Abstract:
The vertical scaleheight of atomic hydrogen gas is observed to
be nearly constant with radius in the inner Galaxy « 8.5 kpc). This has been
a long-standing puzzle (Oort 1962) because the gas scaleheight should increase
exponentially with radius as a response to the decreasing gravitational potential
of the stellar disk alone. We treat the stars, H I and H2 as three gravitationally
coupled components in the Galactic disk and find their scaleheights as a function
of galactocentric radius. This approach not only explains the near-constancy
of H I scaleheight but also reproduces the observed scaleheight variation for H2
and stars in the Galaxy.
