Spatially Resolved Spectroscopic Properties of Low-Redshift Star-Forming Galaxies

I review the spatially resolved spectroscopic properties of low-redshift star-forming galaxies (and their retired counterparts) using results from the most recent optical integral field spectroscopy galaxy surveys. First, I briefly summarize the global spectroscopic properties of these galaxies, discussing the main ionization processes and the global relations described by the star-formation rates, gas-phase oxygen abundances, and average properties of their stellar populations (age and metallicity) in comparison with the stellar mass. Second, I present the local distribution of the ionizing processes down to kiloparsec scales, and I show how the global scaling relations found using integrated parameters (like the star-formation main sequence, mass–metallicity relation, and Schmidt–Kennicutt law) have local/resolved counterparts, with the global ones being, for the most part, just integrated/average versions of the local ones. I discuss the local/resolved star-formation histories (SFHs) and chemical-enrichment histories and their implications on the inside-out growth of galaxies. Third, I present the radial distributions of the surface densities of the properties explored globally and how they depend on the integrated galaxy properties. In conclusion, I find that the evolution of galaxies is mostly governed by local processes but clearly affected by global ones: ▪ Many global scaling relations present resolved counterparts (verified down to kiloparsec scales) that can explain them as well as the observed radial gradients in galaxies. ▪ These relations are consequences of the local SFHs, the narrow range of the depletion times, and a local metal enrichment. ▪ Deviations from these relations are due to dynamical and mixing processes, local exchange of gas (inflows, outflows, and fountains), depletion time differences, and/or differences in the resolved SFHs. ▪ Ionization happens at local scales that may be driven by different physical processes, and it cannot be clearly understood using purely integrated quantities. The dominant ionization in galaxies has a stellar origin.