Multi-Frequency VLBI Observations of GHz-Peaked Spectrum Sou

We report results of pentachromatic VLBI survey for 18 GHz-peaked spectrum sources. Spectral fitting at every pixel across five frequencies allows us to illustrate distribution of optical depth in terms of free-free absorption or synchrotron self absorptio

Proceedingsofthe7thEuropeanVLBINetworkSymposium

Bachiller,R.Colomer,F.,Desmurs,J.F.,deVicente,P.(eds.)

October12th-15th2004,Toledo,Spain

Multi-FrequencyVLBIObservationsofGHz-PeakedSpectrum

Sources

S.Kameno1,M.Inoue1,Z.-Q.Shen2,S.Sawada-Satoh3,andK.Wajima4

arXiv:astro-ph/0412674v1 30 Dec 20041234NationalAstronomicalObservatoryofJapan,2-21-1Osawa,Mitaka,Tokyo181-8588JapanShanghaiAstronomicalObservatory,80NandanRoad,Shanghai200030,ChinaAcademiaSinicaInstituteofAstronomyandAstrophysics,P.O.Box23-141,Taipei106,TaiwanKoreaAstronomyObservatory,61-1Hwaam-dong,Yuseong,Daejeon305-348,KoreaAbstract.WereportresultsofpentachromaticVLBIsurveyfor18GHz-peakedspectrumsources.Spectral ttingateverypixelacross vefrequenciesallowsustoillustratedistributionofopticaldepthintermsoffree–freeabsorptionorsynchrotronselfabsorption.QuasarsandSeyfert1sourcesshowone-sidedmorphologywithacoreattheendwheretheopticaldepthpeaks.RadiogalaxiesandSeyfert2showsymmetricdouble-sidedjetswithaopticallythickcoreatthecenter.1.IntroductionGHz-PeakedSpectrum(GPS)sourcesarepowerfulradiosourcesassociatedwithactivegalacticnuclei,whichshowaconvexradiospectrumpeakedatGHzfrequenciesandacom-pactoverallsizesmallerthankpcdimension(O’Dea,Baum,&Stanghellini1991;O’DeaApower-lawspectrumatfrequencieshigherthanthespec-tralpeakisproducedbyopticallythinsynchrotronradiation.Aspectralcuto indicatesthatthesynchrotronemissionisopti-callythickatlowerfrequenciesthanthepeak,intermsofsyn-chrotronselfabsorption(SSA)orfree–freeabsorption(FFA).O’Dea&BaumandSnellenetal.showedcorrelationbetweenthepeakfrequencyandtheoveralllinearsize,andclaimedthatSSAcontrolsthethepeakfrequency.Ontheotherhand,Bicknell,Dopita,&O’DeapointedoutthatFFAthroughionizedgassurroundingradiolobescanalsoproducethecorrelationbetweenthepeakfrequencyandthe

overallsize.EvidenceforFFAwasfoundviamulti-frequency

VLBIobservationsinparticularGPSsources(e.g.NGC1052;

Kamenoetal.Vermeulenetal.2003;Kamenoetal.

2003;Kadleretal.2004).

Apower-lawspectrumofsynchrotronemitterthroughFFA

willbea ectedas

Sν=S0ναexp( τ0ν 2.1),(1)Fig.1.Morphologyandspectraofatype-1GPSsourceJ0251+4315.Fig.2.Morphologyandspectraofatype-2GPSsourceJ0241 0815.

whereτ0istheopticaldepthat1GHz.τ0isrelated

withtheelectrondensityneandtemperatureTeasτ0= 2 3/20.46ndL.Thus,multi-frequencyVLBIobservationseTeLOSenablespectral ttingateverypixeltomeasureτ0andillustrate

thedistributionofcolddenseplasma.

2.TheSurvey

Wehavecarriedout ve-frequencyVLBIobservationsfor

18GPSsources.TheVSOPwasusedat1.6and4.8GHzto

obtaincomparablebeamsizeswiththoseat2.3,8.4,and15.4

GHzwiththeVLBA.DetailedimageperformanceisshownintheURL.Table1liststhesamplesourceswhichwereselectedfromtheGPScatalogbydeVries,Barthel,&O’DeaSelectioncriteriaof(1)peakfrequencyνmstandwithin1.6GHz<νm<15GHz,(2) uxdensitylimitationofS1.6GHz>0.1Jy,S5GHz>0.5Jy,andS15GHz>0.2Jy,areapplied.Fiveradiogalaxiesand13quasarsareincludedinthesample.Imagesat vefrequenciesarerestoredwithacommonGaussianbeamwhoseFWHMisageometricmeanof vesynthesizedbeams.Theseimagesareregisteredbyreferencing

We report results of pentachromatic VLBI survey for 18 GHz-peaked spectrum sources. Spectral fitting at every pixel across five frequencies allows us to illustrate distribution of optical depth in terms of free-free absorption or synchrotron self absorptio

158S.Kamenoetal.:Multi-FrequencyVLBIobservationsofGPSsourcesTable1.GPSsamplesources.

J0111+3906

J0203+1134

J0241-0815

J0251+4315

J0503+0203

J0650+6001

J0741+3112

J0745+1011

J0745-0044

J0905+4850

J1146-2447

J1335+4542

J1845+3541

J1850+2825

J2052+3635

J2129-1538

J2151+0552

J2340+26410108+3880201+113NGC10520248+4300500+0190646+6000738+3130742+1030743-0060902+4901143-2451333+4591843+3561848+2832050+3642126-1582149+0562337+2640.668473.61090.00491.310.584570.4550.635 0.9942.690 2.4490.7462.560.3543.2680.74 212121111111212111 1.1 0.3 1.0 1.0 1.0 0.6 0.5 0.7 1.0 0.7 0.7 1.2 1.0 0.7 1.5 0.7 0.75 0.7