2026ApJ...999..238A

The supermassive black hole (SMBH) in the giant elliptical galaxy M87 is one of the most well studied in the local Universe, but the stellar- and gas-dynamical SMBH mass measurements disagree. As this galaxy is a key anchor for the upper end of the SMBH mass-host galaxy relations, we revisit the central 3″ × 3″ (∼240 × 240 pc) region of M87 with the Near Infrared Spectrograph (NIRSpec) integral field unit (IFU) on the James Webb Space Telescope. We implement several improvements to the reduction pipeline and obtain high-signal-to-noise ratio spectra (S/N ∼ 150) in single 0$\mathop{.}\limits^{^{\prime\prime} }$05 spaxels across much of the NIRSpec field of view. We measure the detailed shape of the stellar line-of-sight velocity distribution, parameterized by Gauss-Hermite moments up to h₈, in ∼2800 spatial bins, substantially improving upon the prior high-angular-resolution studies of the M87 stellar kinematics. The NIRSpec data reveal velocities with V ∼ ±45 km s^–1, velocity dispersions that rise sharply to ∼420 km s^–1 at a projected radius of 0$\mathop{.}\limits^{^{\prime\prime} }$45 (36 pc), and a slight elevation in h₄ toward the nucleus. We comprehensively test the robustness of the kinematics, including using multiple velocity template libraries and adopting different polynomials to adjust the template spectra. We find that the NIRSpec stellar kinematics seamlessly transition to recently measured large-scale stellar kinematics from optical Keck Cosmic Web Imager (KCWI) IFU data. These combined NIRSpec and KCWI kinematics provide continuous coverage from parsec to kiloparsec scales and will critically constrain future stellar-dynamical models of M87.