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No correlation of the Lyman continuum escape fraction with spectral hardness

Marques-Chaves, R. and Schaerer, D. and Amorín, R. O. and Atek, H. and Borthakur, S. and Chisholm, J. and Fernandez, V. and Flury, S. R. and Giavalisco, M. and Grazian, A. and Hayes, M. J. and Heckman, T. M. and Henry, A. and Izotov, Y. I. and Jaskot, A. E. and Ji, Z. and McCandliss, S. R. and Oey, M. S. and Östlin, G. and Ravindranath, S. and Rutkowski, M. J. and Saldana-Lopez, A. and Teplitz, H. and Thuan, T. X. and Verhamme, A. and Wang, B. and Worseck, G. and Xu, X. (2022) No correlation of the Lyman continuum escape fraction with spectral hardness. Astronomy and Astrophysics, 663 . Art. No. L1. ISSN 0004-6361. doi:10.1051/0004-6361/202243598.

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The properties that govern the production and escape of hydrogen-ionizing photons (Lyman continuum, LyC; with energies > 13.6 eV) in star-forming galaxies are still poorly understood, but they are key to identifying and characterizing the sources that reionized the Universe. Here we empirically explore the relation between the hardness of ionizing radiation and the LyC leakage in a large sample of low-z star-forming galaxies from the recent Hubble Space Telescope Low-z Lyman Continuum Survey. Using Sloan Digital Sky Survey stacks and deep X-shooter observations, we investigate the hardness of the ionizing spectra (Q_(He⁺)/Q_H) between 54.4 eV (He⁺) and 13.6 eV (H) from the optical recombination lines He II 4686 Å and Hβ 4861 Å for galaxies with LyC escape fractions spanning a wide range, f_(esc)(LyC) ≃ 0−90%. We find that the observed intensity of He II/Hβ is primarily driven by variations in the metallicity, but is not correlated with LyC leakage. Both very strong (f_(esc)(LyC)> ≃ 0.5) and nonleakers (f_(esc)(LyC)> ≃ 0) present similar observed intensities of He II and Hβ at comparable metallicity, between ≃0.01 and ≃0.02 for 12 + log(O/H)> 8.0 and Q_(He⁺)/Q_H does not correlate with f_(esc)(LyC), which implies that strong LyC emitters do not show harder ionizing spectra than nonleakers at similar metallicity.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Marques-Chaves, R.0000-0001-8442-1846
Schaerer, D.0000-0001-7144-7182
Atek, H.0000-0002-7570-0824
Giavalisco, M.0000-0002-7831-8751
Henry, A.0000-0002-6586-4446
Oey, M. S.0000-0002-5808-1320
Teplitz, H.0000-0002-7064-5424
Alternate Title:Does Lyman continuum escape fraction correlate with spectral hardness
Additional Information:© R. Marques-Chaves et al. 2022. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Received: 21 March 2022 Accepted: 10 May 2022. The authors thank the referee for useful comments that greatly improved the clarity of this work. Y.I.I. acknowledges support from the National Academy of Sciences of Ukraine by its priority project “Fundamental properties of the matter in the microworld, astrophysics and cosmology”. R.A. acknowledges support from ANID Fondecyt Regular Grant 1202007. Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High Performance Computing at the University of Utah. The SDSS website is
Funding AgencyGrant Number
National Academy of Sciences (Ukraine)UNSPECIFIED
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1202007
Alfred P. Sloan FoundationUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Participating InstitutionsUNSPECIFIED
Subject Keywords:galaxies: starburst / galaxies: high-redshift / dark ages, reionization, first stars
Record Number:CaltechAUTHORS:20220721-8079000
Persistent URL:
Official Citation:No correlation of the Lyman continuum escape fraction with spectral hardness R. Marques-Chaves, D. Schaerer, R. O. Amorín, H. Atek, S. Borthakur, J. Chisholm, V. Fernández, S. R. Flury, M. Giavalisco, A. Grazian, M. J. Hayes, T. M. Heckman, A. Henry, Y. I. Izotov, A. E. Jaskot, Z. Ji, S. R. McCandliss, M. S. Oey, G. Östlin, S. Ravindranath, M. J. Rutkowski, A. Saldana-Lopez, H. Teplitz, T. X. Thuan, A. Verhamme, B. Wang, G. Worseck and X. Xu A&A, 663 (2022) L1 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115721
Deposited By: George Porter
Deposited On:22 Jul 2022 22:58
Last Modified:22 Jul 2022 22:58

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