J/A+A/708/A20ivo://CDS.VizieR/J/A+A/708/A20CDSNedialkov P.Williams B.F.Ivanov V.D.Valcheva A.Solovyeva Y.,Vinokurov A.Malygin EOparin D.Sholukhova O.2026-03-26T07:41:38Z2026-03-26T08:35:22ZCDS support team

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

cds-question@unistra.frgalaxiesquasarsactive-galactic-nucleispectroscopyredshiftedphotometryOur aim is to increase the limited number of quasars behind M 31, necessary for probing the chemical content of the gas and for proper motion reference, with reliable and homogeneous redshift measurements from emission lines. We carried out spectroscopic follow-up of 32 quasar candidates. We confirm 23 quasars. Two are new discoveries (J004029.727+403705.68 and J004215.489+412031.52) and the rest have been reported elsewhere, but with somewhat deficient analysis; 16 spectra are published for the first time. We report new homogeneous redshifts for 34 quasars (from 40 spectra, adding 17 from the archives) and summarize all available information about bona fide quasars with reliable redshift, bringing their number to 124 within the {mu}B=26m/arcsec^2^ isophote. We carried out a comparison of redshifts from different sources and excluded some objects with redshifts derived from low-resolution spectra. We derived the reddening for them from the color excess with respect to dereddened counterparts with similar redshifts in the field. Comparisons of our reddenings with M 31 reddening maps found no significant correlations. Most QSOs behind M 31 show low reddening and do not probe high extinctions, probably due to a bias toward following up brighter and less extinct candidates, which underlines the need to identify fainter quasars behind nearby galaxies, especially behind higher extinction regions. Finally, the redshifts derived from low-resolution spectra must be treated with caution because they can contain significant errors.2026A&A...708A..20Nhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/708/A20CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/708/A20https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/708/A20http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/708/A20https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/708/A20https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/708/A20http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/708/A20GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/708/A20/tableb1 (Redshift and reddening of 125 QSOs behind M31 disk)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/708/A20/tableb1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/708/A20/tableb1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/708/A20/tableb1?GETtext/xml+votable180.050000true9.2044583340.1449250.0055555555555555566/2619 2622-2623 2666-2667 2705 2708-2709 2752https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/708/A20?format=asciidefaultJ/A+A/708/A20/tableb1Redshift and reddening of 125 QSOs behind M31 diskrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeqQSO consecutive number (1)meta.idintNameGaia DR3 unique source identifier or Pan-STARRS unique source identifier (2)meta.id;meta.maincharRAJ2000Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainrhoGalactocentric distance (3)pos.distance;pos.galactocentricfloatGmagThe mean G-band magnitudemagphot.mag;em.optfloate_GmagThe 1{sigma} error in Gmagmagstat.error;phot.magfloatEml6Detected emission line l6meta.id;spect.linecharEml7Detected emission line l7meta.id;spect.linecharzad? Adopted redshift zadsrc.redshift;pos.heliocentricfloatnullablee_zad? The 1{sigma} error in zadstat.errorfloatnullableClassName of best class (Cat. I/356/qsocand)src.classcharPQSO? Probability of being a quasar%statintnullablez1? First measured redshift z1src.redshiftfloatnullablee_z1? The 1{sigma} error in z1stat.errorfloatnullabler_z1The z1 redshift reference (4)meta.ref;pos.framecharz2? Second measured redshift z2src.redshiftfloatnullablee_z2? The 1{sigma} error in z2stat.errorfloatnullabler_z2The z2 redshift reference (4)meta.ref;pos.framecharz3? Third measured redshift z3src.redshift;pos.heliocentricfloatnullablee_z3? The 1{sigma} error in z3stat.errorfloatnullabler_z3The z3 redshift reference (4)meta.ref;pos.framecharz4? Fourth measured redshift z4src.redshift;pos.heliocentricfloatnullablee_z4? The 1{sigma} error in z4stat.errorfloatnullabler_z4The z4 redshift reference (4)meta.ref;pos.framecharz5? Fifth measured redshift z5src.redshift;pos.heliocentricfloatnullablee_z5? The 1{sigma} error in z5stat.errorfloatnullabler_z5The z5 redshift reference (4)meta.ref;pos.framecharz6? Sixth measured redshift z6src.redshift;pos.heliocentricfloatnullablee_z6? The 1{sigma} error in z6stat.errorfloatnullabler_z6The z6 redshift reference (4)meta.ref;pos.framecharEml1Detected emission line l1meta.id;spect.linecharEml2Detected emission line l2meta.id;spect.linecharEml3Detected emission line l3meta.id;spect.linecharEml4Detected emission line l4meta.id;spect.linecharEml5Detected emission line l5meta.id;spect.linecharAV? measured reddening AVmagphys.absorptionfloatnullablee_AV? The 1{sigma} error in AVmagstat.errorfloatnullablerobs[1/32]? Observing log table IDmeta.codeintnullablerspecID in the plot (Fig. 3)meta.codecharJ/A+A/708/A20/tablec1Spectra of QSOs J004029.727+403705.68 and J004215.487+412031.52recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintlambdaWavelength0.1nmem.wlintFluxFlux in arbitrary unitsphot.fluxfloatIndex[1/2] Spectrum identifier (1)meta.codeint