198 8ApJ. . .329. .532K Islands. and attheObservatoriodelRoque delosMuchachos,LaPalma,Canary Science Foundation;attheEuropean SouthernObservatory,LaSilla,Chile; Observatories, operatedbyAURA, Inc.,undercontractwiththeNational Cerro TololoInter-AmericanObservatory, NationalOpticalAstronomy fied inthesouthjetof3G277.3=ComaA(vanBreugelet al. origin (see§IV).Individualcontinuumknotshavebeenidenti- the radiostructuresandatlevelsconsistentwithasynchrotron 31, 3C66B,andPKS0521—36hasbeenreported,matching Hayes andSadun1987).Opticalemissionfromthejetsin 3C 1985). trally distinct,intheoptical(RöserandMeisenheimer1986; The jetof3C273hasmultiplecomponents,spatiallyandspec- Similar conclusionsaremorefragmentaryforotherobjects. ing anupperlimitorbreakintheelectronenergyspectrum. est andhasbeenmeasuredbymanyworkers(see§III).The radio powerlaw,withafallofftowardhighfrequenciessuggest- optical andIRradiationfromthisjetroughlycontinuesthe most jetsatthesewavelengths.TheM87jetisbyfarthebright- generally quitedifficultduetothelowsurfacebrightnessof distributions atmuchhigherenergies(uptoGeV),butare able valueindeterminingthepropertiesofelectron red, andultravioletobservationsareinprincipleofconsider- energy distributionfortheradiatingelectrons.Optical,infra- degrees, clumpystructure,andpower-lawspectralshapesin the centimeter-wavelengthregime,implyingapower-law parsec scales,arecharacterizedbyopeninganglesofafew (see thereviewbyBridleandPerley1984).Thejets,onkilo- seen fromenergyconsiderationsandpolarizationproperties is almostcertainlydominatedbysynchrotronradiation,as pose outstandingastrophysicalproblems.Theirradioemission 1 The AstrophysicalJournal,329:532-550,1988June15 © 1988.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. Basedonobservationsobtainedat KittPeakNationalObservatoryand Attention hasalsobeengiventoopticalemissionfrom“hot The radiojetsofmanyactivegalacticnucleicontinueto 145 Subject headings:galaxies:individual(M87)—jetsphotometryquasars closer tothenucleus.KnotAisanexception,withaspectrumlikefeaturesnearcore. level, implyingthatthejetstructurepreventsparticlesfromstreamingfreelyoverthisdistance(~30pc) Significant changesinturnoverfrequencyoccurfromknottoknot,withanoveralltrendofhigher shapes forvariousknotsfreeofblendingproblems.ThestructurematchesthatseenintheradiotoOl'S power-law spectrafromtheradiotoBband. particle (re)accelerationprocess.Twohotspots(PicAand3C303)differfromthejets,inshowingunbroken critical frequenciesbetween3x10and2Hz.Thismaybeduetofinestructureinthejetsor well-represented bysynchrotronspectrafromtruncatedpower-lawelectrondistributions,withemitted-frame brightest knotintheNGC6251jet,isreported.Inallcases,exceptpartof3C273jetcontinuaare show opticalcounterparts,andtosearchforsuchcounterpartsinadditionalobjects.Onenewdetection,the © American Astronomical Society • Provided by the NASA Astrophysics Data System An Appendixgivesresultsofsurfacephotometryfortheprogramgalaxies. Image restorationhasbeenusedtoexaminethesub-arcsecondstructureofM87jetandderivespectral Multicolor opticalimageshavebeenusedtomeasurethebroad-bandspectralshapesofradiojetsknown I. INTRODUCTION 1 radiation mechanisms—radiosources:galaxies THE OPTICALCONTINUAOFEXTRAGALACTICRADIOJETS Received 1987August11;acceptedDecember William C.Keel Sterrewacht Leiden ABSTRACT various objectssuggestthatcharacteristic scalesareimportant assumptions aboutlocalconditions; regularitiesamong maximum electronenergiesproduced inthejetsundersimple pared tosimplesynchrotron modelsandusedtoderive removed. Thecontinuumshapes measuredhavebeencom- tion oflineemission,where observed,wasevaluatedand jets andhotspots,toallowamoremeaningfulcomparison allow measurementofclosely spacedfeatures.Thecontribu- reconstruction toslightlyincreasetheeffectiveresolution and absolute calibrationofthedata,andinsomecasesimage of theunderlyingstarlightandnuclearlighteachgalaxy, the data havebeenanalyzedwithparticularattentiontoremoval might bedetectablewithcurrentlyavailableequipment. The or forwhichradiodatasuggestedthattheopticalcontinuum optical passbandsforobjectsknowntoshowradiation, of theseclasses,deepimageshavebeenobtainedinseveral exact continuationoftheradiospectrum. uum isopticallywellobserved,featureless,andflat,forming an arized objecthasrecentlybeenfoundinthewesternhotspotof Pictor A(RöserandMeisenheimer1987),inwhichthecontin- and Röser1986;Simkin1986).Amuchbrighter,highlypol- and polarizationmeasurementsforthisobject(Meisenheimer ed bySimkin(1978),thoughdedicatedobservationalefforts have ledtocontinuumshape,possiblebroademissionlines, same istrueoftheobjectinsouthwestlobe3C33report- objects arequitefaint(V=23),sofurtherworkisdifficult.The additional nine(Crane,Tyson,andSaslaw1983).Mostofthese optical objectsinfourradiohotspots,andlaterreportedan polarization. Saslaw,Tyson,andCrane(1978)reportedfaint spots havebeenconvincinglyidentifiedbyposition,color,or hot spotsoccurmanykiloparsecsfromthenuclei.Several galactic nucleisuchashampersstudyofsmallerscalejets,since has theadvantageofnotbeinglostagainststarlightnear show synchrotroncontinua;theirobservationintheoptical spots ”inthelobesofradiogalaxies.Theyarealsoexpectedto To extendourpictureofthehigh-energyparticlecontent 198 8ApJ. . .329. .532K in particleaccelerationkiloparsec-scalejets.InM87,system- environments. position inthesource. atic variationsintheopticalcontinuumslopeareseenalong include thosegalaxieswhicheitherhadknownopticaljets and colorprofilesofprogramgalaxies,ontheir the jet,implyingsomecouplingbetweenlocalconditionsand (1980) withnegativeresults,butinstrumentalimprovements found byexaminingradiomapsofgalaxieslistedBridleand 0521 —36(e.g.,Keel1986).Objectsofthesecondkindwere might beobservable.InthefirstcategoryareM87,3C31and corresponding totheradiostructures,orhavemorphol- warranted anewexamination.Thecriteriaforinclusionof had infactbeenobservedbyButcher,vanBreugel,andMiley 277.3 =ComaA(vanBreugeletal1985),3C273,andPKS ogy andsurfacebrightnesssuggestingthatopticalcontinua vidual systemsappearin§IV. primarily fordifferentpurposesandthedataanalyzedthis radio galaxy(orlow-redshiftQSO)wereroughly 3C 66B(Butcher,vanBreugel,andMiley1980), (mJy) showninthefiguresandusedmodelfittinghavebeen actually observedappearinTable1.Furtherdetailsonindi- study. Overallpropertiesofthegalaxies(andtwoquasars) these categories.Afewothers(CenA,PicA)wereobserved Perley (1984)ashavingprobableradiojets.Severalofthese corrected forgalacticreddening. Burstein andHeiles(1984);forseveralobjectsitisnegligible. Magnitudes quotedinthetablesareasobserved;fluxdensities tories. Sincethestructureinanysynchrotronspectrumoccurs objects inTable1,usingCCDcamerasatseveralobserva- only overaverybroadfrequencyrange,thefullwavelength An Appendixincludesinformationonthesurfacebrightness The primarysampleforthisprogramwasintendedto Time constraintspreventedobservationofallobjectsin 2. redshiftbelowabout0.1,and Galactic reddeningforeachsystemwasestimatedfollowing Images inavarietyofpassbandswereobtainedforthe 3. jetfluxgreaterthanabout0.2Jyat5GHz. 1. apparentjetlengthintherange4"-10", © American Astronomical Society • Provided by the NASA Astrophysics Data System II. OBSERVATIONSANDDATAANALYSIS a) GalaxySelection b) Images Cen A NGC 6251 PKS 3C 277.3.. 3C 273.... 3C219 .... 3C 66B.... 3C 31 M87 PKS Pictor A... B2 3C449 .... 3C 303.... 3C 296.... Galaxy EXTRAGALACTIC RADIOJETS Properties ofProgramGalaxies Designation RedshiftB(t) 0917 +45 0220 +42 0104 +32 0521 -36 0518 -45 0812 +02 2229 +39 1228 +12 1414-1- 11 1251 +27 1226 +02 1322 -42 1321 +31 1638 +82 1441 +52 TABLE 1 1/2 model ofthegalaxyprofile,afullerdescriptionisgivenby (0"2) pixels,areparticularlysuitedforobjectsinwhichcareful emission linesweresuspected. effects, areimportant.TheseeingatKittPeakwasgenerally pared inTable3. properties ofCCDsusedatvariousobservatoriesarecom- high quantumefficiencyofCCDs,theirstability,andlinearity Gunn z,atabout0.95/un,isavailableaswell.Therelatively baseline fromBtoIwasnormallyobserved(fewCCDsbeing disadvantages. AsCayetteandSol(1987)pointout,thelatter galaxy (Keel1986)havebeenusedforthis;eachsuffersfrom van Breugel,andMiley1980)reflectionoftheobserved galaxy lightdistribution.Theoreticalprofiles(Butcher, bution of[Om]25007orHa-h[Nn]226548,6583when BVRI sets;afewimagesthrough70ÂFWHMfilterscentered allowance forseeingorblending,deconvolutionof appear as“perturbations”ongalaxyisophotesatlevelsbelow are allimportantforthisapplication,sincejetsgenerally sufficiently sensitiveatshorterwavelengths);inafewcases, GRASP (orGASP)surface-photometrysoftware,writtenby able. Suchanapproachhasbeenusedhere,basedonthe procedure candegradethejetsignal-to-noiseratiobyafactor the jetsrequiresveryaccuratemodelingandsubtractionof per pixel. to keepstatisticalerrorsintheflatfieldframeswellbelow1% adding reducedimagesinacoordinatesystemfixedonthesky. of exposureswiththetelescopemovedslightlyinbetween,and the imageofPKS0521—36werereducedbytakingasequence to strong,time-variablenight-skyOHemission.Itseffectson on emission-linewavelengthswereusedtomeasurethecontri- Each telescopeisidentifiedbyitsapertureinmeters;the system fitsellipsestotheisophotesatvariousmajoraxisradii, of 2perpixel,andsomekindgalaxymodelingisprefer- and thewholefamilyofellipsessogeneratedistakenasa Franx andtheauthor.Theprofile-determiningroutineofthis M. Cawson,asextendedbyR.Jedrzewskiandfurther Bias-subtraction andflatfieldingwerenormal;carewastaken 1%. Table2liststheindividualobservationsanalyzedhere. 1"0-1"3 FWHMFiltersatKPNOandCTIOwereMould 0.158 0.1744 0.0215 0.0163 0.055 0.004 0.402 0.0350 0.0161 0.0234 0.0171 0.1410 0.0237 0.0857 0.001 The CTIO/imagessufferfromrelativelyseverefringingdue The KPNO2.1mdata,takenwithaTICCDhaving15gm For mostoftheseobjects,measurementopticalfluxesfor c) GalaxySubtractionandJetMeasurement 13.1 14.8 14.0 13.1 16.7 12.8 18.0 13.8 15.4 18.5 16.5 14.6 17.5 9.6 8.0 Twin-jet source NGC 5532 Coma A NGC 4486 NGC 5128 Optical hotspot Quasar BL Lacnucleus Quasar, 4C02.23 Notes 533 198 8ApJ. . .329. .532K 4.0 CTIO RCA 320x5120.6090 BV 2.5 INT,LaPalma RCA320x5120.8363 B 2.2 ESO RCA 320x5120.3540 VRIZ 2.1 KPNOTI#2800x 0.19 16BVRI,Ha 3.6 ESO RCA 320x5120.67545 R 2.1* KPNORCA#1320x512 0.38 75VR 1.5 CTIORCA#5>354x512 0.54 40BVRI,Ha Aperture (m)ObservatoryCCDFormat("per pixel)(electrons)Filters Telescope Scale ReadoutNoise Pictor A PKS 0821+02 PKS 0521-36 NGC 6251 NGC5128 NGC5127 3C449 3C 303 3C 296 3C 277.3... 3C 273 3C219 3C 66B 3C 31.. M87 (Cen A) (B2 1321+21) (Coma A) © American Astronomical Society • Provided by the NASA Astrophysics Data System Object Telescope PassbandExposure(min)U.T.Date 4.0 3.6 1.5 1.5 2.1 1.5 2.2 2.1 2.1 2.1 1.5 2.1 2.1 2.1 2.1 2.5 2.1* 2.1* 2.2 2.1 Imaging Configurations Journal ofObservations >17007 >16563 >17146 R B R R V R B B B V R I V I B V B B R R z V V B I B R V B R I R V B B B R R I V R I V V B V z V I TABLE 3 TABLE 2 534 ' 3 30 20 20 20 40 15 15 40 10 60 60 20 10 10 30 30 60 25 20 20 40 15 25 60 10 25 40 35 20 20 25 20 40 45 25 17 12 16 20 16 16 16 15 10 10 10 8 5 5 6 5 1986 Apr15 1986 Apr15 1986 Apr14 1986 Apr14 1986 Apr16 1986 Apr14 1986 Apr14 1986 Apr4 1983 Sep29 1983 Sep29 1985 May28 1985 May23 1985 May24 1985 May23 1986 Apr17 1986 Apr17 1986 Apr16 1986 Apr16 1986 Apr16 1986 Apr16 1986 Apr16 1985 May23 1985 May23 1985 May25 1985 May24 1985 May24 1985 May24 1985 May24 1985 May25 1985 May25 1985 May24 1985 May24 1985 May24 1985 May24 1985 May24 1985 May27 1985 May25 1985 May25 1985 May23 1985 May25 1985 May25 1987 Feb23 1986 Sep26 1986 Sep26 1986 Sep26 1986 Sep26 1986 Apr7 1986 Apr7 1985 May23 1985 May23 1985 May23 1985 May23 4x5 min 2 x10min [O in] Ha +[Nii] Clouds Clouds Clouds Clouds Large airmass Large airmass Clouds? Clouds Remarks 198 8ApJ. . .329. .532K (consisting ofasetintensityvalues;semimajoraxes,ellip- fitted insomecasesiteratively.Onceasatisfactoryprofile expected jetemissionwereexcludedfromtheregionstobe ishes, stars,othergalaxies,globularclusters(inM87),or Jedrzewski). Aslightmodificationoftheprogramwasneeded Davis etal(1985).Portionsofeachimageaffectedbyblem- cessive isophotes,butinwhichtherealP.A.haschangedby galaxies wheretheformalP.A.swingsby180°betweensuc- to correcttheinterpolationofpositionangleinnearlyround polation betweenthese(usingtheRJSIMGALroutineby to eachimage,amodelgalaxyimagewasgeneratedbyinter- ticities, positionangles,andcentercoordinates)hadbeenfitted ment proceededuntillessthanhalfanisophotewasincludedin galaxy background),anewmaskwasgeneratedandtheimage and hadnotbeenapparentintheoriginaldata(duetostrong and inmanycasesemissionfromthejets.Ifobjectsappeared data, leavingaresidualimageincludingstars,faintgalaxies, only afewdegrees.Themodelwasthensubtractedfromthe counts (ADUs)abovetheskybackground.Programlimi- remeasured. the differenceframesthatmightaffectisophotemeasurement larger dataframeswereeitherbinned2xorthecentralpor- tations allowedonlya512xareatobetreatedatonce; the data,orintensityperpixeldroppedbelowtwoimage of onepixel,increasingbyafactor1.1perstep.Measure- introduced. the galaxies.Thisdoesnotaffectmeasurementofjetemis- blank sky,butcontainacontributionfromtheouterpartsof background foundfromtheedgeregionswillnotbeactual tions alonemeasured(orboth).Forthelargestgalaxies, expression forresidualsfromanellipticalmodel This wastreatedbymeasuringthebest-fittingconstantsin nificantly “boxy”intheregionofinterest.Ithasfactbeen been correctedusingotherdatainordertoreducethebiasso sion, butcertainsurface-photometryresults(AppendixA)have reducing thedetectabilityoffaintfeatures(particularlyinNGC percent oftheoriginalintensityinworstcases,seriously residuals fromasimpleellipticalfitareasmuchfew and strongradioemissionarestatisticallyconnected.The suggested (BenderandMöllenhoff1987)thatboxyisophotes jets, representedasazimuthalsectors. 6251, inwhichacornerofthe“box”isalignedwithjet). than 0.1%intheinnerparts). Figure 2(Plate14)showsimages the highaccuracytowhichgalaxy lightisremoved(tobetter from boxyisophotesappearinthe“boxiest”systems,such as each pointintheimage.Somedetectablesystematicresiduals expected forPoissonnoisefromtheoriginalintensitylevel for Figure 1(Plate13)isahigh-contrast displayofM87,showing is notentirelycorrect,though adequateforthesepurposes. boxiness, theresidualnoiseaftermodelsubtractionwas as of 3C66BandNGC6251 in whichjetemissionappears. ment oftracingthesepointsalongtheellipticalisophotes was evaluated onacircleaboutthecenterofeachgalaxy. The 3C 296,indicatingthatthesimple fourth-ordertreatmenthere amplitude changesslowlyenoughwithradiusthattherefine- galaxy lightfromthedata.Ingalaxieswithoutverystrong unnecessary. Thisfitwasperformedwithmaskingofstars and Most galaxiesweremeasuredwithastartingisophoteradius Several oftheprogramgalaxieshaveisophotesthataresig- This two-stepmodelingwasverysuccessfulinremovingthe © American Astronomical Society • Provided by the NASA Astrophysics Data System /(0) =I+Acos4(0-0),(1) 0O EXTRAGALACTIC RADIOJETS marginally resolvedsubstructureispresent,aswellfor (PSF). Thiswasusuallymeasuredaftersubtractingthegalaxy (1983), aswellnewUBVRlobservationsobtainedin1987 zero pointsweresetbycomparisonwithaperturephotometry (1985). Meanextinctioncoefficientswereusedduetothe (a factor3-4inlimitingsurfacebrightness)isenoughtoshow, ward photometry—summingdetectedcountsinacircle,box, evaluation ofthesurfacephotometryindistantsystems. each image;thisisparticularlyimportantforcasesinwhich (which didnotrequiregalaxysubtraction). 4). Notethatpublishedmagnitudesscatterbyabout0.05even observed throughclouds,andforsomeothersasacheck,the usually smallairmassrangeforstandards.Forobjects emission. ment isagainratherstraightforward,withsomeguidancefrom cases, theopticaldetectionsstandontheirown,andmeasure- for example,thebrightestknotinjetofNGC6251.Inthese processing mayberequired. photometric zeropoints.Forfainterobjectsmoreelaborate sample, theerrorsbeingdominatedbyuncertaintiesin or morespecificshape—sufficesforthebrightestobjectsin able formeasuringtheopticalintensityofajet.Straightfor- and withthePSFwelldetermined,severalstrategiesareavail- by thegalaxies’starlight(exceptforincreasedPoissonnoise), background. Thus,theseeingprofileisaccuratelyknownfor changes maybediscerned).Thiswascountered,whereneeded, low-noise chip,thisleadstoaresidualimageshowingslight instances, involvingtheouterpartsofgalaxiesobservedwitha Figure 3(Plate15)showstheknotsinComaAand3C303 in brightgalaxiesatagivenaperturesize,perhapsdue to taken fromthecompilationbyLongoanddeVaucouleurs or publishedsurfacephotometry.Aperturephotometry was observations ofstandardstarsfromthelistChristianetal smoothed residualimages,intheregionsofstrongestradio after smoothing.Limitsinthesecaseswerederivedfrom the radiodata. were convolvedwithaGaussiansomewhatsmallerthanthe pixel-to-pixel backgroundnoise,thewell-sampledTI2images by scalingthedataafactor10beforemeasurement. ripples (sincetheareasconcernedcovermanypixels,sub-ADU for NGC6251,withameancorrectionfromrtoRmagnitudes. parison withCCDdata.Surfacephotometrywastakenfrom large numberofmeasuresmaybeneededforaccuratecom- uncertainties inexactaperturediameterorcentering,sothat a seeing disk(forexample,0''7FWHMinI'.'Oseeing).Thisgain sured toprovideanestimateofthepoint-spreadfunction densities), thezeropointsgiven byJohnson(1966)wereused. ness, notapplicabletototalintensities ofobjects). image scaleforthenewimages (about4%insurfacebright- difference betweenthepresent dataandpublishedsurfacepho- the workofDavisetal(1985)forM87andYoung(1979) February withthe1mKapteyntelescopeonLaPalma(Table tometry iswithintheerrors set byuncertaintyintheexact For datatakenunderphotometricconditionsthezero-point Having obtainedimagesofradiojetsfreecontamination The GRASProutinesdealonlywithintegerdata.Inafew On photometricnights,themagnitude(flux)scalewassetby As afirststepindetectingemissionwithintensitiesbelowthe Wherever possible,astarimageneareachgalaxywasmea- Some galaxiesshownoopticalemissionfromthejetseven For conversionoftheBVRI dataintoenergyunits(flux d) Calibration 535 198 8ApJ. . .329. .532K covered bythemodel.Anarea100"squareisshown. lack ofsystematicresidualsaroundthejet;numerousglobularclusters and Hafilamentsarevisible.Theringattheedgeofimagereflectslimitinradius Keel {see329,535) Fig. 1.—High-contrastdisplayofanM87imageinR,aftersubtraction of amodelgalaxy.Thesubtractionhasbeenverysuccessful,asmaybejudgedfromthe © American Astronomical Society •Provided bythe NASAAstrophysics Data System Model GalaxySubtracted M87 R PLATE 13 198 8ApJ. . .329. .532K PLATE 14 © American Astronomical Society •Provided bythe NASAAstrophysics Data System
Keel (see 329, 535) 198 8ApJ. . .329. .532K © American Astronomical Society •Provided bythe NASAAstrophysics Data System y O ro ro ro > O > ro pIG 3—Discrete synchrotron knots. Left, Coma A in blue light, with galaxy model subtracted. Right, 3C 303 in the V band. The knots are marked. PLATE 15 198 8ApJ. . .329. .532K before findingthepeakvalue for PSFsubtraction.Inpractice, tions withW.Jaffe,issmoothing thecurrentresidualimage in theimage.Anacceptable remedy, suggestedbyconversa- increasingly positiveandnegative componentstomatchthis encountering thehighestnoise peak,willgeneratepairsof spurious fine-scalestructure, to theexclusionofanythingelse tion withthePSF.NormalapplicationofCLEAN,upon than couldbeproducedbyanypositiveimageafterconvolu- in opticalimagesitexiststheimageplane.Thusthere is structure duetopixel-to-pixelPoissonnoiseonscalesfiner efficient workonopticalimages.Thenoiseinaperture- synthesis mapsisfundamentallyintheFourierdomain,while ties beforeanalysis. usually convolvedwitha“restoringbeam”ofknownproper- sources (oneperpixelinthelimitofanextendedsource), accounted for.Thisyieldsamodeloftheimageassetpoint residual image,foraslongsignificantfluxremainsto be tracting scaledversionsofthePSFfromsuccessivepeaksin (1984). IhaveinsteadusedamodifiedformoftheCLEAN synthesis maps(seeClark1980).Themethodproceedsbysub- algorithm oftenusedtoremovesidelobesinradioaperture- techniques appliedtoimagesofM87byLorreandNieto conserved. Similarobjectionsapplytothepixel-compensation input intensitylevel,andthefluxofimagesubsectionsisnot Nityananda 1986)isappealingfromaninformation-theoretic small regions;resolutionintherestoredimageisafunctionof entropy reconstruction(recentlyreviewedbyNarayanand (factor 2)increaseinlinearresolution,attheexpenseoflocal standpoint buthasseriousdrawbacksinmeasuringcolorsof noise. Severalalgorithmsareavailableforthis.Maximum- can inprinciplebeprocessedseveralwaystoyieldamodest across theseeingprofileandwithindetector’slinearrange, structure wassought. Hence, adirectdeterminationofthesub-arcsecondoptical volved withseeingisprobablyinadequateforthesepurposes. in thejet.Theradiostructureandpresentresultsalsoimply that modelingasasumofpointsourcesorGaussianscon- evaluate thespectralshapesofevenmostprominentknots (Biretta, Owen,andHardee1983).Thecomplexradiostructure suggested thatsomelevelofmodelingwouldberequiredto ture atandjustbelowtheseeingscale,asisseeninradio fitted tothebroad-banddata. bration uncertaintylimitsthedetailwithwhichmodelsmaybe the galaxies’restframes).Insomecases,absolutecali- The meanwavelengthsquotedforjetemissionincorporatethe of thejetwhenseen,andgalaxyredshift(allarequotedin actual filterandCCDresponses,themeasuredspectralshape 536 Minor modificationstothestandardCLEANareneededfor Data ofhighsignal-to-noiseratio,ifwell-enoughsampled The M87jetimagesindicatethatthereisimportantstruc- © American Astronomical Society • Provided by the NASA Astrophysics Data System e) ImageRestoration Coma A1416.641.140.700.541.22 3C 66B2114.011.030.630.690.83 Galaxy (")VB-VU-BV-RV-I Photoelectric AperturePhotometry Aperture TABLE 4 ±0.05 0.020.050.04 ±0.02 0.020.030.01 KEEL perpendicular totheslitwas only 0"65(followingFilippenko ponent ofatmosphericdispersion between3800and7000Â the airmassrangecoveredby theobservations,meancom- along thejetinP.A.302°,35° fromthezenithdirection.Over range 3800-7000Âwithuseful sensitivity.Theslitwasaligned A totalof30minutesexposurewasobtained,covering the images. D’Odorico andDekker1986)wasusedatthe3.6mtelescope. ing itscontinuumnatureandthesteepslopefoundfrom examined thejetofPKS0521—36spectroscopically,confirm- for 3C273toconfirmthatnostronglinesarepresent.Ihave 1982). Fora1'.'5slitcentered on thejet,thiswillhavenotice- been doneindetailfortheM87jet(see§Ilia),andsufficiently continuum sources,withoutunrecognizedstronglineemission that couldcompromisebroad-bandmeasurements.This has data appearsin§III. numbers oftotalcountsinthejet.Furtheranalysisthese similar, sincetheexposuretimeswerechosentogivesimilar image. Thefinalsignal-to-noiseratiosineachpassbandare were measuredforexactlymatchingregionsineachcleaned same structurescouldbeidentifiedineachcase,andfluxes better thanthe0"4leveltoachievethisdetailedagreement. Similar processingwasdonefortheF,R,andIimages; Hardee 1983)verywellindeed;thestructuremustmatchat images oftheM87jet,togetherwithastarimage.Theoptical (Plate 16),whichcomparesobservedandcleanedB-band structure matchesthatseenat2cm(Biretta,Owen,and of 0'.'4setbythe0'.'2pixels. to within10%;thelatterisdueeffectiveresolutionlimit the parametersofparticularCLEANrunsoronPSFsize the results.Noneofconclusionsheredependscriticallyon see whetherseeingchangeswouldhaveimportanteffectson The PSFwasfinallytakenfromstarsinthenearby3C273field CLEAN andthePSFscaledby10%updowninsize,to while certainlyunresolvedenoughforameasurementofthe observed immediatelyafterM87.Testsweremadeusing more distantobject.Genuineglobularclustersinthefield, found byHuchraandBrodie(1984)atz=0.086,oraneven PSF, arealltoofaintforevenaparameterizeddetermination. is perhapsamemberofthebackgroundclustergalaxies est objectwithin1:2,atF=21,isresolvedthe0''5leveland bright stars(abovemagnitude21atV)nearM87.Thebright- cleaning tolessthan1%ofthejet’speakintensity,anduntil the totalfluxfoundbyCLEANconverged. suitable. Thisreduced“noise-locking”sufficientlytoallow a smoothingsizeclosetotheseeing-profileFWHMwasfound The ESOfaintobjectspectrographandcamera(EFOSC; It isimportanttoverifythattheobjectsstudiedareinfact The efficacyofthistechniquemaybejudgedfromFigure4 Evaluation ofaproperPSFwascomplicatedbythelack /) Spectroscopy Vol. 329 198 8ApJ. . .329. .532K Bottom, theCLEANedmodel,convolvedwitha0'.'4FWHMrestoringprofile. Veryfine-scalestructuresherearenotreliable,butoverallknotshapesandfluxesare. Keel (see329,536) PLATE 16 Fig. 4—ResultsofCLEANdeconvolutiontheM87jet,withBdata shownasanexample.Top,thegalaxy-subtractedjetimageandareferencestarimage. © American Astronomical Society •Provided bythe NASAAstrophysics Data System 198 8ApJ. . .329. .532K No. 2,1988 synchrotron radiation.Itsoverallopticalspectrumiscontin- region wereconductedattheKPNO4m,withaTICCDon ment ispossiblefromthesedata.Becauseofuncertaintiesin calibration usedthestandardstarsFeige56andLTT7987at able effectsonlyattheextremeblueendofspectrum.Flux weak incomparisonwiththenucleus,butatcorrectlevel continuum source.Theresiduallightatthejetpositionisquite were removedbyreflectingthespectrumaboutcentral similar zenithdistances. data itisclearthatemissioninlinesfrom6300to6800Ânot duration ataresolutionof2.5Awasobtained.Fromthese the Ritchey-Chrétienspectrograph.Anexposureof3000s the innerstrongknotandrestofjetispresented. the (large)scattered-lightcorrection,noseparationbetween continuum isconsistentwithdeterminationsfromimages,and whole jet,smoothed,isshowninFigure6.Theslopeofthe this jetisalsoa(pure)continuumsource. a significantcontributiontothejetfluxinthispassband,so uum sourcelongwardofabout6000Â,butnostrongerstate- tip (Danzigeretal1979;Keel1986)wasdetectedasacontin- no believablespectralfeaturesarepresent.Theredknotatthe obtained fromimageanalysis(Fig.5).Thespectrumofthe at thejetpositionby assumingsymmetryalongtheslit. The jetofM87haslongbeenknowntoshineprimarilyby Higher resolutionobservationsofthe3C66BjetinHa Scattered lightfromthenucleusandunderlyingstarlight Fig. 5.—EFOSCspectraofthenucleus andjetofPKS0521—36,shownonacommonscale.Scatterednuclear lightandgalaxybackgroundhavebeenremoved III. SPECTRALCHANGESALONGTHEM87JET © American Astronomical Society • Provided by the NASA Astrophysics Data System a) PreviousWork EXTRAGALACTIC RADIOJETS value. Thedifferencesamongspectralslopesdeterminedin (Pronik andShcherbalov1972;Sulentic,Arp,Lorre1979; §1114 make suchmeasurementsdifficult,ifpotentiallyimportant. ration inproducingtheobservedstructure(NietoandLelievre to thestrongbackgroundlightagainstwhichjetisseen. ture ofthejetandresultinginterplaywithresolutioneffects Warren-Smith, King,andScarrott1984).Thecomplexstruc- polarization ofindividualknots,orthejetasawhole radio, suggestingadominantroleformagneticfieldconfigu- the opticalmatchesthatseenwithsimilarresolutionin de VaucouleursandNieto1979;ArpLorre1976; which mustbesimilarforallpartsofthejetwhateveritsexact lengths between0.3and1.0pim(Kinman,Grasdalen, (Pronik, Pronik,andChuvaev1968;PerolaTarenghi clearly steeperthanthatobservedatcentimeterwavelengths and Leievre1982;LorreNieto1984).Themorphologyin sion betweenthem(deVaucouleurs,Angione,andFraser1968; small knots,withatmostweakevidenceforcontinuousemis- various wayshavebeenuncomfortablylarge,mostlikelydue Rieke 1974;Stocke,Rieke,andLebofsky1981;Keel1984), UV spectralshapeiscertainlyclosetoapowerlaw,but uous (BaadeandMinkowski1954;Sulentic,Arp,Lorre 1982; Shklovskii1984;KeelLorreandNietosee 1980). Aspectralbreakhasbeeninferredatvariouswave- 1956; Schmidt,Peterson,andBeaver1978).Theoptical 1979; Keel1984),andtheknotsshowhighpolarization(Baade There havebeenseveralreportsofvariabilityinfluxor The jetstructureatthe1"scaleisdominatedbyaseriesof 537 198 8ApJ. . .329. .532K in particular,justwhatistheshapeofopticalcontinuum, effort toresolvesomeofthediscrepanciesamongearlier an earlySpaceTelescopetarget,techniquesarenowavailable studies. allowing amoreprecisesetofmeasuresthanhithertoreported. and doesthischangealongthejet?WhileM87willcertainlybe Particular carewasgiventotheM87jetinthisstudy,an matches thatseenfrommulticolorimaging;nosignificantspectralfeaturesarepresent. many studies.AsmaybeseenfromFigure1,anyresidual evaluation ofhowaccuratelystarlighthasbeenremovedfrom atically exceed0.1%oftheoriginalintensitynearnucleus. galaxy lightnearthejetmustbeverysmall;itcannotsystem- the jet,whichhasbeenamajorpotentialsourceoferror in 538 Several importaatuncertaintiesremainfromthesestudies— Fig. 6.—EFOSCspectrumofthejetPKS0521—36,smoothedwitha125Ârectangularfilterandshownasfluxperunitfrequency.Thesteep continuum The galaxy-removalprocedureusedhereallowsadirect b) DeconvolvedImagesandKnotMeasurements © American Astronomical Society • Provided by the NASA Astrophysics Data System Fig. 7.—Contourdisplayofcleaned M87 jetdata,showingnomenclatureandsubdivisionsofknots NUC 1231212 ki, r-D—irEii-F-i 0 5 10 1520 I I I SCALE, ARCSEC KEEL pixels matchinginpositionandareaforeachimage.Themea- errors (i.e.,half-pixelpositionaluncertaintiesfromimage to from thejetknotsandoriginalbackgroundlevels,binning listed inTable5.TheerrorestimatesreflectPoissonerrors sured featuresareidentifiedinFigure7,andthemeasurements X(A) measured ineachimagebyintegrationovertheregions of (the sameonescouldbeseenineachpassband),andfluxes between theresults(Fig.4)andFigure1ofBiretta,Owen, complexity issupportedbythedata.Thecloseresemblance ing, sotheCLEANapproachdescribedin§liewasadopted. (Biretta, Owen,andHardee1983)suggestedthatmodeling Hardee indicatesthatthereconstructionisaccurate. This isinessenceamodelingproceduredriventowhatever with asmallsetofsymmetriccomponentswouldbemislead- Features inthejetwereidentifiedfromopticalimages The complexityoftheradiostructureseenathighresolution Vol. 329 198 8ApJ. . .329. .532K the best-fittingtruncatedsynchrotron spectra,asinTable7. with indicationofthelevelsexpectedbyextrapolation nearly powerlaws.ThepresentdataareplottedinFigure8, 0'.'4 resolutionmapprovidedbyF.Owen. image). Similarmeasurementsarealsolistedat6cm,froma No. 2,1988 Fig. 8.—Spectraofindividualknots intheM87jet.Thecurvesrepresent As foundbyotherworkers(§Ilia),thespectraareallvery ^ 0.5- o ■4— + o o o c r* © American Astronomical Society • Provided by the NASA Astrophysics Data System 1.0 - 14.5 15.0 \ X T ,v \ \ \ '\ \ Log 1/(Hz) Total “Tail” . D d D Dj C A Fx E e Ei B' B F F N \ 3 2 2 2 \ '\ Errors areinunitsofthefinalsignificantfigurelisted. Feature \ (Jy) Knot Spectra 9 \ \ M87 Jet C D B E X T EXTRAGALACTIC RADIOJETS Optical FluxesofFeaturesintheM87Jet 0.056 ±2 0.025 ±1 0.053 ±2 0.30 ±1 0.08 ±1 0.44 +2 0.96 ±4 0.069 ±3 0.124 ±4 0.027 ±1 0.097 ±4 0.065 ±2 0.019 ±1 0.100 ±3 0.022 ±1 1.96 B 0.40 +2 0.07 ±1 0.074 ±2 0.136 ±4 0.032 ±2 0.104 ±10 0.073 ±2 0.032 ±1 0.040+ 1 0.121 +2 0.028 ±1 0.057 ±3 0.036 ±3 0.59 ±2 2.40 1.08 ±3 TABLE 5 losses ortotangledfieldstructurewhichconstrainsthe par- ration atUandBbyLorreNieto(1984)impliesamatch of have beensetfortheknotAregion,whichimageresto- ticles tomorenearlyclosedpaths.Themoststringentlimits ating electronsactuallystreamfreely,eitherduetoradiative 0"3 correspondsto30pc.The synchrotronlifetimeforpar- match ofthejetstructure(knotpositions,sizes,shapes)as seen possible differentiallifetimeeffect. Foradistanceof20Mpc, especially theinnerknots(D-I). Theirstructure,throughout 2 cmand0.4¿anstructureatthe0"2level.Thepresentwork at variouswavelengthssetsstronglimitsonhowfartheradi- resolution of0"4,so0"3isa conservativeupperlimittoany the opticalrange,matches that at2cmaneffective extends thisconclusion,atlower resolution,tothewholejet, which returntotheslopeseennearnucleus.Onlyhigh- (optical) jet,withbreaksinthistrendbeingknotsAandE, published values. weightings alongthejetmayaccountforpartofscatter in range reportedintheliteratureforentirejet;different about Aa=0.3goingfromthenucleustotipof tion ofdistancefromthenucleus.Theopticalindexsteepensby spectral index(ignoringcurvaturefornow)isplottedasafunc- along thejet.ThisisshowninFig.9,whichmeanoptical knots arenotexactlyidentical—theresignificantchanges spectra; severalshowcurvatureintheoptical. radio continua.Allknotshavesteeperopticalthan regions atdifferentlocationsinthejet. are differencesintheparticlepopulationsofotherwisesimilar (position withinthesource)propertiesofjetmaterial.There connection betweenlocal(particle-acceleration)andglobal local fieldstrengthischanging.Itis,inanycase,evidenceofa models (§V)indicatesthatthisisachangeincutofffrequency energy partofthespectrumchanges;low-frequencyindex, of themostenergeticelectrons,soeithertheirenergyor determined between6cmand0.8¿un,isintherange —0.65 ±0.02foralltheknots.Comparisonwithsynchrotron As hasbeennotedbyseveralworkers(§Ilia),theclose The opticalspectral-indexchangesalongthejetbracket A newresultofthisanalysisisthatthespectravarious Flux (mJy) 0.039 ±4 0.112 +3 0.182 ±2 0.050 ±1 0.132 ±2 0.081 ±4 0.035 ±3 0.045 ±1 0.127 ±5 0.029 ±1 0.060 ±3 0.45 ±2 0.06 ±1 0.74 +6 2.81 1.25 ±3 (0.182) ±3 0.104 ±1 0.210 ±2 0.046 ±1 0.164 ±2 0.092 ±1 0.032 ±1 0.060 ±1 0.040 ±1 0.097 ±2 0.59 ±2 0.06+1 0.80 +2 3.42 1.48 ±4 c) OpticalStructure 6 cm(Jy) (0.49) 0.84: 0.27 0.13 0.22 5.82 1.20 1.44 1.72 539 198 8ApJ. . .329. .532K 4 15 gyroradius) oftheseelectronstothefieldstructure. field. measuring characteristicscales forstructureinthemagnetic alternative isunlikely,duetothestrongcoupling(small radiating volumebeforelosingmostoftheirenergy.Thelast geneous onsmallscalesthatparticlescanactuallyescapethe lines forsuchdistances,orthatthefieldstrengthissoinhomo- regions issotangledthattheparticlescannotmoveinstraight emitting particles’streamingdistance(lifetimexsinpitch angle xc)belessthan30pc,thatthefieldindetected show whetheranydifferential-lifetime effectsarepresent,thus particles withintheknots.Space Telescopeobservationsmay be requiredtoremovetheneed formagneticchannelingof assumed, butunrealistically large fields(~0.05gauss)would gests typicalfieldstrengthsafewtimeshigherthanpreviously Owen andP.E.Hardee,privatecommunication)clearly sug- small-scale structuredominatingtheradioemission(F. N. lines, butnotthoseseenintheradio.Thepresenceof very for astreaminglengthof30pc.Thusthehighestenergy par- factor 0.01.Thisimpliesalifetimeforthehighestenergy par- example, £(eq)=5x10~gaussforknotD,withafilling ticles might(just)befreetomovelinearlyalongsmooth field ticles seenoptically(v~10Hz)ofslightlyunder100 yr, partition fieldintensityÆ(eq)onradiatingvolumegives, for actually radiating.Evenso,theweakdependenceofequi- rather high,withonlyafewpercentoftheenclosedjetvolume factor ~400.Theobservationsrequireeitherthattheradio- responsible forradiationat6cmandtheBbanddifferbya for vinHzandBgauss.Thelifetimeofparticlesmainly is (followingTucker1975) tides radiatingwithapeakfrequencyvinaneffectivefieldB peak 540 ± ± The 2cmdatasuggestthattheequipartitionfieldmaybe O O o Q. -0.5 - -1.0 - © American Astronomical Society • Provided by the NASA Astrophysics Data System Fig. 9.—MeanopticalspectralindexaasfunctionofpositionalongtheM87jet.Locationsknotcomplexesaremarked. optical 12,3/ T= 10v~Bs(2) ± T 1 Knots: 4 81216 DISTANCE FROMNUCLEUS,ARCSEC J- -L T 1r——T KEEL X spectrum. important inspecifyingthefull behaviorofthesynchrotron might beexpected,giventhe problemofscatteredlightfrom the brilliantnucleus.Observations farthertotheUVwillbe imaging resultsinFigure10. Theagreementisasclose frequency asisseeninM87;thismaywellbe,sincethesense of the gradientanditsamplitudearesimilarinbothcases. yet sufficienttoshowwhetherthisrepresentsashiftinturnover index alongthejet,butopticaldatabythemselvesare not listed inTable6.Thereisagradient2cm-0.4/xmspectral the jetatB,V,and2cm;estimatedtotalfluxIis also be madefortheknot,basedonitsfractionalcontribution to the knot1'.'6fromcore.Anapproximatecorrectioncould reason, thenew/measurementpertainsonlytojetoutside earlier analysis(Keel1986),asGRASPdoesnotmodelade- source, whenrelativelylargepixelsareused.Forthesame quately thestronggradientsfoundnearaverybrightpoint discrete break(Fig.10).ThelistedBandVvaluesarefrom steepening perhapsbetterdescribedasaturnoverthan the newdatawiththosepreviouslypublishedshowsagradual has eitheraspectralbreakorcontinuousturnover.Merging that theopticalcontinuumissteep(a=—2near5000Â)and observations (Keel1986;CayatteandSol1987)haveshown that inM87,thoughbothlargerandmoreluminous.Optical detected. marized inTable6.Notesarealsogivenforobjectsnot described individuallyhere,andthemeasurementssum- NGC 6251.—Theradiojet in thisgalaxyiswell-studied, The spectroscopicdataareplottedalongwithbroad-band PKS 0521—36.—Thejetstructurehereiscomparableto Several additionaljetsweredetectedinthisstudy;theseare X A B IV. OTHERJETS:INTEGRATEDPROPERTIES X Optical SpectralIndex a) NewMeasurements M87 Jet 20 Vol. 329 198 8ApJ. . .329. .532K No. 2,1988 (Saunders etal.1981;Perley,Bridle,andWillis1984).Optical preserves aconelikeenvelopeoftypicalopeningangle3° counterjet isseen(Jonesetal.1986).Themainjetknotty,but projected rangeof1pctoMpc,forH=100).Aweak being nearlystraightonscalesfrom2masto5arcmin(a possibly duetoacentralmassconcentration(Youngetal. fluxes andcontinuumslopecomparabletothoseexpected by The emissionmatchestheradioknotinsizeandhasoptical observations haveshowna“lightcusp”similartothatinM87, shown byPerley,Bridle,andWillis(1984),asseeninFigure 2. B, V,andRatthepositionofstrongestfeatureinmap (1985) indicatedthattwoopticalemissionregionsarepresent investigations byMileyetal.(1981)andvanBreugel al. emission withaknotintheradiojetwasnotedbyGoodson, shape (seeTable6andFig.10)isagainsteeperthanseen in analogy withotheropticallydetectedjets.Thecontinuum implies thatthecontinuumis primarily ofsynchrotronorigin. in thejet,withbothcontinuumandlineemission;polarization M87, perhapsindicatingalowerfrequencyspectralturnover. between continuumandemission-line peaks,withahintthat area (Fig.2);itisnotcompletely clearwhetheroneortwo Palimaka, andBridle(1979).Moredetailedradiooptical the emission-lineknotsarelarger. optical knotsarepresent.These datashowaslightoffset 1979), andevidenceforasmall-scaledustlane(Nietoetal. 1983). Nocleardetectionofthejethasbeenreported. 0 The datatakenhereallowtherecognitionofexcesslightin The continuumemissionhere isconcentratedintoasmall Coma A=3C277.3.—Thepossiblecoincidenceofoptical © American Astronomical Society • Provided by the NASA Astrophysics Data System are takentobeintherangeof5%-7%unlessotherwisenoted. NGC 6251 3C 273. 3C 303 Coma A 3C 66B PKS 0521-36. Notes.—A isintheobjects’emittedframe. Magnitudes areasobserved,withoutgalacticreddeningcorrection;fluxdensitieshavebeencorrected.Photometricerrors (hot spot) (outer) (inner) (both knots) (hot spot) (brightest knot) Object Band K R R R R R R B B B B B B B B V V V V V V V V I I I I I I EXTRAGALACTIC RADIOJETS 0.73 0.73 0.59 0.49 0.39 0.73 0.59 0.49 0.39 0.79 0.48 0.39 0.83 0.59 0.50 0.41 0.68 0.56 0.45 0.61 0.51 0.41 0.67 0.55 0.44 0.77 0.55 0.43 2.03 143 ^0.3: 44.2 26 21.5 35.9 36 86 60 38 19.0 13.5 11.1 16.5 14.9 18 16 +6 13 13.6 Integrated JetFluxes /v(^Jy) 9.5 9.1 9.6 6.6 6.1 5.5 ±0.5 8.0 3.5 1.7 ±0.5 1.1 TABLEÓ ^25.6 Magnitude for themeasurementsbyvanBreugeletal.(1985).Theassump- extended two-sidedstructure, withastrong(knotty)jettothe includes a2.2/mimeasurementfromUKIRTkindlycommu- emission; theVfluxisthusofrelativelylowweight. The 0.95, 0.65,0.45,and1.0(atB,V,R,I)tocorrectfor line not thecontinuum)aremoreextendedthanaperturesused between thetwoasdefinedbyMouldfilters,atabout relatively clean,sincetheHaand[Nn]linesfallingap line fallsclosetothecenterofpassband;Rand/are tron radiation.Thepresent results areinaccordwiththis gested fromtheB-to-radioratio thatthisrepresentssynchro- reported byButcher,vanBreugel, andMiley(1980),whosug- northeast. Thestrongestknot appears2"5fromthecore. and theVLA(Leahy,Jägers,Pooley1986)showvery optical centroid. two radioknotswithdifferentspectralindices,verycloseto the tion oftheoverallspectrumiscomplicatedbypresence of nicated byP.Allan,takenwitha7"aperture.Theinterpreta- steeper thanseenintheradio(vanBreugeletal.1985).Table 6 remaining continuumisclosetoapowerlaw,somewhat On thesegrounds,themeasuredfluxeshavebeenmultiplied by tion wasmadethatthe[Om]andHastructuresaresimilar. emission isespeciallylarge,sinceatz=0.086the[Om]5007 ed byvanBreugeletal.(1985).TheVbandcontributionofline Optical detectionofseveral of theknotsinBbandwas 7125 Â.TheA7146imageindicatesthattheemissionlines(but Ha -h[Nn]imageandviatheemission-linestrengthspresent- 21.74 20.50 21.12 21.43 20.66 21.51 21.24 21.06 21.91 22.25 21.43 22.5 23.8 ±0.4 20.58 20.9 21.01 23.83 21.38 20.62 21.28 20.16 19.58 19.94 19.51 19.35 19.81 18.63 3C bbB.—RadiomapsfromWesterbork(vanBreugel1982) The presenceofemissionlineswascorrectedbothbythe r =17':2-21?6 r =21"6-23"4 From P.Allan Includes 40%assumedknotcontribution Strong emissionlines From Keel1986 From Keel1986 12'.'0-17:2 Notes 541 198 8ApJ. . .329. .532K spectra, thefitsareonlyapproximatebecausefinite-passbandeffectscanbecome important. law, buttheradiofluxlevelclearly impliesaninterveningturn- over. maps. ThetotalVmagnitudeofthisfeatureisabout22.0. The three datapointsareinternally consistentwithasinglepower sion intoknots.Theoptical spectral indexisa=—2.38;the fluxes inTable6andFigure10 refertothewholejetfrom2" diffuse regionisfoundpartiallyprojectedagainstthejet,from clear detectionoftheinnermostknot,thoughjetis well unclear; thereisnocorrespondingstructureinpublishedradio 6"5 to12"5Eand2''68'.'5Nofthenucleus.Itsnature is seen fartherout(Fig.2).Inallthreebands,anadditional, is steeperthantheradio,andfluxlevelindicatesthat a turnover hasoccurredinthenear-infrared. interpretation, andsimilartootherjets;theopticalcontinuum 10" fromthenucleus;theseimages donotallowacleardivi- 542 Fig. 10.—Integratedspectralenergydistributionsoffivejetsandthe3C303hotspot,withbest-fittruncatedsynchrotronmodels(Table7).For thesteepest The coarsescaleofthe3C66Bimagesheredoesnotallow a © American Astronomical Society • Provided by the NASA Astrophysics Data System Log v(Hz),EmittedFrame KEEL jet :theradiohotspot,seenonly longwardofRwithaturnover continuing theradiospectrum.Thisisincontrasttositu- and hotspotimages. seeing forthisframeresulted in significantoverlapoftheQSO and Meisenheimer1987).No R measurementisgiven,aspoor ation injetsproper,andmorelikethecasePictorA(Röser elongation alongthelinetowardnucleus(Fig.3). The Meisenheimer (1986)identify three distinctpartsoftheoptical optical slopeofthespectrumisquiteflat(a=—0.6),neatly spot itselfisresolved,inthesamesenseasradiostructure— object, aQSOatz=1.57.Theopticalcounterpartofthe hot strong emissionfeatures.ThefieldcontainsanotherUV-excess al (1977),whofoundtheopticalspectrumtobedevoid of optical objectcoincidentwitharadiohotspotbyKronberg et 3C 273.—Frommulticolor photopolarimetry, Röserand 3C 303.—Thisdistantradiogalaxywasreportedtoshowan Vol. 329 1988ApJ. . .329. .532K -1 _1 13 coincident withtheinnerradioknots,butroleofextinction (Giles 1986),opticalknotsdoappearthatareapproximately makes identificationofanyopticalcounterparttotheinner emission, butlackofaframeinthenearbycontinuummakes lation plusdust. excess whichtheyinterpretasasynchrotroncontinuumwith a ization nearthestrongestknots.Theyalsoreportacontinuum largely duetostructuresintheinterveningdust.Optical variations ishardtoevaluate;theapparentknotscould be to confirm.Iftheradiocoreisidentifiedwith2.2/unpeak knots ofthejet(Burns,Feigelson,andSchreier1983)difficult and Price1981).Thepatchydustlanecrossingthenucleus excess correspondingtoa25007equivalentwidth(observed)of with thecontinuumshapegivenbyWyckoffetal,suggestsan extended thanthis.Itsbrightnessinthe[Om]image,coupled (1983). Thepresentimagesindicatethattheobjecthasmoder- matching radiopeak. fairly constantspectralindexandevidenceforX-raysfromthe de Vaucouleursprofilefittedto theregionoutsidedustlane dust lane,Ihavesearchedfor thenorthernjetwhereitcomes break, buttheirspectralbreakistoosharpforanypossible and Bowyer(1983),whofoundemissionlinesofpeculiar ion- spectra oftheseregionshavebeenreportedbyBrodie,Königl, outer jetofCenA,5-10'fromthenucleus(see,e.g.,Graham this veryuncertain. about 30Â.Thefeaturetothesouthmayhaveevenstronger Wyckoff etal,usinga3"x4"slit;itmaythusbemore radio lobeissomewhatbrighter(B=20.67)thanmeasuredby 17]). TheBimageindicatesthattheopticalcounterpartto additional emission-linestructuretothesouth(Fig.11[PI. the spectralrangeexaminedbyWyckoffetal),andshows ately strongredshifted[Om]5007emission(justattheedgeof the regionofthisz=0.4quasar’sjetorlobebyWyckoffetal by contrast,seemsmorelikesomeotherradiohotspots,witha by HayesandSadun(1987),addtotheevidencethat dominated byadifferent,unspecifiedmechanism. (shape closetov),asshowninFigure10.Thespectralfits light atB(andperhapsV)superposedonareddercontinuum out frombehindthedustlane. Thestarlightwasmodeledasa synchrotron featureandislikely duetoamixedstellarpopu- same powerlaw(Willingale1981).Note,however,itslackofa objects, withastrongcutoffinthenear-IR.Theopticalknot, radio hotspotalonebehavesmuchlikejetemissioninother object whichhavenotyetbeenfoundinotheropticaljets.The additional optical-radiationmechanismsareactiveinthis and Meisenheimer,therecentlypublishedmeasurements shown accountonlyforthisreddercontinuum;thebluelightis steeply fallingspectrumwhilebothjetregionsshowexcess minimum inBandV17"2fromthecore.Thetipshowsa colors arealsopresent. close tov;anda“plateau”inwardofthisinwhichan frequency ~7x10Hz;anearbyopticalknotwithspectrum “ inner”andouterregionsofthejetitself,dividedatalocal spatial components:averyredtip(theradiohotspot)and tron continuum)mustbepresent.Smallextensionsofvarious unpolarized component(thusadditionaltotheradiosynchro- No. 2,1988 To avoidtheuncertaintiesassociated withstructureinthe NGC 5128.—Emission-linestructureiswellknowninthe The resultshereareinreasonableaccordwiththoseofRöser PKS 0812+02.—Opticalemissionhasbeenreportedfrom These dataalsosuggestadivisionoftheopticaljetintothree © American Astronomical Society • Provided by the NASA Astrophysics Data System b) Nondetections EXTRAGALACTIC RADIOJETS 2 if suchadiscretefeatureispresent, maybeobscureforrealisti- expressions andfunctionaltabulations givenbyGinzburgand monoenergetic synchrotron spectrum, usingtheasymptotic electron distributionshavingcutoffstowardhighenergies of mates oftheirphysicalproperties. inversion oftheobservedspectrumrequiresaccurateobserva- amplitude,” becausetheinterpretation ofaspectralbreak,even observations ismoreusefulthan tryingtomeasurea“break several forms,byconvolvingthesedistributionswith the aid incomparingdifferentobjectsandprovidingrough esti- I willpresentfitstosimple,highlyparameterizedmodels,as an tions overanextremelywidefrequencyrange,onlyavailable Syrovatskii (1965).Directcomparison ofthesespectrawiththe tral featuresregardlessoftheelectronenergyspectrum,direct some, butnotall,hotspotswithopticalcounterparts. and remainunseensofar.Thistypeofturnoverisalsoseen in to beobservingopticalsynchrotronradiation.Notethatmany comparisons aretakenfromtheirwork. was foundclosertothecore.Parametersforhotspotin mag arcsec,implyinga<—0.98forpointlikeknotsinthejet, for suchobjectsastheCrabNebula(Craigetal.1985).Hence, objects couldshowalowerfrequencyturnover,intheinfrared, the spectrum,orturnover,isseenineveryjetwhichweseem other jetsthatarenotsowellresolved,astrongsteepeningof western hotspot(RöserandMeisenheimer1987),noemission GHz. limits donotplacestrongconstraintsonthespectralshapes, companion. Noemissionwasseeninthejet,asmappedby may bepresentinthemoredistanthotspots(Crane,Tyson, emission mightbeseen5"-15"fromthecore.While respectively, forsmallcondensationsinthejet,fromBto2.7 due tothelowradiosurfacebrightness:a<—0.81and—0.77, sources (CornwellandPerley1982;Fantietal.1982).No or a<—0.78iftheyareresolvedatthepublishedbeamsize. and Saslaw1983),nonewasseenfromthejetitself. shows abrightjettothesouth,strongenoughthatoptical sufficiently rarethatnosuitableonehasbeenobserved.These this respectfrommoreone-sidedones,orwhethertheyare source ;itisnotyetclearwhetherthesesourcesaredistinctin optical emissionhasyetbeenseeninanyhighlysymmetric Birkinshaw, Laing,andPeacock(1981),toalevelR=24.8 fixing theisophotecentersinthisobject.Anyjetemissionmust be afactor~4fainterthanthatin3C66B. lane complicatestheanalysis,butitseffectswerelocalizedby (1980) reportedfaintopticalemissionfromtheinnerpartof nucleus. Thisisnotconfirmedinthepresentdata.Thedust northern jet,nearthedustlanewhichcrossesjustnorthof distorted extendedstructure(Fomalontetal.1980;van (taking theparametersfromDufouretal.1979),andsub- Breugel andJägers1982).Butcher,vanBreugel,Miley at distances47"-160"fromthenucleus. tracted toseekresidualemissionfromthejet.Nonewasfound Optically thinsynchrotronspectrahavebeengeneratedfor As seeninthedatadiscussed§IIIforM87,andIV 3C 449andB21321+31.—Thesearesymmetrictwin-jet Since synchrotronspectrashowonlyverybroad-bandspec- Pictor A.—Whilethereisastrongopticalcounterpartto 3C 296.—ThissourceissituatedinanellipticalwithSO 3C 31.—Theradiosourceshowstwinjetsandsomewhat V. OPTICALSYNCHROTRONTURNOVERSANDHIGH-ENERGY 3C 219.—TheradiomappresentedbyPerleyetal.(1980) PARTICLES INJETS 543 198 8ApJ. . .329. .532K the NWandS,butinbothcasesasubstantialfractionmaybelineemission. Keel {see329,543) Fig. 11.—Imagesinredshifted[Om]25007{left)andtheblue(line-free) continuum{right)ofthez=0.4QSOPKS0812+02.Extendedstructureisapparentto © American Astronomical Society •Provided bythe NASAAstrophysics Data System X7007 [on] BLUE 8 ^ *.4»'Wy-'%>*><*v/1*3*?.«4*V«: PKS 0812+02 PLATE 17 198 8ApJ. .,329. .532K 544 cally complexsources(Pacholczyk1975),andinanycasethe modes ofenergyloss.Thisapproachgivesanestimatethe broken powerlawswithdifferentamplitudes,sincetheoretical changing characteristicfrequency,thanawholegroupof data donotnecessarilyimplybrokenpower-lawforms.Itis instantaneous electrondistribution,regardlessofthehistory breaks havedistinctvaluescorrespondingtovariousdominant also simplertosupposeacommonspectralshape,withsingle individual particles,implicitlyassumingthatthejetsareclose to asteadystateininternalenergybalance. Ay/y =0(sharp),0.5,and1. A synchrotronspectrumisimpressivelyindifferenttothe Fig. 12.—Synchrotronspectraforelectrondistributionswithlinearlyrampingcutoffsofapowerlaw,cutoffwidthsrelativetothehighest energiesof © American Astronomical Society • Provided by the NASA Astrophysics Data System Coma A NGC 6251 3C 33hotspot.. 3C 273hotspot 3C66B M87D 3C 273outerjet 3C 273innerjet 3C 273plateau. Pictor A 3C 303 PKS 0521—36. Notes- C A B F E Object =asymptoticlow-frequencyspectral index.v=cutofffrequencyinthegalaxy’sframe. r c Synchrotron ModelsforOpticallyDetectedJetsandHotSpots -0.64 -0.8: -0.7 -0.65 -0.7 -0.69 -0.63 -0.64 -0.64 -0.66 -0.8: -0.6 -0.6 -0.4 -0.60 -0.60 -0.65 15 15 15 15 14 1.0 x10: >3 x10 >5 x10 >5 x10 <2 x10 2.5 ±0.5x 9.1 ±1.0x 2.0 ±0.5x 7.7 ±1.4x 2.6 ±0.3x 2.5 ±0.3x 8.1 ±1.7x 3.0 ±1.0x 3.1 ±0.5x 7.7 ±1.1x 1.2 ±0.1x 1.6 ±0.4x TABLE 7 KEEL 14 14 15 15 15 14 14 14 14 14 14 14 10 10 10 10 10 10 10 10 10 10 10 10 154 from thosedescribingtheshapeofcutoff:itseffectivefre- factor 3,isalmostindistinguishablefromacompletelysharp in Figure12.Afairlygradualenergycutoff,uptoabouta details ofanenergycutoffintheradiatingparticles,asshown Table 7.Inallcases,thecriticalcutofffrequencyisbelowabout been fixedaccordinglyineachcase. quency andthelow-frequencyspectralindex.Thelatteriswell specified fromradiodatafortheobjectsinthissampleandhas one. Thereareinfacttwofreeparametersthesemodelsaside 10 Hz,probablycorrespondingtoy~inatypicaljet. The best-fitspectrausingasharpenergycutoffaregivenin This work;additionalbluelightpresent This work;additionalbluelightpresent Röser andMeisenheimer1986 Röser andMeisenheimer1987 Meisenheimer andRöser1986 Röser andMeisenheimer1986;this work Notes Vol. 329 198 8ApJ. . .329. .532K 14 3/2 10 jets arenotlarge. weak foropticaldetection.Twohotspots,inPictorAand3C Values belowabout2x10Hzwouldresultinradiationtoo large. Thesharpnessoftheobservedcutoffssuggeststhatgra- teristic inparticularoftheradiatingparticleskiloparsec- erating particlestothisenergy,orinretainingthemthe close topowerlaws,andsomustthelow-energyelectron dients inDopplerfactoralonewithinthebrightpartsofthese Doppler effects,ifthebulkmotionofradiatingmatteris scale jets.Notethattheobservedvaluesmaybemodifiedby optical range.Themaximumfrequency(energy)isthencharac- case, theM87jetshowsthatrelevantparameterschange with the(re)accelerationprocessitself,orstructureof radiating region.Thisscalemightthusbeassociatedeither that acharacteristicorlimitingscalehasbeenreachedinaccel- spectra be,onenaturalinterpretationoftheobservedcutoffsis 303, doshowspectrawithoutadiscernableturnoverinthe very smallorthinregions,suchasthesurfaceofjet.Asa the magneticfieldandparticledistributioninjet.Ineither No. 2,1988 cutoff inwhichthedistributionismultipliedbyafactor(1- energies thatwouldotherwisebeproducedhasasuperposed This processwillproduceacutoffinwhichthedistributionof entire systemwilldominatethepopulationattheseenergies. every particlereachinghighenergies,lossestothe becomes alargefractionofL,asitwillduringthelifetime being accelerated(andradiating)onlywhilewithintheslab simple example,considerparticlesinaslabofthicknessL suggests thattheparticlesradiate(orareaccelerated)onlyin only slightly,thoughsystematically,alongthejet. emission certainlycomesfromregionswithfine-scalestructure, constant* y),wheretheconstantisrelatedtoL.Thelength (zero fieldoutside).Whenthegyroradiusr=mcyvJeB cutoff, mostlyresultingfromsynchrotron-lossscalesrather formed byHeavensandMeisenheimer(1987)exhibitasharp calculations ofspectrafromparticlesacceleratedinshocksper- ation process.Similarly,thissuggestsapointatwhichthe or moretangledfilaments. and perhapsfromverythinlyconfinedregions,asathinsheath or thicknessLisquitesmallforhomogeneousconditions,only models. enough toreproducetheseresultsforjetsandwasinfact first than specificphysicalprocesses.Thiscutoffiscertainlysharp resulting energydistributionbreaksdown.Forexample,the scale-free characterimpliedbythepower-lawformof 5 x10cminM87.Ifthisisevenroughlyapplicable,the applied tothe3C273hotspot(MeisenheimerandHeavens the observedfrequencyrange,foraclassofshock-acceleration 1986). BiermannandStrittmatter(1987)predictsuchcutoffs, in measured formostoftheobjects inTable1.Severalofthesehavenopublishedsurfacephotometry, sotheseresultsarepresentedin g profile. Asanaidinevaluating thiscontribution,starshavebeenmeasuredinasmanycases aspossible(onlyforComaAwasthere et al(1985).Thelogarithmic sample spacingresultsinvastlydifferentinfluencesofthe seeing profileatvariouspartsofthegalaxy this Appendix. If thescalegivingcutoffisduetojetstructure,it Since thelowerfrequencyspectraoftheseobjectsareso An alternativepicturehasthecutoffintrinsictoacceler- As aby-productofthegalaxy modelingandsubtractiondescribedin§lie,newsurface-brightness andshapeprofileshavebeen As describedearlier,theisophotes werefittedbyfamiliesofellipses,usingtheGRASPsoftware essentiallyasdescribedbyDavis © American Astronomical Society • Provided by the NASA Astrophysics Data System SURFACE PHOTOMETRYOFRADIOGALAXIES EXTRAGALACTIC RADIOJETS APPENDIX A. 5 1 14 compatible withareprocessing(Compton)originforthe X-rays, forthelocalphysicalconditionsbelievedtoobtainin The relativefluxlevelsinthevariousregimesdonotseem the jet(Schreier,Gorenstein,andFeigelson1982). same regionastheradioandopticalsynchrotronemission. itself suggestsaseparatesourceiftheX-raysinfactarise lie aboveanextrapolationofthe/£/£measurements;thisin lated, athigherenergies.TheM87X-raymeasurementsinfact Cen A(Feigelsonetal1981;Burns,Feigelson,andSchreier the jetsinM87(Schreier,Gorenstein,andFeigelson1982) dominant populationofelectrons.DetectionX-raysfrom model inwhichtheelectronenergydistributionissharply extragalactic radiojets.Inallcases,thespectrumshowsa law. Theturnoversarewellfittedbyasimplesynchrotron the spectralenergydistributionsincontinuaofanumber the M87jetatsub-arcsecondscales,andtoseparatevarious truncated, typicallyaty~10. strong turnoverbelowtheextrapolatedlow-frequencypower for theaccelerationorradiatingregionsinjets,whichmaybe level, suggestingmagneticconstraintsonparticlemotion broken onlybyunusuallyhighvaluesforknotsAandE.The atic dropinturnoverfrequencygoingoutwardalongthejet, structures forspectral-indexmeasurements.Thereisasystem- extremely small,^lOcm,andmayprobeveryfine-scale violated byhotspots.Thisscale,naivelyestimated,is scales ~30pc. optical andradiostructuresareeverywherethesameat0'.'3 exploitation ofallthenecessarysoftware.DonHamilton,Bob Jaffe, MarijnFranx,andMarcodeVosmadepossiblethe Will, W.Binkert,andP.Ugarteatseveraltelescopes.Walter all observedhotspots.Thismayreflectacharacteristicscale 7 x10Hzseemtobeubiquitousamongradiojets,butnot comparison. IacknowledgehelpfuldiscussionswithFrazer in certainseasons.FrazerOwen,RickPerley,AlanBridle, and Argyle, andRudolfLePooleobtainedimagesonmybehalfat structures injets. 1983) mayimplyaseparatepopulation,moresparselypopu- Guy Pooleyprovidedradiomapsofseveralobjectsfordetailed Kitt PeakandLaPalma,whenIcouldnevergetclearweather Hamel forpreparingthefiguresinTucson. Coma A.IthankMyrnaCook,GlennPickens,andJoyce Du Allan providedhisunpublishedinfraredmeasurements of Owen, PhilHardee,RobertLaing,andVincentIcke.Peter Note thattheseargumentsdealonlywiththeoptically Optical imagesinseveralpassbandshavebeenusedtostudy Image restorationhasbeenusedtoexaminethestructureof I amgratefulforthesupportandassistanceprovidedbyG. Energy cutoffscorrespondingtofrequencieslessthan VI. 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