A local clue to the reionization of the universe

Borthakur, Sanchayeeta; Heckman, Timothy M.; Leitherer, Claus; Overzier, Roderik

doi:10.1126/science.1254214

Cited by 198 publications

(275 citation statements)

References 23 publications

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“…In the high-mass range we find that the escape fraction is very high in a few haloes in which feedback was so violent that it removed most of the dense gas in the centre of the halo, causing large outflows. Recent observations have indeed found evidence for leaking ionizing radiation in one such object (Heckman et al 2011;Borthakur et al 2014). Observationally constraining the escape fraction during the epoch of reionization may be possible by targetting strongly lensed galaxies and look for features in the spectra that indicate a high escape fraction ).…”

Section: Discussionmentioning

confidence: 99%

The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

Paardekooper

Khochfar

Vecchia

2015

Monthly Notices of the Royal Astronomical Society

255

280

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Proto-galaxies forming in low-mass dark matter haloes are thought to provide the majority of ionizing photons needed to reionize the Universe, due to their high escape fractions of ionizing photons. We study how the escape fraction in high-redshift galaxies relates to the physical properties of the halo in which the galaxies form, by computing escape fractions in more than 75000 haloes between redshifts 27 and 6 that were extracted from the First Billion Years project, high-resolution cosmological hydrodynamics simulations of galaxy formation. We find that the main constraint on the escape fraction is the gas column density in a radius of 10 pc around the stellar populations, causing a strong mass dependence of the escape fraction. The lower potential well in haloes with M 200 10 8 M results in low column densities that can be penetrated by radiation from young stars (age < 5 Myr). In haloes with M 200 10 8 M supernova feedback is important, but only ∼ 30% of the haloes in this mass range have an escape fraction higher than 1%. We find a large range of escape fractions in haloes with similar properties, caused by different distributions of the dense gas in the halo. This makes it very hard to predict the escape fraction on the basis of halo properties and results in a highly anisotropic escape fraction. The strong mass dependence, the large spread and the large anisotropy of the escape fraction may strongly affect the topology of reionization and is something current models of cosmic reionization should strive to take into account.

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Section: Discussionmentioning

confidence: 99%

The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

Paardekooper

Khochfar

Vecchia

2015

Monthly Notices of the Royal Astronomical Society

255

280

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“…Only three objects are known as LyC leakers, and their absolute escape fraction 1 is only a few percent (Bergvall et al 2006;Leitet et al 2013;Borthakur et al 2014). The vast majority of known high-redshift galaxies are also opaque to their own ionising radiation, as demonstrated by the success of the well-known Lyman-break selection (as emphasised recently in Cooke et al 2014).…”

Section: Ionising Continuum Leakage From Galaxiesmentioning

confidence: 99%

“…The object 0921+45 of the leaking canditates listed by Heckman et al does not meet our criteria for LyC leakage because of its large Lyα absorption trough around the systemic redshift, indicating large amounts of neutral gas and dust. It has recently been observed in the LyC continuum, and its absolute escape fraction is indeed low (∼1%), although the relative escape is higher (∼21% Borthakur et al 2014). Of the non-leakers, three out of four have v peak 150 km s −1 and no Lyα escape bluewards of the systemic redshift.…”

Section: Lyman-break Analoguesmentioning

confidence: 99%

Using Lyman-αto detect galaxies that leak Lyman continuum

Verhamme

Orlitová

Schaerer

et al. 2015

A&A

322

439

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Aims. We propose to infer the output of the ionising continuum-leaking properties of galaxies based upon their Lyα line profiles. Methods. We carried out Lyα radiation transfer calculations in two models of H ii regions. These models are porous to ionising continuum escape: 1) we define Lyman-continuum (LyC) optically thin star clusters, in which massive stars produce enough ionising photons to keep the surrounding interstellar medium transparent to the ionising continuum, in other words, almost totally ionised; and 2) we define riddled ionisation-bounded media that are surrounded by neutral interstellar medium, but have holes, which results in a covering fraction lower than unity. Results. The Lyα spectra that emerge from these configurations have distinctive features: 1) a classical asymmetric redshifted profile in the first case, but with a small shift of the profile maximum compared to the systemic redshift (v peak ≤ 150 km s −1 ); 2) a main peak at the systemic redshift in the second case (v peak = 0), with a non-zero Lyα flux bluewards of the systemic redshift as a consequence. If in a galaxy that leaks ionising photons the Lyα component that emerges from the leaking star cluster(s) is assumed to dominate the total Lyα spectrum, the Lyα shape may be used as a pre-selection tool for detecting LyC-leaking galaxies in objects with high spectral resolution Lyα spectra (R ≥ 4000). Our predictions are corroborated by examination of a sample of ten local starbursts with high-resolution HST/COS Lyα spectra that are known in the literature as LyC leakers or leaking candidates. Conclusions. Observations of Lyα profiles at high resolution are expected to show definite signatures revealing the escape of Lyman-continuum photons from star-forming galaxies.

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“…The success of the selection method of I16a,b in finding LyC leakers at high O 32 ratios may thus be related to compactness, which together with very strong emission lines indicating a high specific SFR implies a high surface density of star formation. Heckman et al (2001Heckman et al ( , 2011 and Borthakur et al (2014) have suggested that strong star formation like this results in strong outflows that clear channels in the ISM, allowing thus the escape of Lyman continuum photons.…”

Section: In Terms Of Their Very High Equivalent Widths Of [O Iii]mentioning

confidence: 99%

The ionizing photon production efficiency of compactz~ 0.3 Lyman continuum leakers and comparison with high-redshift galaxies

Izotov

Verhamme

Orlitová

et al. 2016

A&A

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We have recently discovered five Lyman continuum leaking galaxies at z ∼ 0.3 that were selected for their compactness, intense star formation, and highHere we derive their ionizing photon production efficiency, ξ ion , a fundamental quantity for inferring the number of photons available to reionize the Universe. This is the first time this is done for galaxies with confirmed strong Lyman continuum escape ( f esc ∼ 6-13%). We find an ionizing photon production per unit UV luminosity, ξ ion , that is higher by a factor 2-6 than the canonical value when reported to their observed UV luminosity. After correction for extinction, this value is close to the canonical value. The properties of our five Lyman continuum leakers are found to be very similar to those of the previously reported confirmed z = 3.218 leaker Ion2 and very similar to those of typical star-forming galaxies at z > ∼ 6. Our results suggest that UV bright galaxies at high-z such as Lyman-break galaxies can be Lyman continuum leakers and that their contribution to cosmic reionization may be underestimated.

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A local clue to the reionization of the universe

Cited by 198 publications

References 23 publications

The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

Using Lyman-αto detect galaxies that leak Lyman continuum

The ionizing photon production efficiency of compactz~ 0.3 Lyman continuum leakers and comparison with high-redshift galaxies

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