Decoupled Kinematics and Excitation in the Compton-thick AGN NGC 6552: Spatially Resolved KOOLS-IFU Observations

Abstract

Hard X-ray selected Compton-thick AGNs provide a relatively obscuration-resistant census of accretion, but optical line diagnostics can be strongly shaped by extinction and geometry. Spatially resolved integral-field spectroscopy can mitigate these effects and provides direct constraints on outflow kinematics and ionization state on kiloparsec scales. We present KOOLS-IFU optical integral-field spectroscopy of NGC 6552 obtained on the 3.8 m Seimei Telescope. Using spatially resolved emission-line ratios and non-parametric [O III]5007 kinematics over the central ~2 kpc, we test whether ionized-gas kinematics are locally coupled to excitation. The [O III]5007 width W80 is broadly elevated across the inner region (~530-830 km/s) and declines monotonically with projected galactocentric distance, consistent with a centrally concentrated outflow that decelerates at larger radii. Despite this clear kinematic structure, neither W80 nor the velocity asymmetry parameter dv shows a statistically significant correlation with [O III]5007/Hbeta. Order-of-magnitude outflow energetics yield Edot_K/L_bol ~ 0.01%-0.28% (for assumed n_e = 50-1000 cm^-3), consistent with [O III]-based estimates tracing only the ionized phase of a multi-phase outflow. We conclude that in NGC 6552 both the total line broadening traced by W80 and dv are consistent with being governed primarily by spatial dynamical structure and line-of-sight superposition of multiple kinematic components, with no statistically significant coupling to excitation-driven processes detected at our sensitivity level. A positive W80-[O III]5007/Hbeta coupling does emerge in the small subset of bins for which the two-component fit is most strongly favored statistically, which deeper observations will be needed to confirm.