J/A+A/653/A155ivo://CDS.VizieR/J/A+A/653/A155doi:10.26093/cds/vizier.36530155CDSBerger A.Adebahr B.Herrera Ruiz N.Wright A.H.Prandoni I.,Dettmar R.-J.2021-10-08T11:23:35Z2021-09-28T07:37:29ZCDS support team

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

cds-question@unistra.frmagnetic-fieldspolarimetryradio-continuum-emissionIn the context of structure formation and galaxy evolution, the contribution of magnetic fields is not well understood. Feedback processes originating from active galactic nucleus (AGN) activity and star formation can be actively influenced by magnetic fields, depending on their strength and morphology. One of the best tracers of magnetic fields is polarised radio emission. Tracing this emission over a broad redshift range therefore allows an investigation of these fields and their evolution. We aim to study the nature of the faint, polarised radio source population whose source composition and redshift dependence contain information about the strength, morphology, and evolution of magnetic fields over cosmic timescales. We use a 15-pointing radio continuum L-band mosaic of the Lockman Hole, observed in full polarisation, generated from archival data of the Westerbork Synthesis Radio Telescope (WSRT). The data were analysed using the rotation measure synthesis technique. We achieved a noise of 7uJy/beam in polarised intensity, with a resolution of 15". Using infrared and optical images and source catalogues, we were able to cross-identify and determine redshifts for one-third of our detected polarised sources. Results. We detected 150 polarised sources, most of which are weakly polarised with a mean fractional polarisation of 5.4%. No source was found with a fractional polarisation higher than 21%. With a total area of 6.5deg^2^ and a detection threshold of 6.25{sigma}, we find 23 polarised sources per deg^2^. Based on our multi-wavelength analysis, we find that our sample consists of AGN only. We find a discrepancy between archival number counts and those present in our data, which we attribute to sample variance (i.e. large-scale structures). Considering the absolute radio luminosity, we find a general trend of increased probability of detecting weak sources at low redshift and strong sources at high redshift. We attribute this trend to a selection bias. Further, we find an anti-correlation between fractional polarisation and redshift for our strong-source sample at z>=0.6. A decrease in the fractional polarisation of strong sources with increasing redshift cannot be explained by a constant magnetic field and electron density over cosmic scales; however, the changing properties of cluster environments over cosmic time may play an important role. Disentangling these two effects requires deeper and wider polarisation observations as well as better models of the morphology and strength of cosmic magnetic fields.2021A&A...653A.155Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/653/A155CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/PASJ/53/445 : ASCA Deep survey in Lockman Hole Field (Ishisaki+, 2001)J/ApJS/185/433 : SWIRE/Chandra survey in Lockman Hole Field (Wilkes+, 2009)J/ApJS/198/1 : Photometry catalogs for the Lockman Hole (Fotopoulou+, 2012)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/653/A155https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/653/A155http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/653/A155https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/653/A155https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/653/A155http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/653/A155GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/653/A155/catalog (Full source catalogue)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/653/A155/catalog?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/653/A155/catalog?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/653/A155/catalog?GETtext/xml+votable180.050000true165.28851557.456040.005555555555555556Cone search capability for table J/A+A/653/A155/list (Information on fits image)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/653/A155/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/653/A155/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/653/A155/list?GETtext/xml+votable180.050000true162.537558.025420.005555555555555556Associated datahttps://cdsarc.cds.unistra.fr/assocdata/?obs_collection=J/A+A/653/A1555/1517 1528 6/6047 6077 6088 6090 6120 15475https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/653/A155?format=asciiRadiodefaultJ/A+A/653/A155/catalogFull source cataloguerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIslIdPISource ID, NNN or NNNAmeta.id;meta.maincharRAJ2000Right ascension (J2000)degpos.eq.ra;meta.maine_RAJ2000? Right ascension uncertainty (J2000)degstat.error;pos.eq.radoublenullableDEJ2000Declination (J2000)degpos.eq.dec;meta.maine_DEJ2000? Declination uncertainty (J2000)degstat.error;pos.eq.decdoublenullablePIPolarised intensitymJyphys.polarizationfloate_PIPolarised intensity uncertaintymJystat.errorfloatI? Total intensitymJyspect.line.intensitydoublenullablee_I? Total intensity uncertaintymJystat.errorfloatnullablefracpol? Fractional polarisation%phys.polarizationfloatnullablee_fracpol? Fractional polarisation uncertainty%stat.errorfloatnullableSCodeS_code; see paper appendix for detailsmeta.codecharFlagFlag on intensity (1)meta.code.errorcharSpIndex? Spectral index to 150MHz (2)spect.index;em.radio.100-200MHzfloatnullablezB? Photometric redshift (3)src.redshift;pos.heliocentricfloatnullableb_zB? Photometric redshift minimum (3)src.redshift.phot;stat.minfloatnullableB_zB? Photometric redshift maximum (3)src.redshift.phot;stat.maxfloatnullableBMAG? Absolute B magnitude (3)magphys.magAbsfloatnullableSWIREID of crossmatches SWIRE source (4)meta.idcharJ/A+A/653/A155/listInformation on fits imagerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension of center (J2000)degpos.eq.ra;meta.mainDEJ2000Declination of center (J2000)degpos.eq.dec;meta.mainNxNumber of pixels along X-axismeta.numberintNyNumber of pixels along Y-axismeta.numberintObs.dateObservation datestime.epoch;obsnullablesizeSize of FITS fileKibytephys.size;meta.fitsintFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitscharAssocDataAssociated Data web pagemeta.ref.urlchar