Pop. III stars from turbulent fragmentation at redshift ~ 11

TL;DR

This simulation study reveals that turbulent fragmentation in early universe halos at redshift ~11 leads to the formation of multiple dense clumps, potentially resulting in Population III stars with characteristic masses around 50 solar masses.

Contribution

First detailed cosmological simulation including non-equilibrium chemistry showing turbulent fragmentation as a dominant Pop. III star formation mode at high redshift.

Findings

Approximately 25 gravitationally unstable clumps identified.

Clump masses range from 4,000 to 900,000 solar masses.

Clumps may fragment into stars around 50 solar masses.

Abstract

We report results from a cosmological simulation with non-equilibrium chemistry of 21 species, including H2, HD, and LiH molecular cooling. Starting from cosmological initial conditions, we focus on the evolution of the central 1.8 Kpc region of a 3 x 10^7 Msun halo. The crossing of a few 10^6 Msun halos and the gas accretion through larger scale filaments generate a turbulent environment within this region. Due to the short cooling time caused by the non-equilibrium formation of H2, the supersonic turbulence results in a very fragmented mass distribution, where dense, gravitationally unstable clumps emerge from a complex network of dense filaments. At z=10.87, we find approximately 25 well defined, gravitationally unstable clumps, with masses of 4 x 10^3-9 x 10^5 Msun, temperatures of approximately 300K, and cooling times much shorter than the free-fall time. Only the initial phase of the collapse of individual clumps is spatially resolved in the simulation. Depending on the density reached in the collapse, the estimated average Bonnor-Ebert masses are in the range 200-800 Msun. We speculate that each clump may further fragment into a cluster of stars with a characteristic mass in the neighborhood of 50 Msun. This process at z ~ 11 may represent the dominant mode of Pop. III star formation, causing a rapid chemical enrichment of the protogalactic environment.