The nature of luminous Ly α emitters at z ∼ 2–3: maximal dust-poor starbursts and highly ionizing AGN. Issue 2 (24th March 2018)

• Record Type: Journal Article
• Authors: Sobral, David; Matthee, Jorryt; Darvish, Behnam; Smail, Ian; Best, Philip N; Alegre, Lara; Röttgering, Huub; Mobasher, Bahram; Paulino-Afonso, Ana; Stroe, Andra; Oteo, Iván
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 477:Issue 2(2018)
• Page Start: 2817
• Page End: 2840
• Publication Date: 2018-03-24
• Subjects: galaxies: active -- galaxies: evolution -- galaxies: high-redshift -- galaxies: ISM -- galaxies: starburst -- cosmology: observations; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty782
• Languages: English
• ISSNs: 0035-8711

Abstract

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 ($\rm {\it L}_{\rm Ly\alpha } \gtrsim 10^{42.7}$ erg s −1 ; $L_{\rm Ly\alpha }\gtrsim L^*_{\rm Ly\alpha }$ ). 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 × 10 6 Mpc 3 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 ($\beta =-2.0^{+0.3}_{-0.1}$ ) and high Ly α escape fractions ($50^{+20}_{-15}$ per cent) and span five orders of magnitude in UV luminosity ( M UV ≈ −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 L Lyα > 10 43.3 erg s −1 and/or M UV < −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 ($\log U=-3.0^{+1.6}_{-0.9}$ 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 $2\times \, L^*_{\rm Ly\alpha }$ and $2\times \, M_{\rm UV}^*$ mark a sharp transition in the nature of LAEs, from star formation dominated to AGN dominated.