J/ApJ/769/125ivo://CDS.VizieR/J/ApJ/769/125doi:10.26093/cds/vizier.17690125CDSHodge J.A.Becker R.H.White R.L.Richards G.T.2017-06-26T11:49:45Z2015-01-19T11:50:48ZCDS support team

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

cds-question@unistra.frradio-galaxiesquasarssurveysWe report on a blind survey for extragalactic radio variability that was carried out by comparing two epochs of data from the Faint Images of the Radio Sky at Twenty centimeters survey with a third epoch from a new 1.4GHz survey of SDSS Stripe 82. The three epochs are spaced seven years apart and have an overlapping area of 60deg^2^. We uncover 89 variable sources down to the millijansky level, 75 of which are newly identified, and we find no evidence for transient phenomena. This new sample of variable sources allows us to infer an upper limit to the mean characteristic timescale of active galactic nucleus radio variability of 14yr. We find that only 1% of extragalactic sources have fractional variability f_var_>3, while 44% of Galactic sources vary by this much. The variable sample contains a larger fraction of quasars than a comparable non-variable control sample, though the majority of the variable sources appear to be extended galaxies in the optical. This implies that either quasars are not the dominant contributor to the variability of the sample, or that the deep optical data allow us to detect the host galaxies of some low-z quasars. We use the new, higher resolution data to report on the morphology of the variable sources. Finally, we show that the fraction of sources that are variable remains constant or increases at low flux densities. This may imply that next generation radio surveys with telescopes like Australian Square Kilometer Array Pathfinder and MeerKAT will see a constant or even increasing fraction of variable sources down into the sub-millijansky regime.2013ApJ...769..125Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/769/125CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toVIII/90 : The FIRST Survey Catalog, Version 12Feb16 (Becker+ 2012)VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)VIII/87 : The Allen Telescope Array 20cm Survey (ATATS). I. (Croft+ 2010)J/ApJ/742/49 : Variable radio sources in FIRST (Thyagarajan+, 2011)J/ApJ/740/65 : VLA search for 5GHz radio transients (Ofek+, 2011)J/ApJ/739/76 : Pi GHz Sky Survey (PiGSS). II. (Bower+, 2011)J/ApJ/737/45 : Variable 1.4GHz radio sources from NVSS & FIRST (Ofek+, 2011)J/ApJ/714/1305 : The Deep SWIRE Field (DSF) IV. (Strazzullo+, 2010)J/ApJS/180/67 : Phot. selection of quasars from SDSS. II. (Richards+, 2009)J/MNRAS/397/281 : Radio imaging in Lockman Hole (Ibar+, 2009)J/ApJ/689/108 : MASIV survey. II. First four epochs (Lovell+, 2008)J/ApJ/648/629 : Radio obs. of late M, L, and T dwarfs (Berger+, 2006)J/ApJS/155/257 : NBC Quasar Candidate Catalog (Richards+, 2004)J/AJ/127/2565 : Faint FIRST variable radio sources (de Vries+, 2004)http://sundog.stsci.edu/ : VLA FIRST survey home pagehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/769/125https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/769/125http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/769/125https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/769/125https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/769/125http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/769/125GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/769/125/var (Variable sources from epoch III or from epochs I/II)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/769/125/var?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/769/125/var?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/769/125/var?GETtext/xml+votable180.050000true10.468683330.05060.0055555555555555565/4454 4713 6/17727 17770 17771 17807 17811 17812 17813 17820 17830 17833 17834 17835 17840 17856 18005 18006 18008 18009 18010 18019 18020 18021 18023 18025 18026 18027 18028 18032 18069 18112 18176 18751 18794 18795 18837 18838 18839 18840 18841 18842 18857 18858 18859 18860 18880 19029 19030 19031 19033 19034 19036 19045 19056 19200 192029.276497240453405e-25 9.276497240453405e-25https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/769/125?format=asciiRadiodefaultJ/ApJ/769/125/varVariable sources from epoch III or from epochs I/IIFIRSTFIRST name from VIII/90meta.id;meta.maincharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Hour of right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Degree of declination (J2000)pos.eq.dec;meta.mainSpk1[1/1482]? 1.4GHz peak flux density of Epoch ImJyphot.flux.density;em.radio.750-1500MHzfloatnullableSint1[0.6/1525] Integrated flux density of Epoch ImJyphot.flux.density;em.radio.750-1500MHzfloatrms1[131/778] rms of Epoch IuJystat.stdev;instr.det.noiseintSpk2[1.2/1350]? 1.4GHz peak flux density of Epoch IImJyphot.flux.density;em.radio.750-1500MHzfloatnullableSint2[0.5/1361] Integrated flux density of Epoch IImJyphot.flux.density;em.radio.750-1500MHzfloatrms2[130/250] rms of Epoch IIuJystat.stdev;instr.det.noiseintSpk3[1/1129]? 1.4GHz peak flux density of Epoch IIImJyphot.flux.density;em.radio.750-1500MHzfloatnullableSint3[0.2/1242] Integrated flux density of Epoch IIImJyphot.flux.density;em.radio.750-1500MHzfloatrms3[48/11014]? rms of Epoch IIIuJystat.stdev;instr.det.noiseintnullableMaj[0.09/4] Deconvolved major axis value measured from the Epoch III dataarcsecphys.angSizefloatfvar[1/3.2]? variability amplitude f_var_ (1)src.var.amplitudefloatnullableMFMorphological classification in FIRST (2)meta.code;src.morphcharMSMorphological classification in Stripe 82 (2)meta.code;src.morphcharEpEpoch of the observation: I/II for FIRST 1995/2002, or III for 2007-2009 VLA observations in SDSS Stripe 82 (Hodge+ 2011AJ....142....3H)time.epochcharSDSSDisplay the SDSS-DR7 and -DR9 catalogs (II/2694, V/139) within 1.5"phot.flux.density;em.radio.750-1500MHzcharSloanDisplay the online SDSS data for the nearest objectphot.flux.density;em.radio.750-1500MHzchar