19
Luminosity Distributions -- Spirals
Central bulge
= elliptical, to 1
st
order
Disk
: exponential fcn, I(r) = I
0
e
-r/ro
Vertical Structure
: derivation in text
H =
σ
z
2
/
π
G
μ
(r);
ρ
=
ρ
0
sech
2
(z/H)
sech
2
(z/H) -> 1 – z
2
/4H
2
for small z
4e
-2z/H
for large z