Radiative feedback on supermassive star formation: the massive end of the Population III initial mass function

Daisuke Toyouchi, Kohei Inayoshi, Wenxiu Li, Zoltán Haiman, Rolf Kuiper

Submitted on 29 June 2022


Supermassive stars (SMSs) with masses of M104--105 M are invoked as possible seeds of high-redshift supermassive black holes, but it remains under debate whether their protostar indeed acquires sufficient mass via gas accretion overcoming radiative feedback. We investigate protostellar growth in dynamically heated atomic-cooling haloes (ACHs) found in recent cosmological simulations, performing three-dimensional radiation hydrodynamical (RHD) simulations that consider stellar evolution under variable mass accretion. We find that one of the ACHs feeds the central protostar at rates exceeding a critical value, above which the star evolves in a cool bloating phase and hardly produces ionizing photons. Consequently, the stellar mass reaches M104 M unimpeded by radiative feedback. In the other ACH, where the mass supply rate is lower, the star spends most of its life as a hot main-sequence star, emitting intense ionizing radiation. Then, the stellar mass growth is terminated around 500 M by photoevaporation of the circumstellar disk. A series of our RHD simulations provide a formula of the final stellar mass determined either by stellar feedback or their lifetime as a function of the mass supply rate from the parent cloud in the absence of stellar radiation. Combining the results with the statistical properties of SMS-forming clouds in high-redshift quasar progenitor haloes, we construct a top-heavy mass distribution of primordial stars over M100--105 M, approximately following a power-law spectrum of M1.3 with a steeper decline at M2×104 M. Their massive BH remnants would be further fed via the dense debris disk, powering "milli-quasars" with a bolometric luminosity of Lbol  1043 erg s1.


Comment: 16 pages, 12 figures, and 3 tables, submitted to MNRAS

Subjects: Astrophysics - Astrophysics of Galaxies; Astrophysics - Solar and Stellar Astrophysics