Kinematics of supernova remnants in the galaxy NGC 6946

Abstract We present a kinematical analysis of Hα emission from optical supernova remnant (SNR) candidates in the spiral galaxy NGC 6946, using the UNAM scanning Fabry-Perot interferometer (PUMA). Integrated spectra were obtained. From the high-resolution data, we derived line-of-sight velocity and velocity profiles. Complex profiles consistent with shocks signatures allowed us to kinematically confirm 95 objects as SNRs. Expansion velocities were estimated by fitting multiple radial-velocity components. The results show a broad dispersion, with a mean expansion velocity of ∼149 ± 26 km s−1. These values suggest that the measured velocities arise from secondary shocks induced in dense clouds, triggered by a primary shock wave propagating through a lower-density medium. This interpretation is supported by X-rays detected remnants, which implies higher shock velocities than those we measured in Hα line. We also analyzed Hα velocity profiles for recent supernovae, though without conclusive results. For a representative subset of kinematically confirmed SNRs with available electron densities, we estimated their ages and initial supernova energies. Assuming Sedov-Taylor or radiative phase evolution, derived ages range from less than 104 to 105 years, while initial energies are on the order of a few 1051 erg, typical of supernova explosions in NGC 6946 and other galaxies. The spatial distribution of confirmed SNRs shows a strong concentration along spiral arms, indicating core-collapse supernovae (Type II and similar) from massive, short-lived stars. Finally, although we examined possible correlations to identify evolutionary trends, the large dispersion in the data prevents firm conclusions.