Sobral, David and Matthee, Jorryt and Darvish, Behnam and Smail, Ian and Best, Philip N. and Alegre, Lara and Röttgering, Huub and Mobasher, Bahram and Paulino-Afonso, Ana and Stroe, Andra and Oteo, Iván (2018) 'The nature of luminous Ly α emitters at z ∼ 2–3 : maximal dust-poor starbursts and highly ionizing AGN.', Monthly notices of the Royal Astronomical Society., 477 (2). pp. 2817-2840.
Deep narrow-band surveys have revealed a large population of faint Ly α emitters (LAEs) in the distant Universe, but relatively little is known about the most luminous sources ( LLyα≳1042.7 erg s−1; LLyα≳L∗Lyα ). Here we present the spectroscopic follow-up of 21 luminous LAEs at z ∼ 2–3 found with panoramic narrow-band surveys over five independent extragalactic fields (≈4 × 106 Mpc3 surveyed at z ∼ 2.2 and z ∼ 3.1). We use WHT/ISIS, Keck/DEIMOS, and VLT/X-SHOOTER to study these sources using high ionization UV lines. Luminous LAEs at z ∼ 2–3 have blue UV slopes ( β=−2.0+0.3−0.1 ) and high Ly α escape fractions ( 50+20−15 per cent) and span five orders of magnitude in UV luminosity (MUV ≈ −19 to −24). Many (70 per cent) show at least one high ionization rest-frame UV line such as C IV, N V, C III], He II or O III], typically blue-shifted by ≈100–200 km s−1 relative to Ly α. Their Ly α profiles reveal a wide variety of shapes, including significant blue-shifted components and widths from 200 to 4000 km s−1. Overall, 60 ± 11 per cent appear to be active galactic nucleus (AGN) dominated, and at LLyα > 1043.3 erg s−1 and/or MUV < −21.5 virtually all LAEs are AGNs with high ionization parameters (log U = 0.6 ± 0.5) and with metallicities of ≈0.5 − 1 Z⊙. Those lacking signatures of AGNs (40 ± 11 per cent) have lower ionization parameters ( logU=−3.0+1.6−0.9 and log ξion = 25.4 ± 0.2) and are apparently metal-poor sources likely powered by young, dust-poor ‘maximal’ starbursts. Our results show that luminous LAEs at z ∼ 2–3 are a diverse population and that 2×L∗Lyα and 2×M∗UV mark a sharp transition in the nature of LAEs, from star formation dominated to AGN dominated.
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|Publisher Web site:||https://doi.org/10.1093/mnras/sty782|
|Publisher statement:||This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.|
|Date accepted:||21 March 2018|
|Date deposited:||27 June 2018|
|Date of first online publication:||24 March 2018|
|Date first made open access:||27 June 2018|
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