Photoevaporation of Minihalos during Cosmic Reionization: Primordial and Metal-Enriched Halos. (arXiv:2007.08149v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Nakatani_R/0/1/0/all/0/1">Riouhei Nakatani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fialkov_A/0/1/0/all/0/1">Anastasia Fialkov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yoshida_N/0/1/0/all/0/1">Naoki Yoshida</a>
The density distribution of the inter-galactic medium is an uncertain but
highly important issue in the study of cosmic reionization. It is expected that
there are abundant gas clouds hosted by low-mass “minihalos” in the early
universe, which act as photon sinks until photoevaporated by the emerging
ultra-violet background (UVB) radiation. We perform a suite of radiation
hydrodynamics simulations to study the photoevaporation of minihalos. Our
simulations follow hydrodynamics, non-equilibrium chemistry, and the associated
cooling processes in a self-consistent manner. We conduct a parametric study by
considering a wide range of gas metallicity ($0,Z_odot leq Z leq
10^{-3},Z_odot$), halo mass ($10^3 M_odot leq M leq 10^8 M_odot$), UVB
intensity ($0.01 leq J_{21} leq 1$), and turn-on redshift of ionizing sources
($10leq z_{rm IN} leq 20$). We show that small halos are evaporated in a few
tens million years, whereas larger mass halos survive for ten times longer. We
show that the gas mass evolution of a minihalo can be characterized by a
scaling parameter that is given by a combination of the halo mass, background
radiation intensity, and redshift. Efficient radiative cooling in
metal-enriched halos induces fast condensation of the gas to form a dense,
self-shielded core. The cold, dense core can become gravitationally unstable in
halos with high metallicities. Early metal enrichment may allow star formation
in minihalos during cosmic reionization.
The density distribution of the inter-galactic medium is an uncertain but
highly important issue in the study of cosmic reionization. It is expected that
there are abundant gas clouds hosted by low-mass “minihalos” in the early
universe, which act as photon sinks until photoevaporated by the emerging
ultra-violet background (UVB) radiation. We perform a suite of radiation
hydrodynamics simulations to study the photoevaporation of minihalos. Our
simulations follow hydrodynamics, non-equilibrium chemistry, and the associated
cooling processes in a self-consistent manner. We conduct a parametric study by
considering a wide range of gas metallicity ($0,Z_odot leq Z leq
10^{-3},Z_odot$), halo mass ($10^3 M_odot leq M leq 10^8 M_odot$), UVB
intensity ($0.01 leq J_{21} leq 1$), and turn-on redshift of ionizing sources
($10leq z_{rm IN} leq 20$). We show that small halos are evaporated in a few
tens million years, whereas larger mass halos survive for ten times longer. We
show that the gas mass evolution of a minihalo can be characterized by a
scaling parameter that is given by a combination of the halo mass, background
radiation intensity, and redshift. Efficient radiative cooling in
metal-enriched halos induces fast condensation of the gas to form a dense,
self-shielded core. The cold, dense core can become gravitationally unstable in
halos with high metallicities. Early metal enrichment may allow star formation
in minihalos during cosmic reionization.
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