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Infrared-faint radio sources (IFRSs) are a rare class of object which arerelatively bright at radio wavelengths but very faint at infrared and opticalwavelengths. Here we present sensitive near-infrared observations of a sampleof these sources taken as part of the Spitzer Extragalactic RepresentativeVolume Survey (SERVS). Nearly all the IFRSs are undetected at a level of ~ 1\mu$Jy in these new deep observations, and even the detections are consistentwith confusion with unrelated galaxies. A stacked image implies that the medianflux density is $S_{3.6\mu m} ~ 0.2$ \mu$Jy or less, giving extreme values ofthe radio-infrared flux density ratio. Comparison of these objects with knownclasses of object suggests that the majority are probably high-redshiftradio-loud galaxies, possibly suffering from significant dust extinction.

Deep Spitzer observations of infrared-faint radio sources: high-redshift radio-loud AGN?