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By Usa Byerickj. Guerra, Rutha. Daly Cosmologicaltests and Eds. C. Carilli

Abstract

1.Introduction parameters.CygnusAistheonlylow-redshift(z<0:5)radiogalaxyforwhichwe haveanestimateforD.Wecommentonthesensitivitytothisonelow-redshiftpoint, andresultsincludingandexcludingCygnusAareshown.Alowdensityuniverseis favored,andtheonefreemodelparameterisrelativelywellconstrained. beenshownthatradiosourcesarenot,strictlyspeaking,standardyardsticks[4]. universe,HoistheHubbleconstant,andisthecosmologicalconstant.Ithas cosmologicalconstanto==3Ho2,whereoisthemeanmassdensityofthe afunctionofthedensityparametero=8Go=3Ho2,andthenormalized consideredbymany[1,2,3,4]sinceradiosourcesareobservedtofairlyhighredshift.Thecoordinatedistance(aor),usedtocalculatethesizeofasourceis Theuseofthephysicalsizesofradiosourcesasacosmologicaltesthasbeen However,iftheevolutionwithredshiftofphysicalsizescouldbepredictedand (seex2).Thecosmologicaldependenceoftheratioofthesesizesgoesasapower comparedtoobservations,thenradiosourcescouldbeusedforcosmography[5]. assumingavalueforonemodelparameter.Theevolutionofthesechracteristic sizesforachosensampleshould,forthecorrectparameters(,o,o),track greaterthanoneof(aor)forrealisticvaluesof(seex4).Thus,aswecompare [6,7])forapowerfulextendedradiosourcecanbecalculatedfromobservables theevolutionoftheaveragephysicalsizeofalargesampleofsimilarsources Daly[6]presentsamethodwhereacharacteristicsizeD(calledlbyDaly vL,thelobemagneticeldstrengthB,andthelobewidthaL(seex2).These parameterscanbeextractedfrommulti-frequencyobservationsofradiosources intheusualway:Ho=100hkms�1Mpc�1: thisanalysisareinsensitivetothevalueofHo(seex4);hereHoisparameterized samplesathighredshift,thedependenceof(aor)onoandowillallowust

Year: 2013
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