本文报道了JWST在z=8.16发现的星系RXJ2129-z8HeII，其极蓝紫外光谱斜率和强He II λ1640发射线表明可能存在星族III恒星，光致电离建模支持该解释，为早期宇宙中星族III恒星与富金属族群共存提供了迄今最有力的观测证据。
摘要：
宇宙氢再电离和首批金属的宇宙学产生是宇宙大爆炸后最初十亿年内发生的主要相变，然而这些在观测上仍未得到充分探索。利用JWST NIRSpec棱镜光谱，我们报告了通过探测一系列强的静止系紫外/光学星云发射线和清晰的莱曼截断，发现了一个亚L*星系，其光谱红移为z_spec=8.1623±0.0007，命名为RXJ2129-z8HeII。RXJ2129-z8HeII展现出显著的紫外连续谱，具有极陡（即蓝色）的光谱斜率β=-2.53_{-0.07}^{+0.06}，这是所有光谱证认的z_spec≳7星系中最陡的，支持其具有非常硬的电离谱，可能导致其电离通量的显著泄漏。因此，RXJ2129-z8HeII是驱动宇宙再电离的关键星系群体的代表。更重要的是，我们在其光谱中探测到一条强的He II λ1640发射线，这是该谱线被可靠探测到的最高红移之一。其高静止系等值宽度（EW=21±4埃）以及相对于紫外金属线和巴尔末线的极端通量比，增加了RXJ2129-z8HeII的部分恒星族群可能类似星族III恒星的可能性。通过仔细的光致电离建模，我们展示了具有强质量损失的星族III恒星电离谱的物理校准唯象模型能够成功重现RXJ2129-z8HeII中观测到的发射线通量比。假设爱丁顿极限，该系统内星族III恒星的总质量估计为7.8±1.4×10^5 M_⊙。迄今为止，该星系提供了早期宇宙中最具说服力的案例，表明微量的星族III恒星可能与富含金属的族群共存。
英文摘要：
Cosmic hydrogen reionization and cosmic production of first metals are major phase transitions of the universe occurring during the first billion years after the Big Bang, however these are still underexplored observationally. Using the JWST NIRSpec prism spectroscopy, we report the discovery of a sub-$L_\ast$ galaxy at $z_{\rm spec}=8.1623\pm0.0007$, dubbed RXJ2129-z8HeII, via the detection of a series of strong rest-frame UV/optical nebular emission lines and the clear Lyman break. RXJ2129-z8HeII shows a pronounced UV continuum with an extremely steep (i.e. blue) spectral slope of $β=-2.53_{-0.07}^{+0.06}$, the steepest amongst all spectroscopically confirmed galaxies at $z_{\rm spec}\gtrsim7$, in support of its very hard ionizing spectrum that could lead to a significant leakage of its ionizing flux. Therefore, RXJ2129-z8HeII is representative of the key galaxy population driving the cosmic reionization. More importantly, we detect a strong He II $λ$1640 emission line in its spectrum, one of the highest redshifts at which such a line is robustly detected. Its high rest-frame equivalent width (${\rm EW}=21\pm4$ Angstrom) and extreme flux ratios with respect to UV metal and Balmer lines raise the possibility that part of RXJ2129-z8HeII's stellar populations could be Pop III-like. Through careful photoionization modeling, we show that the physically calibrated phenomenological models of the ionizing spectra of Pop III stars with strong mass loss can successfully reproduce the emission line flux ratios observed in RXJ2129-z8HeII. Assuming the Eddington limit, the total mass of the Pop III stars within this system is estimated to be $7.8\pm1.4\times10^5 M_\odot$. To date, this galaxy presents the most compelling case in the early universe where trace Pop III stars might coexist with metal-enriched populations.
We study six luminous Lyman-alpha emitters (LAEs) with very blue rest-frame UV continua at $5.7\le z \le 6.6$. These LAEs have previous HST and Spitzer IRAC observations. Combining our newly acquired HST images, we find that their UV-continuum slopes $β$ are in a range of $-3.4\le β\le -2.6$. Unlike previous, tentative detections of $β\simeq -3$ in photometrically selected, low-luminosity galaxies, our LAEs are spectroscopically confirmed and luminous ($M_{\rm UV}<-20$ mag). We model their broadband spectral energy distributions (SEDs), and find that two $β\simeq-2.6\pm0.2$ galaxies can be wel…
We report the discovery of a double-peaked Lyman-$α$ (Ly$α$) emitter (LAE) at $z=3.2177\pm0.0001$ in VLT/MUSE data. The galaxy is strongly lensed by the galaxy cluster RXC~J0018.5+1626 recently observed in the RELICS survey, and the double-peaked Ly$α$ emission is clearly detected in the two counter images in the MUSE field-of-view. We measure a relatively high Ly$α$ rest-frame equivalent width (EW) of $\mathrm{EW}_{\mathrm{Ly}α,0}=(63\pm2)\,\mathring{\mathrm{A}}$. Additional near-infrared (NIR) spectroscopy allows us to measure the H$β$, [OIII]$\lambda4959\,\mathring{\mathrm{A}}$ and [OIII]$\…
We present the results of a Lya profile analysis of 12 Lya emitters (LAEs) at z = 2.2 with high-resolution Lya spectra. We find that all 12 objects have a Lya profile with the main peak redward of the systemic redshift defined by nebular lines, and five have a weak, secondary peak blueward of the systemic redshift (blue bump). The average velocity offset of the red main peak (the blue bump, if any) with respect to the systemic redshift is Delta_v_Lya,r = 174+/- 19 km s-1 (Delta_v_Lya,b = -316+/-45 km s-1), which is smaller than (comparable to) that of Lyman-break galaxies (LBGs). The outflow v…
We report the detection of the most luminous high-redshift Lyman Alpha Emitting galaxy (LAE) yet seen, with log L(Ly alpha) = 43.9 ergs/s. The galaxy -- COSMOS Lyman alpha 1, or COLA1 -- was detected in a search for ultra-luminous LAEs with Hyper Suprime-Cam on the Subaru telescope. It was confirmed to lie at z = 6.593 based on a Lyman alpha line detection obtained from followup spectroscopy with the DEIMOS spectrograph on Keck2. COLA1 is the first very high-redshift LAE to show a multi-component Lyman alpha line profile with a blue wing, which suggests that it could lie in a highly ionized re…
A Census of Double-Peaked Lyman-alpha Emitters in MAGPI: Classification, Global Characteristics, and Spatially Resolved Properties
Macquarie University（麦考瑞大学）；Swinburne University of Technology（斯威本科技大学）；Observatori Astronòmic de la Universitat de València（瓦伦西亚大学天文台）；International Centre for Radio Astronomy Research (ICRAR), Curtin University（伊萨研究中心（ICRAR），科廷大学）；Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院悉尼天体物理学研究所）；International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia（伊萨研究中心（ICRAR），西澳大学）
We present herein a systematic X-ray analysis of blue galaxy-clusters at $z=0.84$ discovered by the Subaru telescope. The sample consisted of 43 clusters identified by combining red-sequence and blue-cloud surveys, covering a wide range of emitter fractions (i.e., 0.3--0.8). The spatial extent of the over-density region of emitter galaxies was approximately 1~Mpc in radius. The average cluster mass was estimated as $0.6 (<1.5)\times10^{14}~{\rm M_\odot}$ from the stacked weak-lensing measurement. We analyzed the XMM-Newton archival data, and measured the X-ray luminosity of the hot intracluste…
We assemble a sample of 17 low metallicity (7.45 < log(O/H)+12 < 8.12) galaxies with z < 0.1 found spectroscopically, without photometric pre-selection, in early data from the Hobby Eberly Telescope Dark Energy Experiment (HETDEX). Star forming galaxies that occupy the lowest mass and metallicity end of the mass-metallicity relation tend to be under sampled in continuum-based surveys as their spectra are typically dominated by emission from newly forming stars. We search for galaxies with high [OIII]$λ$5007 / [OII]$λ$3727, implying highly ionized nebular emission often indicative of low metall…
We present a detailed multi-wavelength study (from rest-frame UV to far-IR) of narrow-band (NB) selected, star-forming (SF) H$α$ emitters (HAEs) at $z \sim 2.23$ taken from the High Redshift(Z) Emission Line Survey (HiZELS). We find that HAEs have similar SED-derived properties and colors to $sBzK$ galaxies and probe a well-defined portion of the SF population at $z \sim 2$. This is not true for Ly$α$ emitters (LAEs), which are strongly biased towards blue, less massive galaxies (missing a significant percentage of the SF population). Combining our H$α$ observations with matched, existing Ly$α…
As the James Webb Space Telescope approaches scientific operation, there is much interest in exploring the redshift range beyond that accessible with Hubble Space Telescope imaging. Currently, the only means to gauge the presence of such early galaxies is to age-date the stellar population of systems in the reionisation era. As a significant fraction of $z\simeq7-8$ galaxies are inferred from Spitzer photometry to have extremely intense [OIII] emission lines, it is commonly believed these are genuinely young systems that formed at redshifts $z<10$, consistent with a claimed rapid rise in the s…
The ionizing properties of JWST's compact broad-line emitters
Institute of Science and Technology Austria (ISTA)（奥地利科学技术研究所）；Princeton University（普林斯顿大学）；Massachusetts Institute of Technology（麻省理工学院）；MIT Kavli Institute for Astrophysics and Space Research（麻省理工学院卡弗里天体物理学与空间研究研究所）；University of Hawai’i（夏威夷大学）
We present the first results from the X-SHOOTER Lyman-$α$ survey at $z=2$ (XLS-$z2$). XLS-$z2$ is a deep spectroscopic survey of 35 Lyman-$α$ emitters (LAEs) utilising $\approx90$ hours of exposure time with VLT/X-SHOOTER and covers rest-frame Ly$α$ to H$α$ emission with R$\approx4000$. We present the sample selection, the observations and the data reduction. Systemic redshifts are measured from rest-frame optical lines for 33/35 sources. In the stacked spectrum, our LAEs are characterised by an interstellar medium with little dust, a low metallicity and a high ionisation state. The ionising s…
Using an unconventional single line diagnostic that unambiguously identifies AGNs in composite galaxies we report statistical differences in the properties (stellar age, [OII] luminosity, colour) between active and inactive galaxies at 0.62<z<1.2 extracted from the VIMOS Public Extragalactic Redshift Survey (VIPERS). The nuclear activity is probed by the high-ionization [NeV] emission line and along with their parent samples, the galaxies are properly selected according to their stellar mass, redshift, and colour distributions. We report younger underlying stellar ages and higher [OII] luminos…
Comprehensive JWST+ALMA Study on the Extended Ly$α$ Emitters, Himiko and CR7 at $z\sim 7$: Blue Major Merger Systems in Stark Contrast to Submillimeter Galaxies
We present and discuss new BVI CCD photometry in the field of the globular cluster Arp~2, which is considered a member of the Sagittarius Dwarf Spheroidal Galaxy. The main goal of this investigation is to study of the statistics and spatial distribution of blue straggler stars in the cluster. Blue stragglers are stars observed to be hotter and bluer than other stars with the same luminosity in their environment. As such, they appear to be much younger than the rest of the stellar population. Two main channels have been suggested to produce such stars: (1) collisions between stars in clusters o…
The Local Group starburst galaxy IC10 is the closest example of a blue compact galaxy. Here, we use optical gi imaging from CFHT/MegaCam and near infra-red JHK imaging from UKIRT/WFCAM to conduct a comprehensive survey of the structure of IC10. We examine the spatial distribution of its resolved young, intermediate and old stellar populations to large radius and low effective surface brightness levels. Akin to other dwarfs with multiple populations of different ages, stellar populations of decreasing average age are increasingly concentrated in this galaxy. We find that the young, star-burstin…
We present a multiwavelength spectral study of the quasar HE0359-3959, which has been identified as an extreme radiating source at intermediate redshift (z=1.5209). Along the spectral range, the different ionic species give information about the substructures in the broad line region. The presence of a powerful outflow with an extreme blueshifted velocity of $\sim$-6000$\pm$500 km s$^{-1}$ is shown in the CIVλ1549 emission line. A prominent blueshifted component is also associated with the 1900Å blend, resembling the one observed in CIVλ1549. We detect a strong contribution of very the low-ion…
We have found a sample of extreme emission-line galaxies (EELGs) with strong [OIII]$λ$5007 emission at z $\sim$ 0.5. Using broadband photometric selection and requiring small uncertainties in photometry, we searched the 14th Data Release (DR14) of the Sloan Digital Sky Survey (SDSS) and found 2658 candidates with strong i-band excess (i - z $\leqslant$ r - i - 0.7). We further obtained 649 SDSS spectra of these objects, and visually identified 22 [OIII] emitters lying at 0.40 $<$ z $<$ 0.63. Having constructed their UV-IR spectral energy distributions (SED) we found that they have fairly blue …
We report the first detections of Blue Straggler Stars (BSS) in the bulge of the Milky Way galaxy. Proper motions from extensive space-based observations along a single sight-line allow us to separate a sufficiently clean and well-characterized bulge sample that we are able to detect a small population of bulge objects in the region of the color-magnitude diagram commonly occupied young objects and blue strgglers. However, variability measurements of these objects clearly establish that a fraction of them are blue stragglers. Out of the 42 objects found in this region of the color-magnitude di…
The metal-poor sub-population of globular cluster (GC) systems exhibits a correlation between the GC average colour and luminosity, especially in those systems associated with massive elliptical galaxies. More luminous (more massive) GCs are typically redder and hence more metal-rich. This 'blue tilt' is often interpreted as a mass-metallicity relation stemming from GC self-enrichment, whereby more massive GCs retain a greater fraction of the enriched gas ejected by their evolving stars, fostering the formation of more metal-rich secondary generations. We examine the E-MOSAICS simulations of t…
Faint Lyman-$α$ (Ly$α$) emitters become increasingly rarer towards the re-ionisation epoch (z~6-7). However, observations from a very large (~5deg$^2$) Ly$α$ survey at z=6.6 (Matthee et al. 2015) show that this is not the case for the most luminous emitters. Here we present follow-up observations of the two most luminous z~6.6 Ly$α$ candidates in the COSMOS field: `MASOSA' and `CR7'. We used X-SHOOTER, SINFONI and FORS2 (VLT), and DEIMOS (Keck), to confirm both candidates beyond any doubt. We find redshifts of z=6.541 and z=6.604 for MASOSA and CR7, respectively. MASOSA has a strong detection …
CR7 is the brightest $z=6.6 \, {\rm Ly}α$ emitter (LAE) known to date, and spectroscopic follow-up by Sobral et al. (2015) suggests that CR7 might host Population (Pop) III stars. We examine this interpretation using cosmological hydrodynamical simulations. Several simulated galaxies show the same "Pop III wave" pattern observed in CR7. However, to reproduce the extreme CR7 ${\rm Ly}α$/HeII1640 line luminosities ($L_{\rm α/He II}$) a top-heavy IMF and a massive ($>10^{7}{\rm M}_{\odot}$) PopIII burst with age $<2$ Myr are required. Assuming that the observed properties of ${\rm Ly}α$ and HeII …
We present early results from a detailed analysis of the BSS population in Galactic GCs based on HST data.Using proper motion cleaning of the color-magnitude diagrams we construct a large catalog of BSSs and study some population properties.Stellar evolutionary models are used to find stellar mass and age estimates for the BSS populations in order to establish constraints related to the dynamical interactions in which they may have formed.
Blue Stragglers are stars located in an unexpected region of the color-magnitude diagram of a stellar population, as they appear bluer and more luminous than the stars in the turnoff region. They are ubiquitous, since they have been found among Milky Way field stars, in open and globular clusters, and also in other galaxies of the Local Group. Here we present a study on the blue straggler population of the old and metal-rich open cluster Collinder 261, based on Gaia DR2 data and on a multi-epoch radial velocity survey conducted with FLAMES@VLT. We also analyze the radial distribution of the bl…
Strong He II emission is produced by low-metallicity stellar populations. Here, we aim to identify and study a sample of He II $λ1640$-emitting galaxies at redshifts of $z \sim 2.5-5$ in the deep VANDELS spectroscopic survey.. We identified a total of 33 Bright He II emitters (S/N > 2.5) and 17 Faint emitters (S/N < 2.5) in the VANDELS survey and used the available deep multi-wavelength data to study their physical properties. After identifying seven potential AGNs in our sample and discarding them from further analysis, we divided the sample of \emph{Bright} emitters into 20 \emph{Narrow} (FW…
We present deep 10h VLT/XSHOOTER spectroscopy for an extraordinarily luminous and extended Lya emitter at z=6.595 referred to as Himiko and first discussed by Ouchi et al. (2009), with the purpose of constraining the mechanisms powering its strong emission. Complementary to the spectrum, we discuss NIR imaging data from the CANDELS survey. We find neither for HeII nor any metal line a significant excess, with 3 sigma upper limits of 6.8, 3.1, and 5.8x10^{-18} erg/s/cm^2 for CIV $λ$1549, HeII $λ$1640, CIII] $λ$1909, respectively, assuming apertures with 200 km/s widths and offset by -250 km/s w…
Many classes of active galactic nuclei (AGN) have been observed and recorded since the discovery of Seyfert galaxies. In this paper, we examine the sample of luminous galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS). We find a potentially new observational class of AGN, one with strong and broad MgII $2799$Å line emission, but very weak emission in other normal indicators of AGN activity, such as the broad line H$α$, H$β$, and the near-ultraviolet AGN continuum, leading to an extreme ratio of broad H$α$/MgII flux relative to normal quasars. Meanwhile, these objects' narrow-line f…
We present a multi-passband photometric study of the Blue Straggler Star (BSS) population in the Galactic globular cluster (GC) NGC\,1261, using available space- and ground-based survey data.~The inner BSS population is found to have two distinct sequences in the color-magnitude diagram, similar to double BSS sequences detected in other GCs. These well defined sequences are presumably linked to single short-lived events such as core collapse, which are expected to boost the formation of BSSs.~In agreement with this, we find a BSS sequence in NGC\,1261 which can be well reproduced individually …
We present a study, based on Gaia DR2, of the population of blue straggler stars (BSS) in the open clusters Trumpler 5, Trumpler 20, and NGC 2477. All candidates were selected according to their position in the color-magnitude diagram, to their proper motion components, and to their parallax. We also looked for yellow stragglers, i.e., possible evolved blue stragglers. We found that Trumpler 5 hosts a large BSS population, which allowed us to analyze their radial distribution as a probe of the cluster's dynamical status. The BSS distribution was compared with that of red giant branch stars (RG…
The z = 6.6 Lyman-$α$ emitter 'CR7' has been claimed to have a Population III-like stellar population, or alternatively, be a candidate Direct Collapse Black Hole (DCBH). In this paper we investigate the evidence for these exotic scenarios using recently available, deeper, optical, near-infrared and mid-infrared imaging. We find strong Spitzer/IRAC detections for the main component of CR7 at 3.6 and 4.5 microns, and show that it has a blue colour ([3.6] - [4.5] $= -1.2\pm 0.3$). This colour cannot be reproduced by current Pop. III or pristine DCBH models. Instead, the results suggest that the …
Blue straggler stars (BSS) have been identified in star clusters and in field populations in our own Milky Way galaxy and in its satellite galaxies. They manifest as stars bluer and more luminous than the dominant old population, and usually have a spatial distribution that follows the old population. Their progenitors are likely to have been close binaries. We investigate trends of the BSS population in dwarf spheroidal galaxies (dSph) and in the bulge of the Milky Way and find an anti-correlation between the relative frequency of BSS and the metallicity of the parent population. The rate of …
The Lya emission has been observed from galaxies over a redshift span z ~ 0 - 8.6. However, the evolution of high-redshift Lya emitters (LAEs), and the link between these populations and local galaxies, remain poorly understood. Here, we investigate the Lya properties of progenitors of a local L* galaxy by combining cosmological hydrodynamic simulations with three-dimensional radiative transfer calculations using the new ART^2 code. We find that the main progenitor (the most massive one) of a Milky Way-like galaxy has a number of Lya properties close to those of observed LAEs at z ~ 2 - 6, but…
We present new HST ultraviolet color-magnitude diagrams of 5 massive Galactic globular clusters: NGC 2419, NGC 6273, NGC 6715, NGC 6388, and NGC 6441. These observations were obtained to investigate the "blue hook" phenomenon previously observed in UV images of the globular clusters omega Cen and NGC 2808. Blue hook stars are a class of hot (approximately 35,000 K) subluminous horizontal branch stars that occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. By coupling new stellar evolution models to appropriate non-LTE synthetic spectra, we investigate …
We report the discovery of the most-distant double-peaked emitter, CXOECDFS J033115.0-275518, at z=1.369. A Keck/DEIMOS spectrum shows a clearly double-peaked broad Mg II $\lambda2799$ emission line, with FWHM 11000 km/s for the line complex. The line profile can be well fit by an elliptical relativistic Keplerian disk model. This is one of a handful of double-peaked emitters known to be a luminous quasar, with excellent multiwavelength coverage and a high-quality X-ray spectrum. CXOECDFS J033115.0-275518 is a radio-loud quasar with two radio lobes (FR II morphology) and a radio loudness of f_…
The Pristine HeII Emitter near GN-z11: Constraining the Mass Distribution of the First Stars
Università degli Studi di Firenze（佛罗伦萨大学）；INAF/Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切尔奇天文台）；Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）；Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）；Department of Physics and Astronomy, University College London（伦敦大学学院物理与天文系）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；Scuola Normale Superiore（比萨高等师范学院）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）
