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Published May 20, 2014 | Published + Submitted
Journal Article Open

Constraining the Lyα Escape Fraction with Far-infrared Observations of Lyα Emitters


We study the far-infrared properties of 498 Lyα emitters (LAEs) at z = 2.8, 3.1, and 4.5 in the Extended Chandra Deep Field-South, using 250, 350, and 500 μm data from the Herschel Multi-tiered Extragalactic Survey and 870 μm data from the LABOCA ECDFS Submillimeter Survey. None of the 126, 280, or 92 LAEs at z = 2.8, 3.1, and 4.5, respectively, are individually detected in the far-infrared data. We use stacking to probe the average emission to deeper flux limits, reaching 1σ depths of ~0.1 to 0.4 mJy. The LAEs are also undetected at ≥3σ in the stacks, although a 2.5σ signal is observed at 870 μm for the z = 2.8 sources. We consider a wide range of far-infrared spectral energy distributions (SEDs), including an M82 and an Sd galaxy template, to determine upper limits on the far-infrared luminosities and far-infrared-derived star formation rates of the LAEs. These star formation rates are then combined with those inferred from the Lyα and UV emission to determine lower limits on the LAEs' Lyα escape fraction (f_(esc)(Lyα)). For the Sd SED template, the inferred LAEs f_(esc)(Lyα) are ≳30% (1σ) at z = 2.8, 3.1, and 4.5, which are all significantly higher than the global f_(esc)(Lyα) at these redshifts. Thus, if the LAEs f_(esc)(Lyα) follows the global evolution, then they have warmer far-infrared SEDs than the Sd galaxy template. The average and M82 SEDs produce lower limits on the LAE f_(esc)(Lyα) of ~10%-20% (1σ), all of which are slightly higher than the global evolution of f_(esc)(Lyα), but consistent with it at the 2σ-3σ level.

Additional Information

© 2014 American Astronomical Society. Received 2013 December 16; accepted 2014 March 18; published 2014 April 29. We thank Ian Smail and Fabian Walter for helpful discussions and feedback on this manuscript. J.L.W., A.C., and D.R. thank the Aspen Center for Physics for hospitality during the conception, writing, and editing of this paper. This work is supported in part by the NSF under Grant Numbers PHY-1066293 and AST-1055919. S.M. and J.R. thank the DARK Cosmology Centre and Nordea Fonden in Copenhagen, Denmark, for hospitality during the course of this work. The Dark Cosmology Centre is funded by the Danish National Research Foundation. We acknowledge support from the Science and Technology Facilities Council (grant number ST/I000976/1). Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under programmes 078.F-9028(A), 079.F-9500(A), 080.A-3023(A), and 081.F-9500(A). This research has made use of data from the HerMES project (http://hermes.sussex.ac.uk). HerMES is a Herschel Key Programme utilizing Guaranteed Time from the SPIRE instrument team, ESAC scientists, and a mission scientist. HerMES is described in Oliver et al. (2012). The data presented in this paper will be released through the HerMES Database in Marseille, HeDaM (http://hedam.oamp.fr/HerMES). SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including: Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). Facilities: APEX (LABOCA), Herschel (SPIRE)

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