Hα emission surface brightness as a function of stellar mass. All measurements are expressed as rest-frame surface brightnesses after correcting for cosmological dimming by a factor of (1 + z)⁴. The orange circles and green triangles show star-forming galaxy measurements from H. Zhang et al. (2020) in two bins of scaled projected radius, r_s = r_p/R₁₈₀, where r_p is the projected distance from the galaxy center and R₁₈₀ is the virial radius. The gray shaded region marks the corresponding range of Hα surface brightnesses observed from the inner to outer regions of these star-forming galaxies and groups (H. Zhang et al. 2016, 2020). The cyan hexagon shows the radio-galaxy stack including all background-quasar sight lines, independent of angular position relative to the radio axis (0^∘ ≤ θ ≤ 90^∘). Since the Hα flux stacked over all azimuthal angles is a nondetection (<2σ; see Figure 2(b)), this point should be interpreted as an upper limit. This upper limit is consistent with the Hα surface brightness expected for normal-galaxy halos (H. Zhang et al. 2016; Y.-L. Chang et al. 2024). The blue and purple hexagons show radio-galaxy stacks restricted to sight lines within 20^∘ of the projected radio axis. They are separated into inner sight lines with R_⊥/R_radio ≤ 0.5 and outer sight lines with R_⊥/R_radio > 1.0, which are close to the radio lobes. The Hα emission from jet-aligned sight lines is much stronger and is enhanced by nearly 1–2 orders of magnitude relative to the normal-galaxy baseline at similar stellar mass. This indicates that the Hα emissivity from cool ionized CGM is preferentially brightened along directions where radio jets interact with halo gas.