Identifying and characterising reionised bubbles enables us to track both their size distribution, which depends on the primary ionising sources, and the relationship between reionisation and galaxy evolution. We demonstrate that spectrally resolved $z\gtrsim6$ Lyman-alpha (Ly$α$) emission can constrain properties of reionised regions. Specifically, the distant from a source to a neutral region sets the minimum observable Ly$α$ velocity offset from systemic. Detection of flux on the blue side of the Ly$α$ resonance implies the source resides in a large, sufficiently ionised region that photons can escape without significant resonant absorption, and thus constrains both the sizes of and the residual neutral fractions within ionised bubbles. We estimate the extent of the region around galaxies which is optically thin to blue Ly$α$ photons, analogous to quasar proximity zones, as a function of the source's ionising photon output and surrounding gas density. This optically thin region is typically $\lesssim 0.3$ pMpc in radius (allowing transmission of flux $\gtrsim -250$ km s$^{-1}$), $\lesssim 20$% of the distance to the neutral region. In a proof-of-concept, we demonstrate the $z\approx6.6$ galaxy COLA1 -- with a blue Ly$α$ peak -- likely resides in an ionised region $>0.7$ pMpc, with residual neutral fraction $<10^{-5.5}$. To ionise its own proximity zone we infer COLA1 has a high ionising photon escape fraction ($f_{\mathrm{esc}}>0.50$), relatively steep UV slope ($β< -1.79$), and low line-of-sight gas density ($\sim0.5\times$ the cosmic mean), suggesting it is a rare, underdense line-of-sight.
We show herein that the population of star forming galaxies in the Bremer Deep Field (BDF) have enough ionising power to form two large ionised bubbles which could be in the process of merging into a large one with a volume of 14000 cMpc3. The sources identified in the BDF have been completed with a set of expected low luminosity sources at z $\approx$ 7. We have estimated the number of ionising photons per second produced by the different star forming galaxies in the BDF. This number has been compared with the number that would be required to ionise the bubbles around the two overdense region…
The THESAN project: Lyman-alpha emitters as probes of ionized bubble sizes
Massachusetts Institute of Technology（麻省理工学院）；The University of Texas at Dallas（德克萨斯大学达拉斯分校）；Universidad ECCI（ECCI大学）；York University（约克大学）；The University of Tokyo（东京大学）；University of Edinburgh（爱丁堡大学）
The visibility of LyA emitting galaxies during the Epoch of Reionization is controlled by both diffuse HI patches in large-scale bubble morphology and small-scale absorbers. To investigate the impact on LyA photons, we apply a novel combination of analytic and numerical calculations to three scenarios: (i) the `bubble' model, where only diffuse HI outside ionized bubbles is present; (ii) the `web' model, where HI exists only in overdense self-shielded gas; and (iii) the more realistic 'web-bubble' model, which contains both. Our analysis confirms that there is a degeneracy between the ionizati…
We report the discovery of a double-peaked Lyman-alpha profile in a galaxy at $z=6.803$, A370p\_z1, in the parallel Frontier Field of Abell 370. The velocity separation between the blue and red peaks of the Lyman-$α$ profile ($Δv=101_{-19}^{+38} (\pm48)\,\text{km s}^{-1}$) suggests an extremely high escape fraction of ionising photons $> 59(51)\% (2σ)$. The spectral energy distribution indicates a young ($50$ Myr), star-forming ($12\pm 6 \, \rm{M}_\odot \rm{yr}^{-1}$) galaxy with an IRAC excess implying strong [OIII]+H$β$ emission. On the basis of the high escape fraction measured, we demonstr…
We present the results of a systematic search for Lyman-alpha emitters (LAEs) at $6 \lesssim z \lesssim 7.6$ using the HST WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our total volume over this redshift range is $\sim 8 \times10^5$ Mpc$^3$, comparable to many of the narrowband surveys despite their larger area coverage. We find two LAEs at $z=6.38$ and $6.44$ with line luminosities of L$_{\mathrm{Ly}α} \sim 4.7 \times 10^{43}$ erg s$^{-1}$, putting them among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule o…
The observed properties of the Lyman-$α$ (Ly$α$) emission line are a powerful probe of neutral gas in and around galaxies. We present spatially resolved Ly$α$ spectroscopy with VLT/MUSE targeting VR7, a UV-luminous galaxy at $z=6.532$ with moderate Ly$α$ equivalent width (EW$_0\approx38$ Å). These data are combined with deep resolved [CII]$_{\rm 158 μm}$ spectroscopy obtained with ALMA and UV imaging from {\it HST} and we also detect UV continuum with MUSE. Ly$α$ emission is clearly detected with S/N $\approx40$ and FWHM of 374 km s$^{-1}$. Ly$α$ and [CII] are similarly extended beyond the UV,…
Understanding Ly$α$ emitting galaxies (LAEs) can be a key to reveal cosmic reionization and galaxy formation in the early Universe. Based on halo merger trees and Ly$α$ radiation transfer calculations, we model redshift evolution of LAEs and their observational properties at $z \ge 6$. We consider ionized bubbles associated with individual LAEs and IGM transmission of Ly$α$ photons. We find that Ly$α$ luminosity tightly correlates with halo mass and stellar mass, while the relation with star formation rate has a large dispersion. Comparing our models with the observed luminosity function by Ko…
Distant luminous Lyman-alpha emitters are excellent targets for detailed observations of galaxies in the epoch of reionisation. Spatially resolved observations of these galaxies allow us to simultaneously probe the emission from young stars, partially ionised gas in the interstellar medium and to constrain the properties of the surrounding hydrogen in the circumgalactic medium. We review recent results from (spectroscopic) follow-up studies of the rest-frame UV, Lyman-alpha and [CII] emission in luminous galaxies observed ~500 Myr after the Big Bang with ALMA, HST/WFC3 and VLT/X-SHOOTER. These…
Our understanding of reionization has advanced considerably over the past decade, with several results now demonstrating that the IGM transitioned from substantially neutral at $z=7$ to largely reionized at $z=6$. However, little remains known about the sizes of ionized bubbles at $z\gtrsim7$ as well as the galaxy overdensities which drive their growth. Fortunately, rest-UV spectroscopic observations offer a pathway towards characterizing these ionized bubbles thanks to the resonant nature of Lyman-alpha photons. In a previous work, we presented Ly$α$ detections from three closely-separated Ly…
Life After the Quasar: Overmassive Black Holes and Remnant Ionised Bubbles in and Around Two z~6.6 Galaxies
University of Geneva（日内瓦大学）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；University College London（伦敦大学学院）；Heidelberg University（海德堡大学）；Max Planck Institut für Astronomie（马克斯·普朗克天文学研究所）；University of Hertfordshire（赫特福德大学）；Aix Marseille Université（艾克斯-马赛大学）；Institute of Science and Technology Austria (ISTA)（奥地利科学和技术研究所）
The epoch of reionization (6 < z < 10) marks the period in our universe when the first large galaxies grew to fruition, and began to affect the universe around them. Massive stars, and potentially accreting supermassive black holes, filled the universe with ionizing radiation, burning off the haze of neutral gas that had filled the intergalactic medium (IGM) since recombination (z~1000). The evolution of this process constrains key properties of these earliest luminous sources, thus observationally constraining reionization is a key science goal for the next decade. The measurement of Lyman-al…
The visibility of high-redshift Lyman-alpha emitting galaxies (LAEs) provides important constraints on galaxy formation processes and the Epoch of Reionization (EoR). However, predicting realistic and representative statistics for comparison with observations represents a significant challenge in the context of large-volume cosmological simulations. The THESAN project offers a unique framework for addressing such limitations by combining state-of-the-art galaxy formation (IllustrisTNG) and dust models with the Arepo-RT radiation-magneto-hydrodynamics solver. In this initial study we present Ly…
We present the first results from the ongoing LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization), which is the largest narrowband survey for $z \sim$ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3 deg$^2$ COSMOS field. We have identified 23 Lyman Alpha Emitter (LAE) candidates at $z$ = 6.9 in the central 2-deg$^2$ region, where DECam and public COSMOS multi-band images exist. The resulting luminosity f…
The observability of Lyman-alpha emitting galaxies (LAEs) during the Epoch of Reionization can provide a sensitive probe of the evolving neutral hydrogen gas distribution, thus setting valuable constraints to distinguish different reionization models. In this study, we utilize the new THESAN suite of large-volume (95.5 cMpc) cosmological radiation-hydrodynamic simulations to directly model the Ly$α$ emission from individual galaxies and the subsequent transmission through the intergalactic medium. THESAN combines the AREPO-RT radiation-hydrodynamic solver with the IllustrisTNG galaxy formation…
We show herein that a proto-cluster of Ly$α$ emitting galaxies, spectroscopically confirmed at redshift 6.5, produces a remarkable number of ionising continuum photons. We start from the Ly$α$ fluxes measured in the spectra of the sources detected spectroscopically. From these fluxes we derive the ionising emissivity of continuum photons of the proto-cluster, which we compare with the ionising emissivity required to reionise the proto-cluster volume. We find that the sources in the proto-cluster are capable of ionising a large bubble, indeed larger than the volume occupied by the proto-cluster…
The next generation of telescopes aim to directly observe the first generation of galaxies that initiated the reionization process in our Universe. The Lyman Alpha (Lya) emission line is robustly predicted to be the most prominent intrinsic spectral feature of these galaxies, making it an ideal target to search for and study high redshift galaxies. Unfortunately the large Gunn-Peterson optical depth of the surrounding neutral intergalactic medium (IGM) is thought to render this line extremely difficult to detect prior to reionization. In this paper we demonstrate that the radiative transfer ef…
We discuss new Keck/MOSFIRE spectroscopic observations of four luminous galaxies at z~7-9 selected to have intense optical line emission by Roberts-Borsani et al. (2016). Previous follow-up has revealed Lyman-alpha in two of the four galaxies. Our new MOSFIRE observations confirm that Lyman-alpha is present in the entire sample. We detect Lyman-alpha emission in COS-zs7-1, confirming its redshift as z=7.154, and we detect Lyman-alpha in EGS-zs8-2 at z=7.477, verifying a tentative detection presented in an earlier study. The ubiquity of Lyman-alpha in this sample is puzzling given that the IGM …
Radiation hydrodynamic simulation of the Haro 11 galaxy: the escape of LyC and Ly$α$ in a dwarf galaxy merger
Oskar Klein Centre, Department of Astronomy, Stockholm University（斯德哥尔摩大学天文学系奥斯克·克莱因中心）；Centre de Recherche Astrophysique de Lyon UMR5574, Univ Lyon, Univ Lyon1, Ens de Lyon, CNRS（里昂天体物理研究中心）；Lund Observatory, Division of Astrophysics, Department of Physics, Lund University（隆德大学物理系天体物理学部隆德天文台）
We report the discovery of Lyman-alpha emission (Ly$α$) in the bright galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at the Keck Observatory. First reported by Roberts-Borsani et al. (2015), it was selected for spectroscopic observations because of its photometric redshift ($z_{phot}=8.57^{+0.22}_{-0.43}$), apparent brightness (H$_{160}=25.26\pm0.09$) and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong oxygen emission in the [4.5] band. With a total integration of $\sim$4.3 hours, our data reveal an emission line at $\simeq$11776 Å which we a…
Throughout the epoch of reionization the most luminous Lyα emitters are capable of ionizing their own local bubbles. The CR7 galaxy at $z \approx 6.6$ stands out for its combination of exceptionally bright Lyα and HeII 1640 Angstrom line emission but absence of metal lines. As a result CR7 may be the first viable candidate host of a young primordial starburst or direct collapse black hole. High-resolution spectroscopy reveals a +160 km s$^{-1}$ velocity offset between the Lyα and HeII line peaks while the spatial extent of the Lyα emitting region is $\sim 16$ kpc. The observables are indicativ…
Before the end of the epoch of reionization, the Hydrogen in the Universe was predominantly neutral. This leads to a strong attenuation of Ly$α$ lines of $z\gtrsim6$ galaxies in the intergalactic medium. Nevertheless, Ly$α$ has been detected up to very high redshifts ($z\sim9$) for several especially UV luminous galaxies. Here, we test to what extent the galaxy's local environment might impact the Ly$α$ transmission of such sources. We present an analysis of dedicated Hubble Space Telescope (HST) imaging in the CANDELS/EGS field to search for fainter neighbours around three of the most UV lumi…
We forecast the reionization history constraints, inferred from Lyman-alpha damping wing absorption features, for a future sample of $\sim 20$ $z \geq 6$ gamma-ray burst (GRB) afterglows. We describe each afterglow spectrum by a three-parameter model. First, L characterizes the size of the ionized region (the "bubble size") around a GRB host halo. Second, $\langle{x_{\rm HI}\rangle}$ is the volume-averaged neutral fraction outside of the ionized bubble around the GRB, which is approximated as spatially uniform. Finally, $N_{\mathrm{HI}}$ denotes the column-density of a local damped Lyman-alpha…
An OASIS of Lyman-$α$ within a neutral intergalactic desert: reaffirmed line and blue continuum reveal efficient ionising agents at $z = 13$
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）；Department of Physics, University of Oxford（牛津大学物理系）；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）；Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）；Department of Astronomy & Astrophysics, The Pennsylvania State University（宾夕法尼亚州立大学天文学与天体物理学系）；Space Telescope Science Institute（太空望远镜科学研究所）
We perform a ground-based near-infrared spectroscopic survey using the Keck/MOSFIRE spectrograph to target Ly$α$ emission at $7.0<z<8.2$ from 61 galaxies to trace the ionization state of the intergalactic medium (IGM). We cover a total effective sky area of $\sim10^\prime\times10^\prime$ in the Extended Groth Strip field of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. From our observations, we detect Ly$α$ emission at a $>$4$σ$ level in eight $z>7$ galaxies, which include additional members of the known $z\sim7.7$ Ly$α$-emitter (LAE) cluster (Tilvi et al. 2020). With the…
The ubiquity of Lyman alpha (Ly$α$) emission in a sample of four bright [O III]-strong star-forming galaxies with redshifts above 7 has led to the suggestion that such luminous sources represent a distinct population compared to their fainter, more numerous, counterparts. The presence of Ly$α$ emission within the reionization era could indicate that these sources created early ionized bubbles due to their unusually strong radiation, possibly due to the presence of active galactic nuclei. To test this hypothesis we have secured long integration spectra with XSHOOTER on the VLT for three $z\sime…
Massive stars produce copious quantities of ultraviolet radiation beyond the Lyman limit, photoionizing the interstellar medium (ISM) and producing H II regions. As strong sources of recombination- and forbidden-line emission, infrared continuum, and thermal (free-free) radio continuum, H II regions serve as readily-observable beacons of massive star formation in the Milky Way and external galaxies. Along with supernovae, H II regions are dominant sources of feedback in star-forming galaxies, injecting radiative and mechanical luminosity into the ISM. H II regions may prove more important than…
We present the analysis of deep HST multi-band imaging of the BDF field specifically designed to identify faint companions around two of the few Ly-alpha emitting galaxies spectroscopically confirmed at z~7 (Vanzella et al. 2011). Although separated by only 4.4 proper Mpc these galaxies cannot generate HII regions large enough to explain visibility of their Ly-alpha line, thus requiring a population of fainter ionizing sources in their vicinity. We use deep HST and VLT-Hawk-I data to select z~7 Lyman break galaxies around the emitters. We select 6 new robust z~7 LBGs at Y~26.5-27.5 whose avera…
Distant luminous Lyman-alpha emitters (LAEs) are excellent targets for spectroscopic observations of galaxies in the epoch of reionisation (EoR). We present deep high-resolution (R=5000) VLT/X-SHOOTER observations, along with an extensive collection of photometric data of `COLA1', a proposed double peaked LAE at z=6.6 (Hu et al. 2016). We rule out that COLA1's emission line is an [OII] doublet at z=1.475 on the basis of i) the asymmetric red line-profile and flux ratio of the peaks (blue/red=$0.31\pm0.03$) and ii) an unphysical [OII]/Ha ratio ([OII]/Ha > 22). We show that COLA1's observed B-ba…
Ultraluminous Lyman alpha (Lya) emitting galaxies (ULLAEs) with log L (Lya)>43.5 erg/s near the epoch of reionization (z>5) make up the bright end of the LAE luminosity function (LF) and may provide insight into the process of reionization, including the formation of ionized bubbles around these extreme systems. We present a spectroscopic LF for ULLAEs at z=5.7. We used data from the HEROES ~45 sq. deg Subaru Hyper Suprime-Cam survey, which is centered on the North Ecliptic Pole and has both broadband (grizY) and narrowband (NB816 and NB921) imaging, to select candidate ULLAEs based on a NB816…
Reionization is an inhomogeneous process, thought to begin in small ionized bubbles of the intergalactic medium (IGM) around overdense regions of galaxies. Recent Lyman-alpha (Ly$α$) studies during the epoch of reionization show growing evidence that ionized bubbles formed earlier around brighter galaxies, suggesting higher IGM transmission of Ly$α$ from these galaxies. We investigate this problem using IR slitless spectroscopy from the Hubble Space Telescope (HST) Wide-Field Camera 3 (WFC3) G102 grism observations of 148 galaxies selected via photometric redshifts at $6.0<z<8.2$. These galaxi…
Measuring Magnetic Fields Near and Far with the SKA via the Zeeman Effect
National Research Council Canada（加拿大国家研究委员会）；University of British Columbia（不列颠哥伦比亚大学）；Stanford University（斯坦福大学）；Tsinghua University（清华大学）；SKA Observatory（平方公里阵列射电望远镜天文台）；Univ. of Manchester（曼彻斯特大学）；National Astronomical Research Institute of Thailand（泰国国家天文研究所）；MIT Haystack Observatory（麻省理工学院海斯塔克天文台）
