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Abstract

Observations have revealed a bimodality in galaxy properties such as color and morphology leading to a fundamental classification into passive red galaxies and star-forming blue galaxies, where the latter follow a tight correlation between their stellar mass and their star formation rate (SFR), known as star formation main sequence (SFMS). In this thesis, I use a sample of star-forming galaxies from the multi-wavelength Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey to study the physics that regulate the formation of stars and keep these galaxies on the SFMS, as well as to investigate how they have assembled their stellar mass, and thus, unveil their evolution through cosmic times. The PHANGS survey allows us to perform these analyses, for the first time, at a spatial resolution of ∼ 100 pc, thus, resolving individual star-forming regions and galactic morphological features. I find that correlations between stellar mass surface density (Σ∗), molecular gas sur face density (Σmol), and SFR surface density (ΣSFR) hold at these spatial scales, albeit with an increased scatter compared to lower-resolution measurements. The correlation between Σmol and ΣSFR is the most homogeneous across different galaxies and galactic environments indicating that the amount of molecular gas is regulating the formation of stars. The interplay between Σ∗, Σmol , and ΣSFR reveals significant variations across individual galactic environments implying that an additional mechanism(s) not captured by either Σ∗ or Σmol is playing a role in setting the level of SFR. Analysis of the age and metallicity distributions of the stars across the galaxies shows negative stellar age and metallicity gradients, consistent with an inside-out growth scenario. A clear dependency of the stellar velocity dispersion on age is present in the galaxies, where younger stellar populations at any given radius have lower velocity dispersion than older stars. Variations of the time-averaged SFR across the galactic disk reveal a diffusion of the galactic structure with lookback time – consistent with the progressive dynamical heating of young stellar populations through interactions with molecular gas and/or non-axisymmetric galactic features. The results presented in this thesis show how local processes shape the evolution of galaxies, driving the formation of stars, and modulating the local star formation histories across the galactic disk of nearby galaxies.