Effect of interstellar objects on metallicity of low-mass first stars formed in a cosmological model

Abstract

We investigate metal pollution onto the surface of low-mass population III stars (Pop. III survivors) via interstellar objects floating in the Galactic interstellar medium. Only recently, Tanikawa et al. analytically estimated how much metal should collide to an orbiting Pop. III survivor encouraged by the recent discovery of 'Oumuamua and suggested that ISOs are the most dominant contributor of metal enrichment of Pop. III survivors. When we consider a distribution of interstellar objects in the Galactic disc, Pop. III survivors' orbits are significant properties to estimate the accretion rate of them though Tanikawa et al. assumed one modelled orbit. To take more realistic orbits into calculating the accretion rate, we use a high-resolution cosmological $N$-body simulation that resolves dark matter minihaloes. Pop. III survivors located at solar neighbourhood have a number of chances of ISO($>100$ m) collisions, typically $5\times 10^6$ times in the last $5$ Gyr, which is one order of magnitude greater than estimated in the previous study. When we assume a power-law parameter $\alpha$ of the ISO cumulative number density with size greater than $D$ as $n\propto D^{-\alpha }$, $0.80M_{\odot }$ stars should be typically polluted [Fe/H]$\sim -2$ for the case of $\alpha =2.0$. Even in the cases of $0.70$ and $0.75M_{\odot }$ stars, the typical surface metallicity are around [Fe/H]$=-6\sim -5$. From the presence of stars with their [Fe/H], we can constrain on the lower limit of the power $\alpha$, as $\alpha \gtrsim 2.0$, which is consistent with $\alpha$ of km-size asteroids and comets in the solar system. Furthermore, we provide six candidates as the ISO-polluted Pop. III stars in the case of $\alpha \sim 2.5$. Metal-poor stars so far discovered are possible to be metal-free Pop. III stars on birth.

8 pages, 3 figures, Accepted for publication in MNRAS

References in corpus (10)

• Protostar Formation in the Early Universe
• Primordial Star Formation under the Influence of Far Ultraviolet Radiation: 1540 Cosmological Halos and the Stellar Mass Distribution
• The Mass Spectrum of the First Stars
• Formation Scenario for Wide and Close Binary Systems
• Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 'Oumuamua
• Constraining the primordial initial mass function with stellar archaeology
• Predicting the locations of possible long-lived low-mass first stars: Importance of satellite dwarf galaxies
• The Composition of M-type asteroids II: Synthesis of spectroscopic and radar observations
• Observational constraints on the survival of pristine stars
• Blocking metal accretion onto population III stars by stellar wind

Cited by in corpus (2)

• Merge or survive: Number of Population III stars per minihalo
• Potential signature of Population III pair-instability supernova ejecta in the BLR gas of the most distant quasar at z = 7.54