arXiv subjects

Hidenobu Yajima

Publications and source records attributed to Hidenobu Yajima.

At least 73 records · Page 4Linked to original sources

arXiv2020

FIR-luminous [CII] emitters in the ALMA-SCUBA-2 COSMOS survey (AS2COSMOS): The nature of submillimeter galaxies in a 10 comoving Mpc-scale structure at z~4.6

We report the discovery of a 10 comoving Mpc-scale structure traced by massive submillimeter galaxies (SMGs) at z~4.6. These galaxies are selected from an emission line search of ALMA Band 7 observations targeting 184 luminous submillimeter sources ($S_{850μ{\rm m}}\geq$ 6.2 mJy) across 1.6 degrees$^2$ in the COSMOS field. We identify four [CII] emitting SMGs and two probable [CII] emitting SMG candidates at z=4.60-4.64 with velocity-integrated signal-to-noise ratio of SNR>8. Four of the six emitters are near-infrared blank SMGs. After excluding one SMG whose emission line is falling at the edge of the spectral window, all galaxies show clear velocity gradients along the major axes that are consistent with rotating gas disks. The estimated rotation velocities of the disks are 330-550 km s$^{-1}$ and the inferred host dark-matter halo masses are ~2-8 $\times$ 10$^{12}$M$_{\odot}$. From their estimated halo masses and [CII] luminosity function, we suggest that these galaxies have a high (50-100%) duty cycle and high (~0.1) baryon conversion efficiency (SFR relative to baryon accretion rate), and that they contribute $\simeq$2% to the total star-formation rate density at z=4.6. These SMGs are concentrated within just 0.3% of the full survey volume, suggesting they are strongly clustered. The extent of this structure and the individual halo masses suggest that these SMGs will likely evolve into members of a ~10$^{15}$M$_{\odot}$ cluster at z=0. This survey reveals synchronized dusty starburst in massive halos at z>4, which could be driven by mergers or fed by smooth gas accretion.

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arXiv2020

Starbursting [O III] emitters and quiescent [C II] emitters in the reionization era

Recent observations have successfully detected [O III] $88.3\,{\rm μm}$ and [C II] $157.6\,{\rm μm}$ 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 $\sim 100\,{\rm Myr}$. The slope of the relation between $\log{(\rm SFR/M_{\odot}~yr^{-1})}$ and $\log{(L_{\rm [O_{III}]}/{\rm L_{\odot}})}$ at $z=6-9$ is 1.03, and 1.43 for $\log{(L_{\rm [C_{II}]}/{\rm L_{\odot}})}$. 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 $\sim 10$ to $\sim 1$ because the O/C abundance ratio decreases due to carbon-rich winds from AGB stars and the mass ratio of {\sc H\,ii} to {\sc 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 $\sim 10^{-2}~{\rm mJy~arcsec^{-2}}$ can probe the extended neutral gas disks of high-$z$ galaxies.

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arXiv2020

The CO universe: Modelling CO emission and H$_{\rm 2}$ abundance in cosmological galaxy formation simulations

We devise a physical model of formation and distribution of molecular gas clouds in galaxies. We use the model to predict the intensities of rotational transition lines of carbon monoxide (CO) and the molecular hydrogen (H$_{\rm 2}$) abundance. Using the outputs of Illustris-TNG cosmological simulations, we populate molecular gas clouds of unresolved sizes in individual simulated galaxies, where the effect of the interstellar radiation field with dust attenuation is also taken into account. We then use the publicly available code DESPOTIC to compute the CO line luminosities and H$_{\rm 2}$ densities without assuming the CO-to-H$_{\rm 2}$ conversion factor ($α_{\rm CO}$). Our method allows us to study the spatial and kinematic structures traced by CO(1-0) and higher transition lines. We compare the CO luminosities and H$_{\rm 2}$ masses with recent observations of galaxies at low and high redshifts. Our model reproduces well the observed CO-luminosity function and the estimated H$_{\rm 2}$ mass in the local Universe. About ten per cent of molecules in the Universe reside in dwarf galaxies with stellar masses lower than $10^9~{\rm M_\odot}$, but the galaxies are generally `CO-dark' and have typically high $α_{\rm CO}$. Our model predicts generally lower CO line luminosities than observations at redshifts $z\gtrsim 1$--$2$. We argue that the difference can be explained by the highly turbulent structure suggested for the high-redshift star-forming galaxies.

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arXiv2020

Star cluster formation and cloud dispersal by radiative feedback: dependence on metallicity and compactness

We study star cluster formation in various environments with different metallicities and column densities by performing a suite of three-dimensional radiation hydrodynamics simulations. We find that the photoionization feedback from massive stars controls the star formation efficiency (SFE) in a star-forming cloud, and its impact sensitively depends on the gas metallicity $Z$ and initial cloud surface density $Σ$. At $Z=1~Z_{\odot}$, SFE increases as a power law from 0.03 at $Σ= 10~M_{\odot}{\rm pc^{-2}}$ to 0.3 at $Σ= 300~M_{\odot}{\rm pc^{-2}}$. In low-metallicity cases $10^{-2}- 10^{-1} Z_{\odot}$, star clusters form from atomic warm gases because the molecule formation time is not short enough with respect to the cooling or dynamical time. In addition, the whole cloud is disrupted more easily by expanding H{\sc ii} bubbles which have higher temperature owing to less efficient cooling. With smaller dust attenuation, the ionizing radiation feedback from nearby massive stars is stronger and terminate star formation in dense clumps. These effects result in inefficient star formation in low-metallicity environments: the SFE drops by a factor of $\sim 3$ at $Z=10^{-2}~Z_{\odot}$ compared to the results for $Z=1~Z_{\odot}$, regardless of $Σ$. Newborn star clusters are also gravitationally less bound. We further develop a new semi-analytical model that can reproduce the simulation results well, particularly the observed dependencies of the SFEs on the cloud surface densities and metallicities.

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arXiv2020

High circular polarization of near infrared light induced by micron-size dust grains

We explore the induction of circular polarization (CP) of near-infrared light in star-forming regions using three-dimensional radiative transfer calculations. The simulations trace the change of Stokes parameters at each scattering/absorption process in a dusty gas slab composed of aligned grains. We find that the CP degree enlarges significantly according as the size of dust grains increases and exceeds $\sim 20$ percent for micron-size grains. Therefore, if micron-size grains are dominant in a dusty gas slab, the high CP observed around luminous young stellar objects can be accounted for. The distributions of CP show the asymmetric quadrupole patters regardless of the grain sizes. Also, we find that the CP degree depends on the relative position of a dusty gas slab. If a dusty gas slab is located behind a star-forming region, the CP reaches $\sim 60$ percent in the case of $1.0~{\rm μm}$ dust grains. Hence, we suggest that the observed variety of CP maps can be explained by different size distributions of dust grains and the configuration of aligned grains.

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arXiv2020

ART$^2$: A 3D Parallel Multi-wavelength Radiative Transfer Code for Continuum and Atomic and Molecular Lines

ART$^2$ is a 3D multi-wavelength Monte Carlo radiative transfer (RT) code that couples continuum and emission lines to track the propagation of photons and their interactions with the interstellar medium (ISM). The previous version of ART$^2$, which included continuum and Ly$α$ line, has been extensively applied to hydrodynamics simulations to study multi-band properties of galaxies and ISM. Here, we describe new implementations of non-local thermodynamic equilibrium RT of molecular and atomic fine structure emission lines, and the parallelization of the code using a number of novel methods. The new ART$^2$ can efficiently and self-consistently produce a full spectrum that includes both continuum and lines such as [CII], [NII], [OIII], Ly$α$, and CO. These essential features, together with the multi-phase ISM model and the adaptive grid, make ART$^2$ a multi-purpose code to study multi-wavelength properties of a wide range of astrophysical systems from planetary disks to large-scale structures. To demonstrate the capability of the new ART$^2$, we applied it to two hydrodynamics simulations: the zoom-in Milky Way Simulation to obtain panchromatic properties of individual galaxies, and the large-scale IllustrisTNG100 Simulation to obtain global properties such as the line intensity mappings. These products are essential for a broad array of studies such as the correlations between physical and panchromatic properties and their evolution. By enabling direct comparison between numerical simulations and multi-band observations, ART$^2$ provides a crucial theoretical framework for the interpretations of existing observations, the plan for future surveys, and the synergy between multi-band galaxy surveys and line intensity mappings. Therefore, ART$^2$ is a powerful and versatile tool to bridge the gap between theories and observations of cosmic structures.

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arXiv2019

First Identification of 10-kpc Scale [CII] 158um Halos around Star-Forming Galaxies at z=5-7

We report the discovery of 10-kpc scale [CII] 158um 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 Msun 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 9.2sigma level significantly extended more than the HST stellar continuum data by a factor of ~5 on the exponential-profile basis, as well as the dust continuum. We also compare the radial profiles of [CII] and Lya halos universally found in star-forming galaxies at this epoch, and find that the scale lengths agree within the 1sigma level. While two independent hydrodynamical zoom-in simulations match the dust and stellar continuum properties, the simulations cannot reproduce the extended [CII] 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.

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arXiv2019

Galaxy evolution and radiative properties in the early Universe: multi-wavelength analysis in cosmological simulations

Recent observations have successfully detected UV or infrared flux from galaxies at the epoch of reionization. However, the origin of their radiative properties has not been fully understood yet. Combining cosmological hydrodynamic simulations and radiative transfer calculations, we present theoretical predictions of multi-wavelength radiative properties of the first galaxies at z=6-15. We find that most of the gas and dust are ejected from star-forming regions due to supernova (SN) feedback, which allows UV photons to escape. We show that the peak of SED rapidly shifts between UV and infrared wavelengths on a timescale of 100 Myr due to intermittent star formation and feedback. When dusty gas covers the star-forming regions, the galaxies become bright in the observed-frame sub-millimeter wavelengths. In addition, we find that the escape fraction of ionizing photons also changes between 1-40% at z>10. The mass fraction of HII region changes with the star formation history, resulting in the fluctuations of metal lines and Lyman-alpha line luminosities. In the starbursting phase of galaxies with the halo mass $\sim 10^{11}\,{\rm M_{\odot}}$ ($10^{12}\,{\rm M_{\odot}}$), the simulated galaxy has $L_{\rm [O\,III]} \sim 10^{42}\, (10^{43})\, {\rm erg\,s^{-1}}$, which is consistent with the observed star-forming galaxies at z>7. Our simulations suggest that deep [C II] observation with ALMA can trace the distribution of neutral gas extending over $\sim 20$ physical kpc. We also find that the luminosity ratio $L_{\rm [O\,III]}/L_{\rm [C\,II]}$ decreases with bolometric luminosity due to metal enrichment. Our simulations show that the combination of multi-wavelength observations by ALMA and JWST will be able to reveal the multi-phase ISM structure and the transition from starbursting to outflowing phases of high-z galaxies.

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arXiv2019

CHORUS. III. Photometric and Spectroscopic Properties of Ly$α$ Blobs at $z=4.9-7.0$

We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Ly$α$ blobs (LABs), dubbed z70-1 and z49-1 at $z=6.965$ and $z=4.888$ respectively, that are Ly$α$ emitters with a bright ($\log L_{\rm Lyα}/{\rm [erg\ s^{-1}]}>43.4$) and spatially-extended Ly$α$ emission, and present the photometric and spectroscopic properties of a total of seven LABs; the two new LABs and five previously-known LABs at $z=5.7-6.6$. The z70-1 LAB shows the extended Ly$α$ emission with a scale length of $1.4\pm 0.2$ kpc, about three times larger than the UV continuum emission, making z70-1 the most distant LAB identified to date. All of the 7 LABs, except z49-1, exhibit no AGN signatures such as X-ray emission, {\sc Nv}$λ$1240 emission, or Ly$α$ line broadening, while z49-1 has a strong {\sc Civ}$λ$1548 emission line indicating an AGN on the basis of the UV-line ratio diagnostics. We carefully model the point-spread functions of the HSC images, and conduct two-component exponential profile fitting to the extended Ly$α$ emission of the LABs. The Ly$α$ scale lengths of the core (star-forming region) and the halo components are $r_{\rm c}=0.6-1.2$ kpc and $r_{\rm h}=2.0-13.8$ kpc, respectively. The average $r_{\rm h}$ of the LABs falls on the extrapolation of the $r_{\rm h}$-Ly$α$ luminosity relation of the Ly$α$ halos around VLT/MUSE star-forming galaxies at the similar redshifts, suggesting that typical LABs at $z\gtrsim5$ are not special objects, but star-forming galaxies at the bright end.

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arXiv2019

Osaka Feedback Model: Isolated Disk Galaxy Simulations

We study various implementations of supernova feedback model and present the results of our `Osaka feedback model' using isolated galaxy simulations performed by the smoothed particle hydrodynamics (SPH) code {\small GADGET-3}. Our model is a modified version of Stinson et al.'s work, and we newly add the momentum kick for SN feedback rather than only thermal feedback. We incorporate the physical properties of SN remnants from the results of Chevalier and McKee \& Ostriker, such as the effective radius of SN bubble and the remnant life-time, in the form of Sedov-Taylor (ST)-like solutions with the effect of radiative cooling. Our model utilizes the local, physical parameters such as density and temperature of the ISM rather than galactic or halo properties to determine the galactic wind velocity or mass-loading factor. The Osaka model succeeds in self-regulating star formation, and naturally produces galactic outflow with variable velocities depending on the local environment and available SN energy as a function of time.An important addition to our previous work by Aoyama et al. is the implementation of the {\small CELib} chemistry library which allows us to deal with the time-dependent input of energy and metal yields for type Ia \& II supernovae (SNe) and asymptotic giant branch (AGB) stars. As initial tests of our model, we apply it to isolated galaxy simulations, and examine various galactic properties and compare with observational data including metal abundances.

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arXiv2018

Radiative properties of the first galaxies: rapid transition between blue and red

Recent observations have successfully detected UV-bright and infrared-bright galaxies in the epoch of reionization. However, the origin of their radiative properties has not been understood yet. Combining cosmological hydrodynamic simulations and radiative transfer calculations, we present predictions of multi-wavelength radiative properties of the first galaxies at $z\sim 6-15$. Using zoom-in initial conditions, we investigate three massive galaxies and their satellites in different environment and halo masses: $M_{\rm h} = 2.4\times 10^{10}{\rm M_{\odot}}$ (Halo-10), $1.6\times 10^{11}{\rm M_{\odot}}$ (Halo-11) and $0.7\times 10^{12}{\rm M_{\odot}}$ (Halo-12) at $z=6$. We find that most of gas and dust are ejected from star-forming regions by supernova feedback, which allows UV photons to escape. We show that the peak of the spectral energy distribution (SED) rapidly changes between UV and infrared wavelengths on a time-scale of $\sim$\,100\,Myrs due to intermittent star formation and feedback, and the escape fraction of UV photons fluctuates in the range of $0.2-0.8$ at $z<10$ with a time-averaged value of 0.3. When dusty gas covers the star-forming regions, the galaxies become bright in the observed-frame sub-millimeter wavelengths. We predict the detectability of high-$z$ galaxies with the Atacama Large Millimeter Array (ALMA). For a sensitivity limit of $0.1\,{\rm mJy}$ at $850\,{\rm μm}$, the detection probability of galaxies in halos $M_{\rm h} \gtrsim 10^{11}\,{\rm M_{\odot}}$ at $z\lesssim 7$ exceeds fifty per cent. We argue that supernova feedback can produce the observed diversity of SEDs for high-$z$ galaxies.

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arXiv2018

Rapid Black Hole Growth under Anisotropic Radiation Feedback

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_sun) 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.

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arXiv2018

Stunted accretion growth of black holes by combined effect of the flow angular momentum and radiation feedback

Accretion on to seed black holes (BHs) is believed to play a crucial role in formation of supermassive BHs observed at high-redshift (z>6). Here, we investigate the combined effect of gas angular momentum and radiation feedback on the accretion flow, by performing 2D axially symmetric radiation hydrodynamics simulations that solve the flow structure across the Bondi radius and the outer part of the accretion disc simultaneously. The accreting gas with finite angular momentum forms a rotationally-supported disc inside the Bondi radius, where the accretion proceeds by the angular momentum transport due to assumed alpha-type viscosity. We find that the interplay of radiation and angular momentum significantly suppresses accretion even if the radiative feedback is weakened in an equatorial shadowing region. The accretion rate is O(alpha)\sim O(0.01-0.1) times the Bondi value, where alpha is the viscosity parameter. By developing an analytical model, we show that such a great reduction of the accretion rate persists unless the angular momentum is so small that the corresponding centrifugal radius is \lesssim 0.04 times the Bondi radius. We argue that BHs are hard to grow quickly via rapid mass accretion considering the angular momentum barrier presented in this paper.

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arXiv2018

Detectability of 21cm-signal during the Epoch of Reionization with 21cm-Lyman-$α$ emitter cross-correlation. I

Detection of the redshifted 21cm-line signal from neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR) is complicated by intense foregrounds such as galactic synchrotron and extragalactic radio galaxies. The 21cm-Lyman-$α$ emitter(LAE) cross-correlation is one of the tools available to reduce the foreground effects because the foreground emission from such radio sources is statistically independent of LAE distribution. LAE surveys during the EoR at redshifts $z=6.6$ and $7.3$ are ongoing by the Subaru Hyper Suprime-Cam (HSC). Additionally, Prime Focus Spectrograph (PFS) will provide precise redshift information of the LAEs discovered by the HSC survey. In this paper, we investigate the detectability of the 21cm signal with the 21cm-LAE cross-correlation by using our improved reionization simulations. We also focus on the error budget and evaluate it quantitatively in order to consider a strategy to improve the signal-to-noise ratio. In addition, we explore an expansion of the LAE survey to suggest optimal survey parameters and show a potential to measure a characteristic size of ionized bubbles via the turnover scale of the cross-power spectrum. As a result, we find that the Murchison Widefield Array (MWA) has ability to detect the cross-power spectrum signal on large scales by combining LAE Deep field survey of HSC. We also show that the sensitivity is improved dramatically at small scales by adding redshift information from the PFS measurements. The Square Kilometre Array (SKA) has a potential to measure the turnover scale with an accuracy of $6\times10^{-3}~{\rm Mpc^{-1}}$.

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arXiv2018

Stellar mass dependence of the 21-cm signal around the first star and its impact on the global signal

The 21-cm signal in the vicinity of the first stars is expected to reflect properties of the first stars. In this study we pay special attention to tracing the time evolution of the ionizing photons' escape fraction, which affects the distribution of neutral hydrogen, by performing radiation hydrodynamics (RHD) simulations resolving dense gas in a halo. We find that the radial profile of 21-cm differential brightness temperature is quite sensitive to the stellar and halo masses, which reflects the time evolution of the escape fraction. In the case of a less massive star, ionizing photons hardly escape from its host halo due to the absorption by dense halo gas, thus an deep 21-cm absorption feature at just outside the halo lasts a long time. Whereas photons from a massive star well working to heat the ambient intergalactic medium turn out to cause a spatially extended 21-cm emission signature. Although individual signals are found to be undetectable with the Square Kilometre Array, our analysis using the results from the RHD simulations indicates that the properties of the first stars are imprinted on the 21-cm global signal: its amplitude depends not only on the cosmic star formation rate density, but also on the typical mass of the first stars due to the stellar-mass-dependent heating rate. Thus, we suggest that the initial mass function of the first stars is an essential factor in understanding the global signal.

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arXiv2018

SILVERRUSH. VI. A simulation of Ly$α$ emitters in the reionization epoch and a comparison with Subaru Hyper Suprime-Cam survey early data

The survey of Lyman $α$ emitters (LAEs) with Subaru Hyper Suprime-Cam, called SILVERRUSH (Ouchi et al.), is producing massive data of LAEs at $z\gtrsim6$. Here we present LAE simulations to compare the SILVERRUSH data. In 162$^3$ comoving Mpc$^3$ boxes, where numerical radiative transfer calculations of reionization were performed, LAEs have been modeled with physically motivated analytic recipes as a function of halo mass. We have examined $2^3$ models depending on the presence or absence of dispersion of halo Ly$α$ emissivity, dispersion of the halo Ly$α$ optical depth, $τ_α$, and halo mass dependence of $τ_α$. The unique free parameter in our model, a pivot value of $τ_α$, is calibrated so as to reproduce the $z=5.7$ Ly$α$ luminosity function (LF). We compare our model predictions with Ly$α$ LFs at $z=6.6$ and $7.3$, LAE angular auto-correlation functions (ACFs) at $z=5.7$ and $6.6$, and LAE fractions in Lyman break galaxies at $5<z<7$. The Ly$α$ LFs and ACFs are reproduced by multiple models, but the LAE fraction turns out to be the most critical test. The dispersion of $τ_α$ and the halo mass dependence of $τ_α$ are essential to explain all observations reasonably. Therefore, a simple model of one-to-one correspondence between halo mass and Ly$α$ luminosity with a constant Ly$α$ escape fraction has been ruled out. Based on our best model, we present a formula to estimate the intergalactic neutral hydrogen fraction, $x_{\rm HI}$, from the observed Ly$α$ luminosity density at $z\gtrsim6$. We finally obtain $x_{\rm HI}=0.5_{-0.3}^{+0.1}$ as a volume-average at $z=7.3$.

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arXiv2018

Condition for dust evacuation from the first galaxies

Dust enables low-mass stars to form from low-metallicity gas by inducing fragmentation of clouds via the cooling by its thermal emission. Dust may, however, be evacuated from star-forming clouds due to radiation force from massive stars. We here study the condition for the dust evacuation by comparing the dust evacuation time with the time of cloud destruction due to either expansion of HII regions or supernovae. The cloud destruction time has weak dependence on the cloud radius, while the dust evacuation time becomes shorter for a cloud with the smaller radius. The dust evacuation thus occurs in compact star-forming clouds whose column density is $N_{\rm H} \simeq 10^{24} - 10^{26} ~{\rm cm^{-2}}$. The critical halo mass above which the dust evacuation occurs becomes lower for higher formation redshift, e.g., $\sim 10^{9}~M_{\odot}$ at redshift $z \sim 3$ and $\sim 10^{7}~M_{\odot}$ at $z \sim 9$. In addition, metallicity of the gas should be less than $\sim 10^{-2} ~ Z_{\odot}$. Otherwise the dust attenuation reduces the radiation force significantly. From the dust-evacuated gas, massive stars are likely to form even with metallicity above $\sim 10^{-5}~Z_{\odot}$, the critical value for low-mass star formation due to the dust cooling. This can explain the dearth of ultra-metal poor stars with the metallicity lower than $\sim 10^{-4}~Z_{\odot}$.

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arXiv2018

Suppression of globular cluster formation in metal-poor gas clouds by Lyman-alpha radiation feedback

We study the impact of Ly$α$ radiation feedback on globular cluster (GC) formation. In this Letter, we analytically derive the relation between star formation efficiency (SFE) and metallicity in spherical clouds with the Ly$α$ radiation feedback. Our models show that the SFE becomes small as the metallicity decreases. In metal-poor gas clouds, Ly$α$ photons are trapped for a long time and exert strong radiation force to the gas, resulting in the suppression of star formation. We find that bound star-clusters (SFE $\gtrsim$ 0.5) form only for the metallicity higher than $\sim 10^{-2.5}~Z_{\odot}$ in the case with the initial cloud mass $10^5~{\rm M}_\odot$ and the radius 5 pc. Our models successfully reproduce the lower bound of observed metallicity of GCs. Thus, we suggest that the Ly$α$ radiation feedback can be essential in understanding the formation of GCs.

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