2026ApJ...998..278S

The supernova remnant (SNR) RCW86 is among the few SNRs with Balmer-emission lines containing broad and narrow spectral components that trace fast, nonradiative shocks in partially ionized gas. These are invaluable laboratories for collisionless shock physics, especially for poorly understood phenomena like electron-ion equilibration, and shock precursors. Here we present the first ∼0.3 pc spatial scale integral field unit observations of the southwestern RCW86 shock, obtained as part of the Sloan Digital Sky Survey-V Local Volume Mapper (LVM). The forward shock, clearly visible as thin filaments in narrowband images, exhibits broad component Hα emission, indicating shock velocities varying from 500-900 km s^–1 in the south to 1000-1500 km s^–1 in the north. The varying velocity widths and broad-to-narrow intensity ratios show that electrons and ions have lower equilibration (T_e/T_p → 0.1) in faster (>800 km s^–1) shocks, in line with previous studies. The broad components are generally redshifted from the narrow components by ≲100 km s^–1, likely due to shock-obliquity or non-Maxwellian post-shock distributions. We observe high extinction-corrected Balmer-decrements of 3-5 in the narrow components, indicating that conversion of Lyβ photons to Hα is more efficient than Lyγ to Hβ. Upper limits on the He IIλ4686 in the southern shock are consistent with a moderate-to-high (30%-100%) neutral fraction in the preshock gas. We also find the first evidence of an intermediate Hα component in RCW86, with ΔV(FWHM) = 193-207 km s^–1, likely due to a fast neutral precursor. We also briefly discuss the southwestern radiative shock, and lay out the exciting future of studying astrophysical shocks with LVM.