2014ApJ...797..134S

We mapped 3 mm continuum and line emission from the starburst galaxy M82 using the Combined Array for Research in Millimeter-wave Astronomy. We targeted the HCN, HCO⁺, HNC, CS, and HC₃ N lines, but here we focus on the HCN and HCO⁺ emission. The map covers a field of 1.'2 with an ~5'' resolution. The HCN and HCO⁺ observations are short spacings corrected. The molecular gas in M82 had been previously found to be distributed in a molecular disk, coincident with the central starburst, and a galactic scale outflow which originates in the central starburst. With the new short spacings-corrected maps we derive some of the properties of the dense molecular gas in the base of the outflow. From the HCN and HCO⁺ J = (1-0) line emission, and under the assumptions of the gas being optically thin and in local thermodynamic equilibrium, we place lower limits on the amount of dense molecular gas in the base of the outflow. The lower limits are 7x10⁶ M_☉and 21x10⁶ M_☉, or ≳ 2% of the total molecular mass in the outflow. The kinematics and spatial distribution of the dense gas outside the central starburst suggests that it is being expelled through chimneys. Assuming a constant outflow velocity, the derived outflow rate of dense molecular gas is ≥ 0.3 M_☉/yr, which would lower the starburst lifetime by ≥ 5%. The energy required to expel this mass of dense gas is (1-10)x10⁵² erg.