Accurate optical positions of M 82 knots

Accurate optical measurements of bright and dark knots visible in the peculiar galaxy M82, with an optical error of about 0.7 arcsec, are presented. The positions of the intensity peaks of the knots within the galaxy are measured in great detail, and the data are compared with observations at other wavelengths. It is evident that the knotty structure is dominant in the near infrared light and that only a low percentage of the knots are radio emitters both at 3.7 and 6 cm, while a number of radio features remain embedded within or behind the dark clouds present in the system. The origin of the knotted structure can be ascribed to star formation due to a gas infall from M81 during a close encounter which happened some 180 million years ago. An intrinsic mean absolute magnitude of -12.4 is estimated for each of the knots, much brighter than the brightest globular cluster in our galaxy.