M33 CO(2-1) and HI integrated intensity maps

The HI 21cm VLA archive observations were reduced, and the mosaic was imaged and cleaned using the multi-scale task in the CASA software package, yielding a series of datacube with resolutions ranging from 5" to 25". The HI mass within a radius of 8.5kpc is estimated to be 1.4x10^9^. The azimuthally averaged CO surface brightness decreases exponentially with a scale length of 1.9+/-0.1kpc whereas the atomicgas surface density is constant at {Sigma}_HI_=6+/-2pc^-2^ deprojected to face-on.

For an (H_2_)/I_CO_(1-0) conversion factor twice that of the Milky Way, the central kiloparsec H2 surface density is {Sigma}_HI_=8.5+/-0.2pc^-2^. The star formation rate per unit moecular gas (SF efficiency, the rate of transformation of molecular gas into stars), as traced by the ratio of CO to H{alpha} and FIR brightness, is constant with radus. The SFE, with a N(H2)/I_CO_(1-0) factor twice galactic, appears 2-4 times greater than for large spiral galaxies.

A morphological comparison of molecular and atomic gas with tracers of star formation is presented showing good agreement between these maps both in terms of peaks and holes. A few exceptions are noted. Several spectra, including those of a molecular cloud situated more than 8kpc from the galaxy center, are presented.