Study On The Spectra Of H_? Region And Gas Cooling Functions

We use MAPPINGS III photoionization code to study H ? regions ionized by radiation fields emitted by intermediate-age stellar populations (SPs) including binary systems and the impacts of ?-enhancement on cooling functions.H ? region is a region of interstellar atomic hydrogen that is ionized. Radia-tion fields emitted by O- and B-type stars or young SPs are generally considered as significant central ionizing sources of classic H II regions. In this work,we present photoionization models of H ? regions ionized by radiation fields emitted by SPs including binary systems. H ? regions ionized by radiation fields emitted by intermediate-age SPs including binary systems can produce most line ratios observed, but can't produce observed equivalent widths.The plasma cooling functions plays an important role in understanding the formation and evolution of galaxies, it determines how much gas eventually forms stars. The scaled-solar mixture is usually adopted in the galaxy evolution model,but the cooling functions for the scaled-solar mixture may cause overestima-tion or underestimation cooling contributed by some elements. In this work,MAPPINGS III photoionization model is used to calculate the cooling functions for scaled-solar mixture and ?-enhanced mode, and we discussed the impact of?-enhancement for collisional ionization equilibrium (CIE) and nonequilibrium(NEQ) cooling. The results show that the cooling efficiencies increase at the oxygen-dominated temperature (T ? 105.0 - 105.5 K) and decrease at the iron-dominated temperature (T ? 106.0 - 106.5 K) in the case of ?-enhancement. Due to recombination lags, cooling is less efficient for NEQ than CIE. At the oxygen-dominated temperature, the cooling is more efficient, and departures from equi-librium are larger in the case of ?-enhancement, so that the differences of cooling peak values between alpha-enhanced case and scaled-solar case is smaller than that in CIE assumption.