The VANDELS survey: the ionizing properties of star-forming galaxies at 3 ≤ <i>z</i> ≤ 5 using deep rest-frame ultraviolet spectroscopy

Article Article scientifique Article The VANDELS survey: the ionizing properties of star-forming galaxies at 3 ≤ <i>z</i> ≤ 5 using deep rest-frame ultraviolet spectroscopy eng 2023-04-28 2023 author Saldana Lopez Alberto 0000-0001-8419-3062 Geneva U. 931945 author Schaerer Daniel Olivier Geneva U. 23688 Département d'astronomie (ASTRO) author Chisholm John Peter U. Texas, Austin (main) 861048 author Calabrò A. Rome Observ. author Pentericci L. Rome Observ. author Cullen Fergus author Saxena A. Oxford U. author Amorín Ricardo O. Edinburgh U., Inst. Astron. author Carnall Adam La Serena U. author Fontanot Fabio Trieste Observ. author Fynbo J.P.U. Bohr Inst. author Guaita L. Andres Bello Natl. U. author Hathi Nimish P. Baltimore, Space Telescope Sci. author Hibon Pascale La Serena U. author Ji Z. author McLeod D.J. author Pompei E. author Zamorani G. 6295-6325 10.1093/mnras/stad1283 0035-8711 2211.01351 https://academic.oup.com/mnras/article/522/4/6295/7146833 The physical properties of Epoch of Reionization (EoR) galaxies are still poorly constrained by observations. To better understand the ionizing properties of galaxies in the EoR, we investigate deep, rest-frame ultraviolet (UV) spectra of ≃500 star-forming galaxies at 3 ≤ z ≤ 5 selected from the public ESO-VANDELS spectroscopic survey. The absolute ionizing photon escape fraction ($f_{\rm esc}^{\rm abs}$, i.e. the ratio of leaking against produced ionizing photons) is derived by combining absorption line measurements with estimates of the UV attenuation. The ionizing production efficiency (ξion, i.e. the number of ionizing photons produced per non-ionizing UV luminosity) is calculated by fitting the far-UV (FUV) stellar continuum of the VANDELS galaxies. We find that the $f_{\rm esc}^{\rm abs}$ and ξion parameters increase towards low-mass, blue UV-continuum slopes and strong Ly α emitting galaxies, and both are slightly higher-than-average for the UV-faintest galaxies in the sample. Potential Lyman Continuum Emitters (LCEs, $f_{\rm esc}^{\rm abs} \ge 5{{\ \rm \, per\ cent}}$) and selected Lyman Alpha Emitters (LAEs, WLyα ≤ −20 Å) show systematically higher ξion (log ξion(Hz erg−1) ≈ 25.38, 25.41) than non-LCEs and non-LAEs (log ξion(Hz erg−1) ≈ 25.18, 25.14) at similar UV magnitudes. This indicates very young underlying stellar populations (≈10 Myr) at relatively low metallicities (≈0.2 Z⊙). The FUV non-ionizing spectra of potential LCEs is characterized by blue UV slopes (≤−2), enhanced Ly α emission (≤−25 Å), strong UV nebular lines (e.g. high ${\rm C\, \small {IV}}$1550/${\rm C\, \small {III}}$1908 ≥0.75 ratios), and weak absorption lines (≤1 Å). The latter suggests the existence of low gas-column-density channels in the interstellar medium, which enables the escape of ionizing photons. By comparing our VANDELS results against other surveys in the literature, our findings imply that the ionizing budget in the EoR was likely dominated by UV-faint, low-mass, and dustless galaxies. Dust, extinction Galaxies: high-redshift Galaxies: ISM Galaxies: stellar content Cosmology: dark ages Cosmology: reionization Cosmology: first stars Ultraviolet: galaxies Dewey 520 Danish National Research Foundation 140 DFF 1026-00066 National Science Foundation Studies of Flows, Turbulence and Transport in the Large Plasma Device 1202007 US Directorate for Mathematical & Physical Sciences 26 Département d'astronomie 12 false Monthly notices of the Royal Astronomical Society 522 4 22eeebf8-5027-414d-ab4d-9bc90b828803 Article (Published version) Public Article_scientifique_from_crossref.pdf 23882640 application/pdf CC BY-4.0 fe19b47337b698031df93aefe76d9907ca6c72ad97b9caf8b12e76b12b2420c8 openAccess Faculté des sciences / Département d'astronomie

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The VANDELS survey: the ionizing properties of star-forming galaxies at 3 ≤ z ≤ 5 using deep rest-frame ultraviolet spectroscopy	Monthly notices of the Royal Astronomical Society	2023	58	133
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Chisholm, John Peter