Ratio of Brα to 3.3 μm PAH emission as a function of decreasing Brα EQW (increasing starburst age, the upper x-axis). The circles represent the sources with both 3.3 μm PAH and Brα detections color-coded by the AGN fraction. The upper limits are shown only for the objects with PAH_{3.3 μm} EQW < 0.04 μm and PAH_{6.2 μm} EQW ≥ 0.4 μm. The starburst ages are derived from the Brα EQW using the Starburst99 models (Leitherer et al. 1999, 2010; Vázquez & Leitherer 2005).