The Lyman Continuum Escape Survey. II. Ionizing Radiation as a Function of the [O iii]/[O ii] Line Ratio

Nakajima, Kengo; Ellis, Richard S.; Robertson, Brant; Tang, Mengtao; Stark, Daniel P.

doi:10.3847/1538-4357/ab6604

Cited by 98 publications

(113 citation statements)

References 74 publications

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“…[O ]/[O ] line-ratio has been considered a promising indicator of LyC leakage as it might trace density-bounded nebulae (e.g.,Jaskot & Oey 2013;Nakajima & Ouchi 2014) and has been extensively studied due to the relative brightness of both emission-lines. However, tests of this indicator have produced mixed results (e.g.,Naidu et al 2018;Chisholm et al 2018;Jaskot et al 2019;Bassett et al 2019;Nakajima et al 2020). On the other hand, we identify a stark contrast in [O ]/[O ] across our stacks of LAEs ( §5).…”

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confidence: 64%

“…Behrens et al 2019;Smith et al 2019Smith et al , 2021. It is plausible that a Ly𝛼-selected sample picks out only galaxies viewed at favorable angles, which might minimize the scatter between 𝑓 esc and galaxy properties reported in previous studies (e.g., Fletcher et al 2019;Nakajima et al 2020;Tang et al 2021). Alternatively, it is possible that the Ly𝛼 pre-selection selects for "hidden" parameters that otherwise add scatter to such correlations as well, e.g., the presence of outflows or the relatively low mass of LAEs (e.g.…”

Section: Implications For Constraining Lyc 𝑓 Esc With Jwst: Can Strong Lines Do It All?mentioning

confidence: 99%

“…These ambiguities due to the IGM transmission are further compounded by viewing angle biases that hydrodynamical simulations show to be important due to the strong anisotropy of LyC 𝑓 esc (e.g., Gnedin et al 2008;Wise & Cen 2009;Wise et al 2014;Cen & Kimm 2015;Paardekooper et al 2015). For instance, a galaxy may have high 𝑓 esc , but via holes pointed away from the observed sightline (e.g., Fletcher et al 2019;Nakajima et al 2020;Saxena et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

Naidu

Matthee

Oesch

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The ionizing photon escape fraction (LyC fesc) 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 redshifts. Here we circumvent this uncertainty by inferring fesc using resolved (R > 4000) Lyα profiles from the X-SHOOTER Lyα survey at z = 2 (XLS-z2). With empirically motivated criteria, we use Lyα profiles to select leakers (fesc$>20\%$) and non-leakers (fesc$<5\%$) from a representative sample of >0.2L* Lyman-α emitters (LAEs). We use median stacked spectra of these subsets over λrest ≈ 1000 − 8000Å to investigate the conditions for LyC fesc. Our stacks show similar mass, metallicity, MUV, and βUV. We find the following differences between leakers vs. non-leakers: (i) strong nebular CIV and HeII emission vs. non-detections, (ii) [O iii]/[O ii]≈8.5 vs. ≈3, (iii) Hα/Hβ indicating no dust vs. E(B − V) ≈ 0.3, (iv) MgII emission close to the systemic velocity vs. redshifted, optically thick MgII, (v) Lyα fesc of $\approx 50\%$ vs. $\approx 10\%$. The extreme EWs in leakers ([O iii]+Hβ ≈ 1100 Å rest-frame) constrain the characteristic timescale of LyC escape to ≈3 − 10 Myr bursts when short-lived stars with the hardest ionizing spectra shine. The defining traits of leakers – extremely ionizing stellar populations, low column densities, a dust-free, high ionization state ISM – occur simultaneously in the fesc$>20\%$ stack, suggesting they are causally connected, and motivating why indicators like [O iii]/[O ii] may suffice to constrain fesc at z > 6 with JWST. The leakers comprise half our sample, have a median LyC fesc$\approx 50\%$ (conservative range: $20-55\%$), and an ionising production efficiency $\log ({\xi _{\rm {ion}}/\rm {Hz\ erg^{-1}}})\approx 25.9$ (conservative range: 25.7 − 25.9). These results show LAEs – the type of galaxies rare at z ≈ 2, but that become the norm at higher redshift – are highly efficient ionizers, with extreme ξion and prolific fesc occurring in sync.

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mentioning

confidence: 64%

Section: Implications For Constraining Lyc 𝑓 Esc With Jwst: Can Strong Lines Do It All?mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

Naidu

Matthee

Oesch

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…Nev ertheless, there hav e been many situations where simulations have agreed on emission-line properties of high-redshift galaxies and provide deep insights into or predictions of the early Univ erse. F or e xample, the necessary but insufficient condition that LyC leakers have high O32 (Barrow et al 2020 ;Katz et al 2020b ) as confirmed at z ∼ 2-3 (Nakajima et al 2020 ) or the strong [O I ] 63 μm (hereafter [O I ]) emission line (Olsen et al 2017 ;Katz et al 2019b ), that was recently observed at z > 6 (Rybak et al 2020 ).…”

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confidence: 90%

The nature of high [O iii]88 μ m/[C ii]158 μm galaxies in the epoch of reionization: Low carbon abundance and a top-heavy IMF?

Katz

Rosdahl

Kimm

et al. 2022

Monthly Notices of the Royal Astronomical Society

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ALMA observations of z > 6 galaxies have revealed abnormally high [OIII]88μm/[CII]158μm ratios and [CII]158μm deficits compared to local galaxies. The origin of this behaviour is unknown. Numerous solutions have been proposed including differences in C and O abundance ratios, observational bias, and differences in ISM properties, including ionisation parameter, gas density, or photodissociation region (PDR) covering fraction. In order to elucidate the underlying physics that drives this high-redshift phenomenon, we employ SPHINX20, a state-of-the-art, cosmological radiation-hydrodynamics simulation, that resolves detailed ISM properties of thousands of galaxies in the epoch of reionization which has been post-processed with CLOUDY to predict emission lines. We find that the observed z > 6 [OIII]88μm-SFR and [CII]158μm-SFR relations can only be reproduced when the C/O abundance ratio is ∼8 × lower than Solar and the total metal production is ∼4 × higher than that of a Kroupa IMF. This implies that high-redshift galaxies are potentially primarily enriched by low-metallicity core-collapse supernovae with a more top-heavy IMF. As AGB stars and type-Ia supernova begin to contribute to the galaxy metallicity, both the [CII]158μm-SFR and [CII]158μm luminosity functions are predicted to converge to observed values at z ∼ 4.5. While we demonstrate that ionisation parameter, LyC escape fraction, ISM gas density, and CMB attenuation all drive galaxies towards higher [OIII]88μm/[CII]158μm, observed values at z > 6 can only be reproduced with substantially lower C/O abundances compared to Solar. The combination of [CII]158μm and [OIII]88μm can be used to predict the values of ionisation parameter, ISM gas density, and LyC escape fraction and we provide estimates of these quantities for nine observed z > 6 galaxies. Finally, we demonstrate that [OI]63μm can be used as a replacement for [CII]158μm in high-redshift galaxies where [CII]158μm is unobserved and argue that more observation time should be used to target [OI]63μm at z > 6. Future simulations will be needed to self-consistently address the numerous uncertainties surrounding a varying IMF at high redshift and the associated metal returns.

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“…Constraining the LyC escape fraction as a function of both redshift and galaxy properties has been the subject of numerous observational and theoretical studies as constraining this parameter will allow for the determination of both the reionization history and the primary sources responsible (e.g. Nakajima et al 2020;Kimm et al 2017;Barrow et al 2020). While the global, luminosity-weighted escape fractions cannot be substantially different between the simulations with different PMFs because of the observed consistency in star formation and reionization histories, we may expect slight differences due to the variations in ISM properties.…”

Section: Impact Of Primordial Magnetic Fields On the Lyc Escape Fractionmentioning

confidence: 99%

Introducing SPHINX-MHD: the impact of primordial magnetic fields on the first galaxies, reionization, and the global 21-cm signal

Katz

Martin-Alvarez²,

Rosdahl

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We present the first results from SPHINX-MHD, a suite of cosmological radiation-magnetohydrodynamics simulations designed to study the impact of primordial magnetic fields (PMFs) on galaxy formation and the evolution of the intergalactic medium (IGM) during the epoch of reionization. The simulations are among the first to employ multi-frequency, on-the-fly radiation transfer and constrained transport ideal MHD in a cosmological context to simultaneously model the inhomogeneous process of reionization as well as the growth of primordial magnetic fields. We run a series of (5 cMpc)3 cosmological volumes, varying both the strength of the seed magnetic field and its spectral index. We find that PMFs with a spectral index (nB) and a comoving amplitude (B0) that have $n_B > -0.562\log _{10}\left(\frac{B_0}{1{\rm n}G}\right) - 3.35$ produce electron optical depths (τe) that are inconsistent with CMB constraints due to the unrealistically early collapse of low-mass dwarf galaxies. For nB ≥ −2.9, our constraints are considerably tighter than the ∼nG constraints from Planck. PMFs that do not satisfy our constraints have little impact on the reionization history or the shape of the UV luminosity function. Likewise, detecting changes in the Lyα forest due to PMFs will be challenging because photoionisation and photoheating efficiently smooth the density field. However, we find that the first absorption feature in the global 21cm signal is a particularly sensitive indicator of the properties of the PMFs, even for those that satisfy our τe constraint. Furthermore, strong PMFs can marginally increase the escape of LyC photons by up to 25 per cent and shrink the effective radii of galaxies by $\sim 44{{\ \rm per\ cent}}$ which could increase the completeness fraction of galaxy surveys. Finally, our simulations show that surveys with a magnitude limit of ${\rm M_{UV,1500\mathring{\rm A}}=-13}$ can probe the sources that provide the majority of photons for reionization out to z = 12.

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The Lyman Continuum Escape Survey. II. Ionizing Radiation as a Function of the [O iii]/[O ii] Line Ratio

Cited by 98 publications

References 74 publications

The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

The nature of high [O iii]88 μ m/[C ii]158 μm galaxies in the epoch of reionization: Low carbon abundance and a top-heavy IMF?

Introducing SPHINX-MHD: the impact of primordial magnetic fields on the first galaxies, reionization, and the global 21-cm signal

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