Some statistical properties of spiral galaxies along the Hubble sequence

A statistical study has been made for the variations along the Hubble sequence, os such parameters as the degree of tightness of winding of spiral arm λ, the pitch angle μ, the flatness of the disk H/D₂₅ and the thickness H along the Hubble sequence for 365 spiral galaxies published in A&Ap Supplement Series. The mean values of these quantities for the various Hubble types have been obtained for the first time. The results of the statistics show clearly 1) that the Hubble classification of spiral galaxies is one which has only a qualitative and statistical significance, and 2) that the dispersion relation in the density wave theory is valid for most spiral galaxies, i.e., the arms of most spiral galaxies satisfy the requirements of being tightly wound.