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Intergalactic HII regions, far from the confines of a galactic disk, represent a mode of star formation in low-density gas outside of galaxies. The figure below (left) shows an R-band continuum image of NGC 1533 from the SINGG Hα survey (Meurer et al. 2006) overlaid with HI contours and the location of three intergalactic HII regions discovered by Ryan-Weber et al. (2004). The HI contours are 1.6, 2.0, 2.4, 2.8, 3.2 and 4.0 ×1020 cm−2 and have a resolution of ~1′. ACS/HRC images of the intergalactic HII regions (right) are composites of UV, V, and I bands. The half-light radii of the clusters associated with regions 1, 2, and 5 are 24.7, 21.7, and 17.0 pc, respectively, at the distance to NGC 1533 (21 Mpc; Tonry et al. 2001). Assuming a Salpeter IMF with Mup = 100, Hα/UV ratios indicate a small number of ionizing O stars relative to the total number of UV-emitting O and B stars. These young (4-6 Myr), intergalactic stellar populations lend valuable insight to our understanding of the methods by which star formation is triggered and may even represent the first episodes of star formation in emerging galaxies. [ABSTRACT FROM PUBLISHER]