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Mean Hα+[N II]+[S II] EW inferred for star-forming galaxies at z ∼ 5.1–5.4 using high-quality Spitzer/IRAC photometry

Rasappu, N. and Smit, R. and Labbé, I. and Bouwens, R. J. and Stark, D. P. and Ellis, R. S. and Oesch, P. A. (2016) Mean Hα+[N II]+[S II] EW inferred for star-forming galaxies at z ∼ 5.1–5.4 using high-quality Spitzer/IRAC photometry. Monthly Notices of the Royal Astronomical Society, 461 (4). pp. 3886-3895. ISSN 0035-8711.

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Recent Spitzer/InfraRed Array Camera (IRAC) photometric observations have revealed that rest-frame optical emission lines contribute significantly to the broad-band fluxes of high-redshift galaxies. Specifically, in the narrow redshift range z ∼ 5.1–5.4 the [3.6]–[4.5] colour is expected to be very red, due to contamination of the 4.5 μm band by the dominant Hα line, while the 3.6 μm filter is free of nebular emission lines. We take advantage of new reductions of deep Spitzer/IRAC imaging over the Great Observatories Origins Deep Survey-North+South fields (Labbé et al. 2015) to obtain a clean measurement of the mean Hα equivalent width (EW) from the [3.6]–[4.5] colour in the redshift range z = 5.1–5.4. The selected sources either have measured spectroscopic redshifts (13 sources) or lie very confidently in the redshift range z = 5.1–5.4 based on the photometric redshift likelihood intervals (11 sources). Our z_(phot) = 5.1–5.4 sample and z_(spec) = 5.10–5.40 spectroscopic sample have a mean [3.6]–[4.5] colour of 0.31 ± 0.05 and 0.35 ± 0.07 mag, implying a rest-frame EW (Hα+[N II]+[S II]) of 665 ± 53 and 707 ± 74 Å, respectively, for sources in these samples. These values are consistent albeit slightly higher than derived by Stark et al. at z ∼ 4, suggesting an evolution to higher values of the Hα+[N ii]+[S II] EW at z > 2. Using the 3.6 μm band, which is free of emission line contamination, we perform robust spectral energy distribution fitting and find a median specific star formation rate of sSFR = 17^(+2)_(−5) Gyr−1, 7^(+1)_(−2)× higher than at z ∼ 2. We find no strong correlation (<2σ) between the Hα+[N II]+[S II] EW and the stellar mass of sources. Before the advent of JWST, improvements in these results will come through an expansion of current spectroscopic samples and deeper Spitzer/IRAC measurements.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Smit, R.0000-0001-8034-7802
Labbé, I.0000-0002-2057-5376
Bouwens, R. J.0000-0002-4989-2471
Ellis, R. S.0000-0001-7782-7071
Oesch, P. A.0000-0001-5851-6649
Additional Information:© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 June 17. Received 2016 June 13. In original form 2015 August 18. First published online June 26, 2016. We acknowledge the support of NASA grant NAG5-7697, NASA/STScI grant HST-GO-11563, and an NWO vrij-competitie grant 600.065.140.11N211. RS acknowledges the support of the Leverhulme Trust. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Leverhulme TrustUNSPECIFIED
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)600.065.140.11N211
Subject Keywords:galaxies: evolution galaxies: formation galaxies: high-redshift
Issue or Number:4
Record Number:CaltechAUTHORS:20161017-093552844
Persistent URL:
Official Citation:N. Rasappu, R. Smit, I. Labbé, R. J. Bouwens, D. P. Stark, R. S. Ellis, and P. A. Oesch Mean Hα+[N ii]+[S ii] EW inferred for star-forming galaxies at z ∼ 5.1–5.4 using high-quality Spitzer/IRAC photometry MNRAS (October 01, 2016) Vol. 461 3886-3895 doi:10.1093/mnras/stw1484 first published online June 26, 2016
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71148
Deposited By: Ruth Sustaita
Deposited On:17 Oct 2016 16:55
Last Modified:03 Oct 2019 16:04

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