SIMBAD references

Near-infrared images confirm that the Hubble classification of spiral galaxies does not constrain the morphology of their stellar Population II disk, since galaxies on opposite ends of the spiral sequence can display remarkably similar evolved disk morphologies. Thus, the gas dominated Population I component determines the types (a, b, c), decoupled from the Population II. The underlying mass distributions observed in the infrared are exceptionally regular, suggesting that large scale spiral structure is principally intrinsic, as argued by the modal theory. Moreover, single arms, bisymmetric arms, lopsidedness and/or bars dominate the old stellar disk. The absence of infrared multiple-armed structure is attributed to the efficiency of Inner Lindblad Resonance absorption in the evolved Population II disk. These observations support a coherent framework for galaxy classification based on three parameters: stellar disk "temperature", gas content and active disk mass.