Combing the three‐dimensional radiative transfer (RT) calculation and cosmological smoothed particle hydrodynamics (SPH) simulations, we study the escape fraction of ionizing photons (fesc) of high‐redshift galaxies at z= 3–6. Our simulations cover the halo mass range of Mh= 109–1012 M⊙. We post‐process several hundred simulated galaxies with the Authentic Radiative Transfer (art) code to study the halo mass dependence of fesc. In this paper, we restrict ourselves to the transfer of stellar radiation from local stellar population in each dark matter halo. We find that the average fesc steeply decreases as the halo mass increases, with a large scatter for the lower‐mass haloes. The low‐mass haloes with Mh∼ 109 M⊙ have large values of fesc (with an average of ∼0.4), whereas the massive haloes with Mh∼ 1011 M⊙ show small values of fesc (with an average of ∼0.07). This is because in our simulations, the massive haloes show more clumpy structure in gas distribution, and the star‐forming regions are embedded inside these clumps, making it more difficult for the ionizing photons to escape. On the other hand, in low‐mass haloes, there are often conical regions of highly ionized gas due to the shifted location of young star clusters from the centre of dark matter halo, which allows the ionizing photons to escape more easily than in the high‐mass haloes. By counting the number of escaped ionizing photons, we show that the star‐forming galaxies can ionize the intergalactic medium at z= 3–6. The main contributor to the ionizing photons is the haloes with Mh≲ 1010 M⊙ owing to their high fesc. The large dispersion in fesc suggests that there may be various sizes of H ii bubbles around the haloes even with the same mass in the early stages of reionization. We also examine the effect of UV background radiation field on fesc using simple, four different treatments of UV background.

We report the discovery of 10-kpc [Cii] 158µm halos surrounding star-forming galaxies in the early Universe. We choose deep ALMA data of 18 galaxies each with a star-formation rate of ≃ 10 − 70 M ⊙ with no signature of AGN whose [Cii] lines are individually detected at z = 5.153−7.142, and conduct stacking of the [Cii] lines and dust-continuum in the uv-visibility plane. The radial profiles of the surface brightnesses show a 10-kpc scale [Cii] halo at the 9.2σ level, significantly more extended than the HST stellar continuum data by a factor of ∼ 5 on the exponential-profile basis, as well as the dust continuum. We compare the radial profiles of [Cii] and Lyα halos universally found in star-forming galaxies at this epoch, and find that the scale lengths agree within 1σ level. While two independent hydrodynamical zoom-in simulations match the dust and stellar continuum properties, the simulations cannot reproduce the extended [C ii] line emission. The existence of the extended [Cii] halo is the evidence of outflow remnants in the early galaxies and suggest that the outflows may be dominated by cold-mode outflows expelling the neutral gas.

Recent observations have successfully detected [O iii] 88.3 μm and [C ii] 157.6 μm lines from galaxies in the early Universe with the Atacama Large Millimeter Array (ALMA). Combining cosmological hydrodynamic simulations and radiative transfer calculations, we present relations between the metal line emission and galaxy evolution at z = 6 − 15. We find that galaxies during their starburst phases have high [O iii] luminosity of $\sim 10^{42}~\rm erg~s^{-1}$. Once supernova feedback quenches star formation, [O iii] luminosities rapidly decrease and continue to be zero for ∼100 Myr. The slope of the relation between $\log {(\rm SFR/\rm M_{\odot }~ yr^{-1})}$ and $\log {(L_{\rm [O_{III}]}/L_{\odot })}$ at z = 6 − 9 is 1.03, and 1.43 for $\log {(L_{\rm [C_{II}]}/L_{\odot })}$. As gas metallicity increases from sub-solar to solar metallicity by metal enrichment from star formation and feedback, the line luminosity ratio $L_{\rm [O_{III}]} / L_{\rm [C_{II}]}$ decreases from ∼10 to ∼1 because the O/C abundance ratio decreases due to carbon-rich winds from AGB stars and the mass ratio of H ii to H i regions decreases due to rapid recombination. Therefore, we suggest that the combination of [O iii] and [C ii] lines is a good probe to investigate the relative distribution of ionized and neutral gas in high-z galaxies. In addition, we show that deep [C ii] observations with a sensitivity of ∼10−2 mJy arcsec−2 can probe the extended neutral gas disks of high-z galaxies.

Narrow‐band Lyα line and broad‐band continuum have played important roles in the discovery of high‐redshift galaxies in recent years. Hence, it is crucial to study the radiative transfer of both Lyα and continuum photons in the context of galaxy formation and evolution in order to understand the nature of distant galaxies. Here, we present a three‐dimensional Monte Carlo radiative transfer code, All‐wavelength Radiative Transfer with Adaptive Refinement Tree (), which couples Lyα line and multi‐wavelength continuum, for the study of panchromatic properties of galaxies and interstellar medium. This code is based on the original version of Li et al., and features three essential modules: continuum emission from X‐ray to radio, Lyα emission from both recombination and collisional excitation, and ionization of neutral hydrogen. The coupling of these three modules, together with an adaptive refinement grid, enables a self‐consistent and accurate calculation of the Lyα properties, which depend strongly on the UV continuum, ionization structure and dust content of the object. Moreover, it efficiently produces multi‐wavelength properties, such as the spectral energy distribution and images, for direct comparison with multi‐band observations. As an example, we apply to a cosmological simulation that includes both star formation and black hole growth, and study in detail a sample of massive galaxies at redshifts z= 3.1–10.2. We find that these galaxies are Lyα emitters (LAEs), whose Lyα emission traces the dense gas region, and that their Lyα lines show a shape characteristic of gas inflow. Furthermore, the Lyα properties, including photon escape fraction, emergent luminosity and equivalent width, change with time and environment. Our results suggest that LAEs evolve with redshift, and that early LAEs such as the most distant one detected at z∼ 8.6 may be dwarf galaxies with a high star formation rate fuelled by infall of cold gas, and a low Lyα escape fraction.

Discovery of high-redshift (z > 6) supermassive black holes (BHs) may indicate that the rapid (or super-Eddington) gas accretion has aided their quick growth. Here, we study such rapid accretion of the primordial gas on to intermediate-mass (10 2 −10 5 M ⊙ ) BHs under anisotropic radiation feedback. We perform two-dimensional radiation hydrodynamics simulations that solve the flow structure across the Bondi radius, from far outside of the Bondi radius down to a central part which is larger than a circum-BH accretion disc. The radiation from the unresolved circum-BH disc is analytically modeled considering self-shadowing effect. We show that the flow settles into a steady state, where the flow structure consists of two distinct parts: (1) bipolar ionized outflowing regions, where the gas is pushed outward by thermal gas pressure and super-Eddington radiation pressure, and (2) an equatorial neutral inflowing region, where the gas falls toward the central BH without affected by radiation feedback. The resulting accretion rate is much higher than that in the case of isotropic radiation, far exceeding the Eddington-limited rate to reach a value slightly lower than the Bondi one. The opening angle of the equatorial inflowing region is determined by the luminosity and directional dependence of the central radiation. We find that photoevaporation from its surfaces set the critical opening angle of about ten degrees below which the accretion to the BH is quenched. We suggest that the shadowing effect allows even stellar-remnant BHs to grow rapidly enough to become high-redshift supermassive BHs.