Irregularities in identification of galaxies involved in the Arp list and References used in preparing the tables

In researching the names of galaxies involved in the Arps among various galaxy catalogs, the author and friends noted a number of irregularities or inconsistencies. Perhaps this is a product of having too many galaxy catalogs. These discrepancies may be bothersome to some observers and are provided for their use. Perhaps a very energetic person can resolve the discrepancies or convince the catalog builders to converge on a single interpretation. Perhaps it is better to enjoy the mystery.

Arp 7   PGC lists MCG+3-23-009 (IC2411) rather than MCG-3-23-009 
	which appears to be the same galaxy in the original Arp image.
Arp 30 	Suffix discrepancy: NGC 6365A, B
Arp 32	UGC10770B NED is UGC10770 RC3.  Also, there is no A in RC3
Arp 51  NED identifies as MCG-02-01-024/NGC 7828 but PGC suggests 
	the galaxy in Arp's image is a galaxy at a different location
	called PGC 475.
Arp 54  Should this include PGC 9103?
Arp 57  Positional discrepancies for MCG+03-34-013 and MCG+03-34-012
          between NED and PGC.
Arp 59	Suffix discrepancy: NGC 341A, B
Arp 63  NED proposes MCG+06-21-067 as the companion to NGC 2944 
        while PGC suggests another galaxy PGC27534 which NED 
        does not recognize.  Also suffix discrepancy: NGC 2944A, B
Arp 68	original paper identifies NGC 7756, NED references NGC 7757.
Arp 87	Suffix discrepancy: NGC 3808A, 
Arp 89  Irregularities in MCG: -12-22-006 and +02-22-006 (RC3) are 
        both proposed for the fainter companion to 2648.
Arp 97	CfA Redshift files identify UGC 07085 in a different part 
        of the sky
Arp 102 PGC and RC3 interpret MCG+08-31-042 and -041 differently.
        PCG position for -042 is inconsistent with Arp's picture 
        and Hubble Guide Star Catalog.  RC3 location for -041 is       
        consistent with NED's interpretation of -042 as the 
        southern E0 galaxy.
Arp 105	Suffix discrepancy: NGC 3561A, B
Arp 106	Suffix discrepancy: NGC 4211A
Arp 111 NED references to MCG+06-31-046 galaxies do not appear in 
        Arp's image for Arp 111.
Arp 113 NED identifies only  NGC 70, but Arp's categorization
        identifies it as "E or E-like galaxy close to and perturbing 
        a spiral".  This categorization would imply that NGC 71 (E) or
        NGC 68 (S0) would be the primary galaxy and NGC 70 is the 
        perturbed spiral.  While current redshifts have NGC 71 closer 
        to NGC 70 and NGC 71 is visually closer, both are included.
Arp 114	original paper identifies NGC 2276, NED references NGC 2300.
Arp 118 Historical confusion between NGC 1141 and 1143.
	Historical confusion between NGC 1142 and 1144.
Arp 122	original paper identifies NGC 6039, NED references NGC 6040A&B.
            RC3 suggests that 6039 is a single star
Arp 144	NGC7828 NED A is B in RC3 and NGC7829 NED is B and A in RC3
Arp 145	PGC 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 174	NGC 3068 has a companion (3068 A&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 218 Can't find name of southwest component
Arp 220	Original paper and NED (2 obj) lists IC 4553, DSFG implies
Arp 256	RC3 implies that NGC71 and NGC 68 should be included
Arp 259	Suffix discrepancy: NGC 1741A, B, C, D (IC 399 may be included) 
Arp 272 Arp's paper lists NGC 6054.  Current interpretation of Abell
	2151 labels the galaxies in Arp's image as NGC6050 and IC1179.
Arp 274	Suffix discrepancy: NGC 5679A, B, C,   NGC5679B NED is A in RC3
Arp 278	Suffix discrepancy: NGC 7253A, B
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 295	Original paper identifies IC 1505, NED and RC3 references
Arp 296	Confusion with Arp 299: Original paper identifies NGC 3690 
        and IC 694, 
Arp 299	Confusion with Arp 296: Original paper references No names, 
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) plus confusion between IC 1260 with KAZ 140
Arp 312 NED identifies Arp 312 as MCG+08-31-004.  The PGC
	interpretation suggests that this galaxy (not apparent on
	POSS) is too large and slightly south of the location
	implied by field stars in Arp's image.  MCG+08-31-006 is
	better placed but not in the correct place.  The Hubble 
	GSC misidentifies the involved galaxies as stars.
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	Numbering inconsistencies between NED and 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 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

Arp 331	Original paper identifies NGC 375-88, NED lists NGC 379, 380, 
382-386,  and 388.  Also, sources disagree on labeling and location 
of galaxies NGC387 and 388.

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:
  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:
  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 liston 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.

References used in assembling the lists

  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), accessed during October and November 1998. This site is 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:
  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:
  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:
  6. Digital Sky Survey, (DSS) an online service of the HSTScI with provides downloaded images from the Palomar Sky Survey.
  7. Deep Space CCD Atlas: North, by John C. Vickers, 1994, PO Box 1292, Duxbury, MA 02331 USA
  8. Carnegie Atlas of Galaxies, Allan Sandage and John Bedke, Carnegie Institution of Washington, 1994.

Page updated April 5, 1999 by Dennis Webb.
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