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The CALYMHA survey: Lyα luminosity function and global escape fraction of Lyα photons at z = 2.23

Sobral, D.; Matthee, J.; Best, P.; Stroe, A.; Röttgering, H.; Oteo, I.; Smail, I.; Morabito, L.; Paulino-Afonso, A.

The CALYMHA survey: Lyα luminosity function and global escape fraction of Lyα photons at z = 2.23 Thumbnail


D. Sobral

J. Matthee

P. Best

A. Stroe

H. Röttgering

I. Oteo

A. Paulino-Afonso


We present the CAlibrating LYMan-α with Hα (CALYMHA) pilot survey and new results on Lyman α (Lyα) selected galaxies at z ∼ 2. We use a custom-built Lyα narrow-band filter at the Isaac Newton Telescope, designed to provide a matched volume coverage to the z = 2.23 Hα HiZELS survey. Here, we present the first results for the COSMOS and UDS fields. Our survey currently reaches a 3σ line flux limit of ∼4 × 10−17 erg s−1 cm−2, and a Lyα luminosity limit of ∼1042.3 erg s−1. We find 188 Lyα emitters over 7.3 × 105 Mpc3, but also find significant numbers of other line-emitting sources corresponding to He ii, C iii] and C iv emission lines. These sources are important contaminants, and we carefully remove them, unlike most previous studies. We find that the Lyα luminosity function at z = 2.23 is very well described by a Schechter function up to LLy α ≈ 1043 erg s−1 with L∗=1042.59+0.16−0.08 L∗=1042.59−0.08+0.16 erg s−1, ϕ∗=10−3.09+0.14−0.34 ϕ∗=10−3.09−0.34+0.14 Mpc−3 and α = −1.75 ± 0.25. Above LLy α ≈ 1043 erg s−1, the Lyα luminosity function becomes power-law like, driven by X-ray AGN. We find that Lyα-selected emitters have a high escape fraction of 37 ± 7 per cent, anticorrelated with Lyα luminosity and correlated with Lyα equivalent width. Lyα emitters have ubiquitous large (≈40 kpc) Lyα haloes, ∼2 times larger than their Hα extents. By directly comparing our Lyα and Hα luminosity functions, we find that the global/overall escape fraction of Lyα photons (within a 13 kpc radius) from the full population of star-forming galaxies is 5.1 ± 0.2 per cent at the peak of the star formation history. An extra 3.3 ± 0.3 per cent of Lyα photons likely still escape, but at larger radii.


Sobral, D., Matthee, J., Best, P., Stroe, A., Röttgering, H., Oteo, I., …Paulino-Afonso, A. (2017). The CALYMHA survey: Lyα luminosity function and global escape fraction of Lyα photons at z = 2.23. Monthly Notices of the Royal Astronomical Society, 466(1), 1242-1258.

Journal Article Type Article
Acceptance Date Nov 25, 2016
Online Publication Date Nov 30, 2016
Publication Date Apr 1, 2017
Deposit Date Feb 22, 2017
Publicly Available Date Mar 2, 2017
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 466
Issue 1
Pages 1242-1258
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Published Journal Article (2.5 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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