TY - JOUR
T1 - Ultra steep spectrum radio sources in the Lockman Hole
T2 - SERVS identifications and redshift distribution at the faintest radio fluxes
AU - Afonso, J.
AU - Bizzocchi, L.
AU - Ibar, E.
AU - Grossi, M.
AU - Simpson, C.
AU - Chapman, S.
AU - Jarvis, M.J.
AU - Rottgering, H.
AU - Norris, R. P.
AU - Dunlop, J.
AU - Ivison, R. J.
AU - Messias, H.
AU - Pforr, J.
AU - Vaccari, M.
AU - Seymour, N.
AU - Best, P.
AU - Gonzalez-Solares, E.
AU - Farrah, D.
AU - Fernandes, C. A. C.
AU - Huang, J. -S.
AU - Lacy, M.
AU - Maraston, C.
AU - Marchetti, L.
AU - Mauduit, J. -C.
AU - Oliver, S.
AU - Rigopoulou, D.
AU - Stanford, S. A.
AU - Surace, J.
AU - Zeimann, G.
PY - 2011/12/20
Y1 - 2011/12/20
N2 - Ultra steep spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z greater than or similar to 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 a first detailed analysis of the nature of the faintest USS sources is presented. By using Giant Metrewave Radio Telescope and Very Large Array radio observations of the Lockman Hole at 610 MHz and 1.4 GHz, a sample of 58 USS sources, with 610 MHz integrated fluxes above 100 mu Jy, is assembled. Deep infrared data at 3.6 and 4.5 mu m from the Spitzer Extragalactic Representative Volume Survey (SERVS) are used to reliably identify counterparts for 48 (83%) of these sources, showing an average total magnitude of [3.6](AB) = 19.8 mag. 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 similar to 0.6 and tailing off at high redshifts. The remaining 25 USS sources, with no redshift estimate, include the faintest [3.6] magnitudes, with 10 sources undetected at 3.6 and 4.5 mu m (typically [3.6] greater than or similar to 22-23 mag from local measurements), which suggests the likely existence of higher redshifts among the sub-mJy USS population. The comparison with the Square Kilometre Array Design Studies Simulated Skies models indicates that Fanaroff-Riley type I radio sources and radio-quiet active galactic nuclei may constitute the bulk of the faintest USS population, and raises the possibility that the high efficiency of the USS technique for the selection of high-redshift sources remains even at the sub-mJy level.
AB - Ultra steep spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z greater than or similar to 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 a first detailed analysis of the nature of the faintest USS sources is presented. By using Giant Metrewave Radio Telescope and Very Large Array radio observations of the Lockman Hole at 610 MHz and 1.4 GHz, a sample of 58 USS sources, with 610 MHz integrated fluxes above 100 mu Jy, is assembled. Deep infrared data at 3.6 and 4.5 mu m from the Spitzer Extragalactic Representative Volume Survey (SERVS) are used to reliably identify counterparts for 48 (83%) of these sources, showing an average total magnitude of [3.6](AB) = 19.8 mag. 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 similar to 0.6 and tailing off at high redshifts. The remaining 25 USS sources, with no redshift estimate, include the faintest [3.6] magnitudes, with 10 sources undetected at 3.6 and 4.5 mu m (typically [3.6] greater than or similar to 22-23 mag from local measurements), which suggests the likely existence of higher redshifts among the sub-mJy USS population. The comparison with the Square Kilometre Array Design Studies Simulated Skies models indicates that Fanaroff-Riley type I radio sources and radio-quiet active galactic nuclei may constitute the bulk of the faintest USS population, and raises the possibility that the high efficiency of the USS technique for the selection of high-redshift sources remains even at the sub-mJy level.
KW - galaxies: active
KW - galaxies: evolution
KW - galaxies: high-redshift
KW - radio continuum: galaxies
KW - surveys
KW - ACTIVE GALACTIC NUCLEI
KW - K-Z RELATION
KW - ROSAT DEEP SURVEY
KW - X-RAY SOURCES
KW - SOUTHERN-HEMISPHERE
KW - STAR-FORMATION
KW - FIND OBJECTS
KW - OPTICAL IDENTIFICATIONS
KW - SUBMILLIMETER GALAXIES
KW - PHOTOMETRIC REDSHIFTS
U2 - 10.1088/0004-637X/743/2/122
DO - 10.1088/0004-637X/743/2/122
M3 - Article
SN - 0004-637X
VL - 743
JO - The Astrophysical Journal
JF - The Astrophysical Journal
IS - 2
M1 - 122
ER -