Examinando por Autor "Saxena A."

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    The ionizing photon production efficiency of bright z ~ 2-5 galaxies
    (EDP Sciences, 2023-07) Castellano M.; Belfiori D.; Pentericci L.; Calabrò A.; Mascia S.; Napolitano L.; Caro F.; Charlot S.; Chevallard J.; Curtis Lake E.; Talia M.; Bongiorno A.; Fontana A.; Fynbo J.P.U.; Garilli B.; Guaita L.; McLure R.J.; Merlin E.; Mignoli M.; Moresco M.; Pompei E.; Pozzetti L.; Saldana Lopez A.; Saxena A.; Santini P.; Schaerer D.; Schreiber C.; Shapley A.E.; Vanzella E.; Zamorani G.
    Aims. We investigate the production efficiency of ionizing photons (ξion∗) of 1174 galaxies with secure redshift at z=2 - 5 from the VANDELS survey to determine the relation between ionizing emission and physical properties of bright and massive sources. Methods. We constrained ξion∗ and galaxy physical parameters by means of spectrophotometric fits performed with the BEAGLE code. The analysis exploits the multi-band photometry in the VANDELS fields and the measurement of UV rest-frame emission lines (CIII]λ1909, HeIIλ1640, and OIII]λ1666) from deep VIMOS spectra. Results. We find no clear evolution of ξion∗ with redshift within the probed range. The ionizing efficiency slightly increases at fainter MUV and bluer UV slopes, but these trends are less evident when the analysis is restricted to a complete subsample at log(Mstar/M⊙) > 9.5. We find a significant trend of increasing ξion∗ with increasing EW(Lyα), with an average log(ξion∗/Hz erg-1) > 25 at EW > 50 Åand a higher ionizing efficiency for high-EW CIII]λ1909 and OIII]λ1666 emitters. The most significant correlations are found with respect to stellar mass, specific star formation rate (sSFR), and SFR surface density (ΣSFR). The relation between ξion∗ and sSFR increases monotonically from log(ξion∗/Hz erg-1)~24.5 at log(sSFR)~-9.5yr-1 to ~25.5 at log(sSFR)~-7.5yr-1. This relation has a low scatter and only a weak dependence on mass. The objects above the main sequence of star formation consistently have higher than average ξion∗. A clear increase in ξion∗ with ΣSFR is also found, with log(ξion∗/Hz erg-1) > 25 for objects at ΣSFR>10M⊙ yr-1 kpc-2. Conclusions. Bright (MUV≲20) and massive (log(Mstar/M⊙)≳9.5) galaxies at z=2 - 5 have a moderate ionizing efficiency. However, the correlation between ξion∗ and sSFR, together with the known increase in the average sSFR with redshift at fixed stellar mass, suggests that similar galaxies in the epoch of reionization can be efficient sources of ionizing photons. The availability of sSFR and ΣSFR as proxies for ξion∗ can be fundamentally important in determining the role of galaxy populations at z≳10 that were recently discovered by the James Webb Space Telescope in the onset of reionization. © 2023 EDP Sciences. All rights reserved.
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    The VANDELS survey: the ionizing properties of star-forming galaxies at 3 ≤ z ≤ 5 using deep rest-frame ultraviolet spectroscopy
    (Oxford University Press, 2023-07) Saldana-Lopez A.; Schaerer D.; Chisholm J.; Calabrò A.; Pentericci L.; Cullen F.; Saxena A.; Guaita L.; Hathi N.P.; Hibon P.; Ji Z.; McLeod D.J.; Pompei E.; Zamorani G.
    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. © 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.