アブストラクト：
The conditions of HII regions and the galaxy global properties are physically correlated with each other intricately. Using composite SDSS spectra in the M*-sSFR grid, we measure the gas-phase metallicity Z via the direct method, the electron density n_e, and the ionization parameter U. We find that all the ISM parameters of interest are tightly correlated with sSFR. With simple physically-motivated ansatze, we disentangle the connections between these parameters.