The Star Formation Relation in Nearby Galaxies

TL;DR

This review synthesizes recent multi-wavelength observations of star formation in nearby galaxies, highlighting how molecular gas correlates with star formation rates and how environmental factors influence this process across different galaxy regions.

Contribution

It provides a comprehensive overview of observational data linking molecular gas properties to star formation across diverse galactic environments.

Findings

Star formation correlates with molecular gas in galaxy disks.

Galaxy centers and starbursts show enhanced star formation efficiency.

Outer disks and dwarf galaxies have limited star formation due to atomic gas availability.

Abstract

I review observational studies of the large-scale star formation process in nearby galaxies. A wealth of new multi-wavelength data provide an unprecedented view on the interplay of the interstellar medium and (young) stellar populations on a few hundred parsec scale in 100+ galaxies of all types. These observations enable us to relate detailed studies of star formation in the Milky Way to the zoo of galaxies in the distant universe. Within the disks of spiral galaxies, recent star formation strongly scales with the local amount of molecular gas (as traced by CO) with a molecular gas depletion time of ~2 Gyr. This is consistent with the picture that stars form in giant molecular clouds that have about universal properties. Galaxy centers and starbursting galaxies deviate from this normal trend as they show enhanced star formation per unit gas mass suggesting systematic changes in the molecular gas properties and especially the dense gas fraction. In the outer disks of spirals and in dwarf galaxies, the decreasing availability of atomic gas inevitably limits the amount of star formation, though with large local variations. The critical step for the gas-stars circle seems therefore the formation of a molecular gas phase that shows complex dependencies on various environmental properties and are nowadays investigated by intensive simulational work.