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Far-infrared constraints on the contamination by dust-obscured galaxies of high-z dropout searches

Boone, F. and Blain, A. W. (2011) Far-infrared constraints on the contamination by dust-obscured galaxies of high-z dropout searches. Astronomy and Astrophysics, 534 . Art. No. A124. ISSN 0004-6361.

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The spectral energy distributions (SED) of dusty galaxies at intermediate redshift may look similar to very high-redshift galaxies in the optical/near infrared (NIR) domain. This can lead to the contamination of high-redshift galaxy searches based on broad-band optical/NIR photometry by lower redshift dusty galaxies because both kind of galaxies cannot be distinguished. The contamination rate could be as high as 50%. This work shows how the far-infrared (FIR) domain can help to recognize likely low-z interlopers in an optical/NIR search for high-z galaxies. We analyze the FIR SEDs of two galaxies that are proposed to be very high-redshift (z > 7) dropout candidates based on deep Hawk-I/VLT observations. The FIR SEDs are sampled with PACS/Herschel at 100 and 160 μm, with SPIRE/Herschel at 250, 350 and 500 μm and with LABOCA/APEX at 870 μm. We find that redshifts > 7 would imply extreme FIR SEDs (with dust temperatures >100 K and FIR luminosities >10^(13) L_⊙). At z ~ 2, instead, the SEDs of both sources would be compatible with those of typical ultra luminous infrared galaxies or submillimeter galaxies. Considering all available data for these sources from visible to FIR we re-estimate the redshifts and find z ~ 1.6–2.5. Owing to the strong spectral breaks observed in these galaxies, standard templates from the literature fail to reproduce the visible-to-near-IR part of the SEDs even when additional extinction is included. These sources strongly resemble dust-obscured galaxies selected in Spitzer observations with extreme visible-to-FIR colors, and the galaxy GN10 at z = 4. Galaxies with similar SEDs could contaminate other high-redshift surveys.

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Additional Information:© 2011 ESO. Received: 25 May 2011. Accepted: 11 August 2011. Published online 19 October 2011. We are grateful to the referee for constructive comments and suggestions that helped to improve the paper. We thank the APEX staff for their aid in carrying out the observations. APEX is operated by the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. This work received support from the french Agence Nationale de la Recherche under the reference ANR-09-BLAN-0234. The work of D.S. and M.Z. is supported by the Swiss National Science Foundation. Support from ISSI (International Space Science Institute) in Bern for an International Team is gratefully acknowledged. I.R.S., R.J.I., and A.W.B. acknowledge support from STFC.
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Agence Nationale de la RechercheANR-09-BLAN-0234-01
Swiss National Science FoundationUNSPECIFIED
International Space Science Institute (ISSI)UNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
Subject Keywords:galaxies: distances and redshifts; dust, extinction; gravitational lensing: weak; galaxies: high-redshift
Record Number:CaltechAUTHORS:20111128-110055259
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Official Citation:Far-infrared constraints on the contamination by dust-obscured galaxies of high-z dropout searches F. Boone, D. Schaerer, R. Pelló, D. Lutz, A. Weiss, E. Egami, I. Smail, M. Rex, T. Rawle, R. Ivison, N. Laporte, A. Beelen, F. Combes, A. W. Blain, J. Richard, J.-P. Kneib, M. Zamojski, M. Dessauges-Zavadsky, B. Altieri, P. van der Werf, M. Swinbank, P. G. Pérez-González, B. Clement, R. Nordon, B. Magnelli and K. M. Menten A&A 534 A124 (2011)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:27972
Deposited By: Ruth Sustaita
Deposited On:28 Nov 2011 19:21
Last Modified:03 Oct 2019 03:28

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