MAXIMALLY STAR-FORMING GALACTIC DISKS. II. VERTICALLY RESOLVED HYDRODYNAMIC SIMULATIONS OF STARBURST REGULATION

Abstract

We explore the self-regulation of star formation using a large suite of high\nresolution hydrodynamic simulations, focusing on molecule-dominated regions\n(galactic centers and [U]LIRGS) where feedback from star formation drives\nhighly supersonic turbulence. In equilibrium the total midplane pressure,\ndominated by turbulence, must balance the vertical weight of the ISM. Under\nself-regulation, the momentum flux injected by feedback evolves until it\nmatches the vertical weight. We test this flux balance in simulations spanning\na range of parameters, including surface density $\\Sigma$, momentum injected\nper stellar mass formed ($p_*/m_*$), and angular velocity. The simulations are\n2D radial-vertical slices, including both self-gravity and an external\npotential that confines gas to the disk midplane. After the simulations reach a\nsteady state in all relevant quantities, including the star formation rate\n$\\Sigma_{SFR}$, there is remarkably good agreement between the vertical weight,\nthe turbulent pressure, and the momentum injection rate from supernovae. Gas\nvelocity dispersions and disk thicknesses increase with $p_*/m_*$. The\nefficiency of star formation per free-fall time at the mid-plane density is\ninsensitive to the local conditions and to the star formation prescription in\nvery dense gas. We measure efficiencies $\\sim$0.004-0.01, consistent with low\nand approximately constant efficiencies inferred from observations. For\n$\\Sigma\\in$(100--1000) \\msunpc, we find $\\Sigma_{SFR}\\in$(0.1--4) \\sfrunits,\ngenerally following a $\\Sigma_{SFR}\\propto \\Sigma^2$ relationship. The measured\nrelationships agree very well with vertical equilibrium and with turbulent\nenergy replenishment by feedback within a vertical crossing time. These\nresults, along with the observed $\\Sigma_{SFR}-\\Sigma$ relation in high density\nenvironments, provide strong evidence for the self-regulation of star\nformation.\n