Discovery of ~2200 new supernova remnants in 19 nearby star-forming galaxies with MUSE spectroscopy

We present the largest extragalactic survey of supernova remnant (SNR) candidates in nearby star-forming galaxies using exquisite spectroscopic maps from MUSE. SNRs show distinctive emission-line ratios and kinematic signatures in optical spectroscopy. From the PHANGS-MUSE project, we identify SNRs in 19 nearby galaxies at ~100 pc scales. We use five optical diagnostics: (1) [SII]/Hα line ratio maps; (2) [OI]/Hα line ratio maps; (3) gas velocity dispersion maps; and (4-5) two BPT diagrams to distinguish SNRs from other nebulae. Since SNRs are projected against HII regions and diffuse ionized gas, we search for objects with excess [SII]/Hα or [OI]/Hα relative to expected Hα surface brightness in photoionized gas. We identify 2,233 objects using at least one diagnostic, defining 1,166 high-confidence SNRs detected with at least two diagnostics. The line ratios of these SNRs agree well with the MAPPINGS shock models, and we validate our technique using the well-studied nearby galaxy M83. The remaining 1,067 objects, detected with only one diagnostic, are classified as SNR candidates. About 35% of all objects lie within HII region boundaries from literature catalogs, underscoring the need for indicators beyond line intensity morphology. The [OI]/Hα line ratio selects the most objects (1,368; 61%), but only half are classified as SNRs, highlighting the importance of multiple diagnostics to increase sample size and confidence in SNR classification.