The Interstellar Medium and Star Formation in Edge-On Galaxies. I. NGC
  891
  We analyze images of BIMA 12CO (J = 1 --> 0), VLA HI, and Spitzer 3.6 and 24
\mum emission toward the edge-on galaxy NGC 891 and derive the radial and
vertical distributions of gas and the radial distributions of stellar mass and
recent star formation. We describe our method of deriving radial profiles for
edge-on galaxies, assuming circular motion, and verify basic relationships
between star formation rate and gas and stellar content, and between the
molecular-to-atomic ratio and hydrostatic midplane pressure, that have been
found in other galaxy samples. The Schmidt law index we find for the total gas
(H2 + H I) is 0.85\pm0.55, but the Schmidt law provides a poor description of
the SFR in comparison to a model that includes the influence of the stellar
disk. Using our measurements of the thickness of the gas disk and the
assumption of hydrostatic equilibrium, we estimate volume densities and
pressures as a function of radius and height in order to test the importance of
pressure in controlling the {\rho}H2/{\rho}HI ratio. The gas pressure in two
dimensions P(r, z) using constant velocity dispersion does not seem to
correlate with the {\rho}H2/{\rho}HI ratio, but the pressure using varying
velocity dispersion appears to correlate with the ratio. We test the importance
of gravitational instability in determining the sites of massive star
formation, and find that the Q parameter using a radially varying gas velocity
dispersion is consistent with self-regulation (Q - 1) over a large part of the
disk.
