The role of faint population III supernovae in forming CEMP stars in ultra-faint dwarf galaxies

CEMP-no stars, a subset of carbon enhanced metal poor (CEMP) stars ($\rm [C/Fe]\geq0.7$and$\rm [Fe/H]\lesssim-1$) have been discovered in ultra-faint dwarf (UFD) galaxies, with $M_{\mathrm{v}\mathrm{i}\mathrm{r}}\sim {10}^8$ Msun and $M_{\ast }\sim {10}^3-{10}^4$ Msun at $z=0$, as well as in the halo of the Milky Way (MW). These CEMP-no stars are local fossils that may reflect the properties of the first (Pop~III) and second (Pop~II) generation of stars. However, cosmological simulations have struggled to reproduce the observed level of carbon enhancement of the known CEMP-no stars. Here we present new cosmological hydrodynamic zoom-in simulations of isolated UFDs that achieve a gas mass resolution of $m_{\mathrm{g}\mathrm{a}\mathrm{s}}\sim 60$ Msun. We include enrichment from Pop~III faint supernovae (SNe), with $E_{\mathrm{S}\mathrm{N}}=0.6\times {10}^{51}$ erg, to understand the origin of CEMP-no stars. We confirm that Pop~III and Pop~II stars are mainly responsible for the formation of CEMP and C-normal stars respectively. New to this study, we find that a majority of CEMP-no stars in the observed UFDs and the MW halo can be explained by Pop~III SNe with normal explosion energy ($E_{\mathrm{S}\mathrm{N}}=1.2\times {10}^{51}$~erg) and Pop~II enrichment, but faint SNe might also be needed to produce CEMP-no stars with $[\mathrm{C}\mathrm{/}\mathrm{F}\mathrm{e}]\gtrsim 2$, corresponding to the absolute carbon abundance of $\mathrm{A}(\mathrm{C})\gtrsim 6.0$. Furthermore, we find that while we create CEMP-no stars with high carbon ratio $[\mathrm{C}\mathrm{/}\mathrm{F}\mathrm{e}]\approx 3-4$, by adopting faint SNe, it is still challenging to reproduce CEMP-no stars with extreme level of carbon abundance of $\rm A©\approx 7.0-7.5$, observed both in the MW halo and UFDs.