Yu Bai, Jifeng Liu
Stellar bars can drive gas inflow, shocks, radial mixing, and central mass growth, so they should leave measurable signatures in resolved optical emission-line excitation. The challenge is that line-ratio classifications also respond to low-ionization emission-line region (LIER)-like, weak active-galactic-nucleus (AGN)-like, shock, diffuse ionized gas, metallicity, and post-asymptotic-giant-branch powered emission. We tested whether barred Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) disk galaxies show a lower resolved optical star-forming line-classification probability than matched unbarred controls, without treating this probability as a direct star-formation-rate (SFR) measurement. We constructed a critical-bit-clean MaNGA sample and analyzed 698 complete MaNGA Analysis Pipeline output-products (MAPS) pairs. From Data Release 17 (DR17) Data Analysis Pipeline (DAP) MAPS products, we extracted annular profiles in 0--0.5, 0.5--1.0, 1.0--1.5, and 1.5--2.0,R_e bins; estimated Monte Carlo Baldwin--Phillips--Terlevich (BPT) and WHAN NII /Hα equivalent-width) star-forming classification probabilities; and tested matching, detection, signal-to-noise, nonpositive draw handling, bar-geometry, gas content, and covariance sensitivities. Barred galaxies show lower BPT and WHAN star-forming classification probabilities than unbarred controls in all four radial bins. The BPT probability deltas reveal barred-minus-unbarred differences in the annular BPT star-forming line-classification probability. These values are approximately -0.111, -0.148, -0.124, and -0.109 from 0.25 to 1.75,R_e. The corresponding WHAN deltas are -0.083, -0.141, -0.105, and -0.095. Conditional-on-positive Monte Carlo probabilities remain negative, but the outer annuli also show lower valid-spaxel fractions, lower line signal-to-noise, and additional low-equivalent-width or retired-like emission in barred systems. This robust result represents a barred-host deficit in the optical star-forming line-classification probability under the adopted diagnostics. This is astrophysically significant because it points to systematic changes in the ionized-gas excitation mix of barred disks, plausibly involving bar-driven gas redistributions, shocks, abundance-sensitive line ratios, and weak-line or LIER-like emission. It is not direct evidence that bars uniformly suppress resolved SFR, nor is it population-level causal evidence that bars quench disk galaxies.