J/A+A/569/A52ivo://CDS.VizieR/J/A+A/569/A52doi:10.26093/cds/vizier.35690052CDSSingh V.Beelen A.Wadadekar Y.Sirothia S.Ishwara-Chandra C.H.,Basu A.Omont A.McAlpine K.Ivison R.J.Oliver S.Farrah D.Lacy M.2015-01-02T13:38:17Z2014-12-17T11:50:44ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsurveysradio-galaxiesredshiftedUltra steep spectrum (USS) radio sources are one of the efficient tracers of powerful high-z radio galaxies (HzRGs). In contrast to searches for powerful HzRGs from radio surveys of moderate depths, fainter USS samples derived from deeper radio surveys can be useful in finding HzRGs at even higher redshifts and in unveiling a population of obscured weaker radio-loud AGN at moderate redshifts. Using our 325MHz GMRT observations (5{sigma}~800{mu}Jy) and 1.4GHz VLA observations (5{sigma}~80-100{mu}Jy) available in two subfields (VLA-VIMOS VLT Deep Survey (VLA-VVDS) and Subaru X-ray Deep Field (SXDF)) of the XMM-LSS field, we derive a large sample of 160 faint USS radio sources and characterize their nature. The optical and IR counterparts of our USS sample sources are searched using existing deep surveys, at respective wavelengths. We attempt to unveil the nature of our faint USS sources using diagnostic techniques based on mid-IR colors, flux ratios of radio to mid-IR, and radio luminosities. Redshift estimates are available for 86/116 (~74%) USS sources in the VLA-VVDS field and for 39/44 (~87%) USS sources in the SXDF fields with median values (z_median_)~1.18 and ~1.57, respectively, which are higher than estimates for non-USS radio sources (z_median non-USS_ ~0.99 and ~0.96), in the two subfields. The MIR color-color diagnostic and radio luminosities are consistent with most of our USS sample sources at higher redshifts (z>0.5) being AGN. The flux ratio of radio to mid-IR (S_1.4GHz_/S_3.6{mu}m_) versus redshift diagnostic plot suggests that more than half of our USS sample sources distributed over z~0.5 to 3.8 are likely to be hosted in obscured environments. A significant fraction (~26% in the VLA-VVDS and ~13% in the SXDF) of our USS sources without redshift estimates mostly remain unidentified in the existing optical, IR surveys, and exhibit high radio to mid-IR flux ratio limits similar to HzRGs, and so, can be considered as potential HzRG candidates. Our study shows that the criterion of ultra steep spectral index remains a reasonably efficient method to select high-z sources even at sub-mJy flux densities. In addition to powerful HzRG candidates, our faint USS sample also contains populations of weaker radio-loud AGNs potentially hosted in obscured environments.2014A&A...569A..52Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/569/A52CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toIII/334 : VIDEO: VISTA Deep Extragalactic Observations (Jarvis+, 2013)J/A+A/403/857 : VLA-VIRMOS Deep Field (Bondi+, 2003)J/MNRAS/372/741 : SXDF 100{mu}Jy catalogue (Simpson+, 2006)J/MNRAS/421/3060 : Subaru/XMM Deep Field radio imaging. III. (Simpson+, 2012)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/569/A52https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/569/A52http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/569/A52https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/569/A52https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/569/A52http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/569/A52GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/569/A52/tablea1 (325MHz GMRT observations of the Ultra Steep Spectrum (USS) sample)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/569/A52/tablea1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/569/A52/tablea1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/569/A52/tablea1?GETtext/xml+votable180.050000true34.04875-5.01487220.0055555555555555566/17677 17679 17683 17686 17688-17690 17692 176942.1534725313611987e-25 9.276497240453405e-25https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/569/A52?format=asciiOpticalRadiodefaultJ/A+A/569/A52/tablea1325MHz GMRT observations of the Ultra Steep Spectrum (USS) samplerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSampleSample (B03 or S06) (1)src.samplecharSSources in the S06 and B03 samplesmeta.ref.urlintnullablen_GMRT[*+] low signal or double lobe source (2)meta.notecharGMRTSource name as given in our 325MHz GMRT catalog (Sirothia et al., in prep.) (HHMMSS+DDMMSS)meta.id;meta.maincharRAJ2000Right ascension (J2000) (3)pos.eq.ra;meta.mainDEJ2000Declination (J2000) (3)pos.eq.dec;meta.mainS.325325MHz flux density from our GMRT observationsmJyphot.flux.density;em.radio.200-400MHzfloate_S.325rms uncertainty on S325MHzmJystat.errorfloatS1.41.4GHz flux density from B03 or S06mJyphot.flux.density;em.radio.750-1500MHzfloate_S1.4rms uncertainty on S1.4mJystat.errorfloatalpha[-2.6/-1] Radio spectral index {alpha} between 325MHz to 1.4GHzspect.index;em.radio.200-400MHzfloate_alpharms uncertainty on alphastat.error;pos.eq.rafloatzph[0.03/3.5]? Photometric redshift estimate (4)src.redshiftfloatnullablezsp[0.03/3.9]? Spectroscopic redshift (5)src.redshiftfloatnullablelogL1.4? 1.4GHz radio luminosity (6)log(W.Hz**-1)phys.luminosity;em.radio.750-1500MHzfloatnullableSEDPlot the spectrum with SPECFIND (Vollmer et al. 2009, Cat. VIII/85)meta.ref.urlchar