J/A+A/618/A172ivo://CDS.VizieR/J/A+A/618/A172doi:10.26093/cds/vizier.36180172CDSCorsini E.M.Morelli L.Zarattini S.Aguerri J.A.L.Costantin L.,D'Onghia E.Girardi M.Kundert A.Mendez-Abreu J.Thomas J.2019-01-07T09:20:45Z2018-10-26T09:23:10ZCDS support team

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

cds-question@unistra.frgalaxiesgalaxy-classification-systemsFossil groups (FGs) are galaxy aggregates with an extended and luminous X-ray halo, which are dominated by a very massive early-type galaxy and lack of L* objects. FGs are indeed characterized by a large magnitude gap between their central and surrounding galaxies. This is explained by either speculating that FGs are failed groups which formed without bright satellite galaxies and did not suffer any major merger, or suggesting that FGs are very old systems which had enough time to exhaust their bright satellite galaxies through multiple major mergers. Since major mergers leave signatures in the stellar populations of the resulting galaxy, we study the stellar population parameters of the brightest central galaxies (BCGs) of FGs as a benchmark against which the formation and evolution scenarios of FGs can be compared. We present long-slit spectroscopic observations along the major, minor, and diagonal axis of NGC 6482 and NGC 7556, which are the BCGs of two nearby FGs. The measurements include spatially resolved stellar kinematics and radial profiles of line-strength indices, which we converted into stellar population parameters using single stellar-population models. NGC 6482 and NGC 7556 are very massive (M*~1*10^11.5^M_{sun}_) and large (D_25_~50kpc) galaxies. They host a centrally-concentrated stellar population, which is significantly younger and more metal rich than the rest of the galaxy. The age gradients of both galaxies are somewhat larger than those of the other FG BCGs studied so far, whereas their metallicity gradients are similarly negative and shallow. Moreover, they have negligible gradients of alpha-element abundance ratio. The measured metallicity gradients are less steep than those predicted for massive galaxies which formed monolithically and evolved without experiencing any major merger. We conclude that the observed FGs formed through major mergers rather than being failed groups missing bright satellite galaxies since the beginning.2018A&A...618A.172Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/618/A172CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+A/527/A143 : RX J105453.3+552102 cluster SDSS photometry (Aguerri+, 2011)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/618/A172https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/618/A172http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/618/A172https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/618/A172https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/618/A172http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/618/A172GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/A+A/618/A172/tablea1r-band isophotal parameters of NGC 7556recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintaSemimajor axisarcsecphys.angSize;srcfloatmur-band surface brightnessmag.arcsec**-2phot.mag.sb;em.opt.Rfloate_muError on mu (-1{sigma})mag.arcsec**-2stat.errorfloatE_muError on mu (+1{sigma})mag.arcsec**-2stat.error;stat.maxfloatellEllipticitysrc.ellipticityfloate_ellError of ellstat.errorfloatPAMajor-axis position angle measured from north to eastdegpos.posAngfloate_PAError of PAdegstat.errorfloatJ/A+A/618/A172/tablea23Kinematic parameters (table A2) and line-strength indices (table A3) of NGC 6482 and NGC 7556recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNGCNGC numbermeta.id;meta.mainintrDistance from galaxy centerarcsecpos.angDistancefloatvLine of sight mean velocitykm/sphys.velocfloate_vError of vkm/sstat.errorfloatsigmaLine of sight velocity dispersionkm/sphys.veloc.dispersion;spect.linefloate_sigmaError of sigmakm/sstat.errorfloatH33rd order coeff. of Gaussian Hermite decomposition of the line of sight velocity distribution (LOSVD)stat.fit.paramfloate_H3Error of H3stat.errorfloatH44th order coeff. of Gaussian Hermite decomposition of the LOSVDstat.fit.paramfloate_H4Error of H4stat.errorfloatPASlit position angle measured from north to eastdegpos.posAngintHbeta? Line-strength index Hbeta0.1nmspect.line.eqWidthfloatnullablee_Hbeta? Error of Hbeta0.1nmstat.errorfloatnullableMg2? Line-strength index Mg2magspect.indexfloatnullablee_Mg2? Error of Mg2magstat.errorfloatnullableMgb? Line-strength index Mgb0.1nmspect.line.eqWidthfloatnullablee_Mgb? Error of Mgb0.1nmstat.errorfloatnullableFe5270? Line-strength index Fe52700.1nmspect.line.eqWidthfloatnullablee_Fe5270? Error of Fe52700.1nmstat.errorfloatnullableFe5335? Line-strength index Fe53350.1nmspect.line.eqWidthfloatnullablee_Fe5335? Error of Fe53350.1nmstat.errorfloatnullable