TY - JOUR
T1 - The VANDELS survey: the ionizing properties of star-forming galaxies at 3 ≤ z ≤ 5 using deep rest-frame ultraviolet spectroscopy
AU - Saldana-Lopez, A.
AU - Schaerer, D.
AU - Chisholm, J.
AU - Calabrò, A.
AU - Pentericci, L.
AU - Cullen, F.
AU - Saxena, A.
AU - Amorín, R.
AU - Carnall, A. C.
AU - Fontanot, F.
AU - Fynbo, J. P.U.
AU - Guaita, L.
AU - Hathi, N. P.
AU - Hibon, P.
AU - Ji, Z.
AU - McLeod, D. J.
AU - Pompei, E.
AU - Zamorani, G.
N1 - Funding Information:
The authors thank the anonymous referee for providing useful comments, which have certainly improved the quality of this paper. The authors also thank Hakim Atek, Jorytt Matthee, and Irene Shivaei for kindly providing tabulated data from Atek et al. (), Matthee et al. (), and Shivaei et al. (). ASL and DS acknowledge support from Swiss National Science Foundation. The Cosmic Dawn Center is funded by the Danish National Research Foundation under grant No.140. RA acknowledges support from ANID FONDECYT Regular 1202007. JPUF is supported by the DFF grant 1026-00066.
Funding Information:
The authors thank the anonymous referee for providing useful comments, which have certainly improved the quality of this paper. The authors also thank Hakim Atek, Jorytt Matthee, and Irene Shivaei for kindly providing tabulated data from Atek et al. (2022), Matthee et al. (2017a), and Shivaei et al. (2018). ASL and DS acknowledge support from Swiss National Science Foundation. The Cosmic Dawn Center is funded by the Danish National Research Foundation under grant No.140. RA acknowledges support from ANID FONDECYT Regular 1202007. JPUF is supported by the DFF grant 1026-00066.
Publisher Copyright:
© The Author(s) 2023. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
PY - 2023/7/1
Y1 - 2023/7/1
N2 - 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 (fescabs, 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 fescabs 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, fescabs ≥ 5 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 C IV1550/C III1908 ≥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.
AB - 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 (fescabs, 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 fescabs 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, fescabs ≥ 5 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 C IV1550/C III1908 ≥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.
KW - dark ages
KW - dust
KW - extinction
KW - first stars
KW - galaxies: high-redshift
KW - galaxies: ISM
KW - galaxies: stellar content
KW - reionization
KW - ultraviolet: galaxies
UR - http://www.scopus.com/inward/record.url?scp=85161507559&partnerID=8YFLogxK
U2 - 10.1093/mnras/stad1283
DO - 10.1093/mnras/stad1283
M3 - Article
AN - SCOPUS:85161507559
SN - 0035-8711
VL - 522
SP - 6295
EP - 6325
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -