article published yes Themiya Nanayakkara author Jarle Brinchmann author Leindert Boogaard author Rychard Bouwens author Sebastiano Cantalupo author Anna Feltre author Wolfram Kollatschny author Raffaella Anna Marino author Michael Maseda author Jorryt J Matthee author 7439a258-f3c0-11ec-9501-9df22fe067200000-0003-2871-127X Mieke Paalvast author Johan Richard author Anne Verhamme author Deep optical spectroscopic surveys of galaxies provide a unique opportunity to investigate rest-frame ultra-violet (UV) emission line properties of galaxies at z ∼ 2 − 4.5. Here we combine VLT/MUSE Guaranteed Time Observations of the Hubble Deep 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 at z ≳ 2. The deepest areas of our MUSE pointings reach a 3σ line flux limit of 3.1 × 10−19 erg s−1 cm−2. After discarding broad-line active galactic nuclei, we find 13 He II λ1640 detections from MUSE with a median MUV = −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 the Hubble legacy 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. EDP Sciences2019 eng Space and Planetary ScienceAstronomy and Astrophysicsgalaxies: ISM / galaxies: star formation / galaxies: evolution / galaxies: high-redshift 0004-6361 1432-0746 1902.0596010.1051/0004-6361/201834565 648 https://doi.org/10.1051/0004-6361/201834565e yes Nanayakkara T, Brinchmann J, Boogaard L, Bouwens R, Cantalupo S, Feltre A, Kollatschny W, Marino RA, Maseda M, Matthee JJ, Paalvast M, Richard J, Verhamme A. 2019. Exploring He II λ1640 emission line properties at z ∼2−4. Astronomy &#38; Astrophysics. 648, A89. T. Nanayakkara <i>et al.</i>, “Exploring He II λ1640 emission line properties at z ∼2−4,” <i>Astronomy &#38; Astrophysics</i>, vol. 648. EDP Sciences, 2019. Nanayakkara, T., Brinchmann, J., Boogaard, L., Bouwens, R., Cantalupo, S., Feltre, A., … Verhamme, A. (2019). Exploring He II λ1640 emission line properties at z ∼2−4. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href="https://doi.org/10.1051/0004-6361/201834565">https://doi.org/10.1051/0004-6361/201834565</a> Nanayakkara, Themiya, et al. “Exploring He II Λ1640 Emission Line Properties at z ∼2−4.” <i>Astronomy &#38; Astrophysics</i>, vol. 648, A89, EDP Sciences, 2019, doi:<a href="https://doi.org/10.1051/0004-6361/201834565">10.1051/0004-6361/201834565</a>. Nanayakkara, Themiya, Jarle Brinchmann, Leindert Boogaard, Rychard Bouwens, Sebastiano Cantalupo, Anna Feltre, Wolfram Kollatschny, et al. “Exploring He II Λ1640 Emission Line Properties at z ∼2−4.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2019. <a href="https://doi.org/10.1051/0004-6361/201834565">https://doi.org/10.1051/0004-6361/201834565</a>. Nanayakkara T, Brinchmann J, Boogaard L, et al. Exploring He II λ1640 emission line properties at z ∼2−4. <i>Astronomy &#38; Astrophysics</i>. 2019;648. doi:<a href="https://doi.org/10.1051/0004-6361/201834565">10.1051/0004-6361/201834565</a> T. Nanayakkara, J. Brinchmann, L. Boogaard, R. Bouwens, S. Cantalupo, A. Feltre, W. Kollatschny, R.A. Marino, M. Maseda, J.J. Matthee, M. Paalvast, J. Richard, A. Verhamme, Astronomy &#38; Astrophysics 648 (2019). 114992022-07-06T09:07:06Z2022-07-19T09:36:08Z