Luminosity Distributions -- Spirals
		Central bulge = elliptical, to 1st order Disk: exponential fcn, I(r) = I0e-r/ro Vertical Structure: derivation in text H = σz2/πGμ(r); ρ = ρ0 sech2(z/H) sech2(z/H) -> 1 – z2/4H2 for small z        4e-2z/H for large z