Do Spiral Galaxies Have a Variable Disk Thickness?

Abstract

Estimating the forces in the z-direction that affect the disks of spiral galaxies in reasonable galactic mass models we find (Rohlfs and Kreitsch mann 1981) that all external forces are small compared to the self-gravity of the disk so that Spitzer' s (1942) self-consistent sheet model should give a good description for the z-distribution of the disk where it is well visible. But then the three parameters describing this shape are connected by the formula

EquationSource$$ \Delta (r) = \frac{{ < v_{z}^{2} > }}{{\pi G \cdot \mu (r)}} $$

(1)

Now μ(r) varies strongly with r according to Freeman (1970)

EquationSource$$ \mu (r) = {{\mu }_{o}} \cdot \exp ( - ar) $$

(2)

and therefore either Δ(r) or 〈v ²_z 〉 or both should vary with r too.