Variations in the Σ_SFR − Σ_mol − Σ_⋆ plane across galactic environments in PHANGS galaxies

I. Pessa , E. Schinnerer , A. K. Leroy , E. W. Koch , E. Rosolowsky , T. G. Williams , H. -A. Pan , A. Schruba , A. Usero , F. Belfiore , F. Bigiel , G. A. Blanc , M. Chevance , D. Dale , E. Emsellem (1) , J. Gensior , S. C. O. Glover , K. Grasha , B. Groves , R. S. Klessen , K. Kreckel , J. M. D. Kruijssen , D. Liu , S. E. Meidt , J. Pety (2) , M. Querejeta , T. Saito , P. Sanchez-Blazquez , E. J. Watkins

1 CRAL - Centre de Recherche Astrophysique de Lyon
2 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique

Aims: There exists some consensus that the stellar mass surface density (Σ_⋆) and molecular gas mass surface density (Σ_mol) 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 (Σ_SFR), 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 C_⋆, C_mol, and C_norm that describe the star-forming plane conformed by Σ_⋆, Σ_mol, and Σ_SFR, such that logΣ_SFR = C_⋆logΣ_⋆ + C_mollogΣ_mol + C_norm. We also explored variations in the determined parameters across galactic environments, focusing our analysis on the C_⋆ and C_mol slopes.
Results: We find signs of variations in the posterior distributions of C_⋆ and C_mol across different galactic environments. The dependence of Σ_SFR on Σ_⋆ spans a wide range of slopes, with negative and positive values, while the dependence of Σ_SFR on Σ_mol is always positive. Bars show the most negative value of C_⋆ (−0.41), which is a sign of longer depletion times, while spiral arms show the highest C_⋆ among all environments (0.45). Variations in C_mol also exist, although they are more subtle than those found for C_⋆.
Conclusions: We conclude that systematic variations in the interplay of Σ_⋆, Σ_mol, and Σ_SFR 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 Σ_⋆ or Σ_mol. 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.

Mots clés: galaxies: evolution; galaxies: star formation; galaxies: general; Astrophysics - Astrophysics of Galaxies

Domaines: Planète et Univers [physics]; Astrophysique [astro-ph]

I. Pessa, E. Schinnerer, A. K. Leroy, E. W. Koch, E. Rosolowsky, et al.. Variations in the Σ_SFR − Σ_mol − Σ_⋆ plane across galactic environments in PHANGS galaxies. Astronomy and Astrophysics - A&A, 2022, 663, ⟨10.1051/0004-6361/202142832⟩. ⟨insu-03777344⟩