Shmuel Bialy, Amiel Sternberg, Abraham Loeb
We demonstrate that high abundances of water vapor could have existed in extremely low metallicity ($10^{-3}$ solar) partially shielded gas, during the epoch of first metal enrichment of the interstellar medium of galaxies at high redshifts.
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The star formation and metal enrichment histories of galaxies - at any epoch - constitute one of the key properties of galaxies, and their measurement is a core aim of observational extragalactic astronomy. The lack of deep rest-frame optical coverage at high-redshift has made robust constraints elusive, but this is now changing thanks to the \emph{James Webb Space Telescope (JWST)}. In preparation for the constraints provided by \emph{JWST} we explore the star formation and metal enrichment histories of galaxies at $z=5-13$ using the First Light And Reionisation Epoch Simulations (FLARES) sui…
We carry out Monte-Carlo simulation to study deuterium enrichment of interstellar grain mantles under various physical conditions. Based on the physical properties, various types of clouds are considered. We find that in diffuse cloud regions, very strong radiation fields persists and hardly a few layers of surface species are formed. In translucent cloud regions with a moderate radiation field, significant number of layers would be produced and surface coverage is mainly dominated by photo-dissociation products such as, C,CH_3,CH_2D,OH and OD. In the intermediate dense cloud regions (having n…
The presence of elements heavier than helium ("metals") is of fundamental importance for a large number of astrophysical processes occurring in planet, star and galaxy formation; it also affects cosmic structure formation and evolution in several ways. Even a small amount of heavy elements can dramatically alter the chemistry of the gas, opening the path to complex molecules. Metals might enhance the ability of the gas to radiate away its thermal energy, thus favoring the formation of gravitationally bound objects; they can also condensate in a solid phase (dust grains), partly or totally bloc…
Quasars are powerful systems whose spectrum is rich of metal features that allow us to investigate the chemical evolution of galaxies at very high redshift, even close to the reionization epoch. I review the main observational constraints on the metallicity of quasars host galaxies at high redshift and discuss the implications and issues for models of galaxy evolution in the early universe.
Water D/H in 3I/ATLAS as a Probe of Formation Conditions in Another Planetary System
通过ALMA观测3I/ATLAS的水氘/氢比，发现其氘富集程度远高于地球和太阳系彗星，暗示其形成环境温度更低、辐射更弱，可能来自不同物理化学条件的行星系统。
JWST Reveals Refractory-Rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties across Protoplanetary Disks
JWST观测星际彗星3I/ATLAS，发现其富含耐火材料的水冰聚集体，连接了太阳系彗发与海王星外天体，表明原行星盘冰颗粒性质存在连续谱。
We present X-SHOOTER near-infrared spectroscopy of a large sample of 38 luminous ($M_{1450}=-29.0$ to $-24.4$) quasars at $5.78<z<7.54$, which have complementary CII observations from ALMA. This X-SHOOTER/ALMA sample provides us with the most comprehensive view of reionization-era quasars to date, allowing us to connect the quasar properties with those of its host galaxy. In this work we introduce the sample, discuss data reduction and spectral fitting, and present an analysis of the broad emission line properties. The measured FeII/MgII flux ratio suggests that the broad line regions of all q…
VLBI multi-epoch water maser observations are a powerful tool to study the gas very close to the central engine responsible for the phenomena associated with the early evolution of massive protostars. In this paper we present a summary of the main observational results obtained toward the massive star-forming regions of Cepheus A and W75N. These observations revealed unexpected phenomena in the earliest stages of evolution of massive objects (e.g., non-collimated "short-lived" pulsed ejections in different massive protostars), and provided new insights in the study of the dynamic scenario of t…
Based on very deep photometry, Surface Brightness Fluctuations (SBF) have been traditionally used to determine galaxy distances. We have recently computed SBF spectra of stellar populations at moderately high resolution, which are fully based on empirical stars. We show that the SBF spectra provide an unprecedented potential for stellar population studies that, so far, have been tackled on the basis of the mean fluxes. We find that the SBFs are able to unveil metal-poor stellar components at the one percent level, which are not possible to disentangle with the standard analysis. As these metal…
We present the results of second epoch ALMA observations of 321 GHz H$_2$O emission toward two nearby active galactic nuclei, NGC 4945 and the Circinus galaxy, together with Tidbinbilla 70-m monitoring of their 22 GHz H$_2$O masers. The two epoch ALMA observations show that the strengths of the 321 GHz emission are variable by a factor of at least a few, confirming a maser origin. In the second epoch, 321 GHz maser emission from NGC 4945 was not detected, while for the Circinus galaxy the flux density significantly increased and the velocity gradient and dispersion have been measured. With the…
First Light And Reionization Epoch Simulations (FLARES) XXI: The UV Indices of Galaxies in the Early Universe
本文通过合成光谱建模和宇宙学模拟，研究了高红移星系紫外指数与恒星金属licity及恒星形成历史的关系，建立了理论框架并重现了合成质量-金属licity关系。
How homogeneous was the chemical enrichment of the Milky Way 13 gigayears ago?
利用高精度大气参数和3D NLTE模型重新分析银河系halo最贫金属尾部，发现在[Fe/H]介于-3.5至-2 dex时[Mg/Fe]分布较窄，表明早期镁的随机增丰程度低。
GA-NIFS: ISM properties and metal enrichment in a merger-driven starburst during the Epoch of Reionisation probed with JWST and ALMA
基于JWST和ALMA观测，研究再电离时期星系COS-3018的三个并合组件，通过积分场光谱测量其ISM温度、密度与金属丰度，发现氮富集源于小子结构，并合过程驱动了当前的星暴。
The epoch of reionization and formation of first stars are inter-linked topics that are of considerable interest. We use a simplified approach for studying formation of stars in collapsed haloes, and the resulting ionization of the inter-galactic medium (IGM). We consider a set of LCDM models allowed by observations of CMB temperature and polarization anisotropies for this study. We constrain parameters related to star formation with the help of observations. We constrain subsets of these parameters independently by using the observed metallicity of the inter-galactic medium at z ~ 5 and the r…
Galaxies throughout the last 12 Gyr of cosmic time follow a single, universal relation that connects their star-formation rates (SFRs), stellar masses ($M_\star$) and chemical abundances. Deviation from these fundamental scaling relations would imply a drastic change in the processes that regulate galaxy evolution. Observations have hinted at the possibility that this relation may be broken in the very early universe. However, until recently, chemical abundances of galaxies could be only measured reliably as far back as redshift $z=3.3$. With JWST, we can now characterize the SFR, $M_\star$, a…
AEOS: Star-by-Star Cosmological Simulations of Early Chemical Enrichment and Galaxy Formation
AEOS项目通过1 pc分辨率的逐颗恒星宇宙学模拟，研究早期宇宙中化学增丰与星系形成，揭示了古老恒星化学丰度对早期核合成和星系演化的关键约束作用。
We investigate the formation of metal-poor globular clusters (GCs) at the center of two dark matter halos with $M_{\rm halo} \sim4\times10^7 M_\odot$ at $z>10$ using cosmological radiation-hydrodynamics simulations. We find that very compact ($\lesssim$ 1 pc) and massive ($\sim6\times10^5 M_\odot$) clusters form rapidly when pristine gas collapses isothermally with the aid of efficient Ly$α$ emission during the transition from molecular-cooling halos to atomic-cooling halos. Because the local free-fall time of dense star-forming gas is very short ($\ll 1\,{\rm Myr}$), a large fraction of the c…
We employ our Bayesian Machine Learning framework BINGO (Bayesian INference for Galactic archaeOlogy) to obtain high-quality stellar age estimates for 68,360 red giant and red clump stars present in the 17th data release of the Sloan Digital Sky Survey, the APOGEE-2 high-resolution spectroscopic survey. By examining the denoised age-metallicity relationship of the Galactic disc stars, we identify a drop in metallicity with an increase in [Mg/Fe] at an early epoch, followed by a chemical enrichment episode with increasing [Fe/H] and decreasing [Mg/Fe]. This result is congruent with the chemical…
We report the discovery of Serenity-18, a galaxy at z=5.939 for which we could measure the content of molecular gas, M(H_2)~ 5 x10^9 M_sun, traced by the CO(6-5) emission, together with the metal-poor ([Fe/H]=-3.08 +- 0.12, [Si/H]=-2.86 +- 0.14) gas clump/filament which is possibly feeding its growth. The galaxy has an estimated star formation rate of ~100 M_sun yr^{-1}, implying that it is a typical main sequence galaxy at these redshifts. The metal-poor gas is detected through a damped Lyman-alpha absorber (DLA) observed at a spatial separation of 40 kpc and at the same redshift of Serenity-…
We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M 33 (Triangulum). A new method has been developed by us to use pulsating giant stars to reconstruct the star formation history of galaxies over cosmological time as well as using them to map the dust production across their host galaxies. In first Instance the central square kiloparsec of M33 was monitored and long period variable stars (LPVs) were identified. We give evidence of two epochs of a star formation rate enhanced by a factor of a few. These stars are also imp…
As building blocks of dust, rocky planets, and even complex life, the chemical elements heavier than hydrogen (H) and helium (He) - called "metals" in astronomy - play an essential role in our Universe and its evolution. Up to Fe and Ni, these metals are known to be created by stars and stellar remnants via nuclear fusion and to be ejected into their immediate surroundings to enrich new stellar generations. A spectacular finding, however, is that these processed elements are found even outside stellar systems, in particular in the hot, X-ray atmospheres surrounding early-type galaxies and perv…
We report a multi-epoch, simultaneous 22 GHz H2O and 44 GHz class I CH3OH maser line survey towards 180 intermediate-mass young stellar objects, including 14 Class 0, 19 Class I objects, and 147 Herbig Ae/Be stars. We detected H2O and CH3OH maser emission towards 16 (9%) and 10 (6%) sources with one new H2O and six new CH3OH maser sources. The detection rates of both masers rapidly decrease as the central (proto)stars evolve, which is contrary to the trends in high-mass star-forming regions. This suggests that the excitations of the two masers are closely related to the evolutionary stage of t…
Upper limit on HF(1-0) absorption in a dusty star-forming galaxy at $z = 6$: Constraints on early fluorine enrichment
研究通过观测z=6星系的HF吸收，限制了早期氟元素富集，发现其效率低下，并表明WR星可能未在该时期显著贡献氟生产。
The production and distribution of metals in the diffuse intergalactic medium (IGM) have implications for galaxy formation models and the baryon (re)cycling process. The relative abundance of metals in high versus low-ionization states has also been argued to be sensitive to the Universe's reionization history. However, measurements of the background metallicity of the IGM at z~4 are sparse and in poor agreement with one another, and reduced sensitivity in the near-IR renders detecting individual metal absorbers nearly impossible. We present a new clustering-based technique that enables the de…
EIGER VIII: First stars signatures in the connection between OI absorption and Galaxies in the Epoch of Reionization
EIGER VIII研究了再电离时期银河系与OI吸收系统的关系，发现这些系统与银河系的关联性及金属富集特征。
In this work, we have implemented a detailed physical model of galaxy chemical enrichment into the ${\it Astraeus}$ (semi-numerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dark matter simUlationS) framework which couples galaxy formation and reionization in the first billion years. Simulating galaxies spanning over 2.5 orders of magnitude in halo mass with $M_h \sim 10^{8.9-11.5} M_\odot$ ($M_h \sim 10^{8.9-12.8} M_\odot$) at $z \sim 10 ~ (5)$, we find: (i) smooth-accretion of metal-poor gas from the intergalactic medium (IGM) plays a key role in diluting the…
Ejection activities in S255IR-SMA1 and AFGL 5142 were investigated by multi-epoch VLBI observations of 22 GHz water masers, tracing bowshocks leading collimated jets. The history of ejections, revealed by the 3D maser motions and supplemented by the literature, suggests that these massive stars formed by episodic accretion, inferred via the accretion-ejection connection. This contribution centers on the role of episodic accretion in overcoming the radiation pressure problem of massive star formation - with maser VLBI and single-dish observations providing essential observational tools.
The hot intra-cluster medium (ICM) is rich in metals, which are synthesised by supernovae (SNe) and accumulate over time into the deep gravitational potential well of clusters of galaxies. Since most of the elements visible in X-rays are formed by type Ia (SNIa) and/or core-collapse (SNcc) supernovae, measuring their abundances gives us direct information on the nucleosynthesis products of billions of SNe since the epoch of the star formation peak (z~2-3). In this study, we compare the most accurate average X/Fe abundance ratios (compiled in a previous work from XMM-Newton EPIC and RGS observa…
The ATCA has been used to measure positions with arcsecond accuracy for 379 masers at the 22-GHz transition of water. The principal observation targets were 202 OH masers of the variety associated with star formation regions (SFR)s in the Southern Galactic plane. At a second epoch, most of these targets were observed again, and new targets of methanol masers were added. Many of the water masers reported here are new discoveries. Variability in the masers is often acute, with very few features directly corresponding to those discovered two decades ago. Within our current observations, less than…
Dust enrichment in the circum-galactic medium
本研究开发了星系周介质尘埃增丰模型，发现尘埃破坏与外流供应主导其丰度，且模型结果与SDSS观测一致。
We use synthetic sightlines drawn through snapshots of the Technicolor Dawn simulations to explore how the statistics of neutral oxygen OI absorbers respond to hydrogen reionization. The ionization state of the circumgalactic medium (CGM) initially roughly tracks that of the intergalactic medium, but beginning at $z=8$ the CGM grows systematically more neutral owing to self-shielding. Weak absorbers trace diffuse gas that lies farther from halos, hence they are ionized first, whereas stronger systems are less sensitive to reionization. The overall OI covering fraction decreases slowly with tim…
We present the modeling results of deuterium fractionation of water ice, H2, and the primary deuterium isotopologues of H3+ adopting physical conditions associated with the star and planet formation process. We calculated the deuterium chemistry for a range of gas temperatures (T_gas ~ 10 - 30 K), molecular hydrogen density (n(H2)~ 10^4 - 10^7), and ortho/para ratio (opr) of H2 based on state-to-state reaction rates and explore the resulting fractionation including the formation of a water ice mantle coating grain surfaces. We find that the deuterium fractionation exhibits the expected tempera…
On the importance of the IGM/CGM enrichment in determining chemical abundances during the first 600 Myr
本研究开发纳入IGM/CGM多源富集与高红移星系观测SFHs的化学演化模型，发现IGM/CGM化学组成对z>8星系丰度比的关键作用，且SMSs是早期丰度的重要来源。
Unlike spiral galaxies such as the Milky Way, the majority of the stars in massive elliptical galaxies were formed in a short period early in the history of the Universe. The duration of this formation period can be measured using the ratio of magnesium to iron abundance ([Mg/Fe]), which reflects the relative enrichment by core-collapse and type Ia supernovae. For local galaxies, [Mg/Fe] probes the combined formation history of all stars currently in the galaxy, including younger and metal-poor stars that were added during late-time mergers. Therefore, to directly constrain the initial star-fo…
We present Very Long Baseline Interferometry (VLBI) observations of 22 GHz H$_2$O masers in the high-mass star-forming region of \objectname{W75N}, carried out with VLBI Exploration of Radio Astrometry (VERA) for three-epochs in 2007 with an angular resolution of $\sim$ 1 mas. We detected H$_2$O maser emission toward the radio jet in VLA 1 and the expanding shell-like structure in VLA 2. We have made elliptical fits to the VLA 2 H$_2$O maser shell-like structure observed in the different epochs (1999, 2005, and 2007), and found that the shell is still expanding eight years after its discovery.…
Overdense, metal-rich regions, shielded from stellar radiation might remain neutral throughout reionization and produce metal as well as 21 cm absorption lines. Simultaneous absorption from metals and 21 cm can complement each other as probes of underlying gas properties. We use Aurora, a suite of high resolution radiation-hydrodynamical simulations of galaxy formation, to investigate the occurrence of such "aligned" absorbers. We calculate absorption spectra for 21 cm, OI, CII, SiII and FeII. We find velocity windows with absorption from at least one metal and 21 cm, and classify the aligned …
We find a bright (L_{UV}=2.5 L*_{z=6}) Lyman alpha emitter at redshift z=5.719 at a projected distance of 79 physical kpc from a strong triply ionized carbon (Civ) absorption system at redshift z=5.7238 previously reported in the spectrum of the z_{em} = 6.309 QSO SDSS J1030+0524. This is the highest redshift galaxy-absorber pair detected to-date, supporting the idea that galaxy-wide outflows were already in place at the end of the epoch of reionization. The proximity of this object makes it the most likely source of metals, consistent with models of outflows at lower redshift where significan…
The Local Group (LG) hosts many dwarf galaxies with diverse physical characteristics in terms of morphology, mass, star formation, and metallicity. To this end, LG can offer a unique site to tackle questions about the formation and evolution of galaxies by providing detailed information. While large telescopes are often the first choices for such studies, small telescope surveys that perform dedicated observations are still important, particularly in studying bright objects in the nearby universe. In this regard, we conducted a nine epoch survey of 55 dwarf galaxies called the Local Group dwar…
The earliest phases of CNO enrichment in galaxies
本文通过引入随机恒星形成和星族III超新星增丰的化学演化模型，解释了银河系晕星CNO丰度弥散及GN-z11等遥远星系的高N/O比值，揭示Pop III恒星对早期化学演化的关键作用。
We report the results of a sensitive search for water maser emission in the Local Group Galaxy NGC 6822 with the Karl G. Jansky Very Large Array. The observations provide tentative single-epoch detections of four candidates, associated with two infrared-bright star formation regions (Hubble I/III and Hubble IV). The candidate maser detections are all offset from the velocity range where strong emission from HI neutral gas is observed toward NGC 6822, with the closest offset by 40 kms$^{-1}$. Our observations include the location of NL1K, a previous tentative water maser detection in NGC 6822. …
We investigate the water deuteration ratio and ortho-to-para nuclear spin ratio of H2 (OPR(H2)) during the formation and early evolution of a molecular cloud, following the scenario that accretion flows sweep and accumulate HI gas to form molecular clouds. We follow the physical evolution of post-shock materials using a one-dimensional shock model, with post-processing gas-ice chemistry simulations. This approach allows us to study the evolution of the OPR(H2) and water deuteration ratio without an arbitrary assumption concerning the initial molecular abundances, including the initial OPR(H2).…
We identified and characterized the largest (536) RR Lyrae (RRL) sample in a Milky Way dSph satellite (Sculptor) based on optical photometry data collected over $\sim$24 years. The RRLs display a spread in V-magnitude ($\sim$0.35 mag) which appears larger than photometric errors and the horizontal branch (HB) luminosity evolution of a mono-metallic population. Using several calibrations of two different reddening free and metal independent Period-Wesenheit relations we provide a new distance estimate $μ$=19.62 mag ($σ_μ$=0.04 mag) that agrees well with literature estimates. We constrained the …
The large-scale overdensities of galaxies at z~2-7 known as protoclusters are believed to be the sites of cluster formation, and deep, wide survey projects such as the Large Synoptic Survey Telescope (LSST) and the Wide Field Infrared Survey Telescope (WFIRST) will deliver significant numbers of these interesting structures. Spectroscopic confirmation and interpretation of these targets, however, is still challenging, and will require wide-field multi-plexed spectroscopy on >20 m-class telescopes in the optical and near-infrared. In the coming decade, detailed studies of protoclusters will ena…
An analysis of negative radiative feedback from resident stars in minihalos is performed. It is found that the most effective mechanism to suppress star formation is provided by infrared photons from resident stars via photo-detachment of ${\rm H^-}$. It is shown that a stringent upper bound on (total stellar mass, metallicity) of ($\sim 1000{\rm M_\odot}$, $-3.3\pm 0.2$) in any newly minted atomic cooling halo can be placed, with the actual values possibly significantly lower. This has both important physical ramifications on formation of stars and supermassive black seeds in atomic cooling h…
We use N-body simulations of star cluster evolution to explore the hypothesis that short-lived radioactive isotopes found in meteorites, such as 26-Al, were delivered to the Sun's protoplanetary disc from a supernova at the epoch of Solar System formation. We cover a range of star cluster formation parameter space and model both clusters with primordial substructure, and those with smooth profiles. We also adopt different initial virial ratios - from cool, collapsing clusters to warm, expanding associations. In each cluster we place the same stellar population; the clusters each have 2100 star…
We present results on the formation of Pop III stars at redshift 7.6 from the Renaissance Simulations, a suite of extremely high-resolution and physics-rich radiation transport hydrodynamics cosmological adaptive-mesh refinement simulations of high redshift galaxy formation performed on the Blue Waters supercomputer. In a survey volume of about 220 comoving Mpc$^3$, we found 14 Pop III galaxies with recent star formation. The surprisingly late formation of Pop III stars is possible due to two factors: (i) the metal enrichment process is local and slow, leaving plenty of pristine gas to exist i…
First star formation in extremely early epochs
本研究针对极早宇宙时期的第一代恒星形成问题，通过纳入CMB效应的单区热化学模型模拟发现，不同红移时期第一代恒星质量差异显著，极高红移下可形成超大质量恒星。
Galactic-scale outflows regulate the stellar mass growth and chemical enrichment of galaxies, yet key outflow properties such as the chemical composition and mass loss rate remain largely unknown. We address these properties with Keck/ESI echellete spectra of nine gravitationally lensed z=2-3 star forming galaxies, probing a range of absorption transitions. Interstellar absorption in our sample is dominated by outflowing material, with typical velocities -150 km/s. Approximately 80% of the total column density is associated with a net outflow. Mass loss rates in the low ionization phase are co…
We report the detection of four water masers within the Small Magellanic Cloud (SMC); two discovered with the 70-m Tidbinbilla radio telescope, and two discovered with the Australia Telescope Compact Array (ATCA). Precise positions of all four masers have been derived from ATCA observations, and the characteristics of each water maser have been monitored over a period of several years. Sensitive observations towards two previously detected water masers reported in the literature failed to detect any emission. The detected water masers show evidence of higher levels of temporal variability than…
Recent interferometer observations have found that the D2O/HDO abundance ratio is higher than that of HDO/H2O by about one order of magnitude in the vicinity of low-mass protostar NGC 1333-IRAS 2A, where water ice has sublimated. Previous laboratory and theoretical studies show that the D2O/HDO ice ratio should be lower than the HDO/H2O ice ratio, if HDO and D2O ices are formed simultaneously with H2O ice. In this work, we propose that the observed feature, D2O/HDO > HDO/H2O, is a natural consequence of chemical evolution in the early cold stages of low-mass star formation: 1) majority of oxyg…
State-of-the-art rest-frame UV and FIR photometric and spectroscopic observations are now pushing the redshift frontiers of galaxy formation studies up to $z\sim9-11$ and beyond. Recent HST observations unveiled the presence of a star-forming galaxy exhibiting the Lyman break at $λ_{\rm obs}=1.47\pm0.01$ $μ$m, i.e., a $z=11.09^{+0.08}_{-0.12}$ galaxy with a stellar mass of $\sim10^9 M_\odot$, demonstrating that galaxy build-up was well underway early in the epoch of reionization (EoR) at $z>10$. Targeted spectroscopy of a lensed Lyman break galaxy uncovers the earliest metals known to date up …
We study the efficiency of galactic feedback in the early Universe by stacking the [C II] 158 um emission in a large sample of normal star-forming galaxies at 4 < z < 6 from the ALMA Large Program to INvestigate [C II] at Early times (ALPINE) survey. Searching for typical signatures of outflows in the high-velocity tails of the stacked [C II] profile, we observe (i) deviations from a single-component Gaussian model in the combined residuals and (ii) broad emission in the stacked [C II] spectrum, with velocities of |v|<~ 500 km/s. The significance of these features increases when stacking the s…
Aeos: Transport of Metals from Minihalos following Population III Stellar Feedback
本文使用逐星宇宙学流体动力学模拟Aeos，研究了第三星族恒星反馈如何将金属输运至星际和星系际介质，发现超新星能量将大部分气体和金属驱赶出微型晕位力半径，延迟了富集恒星形成并延长了第三星族恒星形成期，同时揭示了早期化学增丰机制。
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