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X-ray properties of He II λ 1640 emitting galaxies in VANDELS

Saxena, A; Pentericci, L; Schaerer, D; Schneider, R; Amorin, R; Bongiorno, A; Calabrò, A; ... Zamorani, G; + view all (2020) X-ray properties of He II λ 1640 emitting galaxies in VANDELS. Monthly Notices of the Royal Astronomical Society , 496 (3) pp. 3796-3807. 10.1093/mnras/staa1805. Green open access

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Abstract

We explore X-ray emission from a sample of 18 He II λ1640 emitting star-forming galaxies at z ∼ 2.3–3.6 from the VANDELS survey in the Chandra Deep Field South, to set constraints on the role of X-ray sources in powering the He II emission. We find that 4 He II emitters have tentative detections with S/N ∼ 2 and have X-ray luminosities, LX = 1.5−4.9 × 10^{41} erg s^{−1}. The stacked luminosity of all 18 He II emitters is 2.6 × 10^{41} erg s^{−1}, and that of a subset of 13 narrow He II emitters (FHWM(He II) < 1000 km s^{−1}) is 3.1 × 10^{41} erg s^{−1}. We also measure stacked LX for non-He II emitters through bootstrapping of matched samples, and find LX = 2.5 × 10^{41} erg s^{−1}, which is not significantly different from LX measured for He II emitters. The LX per star formation rate for He II emitters (log (LX/SFR) ∼ 40.0) and non-emitters (log (L_{X}/SFR) ∼ 39.9) are also comparable and in line with the redshift evolution and metallicity dependence predicted by models. Due to the non-significant difference between the X-ray emission from galaxies with and without He II, we conclude that X-ray binaries or weak or obscured active galactic nuclei are unlikely to be the dominant producers of He II ionizing photons in VANDELS star-forming galaxies at z ∼ 3. Given the comparable physical properties of both He II emitters and non-emitters reported previously, alternative He II ionizing mechanisms such as localized low-metallicity stellar populations, Pop-III stars, etc. may need to be explored.

Type: Article
Title: X-ray properties of He II λ 1640 emitting galaxies in VANDELS
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/staa1805
Publisher version: https://doi.org/10.1093/mnras/staa1805
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher's terms and conditions.
Keywords: galaxies: evolution, galaxies: high-redshift, X-rays: binaries
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10105257
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