ULTRA STEEP SPECTRUM RADIO SOURCES IN THE LOCKMAN HOLE: SERVS IDENTIFICATIONS AND REDSHIFT DISTRIBUTION AT THE FAINTEST RADIO FLUXES
- Observatorio Astronomico de Lisboa, Faculdade de Ciencias, Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisbon (Portugal)
- UK Astronomy Technology Centre, Royal Observatory, Edinburgh EH9 3HJ (United Kingdom)
- Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Centre for Astrophysics, Science and Technology Research Institute, University of Hertfordshire, Hatfield, Herts AL10 9AB (United Kingdom)
- Leiden Observatory, Leiden University, Oort Gebouw, P.O. Box 9513, 2300 RA Leiden (Netherlands)
- CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710 (Australia)
- SUPA, Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
- Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth PO1 3FX (United Kingdom)
- Department of Astronomy, University of Padova, vicolo Osservatorio 3, 35122 Padova (Italy)
- Mullard Space Science Laboratory, UCL, Holmbury St Mary, Dorking, Surrey RH5 6NT (United Kingdom)
- Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH (United Kingdom)
Ultra steep spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z {approx}> 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]{sub 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 {approx} 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] {approx}> 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.
- OSTI ID:
- 22004477
- Journal Information:
- Astrophysical Journal, Vol. 743, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
A DEEP 1.2 mm MAP OF THE LOCKMAN HOLE NORTH FIELD
IDENTIFICATION OF A COMPLETE 160 {mu}m FLUX-LIMITED SAMPLE OF INFRARED GALAXIES IN THE ISO LOCKMAN HOLE 1 deg{sup 2} DEEP FIELDS: SOURCE PROPERTIES AND EVIDENCE FOR STRONG EVOLUTION IN THE FIR LUMINOSITY FUNCTION FOR ULIRGs