HR-pyPopStar. II. High-spectral-resolution evolutionary synthesis models, low-metallicity expansion, and the properties of the stellar populations of dwarf galaxies

Low-metallicity stellar populations are very abundant in the Universe, either as the remnants of the past history of the Milky Way or similar spiral galaxies, or the young low-metallicity stellar populations that are being observed in the local dwarf galaxies or in the high-z objects with low metal content recently found with JWST. Our goal is to develop new high-spectral-resolution models tailored for low-metallicity environments and apply them to the analysis of stellar population data, particularly in cases in which a significant portion of the stellar content exhibits low metallicity. We used the state-of-the-art stellar population synthesis code HR-pyPopStar with available stellar libraries to create a new set of models focused on low-metallicity stellar populations. We compared the new spectral energy distributions with the previous models of HR-pyPopStar for solar metallicity. Once we verified that the spectra, except for the oldest ones that show some differences in the molecular bands of the TiO and G band, are similar, we re-analysed the high-resolution data from the globular cluster M 15 by finding a better estimate of its age and metallicity. Finally, we analysed a sub-sample of mostly star-forming dwarf galaxies from the MaNGA survey, we found a similar stellar mass-mean stellar metallicity weighted by light to other studies that studied star-forming dwarf galaxies and a slightly higher mean stellar metallicity than the other works that analysed all types of dwarf galaxies at the same time, but that are within the error bars.