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tokens: occupy distinct regions of NUV– r space, and all share some overlap with SPOGs, suggesting that SPOGs are a heterogeneous group comprised of galaxies with different mechanisms for UV emission. In FUV–NUV (bottom panel of Figure 6 ), we find a similar trend, with SPOGs displaying a larger range in FUV–NUV colors compared to the star-forming sample. Once again the E + A, AGN, and interacting samples all share a similar color distribution as SPOGs, but seem to occupy distinct subregions. These plots suggest that UV emission in SPOGs may be an amalgam of the mechanisms that the comparison samples represent in different proportions. Future multiwavelength and high-resolution morphological analyses will clarify which individual SPOGs exhibit similar UV emission mechanisms to each comparison group. Figure 6. Top: k -corrected NUV– r color vs. SDSS i -band absolute magnitude ( M i ) of SPOGS (gray contours) and all comparison samples. Bottom: k -corrected FUV–NUV color vs. SDSS i -band absolute magnitude ( M i ) of SPOGS (gray contours) and all comparison samples. In both plots, the black stars are SPOGs that fall outside the outer contour. While most of the comparison samples fall within the color–magnitude space occupied by SPOGs, no single sample fully covers the SPOGs parameter space, suggesting that SPOGs may be composed of a combination of these samples. All contours are in increments of 10 percentiles of the maximum density. Figure 7 shows the cumulative distribution of FUV–NUV colors for SPOGs compared to each of the comparison samples. We used AD tests to compare the shapes of these 1D UV color distributions. For samples in the full range of masses, all samples, except the AGN sample, have statistically distinct color distributions from SPOGs with greater than 99% significance. The AGN sample is distinct from SPOGs at the 78% significance level. When restricting the comparison to a specific range of masses (−23 M i −21), all samples, except the interacting sample, have statistically distinct color distributions from SPOGs with greater than 99% significance. The interacting sample is distinct from SPOGs at the 85% significance level. This test shows that the differences in UV colors are not attributable to differences in stellar mass distribution. Figure 7. Cumulative distributions of GALEX FUV–NUV color for SPOGs and each of our comparison samples. With Anderson–Darling tests, we show that SPOGs are a distinct distribution from all other comparison samples, except AGN (see Section 3.1 ). 3.2. Mixture Models To further test which of the comparison samples contribute to the FUV–NUV colors of SPOGs and in what fractions, we used the method of Gaussian mixture models (GMMs) 20 20 We provide an example of our code and method at https://github.com/f-ardila/SPOGs-GMMs . . GMM models some underlying distribution whose true probability density function is unknown as the sum multiple Gaussian distributions (Ivezic et al. 2014 ). Here, we first