Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Daisuke Toyouchi, Kohei Inayoshi, Wenxiu Li, Zoltán Haiman, Rolf Kuiper
| Summary:
Supermassive stars (SMSs) with masses of $M_ast simeq 10^4$–$10^5~{rm
M_odot}$ 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 $M_ast gtrsim 10^4~{rm M_odot}$ 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 $500~{rm
M_odot}$ 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 $M_ast simeq 100$–$10^5~{rm M_odot}$, approximately following a
power-law spectrum of $propto M_ast^{-1.3}$ with a steeper decline at $M_ast
gtrsim 2 times 10^4~{rm M_odot}$. Their massive BH remnants would be
further fed via the dense debris disk, powering "milli-quasars" with a
bolometric luminosity of $L_{rm bol}~gtrsim~10^{43}~{rm erg~s^{-1}}$.
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