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Empirical Hα emitter count predictions for dark energy surveys

Geach, J.E.; Cimatti, A.; Percival, W.; Wang, Y.; Guzzo, L.; Zamorani, G.; Rosati, P.; Pozzetti, L.; Orsi, A.; Baugh, C.M.; Lacey, C.G.; Garilli, B.; Franzetti, P.; Walsh, J.R.; Kümmel, M.

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J.E. Geach

A. Cimatti

W. Percival

Y. Wang

L. Guzzo

G. Zamorani

P. Rosati

L. Pozzetti

A. Orsi

B. Garilli

P. Franzetti

J.R. Walsh

M. Kümmel


Future galaxy redshift surveys aim to measure cosmological quantities from the galaxy power spectrum. A prime example is the detection of baryonic acoustic oscillations, providing a standard ruler to measure the dark energy equation of state, w(z), to high precision. The strongest practical limitation for these experiments is how quickly accurate redshifts can be measured for sufficient galaxies to map the large-scale structure. A promising strategy is to target emission-line (i.e. star-forming) galaxies at high redshift (z∼ 0.5–2); not only is the space density of this population increasing out to z∼ 2, but also emission lines provide an efficient method of redshift determination. Motivated by the prospect of future dark energy surveys targeting Hα emitters at near-infrared wavelengths (i.e. z > 0.5), we use the latest empirical data to model the evolution of the Hα luminosity function out to z∼ 2 and thus provide predictions for the abundance of Hα emitters for practical limiting fluxes. We caution that the estimates presented in this work must be tempered by an efficiency factor, ε, giving the redshift success rate from these potential targets. For a range of practical efficiencies and limiting fluxes, we provide an estimate of Graphic, where Graphic is the 3D galaxy number density and P0.2 is the galaxy power spectrum evaluated at k= 0.2 h Mpc−1. Ideal surveys must provide Graphic in order to balance shot-noise and cosmic variance errors. We show that a realistic emission-line survey (ε= 0.5) could achieve Graphic out to z∼ 1.5 with a limiting flux of 10−16 erg s−1 cm−2. If the limiting flux is a factor of 5 brighter, then this goal can only be achieved out to z∼ 0.5, highlighting the importance of survey depth and efficiency in cosmological redshift surveys.


Geach, J., Cimatti, A., Percival, W., Wang, Y., Guzzo, L., Zamorani, G., …Kümmel, M. (2010). Empirical Hα emitter count predictions for dark energy surveys. Monthly Notices of the Royal Astronomical Society, 402(2), 1330-1338.

Journal Article Type Article
Publication Date Feb 21, 2010
Deposit Date Jan 31, 2012
Publicly Available Date Jan 29, 2015
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 402
Issue 2
Pages 1330-1338
Keywords Galaxies: evolution, Galaxies: high-redshift, Cosmology: observations, Large-scale structure of Universe.


Published Journal Article (721 Kb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2010 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved.

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