Variations in the Σ_SFRΣ_molΣ_∗plane across galactic environments in PHANGS galaxies

Aims. There exists some consensus that the stellar mass surface density (Σmol) and molecular gas mass surface density (Σmol) are the main quantities responsible for locally setting the star formation rate. This regulation is inferred from locally resolved scaling relations between these two quantities and the star formation rate surface density (ΣSFR), which have been extensively studied in a wide variety of works. However, the universality of these relations is debated. Here, we probe the interplay between these three quantities across different galactic environments at a spatial resolution of 150 pc. Methods. We performed a hierarchical Bayesian linear regression to find the best set of parameters Cmol, Cmol, and Cnorm that describe the star-forming plane conformed by Σmol, Σmol, and ΣSFR, such that logΣSFR = CmollogΣmol + CmollogΣmol + Cnorm. We also explored variations in the determined parameters across galactic environments, focusing our analysis on the Cmol and Cmol slopes. Results. We find signs of variations in the posterior distributions of Cmol and Cmol across different galactic environments. The dependence of ΣSFR on Σmol spans a wide range of slopes, with negative and positive values, while the dependence of ΣSFR on Σmol is always positive. Bars show the most negative value of Cmol (a 0.41), which is a sign of longer depletion times, while spiral arms show the highest Cmol among all environments (0.45). Variations in Cmol also exist, although they are more subtle than those found for Cmol. Conclusions. We conclude that systematic variations in the interplay of Σmol, Σmol, and ΣSFR across different galactic environments exist at a spatial resolution of 150 pc, and we interpret these variations to be produced by an additional mechanism regulating the formation of stars that is not captured by either Σmol or Σmol. Studying environmental variations in single galaxies, we find that these variations correlate with changes in the star formation efficiency across environments, which could be linked to the dynamical state of the gas that prevents it from collapsing and forming stars, or to changes in the molecular gas fraction.