Physical relations of galaxies emitting He II with SnR > 5.5, measured and cataloged by SB12, detected in X-rays and cataloged in the CSCv2.0. In all subplots, the points are color-coded based on the galaxies’ He II/Hβ ratio. The emission-line ratios have low uncertainties which are not plotted for clarity. BPT SFGs are represented by a circle, and BPT AGNs are represented by a triangle marker. SB12 SFGs are marked with a rhombus. Top left: He II/Hβ ratio as a function of the [N II]/Hα ratio. The black curve represents the SB12 classification curve separating AGNs (top right) from SFGs (bottom left). Top right: [O III]/Hβ as a function of the [N II]/Hα ratio, aka the BPT diagram. The dashed black line shows the Kauffmann et al. (2003) classification curve above which composite galaxies and AGNs are located. Middle left: SFR as a function of M_⋆, aka the main sequence of SFGs. The brown-dotted, and red dashed-dotted lines represent the Popesso et al. (2019), and Kouroumpatzakis et al. (2021) main sequence fits respectively. Middle right: L_X as a function of SFR. The black dashed-dotted line represents the Mineo et al. (2014) relation. Bottom left: L_X/SFR as a function of metallicity. The orange continuous, black dashed-doted, green dashed, and magenta dashed-dotted lines represent the Fragos et al. (2013b), Mineo et al. (2014), Brorby et al. (2016), and Lehmer et al. (2021) relations respectively. Bottom right: L_X/SFR as a function of He II/Hβ ratio. The black dashed-dotted line represents the Mineo et al. (2014) relation. The red dashed line shows the best linear regression fit involving all sources regardless of their class.