The nature of luminous Ly α emitters at z ~ 2–3: maximal dust-poor starbursts and highly ionizing AGN
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 (L_(Lyα) ≳ 10^(42.7) erg s^(−1); L_(Lyα) ≳ 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 × 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 (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 (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 (logU = −3.0^(+1.6)_(−0.9) and log ξ_(ion) = 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.
Additional Information
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) Accepted 2018 March 21. Received 2018 March 17; in original form 2018 February 27. We thank the anonymous reviewer for their timely and constructive comments that greatly helped us to improve the manuscript. DS acknowledges financial support from the Netherlands Organization for Scientific research (NWO) through a Veni fellowship and from Lancaster University through an Early Career Internal Grant A100679. JM acknowledges the support of a Huygens PhD fellowship from Leiden University. BD acknowledges financial support from NASA through the Astrophysics Data Analysis Program (ADAP), grant number NNX12AE20G, and the National Science Foundation, grant number 1716907. IRS acknowledges support from the ERC Advanced Grant DUSTYGAL (321334), STFC (ST/P000541/1), and a Royal Society/Wolfson Merit Award. PNB is grateful for support from STFC via grant ST/M001229/1. We thank Anne Verhamme, Kimihiko Nakajima, Ryan Trainor, Sangeeta Malhotra, Max Gronke, James Rhoads, Fang Xia An, Matthew Hayes, Takashi Kojima, Mark Dijkstra, and Anne Jaskot for many helpful and engaging discussions, particularly during the SnowCLAW Ly α workshop. We thank Bruno Ribeiro, Stephane Charlot, and Joseph Caruana for comments on the manuscript. The authors would also like to thank Ingrid Tengs, Meg Singleton, Ali Khostovan, and Sara Perez for participating in part of the observations. We also thank João Calhau, Leah Morabito, Sérgio Santos, and Aayush Saxena for their assistance with the narrow-band observations which allowed to select some of the sour ces. Based on observations obtained with the William Herschel Telescope, program: W16AN004; the Very Large Telescope, programs: 098.A-0819 & 099.A-0254; and the Keck II telescope, program: C267D. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under ESO programme IDs 294.A-5018, 294.A-5039, 092.A-0786, 093.A-0561, 097.A-0943, 098.A-0819, 099.A-0254 and 179.A-2005. The authors acknowledge the award of service time (SW2014b20) on the WHT. WHT and its service programme are operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The authors would also like to thank all the extremely helpful observatory staff that have greatly contributed towards our observations, particularly Fiona Riddick, Lilian Dominguez, Florencia Jimenez, and Ian Skillen. We have benefited greatly from the publicly available programming language PYTHON, including the NUMPY & SCIPY (Van Der Walt, Colbert & Varoquaux 2011; Jones et al. 2001), MATPLOTLIB (Hunter 2007), ASTROPY (Astropy Collaboration et al. 2013), and the TOPCAT analysis program (Taylor 2013). This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France. The samples and parent samples used for this paper are publicly available (Matthee et al. 2017b; Sobral et al. 2017b, 2018). We also make all our 1D (binned to one-third of the resolution, flux calibrated, without any slit correction) spectra public on-line with the final refereed version of this paper, together with the catalogue of luminous LAEs and electronic versions of relevant tables (see Appendix A2).Attached Files
Published - sty782.pdf
Accepted Version - 1802.10102
Supplemental Material - sty782_supp.zip
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Additional details
- Eprint ID
- 87414
- Resolver ID
- CaltechAUTHORS:20180627-144850859
- Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)
- A100679
- Lancaster University
- Leiden University
- NNX12AE20G
- NASA
- AST-1716907
- NSF
- 321334
- European Research Council (ERC)
- ST/P000541/1
- Science and Technology Facilities Council (STFC)
- Royal Society
- ST/M001229/1
- Science and Technology Facilities Council (STFC)
- Created
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2018-06-27Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field