%0 Journal Article %T Variations of the Stellar Initial Mass Function in the Progenitors of Massive Early-type Galaxies and in Extreme Starburst Environments %+ Centre de Recherche Astrophysique de Lyon (CRAL) %+ Institut d'Astrophysique de Paris (IAP) %A Chabrier, Gilles %A Hennebelle, Patrick %A Charlot, Stéphane %< avec comité de lecture %@ 0004-637X %J The Astrophysical Journal %I American Astronomical Society %V 796 %8 2014 %D 2014 %Z 1409.8466 %Z 2014ApJ...796...75C %R 10.1088/0004-637X/796/2/75 %K galaxies: evolution %K galaxies: stellar content %K ISM: clouds %K stars: formation %K turbulence %K Astrophysics - Astrophysics of Galaxies %Z Sciences of the Universe [physics]Journal articles %X We examine variations of the stellar initial mass function (IMF) in extreme environments within the formalism derived by Hennebelle & Chabrier. We focus on conditions encountered in progenitors of massive early-type galaxies and starburst regions. We show that, when applying the concept of turbulent Jeans mass as the characteristic mass for fragmentation in a turbulent medium, the peak of the IMF in such environments is shifted toward smaller masses, leading to a bottom-heavy IMF, as suggested by various observations. In very dense and turbulent environments, we predict that the high-mass tail of the IMF can become even steeper than the standard Salpeter IMF, with a limit for the power-law exponent α ~= -2.7, in agreement with recent observational determinations. This steepening is a direct consequence of the high densities and Mach values in such regions but also of the time dependence of the fragmentation process, as incorporated in the Hennebelle-Chabrier theory. We provide analytical parameterizations of these IMFs in such environments to be used in galaxy evolution calculations. We also calculate the star-formation rates and the mass-to-light ratios expected under such extreme conditions and show that they agree well with the values inferred in starburst environments and massive high-redshift galaxies. This reinforces the paradigm of star formation as being a universal process, i.e., the direct outcome of gravitationally unstable fluctuations in a density field initially generated by large-scale, shock-dominated turbulence. This globally enables us to infer the variations of the stellar IMF and related properties for atypical galactic conditions. %G English %L insu-03645240 %U https://insu.hal.science/insu-03645240 %~ ENS-LYON %~ INSU %~ CNRS %~ UNIV-LYON1 %~ CRAL %~ IAP %~ SORBONNE-UNIVERSITE %~ SU-INF-2018 %~ SU-SCIENCES %~ UDL %~ UNIV-LYON %~ SU-TI %~ ALLIANCE-SU