Quantifying Errors and Biases in Pitch Angle Measurements

Supermassive black holes (SMBHs) have masses which correlate well with properties of their host galaxies, suggesting the galaxies and their central black holes grew up together. Because of this, studying how SMBH masses increase over time is an important tool for understanding galaxy evolution. Several groups have determined a black hole mass function for the local universe, but our ability to extend it to the distant universe (and thereby see how it has varied through time) is hampered by the difficulty of directly measuring black hole masses. One promising way to estimate SMBH masses is to use the relationship between the pitch angle of a spiral galaxy and the mass of its SMBH. In order to use this relation we need to have a good understanding of what errors and selection biases affect our pitch angle measurements. One method of measuring pitch angles of spiral galaxies is via the MATLAB code Spirality. By utilizing Spirality on simulated galaxy images, we have mapped Spirality's margins of error and selection biases against various galaxy properties, such as (true) pitch angle, arm-interarm contrast, and magnitude. The goal is to use this information to correct pitch angle measurements made on real galaxies.