Bubbles and jets in the center of M51

Abstract

Optical and radio observations of the nucleus of the galaxy M51 are presented. The observations show that M51 appears to have a bidirectional jet which emanates from the nucleus and interacts with the surrounding interstellar medium. H-alpha + forbidden N II monochromatic photographs and VLA 20 cm and 6 cm radio maps reveal a bright, resolved cloud and an extraordinary ring paired across the nucleus. The spectrophotometry shows that the nuclear emission-line characteristics change abruptly at the edges of the ring and the cloud, and that the cloud has internal velocities larger than the nucleus and a spectrum similar to some galactic supernova remnants. The physical characteristics of the nuclear emission regions are derived and used to discuss the ionization and excitation of the ring and cloud. It is argued that these features have their origin in a jet flowing from the nucleus.