Source count histograms for the different Spitzer wave bands in black (bin size is 0.2 mag). The bottom axis scale, stellar magnitudes, is shared between panels. The top axis scale, stellar flux, is different in each panel due to the different magnitude zero points. The photometric completeness thresholds estimated based on 10 times the sensitivities of the images are indicated by the dashed vertical lines: 7, 11, 80, 65, 430, and 50,000 μJy for the 3.6 to 70 μm wave bands, respectively. The solid lines indicate the peak of the source count histograms, below which the photometry is clearly incomplete: 31, 24, 80, 80, 400, and 40,000 μJy, respectively. The completeness of the photometry in the 3.6 and 4.5 μm wave bands, where the source densities are higher and confusion is more severe, is consequently worse than expected based on the sensitivity of the images alone. The white histograms show the source counts for the classes of sources identified in § 5.5. A large fraction (~50%) of the brightest sources in each wave band fall into one of the identified classes.