In this work we present the first complete CO J=3-2 map of M 81, observed as part of the Nearby Galaxies Legacy Survey. M 81 is a nearby spiral galaxy (3.64 Mpc) known for hosting a high level of star formation. Previous studies, mainly in the J=1-0 line, have found little CO. The CO measured in a galaxy allows, through an empirical conversion factor, to know its content of molecular hydrogen.
We have detected nine regions of important emission in the CO J=3-2 line, located at different regions of the spiral arm and confirmed that the global CO emission is low. Using a new Halpha map obtained with the Isaac Newton Telescope, located on the island of La Palma, and archival data, we discuss the correlation between the molecular hydrogen traced by the CO and regions of star formation.
By using the theoretical model presented by Irwin et al. (2010) we determine that the density of the molecular gas detected is in the range from 1000 to 10000 particles per cubic centimeter.
We conclude that the interaction between the molecular gas and the star formation in M 81 is complex and not well explained yet. This work, however, opens a door to new studies to understand the recent evolution of this galaxy.