The near-infrared spectrum of Mrk 1239: direct evidence of the dusty torus?

0.24 MB·English

by  A. Rodriguez-Ardila

Mon.Not.R.Astron.Soc.000,1–5(AcceptedtoMNRASLetters,2006) Printed5February2008 (MNLATEXstylefilev2.2)
The near-infrared spectrum of Mrk 1239: direct evidence of the
dusty torus?
A. Rodr´ıguez-Ardila1⋆ and X. Mazzalay2
1Laborato´rioNacionaldeAstrof´ısica/MCT,RuadosEstadosUnidos154,CEP37500-000,Itajuba´,MG,Brazil.E-mail:[email protected]
6 2IATE,ObservatorioAstrono´micoCo´rdoba,Laprida854,X5000BGR,Co´rdoba,Argentina.E-mail:[email protected]
0
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2

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ABSTRACT
5 Wereport0.8−4.5µmSpeXspectroscopyofthenarrow-lineSeyfert1galaxyMrk1239.The
1
spectrumisoutstandingbecausethenuclearcontinuumemissioninthenear-infraredisdom-

inatedbyastrongbumpofemissionpeakingat2.2µm,withastrengthnotreportedbeforein
1
anAGN.AcomparisonoftheMrk1239spectrumtothatofArk564allowedustoconclude
v
thatthecontinuumisstronglyreddenedbyE(B-V)=0.54.Theexcessofemission,confirmed
3
1 byaperturephotometryandadditionalNIRspectroscopy,followsa simpleblackbodycurve
3 atT∼1200K.Thissuggestthatwemaybeobservingdirectevidenceofdustheatednearto
1 the sublimationtemperature,likely producedby the putativetorusof the unificationmodel.
0 Althoughotheralternativesarealsoplausible,thelackofstarformation,thestrongpolariza-
6 tionandlowextinctionderivedfortheemissionlinessupportthescenariowherethehotdust
0 islocatedbetweenthenarrowlineregionandthebroadlineregion.
/
h
Key words: galaxies:Seyfert – galaxies:individual:Mrk 1239 – galaxies:active – galax-
p
ies:nuclei
-
o
r
t
s
a
1 INTRODUCTION theNIRbump,confirmingthatitfollowsasimpleblackbodyfunc-
:
v tionatT=1200K.Theyfoundthatthehostdustemissionaccounted
i Unifiedschemesofactivegalacticnuclei(AGN)invokethepres-
X forupto28%ofthetotalNIRcontinuumfluxinthatobject.
enceofanobscuringdustytorusaroundthecentralengine,giving
Fromabove,thegrowingobservationalevidenceofNIRther-
r rise to type 1 objects for for pole-on viewing and type 2 objects
a malemissionattemperaturesclosetothesublimationtemperature
inedges-onsources.Thisobscuringstructurewouldalsoabsorbsa
ofgraphitegrainsinSeyfert1galaxiesstronglysupportstheunified
significantfractionoftheoptical/UV/X-raycontinuumofthecen-
modelsfor AGNs.Meanwhile, additional evidence isneeded and
tralsourceandshouldradiatebackthisenergyatIRwavelengths.
manyopenquestionshavetobeanswered.Inparticular,itisneces-
Infact,dustreprocessing isregardedasthemostlikelysourceof
sarytoinvestigateifthethermalemissioncouldberelatedtoacom-
thestrongnear-andmid-infrared(NIRandMIR,respectively)con-
pactdust/molecularthicktorusliketheonesintheunifiedmodels
tinuum emission in radio-quiet quasars and Seyfert galaxies. Ob-
ofPier&Krolik(1992)andEfstathiou&Rowan-Robinson(1995),
servational evidence favoring models in which the IR continuum
forinstance,orifitresultsfromemissionbyhotdust(T>900K)
between 1 and 10 µm ispredominantly or entirely dominated by
mixedwithgasintheNLR/BLRinterfaceregion,shieldedfromthe
emission from heated dust is abundant (Edelson&Malkan 1986;
intenseUVradiationfield(Marco&Alloin2000).
Barvainis 1987; Alonso-Herreroetal. 2003). Indeed, evidence of
the presence of hot dust near the sublimation temperature in Here,wecontributetothisdiscussionbypresentingthemost
Seyfert1galaxiescomesfromtheobservationofapeakofemission outstanding evidence of a NIR bump reported to date. It corre-
with central wavelength between 2.2−3.5 µm found from JHKL spondstotheonedisplayedbyMrk1239,acompactgalaxy,clas-
and L’ photometry (Glass 1992; Marco&Alloin 1998, 2000) in sified as narrow-line Seyfert 1 (NLS1) by Osterbrock&Pogge
a few objects. Moreover, very recently, Rodr´ıguez-Ardilaetal. (1985).DatacollectedoverthepastyearspointoutthatMrk1239
(2005) found in the inner 250 pc of Mrk 766, a narrow-line isindeeddusty.Goodrich(1989),forinstance,reportsthatitisone
Seyfert 1 galaxy, this same excess of emission by means of NIR ofthethreegalaxiesthatdisplaythelargestpercentageofpolariza-
spectroscopy. Theywereabletodetermineaccuratelytheformof tion,bothinthelineandcontinuum,inthesampleof18NLS1he
studied.Smithetal.(2004)modeledthepolarizationnatureofthis
objectandfoundthatitwasoneoftherarecasesofSeyfert1galax-
⋆ VisitingAstronomerattheInfraredTelescopeFacility,whichisoperated iesthatappeartobedominatedbyscatteringinanextendedregion
bytheUniversityofHawaiiunderCooperativeAgreementno.NCC5-538 alongthepolesofthetorus.Accordingtotheirresults,theline-of-
withtheNationalAeronauticsandSpaceAdministration, OfficeofSpace sighttothenucleuswouldpassthroughtherelativelytenousupper
Science,PlanetaryAstronomyProgram. layersofthetorus,extinguishingthecontinuumandBLRemission.
2 A. Rodr´ıguez-Ardilaand X. Mazzalay
ingdominatedbytheunresolvedemissionfromtheAGN.Thedata
reduction, extraction and calibration procedures were done using
12
thein-housesoftwareSpextool(Cushingetal.2004)andXtellcor
10 (Vaccaetal.2003),providedbytheIRTFObservatory.Thespectra
intheSXDandLXDsettings,observedonconsecutivenights,were
8 mergedtoformasingle0.8−4.9µmspectrum.Theagreementin
thecontinuumlevelintheoverlappingregionwasexcellent,with
6
lessthan5%ofuncertainty.TheSXDspectraobtainedinOctober
2003 alsoagreed, within10%of uncertainty, withthecontinuum
4
levelmeasuredintheobservationtakenin2002.
Figure1showthefinalNIRspectraofMrk1239intherest-
2
frameoftheobject.Intheregionswheretheatmospherictransmis-
0 siondrops tozero, astraight linewasinterpolated toconnect the
10000 20000 30000 40000 50000
adjacentbands.ItcanbeseenthattheNIRspectrumisdominated
by a strong bump of emission, peaking at 22000 A˚, also present
Figure 1. Observed NIR spectra of Mrk 1239 in the rest-frame of the intheOctober24,2003observation.Alsoprominentinthespectra
galaxy. Thespectrum taken onOctober 24has been offset by2×10−15 areemissionlinesofHI,HeIand[SIII].Noabsorptionlinesthat
ergcm−2s−1A˚−1relativetothatofApril21forvisualizationpurposes. mayindicatethepresenceofcircumnuclearstellarpopulationwere
The most important permitted and forbidden lines are marked. Note the detected.Sincethemainfocusofthisworkisthecontinuumemis-
strongexcessofemissionpresentinbothspectra,startingat10000A˚,with sion,theanalysisofthelinespectraisleftforafuturepublication.
peakat22000A˚. Toourknowledge,theonlyNIRspectroscopyavailableintheliter-
atureonthissourceistheJandKspectraofHeisler&DeRobertis
(1999).Becauseof thenon-photometric conditionsinwhichthey
Thisradiation, would bepolarized further offby thedust located
weretaken,thereisalackofcontinuityinthecontinuumlevelbe-
aboveorbelowthetorus.
tween the bands, preventing us to make any meaningful compar-
X-rays observations also confirm the dusty nature of
ison. However, inFig.2gof Heisler&DeRobertis(1999),theJ
Mrk 1239. XMM-Newton EPIC PN data suggest two light paths
continuumrisestowardlongerwavelengths.IntheK-band,itcon-
betweenthecontinuumsourceandtheobserver,oneindirectscat-
tinuesrisingupto2.2µm,whereitseemstobecomeflat,inaccor-
teredone,whichislessabsorbed,andahighlyabsorbeddirectlight
dancetoourobservations.
path, in agreement to the wavelength-dependent degree of polar-
InadditiontotheNIRdata,long-slitopticalspectroscopyon
ization in the optical/UV. Moreover, Mrk 1239 is classified as a
Mrk1239wasobtained onthenightsof March19and20, 2002,
60µmpeaker(Heisler&DeRobertis1999)becauseofits“warm”
withtheCassegrainspectrographattachedtothe2.15mtelescope
far-infrared colours and spectral energy distribution peaking near
oftheCASLEOObservatory,Argentina.Thespectracoverthein-
60 µm. They attributed these properties to dust-obscured active
terval3700–9600 A˚ andwereobtainedwitha2′′ slitwidthanda
galactic nuclei (Keeletal. 1994; Hesetal. 1995), the obscuring
300 l/mmgrating. Theextraction and reduction process followed
materiallikelyassociatedtotheputativetorusoftheunifiedmodel.
thestandardIRAFprocedure.AsintheNIRregion,thelightpro-
Thisletter isorganized asfollows. In Section2wedescribe
filedistributionofthegalaxyisdominatedbytheunresolvedemis-
theobservations,datareductionandresultingspectrum.Section3
sionoftheAGN.Theaimoftheopticaldataistocomplementthe
determines the internal reddening affecting the nuclear spectrum
NIR spectrum to map the optical-NIR continuum of this source.
of Mrk 1239 and compares the observed NIR SED with that of
Nosignificant variation (less than 5%) in the level of the contin-
Ark564.Italsoanalyzesthedifferentcomponentsthatcontribute
uumemissionwasdetectedintheoverlappingregionbetweenthe
totheobservedcontinuum.Section4examinesthehotdusthypoth-
opticalandNIRspectra(0.8−0.95µm).
esisforMrk1239inthelightofthestrongthermalNIRexcessof
emission detected. Conclusions areinSection5. Throughout this
workweadoptaHubbleconstantofH =75kms−1Mpc−1.
o
3 THEINTERNALEXTINCTIONINMRK1239AND
THECONTINUUMEMISSION
2 OBSERVATIONS,DATAREDUCTIONANDRESULTS
InordertoproperlyinterpretthestrongexcessofNIRemissionin
NIR spectra of Mrk 1239 in the intervals 0.8−2.4 µm and Mrk1239,itisfirstnecessarytode-reddenitsoptical-NIRcontin-
2.0−4.9µm(hereafterSXDandLXD,respectively)wereobtained uum. To this purpose, we used as reference, the spectrum of the
attheNASA3mInfraredTelescopeFacility(IRTF)withtheSpeX NLS1galaxyArk564,whosecontinuumemissioniswellknown
spectrograph (Rayneretal. 2003), atop Mauna Kea, on April 21, and we assumed as typical of a NLS1 galaxy. Flux-calibrated
2002 (UT) and October 24, 2003 (UT) for the SXD data and on FOS HST spectra in the optical region and SpeX IRTF spectra
April22,2002(UT)fortheLXDspectrum.Thedetectorconsisted (Continietal.2003)wereemployed.
of a 1024×1024 ALADDIN 3 InSb array with a spatial scale of We started by derreddening the Ark 564 data by Galac-
0.15′′/pixel. A 0.8′′×15′′ slit, oriented east-west, was used dur- tic (E(B-V)=0.03) and internal extinction (E(B-V)=0.14), as
ing the observations. The spectral resolution was 360 kms−1 at determined by Crenshawetal. (2002). The reddening law of
bothsetups.Thetotalon-sourceexposuretimesamountto1900s Cardellietal.(1989)withRV=3.1wasusedtothispurpose.Then,
and1200sfortheApril21and22,2002,and1200sfortheSXD assuming that the form and slope of the extinction-corrected op-
observation of October 24, 2003. The signal within the central tical continuum in Ark 564 represents the intrinsic continuum of
0.8′′×1′′ (1′′=380pc)wassummeduptoobtainthenuclearspec- Mrk1239,wede-reddenedtheobservedspectraofthelatterobject
trum.Thelightdistributionofthegalaxywasfoundtobecuspy,be- (alreadycorrectedbyaGalacticE(B-V)of0.065)insmallsteeps
Thenear-infraredspectrumof Mrk1239 3
fromdustgrains.ThefactthatArk564displaysalowpercentage
20 ofpolarization(Goodrich1989)bothinlineandcontinuum,indi-
catesthatthedustcontentintheBLRofthisobjectissmall(also
confirmedbythesmallvalueofintrinsicextinction).Itmeansthat
in Ark 564 we are observing the true near-infrared shape of the
bigbluebumpcomponent,whichuptodateisessentiallyunknown
15 (Kishimotoetal.2005).
3.1 ThecomponentsoftheNIRcontinuumemissionin
Mrk1239
10
The continuum emission displayed by Mrk1239 in the interval
0.8−4.9µmiscomplexandratherdifferentfromtheonedisplayed
byotherNLS1galaxies(seeforexample,theNIRspectraofother
AGN presented by Rodr´ıguez-Ardilaetal. 2002). A comparison
withthecontinuumofArk564is,infact,striking.
5
In order to characterize the NIR continuum emission in
Mrk1239, we used, as reference, the much simpler optical-NIR
continuumofArk564. Tothispurpose, acompositefunctionde-
scribedbythesumoftwopower-lawsoftheformF ∝ λα was
λ
0 fittedtothedatausingthetasknfit1doftheSTSDASpackage of
10000 20000 30000 40000 50000
IRAF.Thiscompositefunctionwaschosenbecauseitwasclearthat
a single power-law cannot reproduce the optical-NIR continuum.
Specialcarewastakentonotincludeemissionlinesinthespectral
Figure2.Comparisonoftheoptical-NIRspectrumofMrk1239,afterbeing
derreddenedbyE(B-V)=0.54,withthatofArk564.Theboxintheupper windowsusedinthefit.TheresultsareshowninFigure2.Thede-
rightcornershowsazoomintheopticalregionofbothgalaxies.Thecon- rivedspectralindicesareαopt =−1.93andαNIR =−0.2forthe
tinuumemissionofthelatterobjectwasmodeledintermsofasumoftwo opticalandNIRregions,respectively. FromFigure2,weseethat
powerlaws(dashedline):onethatdominatestheopticalregion(dot-dashed thiscompositefunctioncannotdescribethecontinuumemissionin
line) and another that dominates the NIR (dotted line). Note the lack of the1−4µmregionofMrk1239.Thestrongexcessofemissionthat
significantNIRexcessofemissioninArk564. risesabovethelevelpredictedbytheopticalplusNIRpower-laws
indicatesthenecessityofanadditionalcomponent.
Aninspectiontotheoverallshapeofthebumpsuggeststhat
untiltheformofitsopticalcontinuummatchesthatofformer.An itapproachesthatofablackbodydistribution.Inordertotestthis
E(B-V)=0.54magwasnecessaryandwastakenastheintrinsicred- hypothesis,wefittedacompositefunction−twopower-laws,plus
deningofMrk1239.Thisvalueisinexcellentagreementtotheone aPlanckcurve,totheobservedoptical-NIRSED.Additionalcon-
predicted by the polar scattering region scenario (E(B-V)>0.36) straints to the fit was imposed by adding photometric points for
proposed by Smithetal. (2004) if that mechanism becomes the theL (3.5µm) andN (10.5 µm) bands, taken fromthe literature
dominant source of polarization. Note that had we used the NIR (Spinoglioetal.1995;Maiolinoetal.1995).Inthefit,thepower-
HI line ratios to determine the extinction, we would have ob- lawindiceswereconstrainedtothevaluesfoundforArk564(see
tainedzeroextinction.ThemeasuredBγfluxis2.76±0.20×10−14 above)whilethetemperatureandamplitudeoftheblackbodyfunc-
ergcm−2s−1whilethatofPaβis1.91±0.1×10−13ergcm−2s−1. tionwereleftasfreeparameters.Theresults,displayedinFigure3,
Thus,theratioBγ/Paβequals0.14±0.01,somewhatlowerthanthe show that acomposite function, withablackbody oftemperature
intrinsicCaseBvalue (0.17). Thisapparent inconsistency can be T =1210 K, provides an excellent description to the the excess
bb
explainedifNIRBLRhydrogenlinesstronglydeviatesfromCase ofemissionover thepower-laws.Itshould benotedherethatthe
Bduetocollisionalandradiationtransfereffects,asitthecasefor use of blackbody instead of a greybody is preferred because of
theopticallines. thesmallernumberoffreeparametersthattheformerfunctionre-
Figure 2 shows the extinction corrected spectrum of quieres.Intheabsenceofobservationalconstraintsthatjustifiesthe
Mrk 1239. It can be seen that after dereddening, the optical con- useofamorecomplexfunction,theychoiceisfortheonethatof-
tinuum of Mrk 1239 has the same steepness as that of Ark 564. fersanadequatesolutionwiththeminimumnumberofparameters
Notethebroadbumpofemissionstartingat∼1µm,withpeakat tofit.SeealsoSect.4
22000A˚.ItdominatestheNIRcontinuumdistributioninMrk1239 What is the origin of each of the three continuum compo-
butisabsentinArk564. nents,allemittedintheinner380pcoftheAGN?Weassociatethe
Figure 2 also shows that at ∼ 1 µm there is a break in the power-lawthatdominatestheopticalregiontothelong-wavelength
steepnessofthecontinuum.IftheUV-opticalcontinuumiswellde- side of the UV/optical continuum component, often called the
scribedbytheapower-lawoftheformF ∝λα,theextrapolation big blue bump (BBB), thought to be emitted from an accretion
λ
ofthisfunctiontotheNIRregionlacksofenoughpowertoexplain diskaroundasupermassiveblackhole(Malkan1983;Zhengetal.
theNIRcontinuumemission.InArk564, forinstance,wherethe 1997; Constantin&Shields 2003). The NIR power-law is likely
strongbumpofemissionisnotobserved,anadditionalpowerlaw associated to the blue-end tail of the much broader infrared ex-
is necessary in order to reproduce the NIR SED. If we consider cessthatdominatestheIRSEDofAGN,usuallyattributedtocold
thecontinuumofArk564astypicalforaNLS1galaxy,thebreak dust (T ∼40-80 K), warmer than dust in normal spiral galaxies
representstheendofthelongwavelengthsideofthecontinuumat- (Edelson&Malkan1986),withpeakemissionat60µm,andob-
tributedtothecentralengineandtheonsetofthethermalemission servedinMrk1239(Heisler&DeRobertis1999).
4 A. Rodr´ıguez-Ardilaand X. Mazzalay
Table1.MassesofhotdustfoundinAGNs
20
Galaxy Mass(M⊙) Reference
Mrk1239 2.7×10−2 Thiswork
NGC7469 5.2×10−2 Marco&Alloin1998
15 Fairall9 2.0×10−2 Claveletal.1989
NGC3783 2.5×10−3 Glass1992
Mrk766 2.1×10−3 Rodr´ıguez-Ardilaetal.2005
NGC1566 7.0×10−4 Baribaudetal.1992
10
and higher than the sublimation temperature of silicate grains
(T∼1000 K; Granato&Danese 1994). Considering that our spa-
tial resolution islimited to∼380 pc, it is very likely that dust at
5 higher temperatures exists closer to thecentral source, ruling out
the possibility of silicates as the main component of the nuclear
dustgrains.
Using the temperature of the blackbody as the average tem-
peratureof thegraphitegrains and aK band fluxof 5.93×10−25
0 erg s−1 cm−2 Hz−1 at 2.2µm found for the blackbody compo-
10000 100000
nent after subtracting the underlying composite power-laws, we
can roughly estimate the dust mass associated with the bump.
Figure3.Intrinsicoptical,NIRandMIRSEDofMrk1239.Thefullcircles Following Barvainis (1987), the infrared spectral luminosity, in
areaperturephotometry.IntheJHKbands,theyweretakenfrom2MASS. ergs s−1 Hz−1, of an individual graphite grain is Lgr =
ν,ir
FortheLandNregion,theyweretakenfromtheliterature(seetext).The 4π a2 πQνBν(Tgr),where a isthegrain radius, Qν = qirνγ is
dotted-dashed and the dotted curves are the optical and NIR power-law
functions,respectively,foundforArk564.Thedashedcurveistheblack- theabsorption efficiencyof thegrainsandBν(Tgr) isthePlanck
bodydistributionofTbb=1210KthatbestreproducestheNIRbump.The functionforagrainoftemperatureTgr.Adopting,asinBarvainis
thicklinerepresentthesumofthesethreecomponents. (1987),avalueofa=0.05µmforgraphitegrainsandQν=0.058and
settingTgr=1220K,wefindLgνr,ir=9.29×10−18ergss−1Hz−1.
Thetotalnumberofemittinggrains(hotdust)canbeapprox-
The third component, well described by a Planck function imatedasNHD ≈LNIR/Lgνr,ir.
of Tbb ∼1200 K willbe examined inthe following section. Un- Finally, for graphite grains, with density ρg=2.26 g cm−3,
fortunately, the lack of a spectroscopic survey of AGNs in the MHD ≈ 4.12a3NHDρg. Taking Mrk 1239 at a distance
NIRpreventsustodetermineifthatfeatureiscommoninSeyfert of 79.7 Mpc (z=0.00199, H =75 kms−1/Mpc), we obtained
o
galaxies.Theonlyreportstodateofasimilarfeaturecomesfrom NHD=4.51×1046andMHD=2.7×10−2M⊙.
spectroscopy observations of IZw1 (Rudyetal. 2000), Mrk478 Table1comparesthemassofhotdustderivedforMrk1239
(Rudyetal.2001)andMrk766(Rodr´ıguez-Ardilaetal.2005),no- tothatfoundinotherAGNs.OurcalculationsshowthatMrk1239
tably all NLS1 galaxies. In the former two objects, an excess of harborsthesecondlargestmassofhotdustreportedtodateinthe
emissionredwardsof1.3µmovertheunderlyingfeaturelesscon- literaturefor an AGN,only surpassed byNGC 7469. Note, how-
tinuum,isobserved.TheIZw1andMrk478data,however,arelim- ever,thatexceptforMrk766,allotherpreviousmeasurementsare
itedto2.4µm.Itisnotpossibletosaywhathappensbeyondthat basedonphotometricdata,whichdonottakeintoaccounttheun-
point.Notethatthenarrownessofthiscomponentturnsitdifficult derlying featureless continuum that we subtracted. Had we used
to be detected in broad band photometry studies based on IRAS the peak flux of the continuum, we would have obtained a value
observations,forinstance.Itspresence,however,canbeconfirmed of5.3M⊙,rankingMrk1239astheAGNwiththelargestcontent
bymeansof2MASSphotometry.InFigure3,wehaveplottedthe ofhotdustfoundtodate.Thepresenceofdustneartosublimation
JHKfluxes(fullcircles)reportedforMrk1239,takenfromNED. temperatureinMrk1239hasbeenlargelypredictedbydustemis-
No photometry is the optical is available. Overall, the photomet- sionmodels.Infact,theonsetofthebroadstrongbumpofemission
ricpointsfollowtheNIRexcess.Thesmalloverestimationofthe at1µm,withpeakat∼ 60µm,issetbythedustsublimationtem-
photometricJandHfluxoverthespectroscopicone(∼16%)can peratureofgraphitegrainsatT∼1500K.WhyinMrk1239exists
be due to line emission (HI and HeI) and probably, underlying suchalargeamountofhotdust,totheextentofcreatinganotice-
continuumemissionfromthehostgalaxy.Recallthatthe2MASS ableshoulderinthemuchbroaderIRSEDattributedtowarmdust,
dataplottedisextractedfromaperturephotometry,ofradiusof14′′, cannotbetellfromourdata.NodoubtthatMrk1239isanexcellent
whichmayincludecontributionfromthehost-galaxy. targettobestudiedspectroscopicallywithSpitzerinordertostudy
thebroadbandIRemissionofthisobject.
Regardingtothelocationofthehotdust,ouraperturesizeim-
plies that it must reside within the inner 380pc from the centre.
4 THEHOTDUSTHYPOTHESIS
However, thehightemperature ofthedustimposes atightercon-
TheadequaterepresentationoftheNIRbumpbyablackbodydis- strainttothelocationofitsemittingregion:theinner100pc.This
tribution leads us to propose that it is due to emission from hot value is deduced by inspecting Fig. 3 of Marco&Alloin (1998),
dustgrains.Thetemperaturederivedfromthefit,T =1200K,is whereaplotofdust temperatureasfunctionofdistancefromthe
bb
closetotheevaporationtemperatureofgraphitegrains,T∼1500K, nucleus was constructed for NGC 7469. Note that we have as-
Thenear-infraredspectrumof Mrk1239 5
sumed that the dust inMrk1239 has similar properties tothat of ratory,CaliforniaInstituteofTechnology, under contractwiththe
NGC 7469. Further support to this distance can be obtained fol- NationalAeronauticsandSpaceAdministration.
lowing the results for NGC 1068 (Marco&Alloin 2000). These
authorsconcludedthathotdust(Tgr=1500K)shouldbeextremely
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This research has been partly supported by the Brazilian agency
Zheng,W.,Kriss,G.A.,Telfer,R.C.,Grimes,J.P.,Davidsen,A.
CNPq (309054/03-6) to ARA and the European Commission’s
F.,1997,ApJ,475,469
ALFA-IIprogram through itsfunding of theLatin-American Eu-
ropeanNetworkforAstrophysicsandCosmology,LENACtoXM.
This research has made use of the NASA/IPAC Extragalactic
Database (NED) which is operated by the Jet Propulsion Labo-