The Keck Lyman Continuum Spectroscopic Survey (KLCS): The Emergent Ionizing Spectrum of Galaxies at z ∼ 3

By C. Steidel, M. Bogosavljević, A. Shapley, Naveen A. Reddy, G. Rudie, M. Pettini, R. Trainor, A. Strom. Astrophysical Journal, 2018

211 citations recorded by the source corpus.

We present results of a deep spectroscopic survey quantifying the statistics of the escape of ionizing radiation from star-forming galaxies at z ∼ 3. We measure the ratio of ionizing to non-ionizing UV flux density , where f900 is the mean flux density evaluated over the range [880, 910] Å. We quantify the emergent ratio of ionizing to non-ionizing UV flux density by analyzing high signal-to-noise ratio composite spectra formed from subsamples with common observed properties and numbers sufficient to reduce the statistical uncertainty in the modeled IGM+CGM correction to obtain precise values of , including a full-sample average = 0.057 ± 0.006. We show that increases monotonically with , inducing an inverse correlation with UV luminosity as a by-product. We fit the composite spectra using stellar spectral synthesis together with models of the ISM in which a fraction fc of the stellar continuum is covered by gas with column density . We show that the composite spectra simultaneously constrain the intrinsic properties of the stars (L900/L1500)int along with fc, , , and fesc,abs, the absolute escape fraction of ionizing photons. We find a sample-averaged fesc,abs = 0.09 ± 0.01, with subsamples falling along a linear relation . Using the far-UV luminosity function, the distribution function n(W(Lyα)), and the relationship between and , we estimate the total ionizing emissivity of z ∼ 3 star-forming galaxies with Muv ≤ −19.5, which exceeds the contribution of quasi-stellar objects by a factor of ∼3, and accounts for ∼50% of the total ϵLyC at z ∼ 3 estimated using indirect methods.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

1. P. Oesch
2. Richard S. Ellis
3. C. Conroy
4. M. Ouchi
5. P. V. van Dokkum
6. T. Treu
7. R. Bouwens
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In Instrumentation

1. C. Conroy
2. P. Oesch
3. P. V. van Dokkum
4. Richard S. Ellis
5. M. Ouchi
6. T. Treu
7. M. Franx
8. I. Labbé

Citations in the corpus

• The GLASS-JWST Early Release Science Program. I. Survey Design and Release Plans (2022, background): “If ionizing photon escape fractions for Lyman-break galaxies (LBGs) are as low as inferred from z∼ 3 observations ( fesc ∼10%, e.g., Steidel et al. 2018; Begley et al. 2022), providing sufficient photons to ionize the universe requires the UV LF to extend to fainter sources than HST is able to…”
• Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, methodology): “Until very recently, these galaxies were measured to have negligible ionizing photon escape fractions (e.g., Steidel et al. 2018).”
• JWST Census for the Mass–Metallicity Star Formation Relations at z = 4–10 with Self-consistent Flux Calibration and Proper Metallicity Calibrators (2023, background): “…regarding the escape of ionizing photons ( and that of Ly α photons ) are also discussed ( e.g., Nakajima & Ouchi 2014; Izotov et al. 2016, 2018; Verhamme et al. 2017; Steidel et al. 2018; Fletcher et al. 2019; Erb et al. 2019; Nakajima et al. 2020; Katz et al. 2020; Flury et al. 2022 ) .”
• Inferences on the timeline of reionization at z ∼ 8 from the KMOS Lens-Amplified Spectroscopic Survey (2019, background): “…significantly to reionization our result suggests reionization can be completed with low escape fractions, consistent with low redshift MNRAS 000, 1–25 (2019) KLASS z ∼ 8 15 estimates of the average escape fraction (Marchi et al. 2018; Rutkowski et al. 2017; Naidu et al. 2018; Steidel et al. 2018).”
• Evolution of the AGN UV luminosity function from redshift 7.5 (2018, background): “…et al. 2010; Borthakur et al. 2014; Mostardi et al. 2015; Grazian et al. 2016; Izotov et al. 2016; Shapley et al. 2016; Japelj et al. 2017; Steidel et al. 2018; Fletcher et al. 2018; Matthee et al. 2018; Chisholm et al. 2018; Izotov et al. 2018b,a), but the average escape fraction is…”