A search for the infrared counterpart of type II OH masers - I. A model for the IR background source confusion

A simple exponential disc model for the distribution of stars and extinction (dust) in the galaxy is developed for the purpose of predicting the infrared stellar luminosity function along an arbitrary line of sight at any given wavelength and apparent magnitude limit. The model luminosity function is used to determine the extent to which the stellar field will contaminate searches for the infrared counterpart of type II OH masers. The model parameters are calibrated using 2.2 µm source count data available in the literature, and new data presented here for the first time. In the plane, contamination by the field is found to be serious by 8th magnitude at 2.2 µm and 7th magnitude at 3.5 µm for a 20 arcsec radius search area.