A Parameterized Model for Differential Galaxy Counts at Any Wavelength

Certain astronomy problems, such as the probabilistic cross-matching algorithms of Wilson & Naylor, require descriptions of galaxy counts as a function of brightness in many different filter sets, for which we often lack dedicated observations. With this motivation in mind, I present a simple model for calculating differential galaxy counts for an arbitrary bandpass or wavelength. The model uses a double Schechter function to describe the number density of galaxies as a function of absolute magnitude, including redshift-driven galaxy evolution, for both “blue” and “red” galaxy types. Collating previously derived values for the parameterization of the evolving Schechter function— M 0 * , ϕ 0 * , P, Q, and α—I fit the dependencies of these parameters as a function of wavelength, allowing for the tabulation of differential galaxy counts in a new filter for which observations are unavailable. Finally, I briefly compare the model with some differential galaxy counts obtained from the literature.