NEW ESTIMATES OF THE INCLINATION, POSITION ANGLE, PITCH ANGLE, AND SCALE HEIGHT OF THE WHIRLPOOL GALAXY

Abstract

The inclination (i) and position angle (PA) of the Whirlpool galaxy (M51) are critical to modeling and interpreting observations. Here we make improved estimates of these parameters by fitting logarithmic spirals to the main arms. From separate fits to each major arm, we obtain i = 203 ± 28 and PA = 120 ± 25. We then use Poisson's equation for the logarithmic perturbation of the density to estimate the mean vertical scale height (H) of M51 to be 95-178 pc.