Arp Peculiar Galaxy Program – Appendix C


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Appendix C – Additional Information


Sources and References

  1. Atlas of Peculiar Galaxies, Halton Arp, Astrophysical Journal Supplement 123, Volume XIV, November 1966, University of Chicago Press
  2. Deep Sky Field Guide (DSFG) to Uranometria 2000.0, Murray Cragin, James Lucyk, Barry Rappaport, Willmann-Bell Inc, 1993
  3. NASA/IPAC Extragalactic Database (NED), Version 1.7, Database updated 3/9/95. This is an internet telnet site ( – logon using "ned" as an ID) operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. NED is an object-oriented database built around a master list of extragalactic objects for which cross-identifications or names have been established. Through NED, several unusual galaxy catalogs (beyond RC2/3 NGC, UGC, ESO, and MCG) were accessed in context of the Arp list:

    • Vorontsov-Velyaminov Atlas and Catalog of Interacting Galaxies, 1959 and 1977, Sternberg Institute, Moscow State University Galaxy names VV1-VV852;
    • IRAS Faint Source Catalog, 1988. 172,000 infrared sources;
    • Lick Northern Proper Motion Program, 1987. 50,517 galaxies Galaxy name: NPM1G -XX.XXXX.
  4. Selected Astronomical Catalogs Volume 1, Astronomical Data Center CD-ROM, National Space Science Data Center, NASA, GSFC. This CD-ROM provided access to the following catalogs which were useful in identifying galaxy types and magnitudes:

    • RC2: de Vancouleurs, G., de Vancouleurs, A. and Corwin Jr., H. G. 1976, Second Reference Catalogue of Bright Galaxies, University of Texas Press 4364 galaxies;
    • NGC 2000.0 – Edited by R.W. Sinnott, 1988, Sky Publishing Corporation;
    • MGC – Morphological Catalogue of Galaxies, Vorontsov-Velyaminov et al. 1962-1968) – 34,000 galaxies;
    • The Uppsala General Catalogue of Galaxies (UGC), P. Nilson, 1973, Uppsala Astronomical Observatory, (Wayne H. Warren, 1982) Galaxies above 1.0' and brighter than magnitude 14.5;
    • MERCG – "Merged Catalogue of Galaxies", Kogoshvili 1986) 31,917 galaxies;
    • The Center for Astrophysics (CFA), REDSHIFT CATALOGUE, John P. Huchra, Harvard-Smithsonian Center for Astrophysics May 5, 1990 (While the point of this database is redshift, it had some unique information about some objects and was the only one on the CD ROM which referenced some Arp numbers);
    • The ESO/Uppsala Survey of the ESO(B) Atlas, (A. Lauberts 1982), June 1985, Lee E. Brotzman and Robert S. Hill.
  5. MegaStar Deep Sky Atlas, Windows Version 2.1 CD, E. L. B. Software. The database feature identified about 140 Arp objects explicitly. The finderchart plotting feature supported analysis of the original Arp photographs through inclusion of galaxies in:

    • RC3 – Third Reference Catalog of Bright Galaxies, de Vancouleurs et. al, 1991;
    • PGC – "Principal Galaxies Catalog", Paturel et al., 1989, Observatoir de Lyon.

Irregularities Among Galaxy Catalogs – the Arp Catalog

In comparing the various sources, the Dennis Webb and friends noted quite a number of irregularities in identifying the involved galaxies. Perhaps this is a product of having too many galaxy catalogs and too much time. Since these discrepancies will be bothersome to observers, he has included the following list. Perhaps a very inspired person can resolve the discrepancies or convince the catalog builders to converge on a single interpretation. Perhaps it is better just to enjoy the mystery.

In general, this paper generally assumes the NED database to be the most authoritative source of what galaxies are in an Arp view. NED occasionally omits a companion galaxies and these are noted in this list. Also noted are the rare apparent NED errors.

Arp 4 NED omits companion MCG-02-05-50A.

Arp 17 Megastar chart orientation does not appear to match picture.

Arp 24 Megastar chart orientation does not appear to match picture.

Arp 30 Suffix discrepancy: NGC 6365A, B.

Arp 32 UGC10770B NED is UGC10770 RC3. There is no A in RC3 and an anonymous galaxy is in the wrong place.

Arp 54 NED omits the companion (PGC 9107).

Arp 59 Suffix discrepancy: NGC 341A, B DSFG says the galaxies are near the same size, Arp's photo has A bigger.

Arp 63 Suffix discrepancy: NGC 2944A, B.

Arp 68 original paper identifies NGC 7756, NED references NGC 7757.

Arp 78 NED omits the apparent companion (NGC 770).

Arp 87 Suffix discrepancy: NGC 3808A, Megastar chart rotation appears different from picture.

Arp 95 NED omits MCG+5-34-76 which is in the field and peculiar.

Arp 97 Megastar chart does not appear to match picture.

Arp 102 UGC10814A/B NED is MCG+8-31-41/UGC10814 in RC3.

Arp 105 Suffix discrepancy: NGC 3561A, B.

Arp 106 Suffix discrepancy: NGC 4211A.

Arp 108 Megastar (RC3) chart orientation does not appear to match picture.

Arp 114 original paper identifies NGC 2276, NED references NGC 2300.

Arp 118 Coordinates different in RC3 and NED and no size data on two objects.

Arp 121 Megastar (RC3) chart orientation does not appear to match picture.

Arp 122 original paper identifies NGC 6039, NED references NGC 6040A&B. RC3 suggests that 6039 is a single star.

Arp 129 Large magnitude discrepancy between NED and other sources.

Arp 138 NED galaxy descriptions disagree with RC3 and PGC.

Arp 144 NGC7828 NED A is B in RC3 and NGC7829 NED is B and A in RC3.

Arp 145 The NED entries do not relate well to Arp's photo.   RC3 implies that the objects are UGC 1840 and PGC 9060.

Arp 146 Ring A NED is Ring B and VV790 coordinates differ in PGC.

Arp 147 Suffix discrepancy IC298/298A.

Arp 150 Suffix discrepancy: NGC 7609A.

Arp 170 Suffix discrepancy: NGC 7578A, B.

Arp 176 NED A & B is RC3 B & A.

Arp 181 Original paper identifies NGC 3210 and 12, NED references 3212 and 15.

Arp 191 Megastar (RC3) chart orientation does not appear to match picture.

Arp 220 Original paper and NED (2 obj) lists IC 4553, DSFG implies IC4553 & 4554.

Arp 237 RC3 is not consistent with NED (can't tell which galaxy is which).

Arp 243 Triple object data as one in RC3.

Arp 244 Megastar (RC3) chart orientation of galaxy 4039 does not match picture.

Arp 246 Megastar (RC3) chart orientation does not appear to match picture.

Arp 247 Megastar (RC3) chart orientation does not appear to match picture and no third object data in RC3.

Arp 253 Megastar (RC3) chart orientation does not appear to match picture.

Arp 256 RC3 implies that NGC71 and NGC 68 should be included.

Arp 257 Megastar (RC3) chart orientation does not appear to match picture.

Arp 258 NED lists UGC 2140, RC3 coordinates well with the photo and references Hickson 18C and D as well.

Arp 259 Suffix discrepancy: NGC 1741A, B, C, D (IC 399 may be included).

Arp 274 Suffix discrepancy: NGC 5679A, B, C, NGC5679B NED is A in RC3.

Arp 278 Suffix discrepancy: NGC 7253A, B.

Arp 280 Megastar (RC3) chart orientation does not appear to match picture.

Arp 282 NED includes NGC 169A, DSFG implies it should be IC 1559.

Arp 288 original paper identifies NGC 5221, 22 & 26, NED omits 3226.

RC3 implies that 5222 is a double galaxy and 5226 is out of the field.

Arp 292 Megastar chart (RC3) orientation does not appear to match picture.

Arp 295 Original paper identifies IC 1505, NED and RC3 references MCG-01-60-21.

Arp 296 Confusion with Arp 299: Original paper identifies NGC 3690 and IC 694, NED references no names. Arp's photograph shows a group of at least 3 wide interacting galaxies MCG+10-17-2A appears involved but is also named VV118C (Arp 299).

Arp 299 Confusion with Arp 296: Original paper references No names, NED Identifies NGC 3690 (2 galaxies) and IC 694 Arp's photograph shows two tightly interacting galaxies. All sources agree that Arp 299 is VV118.

Arp 310 NED and original paper list IC 1259. RC3 implies it should be 1258 No IC1259 objects in RC3.

Arp 311 (same as for Arp 310).

Arp 312 Object coordinates in PCG are different from NED.

Arp 314 MCG-03 objects in NED are MCG-01 in RC3 and agree w/picture.

Arp 316 Original paper identifies NGC 3190, NED references 3187, 89 and 93.   NGC2000 also implies that 3190 should be a part of the group. 3189 is not in RC2 but is listed in NGC2000. DSFG implies a group of 3187, 90 and 93.

Arp 319 Suffix discrepancy: NGC 7318A, B.

Arp 321 Orientation of MCG-1-25-11 & -8 different in Megastar and some numbering NED to RC3: -10 to -12; -9 to -8; -8 to -9; -11 to -12.

Arp 323 Suffix discrepancy: NGC 7783B, RC3 suggests MCG+0- 60-58/+0-60-59.

Arp 324 Arp324 NED is UGC10143 RC3, UGC10143B NED is MCG+3-41-52 RC3, UGC10143C NED is MCG+3-41-51 RC3, no RC3 object for other NED's in Arp324.

Arp 325 NED identifies this as ESO 601- G 018. ESO on NASA CD-ROM does not recognize such a galaxy but has ESO 532- G 18 near the same location. MegaStar identifies ESO 601-18B (MCG-04-52-14).

Arp 329 RC3 indicates that UGC 6514 is MCG+12-11-28 A through E.

Arp 331 Original paper identifies NGC 375-88, NED lists NGC 379, 80, 82-86, &88.

Arp 332 NED omits MCG-4-8-29 and NGC 1230.

Additional Notes on Irregularities:

  1. There are several galaxies that are included in two Arp objects. From footnotes in the original paper, these seem to be on purpose:

    NGC 2276 is considered part of Arp 114 and Arp 25.
    IC 1259 is considered part of Arp 310 and 311. 311 includes IC 1258 & 60 as well.
    Messier 66 is considered all of Arp 16 and part of Arp 317.
  2. The galaxies in the Arp list represent a challenge to galaxy catalog builders. The catalog builders have responded in different ways to the peculiarities:

    • The UGC catalog accepts groups as single entities so some multi-galaxy systems are labeled with a single UGC name.
    • The VV catalog is composed entirely of interacting galaxies. Arp relied on the early edition of the VV catalog in assembling his list and the VV reference is the common in his original tables. Some interpreters add A, B, C… suffixes to these. The VV catalog would be well worth an exploration.
  3. To try to define which galaxies are included in Arp's object views is to explore the central feature in the debate around Halton Arp's hypotheses. Whether a given galaxy in an Arp view is interacting with the others is subject to some discussion. Many of the photographs are deep exposures of dark corners of remote galaxy clusters. Many faint anonymous background galaxies appear in some photographs.  Some students might omit these background galaxies from a comprehensive list on the basis of their relatively fainter magnitude or bigger redshift. Such omission would conflict with Dr. Arp's contention that these may not be further away, just mysteriously redshifted. I omitted no galaxies from the NED download for this very reason, although it is possible that the NED assemblers omitted some galaxies. Our comparison of Arp's photographs with RC3/PGC via MegaStar's plots, and the NED download did identify a few that dropped off NED.

Related Links

Arp Peculiar Galaxy Program Introduction
Arp Peculiar Galaxy Program Appendix A
Arp Peculiar Galaxy Program Appendix B
More about Halton C. Arp
Find Your Arp Peculiar Galaxy Program Award

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