Escape of about five per cent of Lyman-alpha photons from high-redshift star-forming galaxies
Matthew Hayes, Goran Ostlin, Daniel Schaerer, J. Miguel Mas-Hesse, Claus Leitherer, Hakim Atek, Daniel Kunth, Anne Verhamme, Stephane de Barros, Jens Melinder
备注：
Letter to Nature, in press. Under terms of the press embargo, authors may not converse with the media before publication. 24 pages, 5 images, Supplementary Information included
The Lyman-alpha (Lya) emission line is the primary observational signature of star-forming galaxies at the highest redshifts, and has enabled the compilation of large samples of galaxies with which to study cosmic evolution. The resonant nature of the line, however, means that Lya photons scatter in the neutral interstellar medium of their host galaxies, and their sensitivity to absorption by interstellar dust may therefore be enhanced greatly. This implies that the Lya luminosity may be significantly reduced, or even completely suppressed. Hitherto, no unbiased empirical test of the escaping fraction (f_esc) of Lya photons has been performed at high redshifts. Here we report that the average fesc from star-forming galaxies at redshift z = 2.2 is just 5 per cent by performing a blind narrowband survey in Lya and Ha. This implies that numerous conclusions based on Lya-selected samples will require upwards revision by an order of magnitude and we provide a benchmark for this revision. We demonstrate that almost 90 per cent of star-forming galaxies emit insufficient Lya to be detected by standard selection criteria. Both samples show an anti-correlation of fesc with dust content, and we show that Lya- and Ha-selection recovers populations that differ substantially in dust content and fesc.
The Lyman-alpha (Lya) recombination line is a fundamental tool for galaxy evolution studies and modern observational cosmology. However, subsequent interpretations are still prone to a number of uncertainties. Besides numerical efforts, empirical data are urgently needed for a better understanding of Lya escape process. We empirically estimate the Lyman-alpha escape fraction fesc(Lya) in a statistically significant sample of z ~ 0 - 0.3 galaxies in order to calibrate high-redshift Lyman-alpha observations. An optical spectroscopic follow-up of a sub-sample of 24 Lyman-alpha emitters (LAEs) det…
We discuss the evolution of the ratio in number of recombinations due to 2s two photon escape and due to the escape of Lyman-$α$ photons from the resonance during the epoch of cosmological recombination, within the width of the last scattering surface and near its boundaries. We discuss how this ratio evolves in time, and how it defines the profile of the Lyman-$α$ line in the spectrum of CMB. One of the key reasons for explaining its time dependence is the strong overpopulation of the 2p level relative to the 2s level at redshifts $z \la 750$.
We use very large cosmological Smoothed-Particle-Hydrodynamics simulations to study the properties of high redshift Lyman-alpha emitters (LAEs). We identify star-forming galaxies at z=3.1 in a cosmological volume of 100 h^-1Mpc on a side. We develop a phenomenological model of absorption, scattering and escape of Lyman-alpha photons on the assumption that the clumpiness of the inter-stellar medium in a galaxy is correlated with the larger scale substructure richness. The radiative transfer effect proposed by Neufeld (1991) allows a large fraction of Lyman-alpha photons to escape from a clumpy …
It is essential to know galactic emissivity and spectrum of Lyman continuum (LyC) in order to understand the cosmic reionization. Here we consider an escape of nebular LyC from galaxies and examine the consequent spectral energy distribution. It is usually assumed that hydrogen nebular LyC mostly produced by bound-free transitions is consumed within photo-ionized nebulae (so-called "on-the-spot" approximation). However, an escape of the continuum should be taken into account if stellar LyC escapes from galaxies through "matter-bounded" nebulae. We show that the escaping hydrogen bound-free LyC…
We present observations of a peculiar Lyman alpha-emitting galaxy at redshift 3.344, discovered in a deep, blind spectroscopic survey for faint Lyman alpha emitters with the Magellan II telescope in the Hubble Ultra Deep Field (HUDF). The galaxy exhibits complex Lyman alpha emission, including an extended, asymmetric component that is partially suppressed by damped Lyman alpha absorption, and two spatially elongated, narrow emission features. Archival HST ACS imaging shows evidence for tidal disruption of the stellar component. This V=27 galaxy appears to give us unprecedented insights into tw…
The usefulness of H I Lyman-alpha photons for characterizing star formation in the distant universe is limited by our understanding of the astrophysical processes that regulate their escape from galaxies. These processes can only be observed in detail out to a few x100 Mpc. Past nearby (z<0.3) spectroscopic studies are based on small samples and/or kinematically unresolved data. Taking advantage of the high sensitivity of HST's COS, we observed the Lyman-alpha lines of 20 H-alpha-selected galaxies located at <z>=0.03. The galaxies cover a broad range of luminosity, oxygen abundance, and redden…
Using CLARA (Code for Lyman Alpha Radiation Analysis) we constrain the escape fraction of Lyman-Alpha radiation in galaxies in the redshift range 5<z<7, based on the MareNostrum High-z Universe, a SPH cosmological simulation with more than 2 billion particles. We approximate Lyman-Alpha Emitters (LAEs) as dusty gaseous slabs with Lyman-Alpha radiation sources homogeneously mixed in the gas. Escape fractions for such a configuration and for different gas and dust contents are calculated using our newly developed radiative transfer code CLARA. The results are applied to the MareNostrum High-z Un…
We present the results of rest-frame, UV slitless spectroscopic observations of a sample of 32 z~0.7 Lyman break galaxy (LBG) analogs in the COSMOS field. The spectroscopic search was performed with the Solar Blind Channel (SBC) on Hubble Space Telescope. We report the detection of leaking Lyman continuum (LyC) radiation from an AGN-starburst composite. While we find no direct detections of LyC emission in the remainder of our sample, we achieve individual lower limits (3 sigma) of the observed non-ionizing UV to LyC flux density ratios, f_{nu}(1500A)/f_{nu}(830A) of 20 to 204 (median of 73.5)…
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…
We present results from the LymAn Continuum Escape Survey (LACES), a Hubble Space Telescope (HST) program designed to characterize the ionizing radiation emerging from a sample of Lyman alpha emitting galaxies at redshift $z\simeq 3.1$. As many show intense [O III] emission characteristic of $z>6.5$ star-forming galaxies, they may represent valuable low redshift analogs of galaxies in the reionization era. Using HST Wide Field Camera 3 / UVIS $F336W$ to image Lyman continuum emission, we investigate the escape fraction of ionizing photons in this sample. For 61 sources, of which 77% are spectr…
We have coadded X-ray flux of all known Lyman Alpha Emitters (LAEs) in the 4 Msec Chandra Deep Field South (CDF-S) region, to place sensitive upper limits on the average unobscured star-formation rate (SFR_X) in these galaxies. A very small fraction of Lyman-Alpha galaxies in the field are individually detected in the X-rays, implying a low fraction of AGN activity. After excluding the few X-ray detected LAEs, we stack the undetected LAEs located in the 4 Ms CDF-S data and 250 ks Extended CDF-S (ECDFS) data, and compute a 1-σupper limit on SFR_X < 14, 28, 28, 140, 440, 880 M$_{\sun}$ yr$^{-1}$…
We present a semi-analytical model of star formation which explains simultaneously the observed UV luminosity function of high redshift Lyman break galaxies (LBGs) and luminosity functions of Lyman-alpha emitters. We consider both models that use the Press-Schechter (PS) and Sheth-Tormen (ST) halo mass functions to calculate the abundances of dark matter halos. The Lyman-alpha luminosity functions at z < 4 are well reproduced with only <10% of the LBGs emitting Lyman-alpha lines with rest equivalent width greater than the limiting equivalent width of the narrow band surveys. However, the obser…
The Lyman continuum (LyC) escape fraction is a key quantity to determine the contribution of galaxies to cosmic reionization. It has been known that the escape fractions estimated by observations and numerical simulations show a large diversity. However, the origins of the diversity are still uncertain. In this work, to understand what quantities of galaxies are responsible for controlling the escape fraction, we numerically evaluate the escape fraction by performing ray-tracing calculation with simplified disc galaxy models. With a smooth disc model, we explore the dependence of the escape fr…
We use ultra-deep ultraviolet VLT/VIMOS intermediate-band and VLT/FORS1 narrow-band imaging in the GOODS Southern field to derive limits on the distribution of the escape fraction (f_esc) of ionizing radiation for L >~ L*(z=3) Lyman Break Galaxies (LBGs) at redshift 3.4--4.5. Only one LBG, at redshift z=3.795, is detected in its Lyman continuum (LyC; S/N~5.5), the highest redshift galaxy currently known with a direct detection. Its ultraviolet morphology is quite compact (R_eff=0.8, kpc physical). Three out of seven AGN are also detected in their LyC, including one at redshift z=3.951 and z850…
We present theoretical results for the expected fraction of Lyman Break Galaxies (LBGs) to be detected as strong Lyman alpha emitters (LAEs) in the redshift range 5 < z < 7. We base our analysis on the 2-billion particle SPH simulation MareNostrum High-z Universe. We approximate galaxies as static dusty slabs with an additional clumpy dust distribution affecting stellar populations younger than 25 Myr. The model for the Lyman alpha escape fraction is based on the results of our Monte-Carlo radiative transfer code (CLARA) for a slab configuration. We also fix the transmission of Lyman alpha pho…
The Mg II 2796, 2803 doublet has been suggested to be a useful indirect indicator for the escape of Ly-alpha and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg II or strong LyC emission. Here we present the first study of Mg II probing a large dynamic range of galaxy properties, using newly obtained high signal-to-noise, moderate-resolution spectra of Mg II for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg II profiles …
The escape fraction of hydrogen ionizing photons (f_esc) from galaxies has been suggested to be evolving with time, but the picture is far from clear. While evidence for significant escape fractions has been found at high redshifts in several studies, the picture looks different in the more nearby universe. Here, we apply a new background subtraction routine on archival data from the Far Ultraviolet Spectroscopic Explorer (FUSE), in order to study local galaxies in search for possible Lyman Continuum (LyC) leakage. In the process, for the first time a stacked spectrum in the LyC is produced fo…
The fraction of ionizing photons that escape from young star-forming galaxies is one of the largest uncertainties in determining the role of galaxies in cosmic reionization. Yet traditional techniques for measuring this fraction are inapplicable at the redshifts of interest due to foreground screening by the Lyman alpha forest. In an earlier study, we demonstrated a reduction in the equivalent width of low-ionization absorption lines in composite spectra of Lyman break galaxies at z=4 compared to similar measures at z=3. This might imply a lower covering fraction of neutral gas and hence an in…
We study the far-infrared properties of 498 Lyman Alpha Emitters (LAEs) at z=2.8, 3.1 and 4.5 in the Extended Chandra Deep Field-South, using 250, 350 and 500 micron data from the Herschel Multi-tiered Extragalactic Survey (HerMES) and 870 micron data from the LABOCA ECDFS Submillimeter Survey (LESS). None of the 126, 280 or 92 LAEs at z=2.8, 3.1 and 4.5, respectively, are individually detected in the far-infrared data. We use stacking to probe the average emission to deeper flux limits, reaching $1σ$ depths of ~0.1 to 0.4 mJy. The LAEs are also undetected at $\ge3σ$ in the stacks, although a …
A large number of high-redshift galaxies have been discovered via their narrow-band Lya line or broad-band continuum colors in recent years. The nature of the escaping process of photons from these early galaxies is crucial to understanding galaxy evolution and the cosmic reionization. Here, we investigate the escape of Lya, non-ionizing UV-continuum (l = 1300 - 1600 angstrom in rest frame), and ionizing photons (l < 912 angstrom) from galaxies by combining a cosmological hydrodynamic simulation with three-dimensional multi-wavelength radiative transfer calculations. The galaxies are simulated…
We investigate the stellar populations of Lyman alpha emitters (LAEs) at z=5.7 and 6.6 in a 0.65 deg^2 sky of the Subaru/XMM-Newton Deep Survey (SXDS) Field, using deep images taken with Subaru/Suprime-Cam, UKIRT/WFCAM, and Spitzer/IRAC. We produce stacked multiband images at each redshift from 165 (z=5.7) and 91 (z=6.6) IRAC-undetected objects, to derive typical spectral energy distributions (SEDs) of z~6-7 LAEs for the first time. The stacked LAEs have as blue UV continua as the HST/WFC3 z-dropout galaxies of similar Muv, with a spectral slope beta ~ -3, but at the same time they have red UV…
Population III stars can regulate star formation in the primordial Universe in several ways. They can ionize nearby halos, and even if their ionizing photons are trapped by their own halos, their Lyman-Werner (LW) photons can still escape and destroy H$_2$ in other halos, preventing them from cooling and forming stars. LW escape fractions are thus a key parameter in cosmological simulations of early reionization and star formation but have not yet been parametrized for realistic halos by halo or stellar mass. To do so, we perform radiation hydrodynamical simulations of LW UV escape from 9--120…
[abridged] Among the different observational techniques used to select high-redshift galaxies, the hydrogen recombination line Lyman-alpha (Lya) is of particular interest as it gives access to the measurement of cosmological quantities such as the star formation rate of distant galaxy populations. However, the interpretation of this line and the calibration of such observables is still subject to serious uncertainties. Therefore, it important to understand under what conditions the Lya line can be used as a reliable star formation diagnostic tool. We use a sample of 24 Lya emitters at z ~ 0.3 …
Galaxies are believed to be the main providers of Lyman continuum (LyC) photons during the early phases of the cosmic reionization. Little is known however, when it comes to escape fractions and the mechanisms behind the leakage. To learn more one may look at local objects, but so far only one low-z galaxy has shown any sign of emitting LyC radiation. With data from the Far Ultraviolet Spectroscopic Explorer (FUSE), Bergvall et al. (2006) found an absolute escape fraction of ionizing photons (f_esc) of 4-10% for the blue compact galaxy Haro 11. However, using a newer version of the reduction p…
The timing and duration of the reionization epoch is crucial to the emergence and evolution of structure in the universe. The relative roles that star-forming galaxies, active galactic nuclei and quasars play in contributing to the metagalactic ionizing background across cosmic time remains uncertain. Deep quasar counts provide insights into their role, but the potentially crucial contribution from star-formation is highly uncertain due to our poor understanding of the processes that allow ionizing radiation to escape into the intergalactic medium (IGM). The fraction of ionizing photons that e…
The Mg II 2796,2803 doublet is often used to measure interstellar medium absorption in galaxies, thereby serving as a diagnostic for feedback and outflows. However, the interpretation of Mg II remains confusing, due to resonant trapping and re-emission of the photons, analogous to Lyman Alpha. Therefore, in this paper, we present new MMT Blue Channel Spectrograph observations of Mg II for a sample of 10 Green Pea galaxies at z~0.2-0.3, where Lyman Alpha was previously observed with the Cosmic Origins Spectrograph on Hubble Space Telescope. With strong, (mostly) double-peaked Lyman Alpha profil…
We extend the existing analytical model of reionization by Furlanetto et al. (2004) to include the biasing of reionization sources and additional absorption by Lyman Limit systems. Our model is, by construction, consistent with the observed evolution of the galaxy luminosity function at z<8 and with the observed evolution of Ly-α forest at z<6. We also find that, for a wide range of values for the relative escape fraction that we consider reasonable, and which are consistent with the observational constraints on the relative escape fraction from lower redshifts, our reionization model is consi…
We use deep integral field spectroscopy data from the CALIFA survey to study the warm interstellar medium (WIM) of 32 nearby early-type galaxies (ETGs). We propose a tentative subdivision of our sample ETGs into two groups, according to their Ha equivalent width (EW) and Lyman continuum (LyC) photon escape fraction (PLF). Type i ETGs show nearly constant EWs and a PLF~0, suggesting that photoionization by post-AGB stars is the main driver of their faint extranuclear nebular emission. Type ii ETGs are characterized by very low, outwardly increasing EWs, and a PLF as large as ~0.9 in their cente…
We study the effect of H I ionizing photons escaping from high-redshift (high-z) galaxies have on the He II ionizing ultraviolet background (UVB) radiation. While these photons do not directly interact with He II ions, we show that they play an important role, through radiative transport, in modifying the shape of He II ionizing part of UVB spectrum. Within the observed range of UV escape from galaxies, we show that the rapid increase in He II Lyman alpha effective optical depth at z~2.7 can naturally be explained by radiative transport effects. Therefore, the relationship between a well measu…
We extend a previous study of Lyman Alpha Emitters (LAEs) based on hydrodynamical cosmological simulations, by including two physical processes important for LAEs: (a) Lyman Alpha and continuum luminosities produced by cooling of collisionally excited HI in the galaxy, (b) dust formation and evolution; we follow these processes on a galaxy-by-galaxy basis. HI cooling on average contributes 16-18% of the Lyman Alpha radiation produced by stars, but this value can be much higher in low mass LAEs and further increased if the HI is clumpy. The continuum luminosity is instead almost completely domi…
The Lyman alpha emission line is an essential diagnostic tool for probing galaxy formation and evolution. Not only is it commonly the strongest observable line from high-redshift galaxies but from its shape detailed information about its host galaxy can be revealed. However, due to the scattering nature of Lya photons increasing their path length in a non-trivial way, if dust is present in the galaxy the line may be severely suppressed and its shape altered. In order to interpret observations correctly, it is thus of crucial significance to know how much of the emitted light actually escapes t…
We derive empirical constraints on the volume averaged `effective' escape fraction of Lyman Alpha (Lya) photons from star forming galaxies as a function of redshift, by comparing star formation functions inferred directly from observations, to observed Lya luminosity functions. Our analysis shows that the effective escape fraction increases from f_esc^eff ~ 1-5 % at z=0, to f_esc^eff ~ 10 % at z=3-4, and to f_esc^eff=30-50 % at z=6. Our constraint at z=6 lies above predictions by models that do not include winds, and therefore hints at the importance of winds in the Lya transfer process (even)…
We build a physical model for high-redshift Lyman Alpha emitters (LAEs) by coupling state of the art cosmological simulations (GADGET-2) with a dust model and a radiative transfer code (pCRASH). We post-process the cosmological simulation with pCRASH using five different values of the escape fraction of hydrogen ionizing photons (f_esc=0.05,0.25,0.5,0.75,0.95) until reionization is complete, i.e. the average neutral hydrogen fraction drops to <X_HI>~10^-4. Then, the only free-parameter left to match model results to the observed Lya and UV luminosity functions of LAEs at z~6.6 is the relative …
The intrinsic escape fraction of ionizing Lyman continuum photons ($f_{esc}$) is crucial to understand whether galaxies are capable of reionizing the neutral hydrogen in the early universe at z>6. Unfortunately, it is not possible to access $f_{esc}$ at z>4 with direct observations and the handful of measurements from low redshift galaxies consistently find $f_{esc}$ < 10%, while at least $f_{esc}$ ~ 10% is necessary for galaxies dominate reionization. Here, we present the first empirical prediction of $f_{esc}$ at z>6 by combining the (sparsely populated) relation between [OIII]/[OII] and $f_…
The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the epoch of reionization is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with HST/COS for a z=0.2-0.4 sample of 66 galaxies. After careful proce…
Recent observations show that a large number of Lyman-alpha emitters (LAEs) at high redshift z >= 3 have unusually high Lya equivalent widths (EW > 400 angstrom). However, the origin of these high EWs is an open question. Here, we investigate the impacts of photon trapping on the Lya EW and other properties by tracking the Lya radiative transfer in spherical galactic clouds. We find that the delayed escape of the Lya photons can change the Lya properties significantly. During the transition phase from optically thick to optically thin where the Lya photons can escape simultaneously, the EW can…
It has been suggested that radiative transfer effects may explain the unusually high equivalent widths (EWs) of the Lya line, observed occasionally from starburst galaxies, especially at high redshifts. If the dust is locked up inside high-density clouds dispersed in an empty intercloud medium, the Lya photons could scatter off of the surfaces of the clouds, effectively having their journey confined to the dustless medium. The continuum radiation, on the other hand, does not scatter, and would thus be subject to absorption inside the clouds. This scenario is routinely invoked when Lya EWs high…
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…
Hydrogen emission lines can provide extensive information about star-forming galaxies in both the local and high-redshift Universe. We present a detailed Lyman continuum (LyC), Lyman-alpha (Lyα), and Balmer line (Hα and H\b{eta}) radiative transfer study of a high-resolution isolated Milky-Way simulation using the Arepo-RT radiation hydrodynamics code with the SMUGGLE galaxy formation model. The realistic framework includes stellar feedback, non-equilibrium thermochemistry, and dust grain evolution in the interstellar medium (ISM). We extend our Cosmic Lyα Transfer (COLT) code with photoioniza…
We investigate spectroscopically measured Lyα equivalent widths and escape fractions of 244 sources of which 95 are Lyman Break Galaxies (LBGs) and 106 Lyman Alpha Emitters (LAEs) at z~4.2, z~4.8, and z~5.6 selected from intermediate and narrow band observations. The sources were selected from the Cosmic Evolution Survey (COSMOS), and observed with the DEIMOS spectrograph. We find that the distribution of equivalent widths shows no evolution with redshift for both the LBG selected sources and the intermediate/narrowband LAEs. We also find that the Lyα escape fraction of intermediate and narrow…
The Ly-alpha emission line has been proven a powerful tool by which to study evolving galaxies at the highest redshifts. However, in order to use Lya as a physical probe of galaxies, it becomes vital to know the Lya escape fraction (fescLya). Unfortunately, due to the resonant nature of Lya, fescLya may vary unpredictably and requires empirical measurement. Here we compile Lya luminosity functions between redshift z=0 and 8 and, combined with H-alpha and ultraviolet data, assess how fescLya evolves with redshift. We find a strong upwards evolution in fescLya over the range z=0.3-6, which is we…
Lyman-alpha (Lya) is intrinsically the brightest line emitted from active galaxies. While it originates from many physical processes, for star-forming galaxies the intrinsic Lya luminosity is a direct tracer of the Lyman-continuum (LyC) radiation produced by the most massive O- and early-type B-stars with lifetimes of a few Myrs. As such, Lya luminosity should be an excellent instantaneous star formation rate (SFR) indicator. However, its resonant nature and susceptibility to dust as a rest-frame UV photon makes Lya very hard to interpret due to the uncertain Lya escape fraction, f$_{esc,Lyα}$…
We investigate the radiative transfer of Lyman alpha photons through simplified anisotropic gas distributions, which represent physically motivated extensions of the popular 'shell-models'. Our study is motivated by the notion that (i) shell models do not always reproduce observed Lyman alpha spectral line profiles, (ii) (typical) shell models do not allow for the escape of ionizing photons, and (iii) the observation & expectation that winds are more complex, anisotropic phenomena. We examine the influence of inclination on the Lyman alpha spectra, relative fluxes and escape fractions. We find…
Finding reliable indicators of Lyman continuum (LyC) photon leakage from galaxies is essential in order to infer their escape fraction in the epoch of reionisation, where direct measurements of LyC flux are impossible. To this end, here we investigate whether strong C IV $λλ1548,1550$ emission in the rest-frame UV spectra of galaxies traces conditions ripe for ample production and escape of LyC photons. We compile a sample of 19 star-forming galaxies in the redshift range $z=3.1-4.6$ from the VANDELS survey that exhibit strong C IV emission, producing a stacked spectrum where all major rest-UV…
We present results from a survey for z~2.85 Lyman-Continuum (LyC) emission in the HS1549+1933 field and place constraints on the amount of ionizing radiation escaping from star-forming galaxies. Using a custom narrowband filter (NB3420) tuned to wavelengths just below the Lyman limit at z>=2.82, we probe the LyC spectral region of 49 Lyman break galaxies (LBGs) and 91 Lya-emitters (LAEs) spectroscopically confirmed at z>=2.82. Four LBGs and seven LAEs are detected in NB3420. Using V-band data probing the rest-frame non-ionizing UV, we observe that many NB3420-detected galaxies exhibit spatial …
We have compiled a library of stellar Lyman-alpha equivalent widths in O and B stars using the model atmosphere codes CMFGEN and TLUSTY, respectively. The equivalent widths range from about 0 to 30 Åin absorption for early-O to mid-B stars. The purpose of this library is the prediction of the underlying stellar Lyman-alpha absorption in stellar populations of star-forming galaxies with nebular Lyman-alpha emission. We implemented the grid of individual equivalent widths into the Starburst99 population synthesis code to generate synthetic Lyman-alpha equivalent widths for representative star-fo…
We study the production rate of ionizing photons of a sample of 588 H$α$ emitters (HAEs) and 160 Lyman-$α$ emitters (LAEs) at $z=2.2$ in the COSMOS field in order to assess the implied emissivity from galaxies, based on their UV luminosity. By exploring the rest-frame Lyman Continuum (LyC) with GALEX/$NUV$ data, we find f$_{\rm esc} < 2.8\, (6.4)$% through median (mean) stacking. By combining the H$α$ luminosity density with IGM emissivity measurements from absorption studies, we find a globally averaged $\langle$f$_{\rm esc}\rangle$ of $5.9^{+14.5}_{-4.2}$ % at $z=2.2$ if we assume HAEs are t…
The fraction of ionizing photons (fesc) that escape from z>6 galaxies is an important parameter when assessing the role of these objects in the reionization of the Universe, but the opacity of the intergalactic medium precludes a direct measurement of fesc for individual galaxies at these epochs. We argue, that since fesc regulates the impact of nebular emission on the spectra of galaxies, it should nonetheless be possible to indirectly probe fesc well into the reionization epoch. As a first step, we demonstrate that by combining measurements of the rest-frame UV slope beta with the equivalent…
Although low-mass star-forming galaxies are the leading candidates of the reionisation process, we cannot conclusively rule out high-mass star-forming galaxies as candidates. While most simulations indicate the former is the best candidate some models suggest that at z > 6 massive, UV-bright galaxies - "oligarchs" - account for at least 80% of the ionising budget. To test this hypothesis we target massive (log10 (M*[Msol]) > 10), UV-bright (MUV ~ -22) Lya emitters at z > 7 in archival data, observed with similar resolution spectrographs (VLT/X-shooter and Keck/MOSFIRE). To increase the reliabi…
[abridged] Aims. The aim of this paper is to assess the impact of the interstellar medium (ISM) physics on Lyman-alpha (Lya) radiation transfer and to quantify how galaxy orientation with respect to the line of sight alters observational signatures. Methods. We compare the results of Lya radiation transfer calculations through the ISM of a couple of idealized galaxy simulations with different ISM models. Results. First, the small-scale structuration of the ISM plays a determinant role in shaping a galaxys Lya properties.The artificially warm, and hence smooth, ISM of G1 yields an escape fracti…
We have obtained deep Hubble Space Telescope far-UV images of 15 starburst galaxies at z~1.3 in the GOODS fields to search for escaping Lyman continuum photons. These are the deepest far-UV images m_{AB}=28.7, 3σ, 1" diameter) over this large an area (4.83 arcmin^2) and provide the best escape fraction constraints for any galaxy at any redshift. We do not detect any individual galaxies, with 3σlimits to the Lyman Continuum (~700 Å) flux 50--149 times fainter (in f_nu) than the rest-frame UV (1500 Å) continuum fluxes. Correcting for the mean IGM attenuation (factor ~2), as well as an intrinsic …
The Lyman continuum (LyC) cannot be observed at the epoch of reionization (z {\gtrsim} 6) due to intergalactic H I absorption. To identify Lyman continuum emitters (LCEs) and infer the fraction of escaping LyC, astronomers have developed various indirect diagnostics of LyC escape. Using measurements of the LyC from the Low-redshift Lyman Continuum Survey (LzLCS), we present the first statistical test of these diagnostics. While optical depth indicators based on Lyα, such as peak velocity separation and equivalent width, perform well, we also find that other diagnostics, such as the [O III]/[O …
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 …
