The Impact of Feedback in Massive Star Formation. II. Lower Star Formation Efficiency at Lower Metallicity

TL;DR

This study models massive star formation across various metallicities, revealing feedback processes and their influence on star formation efficiency, especially highlighting the rarity of massive stars in extremely metal-poor environments.

Contribution

It provides a comprehensive theoretical analysis of feedback mechanisms affecting star formation efficiency at different metallicities, emphasizing the roles of outflows and photoevaporation.

Findings

Magneto-centrifugal outflows dominate feedback at solar metallicity.

Radiation pressure has minor impact even for stars over 100 solar masses.

Massive stars are less common in environments with metallicity below 1e-3Zsun.

Abstract

We conduct a theoretical study of the formation of massive stars over a wide range of metallicities from 1e-5 to 1Zsun and evaluate the star formation efficiencies (SFEs) from prestellar cloud cores taking into account multiple feedback processes. Unlike for simple spherical accretion, in the case of disk accretion feedback processes do not set upper limits on stellar masses. At solar metallicity, launching of magneto-centrifugally-driven outflows is the dominant feedback process to set SFEs, while radiation pressure, which has been regarded to be pivotal, has only minor contribution even in the formation of over-100Msun stars. Photoevaporation becomes significant in over-20Msun star formation at low metallicities of <1e-2Zsun, where dust absorption of ionizing photons is inefficient. We conclude that if initial prestellar core properties are similar, then massive stars are rarer in extremely metal-poor environments of 1e-5 - 1e-3Zsun. Our results give new insight into the high-mass end of the initial mass function and its potential variation with galactic and cosmological environments.