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ABSTRACT One of the key mysteries of star formation is the origin of the stellar initial mass function (IMF). The IMF is observed to be nearly universal in the Milky Way and its satellites, and significant variations are only inferred in extreme environments, such as the cores of massive elliptical galaxies and the Central Molecular Zone. In this work, we present simulations from the STARFORGE project that are the first cloud-scale radiation-magnetohydrodynamic simulations that follow individual stars and include all relevant physical processes. The simulations include detailed gas thermodynamics, as well as stellar feedback in the form of protostellar jets, stellar radiation, winds, and supernovae. In this work, we focus on how stellar radiation, winds, and supernovae impact star-forming clouds. Radiative feedback plays a major role in quenching star formation and disrupting the cloud; however, the IMF peak is predominantly set by protostellar jet physics. We find that the effect of stellar winds is minor, and supernovae ‘occur too late’ to affect the IMF or quench star formation. We also investigate the effects of initial conditions on the IMF. We find that the IMF is insensitive to the initial turbulence, cloud mass, and cloud surface density, even though these parameters significantly shape the star formation history of the cloud, including the final star formation efficiency. Meanwhile, the characteristic stellar mass depends weakly on metallicity and the interstellar radiation field, which essentially set the average gas temperature. Finally, while turbulent driving and the level of magnetization strongly influence the star formation history, they only influence the high-mass slope of the IMF.
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This content will become publicly available on November 25, 2026
The Stellar Content of NGC 3603 Revisited: Is the IMF Top Heavy? ∗
Abstract Studies of the resolved stellar populations of young massive clusters have shown that the slope of the initial mass function (IMF) appears to be the same everywhere, with no dependence on stellar density or metallicity. At the same time, studies of integrated properties of galaxies usually conclude that the IMF does vary and must be top-heavy in starburst regions. In order to investigate this, we have carried out a long-term project to characterize the massive-star content of NGC 3603, the nearest giant Hiiregion, known to have a rich population of massive stars. We used both ground-based and Hubble Space Telescope (HST) imaging to obtain photometry, and we employed Gaia to establish membership. We obtained spectra of 128 stars using the Magellan 6.5 m telescope and HST, and we combine these data to produce a reddening map. After analyzing the data in the same way as we have for 25 other star-forming regions in the Milky Way and the Magellanic Clouds, we find that the IMF slope of NGC 3603 is quite normal compared to other clusters, with Γ = −0.9 ± 0.1. If anything, there are fewer very high mass (>65M⊙) stars than one would expect by extrapolation from lower masses. This slope is also indistinguishable from what several studies have shown for R136 in the LMC, an even richer region. We speculate that the depreciation of the highest-mass bins in NGC 3603, but not in R136, may indicate that it is harder to form extremely massive stars at the higher metallicity of the Milky Way compared to that of the LMC.
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- PAR ID:
- 10655036
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 994
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 176
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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