Purely Morphological Schemes

Systems of classification that in fact are more descriptive than interpretive can be traced back to the early work of Wolf, M. [208] which captured the development of complexity of forms, and that of Shapley, H. [169, 170]. The most extensive application of this approach to galaxy taxonomy is the work of Vorontsov-Velyaminov and his colleagues as published in the five volumes of the Morphological Catalogue of Galaxies [200].

In the MCG no attempt is made to systematize and/or distill the forms found; rather the essential components are all laid out in as much complexity (or simplicity) as the system demonstrates, ordered simply as a function of radial zones within the galaxy; different zones are divided by a semicolon, those referring to the same zone are separated by a colon. A double colon means that the outer details are completely detached from the inner ones. Symbols are placed inside of parentheses, if they are doubtful. An exclamation mark, or the repetition of the lowercase descriptors are used to accentuate a detail or quantity. The following table lists the essential features of this powerful, albeit infrequently used system.

Morphological Catalogue Symbols [200]
Symbol used in MCGDescription
Fflat galaxies
usually highly inclined, with no distinguishable form
Gsmall galaxies, difficult to describe but not stellar
Nlarge nucleus
nsmall nucleus
Ne and neelongated nuclei
(N)overexposed image with traces of structure which imitate a nucleus
Nn and nnnebulous nuclei
H haze or halo
Hpvery asymmetrical or disturbez Haze
D-incomplete disk
RRseveral rings
R-incomplete ring
D ->Rdisk is brighter at its rim (ring effect)
Bshort bar with no nucleus
B-very short bar
BBlong bar
BBBvery long bar
2Bbar seen on both sides of N or L
N;2Bbar is faint relative to nucleus
N,2Bnucleus and bar are of comparable strength
S and Zlong spiral arms
2S = two arms, 3S = three spiral arms, etc.
s and zshort spiral arms
SS and zzindefinite numbers of arms
SS' and ss'arms with indefinite direction of winding
ZSarms wind in opposite directions
Sssbranching spiral arm
gammaemergent spiral arms form a gamma-shape
gamma -> Rgamma-arm tends to form a ring
2S -> 8spiral returns to nucleus forming a figure-eight
S -> Rarm merges into a ring
(N);ss or F;ssends of a flat system are visible
D, (2S) or L, (2s)arms are suspected in a D or L system
2ltwo wings (flattened component seen edge-on)
Pindefinite patch
Aabsorption feature
Cconnecting filament (in interacting systems)
+*star superimposed
wwide open arms
ttightly wound arms
oopen arms
zarms start at right-angles to the bar
->appears to transform to
-> 8transforms to a figure-eight or loop
avery smooth
dvery patchy
iirregular patchiness
pdeformed detail (not the peculiarity in general)
used to accentuate any particular detail
( )symbols are put in parentheses when a detail is only suspected

Examples (click on the figures to see larger versions) :

Figure 1 Figure 2

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