Deep Fabry-Perot Hα Observations of NGC 7793: A Very Extended Hα Disk and A Truly Declining Rotation Curve

Deep H? observations of the Sculptor Group galaxy NGC 7793 were obtained on the ESO 3.60 m and the Marseille 36 cm telescopes at La Silla, Chile. H? emission is detected all the way to the edge of the H I disk, making the H II disk of NGC 7793 one of the largest ever observed in a quiet non-active galactic nucleus (AGN) late-type system. Even in the very outer parts, the H II ionizing sources are probably mainly internal (massive stars in the disk) with an unlikely contribution from the extragalactic ionizing background. The H? kinematics confirms what had already been seen with the H I observations: NGC 7793 has a truly declining rotation curve. However, the decline is not Keplerian and a dark halo is still needed to explain the rotation velocities in the outer parts.