•M(total) = V2rot R/G
•Recall M/L = constant (at least within class – and
is more true across classes
for H-band)
•L ~ V2rot R/G
•Also, surface
brightness, μ, L/R2 ~ constant (“Freeman’s Law,” μ(r) = μ0exp(-r/r0))
•Spiral central surface density = 21.65 B-mag arcsec-2
•Together these give L ~ V4, or in terms of Absolute magnitude, M = -10logV + constant
•Next
chapter, Faber-Jackson equivalent for ellipticals