研究指出 GS 3073 中高达 0.46 的极端 N/O 比例无法由已知恒星解释，提出 1000-10,000 M$_\odot$ 原初恒星是唯一能解释该星系氮超丰及 C/O、Ne/O 比例的候选者，为宇宙黎明时期存在超大质量 Pop III 恒星提供了首个确凿证据。
摘要：
James Webb Space Telescope 的出现揭示了宇宙大爆炸后仅几亿年内的大量新星系。其中一些星系表现出不寻常的 N/O 比例，难以用当今的恒星群体来解释。尽管多次爆发星族中的 Wolf-Rayet 恒星、超大质量或快速旋转的原初恒星、金属富集超大质量恒星的广义相对论性爆炸，或球状星团的前身，原则上可以解释星系 GN-z11 和 CEERS 1019 中的氮超丰，但没有任何已知恒星或超新星能够解释红移 z = 5.55 处 GS 3073 中高达 0.46 的 N/O 比例。在此我们表明，GS 3073 中极端的氮丰度可以由 1000 - 10,000 M$_{\odot}$ 原初恒星产生。我们发现这些是唯一能够解释其巨大 N/O 比例以及 C/O 和 Ne/O 比例的候选者。因此，GS 3073 是宇宙黎明时期存在超大质量 Pop III 恒星的化石丰度记录中的首个确凿证据。
英文摘要：
The advent of the James Webb Space Telescope has revealed a wealth of new galaxies just a few hundred Myr after the Big Bang. Some of these galaxies exhibit unusual N/O ratios that are difficult to explain with stellar populations today. While Wolf-Rayet stars in multiple-burst populations, very massive or rapidly-rotating primordial stars, general relativistic explosions of metal-enriched supermassive stars, or the precursors of globular clusters can in principle account for the nitrogen excess in the galaxies GN-z11 and CEERS 1019, no known stars or supernovae can explain the far higher N/O ratio of 0.46 in GS 3073 at redshift $z =$ 5.55. Here we show that the extreme nitrogen abundances in GS 3073 can be produced by 1000 - 10,000 M$_{\odot}$ primordial (Pop III) stars. We find that these are the only candidates that can account for its large N/O ratios and its C/O and Ne/O ratios. GS 3073 is thus the first conclusive evidence in the fossil abundance record of the existence of supermassive Pop III stars at cosmic Dawn.
The first stars are known to form in primordial gas, either in minihalos with about $10^6$~M$_\odot$ or so-called atomic cooling halos of about $10^8$~M$_\odot$. Simulations have shown that gravitational collapse and disk formation in primordial gas yield dense stellar clusters. In this paper, we focus particularly on the formation of protostellar binary systems, and aim to quantify their properties during the early stage of their evolution. For this purpose, we combine the smoothed particle hydrodynamics code GRADSPH with the astrochemistry package KROME. The GRADSPH-KROME framework is employ…
We present new evolutionary models of primordial very massive stars, with initial masses ranging from $100\,\mathrm{{M}_{\odot}}$ to $1000\,\mathrm{{M}_{\odot}}$, that extend from the main sequence until the onset of dynamical instability caused by the creation of electron-positron pairs during core C, Ne, or O burning, depending on the star's mass and metallicity. Mass loss accounts for radiation-driven winds as well as pulsation-driven mass-loss on the main sequence and during the red supergiant phase. After examining the evolutionary properties, we focus on the final outcome of the models a…
Supermassive stars forming at $z \sim$ 15 - 20 are one of the leading contenders for the origin of the first quasars, over 200 of which have now been discovered at $z >$ 6. These stars likely form in pristine, atomically cooled haloes immersed in strong Lyman-Werner UV backgrounds or in highly supersonic baryon streaming flows. Atomic cooling triggers catastrophic baryon collapse capable of building up stars at rates of up to $\sim$1 M$_{\odot}$ yr$^{-1}$. Here we examine the evolution of supermassive stars with a much larger and finer grid of accretion rates than in previous studies with the …
In this paper, we address two issues related to primordial disk evolution in three clusters (NGC 1333, IC 348, and Orion A) observed by the INfrared Spectra of Young Nebulous Clusters (IN-SYNC) project. First, in each cluster, averaged over the spread of age, we investigate how disk lifetime is dependent on stellar mass. The general relation in IC 348 and Orion A is that primordial disks around intermediate mass stars (2--5$M_{\odot}$) evolve faster than those around loss mass stars (0.1--1$M_{\odot}$), which is consistent with previous results. However, considering only low mass stars, we do …
Evolution of a cluster of primordial black holes in the two-body relaxation approximation based on the Fokker-Planck equation is discussed. In our calculation, we consider the self-gravitating cluster with a wide range of black holes masses from $10^{-4} M_{\odot}$ up to $100 M_{\odot}$ and the total mass $10^5 M_{\odot}$. Moreover, we included a massive black hole in the cluster center which determines the evolution rate of the density profile in its vicinity.
Gas-Phase Metallicity and Nitrogen Abundances in Low-Mass Galaxies Down to $M_\star\simeq10^{5.7}\,M_\odot$ at $z\simeq4.5$--$10.1$ from JWST Lensing Cluster Surveys
University of Tsukuba（筑波大学）；The University of Tokyo（东京大学）；National Astronomical Observatory of Japan（日本国立天文台）；Kanazawa University（金泽大学）；SOKENDAI (The Graduate University for Advanced Studies)（综合研究大学院大学）
Very Massive Stars and High N/O: A Tale of the Nitrogen-enriched Super Star Cluster in the Sunburst Arc
Canadian Institute for Theoretical Astrophysics, University of Toronto（加拿大理论天体物理研究所，多伦多大学）；David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto（多伦多大学大卫·邓普克天文与天体物理系）
The idea that dark matter can be made of intermediate-mass primordial black holes in the $10M_\odot \lesssim M \lesssim 200M_\odot$ range has recently been reconsidered, particularly in the light of the detection of gravitational waves by the LIGO experiment. The existence of even a small fraction of dark matter in black holes should nevertheless result in noticeable quasar gravitational microlensing. Quasar microlensing is sensitive to any type of compact objects in the lens galaxy, to their abundance, and to their mass. We have analyzed optical and X-ray microlensing data from 24 gravitation…
Magnetic fields are considered as a vital ingredient of contemporary star formation, and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations, and are subsequently amplified by the small-scale dynamo, leading to a strong tangled magnetic field. Here we explore how the magnetic field provided by the small-scale dynamo is further amplified via the $α-Ω$ dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typi…
Recent observational studies of ultra-compact dwarf galaxies (UCDs) have discovered massive black holes (MBHs) with masses of more than ${10^6~\rm M_\odot}$, in their central regions. We here consider that these MBHs can be formed through merging of intermediate-mass black holes (IMBH), with masses of ${[10^3-10^5]~{\rm M}_{\odot}}$, within the stellar nuclei of dwarf galaxies, which are progenitors of UCDs. We numerically investigate this formation process for a wide range of model parameters using N-body simulations. This means that IMBH growth and feedback is neglected in this study. We fin…
Stellar Yields of Rapidly Rotating Population III Stars for the High Redshift Universe
Center for Astrophysics, Harvard and Smithsonian（哈佛与史密森尼天体物理中心）；Aristotle University of Thessaloniki（塞萨洛尼基亚里士多德大学）；University of Virginia（弗吉尼亚大学）；University of Chicago（芝加哥大学）；Carleton College（卡尔顿学院）；University of Texas at Austin（德克萨斯大学奥斯汀分校）；Portsmouth University（朴茨茅斯大学）；University of Geneva（日内瓦大学）；Keele University（基尔大学）；University of Tokyo（东京大学）
We study the gas phase metallicity (O/H) and nitrogen abundance gradients traced by star forming regions in a representative sample of 550 nearby galaxies in the stellar mass range $\rm 10^9-10^{11.5} M_\odot$ with resolved spectroscopic data from the SDSS-IV MaNGA survey. Using strong-line ratio diagnostics (R23 and O3N2 for metallicity and N2O2 for N/O) and referencing to the effective (half-light) radius ($\rm R_e$), we find that the metallicity gradient steepens with stellar mass, lying roughly flat among galaxies with $\rm log(M_\star/M_\odot) = 9.0$ but exhibiting slopes as steep as -0.1…
Interstellar gas heating is a powerful cosmology-independent observable for exploring the parameter space of primordial black holes (PBHs) formed in the early Universe that could constitute part of the dark matter (DM). We provide a detailed analysis of the various aspects for this observable, such as PBH emission mechanisms. Using observational data from the Leo T dwarf galaxy, we constrain the PBH abundance over a broad mass-range, $M_{\rm PBH} \sim \mathcal{O}(1) M_{\odot}-10^7 M_{\odot}$, relevant for the recently detected gravitational wave signals from intermediate-mass BHs. We also cons…
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 …
Turbulence in Primordial Dark Matter Halos and Its Impact on the First Star Formation
Institute of Astronomy and Astrophysics, Academia Sinica（中央研究院天文及天文物理研究所）；Department of Physics, National Taiwan University（国立台湾大学物理系）；Department of Physics and Astronomy, University of California, Riverside（加州大学河滨分校物理与天文学系）；Heidelberg Institute for Theoretical Studies（海德堡理论研究所）
Stellar microlensing observations tightly constrain compact object dark matter in the mass range $(10^{-11} - 10^{3}) M_{\odot}$. Primordial Black Holes (PBHs) form clusters, and it has been argued that these microlensing constraints are consequently weakened or evaded. For the most commonly studied PBH formation mechanism, the collapse of large gaussian curvature perturbations generated by inflation, the clusters are sufficiently extended that the PBHs within them act as individual lenses. We find that if the typical mass of the clusters is sufficiently large, $ \gtrsim 10^{6} M_{\odot}$, the…
We show that quasar microlensing magnification statistics induced by a population of point microlenses distributed according to a mass-spectrum can be very well approximated by that of a single-mass, "monochromatic", population. When the spatial resolution (physically defined by the source size) is small as compared with the Einstein radius, the mass of the monochromatic population matches the geometric mean of the mass-spectrum. Otherwise, the best-fit mass can be larger. Taking into account the degeneracy with the geometric mean, the interpretation of quasar microlensing observations under t…
Using a set of cosmological hydro-dynamical simulations, we constrained the properties of primordial magnetic fields by studying their impact on the formation and evolution of dwarf galaxies. We performed a large set of simulations (8 dark matter only and 72 chemo-hydrodynamical) including primordial magnetic fields through the extra density fluctuations they induce at small length scales ($k \geq 10\,h\,\rm{Mpc^{-1}}$) in the matter power spectrum. We explored a large variety of primordial magnetic fields with strength $B_λ$ ranging from $0.05$ to $0.50\,\textrm{nG}$ and magnetic energy spect…
High redshift quasars emit copious X-ray photons which heat the intergalactic medium to temperatures up to $\sim$ 10$^6$ K. At such high temperatures the primordial gas will not form stars until it is assembled into dark matter haloes with masses of up to $\sim$ 10$^{11}$ M$_{\odot}$, at which point the hot gas collapses and cools under the influence of gravity. Once this occurs, there is a massive reservoir of primordial gas from which stars can form, potentially setting the stage for the brightest Population (Pop) III starbursts in the early Universe. Supporting this scenario, recent observa…
We perform a set of cosmological simulations of early structure formation with incorporating baryonic streaming motions. We present a case where a significantly elongated gas cloud with $\sim\!10^4\,$solar masses (${\rm M_\odot}$) is formed in a pre-galactic ($\sim\!10^7\,{\rm M_\odot}$) dark halo. The gas streaming into the halo compresses and heats the massive filamentary cloud to a temperature of $\sim\!10,000\,$Kelvin. The gas cloud cools rapidly by atomic hydrogen cooling, and then by molecular hydrogen cooling down to $\sim\!400\,$Kelvin. The rapid decrease of the temperature and hence o…
We show that some or all of the inventory of $r$-process nucleosynthesis can be produced in interactions of primordial black holes (PBHs) with neutron stars (NSs) if PBHs with masses ${10}^{-14}\,{\rm M}_\odot < {\rm M}_{\rm PBH} < {10}^{-8}\,{\rm M}_\odot$ make up a few percent or more of the dark matter. A PBH captured by a neutron star (NS) sinks to the center of the NS and consumes it from the inside. When this occurs in a rotating millisecond-period NS, the resulting spin-up ejects $\sim 0.1-0.5\,{\rm M}_{\odot}$ of relatively cold neutron-rich material. This ejection process and the acco…
