---
_id: '11523'
abstract:
- lang: eng
  text: We present the first results from the X-SHOOTER Lyman α survey at z = 2 (XLS-z2).
    XLS-z2 is a deep spectroscopic survey of 35 Lyman α emitters (LAEs) utilizing
    ≈90 h of exposure time with Very Large Telescope/X-SHOOTER and covers rest-frame
    Ly α to H α emission with R ≈ 4000. We present the sample selection, the observations,
    and the data reduction. Systemic redshifts are measured from rest-frame optical
    lines for 33/35 sources. In the stacked spectrum, our LAEs are characterized by
    an interstellar medium with little dust, a low metallicity, and a high ionization
    state. The ionizing sources are young hot stars that power strong emission lines
    in the optical and high-ionization lines in the ultraviolet (UV). The LAEs exhibit
    clumpy UV morphologies and have outflowing kinematics with blueshifted Si II absorption,
    a broad [O III] component, and a red-skewed Ly α line. Typically, 30 per cent
    of the Ly α photons escape, of which one quarter on the blue side of the systemic
    velocity. A fraction of Ly α photons escape directly at the systemic suggesting
    clear channels enabling an ≈10 per cent escape of ionizing photons, consistent
    with an inference based on Mg II. A combination of a low effective H I column
    density, a low dust content, and young starburst determines whether a star-forming
    galaxy is observed as an LAE. The first is possibly related to outflows and/or
    a fortunate viewing angle, while we find that the latter two in LAEs are typical
    for their stellar mass of 109 M⊙.
acknowledgement: "We thank the referee for constructive comments and suggestions.
  We thank Dawn Erb, Ruari Mackenzie, Ivan Oteo, Ryan Sanders, and Johannes Zabl for
  useful discussions and suggestions. It is a pleasure to thank the ESO User Support,
  in particular Giacomo Beccari, Carlo Manara, John Pritchard, Marina Rejkuba, and
  Lowell Tacconi-Garman for assistance in the preparation and execution of the observations.
  Based on observations obtained with the VLT, programs 084.A-0303, 088.A-0672, 091.A-0413,
  091.A-0546, 092.A0774, 097.A-0153, 098.A-0819, 099.A-0758, 099.A-0254, 101.B0779,
  and 102.A-0652. Based on data products from observations made with ESO Telescopes
  at the La Silla Paranal Observatory under ESO programme ID 179.A-2005 and on data
  products produced by CALET and the Cambridge Astronomy Survey Unit on behalf of
  the UltraVISTA consortium. Based on observations made with the NASA/ESA HST through
  programs 9133, 9367, 11694, and 12471, and obtained from the Hubble Legacy Archive,
  which is a collaboration between the Space Telescope Science Institute (STScI/NASA),
  the Space Telescope European Coordinating Facility (ST-ECF/ESA), and the Canadian
  Astronomy Data Centre (CADC/NRC/CSA). This work is based on observations taken by
  the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST, which is operated
  by the Association of Universities for Research in Astronomy, Inc., under NASA contract
  NAS5-26555. MG was supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51409
  and acknowledges support from HST grants\r\nHST-GO-15643.017-A, HST-AR-15039.003-A,
  and XSEDE grant TG-AST180036. GP acknowledges support from the Netherlands Research
  School for Astronomy (NOVA). RA acknowledges the support of ANID FONDECYT Regular
  Grant 1202007. We gratefully acknowledge the PYTHON programming language, its NUMPY,
  MATPLOTLIB, SCIPY, LMFIT (Jones et al. 2001; Hunter 2007; van der Walt, Colbert
  & Varoquaux 2011), PANDAS (McKinney 2010), and ASTROPY (Astropy Collaboration 2013)
  packages, and the TOPCAT analysis tool (Taylor 2013). Dedicated to the memory of
  A. C. J.Matthee (1953–2020)."
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: Jorryt J
  full_name: Matthee, Jorryt J
  id: 7439a258-f3c0-11ec-9501-9df22fe06720
  last_name: Matthee
  orcid: 0000-0003-2871-127X
- first_name: David
  full_name: Sobral, David
  last_name: Sobral
- first_name: Matthew
  full_name: Hayes, Matthew
  last_name: Hayes
- first_name: Gabriele
  full_name: Pezzulli, Gabriele
  last_name: Pezzulli
- first_name: Max
  full_name: Gronke, Max
  last_name: Gronke
- first_name: Daniel
  full_name: Schaerer, Daniel
  last_name: Schaerer
- first_name: Rohan P
  full_name: Naidu, Rohan P
  last_name: Naidu
- first_name: Huub
  full_name: Röttgering, Huub
  last_name: Röttgering
- first_name: João
  full_name: Calhau, João
  last_name: Calhau
- first_name: Ana
  full_name: Paulino-Afonso, Ana
  last_name: Paulino-Afonso
- first_name: Sérgio
  full_name: Santos, Sérgio
  last_name: Santos
- first_name: Ricardo
  full_name: Amorín, Ricardo
  last_name: Amorín
citation:
  ama: 'Matthee JJ, Sobral D, Hayes M, et al. The X-SHOOTER Lyman α survey at z =
    2 (XLS-z2) I: What makes a galaxy a Lyman α emitter? <i>Monthly Notices of the
    Royal Astronomical Society</i>. 2021;505(1):1382-1412. doi:<a href="https://doi.org/10.1093/mnras/stab1304">10.1093/mnras/stab1304</a>'
  apa: 'Matthee, J. J., Sobral, D., Hayes, M., Pezzulli, G., Gronke, M., Schaerer,
    D., … Amorín, R. (2021). The X-SHOOTER Lyman α survey at z = 2 (XLS-z2) I: What
    makes a galaxy a Lyman α emitter? <i>Monthly Notices of the Royal Astronomical
    Society</i>. Oxford University Press. <a href="https://doi.org/10.1093/mnras/stab1304">https://doi.org/10.1093/mnras/stab1304</a>'
  chicago: 'Matthee, Jorryt J, David Sobral, Matthew Hayes, Gabriele Pezzulli, Max
    Gronke, Daniel Schaerer, Rohan P Naidu, et al. “The X-SHOOTER Lyman α Survey at
    z = 2 (XLS-Z2) I: What Makes a Galaxy a Lyman α Emitter?” <i>Monthly Notices of
    the Royal Astronomical Society</i>. Oxford University Press, 2021. <a href="https://doi.org/10.1093/mnras/stab1304">https://doi.org/10.1093/mnras/stab1304</a>.'
  ieee: 'J. J. Matthee <i>et al.</i>, “The X-SHOOTER Lyman α survey at z = 2 (XLS-z2)
    I: What makes a galaxy a Lyman α emitter?,” <i>Monthly Notices of the Royal Astronomical
    Society</i>, vol. 505, no. 1. Oxford University Press, pp. 1382–1412, 2021.'
  ista: 'Matthee JJ, Sobral D, Hayes M, Pezzulli G, Gronke M, Schaerer D, Naidu RP,
    Röttgering H, Calhau J, Paulino-Afonso A, Santos S, Amorín R. 2021. The X-SHOOTER
    Lyman α survey at z = 2 (XLS-z2) I: What makes a galaxy a Lyman α emitter? Monthly
    Notices of the Royal Astronomical Society. 505(1), 1382–1412.'
  mla: 'Matthee, Jorryt J., et al. “The X-SHOOTER Lyman α Survey at z = 2 (XLS-Z2)
    I: What Makes a Galaxy a Lyman α Emitter?” <i>Monthly Notices of the Royal Astronomical
    Society</i>, vol. 505, no. 1, Oxford University Press, 2021, pp. 1382–412, doi:<a
    href="https://doi.org/10.1093/mnras/stab1304">10.1093/mnras/stab1304</a>.'
  short: J.J. Matthee, D. Sobral, M. Hayes, G. Pezzulli, M. Gronke, D. Schaerer, R.P.
    Naidu, H. Röttgering, J. Calhau, A. Paulino-Afonso, S. Santos, R. Amorín, Monthly
    Notices of the Royal Astronomical Society 505 (2021) 1382–1412.
date_created: 2022-07-07T09:33:39Z
date_published: 2021-07-01T00:00:00Z
date_updated: 2022-08-18T10:49:00Z
day: '01'
doi: 10.1093/mnras/stab1304
extern: '1'
external_id:
  arxiv:
  - '2102.07779'
intvolume: '       505'
issue: '1'
keyword:
- Space and Planetary Science
- Astronomy and Astrophysics
- 'galaxies: formation'
- 'galaxies: ISM'
- 'galaxies: starburst'
- dark ages
- reionization
- first stars
language:
- iso: eng
main_file_link:
- open_access: '1'
  url: https://arxiv.org/abs/2102.07779
month: '07'
oa: 1
oa_version: Preprint
page: 1382-1412
publication: Monthly Notices of the Royal Astronomical Society
publication_identifier:
  eissn:
  - 1365-2966
  issn:
  - 0035-8711
publication_status: published
publisher: Oxford University Press
quality_controlled: '1'
scopus_import: '1'
status: public
title: 'The X-SHOOTER Lyman α survey at z = 2 (XLS-z2) I: What makes a galaxy a Lyman
  α emitter?'
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 505
year: '2021'
...
---
_id: '11557'
abstract:
- lang: eng
  text: 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.
acknowledgement: '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 Joao Calhau, Leah Morabito, Sergio 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.'
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: David
  full_name: Sobral, David
  last_name: Sobral
- first_name: Jorryt J
  full_name: Matthee, Jorryt J
  id: 7439a258-f3c0-11ec-9501-9df22fe06720
  last_name: Matthee
  orcid: 0000-0003-2871-127X
- first_name: Behnam
  full_name: Darvish, Behnam
  last_name: Darvish
- first_name: Ian
  full_name: Smail, Ian
  last_name: Smail
- first_name: Philip N
  full_name: Best, Philip N
  last_name: Best
- first_name: Lara
  full_name: Alegre, Lara
  last_name: Alegre
- first_name: Huub
  full_name: Röttgering, Huub
  last_name: Röttgering
- first_name: Bahram
  full_name: Mobasher, Bahram
  last_name: Mobasher
- first_name: Ana
  full_name: Paulino-Afonso, Ana
  last_name: Paulino-Afonso
- first_name: Andra
  full_name: Stroe, Andra
  last_name: Stroe
- first_name: Iván
  full_name: Oteo, Iván
  last_name: Oteo
citation:
  ama: 'Sobral D, Matthee JJ, Darvish B, et al. The nature of luminous Ly α emitters
    at z ∼ 2–3: Maximal dust-poor starbursts and highly ionizing AGN. <i>Monthly Notices
    of the Royal Astronomical Society</i>. 2018;477(2):2817-2840. doi:<a href="https://doi.org/10.1093/mnras/sty782">10.1093/mnras/sty782</a>'
  apa: 'Sobral, D., Matthee, J. 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. <i>Monthly Notices of the Royal Astronomical
    Society</i>. Oxford University Press. <a href="https://doi.org/10.1093/mnras/sty782">https://doi.org/10.1093/mnras/sty782</a>'
  chicago: 'Sobral, David, Jorryt J Matthee, Behnam Darvish, Ian Smail, Philip N Best,
    Lara Alegre, Huub Röttgering, et al. “The Nature of Luminous Ly α Emitters at
    z ∼ 2–3: Maximal Dust-Poor Starbursts and Highly Ionizing AGN.” <i>Monthly Notices
    of the Royal Astronomical Society</i>. Oxford University Press, 2018. <a href="https://doi.org/10.1093/mnras/sty782">https://doi.org/10.1093/mnras/sty782</a>.'
  ieee: 'D. Sobral <i>et al.</i>, “The nature of luminous Ly α emitters at z ∼ 2–3:
    Maximal dust-poor starbursts and highly ionizing AGN,” <i>Monthly Notices of the
    Royal Astronomical Society</i>, vol. 477, no. 2. Oxford University Press, pp.
    2817–2840, 2018.'
  ista: 'Sobral D, Matthee JJ, Darvish B, Smail I, Best PN, Alegre L, Röttgering H,
    Mobasher B, Paulino-Afonso A, Stroe A, 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.'
  mla: 'Sobral, David, et al. “The Nature of Luminous Ly α Emitters at z ∼ 2–3: Maximal
    Dust-Poor Starbursts and Highly Ionizing AGN.” <i>Monthly Notices of the Royal
    Astronomical Society</i>, vol. 477, no. 2, Oxford University Press, 2018, pp.
    2817–40, doi:<a href="https://doi.org/10.1093/mnras/sty782">10.1093/mnras/sty782</a>.'
  short: D. Sobral, J.J. Matthee, B. Darvish, I. Smail, P.N. Best, L. Alegre, H. Röttgering,
    B. Mobasher, A. Paulino-Afonso, A. Stroe, I. Oteo, Monthly Notices of the Royal
    Astronomical Society 477 (2018) 2817–2840.
date_created: 2022-07-12T07:18:02Z
date_published: 2018-06-01T00:00:00Z
date_updated: 2022-08-19T07:01:08Z
day: '01'
doi: 10.1093/mnras/sty782
extern: '1'
external_id:
  arxiv:
  - '1802.10102'
intvolume: '       477'
issue: '2'
keyword:
- Space and Planetary Science
- Astronomy and Astrophysics
- 'galaxies: active'
- 'galaxies: evolution'
- 'galaxies: high-redshift'
- 'galaxies: ISM'
- 'galaxies: starburst'
- 'cosmology: observations'
language:
- iso: eng
main_file_link:
- open_access: '1'
  url: https://arxiv.org/abs/1802.10102
month: '06'
oa: 1
oa_version: Preprint
page: 2817-2840
publication: Monthly Notices of the Royal Astronomical Society
publication_identifier:
  eissn:
  - 1365-2966
  issn:
  - 0035-8711
publication_status: published
publisher: Oxford University Press
quality_controlled: '1'
scopus_import: '1'
status: public
title: 'The nature of luminous Ly α emitters at z ∼ 2–3: Maximal dust-poor starbursts
  and highly ionizing AGN'
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 477
year: '2018'
...