Objective classification of spiral galaxies

[henrco]

I have question that has been troubling me and I was hoping someone may be able to help me.

I've always thought the Hubble classification of galaxies was a bit subjective. I was recently looking at some images online of galaxies and I was wondering how you might objectively observe and compare the morphological types of galaxies, from CCD images.With Elliptical galaxies you can derive the En number where the number n describes the apparent axial ratio (b/a) by the formula: n=10 [1 – (b/a)], (1) where a and b represent the length of the semi‐major and semi‐minor axis, respectively, of the galaxy. So that's pretty objective.However how do you objectively do the same for Spiral galaxies? After numerous searches I haven't found a method that is similar to the one for elliptical galaxies above.

 

[phyzguy]

The Hubble classification is quite subjective. If you want a more objective classification scheme, try looking at these color-mass diagrams, which effectively separate galaxies into ellipticals and spirals.