We analyze images of BIMA ^ { 12 } CO ( J = 1 \rightarrow 0 ) , VLA H i , and Spitzer 3.6 and 24 \micron 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 ( H _ { 2 } + H i ) is 0.85 \pm 0.55 , 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 _ { { H _ { 2 } } } / \rho _ { HI } ratio .
The gas pressure in two dimensions P ( r,z ) using constant velocity dispersion does not seem to correlate with the \rho _ { { H _ { 2 } } } / \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 \sim 1 ) over a large part of the disk .