Published in

Astronomy & Astrophysics, (624), p. A89, 2019

DOI: 10.1051/0004-6361/201834565

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Exploring He II λ1640 emission line properties atz∼2−4

This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Data provided by SHERPA/RoMEO

Abstract

Deep optical spectroscopic surveys of galaxies provide a unique opportunity to investigate rest-frame ultra-violet (UV) emission line properties of galaxies atz ∼ 2 − 4.5. Here we combine VLT/MUSE Guaranteed Time Observations of theHubbleDeep Field South, Ultra Deep Field, COSMOS, and several quasar fields with other publicly available data from VLT/VIMOS and VLT/FORS2 to construct a catalogue of He II λ1640 emitters atz ≳ 2. The deepest areas of our MUSE pointings reach a 3σline flux limit of 3.1 × 10−19erg s−1cm−2. After discarding broad-line active galactic nuclei, we find 13 He II λ1640 detections from MUSE with a medianMUV = −20.1 and 21 tentative He II λ1640 detections from other public surveys. Excluding Lyα, all except two galaxies in our sample show at least one other rest-UV emission line, with C III]λ1907,λ1909 being the most prominent. We use multi-wavelength data available in theHubblelegacy fields to derive basic galaxy properties of our sample through spectral energy distribution fitting techniques. Taking advantage of the high-quality spectra obtained by MUSE (∼10 − 30 h of exposure time per pointing), we use photo-ionisation models to study the rest-UV emission line diagnostics of the He II λ1640 emitters. Line ratios of our sample can be reproduced by moderately sub-solar photo-ionisation models, however, we find that including effects of binary stars lead to degeneracies in most free parameters. Even after considering extra ionising photons produced by extreme sub-solar metallicity binary stellar models, photo-ionisation models are unable to reproduce rest-frame He II λ1640 equivalent widths (∼0.2 − 10 Å), thus additional mechanisms are necessary in models to match the observed He II λ1640 properties.

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