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

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 cosmic microwave background temperature for a metallicity of Z/Z_⊙ = 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_⊙ = 10^-2 or a carbon abundance as in SMSS J031300.36-670839.3.