Environmental variation of the low-mass IMF

Abstract

Abstarct We use a series of magnetohydrodynamic simulations including both radiative and protostellar outflow feedback to study environmental variation of the initial mass function. The simulations represent a carefully-controlled experiment whereby we keep all dimensionless parameters of the flow constant except for those related to feedback. We show that radiation feedback suppresses the formation of lower mass objects more effectively as the surface density increases, but this only partially compensates for the decreasing Jeans mass in denser environments. Similarly, we find that protostellar outflows are more effective at suppressing the formation of massive stars in higher surface density environments. The combined effect of these two trends is towards an IMF with a lower characteristic mass and a narrower overall mass range in high surface density environments. We discuss the implications for these findings for the interpretation of observational evidence of IMF variation in early type galaxies.

The Interplay between the Initial Mass Function and Star Formation Efficiency through Radiative Feedback at High Stellar Surface Densities

“…For metallicities that seem to be typical at the highest redshifts where we have reliable estimates, z ∼ 8-10, i.e., Z ∼ 0.1-0.3 Z ☉ (Curti et al 2023;Nakajima et al 2023), and assuming a linear relation between dust-to-gas ratio and metallicity, 13 the SFE is higher for a given Ψ UV and completely counteracts the effects of Ψ UV for highly compact clouds (10 4 M ☉ pc −2 ). Moreover, the nature of the IMF for conditions at z ∼ 10 is highly uncertain, with works suggesting that it could even be bottom-heavy (e.g., Conroy & van Dokkum 2012;Tanvir et al 2022;Tanvir & Krumholz 2024); that being said, these studies probe the IMF in a mass range (1 M ☉ ) that does not contribute to Ψ UV . Even if this scenario were true for the highmass end of the IMF, it would only imply that even more efficient star formation would be required, as Ψ UV would be even lower than with a standard IMF.…”

Star Formation in Self-gravitating Disks in Active Galactic Nuclei. III. Efficient Production of Iron and Infrared Spectral Energy Distributions

“…The protostars are corotating with surrounding gas around the central SMBHs, and thus we neglect possible collisions or mergers after their formation (e.g., Tan 2000). On the other hand, the intensive radiation field of the AGN disk disfavors the formation of very low-mass stars because radiation pressure prevents the ongoing collapse as shown by both analytical studies (Krumholz & McKee 2008) and detailed numerical simulations (e.g., Tanvir et al 2022). Moreover, the high-metallicity environments tend to be the Salpeter (see M which is usually regarded as the typical lifetime of AGNs.…”

The universal variability of the stellar initial mass function probed by the TIMER survey

“…However, the simplicity of a universal IMF faces serious challenges. From a theoretical perspective, it remains unclear as to why, for example, the IMF should or should not depend on the local conditions of the gas from which new stars are formed (Hennebelle & Chabrier 2008;Myers et al 2011;Hopkins 2012;Krumholz 2014;Chabrier et al 2014;Fontanot et al 2018;Guszejnov et al 2019;Davis & van de Voort 2020;Sharda & Krumholz 2022;Tanvir et al 2022). Furthermore, even within the Milky Way, systematic deviations from a universal IMF have been evoked in order to explain the observed properties of Galactic globular clusters (Marks et al 2012).…”