The mean H$α$ EW and Lyman-continuum photon production efficiency for faint $z\approx4-5$ galaxies
Daniel Lam, Rychard J. Bouwens, Ivo Labbe, Joop Schaye, Kasper B. Schmidt, Michael V. Maseda, Roland Bacon, Leindert A. Boogaard, Themiya Nanayakkara, Johan Ric… 展开作者
Daniel Lam, Rychard J. Bouwens, Ivo Labbe, Joop Schaye, Kasper B. Schmidt, Michael V. Maseda, Roland Bacon, Leindert A. Boogaard, Themiya Nanayakkara, Johan Richard, Guillaume Mahler, Tanya Urrutia
We present the first measurements of the Lyman-continuum photon production efficiency $ξ_{\textrm{ion,0}}$ at $z\sim4$-5 for galaxies fainter than 0.2 $L^*$ ($-$19 mag). $ξ_{\textrm{ion,0}}$ quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero. Extending previous measurements of $ξ_{\textrm{ion,0}}$ to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity. We probe $ξ_{\textrm{ion,0}}$ to such faint magnitudes by taking advantage of 200-hour depth Spitzer/IRAC observations from the GREATS program and $\approx$300 3<$z$<6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs. Stacked IRAC [3.6]$-$[4.5] colors are derived and used to infer the H$α$ rest-frame equivalent widths, which range from 403Å to 2818Å. The derived $ξ_{\textrm{ion,0}}$ is $\log_{10}(ξ_{\textrm{ion,0}} / \textrm{Hz erg}^{-1}) = 25.36 \pm 0.08$ over $-$20.5 < M$_{\textrm{UV}}$ < $-$17.5, similar to those derived for brighter galaxy samples at the same redshift and therefore suggesting that $ξ_{\textrm{ion}}$ shows no strong dependence on $M_{UV}$. The $ξ_{\textrm{ion,0}}$ values found in our sample imply that the Lyman-continuum escape fraction for $M_{\textrm{UV}} \approx -19$ star-forming galaxies cannot exceed $\approx$8-20\% in the reionization era.
While low-luminosity galaxies dominate number counts at all redshifts, their contribution to cosmic Reionization is poorly understood due to a lack of knowledge of their physical properties. We isolate a sample of 35 z~4-5 continuum-faint Lyman-alpha emitters from deep VLT/MUSE spectroscopy and directly measure their Halpha emission using stacked Spitzer/IRAC Ch. 1 photometry. Based on Hubble Space Telescope imaging, we determine that the average UV continuum magnitude is fainter than -16 (~0.01 L_star), implying a median Lyman-alpha equivalent width of 249 Angstroms. By combining the Halpha m…
Galaxies at high redshifts provide a valuable tool to study cosmic dawn, and therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyman-alpha emission and the Lyman break from a z = 7.512+/- 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with G102 grism on Hubble Space Telescope (HST), show a significant emission line detection (6 sigma) in multiple observational position angles (PA), with total integrated Lyα line flux of 1.06+/- 0.12 e10-17erg s-1cm-2. The line flux is…
We propose to infer ionising continuum leaking properties of galaxies by looking at their Lyman-alpha line profiles. We carry out Lyman-alpha radiation transfer calculations in two models of HII regions which are porous to ionising continuum escape: 1) the so-called "density bounded" media, in which massive stars produce enough ionising photons to keep the surrounding interstellar medium transparent to the ionising continuum, i.e almost totally ionised, and 2) "riddled ionisation-bounded" media, surrounded by neutral interstellar medium, but with holes, i.e. with a covering factor lower than u…
Escaping Lyman continuum photons from galaxies likely reionized the intergalactic medium at redshifts $z\gtrsim6$. However, the Lyman continuum is not directly observable at these redshifts and secondary indicators of Lyman continuum escape must be used to estimate the budget of ionizing photons. Observationally, at redshifts $z\sim2-3$ where the Lyman continuum is observationally accessible, surveys have established that many objects that show appreciable Lyman continuum escape fractions $f_{esc}$ also show enhanced [OIII]/[OII] (O$_{32}$) emission line ratios. Here, we use radiative transfer…
We report on the detection of Lyman continuum radiation in two nearby starburst galaxies. Tol 0440-381, Tol 1247-232 and Mrk 54 were observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescopes. The three galaxies have radial velocities of ~13,000 km/s, permitting a ~35 A window on the restframe Lyman continuum shortward of the Milky Way Lyman edge at 912 A. The chosen instrument configuration using the G140L grating covers the spectral range from 912 to 2,000 Å. We developed a dedicated background subtraction method to account for temporal and spatial background variation…
We discuss the rest-frame ultraviolet emission line spectra of a large (~100) sample of low luminosity redshift z~3.1 Lyman alpha emitters (LAEs) drawn from a Subaru imaging survey in the SSA22 survey field. Our earlier work based on smaller samples indicated that such sources have high [OIII]/[OII] line ratios possibly arising from a hard ionising spectrum that may be typical of similar sources in the reionisation era. With optical spectra secured from VLT/VIMOS, we re-examine the nature of the ionising radiation in a larger sample using the strength of the high ionisation diagnostic emission…
We have recently discovered five Lyman continuum leaking galaxies at z~0.3, selected for their compactness, intense star-formation, and high [OIII]/[OII] ratio (Izotov et al. 2016ab). Here we derive their ionizing photon production efficiency, a fundamental quantity for inferring the number of photons available to reionize the Universe, for the first time for galaxies with confirmed strong Lyman continuum escape (fesc~6-13%). We find an ionizing photon production per unit UV luminosity, which is a factor 2-6 times higher than the canonical value when reported to their observed UV luminosity. A…
High redshift star-forming galaxies are likely responsible for the reionization of the Universe, yet direct detection of their escaping ionizing (Lyman continuum) photons has proven to be extremely challenging. In this study, we search for escaping Lyman continuum of the Cosmic Horseshoe, a gravitationally lensed, star-forming galaxy at z=2.38 with a large magnification of $\sim24$. Transmission at wavelengths of low ionization interstellar absorption lines in the rest-frame ultraviolet suggest a patchy, partially transparent interstellar medium. This makes it an ideal candidate for direct det…
Compact starburst galaxies are thought to include many or most of the galaxies from which substantial Lyman continuum emission can escape into the intergalactic medium. Li and Malkan (2018) used SDSS photometry to find a population of such starburst galaxies at z~0.5. They were discovered by their extremely strong [OIII]4959+5007 emission lines, which produce a clearly detectable excess brightness in the i bandpass, compared with surrounding filters. We therefore used the HST/COS spectrograph to observe two of the newly discovered i-band excess galaxies around their Lyman limits. One has stron…
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…
We discuss the rest-frame optical emission line spectra of a large (~50) sample of z=3.1 Lyman alpha emitters (LAEs) whose physical properties suggest such sources are promising analogs of galaxies in the reionization era. Reliable Lyman continuum escape fractions have now been determined for a large sample of such LAEs from the Lyman Continuum Escape Survey (LACES) undertaken via deep HST imaging in the SSA22 survey area reported in Fletcher et al. (2019). Using new measures of [OII] emission secured from Keck MOSFIRE spectra we re-examine, for a larger sample, earlier claims that Lyman conti…
We report the first direct and robust measurement of the faint-end slope of the Lyman-alpha emitter (LAE) luminosity function at z = 5.7. Candidate LAEs from a low-spectral-resolution blind search with IMACS on Magellan-Baade were targeted at higher resolution to distinguish high redshift LAEs from foreground galaxies. All but 2 of our 42 single-emission-line systems have flux F $< 2.0 \times 10^{-17}$ ergs s$^{-1}$ cm$^{-2}$, making these the faintest emission-lines observed for a z = 5.7 sample with known completeness, an essential property for determining the faint end slope of the LAE lumi…
Using an ultra-deep blind survey with the MUSE integral field spectrograph on the ESO Very Large Telescope, we obtain spectroscopic redshifts to a depth never explored before: galaxies with observed magnitudes m > 30 - 32. Specifically, we detect objects via Lyman-alpha emission at 2.9 < z < 6.7 without individual continuum counterparts in areas covered by the deepest optical/near-infrared imaging taken by the Hubble Space Telescope, the Hubble Ultra Deep Field. In total, we find 102 such objects in 9 square arcminutes at these redshifts. Detailed stacking analyses confirm the Lyman-alpha emis…
We predict Lyman-$α$ (Ly$α$) luminosity functions (LFs) of Ly$α$-selected galaxies (Ly$α$ emitters, or LAEs) at $z=3-6$ using the phenomenological model of Dijkstra & Wyithe (2012). This model combines observed UV-LFs of Lyman-break galaxies (LBGs, or drop out galaxies), with constraints on their distribution of Ly$α$ line strengths as a function of UV-luminosity and redshift. Our analysis shows that while Ly$α$ LFs of LAEs are generally not Schechter functions, these provide a good description over the luminosity range of $\log_{10}( L_α/{\rm erg}\,{\rm s}^{-1})=41-44$. Motivated by this resu…
The leakage of Lyman continuum photons from star forming galaxies is an elusive parameter. When observed, it provides a wealth of information on star formation in galaxies and the geometry of the interstellar medium, and puts constraints on the role of star forming galaxies in the reionization of the universe. H-alpha-selected galaxies at z~2 trace the highest star formation population at the peak of cosmic star formation history, providing a base for directly measuring Lyman continuum escape. Here we present this method, and highlight its benefits as well as caveats. We also use the method on…
We present the results obtained with VLT/MUSE on the faint-end of the Lyman-alpha luminosity function (LF) based on deep observations of four lensing clusters. The precise aim of the present study is to further constrain the abundance of Lyman-alpha emitters (LAEs) by taking advantage of the magnification provided by lensing clusters. We blindly selected a sample of 156 LAEs, with redshifts between $2.9 \le z \le 6.7$ and magnification-corrected luminosities in the range $ 39 \lesssim \log L_{Ly_α}$ [erg s$^{-1}$] $\lesssim 43$. The price to pay to benefit from magnification is a reduction of …
Star forming galaxies are believed to be a major source of Lyman Continuum (LyC) radiation responsible for reionizing the early Universe. Direct observations of escaping ionizing radiation have however been few and with low escape fractions. In the local Universe, only ~10 emitters have been observed, with typical escape fractions of a few percent. The mechanisms regulating this escape need to be strongly evolving with redshift in order to account for the Epoch of Reionization. Gas content and star formation feedback are among the main suspects, known to both regulate neutral gas coverage and …
The reionization of the Universe is one of the most important topics of present day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the HI ionizing background at z~3. We aim at measuring the Lyman continuum escape fraction, which is one of the key parameters to compute the contribution of star-forming galaxies to the UV background. We have used ultra-deep U-band imaging (U=30.2mag at 1sigma) by LBC/LBT in the CANDELS/GOOD…
[Abridged] We investigate the physical properties of a Lyman continuum emitter candidate at $z=3.212$ with photometric coverage from $U$ to MIPS 24$μ$m band and VIMOS/VLT and MOSFIRE/Keck spectroscopy. Investigation of the UV spectrum confirms a direct spectroscopic detection of the Lyman continuum emission with $S/N>5$. Non-zero Ly$α$ flux at the systemic redshift and high Lyman-$α$ escape fraction suggest a low HI column density. The weak C and Si low-ionization absorption lines are also consistent with a low covering fraction along the line of sight. The [OIII]$λ\lambda4959,5007+\mathrm{H}β…
We present new Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet (far-UV) spectroscopy and Keck Echellete optical spectroscopy of 11 ultraluminous infrared galaxies (ULIRGs), a rare population of local galaxies experiencing massive gas inflows, extreme starbursts, and prominent outflows. We detect H Lyman alpha emission from 8 ULIRGs and the companion to IRAS09583+4714. In contrast to the P Cygni profiles often seen in galaxy spectra, the H Lyman alpha profiles exhibit prominent, blueshifted emission out to Doppler shifts exceeding -1000 km/s in three HII-dominated and two AGN…
We report on the serendipitous discovery of a z=4.0, M1500=-22.20 star-forming galaxy (Ion3) showing copious Lyman continuum (LyC) leakage (~60% escaping), a remarkable multiple peaked Lya emission, and significant Lya radiation directly emerging at the resonance frequency. This is the highest redshift confirmed LyC emitter in which the ionising and Lya radiation possibly share a common ionised cavity (with N_HI<10^17.2 cm^-2). Ion3 is spatially resolved, it shows clear stellar winds signatures like the P-Cygni NV1240 profile, and has blue ultraviolet continuum (β= -2.5 +/- 0.25, F_λ~ λ^β) wit…
Identifying non-contaminated sample of high-redshift galaxies with escaping Lyman continuum (LyC) flux is important for understanding the sources and evolution of cosmic reionization. We present CLAUDS $u$-band photometry of the COSMOS field to probe LyC radiation from spectroscopically confirmed galaxies at $z\geq3.5$ and outside the standard Lyman-break galaxy colour selection expectations. Complementary to the CLAUDS data, we use Subaru multi-filter photometry, \textit {Hubble Space Telescope} ($HST$) multi-filter imaging, and the spectroscopic surveys D10K, VUDS and 3D-HST. We present a sa…
Lyman break galaxies (LBGs) at z ~ 3-4 are targeted to measure the fraction of Lyman continuum (LyC) flux that escapes from high redshift galaxies. However, z ~ 3-4 LBGs are identified using the Lyman break technique which preferentially selects galaxies with little or no LyC. We re-examine the standard LBG selection criteria by performing spectrophotometry on composite spectra constructed from 794 U_nGR-selected z ~ 3 LBGs from the literature while adding LyC flux of varying strengths. The modified composite spectra accurately predict the range of redshifts, properties, and LyC flux of LBGs i…
We model the transmission of the Lyman-alpha line through the circum- and intergalactic media around dark matter haloes expected to host Lyman-alpha emitters (LAEs) at z > 5.7, using the high-dynamic-range Sherwood simulations. We find very different CGM environments around more massive haloes (~10^11 M_sun) compared to less massive haloes (~10^9 M_sun) at these redshifts, which can contribute to a different evolution of the Lyman-alpha transmission from LAEs within these haloes. Additionally we confirm that part of the differential evolution could result from bright LAEs being more likely to …
Using new Keck DEIMOS spectroscopy, we examine the origin of the steep number counts of ultra-faint emission-line galaxies recently reported by Dressler et al. (2011). We confirm six Lyman Alpha emitters (LAEs), three of which have significant asymmetric line profiles with prominent wings extending 300-400 km/s redward of the peak emission. With these six LAEs, we revise our previous estimate of the number of faint LAEs in the Dressler et al. survey. Combining these data with the density of bright LAEs in the Cosmic Origins Survey and Subaru Deep Field provides the best constraints to date on …
Simulations have indicated that most of the escaped Lyman continuum photons escape through a minority of solid angles with near complete transparency, with the remaining majority of the solid angles largely opaque, resulting in a very broad and skewed probability distribution function (PDF) of the escape fraction when viewed at different angles. Thus, the escape fraction of Lyman continuum photons of a galaxy observed along a line of sight merely represents the properties of the interstellar medium along that line of sight, which may be an ill-representation of true escape fraction of the gala…
Star forming galaxies have long been considered the dominant sources of the cosmic ultraviolet background radiation at early epochs. However, observing and characterizing the galaxy population with significant ionizing emission has proven to be challenging. In particular, the fraction of ionizing radiation that escapes the local environment to the intergalactic medium is poorly known. We investigate the relation between the escape fraction and galaxy luminosity. We combine the deep ultraviolet observations of Hubble Ultra Deep Field (UVUDF) with the deep Multi Unit Spectroscopic Explorer (MUSE…
Subaru/SuprimeCam narrowband photometry of the SSA22 field reveals the presence of four Lyman continuum (LyC) candidates among a sample of 14 AGN. Two show offsets and likely have stellar LyC in nature or are foreground contaminants. The remaining two LyC candidates are Type I AGN. We argue that the average LyC escape fraction of high redshift low luminosity AGN is not likely to be unity, as often assumed in the literature. From direct measurement we obtain the average LyC-to-UV flux density ratio and ionizing emissivity for a number of AGN classes and find it at least a factor of two lower th…
We have obtained the first complete ultraviolet (UV) spectrum of a strong Lyman continuum(LyC) emitter at low redshift -- the compact, low-metallicity, star-forming galaxy J1154+2443 -- with a Lyman continuum escape fraction of 46% discovered recently. The Space Telescope Imaging Spectrograph spectrum shows strong Lya and CIII] 1909 emission, as well as OIII] 1666. Our observations show that strong LyC emitters can have UV emission lines with a high equivalent width (e.g. EW(CIII])$=11.7 \pm 2.9 Å$ rest-frame), although their equivalent widths should be reduced due to the loss of ionizing phot…
We present statistical properties of diffuse Lyman-alpha halos (LAHs) around high-$z$ star-forming galaxies with large Subaru samples of Lyman-alpha emitters (LAEs) at $z=2.2$. We make subsamples defined by the physical quantities of LAEs' central Lyman-alpha luminosities, UV magnitudes, Lyman-alpha equivalent widths, and UV slopes, and investigate LAHs' radial surface brightness (SB) profiles and scale lengths $r_n$ as a function of these physical quantities. We find that there exist prominent LAHs around LAEs with faint Lyman-alpha luminosities, bright UV luminosities, and small Lyman-alpha …
Using a sample of galaxies at $z\approx 3$ with detected Lyman Continuum (LyC) leakage in the SSA22 field, we attempt to verify a proposed indirect method for identifying cases with high LyC escape fraction $f_\mathrm{esc}$ based on measurements of the H$β$ equivalent width (EW) and the $β$ slope of the UV continuum. To this end, we present Keck/MOSFIRE H$β$ emission line flux measurements of LyC galaxies (LCGs) at spectroscopic redshifts $z_{\mathrm{spec}} \sim 3.3$, Lyman break galaxies (LBGs) at photometric redshifts $z_{\mathrm{phot}} = 2.7$--$3.7$, and Ly$α$ emitters at $z_{\mathrm{phot}}…
We have recently reported the discovery of five low redshift Lyman continuum (LyC) emitters (LCEs, hereafter) with absolute escape fractions fesc(LyC) ranging from 6 to 13%, higher than previously found, and which more than doubles the number of low redshift LCEs.We use these observations to test theoretical predictions about a link between the characteristics of the Lyman-alpha (Lya) line from galaxies and the escape of ionising photons. We analyse the Lya spectra of eight LCEs of the local Universe observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope (our five lea…
Questions as to what drove the bulk reionization of the Universe, how that reionization proceeded, and how the hard ionizing radiation reached the intergalactic medium remain open and debated. Observations probing that epoch are severely hampered by the increasing amounts of neutral gas with increasing redshift, so a small, but growing number of experiments are targeting star forming galaxies ($z\sim3$) as proxies. However, these studies, while providing fantastic detail, are time intensive, contain relatively few targets, and can suffer from selection biases. As a complementary alternative, w…
We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of seven compact low-mass star-forming galaxies at redshifts, z,in the range 0.3161-0.4276, with various O3Mg2=[OIII]5007/MgII 2796+2803 and Mg2=MgII 2796/MgII 2803 emission-line ratios. We aim to study the dependence of leaking Lyman continuum (LyC) emission on the characteristics of MgII emission together with the dependences on other indirect indicators of escaping ionizing radiation. LyC emission with escape fractions fesc(LyC)=3.1-4.6 per cent is detected in four galaxies, whereas only 1sigma u…
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 Bayesian inference on the neutral hydrogen fraction of the intergalactic medium (IGM), $x_{\textrm{HI}}$, at $z \sim$ 6-8 using the properties of Lyman break galaxies during the Epoch of Reionization. We use large samples of LBG candidates at $5.5 \leq z \leq 8.2$ with spectroscopy from Keck/DEIMOS and Keck/MOSFIRE. For each galaxy, we incorporate either the Lyman-$α$ equivalent width (EW) for detections or the EW limit spectrum for nondetections to parameterize the EW distribution at various ultraviolet brightnesses for a given redshift. Using our reference sample of galaxy candi…
We present size measurements of 78 high-redshift ($z\geq 5.5$) galaxy candidates from the Reionisation Lensing Cluster Survey (RELICS). These distant galaxies are well-resolved due to the gravitational lensing power of foreground galaxy clusters, imaged by the Hubble Space Telescope (HST) and the Spitzer Space Telescope. We compute sizes using the forward-modeling code Lenstruction and account for magnification using public lens models. The resulting size-magnitude measurements confirm the existence of many small galaxies with effective radii $R_{\rm{eff}}<200$ pc in the early universe, in agr…
We use Hubble space telescope data of 45 nearby star-forming galaxies to investigate properties of Lyman-alpha (Ly$α$) halos, Ly$α$ morphology, and the star-forming characteristics of galaxies. We study how the morphology of Ly$α$ emission is related to other Ly$α$ observables. Furthermore, we study the interdependencies of Ly$α$ morphological quantities. We studied the spatial extent of Ly$α$ using surface brightness profiles in i) using circular apertures and ii) within faint Ly$α$ isophotes. We measured the average intensity and the size of the regions with a high star formation rate densit…
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…
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…
We report the discovery of a multiply lensed Lyman-$α$ blob (LAB) behind the galaxy cluster AS1063 using the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT). The background source is at $z=$ 3.117 and is intrinsically faint compared to almost all previously reported LABs. We used our highly precise strong lensing model to reconstruct the source properties, and we find an intrinsic luminosity of $L_{\rm Lyα}$=$1.9\times10^{42}$ erg s$^{-1}$, extending to 33 kpc. We find that the LAB is associated with a group of galaxies, and possibly a protocluster, in agreement with…
We investigate the relation between the turbulent Mach number (\mach) and the escape fraction of Lyman continuum photons ($f_{\rm esc}$) in high-redshift galaxies. Approximating the turbulence as isothermal and isotropic, we show that the increase in the variance in column densities from $\mathcal{M}=1$ to $\mathcal{M}=10$ causes $f_{\rm esc}$ to increase by $\approx 25$\%, and the increase from $\mathcal{M}=1$ to $\mathcal{M}=20$ causes $f_{\rm esc}$ to increases by $\approx 50$\% for a medium with opacity $τ\approx1$. At a fixed Mach number, the correction factor for escape fraction relative…
The source responsible for the reionization of the Universe is believed to be the population of star-forming galaxies at $z\sim6$ to 12. The biggest uncertainty concerns the fraction of Lyman-continuum photons that actually escape from the galaxies. In recent years, several relatively small samples of "leaky" galaxies have been uncovered, and clues have begun to emerge as to both the indirect signposts of leakiness and of the conditions/processes that enable the escape of ionizing radiation. In this paper we present the results of a pilot program aimed to test a new technique for finding leaky…
Characterizing high-z quasar environments is key to understanding the co-evolution of quasars and the surrounding galaxies. To restrict their global picture, we statistically examine the g-dropout galaxy overdensity distribution around 570 faint quasar candidates at z ~ 4, based on the Hyper Suprime-Cam Subaru Strategic Program survey. We compare the overdensity significances of g-dropout galaxies around the quasars with those around g-dropout galaxies, and find no significant difference between their distributions. A total of 4 (22) out of the 570 faint quasars, 0.7_{-0.4}^{+0.4} (3.9_{-0.8}^…
Understanding the relationship between the underlying escape fraction of Lyman continuum (LyC) photons ($f_{\rm esc}$) emitted by galaxies and measuring the distribution of observed $f_{\rm esc}$ values at high redshift is fundamental to the interpretation of the reionization process. In this paper we perform a statistical exploration of the attenuation of LyC photons by neutral hydrogen in the intergalactic medium using ensembles of simulated transmission functions. We show that LyC detected galaxies are more likely to be found in sightlines with higher-than-average transmission of LyC photon…
The Lyman Continuum photon production efficiency ($ξ_{\rm ion}$) is a critical ingredient for inferring the number of photons available to reionise the intergalactic medium. To estimate the theoretical production efficiency in the high-redshift Universe we couple the BlueTides cosmological hydrodynamical simulation with a range of stellar population synthesis models. We find Lyman Continuum photon production efficiencies of $\log_{10}(ξ_{\rm ion}/{\rm erg^{-1}\, Hz})\approx 25.1-25.5$ depending on the choice of stellar population synthesis model. These results are broadly consistent with recen…
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 combined deep U-band imaging from the KPNO-4m/MOSAIC camera with very deep multi-waveband data from the optical to infrared, to select Lyman Break Galaxies (LBGs) at z~3 using U-V and V-R colors in the Subaru Deep Field. With the resulting sample of 5161 LBGs, we construct the UV luminosity function down to $M_{UV} = -18$ and find a steep faint-end slope of $α=-1.78 \pm 0.05$. We analyze rest-frame UV-to-IR spectral energy distributions generated from the median optical photometry and photometry on median-stacked IR images. In the stacks of faint LBGs, we find a background depression center…
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…
Star-forming galaxies are considered the likeliest source of the H I ionizing Lyman Continuum (LyC) photons that reionized the intergalactic medium at high redshifts. However, above z >~ 6, the neutral intergalactic medium prevents direct observations of LyC. Therefore, recent years have seen the development of indirect indicators for LyC that can be calibrated at lower redshifts and applied in the Epoch of Reionization. Emission from Mg II \ly\ly 2796, 2803 doublet has been proposed as a promising LyC proxy. In this paper, we present new Hubble Space Telescope/Cosmic Origins Spectrograph obse…
Most of the hydrogen in the intergalactic medium (IGM) was rapidly ionized at high-redshifts. While observations have established that reionization occurred, observational constraints on the emissivity of ionizing photons at high-redshift remains elusive. Here, we present a new analysis of the Low-redshift Lyman Continuum Survey (LzLCS) and archival observations, a combined sample of 89 star-forming galaxies at z~0.3 with Hubble Space Telescope observations of their ionizing continua (or Lyman Continuum, LyC). We find a strong (6$σ$ significant) inverse correlation between the continuum slope …
We present new results from the widest narrow band survey search for Lyman-alpha (Lya) emitters at z=5.7, just after reionization. We survey a total of 7 deg$^2$ spread over the COSMOS, UDS and SA22 fields. We find over 11,000 line emitters, out of which 514 are robust Lya candidates at z=5.7 within a volume of 6.3x10$^6$ Mpc$^3$. Our Lya emitters span a wide range in Lya luminosities, from faint to bright (L$_{\rm Lyα}\sim10^{42.5-44}$ erg s$^{-1}$) and rest-frame equivalent widths (EW$_0$~25-1000 Å) in a single, homogeneous data-set. By combining all our fields we find that the faint end slo…
To date no direct detection of Lyman continuum emission has been measured for intermediate--redshift z~1 star-forming galaxies . We combine HST grism spectroscopy with GALEX UV and ground--based optical imaging to extend the search for escaping Lyman continuum to a large (~600) sample of z~1 low-mass, moderately star-forming galaxies selected initially on H$α$ emission. The characteristic escape fraction of LyC from SFGs that populate this parameter space remains weakly constrained by previous surveys, but these faint SFGs are assumed to play a significant role in the reionization of neutral h…
Identifying the mechanism by which high energy Lyman continuum (LyC) photons escaped from early galaxies is one of the most pressing questions in cosmic evolution. Haro 11 is the best known local LyC leaking galaxy, providing an important opportunity to test our understanding of LyC escape. The observed LyC emission in this galaxy presumably originates from one of the three bright, photoionizing knots known as A, B, and C. It is known that Knot C has strong Ly$α$ emission, and Knot B hosts an unusually bright ultraluminous X-ray source, which may be a low-luminosity AGN. To clarify the LyC sou…
We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of five star-forming galaxies at redshifts z in the range 0.2993-0.4317 and with high emission-line flux ratios O32=[OIII]5007/[OII]3727 ~ 8-27 aiming to detect the Lyman continuum (LyC) emission. We detect LyC emission in all galaxies with the escape fractions fesc(LyC) in a range of 2-72 per cent. A narrow Ly-alpha emission line with two peaks in four galaxies and with three peaks in one object is seen in medium-resolution COS spectra with a velocity separation between the peaks Vsep varying from …
We report the detection of a large ($\sim90$ kpc) and luminous $\mathrm{Lyα}$ nebula [$L\mathrm{_{Lyα}}$ = $(6.80\pm0.08)\times 10^{44}$] $\rm{\,erg\,s^{-1}}$ around an optically faint (r$>23$ mag) radio galaxy M1513-2524 at $z\mathrm{_{em}}$=3.132. The double-lobed radio emission has an extent of 184 kpc, but the radio core, i.e., emission associated with the active galactic nucleus (AGN) itself, is barely detected. This object was found as part of our survey to identify high-$z$ quasars based on Wide-field Infrared Survey Explorer (WISE) colors. The optical spectrum has revealed $\mathrm{Lyα…
