Using new VLT/XShooter spectral observations we analyse the physical properties of five z~0.3-0.4 confirmed LyC leakers. Strong resonant MgII 2796,2803 emission lines (I(2796,2803)/I(Hbeta)=10-38 per cent) and non-resonant FeII* 2612,2626 emission lines are observed in spectra of five and three galaxies, respectively. We find high electron densities Ne~400cm-3, significantly higher than in typical low-z, but comparable to those measured in z~2-3 star-forming galaxies. The galaxies have a mean value of logN/O=-1.16, close to the maximum values found for star-forming (SF) galaxies in the metallicity range of 12+logO/H=7.7-8.1. All 11 low-z LyC emitting galaxies found by Izotov et al. (2016, 2018), including the ones considered in the present study, are characterised by high EW(Hbeta)~200-400A, high ionisation parameter (log(U)=-2.5 to -1.7), high average ionising photon production efficiency ξ= 10^{25.54} Hz erg-1 and hard ionising radiation. On the BPT diagram we find the same offset of our leakers from low-$z$ main-sequence SFGs as that for local analogues of LBGs and extreme SF galaxies at z~2-3. We confirm the effectiveness of the HeI emission lines diagnostics proposed by Izotov et al. (2017) in searching for LyC leaker candidates and find that their intensity ratios correspond to those in a median with low neutral hydrogen column density N(HI)=10^{17}-5x10^{17} cm-2 that permit leakage of LyC radiation, likely due to their density-bounded HII regions.
We use the SPHINX$^{20}$ cosmological radiation hydrodynamics simulation to study how Lyman Continuum (LyC) photons escape from galaxies and the observational signatures of this escape. We define two classes of LyC leaker: Bursty Leakers and Remnant Leakers, based on their star formation rates (SFRs) that are averaged over 10 Myr (SFR$_{10}$) or 100 Myr (SFR$_{100}$). Both have $f_{\rm esc}>20\%$ and experienced an extreme burst of star formation, but Bursty Leakers have ${\rm SFR_{10}>SFR_{100}}$, while Remnant Leakers have ${\rm SFR_{10}<SFR_{100}}$. The maximum SFRs in these bursts were typ…
MAMMOTH-LyC: Investigating the Role of Galaxy Mergers in a Strong Lyman Continuum Leaker at $z=2.39$
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences (UCAS)（中国科学院大学天文与空间科学学院）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天体物理前沿研究院）；Department of Physics and Astronomy, University of California, Los Angeles（加州大学洛杉矶分校物理与天文学系）；Infrared Processing and Analysis Center, Caltech（加州理工学院红外处理与分析中心）；Centre for Astrophysics and Supercomputing, Swinburne University of Technology（斯威本科技大学天体物理学与超级计算中心）
Confirmation and Refutation of Lyman Continuum Leakers at $z\sim3$ with JWST NIRSpec/IFU
University of Chinese Academy of Sciences (UCAS)（中国科学院大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）
Identifying low-redshift galaxies that emit Lyman Continuum radiation (LyC leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. However, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift LyC leakers are truly "analogues" of the sources that reionized the Universe. Here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed LyC leakers at $z\sim3…
An analysis of the dynamics of a star formation event is performed. It is shown that galaxies able to drive leftover gas to sufficient altitudes in a few million years are characterized by two basic properties: small sizes (<1kpc) and high star formation rate surface densities (Sigma_SFR > 10 Msun/yr/kpc2). For the parameter space of relevance, the outflow is primarily driven by supernovae with radiation pressure being significant but subdominant. Our analysis provides the unifying physical origin for a diverse set of observed LyC leakers, including the green-peas galaxies, [SII]-weak galaxies…
We present $U_{336}V_{606}J_{125}H_{160}$ follow-up $HST$ observations of 16 $z\sim3$ candidate LyC emitters in the HS1549+1919 field. With these data, we obtain high spatial-resolution photometric redshifts of all sub-arcsecond components of the LyC candidates in order to eliminate foreground contamination and identify robust candidates for leaking LyC emission. Of the 16 candidates, we find one object with a robust LyC detection that is not due to foreground contamination. This object (MD5) resolves into two components; we refer to the LyC-emitting component as MD5b. MD5b has an observed 150…
A Lyman continuum analysis for $\sim 100$ galaxies at $z_{\text{spec}} \sim 3$ in the Abell 2744 Cluster Field
INAF – Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）；Department of Astronomy, School of Physics, Peking University（北京大学物理学院天文学系）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；Institute of Science and Technology Austria (ISTA)（奥地利科学技术研究所）；INAF – Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；IPAC, California Institute of Technology（加州理工学院IPAC）；Dipartimento di Fisica, Università degli Studi di Milano（米兰大学物理系）；University of Ljubljana, Faculty of Mathematics and Physics（卢布尔雅那大学数学与物理学院）；Department of Physics and Astronomy, University of California Davis（加州大学戴维斯分校物理与天文学系）；Centre for Astrophysics and Supercomputing, Swinburne University of Technology（斯威本科技大学天体物理学与超级计算中心）；Space Telescope Science Institute（太空望远镜科学研究所）
In this work, we investigate upper limits on the global escape fraction of ionizing photons ($f_{\rm esc/global}^{\rm abs}$) from a sample of galaxies probed for Lyman-continuum (LyC) emission characterized as non-LyC and LyC leakers. We present a sample of 9 clean non-contaminated (by low redshift interlopers, CCD problems and internal reflections of the instrument) galaxies which do not show significant ($>$ $3σ$) LyC flux between 880Å $<λ_{rest}<$ 910Å. The 9 galaxy stacked spectrum reveals no significant LyC flux with an upper limit of $f_{\rm esc}^{\rm abs} \leq 0.06$. In the next step of…
Ionizing photons must have escaped from high-redshift galaxies, but the neutral high-redshift intergalactic medium makes it unlikely to directly detect these photons during the Epoch of Reionization. Indirect methods of studying ionizing photon escape fractions present a way to infer how the first galaxies may have reionized the universe. Here, we use HET/LRS2 observations of J0919+4906, a confirmed z$\approx$0.4 emitter of ionizing photons to achieve spatially resolved (12.5 kpc in diameter) spectroscopy of \ion{Mg}{II}$\lambda2796$, \ion{Mg}{II}$\lambda2803$, [\ion{O}{II}]$λ\lambda3727,3729$…
Contemporary research suggests that the reionisation of the intergalactic medium (IGM) in the early Universe was predominantly realised by star-forming (proto-)galaxies (SFGs). Due to observational constraints, our knowledge on the origins of sufficient amounts of ionising Lyman continuum (LyC) photons and the mechanisms facilitating their transport into the IGM remains sparse. Recent efforts have thus focussed on the study of local analogues to these high-redshift objects. We used archival spectroscopic SDSS DR12 data to select a sample of low-z He II 4686 emitters and restricted it to a set …
To reionize the early universe, high-energy photons must escape the galaxies that produce them. It has been suggested that stellar feedback drives galactic outflows out of star-forming regions, creating low density channels through which ionizing photons escape into the inter-galactic medium. We compare the galactic outflow properties of confirmed Lyman continuum (LyC) leaking galaxies to a control sample of nearby star-forming galaxies to explore whether the outflows from leakers are extreme as compared to the control sample. We use data from the Cosmic Origins Spectrograph on the Hubble Spac…
Synergistic Radiative Transfer Modeling of MgII and Lyα Emission in Multiphase, Clumpy Galactic Environments: Application to Low-Redshift Lyman Continuum Leakers
We analyze spectra of a gravitationally lensed galaxy, known as the Sunburst Arc, that is leaking ionizing photons, also known as the Lyman continuum (LyC). Magnification from gravitational lensing permits the galaxy to be spatially resolved into one region that leaks ionizing photons, and several that do not. Rest-frame ultraviolet and optical spectra from Magellan target ten different regions along the lensed Arc, including six multiple images of the LyC leaking region, as well as four regions that do not show LyC emission. The rest-frame optical spectra of the ionizing photon emitting regio…
The ionizing photon escape fraction (LyC $f_{\rm{esc}}$) of star-forming galaxies is the single greatest unknown in the reionization budget. Stochastic sightline effects prohibit the direct separation of LyC leakers from non-leakers at significant redshift. Here we circumvent this uncertainty by inferring $f_{\rm{esc}}$ with resolved (R>4000) LyA profiles from the X-SHOOTER LyA survey at z=2 (XLS-z2). We select leakers ($f_{\rm{esc}}>20$%) and non-leakers ($f_{\rm{esc}}<5$%) from a representative sample of $>0.2 L^{*}$ LyA emitters (LAEs). With median stacked spectra of these subsets covering …
Finding and elucidating the properties of Lyman-continuum(LyC)-emitting galaxies is an important step for our understanding of cosmic reionization. Although the z - 0.3-0.4 LyC emitters found recently show strong optical emission lines, no consistent quantitative photoionization model taking into account the escape of ionizing photons and inhomogenous interstellar medium (ISM) geometry of these galaxies has yet been constructed. We hence construct one- and two-zone photoionization models accounting for the observed LyC escape, which we compare to the observed emission line measurements. We fin…
ODIN: Searching for LyC emission from Lyman-$α$ emitters at $z=4.5$ in the E-COSMOS and XMM-LSS fields
Chungnam National University（忠南国立大学）；Universidad Andres Bello（安德烈斯贝略大学）；Millennium Nucleus for Galaxies (MINGAL)（银河系千年核团 (MINGAL)）；Purdue University（普渡大学）；Rutgers, the State University of New Jersey（新泽西州立罗格斯大学）；The Pennsylvania State University（宾夕法尼亚州立大学）；Institute for Gravitation and the Cosmos, The Pennsylvania State University（宾夕法尼亚州立大学引力与宇宙学研究所）；NSF’s National Optical-Infrared Astronomy Research Laboratory（美国国家光学-红外天文研究实验室）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；Herzberg Astronomy and Astrophysics Research Centre（赫茨伯格天文学与天体物理研究中心）
Using the Space Telescope Imaging Spectrograph, we have obtained ultraviolet (UV) spectra from $\sim 1200$ to 2000 Å of known Lyman continuum (LyC) emitting galaxies at low redshift ($z \sim 0.3-0.4$) with varying absolute LyC escape fractions (fesc $\sim 0.01 - 0.72$). Our observations include in particular the galaxy J1243+4646, which has the highest known LyC escape fraction at low redshift. While all galaxies are known Lyman alpha emitters, we consistently detect an inventory of additional emission lines, including CIV 1550, HeII 1640, OIII] 1666, and CIII] 1909, whose origin is presumably…
A faint M$_{\rm UV} = -14.5$ Lyman-continuum leaker candidate in the epoch of reionization: Unprecedented Ly$α$ properties at z=5.725
INAF – OAS, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（意大利国家天体物理研究所 - 博洛尼亚天文与空间科学观测站）；IPAC, California Institute of Technology（加州理工学院 IPAC）；Astronomical Institute, Tohoku University（东北大学天文学研究所）；Space Telescope Science Institute (STScI)（太空望远镜科学研究所）；Department of Physics and Astronomy, University of California, Los Angeles（加州大学洛杉矶分校物理与天文学系）；MIT Kavli Institute for Astrophysics and Space Research（麻省理工学院卡弗里天体物理与空间研究研究所）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理研究所）；Univ Lyon, Univ Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophy（里昂大学、里昂第一大学、巴黎高等师范学校里昂校区、法国国家科学研究中心、天体物理研究中心）
Recent work suggests that strong emission line, star-forming galaxies may be significant Lyman Continuum leakers. We combine archival HST broadband ultraviolet and optical imaging (F275W and F606W, respectively) with emission line catalogs derived from WFC3 IR G141 grism spectroscopy to search for escaping Lyman Continuum (LyC) emission from homogeneously selected $z\simeq$2.5 SFGs. We detect no escaping Lyman Continuum from SFGs selected on [OII] nebular emission (N=208) and, within a narrow redshift range, on [OIII]/[OII]. We measure 1$σ$ upper limits to the LyC escape fraction relative to t…
The relationship between galaxy characteristics and the reionization of the universe remains elusive, mainly due to the observational difficulty in accessing the Lyman continuum (LyC) at these redshifts. It is thus important to identify low-redshift LyC-leaking galaxies that can be used as laboratories to investigate the physical processes that allow LyC photons to escape. The weakness of the [S II] nebular emission lines relative to typical star-forming galaxies has been proposed as a LyC predictor. In this paper, we show that the [S II]-deficiency is an effective method to select LyC-leaking…
We have recently reported the discovery of five low redshift Lyman continuum (LyC) emitters (LCEs, hereafter) with absolute escape fractions fesc(LyC) ranging from 6 to 13%, higher than previously found, and which more than doubles the number of low redshift LCEs.We use these observations to test theoretical predictions about a link between the characteristics of the Lyman-alpha (Lya) line from galaxies and the escape of ionising photons. We analyse the Lya spectra of eight LCEs of the local Universe observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope (our five lea…
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 use the wealth of deep archival optical spectroscopy on the GOODS-South field from Keck, the VLT, and other facilities to select candidate high-redshift Lyman continuum (LyC) leakers in the Hubble Deep UV Legacy Survey (HDUV) dataset. We select sources at $2.35 < z < 3.05$, where the HST/WFC3 F275W filter probes only the redshifted LyC. We find five moderately F275W-bright sources (four detected at $\gtrsim3σ$ significance) in this redshift range. However, two of these show evidence in their optical spectra for contamination by foreground galaxies along the line-of-sight. We then perform an…
We used the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) to observe the semi-forbidden CIII] emission in Green Pea galaxies at 0.13 < z < 0.3. We detect CIII] emission in 7/10 galaxies with CIII] equivalent widths that range from 2-10Å~. The observed CIII] emission line strengths are consistent with the predictions from photoionization models which incorporate the effects of binary stellar evolution with young stellar ages < 3-5 Myrs, and high ionization parameters (logU > -2). The hard ionizing radiation from young massive stars, and high nebular temperature…
We explore the production and escape of ionizing photons in young galaxies by investigating the ultraviolet and optical emission-line properties of models of ionization-bounded and density-bounded HII regions, active-galactic-nucleus (AGN) narrow-line regions and radiative shocks computed all using the same physically-consistent description of element abundances and depletion on to dust grains down to very low metallicities. We compare these models with a reference sample of metal-poor star-forming galaxies and Lyman-continuum (LyC) leakers at various redshifts, which allows the simultaneous e…
The properties that govern the production and escape of hydrogen ionizing photons (Lyman continuum, LyC; with energies >13.6 eV) in star-forming galaxies are still poorly understood, but they are key to identifying and characterizing the sources that reionized the Universe. Here we empirically explore the relationship between the hardness of ionizing radiation and the LyC leakage in a large sample of low-$z$ star-forming galaxies from the recent Hubble Space Telescope Low-$z$ Lyman Continuum Survey. Using Sloan Digital Sky Survey stacks and deep XShooter observations, we investigate the hardne…
Limited constraints on the evolution of the Lyman Continuum (LyC) escape fraction represent one of the primary uncertainties in the theoretical determination of the reionization history. Due to the intervening intergalactic medium (IGM), the possibility of observing LyC photons directly in the epoch of reionization is highly unlikely. For this reason, multiple indirect probes of LyC escape have been identified, some of which are used to identify low-redshift LyC leakers (e.g. O32), while others are primarily useful at $z>6$ (e.g. [OIII]/[CII] far infrared emission). The flux ratio of the reson…
LBT observations of compact star-forming galaxies with extremely high [OIII]/[OII] flux ratios: HeI emission-line ratios as diagnostics of Lyman continuum leakage
We present Lyman continuum (LyC) radiation escape fraction $f_{\rm{esc}}$ measurements for 183 spectroscopically confirmed star-forming galaxies in the redshift range $3.11 < z < 3.53$ in the \textit{Chandra} Deep Field South. We use ground-based imaging to measure $f_{\rm{esc}}$, and use ground- and space-based photometry to derive galaxy physical properties using spectral energy distribution (SED) fitting. We additionally derive [O III]+H$β$ equivalent widths (that fall in the observed K band) by including nebular emission in the SED fitting. After removing foreground contaminants, we report…
The processes allowing the escape of ionizing photons from galaxies into the intergalactic medium are poorly known. To understand how Lyman continuum (LyC) photons escape galaxies, we constrain the HI covering fractions and column densities using ultraviolet HI and metal absorption lines of 18 star-forming galaxies which have Lyman series observations. Nine of these galaxies are confirmed LyC emitters. We fit the stellar continuum, dust attenuation, metal, and HI properties to consistently determine the UV attenuation, as well as the column densities and covering factors of neutral hydrogen an…
We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of eight compact star-forming galaxies at redshifts z=0.02811-0.06540, with low oxygen abundances 12+log(O/H)=7.43-7.82 and extremely high emission-line flux ratios O32=[OIII]5007/[OII]3727~22-39, aiming to study the properties of Ly-alpha emission in such conditions. We find a diversity in Ly-alpha properties. In five galaxies Ly-alpha emission line is strong, with equivalent width (EW) in the range 45-190A. In the remaining galaxies, weak Ly-alpha emission with EW(Ly-alpha)~2-7A is superposed on a…
Identifying the mechanisms driving the escape of Lyman Continuum (LyC) photons is crucial to find Lyman Continuum Emitter (LCE) candidates. To understand the physical properties involved in the leakage of LyC photons, we investigate the connection between the HI covering fraction, HI velocity width, the Lyman alpha (LyA) properties and escape of LyC photons in a sample of 22 star-forming galaxies including 13 LCEs. We fit the stellar continua, dust attenuation, and absorption lines between 920 and 1300 A to extract the HI covering fractions and dust attenuation. Additionally, we measure the HI…
Combining 66 ultraviolet (UV) spectra and ancillary data from the Low-Redshift Lyman Continuum Survey (LzLCS) and 23 LyC observations by earlier studies, we form a statistical sample of star-forming galaxies at $z \sim 0.3$ to study the role of the cold interstellar medium (ISM) gas in the leakage of ionizing radiation. We first constrain the massive star content (ages and metallicities) and UV attenuation, by fitting the stellar continuum with a combination of simple stellar population models. The models, together with accurate LyC flux measurements, allow to determine the absolute LyC photon…
We present a systematic study for ionization state of inter-stellar medium in galaxies at z=0-3 with ~140,000 SDSS galaxies and 108 intermediate to high redshift galaxies from the literature, using an ionization-parameter sensitive line ratio of [OIII]5007/[OII]3727 and photoionization models. We confirm that z=2-3 galaxies show an [OIII]/[OII] ratio significantly higher than a typical star-forming galaxy of SDSS by a factor of >~10, and the photoionization models reveal that these high-z galaxies have an ionization parameter of log(qion/cm s^{-1})~7.6-9.0, a factor of ~4-10 higher than local …
