– 25 – Fig. 4.— SDWFS mid-IR color-color diagrams for the Bo¨ otes field. The green contours show the distribution of all 39,522 Photometry Group 3 sources. The objects are binned in 0.05 mag bins in both axes, and the contours are drawn at levels of 2, 10, 20, 50, 100, and 150 objects per bin, counting from the outer contour. Top-left panel: black dashed and solid line “wedges” show the original Stern et al. (2005) AGN selection region and the modified AGN region we define to encompass the distribution of XBo¨ otes X-ray sources discussed in Gorjian et al. (2008). The black box at color zero is the region occupied by normal stars and also nearby galaxies without PAH emission. The blue solid, dotted, and dashed lines show the evolution of the mid-IR colors of late-type spiral, irregular, and early-type galaxies with redshift based on the SED models of Assef et al. (2010b). The red dotted and solid lines show the evolution of a pure AGN and a composite with equal contributions from the AGN and its late-type host to the bolometric luminosity. The dots on each track mark redshift increments of 0.5 (1.0) from z = 0 to 3 (to 6) for galaxies (AGNs) that start at the z = 0 . 0 bulls eye. Other panels: Photometry Group 3 mid-IR counterparts of radio sources (top right), X-ray sources (bottom left), and MIPS 24 µ m AGN candidates (bottom right) are shown.