Hα luminosity versus central entropy values measured at 1 kpc for our sample. Filamentary sources are shown with blue stars, compact disks with orange circles, and extended disks with orange left-pointing triangles. As a matter of comparison, we have included the sample from Cavagnolo et al. (2008) as a reference for BCGs with yellow circles, Hα upper limits are shown with black circles. The entropy values correspond to core entropy, K₀, for the Cavagnolo sample. The dashed gray line is the entropy value of 30 keV cm². We note that this entropy threshold should be a wide range of values as K can vary enormously in groups in comparison to clusters that are more self-similar (Sun et al. 2009; Oppenheimer et al. 2021).