https://arxiv.org/abs/1807.09949
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Abstract: The birth of stars and the formation of galaxies are cornerstones of modern astrophysics. While much is known about how galaxies globally and their stars individually form and evolve, one fundamental property that affects both remains elusive. This is problematic because this key property, the birth mass distribution of stars, referred to as the stellar initial mass function (IMF), is a key tracer of the physics of star formation that underpins almost all of the unknowns in galaxy and stellar evolution. It is perhaps the greatest source of systematic uncertainty in star and galaxy evolution. A star’s initial mass determines its luminosity, lifetime, and eventual return of material enriched by nuclear fusion back to the interstellar medium to be incorporated in later generations of stars. The distribution of stellar masses created in star formation events therefore determines the evolution of galaxies over cosmic time, and accurately measuring it is crucial. The past decade has seen a growing number and variety of methods for measuring or inferring the shape of the IMF, along with progressively more detailed simulations, paralleled by refinements in the way the concept of the IMF is applied or conceptualised on different physical scales. This range of approaches and evolving definitions of the quantity being measured has in turn led to conflicting conclusions regarding whether or not the IMF is universal. Here I review and compare the growing wealth of approaches to our understanding of this fundamental property that defines so much of astrophysics. I summarise the observational measurements from stellar analyses, extragalactic studies and cosmic constraints, and highlight the importance of considering potential IMF variations, reinforcing the need for measurements to quantify their scope and uncertainties carefully, in order for this field to progress. I present a new framework to aid the discussion of the IMF and promote clarity in the further development of this fundamental field.
Keywords : stars: formation – stars: luminosity function, mass function – galaxies: evolution – galaxies: formation – galaxies: star formation
The Dawes Reviews are substantial reviews of topical areas in astronomy, published by authors of international standing at the invitation of the PASA Editorial Board. The reviews recognise William Dawes (1762-1836), second lieutenant in the Royal Marines and the astronomer on the First Fleet. Dawes was not only an accomplished astronomer, but spoke five languages, had a keen interest in botany, mineralogy, engineering, cartography and music, compiled the first Aboriginal-English dictionary, and was an outspoken opponent of slavery.
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