First detection of Lyman continuum escape from a local starburst galaxy (original) (raw)
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LYMAN CONTINUUM ESCAPE FRACTION OF STAR-FORMING DWARF GALAXIES AT z ∼ 1
The Astrophysical Journal, 2016
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 groundbased optical imaging to extend the search for escaping Lyman continuum to a large (∼600) sample of z ∼ 1 low-mass (log(M) 9.3M), moderately star-forming (Ψ 10M yr −1) galaxies selected initially on Hα emission. The characteristic escape fraction of LyC from SFGs that populate this parameter space remains weakly constrained by previous surveys, but these faint (sub-L) SFGs are assumed to play a significant role in the reionization of neutral hydrogen in the intergalactic medium (IGM) at high redshift z > 6. We do not make an unambiguous detection of escaping LyC radiation from this z ∼ 1 sample, individual non-detections to constrain the absolute Lyman continuum escape fraction, f esc < 2.1% (3σ). We measure an upper limit of f esc < 9.6% from a sample of SFGs selected on high Hα equivalent width (EW> 200Å), which are thought to be close analogs of high redshift sources of reionization. For reference, we also present an emissivity-weighted escape fraction which is useful for measuring the general contribution SFGs to the ionizing UV background. In the discussion, we consider the implications of these intermediate redshift constraints for the reionization of hydrogen in the intergalactic medium at high (z > 6) redshift. If we assume our z ∼ 1 SFGs, for which we measure this emissivity-weighted f esc , are analogs to the high redshift sources of reionization, we find it is difficult to reconcile reionization by faint (M U V −13) SFGs with a low escape fraction (f esc < 3%), with constraints from independent high redshift observations. If f esc evolves with redshift, reionization by SFGs may be consistent with observations from Planck.
The escape of Lyman photons from a young starburst: the case of Haro 11
Monthly Notices of the Royal Astronomical Society, 2007
Lyman-alpha (Lyα) is one of the dominant tools used to probe the star-forming galaxy population at high-redshift (z). However, astrophysical interpretations of data drawn from Lyα alone hinge on the Lyα escape fraction which, due to the complex radiative transport, may vary greatly. Here we map the Lyα emission from the local luminous blue compact galaxy Haro 11, a known emitter of Lyα and the only known candidate for low-z Lyman continuum emission (LyC). To aid in the interpretation we perform a detailed UV and optical multi-wavelength analysis and model the stellar population, dust distribution, ionising photon budget, and star-cluster population. We use archival X-ray observations to further constrain properties of the starburst and estimate the neutral hydrogen column density.
Astrophysical Journal, 1997
We have reevaluated the constraints on the Lyman continuum emission from four starburst galaxies observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 mission. Applying a detailed model of the absorption by interstellar gases in our Galaxy, and using the latest HUT data products, we find upper limits to the redshifted Lyman continuum that are less restrictive than those reported previously (Leitherer et al. 1995 ApJ, 454, L19). Well determined astrophysical and instrumental effects permit 2 σ upper limits no tighter than 5.2%, 11%, 57%, and 3.2% to be set on the escape fraction of Lyman continuum photons from IRAS 08339+6517, Mrk 1267, Mrk 66, and Mrk 496, respectively. Absorption from undetected interstellar components (including H 2 ) or modulation of the emergent spectrum by gas or dust in the parent galaxy could allow the true escape fractions to exceed these revised upper limits.
Monthly Notices of the Royal Astronomical Society, 2020
The physical origin of low escape fractions of ionizing radiation derived from massive star-forming galaxies at z ∼ 3–4 is not well understood. We perform idealized disc galaxy simulations to understand how galactic properties such as metallicity and gas mass affect the escape of Lyman continuum (LyC) photons using radiation-hydrodynamic simulations with strong stellar feedback. We find that the luminosity-weighted escape fraction from a metal-poor (Z = 0.002) galaxy embedded in a halo of mass Mrmhsimeq1011,mathrmModotM_{\rm h}\simeq 10^{11}\, \mathrm{M}_\odotMrmhsimeq1011,mathrmModot is leftlanglefrmescrm3Drightranglesimeq10,rmpercent\left\langle {f_{\rm esc}^{\rm 3D}}\right\rangle \simeq 10\, {{\ \rm per\ cent}}leftlanglefrmescrm3Drightranglesimeq10,rmpercent. Roughly half of the LyC photons are absorbed within scales of 100 pc, and the other half is absorbed in the ISM ($\lesssim 2\, {\rm kpc}$). When the metallicity of the gas is increased to Z = 0.02, the escape fraction is significantly reduced to leftlanglefrmescrm3Drightranglesimeq1rmpercent\left\langle {f_{\rm esc}^{\rm 3D}}\right\rangle \simeq 1{{\ \rm per\ cent}}leftlanglefrmescrm3Drightranglesimeq1rmpercent because young stars are enshrouded by the...
High Lyman Continuum Escape Fraction in a Lensed Young Compact Dwarf Galaxy at z = 2.5
The Astrophysical Journal, 2017
We present the HST WFC3/F275W UV imaging observations of A2218-Flanking, a lensed compact dwarf galaxy at redshift » z 2.5. The stellar mass of A2218-Flanking is () * =-+ M M log 9.14 0.04 0.07 and SFR is-+ 12.5 7.4 3.8 M yr −1 after correcting the magnification. This galaxy has a young galaxy age of 127Myr and a compact galaxy size of = r 2.4 kpc 1 2. The HST UV imaging observations cover the rest-frame Lyman continuum (LyC) emission (∼800 Å) from A2218-Flanking. We firmly detect (s 14) the LyC emission in A2218-Flanking in the F275W image. Together with the HST F606W images, we find that the absolute escape fraction of LyC is-> f 28% 57% abs,esc based on the flux density ratio between 1700 and 800 Å (f f 1700 800). The morphology of the LyC emission in the F275W images is extended and follows the morphology of the UV continuum morphology in the F606W images, suggesting that the f 800 is not from foreground contaminants. We find that the region with a high star formation rate surface density has a lower f f 1700 800 (higher f f 800 1700) ratio than the diffused regions, suggesting that LyC photons are more likely to escape from the region with the intensive star-forming process. We compare the properties of galaxies with and without LyC detections and find that LyC photons are easier to escape in low-mass galaxies.
Lyman-continuum galaxies and the escape fraction of Lyman-break galaxies
Monthly Notices of the Royal Astronomical Society, 2014
Lyman-break galaxies (LBGs) at z ∼ 3-4 are targeted to measure the fraction of Lymancontinuum (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 n GR-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 in the literature that have spectroscopic LyC measurements while predicting the existence of a significant fraction of galaxies outside the standard selection region. These galaxies, termed Lymancontinuum galaxies (LCGs), are expected to have high levels of LyC flux and are estimated to have a number density ∼30-50 per cent that of the LBG population. We define R obs (U n ) as the relative fraction of observed LyC flux, integrated from 912 Å to the shortest restframe wavelength probed by the U n filter, to the observed non-ionizing flux (here measured at 1500 Å). We use the 794 spectra as a statistical sample for the full z ∼ 3 LBG population, and find R obs (U n ) = 5.0 +1.0 −0.4 (4.1 +0.5 −0.3 ) per cent, which corresponds to an intrinsic LyC escape fraction of f LyC esc = 10.5 +2.0 −0.8 (8.6 +1.0 −0.6 ) per cent (contamination corrected). From the composite spectral distributions we estimate R obs (U n ) ∼ 16 ± 3, f LyC esc ∼ 33 ± 7 per cent for LCGs and R obs (U n ) ∼ 8 ± 3, f LyC esc ∼ 16 ± 4 per cent for the combined LBG+LCG z ∼ 3 sample. All values are measured in apertures defined by the ultraviolet continuum and do not include extended and/or offset LyC flux. A complete galaxy census and the total emergent LyC flux at high redshift are essential to quantify the contribution of galaxies to the ionizing photon budget of the Universe, particularly during the epoch of reionization.
On the influence of physical galaxy properties on Lyman alpha escape in star-forming galaxies
Astronomy and Astrophysics
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 with an optical spectroscopic follow-up to calculate the Lya escape fraction and its dependency upon different physical properties. We also examine the reliability of Lya as a star formation rate indicator. We combine these observations with a compilation of Lya emitters selected at z = 0 - 0.3 to assemble a larger sample. The Lya escape fraction depends clearly on the dust extinction following the relati...
Escape of about five per cent of Lyman-α photons from high-redshift star-forming galaxies
Nature, 2010
The Lyman-α (Lyα) emission line is the primary observational signature of starforming galaxies at the highest redshifts 1 , and has enabled the compilation of large samples of galaxies with which to study cosmic evolution 2-5 . The resonant nature of the line, however, means that Lyα 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 Lyα luminosity may be significantly reduced, or even completely suppressed. Hitherto, no unbiased empirical test of the escaping fraction (f esc ) of Lyα photons has been performed at high redshifts. Here we report that the average f esc from star-forming galaxies at redshift z = 2.2 is just 5 per cent by performing a blind narrowband survey in Lyα and Hα. This implies that numerous conclusions based on Lyα-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 starforming galaxies emit insufficient Lyα to be detected by standard selection criteria 2-5 . Both samples show an anti-correlation of f esc with dust content, and we show that Lyα-and Hα-selection recovers populations that differ substantially in dust content and f esc .
CLARA’s view on the escape fraction of Lyman α photons in high-redshift galaxies
Monthly Notices of the Royal Astronomical Society, 2011
Using CLARA (Code for Lyman Alpha Radiation Analysis) we constrain the escape fraction of Lyman-α 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-α Emitters (LAEs) as dusty gaseous slabs with Lyman-α 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 Universe numerical galaxies. The model shows a weak redshift evolution and good agreement with estimations of the escape fraction as a function of reddening from observations at z ∼ 2.2 and z ∼ 3. We extend the slab model by including additional dust in a clumpy component in order to reproduce the UV continuum luminosity function and UV colours at redshifts z 5. The LAE Luminosity Function (LF) based on the extended clumpy model reproduces broadly the bright end of the LF derived from observations at z ∼ 5 and z ∼ 6. At z ∼ 7 our model over-predicts the LF by roughly a factor of four, presumably because the effects of the neutral intergalactic medium are not taken into account. The remaining tension between the observed and simulated faint end of the LF, both in the UV-continuum and Lyman-α at redshifts z ∼ 5 and z ∼ 6 points towards an overabundance of simulated LAEs hosted in haloes of masses 1.0 × 10 10 h −1 M ⊙ ≤ M h ≤ 4.0 × 10 10 h −1 M ⊙ . Given the difficulties in explaining the observed overabundance by dust absorption, a probable origin of the mismatch are the high star formation rates in the simulated haloes around the quoted mass range. A more efficient supernova feedback should be able to regulate the star formation process in the shallow potential wells of these haloes.
Astronomy & Astrophysics, 2014
Context. Though Lyα emission is one of the most used tracers of massive star formation at high redshift, it is strongly affected by neutral gas radiation transfer effects. A correct understanding of these effects is required to properly quantify the star formation rate along the history of the Universe. Aims. We aim to parameterize the escape of Lyα photons as a function of the galaxy properties, in order to properly calibrate the Lyα luminosity as a tracer of star formation intensity at any age of the Universe. Methods. We are embarked in a program to study the properties of the Lyα emission (spectral profile, spatial distribution, relation to Balmer lines intensity,...) in a number of starburst galaxies in the Local Universe. The study is based on HST spectroscopic and imaging observations at various wavelengths, X-ray data and ground-based spectroscopy, complemented with the use of evolutionary population synthesis models. Results. We present here the results obtained for one of those sources, IRAS 08339+6517, a strong Lyα emitter in the Local Universe which is undergoing an intense episode of massive star formation. We have characterized the properties of the starburst, which transformed 1.4 × 10 8 M ⊙ of gas into stars around 5 − 6 Myr ago. The mechanical energy released by the central Super Stellar Cluster (SSC) located in the core of the starburst has created a cavity devoid of gas and dust around it, leaving a clean path through which the UV continuum of the SSC is observed, with almost no extinction. While the average extinction affecting the stellar continuum is significantly larger out of the cavity, with E(B-V)=0.15 in average, we have not found any evidence for regions with very large extinctions, which could be hiding some young, massive stars not contributing to the global UV continuum. The observed soft and hard X-ray emissions are consistent with this scenario, being originated by the interstellar medium heated by the release of mechanical energy in the first case, and by a large number of active High Mass X-ray Binaries (HMXBs) in the second. In addition to the central compact emission blob, we have identified a diffuse Lyα emission component smoothly distributed over the whole central area of IRAS 08339+6517. This diffuse emission is spatially decoupled from the UV continuum, the Hα emission or the Hα/Hβ ratio. Both locally and globally, the Lyα/Hα ratio is lower than the Case B predictions, even after reddening correction, with an overall Lyα escape fraction of only 4%. Conclusions. We conclude that in IRAS 08339+6517 the Lyα photons resonantly scattered by an outflowing shell of neutral gas are being smoothly redistributed over the whole central area of the galaxy. Their increased probabibility of being destroyed by dust would explain the low Lyα escape fraction measured. In any case, in the regions where the diffuse Lyα emission shows the largest Lyα/Hα ratios, no additional sources of Lyα emission are required, like ionization by hot plasma as proposed for Haro 2, another galaxy in our sample. These results stress again the importance of a proper correction of scattering and transfer effects when using Lyα to derive the star formation rate in high-redshift galaxies.