Color–Magnitude Sequence in the Clusters at z ∼ 1.2 near the Radio Galaxy 3C 324

[摘要] Wehaveinvestigatedtheopticalandnear-infraredcolorsofK′-selectedgalaxiesinclustersatz∼1.2neartotheradiogalaxy3C324usingimagesobtainedwiththeSubarutelescopeandarchivalHSTdata.Thedistributionofcolorsofthegalaxiesintheclusterregionisfoundtobefairlybroad,anditmayimplysignificantscatterintheirstar-formationhistories,althoughtheeffectofcontaminationoffieldgalaxiesisuncertain.TheredsequenceofgalaxieswhoseR–KcolorsareconsistentwithpassiveevolutionmodelsforoldgalaxiesisfoundtobetruncatedatK′∼20mag,andtherearefewfaintergalaxieswithsimilarredcolorsintheclusterregion.Wefindthatthebulge-dominatedgalaxiesselectedbyquantitativemorphologicalclassificationformabroadsequenceinthecolor-magnitudediagram,whoseslopeismuchsteeperthanthatexpectedfrommetallicityvariationswithinapassivelyevolvingcoevalgalaxypopulation.Wearguethattheobservedcolor-magnitudesequencecanbeexplainedbymetallicityandagevariations,andthefaintergalaxieswithK′gt;20magmaybe1–2Gyryoungerthanthebrightergalaxies.SomespatialsegregationofthecolorandK′-bandluminosityisseenintheskydistribution;theredderandthebrighterobjectstendtobelocatednear3C324.

[学科分类] 天文学(综合)

[关键词] "galaxies: clusters";"galaxies: evolution";"galaxies: formation"