The nature of luminous Lyman-alpha emitters at z~2-3:maximal dust-poor starbursts and highly ionising AGN

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 Lyman-alpha emitters at z~2-3:maximal dust-poor starbursts and highly ionising AGN. Monthly Notices of the Royal Astronomical Society, 477 (2). 2817–2840. ISSN 0035-8711

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Abstract

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≳1042.7LLyα≳1042.7 erg s−1; LLyα≳L∗LyαLLyα≳LLyα∗⁠). 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+0.3−0.1β=−2.0−0.1+0.3⁠) and high Ly α escape fractions (⁠50+20−1550−15+20 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+1.6−0.9log⁡U=−3.0−0.9+1.6and 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∗Lyα2×LLyα∗ and 2×M∗UV2×MUV∗ mark a sharp transition in the nature of LAEs, from star formation dominated to AGN dominated.

Item Type:
Journal Article
Journal or Publication Title:
Monthly Notices of the Royal Astronomical Society
Additional Information:
This is a pre-copy-editing, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The definitive publisher-authenticated version David Sobral, Jorryt Matthee, Behnam Darvish, Ian Smail, Philip N Best, Lara Alegre, Huub Röttgering, Bahram Mobasher, Ana Paulino-Afonso, Andra Stroe, Iván Oteo; 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, Volume 477, Issue 2, 21 June 2018, Pages 2817–2840, https://doi.org/10.1093/mnras/sty782 is available online at: https://academic.oup.com/mnras/article/477/2/2817/4953429
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/1900/1912
Subjects:
ID Code:
124194
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Deposited On:
22 Mar 2018 16:44
Refereed?:
Yes
Published?:
Published
Last Modified:
23 Sep 2020 04:06