The Relative Importance of Thermal Gas, Radiation, and Magnetic Pressures Around Star-Forming Regions in Normal Galaxies and Dusty Starbursts

Abstract

In this paper, an investigation on the relative importance of the thermal gas, radiation, and (minimum-energy) magnetic pressures around $\approx$200 star-forming regions in a sample of nearby normal and luminous infrared galaxies is presented. Given the range of galaxy distances, pressure estimates are made on spatial scales spanning $\sim$0.1$-3$kpc. The ratio of thermal gas-to-radiation pressures does not appear to significantly depend on star formation rate surface density ($\Sigma_{\rm SFR}$), but exhibits a steady decrease with increasing physical size of the aperture over which the quantities are measured. The ratio of magnetic-to-radiation pressures appears to be relatively flat as a function of $\Sigma_{\rm SFR}$ and similar in value for both nuclear and extranuclear regions, but unlike the ratio of thermal gas-to-radiation pressures, exhibits a steady increase with increasing aperture size. Furthermore, it seems that the magnetic pressure is typically weaker than the radiation pressure on sub-kpc scales, and only starts to play a significant role on few-kpc scales. When the internal pressure terms are summed, their ratio to the ($\Sigma_{\rm SFR}$-inferred) kpc-scale dynamical equilibrium pressure estimates is roughly constant. Consequently, it appears that the physical area of the galaxy disk, and not necessarily environment (e.g., nuclear vs. extranuclear regions) or star formation activity, may play the dominant role in determining which pressure term is most active around star-forming regions. These results are consistent with a scenario in which a combination of processes acting primarily on different physical scales work collectively to regulate the star formation process in galaxy disks.