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The nature of luminous Ly α emitters at z ∼ 2–3: maximal dust-poor starbursts and highly ionizing AGN

Sobral, David; Matthee, Jorryt; Darvish, Behnam; Smail, Ian; Best, Philip N.; Alegre, Lara; Röttgering, Huub; Mobasher, Bahram; Paulino-Afonso, Ana; Stroe, Andra; Oteo, Iván

The nature of luminous Ly α emitters at z ∼ 2–3: maximal dust-poor starbursts and highly ionizing AGN Thumbnail


Authors

David Sobral

Jorryt Matthee

Behnam Darvish

Philip N. Best

Lara Alegre

Huub Röttgering

Bahram Mobasher

Ana Paulino-Afonso

Andra Stroe

Iván Oteo



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≳1042.7  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.

Citation

Sobral, D., Matthee, J., Darvish, B., Smail, I., Best, P. N., Alegre, L., …Oteo, I. (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), 2817-2840. https://doi.org/10.1093/mnras/sty782

Journal Article Type Article
Acceptance Date Mar 21, 2018
Online Publication Date Mar 24, 2018
Publication Date Jun 21, 2018
Deposit Date Jun 27, 2018
Publicly Available Date Mar 29, 2024
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 477
Issue 2
Pages 2817-2840
DOI https://doi.org/10.1093/mnras/sty782

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Copyright 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.





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