J/A+A/578/A67ivo://CDS.VizieR/J/A+A/578/A67doi:10.26093/cds/vizier.35780067CDSHerzog A.Middelberg E.Norris R.P.Spitler L.R.Deller A.T.,Collier J.D.Parker Q.A.2018-01-02T13:42:54Z2015-11-03T13:59:40ZCDS support team

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

cds-question@unistra.fractive-galactic-nucleivery-long-baseline-interferometryradio-sourcesInfrared-faint radio sources (IFRS) form a new class of galaxies characterised by radio flux densities between tenths and tens of mJy and faint or absent infrared counterparts. It has been suggested that these objects are radio-loud active galactic nuclei (AGNs) at significant redshifts (z>2). Whereas the high redshifts of IFRS have been recently confirmed based on spectroscopic data, the evidence for the presence of AGNs in IFRS is mainly indirect. So far, only two AGNs have been unquestionably confirmed in IFRS based on very long baseline interferometry (VLBI) observations. In this work, we test the hypothesis that IFRS contain AGNs in a large sample of sources using VLBI. We observed 57 IFRS with the Very Long Baseline Array (VLBA) down to a detection sensitivity in the sub-mJy regime and detected compact cores in 35 sources. Our VLBA detections increase the number of VLBI-detected IFRS from 2 to 37 and provide strong evidence that most - if not all - IFRS contain AGNs. We find that IFRS have a marginally higher VLBI detection fraction than randomly selected sources with mJy flux densities at arcsec-scales. Moreover, our data provide a positive correlation between compactness - defined as the ratio of milliarcsec- to arcsec-scale flux density - and redshift for IFRS, but suggest a decreasing mean compactness with increasing arcsec-scale radio flux density. Based on these findings, we suggest that IFRS tend to contain young AGNs whose jets have not formed yet or have not expanded, equivalent to very compact objects. We found two IFRS that are resolved into two components. The two components are spatially separated by a few hundred milliarcseconds in both cases. They might be components of one AGN, a binary black hole, or the result of gravitational lensing.2015A&A...578A..67Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/578/A67CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/MNRAS/439/545 : Infrared-faint radio sources catalog (Collier+, 2014)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/578/A67https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/578/A67http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/578/A67https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/578/A67https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/578/A67http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/578/A67GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/578/A67/table1 (Component catalogue of 57 IFRS observed with the VLBA)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/578/A67/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/578/A67/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/578/A67/table1?GETtext/xml+votable180.050000true26.07581667-9.365213890.0055555555555555566/47 5407 5503 5597 6014 6036 6098 7222 7245 8212 8299 8339 8487 8615 8948 9075 9383 9479 9546 9677 9690 9714 9899 10112 10228 10252 10321 10420 10519 10526 10795 10910 10983 10986 11009 11049 11063 11098 11118 11226 11234 11438 11514 11809 17510 17665 17725 17729 17736 25997 26059 26084 26119 26446-26447 36840 45051https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/578/A67?format=asciiRadiodefaultJ/A+A/578/A67/table1Component catalogue of 57 IFRS observed with the VLBArecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintC2014Display the data of Collier et al. (2014, Cat. J/MNRAS/439/545)meta.ref.urlcharNameIdentifier, FNNNN or FNNNN_N (1)meta.id;meta.maincharNVSSNVSS name (JHHMMSS+DDMMSS) (2)meta.idcharRAJ2000FIRST right ascension (J2000) (3)pos.eq.ra;meta.mainDEJ2000FIRST declination (J2000)pos.eq.dec;meta.mainSpeakNNVSS peak flux (in mJy/beam) (3)mJyphot.flux.density;em.radio.750-1500MHzfloatSintNNVSS integrated flux (3)mJyphot.flux.density;em.radio.750-1500MHzfloatl_SpeakVLimit flag on SpeakV (4)meta.code.errorcharSpeakVVLA peak flux (in mJy/beam) (3)mJyphot.flux.density;em.radio.750-1500MHzfloatSintV? VLA integrated flux (3)mJyphot.flux.density;em.radio.750-1500MHzfloatnullableS/N? VLBA signal-to-noise ratiostat.snrfloatnullableamaj? Major axis of the VLBA beammagphys.angSize;srcfloatnullableamin? Minor axis of the VLBA beammagphys.angSize;srcfloatnullableSimbadSimbad column added by the CDSmeta.ref.urlchar