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

Sobral, D. and Matthee, J. and Best, P. and Stroe, A. and Röttgering, H. and Oteo, I. and Smail, I. and Morabito, L. and 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). pp. 1242-1258.

Abstract

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.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1093/mnras/stw3090
Publisher 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.
Date accepted:25 November 2016
Date deposited:02 March 2017
Date of first online publication:30 November 2016
Date first made open access:02 March 2017

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