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.