The Initial Mass Function of the First Stars Inferred from Extremely Metal-poor Stars

Abstract

We compare elemental abundance patterns of ∼ 200 extremely metal-poor (EMP; [Fe/H]< −3) stars with supernova yields of metal-free stars in order to obtain insights into the characteristic masses of the first (Population III or Pop III) stars in the Universe. Supernova yields are prepared with nucleosynthesis calculations of metal-free stars with various initial masses (M =13, 15, 25, 40 and 100 M ⊙ ) and explosion energies (E 51 = E/10 51 [erg]= 0.5 − 60) to include low-energy, normal-energy, and high-energy explosions. We adopt the mixing-fallback model to take into account possible asymmetry in the supernova explosions and the yields that best-fit the observed abundance patterns of the EMP stars are searched by varying the model parameters. We find that the abundance patterns of the EMP stars are predominantly best-fitted with the supernova yields with initial masses M < 40M ⊙ , and that more than than half of the stars are best fitted with the M = 25M ⊙ hypernova (E 51 = 10) models. The results also indicate that the majority of the primordial supernovae have ejected 10 −2 − 10 −1 M ⊙ of 56 Ni leaving behind a compact remnant, either a neutron star or a black hole, with mass in a range of ∼ 1.5 − 5M ⊙ . The results suggest that the masses of the first stars responsible for the first metalenrichment are predominantly < 40M ⊙ . This implies that the higher mass first stars were either less abundant or directly collapsing into a blackhole without ejecting heavy elements or that a supernova explosion of a higher-mass first star inhibits the formation of the next generation of low-mass stars at [Fe/H]< −3.

Metal-poor Stars Observed with the Automated Planet Finder Telescope. II. Chemodynamical Analysis of Six Low-metallicity Stars in the Halo System of the Milky Way

“…In general, our comparison suggested that massive stellar progenitors shall be the pollutant source of their birth cloud, and these pollutants then acted as cooling agents. Our result is consistent with recent conclusions given by Ishigaki et al (2018), which suggest possible progenitors in the 15-25 M ⊙ mass range. This peak (∼ 20 M ⊙ ) may reflect the PopIII initial mass function.…”

Modelling the chemical enrichment of Population III supernovae: The origin of the metals in near-pristine gas clouds.

“…In contrast to this, a similar analysis performed by Grimmett et al (2018) found that the abundance patterns of EMP halo stars are best described by the yields of (5 − 10) × 10 51 erg explosions (i.e hypernovae). This preference towards enrichment by a population of high energy SNe was also reported by Cooke et al (2017) and Ishigaki et al (2018). Furthermore, the observed overabundance of [Zn/Fe] in the most metal-poor halo stars (Primas et al 2000;Cayrel et al 2004), is thought to be due to enrichment by a population of hypernovae (Umeda & Nomoto 2002).…”

“…(iv) Our model suggests that the stars that enriched the most metal-poor DLAs had a typical explosion energy E exp = 1.8 +0.3 −0.2 × 10 51 erg, which is somewhat lower than that found by recent works that model the enrichment of metal-poor halo stars (Ishigaki et al 2018;Grimmett et al 2018).…”

The role of the H2 adiabatic index in the formation of the first stars

“…The observation that primordial gas clouds do fragment naturally raises the question of what initial mass function (IMF) this process yields. Determining the IMF of first stars has thus become a central goal of modern first star research (Tumlinson et al 2004;Schneider et al 2006;Susa 2013;Susa et al 2014;Ishigaki et al 2018).…”