The Interstellar Medium and Star Formation in Edge-On Galaxies. II. NGC
  4157, 4565, and 5907
  We present a study of the vertical structure of the gaseous and stellar disks
in a sample of edge-on galaxies (NGC 4157, 4565, and 5907) using BIMA/CARMA
12CO (J = 1 --> 0), VLA H I, and Spitzer 3.6 micron data. In order to take into
account projection effects when we measure the disk thickness as a function of
radius, we first obtain the inclination by modeling the radio data. Using the
measurement of the disk thicknesses and the derived radial profiles of gas and
stars, we estimate the corresponding volume densities and vertical velocity
dispersions. Both stellar and gas disks have smoothly varying scale heights and
velocity dispersions, contrary to assumptions of previous studies. Using the
velocity dispersions, we find that the gravitational instability parameter Q
follows a fairly uniform profile with radius and is greater than or equal to 1
across the star forming disk. The star formation law has a slope that is
significantly different from those found in more face-on galaxy studies, both
in deprojected and pixel-by-pixel plots. Midplane gas pressure based on the
varying scale heights and velocity dispersions appears to roughly hold a
power-law correlation with the midplane volume density ratio.
