Last updated: July-7-99

Peculiar and Interacting Galaxies

A preliminary scheme for grouping peculiar galaxies was given in [4, 5]. Independently, Arp and Madore [6] give 24 natural groups listed in Table A. Karachentsev [59], on the other hand, suggests a much more modest morphological classification for non-equilibrium systems as outlined in Table B. Because of the very nature of peculiar galaxies none of these systems has found wide application.

Ring galaxies, as a subset of peculiar and interacting galaxies, are widely recognized [27], sub-divided and internally classified as in [185], as explained in Table C; or as outlined in [43] and Table D; while [41] presents a report on classifying ring galaxies according to the morphology of their nuclear component alone. ``Ringed'' galaxies, on the other hand, are discussed in detail in [19]; shells and rings around galaxies are reviewed in [8]; warped disks and inclined rings are the topics in [22].

Table A. Arp-Madore Codings and Descriptions of Peculiar Galaxies and Associations [6]
CodeGeneral descriptionPercentage
1Galaxies with interacting (smaller) companion(s)5.5
2Interacting doubles (galaxies of comparable size)12.6
3Interacting triples2.0
4Interacting quartets0.5
5Interacting quintets0.1
6Ring galaxies (or morphologically similar objects)3.1
7Galaxies with jets2.4
8Galaxies with an apparent (smaller) companion(s)11.5
9M51 types (companion at end of spiral arm)2.0
10Galaxies with peculiar spiral arm(s)4.1
11Three-armed and multiple-armed spiral galaxies0.5
12Peculiar disks (major asymmetry or deformation)2.8
13Compact (very high-surface-brightness) galaxies6.4
14Galaxy with prominent or unusual dust absorption1.6
15Galaxy with tails, loops of material or debris3.5
16Irregular or disturbed (apparently isolated) galaxies4.2
17Chain of galaxies (four or more galaxies aligned)4.0
18Group of galaxies (four or more galaxies not aligned)4.9
19Cluster of galaxies (only very conspicuous, rich clusters)1.6
20Dwarf galaxy (low surface brightness)6.8
21Stellar object with associated nebulosity0.7
22Miscellaneous (very rare or distinctive objects)1.4
23Close pairs (not visibly interacting)11.4
24Close triples (not visibly interacting)5.6

Table B. Karachentsev's Classification of Non-Equilibrium Galaxies [59]
LINGalaxies exhibiting strong interaction in the form of
- bridges = LIN(br)
- tails = LIN(ta)
- bridges and tails = LIN(br+ta)
ATMSystems with two or more components in a common halo.
DIS (n)Systems with signs of distortion in (n) individual components.

Table C. Theys' and Spiegel's Classification of Ring Galaxies [185]
Ring typeDescriptionExamples
RECrisp, elliptical ring with photographically empty interiorArp 146, Arp 147, VII ZW 466
RNElliptical ring with an off-center nucleusII Hz 4, Lindsay-Shapley Ring
RKRing with a single, very prominent knot the ring; large-scale brightness distribution is markedly asymmetricalI ZW 45, II ZW 028

Table D. Few and Madore's Classification of Ring Galaxies [43]
Ring typeDescription
O-typesmooth structure and centrally located nucleus
P-typecrisp, knotty structure and often displaced nucleus

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