19 64Apj. . .139. .7815 No. 2, 1964 LETTERS to the EDITOR 781

19 64ApJ. . .139. .7815 focus spectrographofthe 200-inchtelescopewithadispersionof400Â/mm inNovem- be representedtowithin afewAngstroms(Table2)ontheassumptionthat theyare ber, 1963,showedemission linesatXX3986,4885,and5510.Thesewavelengths could object ofvisualmagnitude18;thisisnotably blueontheplatesofNational ferometric dataon3C47(Maltby1962;Allen, Anderson, Conway,Palmer,Reddish, distribution withaxesof1''9bylessthan1"(Rowson 1963). of thefluxandacore4"diameter.Alternatively, thesourcemaybeadoublewith and Rosen1962)showthatitmayhaveahaloof 2'indiametercontaining75percent tion 2''4,eachcomponentbeingsmallerthan1",but apossiblealternativeisanelliptical component separationofabout70".Thesource3C 147isprobablyadoublewithsepara- Geographic Society-PalomarObservatorySkySurvey. Spectratakenwiththeprime- interferometer intheOwensValley.ThedeclinationshavebeenpublishedbyRead position determinationscarriedoutwiththeCaliforniaInstituteofTechnologytwin the fluxdensityat400Mc/sandspectralindex (Kellermann1963).Existinginter- o 3C 47: 3C 147: (1963), thepositionofopticalobjectin3C147 by Griffin(1963).Thetablealsogives sources giveninTable1weredeterminedthecourseofanextensiveprogram 3C 47and147asquasi-stellarobjectswithlargeredshifts.Thepositionsoftheradio Lenouvel, F.1957,1.A.U.SymposiumNo.J,ed.G.Herbig(Cambridge:CambridgeUniversityPress), Walker, M.F.1957,1.A.XJ.SymposiumNo.3,ed.G.Herbig(Cambridge:CambridgeUniversityPress), Kraft, R.P.1958,Ap./.,127,625. light variationsaslarge0.5magnitudeshavepreviouslybeenrecordedinTCrB No. 2,1964LETTERSTOTHEEDITOR781 Deutsch, A.J.1948,Pub.A.S.P.,60,123. of AEAqrandSSCygand,ingeneral,tosuchdwarfvariableshasbeennoted(Kraft 1958). VerysimilardisturbanceshavebeenobservedinAEAqr(Lenouvel1957)and (Walker 1957). Opt. Opt Radio Radio © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The positionoftheradiosource3C47practically coincideswiththatofastarlike The purposeofthisletteristocommunicatetheidentificationsradiosources p. 35. p 46. U.S. NavalObservatory Source Flagstaff Station January 8,1964 hm 05 38435+01 05 38441+05 01 33398+02 013340?6± 1?0 REDSHIFTS OFTHEQUASI-STELLARRADIO a(1950) Observed Datafor3C47and147 SOURCES 3C47AND147 o, REFERENCES +49 4943±1 +49 4939±3 +20 4211±3 +204156"±8' TABLE 1 5(1950) 10-26 Wm-2(c/s)~i 46 3+2 5(400 Mc/s) 12 9+05 Philip A.Ianna 0 56+06 0 89+04 19 64ApJ. . .139. .7815 plates inDecember,1963,didshowthelineat7136À,aswellfainter,^of plates atthewavelengthofinterest.Abroadbandemissionobservedaround6200Â lines ofMgn,[Nev],andm],witharedshifts=(X—Xo)/Xo0.425.Onthis optical luminositiesconsiderablylargerthanthoseofthebrightestgalaxies. measured. is ablendofH7andtheX4363line[0m].Thewidthsotherlinesareabout basis theNilineof[0m]wouldbeexpectedat7135Â.Twospectrataken,on103a-U Hß, respectively.Theintensityratioofthelines doesnotfavorthisexplanation:the object wassuspectedtobeagalaxyrelatedwiththeradiosource.Aspectrumin faint stars,ofvisualmagnitudesabout18,19,and20.Atfirstthetwentieth-magnitude and 3C48(GreensteinMatthews1963).Theseobjectsofstellarappearancehave clearly belongstotheclassofquasi-stellarradiosources,suchas3C273(Schmidt1963) 3C47 becomes1275Mpc,anditsabsolutevisualmagnitudeabout—23.Thisobject about threetimesfainterthantheoneatX3426,issuspectedonofplates.The [O m].ThefactthatHßwasnotdetectedmustbeduetothelowspeedofbothFandU available spectraweresearched forotherlinesatthewavelengthspredicted onthe line isusuallymuchfainter, andneverbrighter,thanHßinplanetary nebulae. All plates andmostprobablydonotexist.Variability inthelinesthatdoexisthasnotbeen blue withtheslitacrossitandeighteenth-magnitudeobjecttakeninOctober,1962, 20 Â.TheX3727lineof[011]isquiteweak.3346[Nev],whichshouldbe 782 LETTERSTOTHEEDITORVol.139 line at5760Âistwotothree timesstrongerthantheoneat5976À;however, theHe11 identified withemissionlinesoftenseeninplanetary nebulae,radiogalaxies,andquasi- sion featuresaredeterminedbyasmallnumber ofgrainsintheunwidenedspectra. in wavelengthandintensity;asaconsequence,considerablenumberofspectra,mostly appeared tohaveunusuallyhighbrightnessintheultravioletrelativethat showed noemissionlinesinthefainterobject.Thespectrumofbrighterobject stellar objects.If0=0.229thelineswouldbeidentified withtheX4686lineofHe11and confirmed. with adispersionof400Â/mm,wastakenthis object.Theweak,low-contrastemis- near 5800Â.Thefirstspectraseemedtoindicatethattheemissionfeatureswerevariable blue. Spectratakensubsequentlyinthevisualregionshowedseveralemissionfeatures given inTable3.Therearetwovaluesoftheredshift zforwhichthesetwolinescanbe 5976 Â.Thewidthofthelinesisabout30Allindividual measuresofwavelengthsare Some oftheweakemissionlinesoriginallysuspected havenotbeenfoundonsubsequent X3968 lineof[Nein]isseenquiteweakly,asexpected;itswavelengthhasnotbeen o e l © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The positionoftheradiosource3C147isclosetothatacompactgroupthree Two emissionlinesexistwithoutanydoubt.Their observedwavelengthsare5760and With aHubbleconstantHof100km/secperMpcthenominaldistanceczH~ 4885 3986 5310 6200 5510 7136 7072 Wavelengths andIdentificationsof Ht, [OIII] Mg II [Ne III] [O HI] [O III] [On] [NeV] Identif Emission Linesin3C47 TABLE 2 4959 4340,4363 3426 3727 2798 3869 5007 Xo 4882 3987 5312 5513 7066 6185, 6217 7135 1 425Xo 19 64ApJ. . .139. .7815 11 7 l line. Thecombinedevidencemakestheabovevalueforredshiftquiteunattractive. basis oftheaboveredshift.Nonewerefound,notablynotthose[Om]and[Nev] No. 2,1964LETTERSTOTHEEDITOR783 uncertain, thesmallrangeinmeasuredwavelengthsandfactthatfivefeatures fied withtheX3727lineof[0n]and3869[Nem],respectively.Asearchfor that arealwaysseeninhigh-excitationplanetariosandradiogalaxiesshowtheHen of afeaturenear4840Âontwoplates(cf.Table3).Thewavelengthstheseemissions other linestobeexpectedonthebasisofthisredshiftwasmoderatelysuccessful.The O in,respectively.Althoughtherealityoftheseemissionsoneachindividualplateis correspond closelytothatoftheX3426line[Nev]and3133 certain measurementsweremadeofanemissionfeaturenear5290Âonfourplates,and frequency of10c/s.Theloweremittedcutoff wasassumedtobe10c/s X 3968lineof[Nem]couldbefoundnear6130Âonfourexposures.Individuallyun- about —25,wherewehavecorrectedfor1 magnitudeabsorptionintheGalaxy responding nominaldistanceczH~of1635Mpcyields anabsolutevisualmagnitudeof redshift z=0.545isindeedcorrect.Thisthelargestonedeterminedsofar, detected arethosethatstrongestintherelevantrangeofwavelengthsplane- unless statedotherwiseinTable4.Themajor uncertainty inthecalculatedradio radio sourceontheassumptionthatitisindeeddouble. Theradioluminositieshavebeen collected inTable4.The“size”givenistheseparation ofthetwocomponents exceeding thatof3C295(0.461,Minkowski1960)byabout20percent.Thecor- tary nebulaNGC7027(Aller,Bowen,andWilson1963)leavelittledoubtthatthe luminosities comesfromtheuncertaintyin upper cutofffrequencies.Bothlumi- computed byintegrationofthepowerlawfor fluxdensitytoanassumedemitted with zerocosmologicalconstant anddecelerationparametergo=0(Sandage 1961). nosities andlinearsizeshavebeencomputedon the basisofanevolvingworldmodel that ofthemostpowerful radiogalaxiesCygA,Herand3C295.The quasi-stellar (Sandage 1964). © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The alternatevalueoftheredshiftis0.545,onwhichbasistwolinesareidenti- Redshifts arenowavailableforfourquasi-stellar radio sources.Themainresultsare All foursourcesareseen to haveverylargeradioluminosities,ofthesame orderas N 1818(1) Identif. Mean X Ao 1 545Xo 2132 1854(1) 1852.. 1882 1879 1858 1856 1860 Plate No (2) (2) (3) Individually MeasuredWavelengthsandIdentifications 4836 4843: 4839: 4840 3133 O III of EmissionLinesin3C147 5291: 5296: 5287 3426 5288: 5290: 5293 [Nev] TABLE 3 Wavelength (Â) 5762: 5760 3727 5759 5758 5762 5757 5763 5762 5762 5755 5754: 5760 5761 5759 [O II] 5981 5976 5976 5976 5975 5972 5980 3869 5978 5970 5975 5976 5977 [Ne ill] 3968 6137 6136 6126: 6127 6132 6130 [Ne III] 784 LETTERS TO THE EDITOR Vol. 139

source 3C 147 has the largest radio luminosity, 2 X 1045 erg/sec, equal to that of the intrinsically brightest radio galaxy, 3C 295. The radio spectrum of 3C 147 shows marked curvature at the low-frequency end (Conway, Kellermann, and Long 1963). The total optical luminosities of the objects depend to a large extent on the bolometric correction. They probably range roughly from 1045 to 1046 erg/sec, and are for each source larger than the radio luminosity. Sandage has measured the colors of all these objects and will discuss them shortly. The source 3C 47 is the weakest member of the group, both in radio output and in optical luminosity; it also has the largest radio size and might be the oldest member of the group. In addition it has a straight spectrum at low frequencies, unlike the other quasi-stellar sources. The optical flux for 3C 47 falls on or above a straight-line extrap- olation of the unusually steep radio spectrum. This is quite different from the other quasi-stellar objects for which the optical flux is well below the straight-line extrapola- tion (Matthews and Sandage 1963). TABLE 4 Data for Four Quasi-Stellar Radio Sources with Known Redshifts

L (Radio)* “Size” Source Mv (Radio) (erg/sec) (kpc) 3C 47 0 425 -23 1 5X1044 250 3C 48. 367 -25 4 7X1044 < 3 3C 147 545 -25 2 0X1045 10 3C 273 0 158 -26 3 1X1044 40

* Computed by integration between emitted frequencies of 107 c/s and 10u c/s, except for the following lower limits of observed frequency: 108 c/s for 3C 48, 5 X 107 c/s for 3C 147, 109 c/s for component B of 3C 273 The optical spectra of these four quasi-stellar objects vary more among themselves than those of radio galaxies (Schmidt 1964). The X 3727 line of [O n] is prominent in 3C 48 and 3C 147, weak in 3C 47, probably absent in 3C 273. The X 2798 doublet of Mg ii first found in 3C 273 is also prominent in 3C 48, clearly present in 3C 47, but weak or absent in 3C 147. These differences are presumably due to variations in ioniza- tion, excitation, electron temperature and density (Greenstein and Schmidt 1964). A practical consequence is that the redshift of a quasi-stellar object cannot be determined with reasonable certainty from a single emission line only. For that reason an attempt by Shklovsky (1963) to determine the redshift of the quasi-stellar radio source 3C 286 from a single emission line (Schmidt 1962) must be considered premature until at least one other emission feature has been detected and identified.

One of us (M. S.) wishes to thank Dr. I. S. Bowen for a valuable discussion. The other (T. A. M.) has conducted this investigation under the program of research in radio astron- omy at the California Institute of Technology which is supported by the United States Office of Naval Research under contract Nonr 220(19). Maarten Schmidt Thomas A. Matthews February 28, 1964 Mount Wilson and Palomar Observatories Carnegie Institution oe Washington California Institute of Technology and Owens Valley Radio Observatory California Institute of Technology

REFERENCES Allen, L. R , Anderson, B , Conwav, R G , Palmer, H. P., Reddish, V. C., and Rosen, B. 1962, M.N., 124, 477. Aller, L. H , Bowen, I S , and Wilson, O. C 1963, Ap. J., 138,1013. Conway, R. G., Kellermann, K. I., and Long, R. J. 1963, M.N., 125, 261. Greenstein, J. L., and Matthews, T A 1963, Nature, 197, 1041 Greenstein, J. L , and Schmidt, M 1964, to be published. Griffin, R. G. 1963, AJ , 68, 421 Kellermann, K. I 1963, thesis, Cahfornia Institute of Technology. Maltby, P 1962, Ap J. Suppl , 7,124. Matthews, T. A., and Sandage, A R. 1963, Ap. J , 138, 30 Minkowski, R. 1960, Ap /., 132,908. Read, R B. 1963, Ap. J , 138, 1. Rowson, B. 1963, M.N , 125, 177. Sandage, A. R. 1961, Ap J , 133, 355 . 1964, private communication Schmidt, M. 1962, Ap J., 136, 684. —. 1963, Nature, 197, 1040. 1964, in preparation. Shklovsky, I S. 1963, Astr. Cire U S.S R , No 250.