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Deep Spitzer Observations of Infrared-faint Radio Sources: High-redshift Radio-loud Active Galactic Nuclei?

R. P. Norris, J. Afonso, A. Cava, D. Farrah, M. Huynh, R. J. Ivison, M. Jarvis, M. Lacy, M. Y. Mao, C. Maraston, J.-C. Mauduit, E. Middelberg, S. Oliver, N. Seymour, J. A. Surace

Abstract
Infrared-faint radio sources(IFRSs) are a rare class of objects which are relatively bright at radio wavelengths but very faint at infrared and optical wavelengths. Here we present sensitive near-infrared observations of a sample of these sources taken as part of the Spitzer Extragalactic Representative Volume Survey. Nearly all the IFRSs are undetected at a level of ~1 muJy in these new deep observations, and even the detections are consistent with confusion with unrelated galaxies. A stacked image implies that the median flux density is S 3.6 mum ~ 0.2 muJy or less, giving extreme values of the radio-infrared flux density ratio. Comparison of these objects with known classes of object suggests that the majority are probably high-redshift radio-loud galaxies, possibly suffering from significant dust extinction.

Keywords
galaxies: evolution - galaxies: formation - galaxies: starburst

The Astrophysical Journal
Volume 736, Number 1, Page 55_1
2011 July

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Fundação para a Ciência e a Tecnologia
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