Ultra steep spectrum radio sources in the Lockman Hole: SERVS identifications and redshift distribution at the faintest radio fluxes
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Ultra Steep Spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z > 2). Typically restricted to large-sky surveys and relatively bright radio flux densities, it has gradually become possible to extend the USS search to sub-mJy levels, thanks to the recent appearance of sensitive low-frequency radio facilities. Here we present a first detailed analysis of the nature of the faintest USS sources. By using GMRT and VLA radio observations of the Lockman Hole (LH) at 610MHz and 1.4GHz, a sample of 58 micro-Jansky USS sources is assembled. Deep infrared data at 3.6 and 4.5µm from the Spitzer Extragalactic Representative Volume Survey (SERVS) is used to reliably identify counterparts for 48 (83%) of these sources, showing an average magnitude of [3.6]=19.7 mag(AB). Spectroscopic redshifts for 14 USS sources, together with photometric redshift estimates, improved by the use of the deep SERVS data, for a further 19 objects, show redshifts ranging from z =0.1 to z=2.8, peaking at z~0.6 and tailing off at high redshifts.
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Ultra steep spectrum radio sources in the lockman hole: Servs identifications and redshift distribution at the faintest radio fluXESAfonso, J.; Bizzocchi, L.; Ibar, E.; Grossi, M.; Simpson, C.; Chapman, S.; Jarvis, M.; Rottgering, H.; Norris, R.; Dunlop, J.; Ivison, R.; Messias, H.; Pforr, J.; Vaccari, M.; Seymour, Nick; Best, P.; Gonzlez-Solares, E.; Farrah, D.; Fernandes, C.; Huang, J.; Lacy, M.; Maraston, C.; Marchetti, L.; Mauduit, J.; Oliver, S.; Rigopoulou, D.; Stanford, S.; Surace, J.; Zeimann, G. (2011)Ultra steep spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z ~>2). Typically restricted to large-sky surveys and relatively bright radio flux densities, it has ...
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