Can we indirectly prove the existence of Pair Instability SuperNovae?
The chemical fingerprints of the first stars are retained within the photospheres of ancient unevolved metal-poor stars. A significant fraction of these stellar fossils is represented by stars known as Carbon-Enhanced Metal-Poor (CEMP), [C/Fe]>+0.7[C/Fe]>+0.7 and [Fe/H]<−2[Fe/H]<−2, which are likely imprinted by low-energy primordial supernovae. These CEMP stars are largely observed in the Galactic halo and ultra-faint dwarf galaxies, with values reaching [C/Fe]=+4.5[C/Fe]=+4.5. The Galactic bulge is predicted to host the oldest stars, but it shows a striking dearth of CEMP stars with [C/Fe]≳+2.0[C/Fe]≳+2.0.
We suggest that the dearth of CEMP stars with high [C/Fe][C/Fe] is not due to the low statistics of observed metal-poor stars but is the result of the different formation process of the bulge. N-body simulations show that the first star-forming halos which end up in the bulge are characterized by the highest star-formation rates. These rates enable the formation of rare massive first stars exploding as pair-instability supernovae (PISNe), which wash out the signature of primordial faint supernovae.
demonstrate that the mean [C/Fe] of first stars polluted environments decreases with the increasing contribution of PISNe, and thus with the characteristic mass of the first stars. We conclude that the dearth of C-enhanced metal-poor stars in the Galactic bulge indirectly probes the existence of elusive PISNe, and propose a novel method which exploits this lack to constrain the mass distribution of the first stars.
Pagnini, Salvadori, Rossi, Aguado, Koutsouridou, Skuladottir 2023, MNRAS