Formation of carbon-enhanced metal-poor stars in the presence of far ultraviolet radiation

TL;DR

This study uses cosmological simulations to explore how far-ultraviolet radiation influences the formation of carbon-enhanced metal-poor stars, revealing that metals impact collapse more than radiation and that UV flux can delay star formation.

Contribution

First cosmological simulations with detailed chemical networks including primordial and metal species to study formation of carbon-enhanced metal-poor stars under UV radiation.

Findings

UV flux delays collapse from z=21 to z=15 at low metallicity

Metals have a stronger effect on collapse than radiation

Radiative backgrounds do not delay collapse at higher metallicity or carbon abundance

Abstract

Recent discoveries of carbon-enhanced metal-poor stars like SMSS J031300.36-670839.3 provide increasing observational insights into the formation conditions of the first second-generation stars in the Universe, reflecting the chemical conditions after the first supernova explosion. Here, we present the first cosmological simulations with a detailed chemical network including primordial species as well as C, C$^+$, O, O$^+$, Si, Si$^+$, and Si$^{2+}$ following the formation of carbon-enhanced metal poor stars. The presence of background UV flux delays the collapse from $z=21$ to $z=15$ and cool the gas down to the CMB temperature for a metallicity of Z/Z$_\odot$=10$^{-3}$. This can potentially lead to the formation of lower mass stars. Overall, we find that the metals have a stronger effect on the collapse than the radiation, yielding a comparable thermal structure for large variations in the radiative background. We further find that radiative backgrounds are not able to delay the collapse for Z/Z$_\odot$=10$^{-2}$ or a carbon abundance as in SMSS J031300.36-670839.3.