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The classification of a large sample of galaxies in the CVRHS system allows investigation of the systematics of different morphological types and classes, i.e. how aspects of morphology might vary with stage and family. Figure 1.25 first shows the distribution of stages for three galaxy samples: (a) a sample of 1240 galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S⁴G; Buta et al. 2015); (b) a sample of 441 galaxies from the Analysis of the Interstellar Medium in Isolated Galaxies (AMIGA; Buta et al. 2019; Verdes-Montenegro et al. 2005); and (c) a sample of 2,628 galaxies from the Extraction of the Forms of Galaxies from Images survey (French acronym: EFIGI; Buta 2019; Baillard et al. 2011). Each plot is restricted to galaxies inclined at ≤60°. The three graphs show how the distribution of stages depends sensitively on the selection criteria for a given sample. The S⁴G sample is distance-limited and used 21 cm radial velocities to judge distances; this accounts for the significant emphasis of this sample on extreme late-type (Sd-Sm) spirals and Magellanic irregulars (Im). The EFIGI sample was selected largely on the basis of angular diameter and emphasizes mainly Sb-Sc spirals. The AMIGA sample of isolated spirals is similar in showing an emphasis on Sb-Sc spirals.

Figure 1.25. Distribution of CVRHS stages from (a) Buta (2019; EFIGI), (b) Buta et al. (2019; AMIGA) and (c) Buta et al. (2015; S⁴G). The histograms are each restricted to relatively face-on galaxies (i ≤ 60°)

Figure 1.26 shows the bar, inner variety and outer variety fractions ( fbar, fIV, and fOV, respectively) as a function of stage for subsets of EFIGI galaxies inclined ≤66°. The numbers are N = (a) 2,440, (b) 749, (c) 1,309, (d) 260 and (e) 2,642 galaxies. Figure 1.26(a) shows that the bar fraction has a minimum near stage Sc, with the highest bar fractions for extreme late-type spirals; Figure 1.26(b) shows that inner rings and well-defined inner pseudorings have the highest fraction around stage Sab; Figure 1.26(c) shows that (s) variety is uncommon for types Sab and earlier, but jumps to ≥80% for stages Sc and later; Figure 1.26(d) shows that lenses, ring-lenses and pseudoring-lenses are found mainly among stages Sb and earlier; and Figure 1.26(e) shows that outer features (rings, pseudorings, lenses and ring lenses) are most common between stages S0⁺ and Sb. Although outer features are rare for types later than Sb, Figure 1.26 shows a secondary peak among extreme late-type spirals.

Figure 1.26. Systematics of CVRHS classifications from Buta (2019; EFIGI). The samples used for these graphs were restricted to inclinations ≤66°