Transition of the initial mass function in the metal-poor environments

Abstract

We study star cluster formation in a low-metallicity environment using three dimensional hydrodynamic simulations. Starting from a turbulent cloud core, we follow the formation and growth of protostellar systems with different metallicities ranging from 10 −6 to 0.1 Z . The cooling induced by dust grains promotes fragmentation at small scales and the formation of low-mass stars with M * ∼ 0.01-0.1 M when Z/Z 10 −5 . While the number of low-mass stars increases with metallicity, the stellar mass distribution is still top-heavy for Z/Z 10 −2 compared to the Chabrier initial mass function (IMF). In these cases, star formation begins after the turbulent motion decays and a single massive cloud core monolithically collapses to form a central massive stellar system. The circumstellar disk preferentially feeds the mass to the central massive stars, making the mass distribution top-heavy. When Z/Z = 0.1, collisions of the turbulent flows promote the onset of the star formation and a highly filamentary structure develops owing to efficient fine-structure line cooling. In this case, the mass supply to the massive stars is limited by the local gas reservoir and the mass is shared among the stars, leading to a Chabrier-like IMF. We conclude that cooling at the scales of the turbulent motion promotes the development of the filamentary structure and works as an important factor leading to the present-day IMF.

Properties of High-Redshift GRBs

“…where we vary f IMF from 0-0.4 and vary z 0 from 2.5 to 9. A z 0 = 2.5 − 5 assumes a flattening of the IMF much earlier than expected in simulations but in line with more recent results (Chon et al 2021). As we shall see in our comparison to GRB observations, either this is required or a drastic change in the currently-predicted star history at high redshift (or both) is necessary.…”

“…In general, it is believed that, until the metallicity is very low, metaldriven cooling is sufficiently efficient to minimize the effect on the initial mass function. However, more recent studies argue that there is significant flattening of the IMF at a metallicity between 0.01 − 0.1z (Chon et al 2021) corresponding to a redshift of 2.5-5 (see Section 2.3.3).…”

Far and extreme UV radiation feedback in molecular clouds and its influence on the mass and size of star clusters

“…Turbulent motions can contribute to the heating of gas via shock. At 𝑛 H 10 2 cm −3 , that is higher than the initial number density of the clouds, the gas is in the high temperature states (e.g., Chon et al 2021). At 𝑡 ∼ 𝑡 ff , stars start to form in the high-density gas, and their radiative feedback alters the distributions in the 𝑛 H − 𝑇 plane.…”

Deciphering stellar metallicities in the early Universe: Case study of a young galaxy at z = 4.77 in the MUSE eXtremely Deep Field

“…In the metallicity range [Z/H] −2 it is theoretically expected that the IMF is top-heavy compared to the Chabrier IMF (e.g. Chon et al 2021). As detailed in Stanway & Eldridge (2019), the number of ionising photons can vary by an order of magnitude when changing the upper mass or the slope of the IMF.…”