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We have combined observations of the Antennae galaxies from the radiointerferometer ALMA (Atacama Large Millimeter/submillimeter Array) and from theoptical interferometer GH$\alpha$FaS (Galaxy H$\alpha$ Fabry-Perot System). Thetwo sets of observations have comparable angular and spectral resolutions,enabling us to identify 142 giant molecular clouds (GMCs) and 303 HII regions.We have measured, and compared, their basic physical properties (radius,velocity dispersion, luminosity). For the HII regions, we find two physicalregimes, one for masses $>10^{5.4} \mathrm{M_{\odot}}$ of ionized gas, wherethe gas density increases with gas mass, the other for masses $<10^{5.4}\mathrm{M_{\odot}}$ of ionized gas, where the gas density decreases with gasmass. For the GMCs, we find, in contrast to previous studies in other galaxiesover a generally lower mass range of clouds, that the gas surface densityincreases with the radius, hinting at two regimes for these clouds if weconsider both sources of data. We also find that the GMC mass function has abreak at $10^{6.7}\mathrm{M_{\odot}}$. Using the velocity dispersionmeasurements, we claim that the difference between the regimes is the nature ofthe dominant binding force. For the regions in the lower mass range, thedominant force is the external pressure, while in the higher mass range it isthe internal gravity of the clouds. In the regime where gravity is dominant,the star formation rate, derived from the dust-corrected H$\alpha$ luminosity,increases super-linearly with the velocity dispersion, and the gas densityincreases with the gas mass.

Two physical regimes for the Giant HII Regions and Giant Molecular Clouds in the Antennae Galaxies