Integral field spectroscopy of the radio galaxy 3C 171

Integral field spectroscopy of the radio galaxy 3C 171

A&Amanuscriptno.

(willbeinsertedbyhandlater)

ASTRONOMY

AND

ASTROPHYSICS

arXiv:astro-ph/0007016v1 3 Jul 2000

1.Introduction

Anumberofradiogalaxiesandquasarsatvariousred-shiftsexhibitlineemissionfromionizedgasuptoseveraltensorevenhundredsofkiloparcsecsfromthenucleus.Theexistenceofsuchgaseousenvelopesismostprobablylinkedtotheformationofgalaxiesandactivenuclei.Con-versely,theexistenceofanactivenucleusin uencesthephysicalconditionsofthegas,itskinematics,andstarformationinthehostgalaxy.However,illuminationofthegasbytheultravioletradiationemittedbytheactive

Integral field spectroscopy of the radio galaxy 3C 171

2I.M´arquezetal.:Integral eldspectroscopyoftheradiogalaxy3C171.

longslitspectraalongtheradioaxis(PA=102)C98have

shownevidenceforshocksinducedbyjet-cloudinterac-tions:closeradio/opticalassociation,ionizationminimaalmostcoincidentwithbothradiohotspots,highveloc-itylinesplittingspatiallyassociatedwiththetwoinnerhotspots,largelinewidthsintheexternalgasandanti-correlationbetweenlinewidthandionizationstateintheexternalgas.

Inthispaperwepresent2Dspectroscopicdataon3C171,whichallowustospatiallyanalyselineratiosandkinematicsand,usedtogetherwithradioimages,tointer-pretthemintermsofanimportantcontributionofshocksintheregionsclosetoradiohotspots,asinthescenarioreportedbyC98.Thedataarepresented

in

Section

2,

the

morphology

andexcitationoftheionizedgasarestudiedinSection3,thekinematicsinSection4andthediscussionandconclusionsinSections5and6.2.Thedata

3C171wasobservedonFebruary7-9,1995duringatotalexposuretimeof4hoursand13minuteswiththeTIGERinstrumentatthe3.60mCanadaFranceHawaiitelescope.Individualexposureswereo setfromoneanotherintheEast-Westdirectioninordertocovercompletelytheob-ject.Airmasseswerebetween1.2and1.3.ThegrismusedwasR300,givingaspectralresolutionof6.9 AFWHM

inaspectralintervalcontainingtheHeII46861

,Hβand[OIII]4959-5007lines,correspondingtoavelocityresolu-tionof350kms 1at6200 A.Thespatialsamplingwas0.39arcsecandeachindividual eldabout7×7arcsec2;theseeingwas0.9arcsecFWHM.Thetotalspatialcover-ageisabout9×4arcsec2.ReferencesforafulldescriptionoftheTIGERinstrumentandofthedatareductionmeth-odsforthiskindofobjectcanbefoundinDurretetal.(1994).

The rststepsofthedatareduction(fromspectraextractiontowavelengthcalibration)stronglydependontheinstrumentopticsandwerethusperformedwiththeTIGERdataprocessingsoftware.Thefollowingstages(cosmicrayremoval,photometriccalibration,exposuremerging,imagereconstruction)wereachievedusingtheXOasisdatareductionpackage,dedicatedtotheCFHTintegral eldspectrographOASIS.Thealgorithmsofthisnewpackageareindeedmorepowerfulthanthepreviousones,especiallyforcosmicremovalandexposuremerging.Thereadercan ndacompletedescriptionofthispack-ageintheXOasisusermanualathttp://www-obs.univ-lyon1.fr/～oasis/reduc/reduc

frames.html.WealsomakeuseoftheHSTimage(twoexposuresof300stakenbytheWFPC2withtheredF702W lterretrievedfromthearchive,realignedandsummed)pub-lishedbyKo etal.(1996).

Integral field spectroscopy of the radio galaxy 3C 171

I.M´arquezetal.:Integral eldspectroscopyoftheradiogalaxy3C171.

3

Fig.2.ContoursoftheHβemissionreconstructedfrom

theTIGERdata,withthefollowingvalues:0.03,0.05,0.1,0.15,0.2,0.25,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1,1.1,1.2,1.4(10 19Wm 2

).

Fig.4.[OIII]contoursoverHSTimage( lterF702W).Thedot-dashedlinejoinsthetworadiohotspots.samepositionastheeasternradiohotspot.A lamentary-likefeatureisalsoobservedtotheWestofthenucleus,correspondingtoourWestblobbutthistimenotexactlyalignedwiththeradioemission.

AsshowninSection4,thespectraobtainedinsomeregionsclearlyindicatelinesplitting,withatleasttwocomponentsshowingdi erentexcitationsandkinematicalbehaviours:oneabout3arcsectotheWestandanotherone2.5arcsectotheEast.Twoandthreecomponentsarenecessaryto tthespectraintheformerandlatterregionsrespectively;however,thesignaltonoiseratio(S/N)isnothighenoughtoallowtheindividual ttingofeachspectrum.ThesetworegionsarealsomarkedinFig.1withcrosses.Wehavereconstructedtwoemissionlineimagesinordertoseparateeachoftheblueandredcomponentsof[OIII]andHβintheregionclosetoW1.TheyareshowninFigs.5and6.Westressthatthepeakat2.5arcsectotheEastinFig.5islocatedintheregionwherethreecomponentsarepresent.Whilethemorphologyofthebluecomponentisquitesimilarfor[OIII]andHβ,theredcomponentsarenotablydi erent,withemissionpeaksshiftedbyabout2arcsec,correspondingtoregionsW1andW2,respectively.

Wehavecomputed[OIII]/Hβratiosfortheblueandredcomponents,rejectingthespectrawheretheS/NforHβissmallerthan1.5.TheresultingimagesaredisplayedinFig.7.Itcanbenoticedthat,forthebluecomponent,theregionsofhighestexcitationarelocatedalmostsym-metricallywithrespecttothenucleusat≈1arcsecinadirectionalmostperpendicular(PA=124)tothatoftheelongationofthecentralisophotesinFig.5(PA=64).Therearetwolocalmaxima,onewith[OIII]/Hβ=5cor-respondingtothe3 componentregion,andanotheronewith[OIII]/Hβ=6placedat( 2, 1)arcsec.Fortheredcomponent,thehighestexcitationisreachedintheregionclosesttothecenteroftheradiogalaxy,withdecreasingvaluestowardstheoutskirts.

InordertohaveahighenoughS/NratioforHβtobeableto t[OIII]andHβwithoutconstrainingtheirredshiftstobethesame,wehave lteredourdata-cubes

Fig.3.Surfacebrightnesspro leobtainedfromthecon-tinuumimage.The tbyadeVaucouleurslawisdisplayedasasolidline.

closertotheradiohotspot.WewillrefertoitasregionW2.

Wehavealsoextractedthecontinuumimage,recon-structedbyintegratingthewholewavelengthrangeafterapolynomial ttothecontinuum.Itonlyshowsthecentralspotwhichisslightlyresolved(FWHM≈1.3arcsec).We tellipsestothecontoursand

obtainedtheresultingsur-facebrightnesspro leshowninFig.3.Ar1/4law ttingresultsinascalelength(e ectiveradius)of4.8arcsec,i.e.,15kpc,atypicalvalueforanellipticalgalaxy.

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