Star formation laws, like i.e. the Schmidt law relating star formation rate and total gas density, have been studied in several spiral galaxies but the underlying physics are not yet well understood. M51, as a nearby face-on, grand design spiral gala
xy studied in many line transitions, is an ideal target to study the connection between physical conditions of the gas and star formation activity. In this contribution we combine molecular, atomic, total gas and stellar surface densities and study the gravitational stability of the gas (Schuster et al.2007, Hitschfeld et al. in prep.). From our IRAM-30m 12 CO2-1 map and complementary HI-, Radio Continuum- and ACS-HST B-band-data we derive maps of the total gas density and the stellar surface density to study the gravitational stability of the gas via the Toomre Q parameter.
