maly]

I was now going through my notes from last October, checking some identifications. Observing the core of Abell 2634 in Pegasus at 225x with my 16” from the Cherry Springs Dark Sky Park, I recorded:

To the SE of NGC 7720 is a faint star, and just beyond it, a small galaxy. Despite its size and relative difficulty, it is a nice sharp edge-on.

It is indicated on the attached DSS (archive.stsci.org).

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Astoundingly for something this attractive visually, this galaxy’s name on NED is 2MASX J23383626+2701467. No common professional catalog lists it - MCG, CGCG, UGC, or PGC - according to NED. I cannot check if it is in the extended 7-digit PGC, because the only ready reference I know for the extended version - Wikisky - mislabels it as NGC 7726. It was noted, however, as #74 in Abell 2634 in Dressler’s 1980 catalog of galaxies in 55 selected clusters. Since it is next to a Herschel NGC in the core of an Abell, I would also almost expect it to be in the Mitchell Anonymous Catalog, but have no means of readily checking it.

It is classified on NED as a group member and an S0. The magnitude and size are given as 15.85 and 0.54x0.29'. It is more extended visually according to my memory. The photographic magnitude is about right according to my visual perception. Light-travel time is 354 My, i.e. roughly consistent with membership in Abell 2634.

[Marko]

That designation does show up for 2MASS data in Aladin7 but of note is using Simbad data in Aladin that galaxy comes up as 2MASX J23383327+2702057. In any case my AGC2636 did not include that galaxy and I'll have to go back for it. Nice post and interesting but I cannot help you on history of that galaxy. NGC/IC project picture of Ngc7720 does NOT highlight that galaxy as an NGC or IC object and I think it would if that were the case.

As far as what NGC/IC project notes from Steve Gottlieb have to say it looks like there is some confusion for Ngc7726 but Ngc/Ic project shows that Ngc7726 is NOT this interesting and rather bright elongated galaxy but rather is NE of 7720 by a good 10'. Here are Steves's notes from NGC/IC project.


NGC 7726 = UGC 12721 = MCG +04-55-040 = CGCG 476-098
23 39 11.9 +27 06 55
V = 14.2; Size 1.5x0.5; SB = 13.8; PA = 60d

17.5": very faint, small, elongated 3:2 WSW-ENE, weak concentration. A mag 11
star is 2.6' SW. Located 10.7' NE of N7720 in Abell 2634. N7728 lies 11' E and
Z476-095 11' NW. This identification (Swift discovery) is uncertain although
N7726 is certainly misidentified in the RNGC as IC 5342 which lies 2.4' SE of
N7720.

Discovered by Lewis Swift on 8 Aug 1886 within the rich galaxy cluster Abell
2634. His discovery position is 23 37 00 +26 42 36 (1950) or 14' ESE of N7720,
the brightest member of the cluster.

Not found by Bigourdan and there is no object near his position and the RNGC has
misidentified N7726 with IC 5342 = CGCG 476-092 which was discovered by Howe and
correctly placed at 23 36 08 +26 44.1 (1950). This galaxy is one of the several
very close companions of N7720 and lies just 2.4' SE.

As a more plausible candidate, Harold Corwin has suggested N7726 = U12721 = MCG
+04-55-040 = CGCG 476-098 at 23 36 41.4 +26 50 18 (1950) which is closer to
Swift's position. This identification is uncertain, though, as Swift mentions a
"pB* nr f" and the mag 9 star is actually 9' following altlhough Swift mentioned
that N7728 is north-following which does match U12721.

In any case, the RNGC identification is certainly incorrect. I described this
object as nonexistent in RNGC Corrections #4. Relisted in RNGC Corrections #6.
See NGCBUGS.

- by Steve Gottlieb

[Steve Gottlieb]

Really nice rich cluster, though when galaxies are packed together like this, you'll often find catalogue confusion galore. 2MASX J23383626+2701467 does have a regular PGC number -- 71991 -- but the PGC and RC3 misidentify the galaxy as NGC 7726, so you have to look for that designation.

The LEDA data for PGC 71991 is here (http://leda.univ-lyon1.fr/ledacat.cgi?o=2MASX%20J23383626+2701467), and the SDSS photometry is here (http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?ra=354.65174&dec=27.02939). Megastar includes it as MAC 2338+2701A.

There's another little dim sucker, by the way, just 45" WNW of PGC 71991, to the north of the star you mentioned. It's only slightly fainter than PGC 71991, according to my notes from 21 years back!

452

[Ivan Maly]

Thank you, gentlemen. To make the circle complete, NED thinks that PGC 71991 is IC 5342 at the position of the compact galaxy a bit SE of the edge-on in question, and that this IC is not NGC 7726. Wikisky thinks that PGC 71991 is my nice edge-on, identifying it with NGC 7726, as I mentioned, but not with IC 5342. In the end I am pleased that there is still some semblance of order in this world and I don't get to enjoy the visual splendors of unquestionably non-PGC galaxies in my 16". For myself I am taking it that the identification of this galaxy with PGC 71991 is relatively unambiguous (disregarding NED), but its identity with either NGC 7726 (probably much farther NE) or IC 5342 (probably farther SE) is historically unlikely and the idiosyncratic opinions of modern professional databases on this account should be disregarded.

[Steve Gottlieb]

Another very cool feature about this cluster is that NGC 7720 (the central cD galaxy) is double, with a companion superimposed in the halo on the north side.

Since I last viewed this cluster in 1991, I just went over my notes, adding data culled from HyperLeda, NED and SDSS. I have no idea what chart or reference I used at the time, but I picked up 17 galaxies in the cluster at 220x with a 17.5".

CGCG 476-086 = PGC 71976
23 38 22.8 +27 09 29
V = 14.6; Size 0.65'x0.5; PA = 112d
Extremely faint and small, round. A mag 15 star is 20" SSW. Forms a pair with CGCG 476-095 6' NE.

IC 5341 = CGCG 476-087 = MCG +04-55-035 = PGC 71981
23 38 26.8 +26 59 06
V = 14.4; Size 0.4'x0.4'
Very faint, extremely small, round. Located 2.8' SSW of NGC 7720. First of three very close, extremely faint and small galaxies with CGCG 476-090 40" SE and CGCG 476-092 1.7' E.

CGCG 476-090 = MCG +04-55-037 = PGC 71987
23 38 29.2 +26 58 43
V = 14.3; Size 0.6'x0.5'
Very faint, extremely small, round. A mag 11 star is 2.1' E. This is the central galaxy in a very tight trio 3' S of NGC 7720 in the core of AGC 2634. IC 5341 is just 40" NW and CGCG 476-092 1.2' E. Appears very similar in brightness and size to companion IC 5341. This galaxy is misidentified in the MCG as IC 5342.

NGC 7720 = UGC 12716 = MCG +04-55-036 = CGCG 476-091 = 3C 465 = PGC 71985
23 38 29.4 +27 01 55
V = 12.3; Size 1.6'x1.3'; Surf Br = 13.1; PA = 20d
Located at the center of the rich cluster AGC 2634. Fairly faint, small, small bright core, elongated SSW-NNE. Forms a double system with a companion (NGC 7720A) attached at the north side. The system appears visually as overlapping galaxies with double nuclei. A dense swarm of galaxies are nearby to the south and east; IC 5341 2.8' SSW, CGCG 476-090 3.2' S, CGCG 476-092 3.3' SSE, IC 5342 2.4' SE, PGC 85575 0.9' E and PGC 71991 1.5' E! A mag 15.5 star is 1.5' SW and two mag 11 stars lie 4' SSE and 7' SSE.

NGC 7720A = UGC 12716 NED2 = MCG +04-55-036 NED2 = CGCG 476-091 NED 2 = PGC 85570
23 38 29.5 +27 02 05
V = 14.5; Size 0.15'x0.15'
Very faint, extremely small, round. Superimposed on NGC 7720! Appears as a second nucleus or a knot attached to NGC 7720 at the north end. Several galaxies are very near to the east and south.

PGC 85575 = 2MASX J23383327+2702057
23 38 33.3 +27 02 06
V = 15.7; Size 15"x12"
Extremely faint and small, round, <5" diameter. Located just 0.9' E of the center of NGC 7720. 2MASX J23383626+2701467 (perhaps PGC 71991) is 45" ESE. Appears virtually stellar on the POSS.

CGCG 476-092 = PGC 85577 = PGC 1794221
23 38 34.5 +26 58 46
V = 15.3; Size 0.4'x0.3'
Extremely faint and small, barely nonstellar, 6" diameter. A mag 11 star lies 1.0' ESE. Located 3.3' SSE of NGC 7720. Third of three in a close trio within AGC 2634 with CGCG 476-090 1.2' W and IC 5341 1.7' W. Also nearby is IC 5342 2.1' NNE. Appears virtually stellar on the POSS. Misidentified as IC 5342 in the CGCG.

2MASX J23383626+2701467 = PGC 71991?
23 38 36.3 +27 01 46
V = 15.0; Size 0.7'x0.3'; PA = 174d
Located just 1.5' E of NGC 7720. Appears extremely faint and small, slightly elongated N-S. A mag 14 star is 30" WSW. Nearby are IC 5342 1.2' SSE and PGC 85575 45" WNW. Mentioned in UGC notes to NGC 7720 but not included in the CGCG.

IC 5342 = CGCG 476-094 = MCG +04-55-039 = PGC 71984
23 38 38.8 +27 00 40
V = 14.6; Size 0.7'x0.5'; Surf Br = 11.6; PA = 26d
Very faint, small, round, bright core. Located 2' N of a mag 11 star and 2.4' SE of NGC 7720 in the core of AGC 2634. 2MASX J23383626+2701467 (perhaps PGC 71991) is 1.5' NNW. IC 5342 is probably the brightest of several close companions to NGC 7720.

CGCG 476-095 = PGC 71994
23 38 43.6 +27 12 55
V = 14.1; Size 0.8'x0.4'; PA = 121d
Faint, small, elongated 2:1 WNW-ESE, bright core. Forms a trio with CGCG 476-096 3' NNE and CGCG 476-086 6' SW. UGC 12721 lies 11' SE. A faint companion 1.5' E was not seen.

CGCG 476-096 = PGC 71999
23 38 50.6 +27 16 03
V = 13.8; Size 0.9'x0.7'; PA = 130d
Faint, small, round, bright core. Forms a pair with CGCG 476-095 3' SSW.

NGC 7726 = UGC 12721 = MCG +04-55-040 = CGCG 476-098 = PGC 72024
23 39 11.9 +27 06 55
V = 14.2; Size 1.5'x0.5'; Surf Br = 13.8; PA = 60d
Very faint, small, elongated 3:2 WSW-ENE, weak concentration. A mag 11 star is 2.6' SW. Located 10.7' NE of NGC 7720 in AGC 2634. NGC 7728 lies 11' E and CGCG 476-095 is 11' NW. The identification of this galaxy with NGC 7726 (discovered by Lewis Swift) is uncertain although the RNGC has certainly misapplied the NGC number to IC 5342 which lies 2.4' SE of NGC 7720.

CGCG 476-101 = PGC 72056
23 39 49.4 +27 22 33
V = 14.4; Size 0.6'x0.5'
Very faint, very small, round, bright core. Located 8' SSW of mag 6.7 HD 222390. Appears similar to CGCG 476-109.

NGC 7728 = UGC 12727 = MCG +04-55-041 = CGCG 476-103 = PGC 72064
23 40 00.8 +27 08 01
V = 13.1; Size 1.0'x0.8'; Surf Br = 12.9; PA = 75d
Fairly faint, small, slightly elongated WSW-ENE, bright core, stellar nucleus. Located 2.3' NE of a mag 10 star. Forms a pair with PGC 85623 = 2MASX J23400320+2710014 2.5' NNE. UGC 12721 lies 11' W.

PGC 85623 = 2MASX J23400320+2710014
23 40 03.2 +27 10 02
V = 15.4; Size 0.4'x0.3'; PA = 105d
Extremely faint and small, cannot hold with averted. Located 2.1' NNE of NGC 7728 and 30" SSW of a mag 15 star on a line. Also 4' NE of mag 9.1 SAO 091408.

CGCG 476-105 = PGC 72071
23 40 19.0 +27 33 40
V = 13.8; Size 0.7'x0.5'; PA = 85d
Faint, small, round. Situated between two mag 13.5 stars with a separation of 2.5' oriented NW-SE. Located 5' NE of mag 6.7 HD 222390 which detracts from viewing.

CGCG 476-109 = PGC 72099
23 40 54.2 +27 30 34
V = 14.4; Size 0.6'x0.5'
Very faint, very small, round. Located 12' E of mag 6.7 HD 222390.

[Ivan Maly]

Although I was not doing the cluster specifically but was pretty much just interested what was in the field with Herschel's NGC 7720, I did pick out NGC 7720A, the edge-on that is probably safest to identify by its 2MASX number, IC 5342 just to its SE, IC 5341 - the NW component of the pair of compact galaxies S of the NGC, and the SE component of that pair, MCG+4-55-37. I agree in particular that this MCG is pretty much a twin of its IC neighbor visually. Overall, as I recorded, "The core of [Abell] 2634 is a fantastic sight. It is a tight group resolved in detail by the Ethos at 225x with ample framing to underscore its isolation."

Incidentally, I suspect that the Herschel object is not the NGC, but the entire core of the cluster. Herschel described his III.146 as "very faint and extended, some faint stars with nebulosity".