The innermost dusty structure in active galactic nuclei as probed by the Keck interferometer

0.28 MB·English

by  Makoto Kishimoto

Astronomy&Astrophysicsmanuscriptno.ki10may˙astroph˙v2 (cid:13)c ESO2011
January18,2011
The innermost dusty structure in active galactic nuclei as probed
by the Keck interferometer
MakotoKishimoto1,SebastianF.Ho¨nig2,RobertAntonucci2,RichardBarvainis3,TakayukiKotani4,Konrad
R.W.Tristram1,GerdWeigelt1,andKenLevin5
1Max-Planck-Institutfu¨rRadioastronomie,AufdemHu¨gel69,53121Bonn,Germany;e-mail:[email protected]. 2Physics
Department, University of California, Santa Barbara, CA 93106, USA. 3National Science Foundation, 4301 Wilson Boulevard,
Arlington,VA22230,USA.4ISAS,JAXA,3-1-1Yoshinodai,Sagamihara,Kanagawa,229-8510Japan.5SilverSpringObservatory,
1 10712MeadowhillRd,SilverSpring,MD20901
1
0 Submitted3November2010/Accepted23December2010
2
ABSTRACT
n
a Wearenow exploring theinner regionof Type 1activegalacticnuclei (AGNs)withtheKeckinterferometer inthenear-infrared.
J
Adding to the four targets previously studied, we report measurements of the K-band (2.2 µm) visibilities for four more targets,

7 namely AKN120, IC4329A, Mrk6, and theradio-loud QSO 3C273 at z=0.158. Theobserved visibilitiesarequitehigh for all the
1 targets,whichweinterpretasanindicationofthepartialresolutionofthedustsublimationregion.Theeffectiveringradiiderived
fromtheobservedvisibilitiesscaleapproximatelywithL1/2,whereListheAGNluminosity.Comparingtheradiiwiththosefrom

] independent optical-infraredreverberationmeasurements,thesedatasupportourpreviousclaimthattheinterferometricringradius
O
iseitherroughlyequaltoorslightlylargerthanthereverberationradius.WeinterprettheratioofthesetworadiiforagivenLasan
C approximateprobeoftheradialdistributionoftheinneraccretingmaterial.Weshowtentativeevidencethatthisinnerradialstructure
mightbecloselyrelatedtotheradio-loudnessofthecentralengine.Finally,were-observedthebrightestSeyfert1galaxyNGC4151.
.
h Its marginally higher visibilityat a shorter projected baseline, compared to our previous measurements obtained one year before,
p further supportsthepartialresolutionof theinnerstructure. Wedidnot detect anysignificantchange intheimpliedemissionsize
- whentheK-bandfluxwasbrightenedbyafactorof1.5overatimeintervalofoneyear.
o
r Keywords.Galaxies:active,Galaxies:Seyfert,Infrared:galaxies,Techniques:interferometric
t
s
a
[
1. Introduction werepartlychosenbasedonthebrightopticalmagnitudesmea-

2 sured from the pre-imaging data obtained in Oct 2009 at Tiki
v Withlong-baselineinterferometryinthe mid-IR,theinnerdust Observatory (French Polynesia) by N. Teamo and J. C. Pelle,
9 distribution in active galactic nuclei (AGN) has been studied andatSilverSpringObservatory(USA).
5 over the past several years (e.g. early results on Seyfert 2
The Adaptive Optics system at each Keck telescope was
3 galaxiesby Jaffeetal. 2004, Tristrametal. 2007; radio galaxy,
locked on the nucleus of each target galaxy at visible wave-
5 Meisenheimeretal. 2007; Type 1 AGNs, Beckertetal. 2008,
lengths. The fringe tracker was operated in the K-band at the
. Kishimotoetal. 2009b, Burtscheretal. 2009; snapshot survey,
2 rates of 100Hz and 200Hz in our observing runs in Nov 2009
1 Tristrametal.2009).Inthenear-IR,aftertheveryearlyresults andMay2010,respectively.Theangle-trackingwasperformed
0 forthebrightestSeyfert1galaxyNGC4151(Swainetal.2003)
in H-bandat therate of either40 or80Hz. The data werefirst
1 and Seyfert2 galaxyNGC1068(Wittkowskietal. 2004), long- reducedwith Kvis1 to produceraw squaredvisibility (V2) data
: baseline interferometry has now started to explore the inner-
v averagedoverblocksof5seceach.
mostdustystructureextensivelyatmilli-arcsec(mas)resolution
i Duringthe observingnightin Nov2009,we oftendetected
X (Kishimotoetal.2009a,hereafterPaperI;Pottetal.2010).We
aquiteunevenleveloffluxfromthetwotelescopes,resultingin
r focusonType1AGNs,whichareconsideredtoprovideuswith visibilityattenuation.IntheMay2010run,thiswasseenonlyfor
a a direct view of the region and thus can be used to scrutinize
the calibrators observedat large air masses. The standard soft-
the inner structure. Here we report on new measurements for
warewbCalib2 hasbeenshowntobeabletocorrectforthisef-
fourmoretargets,whichdoublethesamplesizeofourprevious
fect3,butwealsorejectedblocksassociatedwithadiscrepantly
studyinPaperI.
largefluxratioofthetwobeams(&8).Thewide-bandsideofthe
datawerethenreducedusingwbCalibwiththecorrectionforthe
fluxratioandfluxbias.Theblockswereaveragedintoscansover
2. Observationsanddatareduction
a fewtoseveralminuteseach,with itserrorbeingestimatedas
2.1.Keckinterferometry astandarddeviationwithinascan.Figure1showstheobserved
visibilitiesofallthetargetsandcalibrators(afterthecorrections
The Keck Interferometer (KI; Colavita&Wizinowich 2003) above),plottedagainsttheobservingtime.
combines the two beams from the two Keck 10 m telescopes
which are separated by 85 m along the direction 38◦ east of 1 http://nexsci.caltech.edu/software/KISupport/v2/V2reductionGuide.pdf
north.WeobservedType1AGNslistedinTable1andassociated 2 http://nexsci.caltech.edu/software/V2calib/wbCalib/index.html
calibratorswiththeKIinNov2009andMay2010.Thetargets 3 http://nexsci.caltech.edu/software/KISupport/dataMemos/KI ratio.pdf
1
Kishimotoetal.:Theinnermostdustystructureinactivegalacticnuclei
Fig.1.ObservedV2(afterflux-ratioandflux-biascorrections;seesect.2.1)plottedagainstobservingtime.Graydotsareindividualmeasurements
forblocksof5seceach.Theseblocksareaveragedintoscansoverafewtoseveralminuteseach.Thesescansareindicatedbyvarioussymbols
witherrorbarscorrespondingtostatisticalerrors,calculatedasstandarddeviationsoftheblockswithineachscan.Graycirclesaretheestimated
systemV2atthetimeoftargetobservations(plottedslightlyshiftedintimeforclarity).
Table1.SummaryoftheresultsofourKIobservationsandradiodataforthepresentandremainingprevioustargets.
name date(UT) za scaleb EB−Vc Bpd PA V2 Rringe radiofluxf AV
corr. (pcmas−1) (mag) (m) (◦) (mas) (pc) (mJy) (GHz) (mag)
AKN120 2009-11-07 0.0327 0.653 0.128 74.6 31.9 0.843±0.097 0.56±0.19 0.36±0.12 9.3g 1.4
IC4329A 2010-05-01 0.0170 0.345 0.059 69.8 49.6 0.868±0.084 0.54±0.18 0.19±0.06 10.7h 8.4 2±1n
MRK6 2010-05-01 0.0188 0.382 0.136 71.5 −1.4 0.909±0.048 0.44±0.12 0.17±0.05 39.5i 8.4
3C273 2010-05-02 0.159 2.75 0.021 83.5 39.9 0.958±0.034 0.25±0.10 0.69±0.28 3.20E4j 4.8
NGC4151 2010-05-01 0.00414 0.0855 0.028 72.4 51.0 0.920±0.017 0.40±0.05 0.034±0.004 125.k 4.9
2010-05-01 81.3 40.7 0.878±0.049 0.45±0.10 0.038±0.008
2010-05-02 84.9 21.7 0.883±0.048 0.42±0.09 0.036±0.008
NGC4051 0.00309 0.0639 6.0k 4.9
MRK231 0.0427 0.841 173.l 5.0
IRAS13349o 0.109 1.98 19.9m 1.4
a CMBcorrectedvaluefromNED.b H0 = 70kms−1 Mpc−1,Ωm = 0.3,andΩΛ = 0.7.c GalacticreddeningfromSchlegeletal.(1998).d Projectedbaseline
lengths. e Thin-ring radius. f Radio fluxobserved at frequency given. Forradio-quiet objects, fluxfrom linear (double ortriple) structure at ∼100pc scale is
given,exceptforAKN120,IC4329A,andIRAS13349+2438,forwhichfluxfromasourceunresolvedatresolutionof6”(3.9kpc),1”(350pc),and5.4”(11kpc),
respectively, isgiven. g Condonetal. (1998).h Nagaretal.(1999).i Schmittetal. (2001). j Tingayetal.(2003).k Ulvestad&Wilson (1984).l Ulvestadetal.
(1999).mWhiteetal.(1997).nWinkleretal.(1992).oIRAS13349+2438.
All the calibrators used4 (Fig. 1) are expected to be unre- (Fig.1;AKN120,IC4329A,3C273).Thefinalcalibratedvisibil-
solvedbytheKI atK-band(V2 ≥ 0.999).The calibratorsspan ities with the errorsincludingthe systematic uncertaintyadded
a relatively wide range of brightness, and some were found to inquadratureareshowninTable1.
have lower injected flux countsat K-bandthan the science tar-
gets(forthesameK-bandmagnitude,calibratorcountsareoften
2.2.UKIRTimaging
higherduepartlytotheirbluercolorswhichleadtoabetterAO
performanceintheoptical.)AsinPaperI,weassign0.01tobe
To obtain contemporaneousflux measurements of the variable
thepossiblesystematicuncertaintyinthesystemvisibilityesti-
nuclei,weobservedalltheKItargetswithWFCAMonUKIRT
mate, basedon thedifferencebetweenthe correctedvisibilities
(exceptforMrk6,whichwasoutsidetheUKIRTpointinglimit)
ofbrightercalibratorsandthoseoffainterones,thoughinmany
about five to six weeks after each KI observing run, which is
cases the total uncertainty is dominated by much larger statis-
generally shorter than the variability timescale, at five broad
tical errors. For each target measurement, the system visibility
bandsfrom0.9to2.2µm.Theobservationsweredoneunderthe
V2 was estimated fromthese calibratorobservationswith wb-
sys UKIRTserviceprogram.Thedatawerehandledinthesameway
Calibusingitstimeandskyproximityweightingscheme(using
thedefault5 timeconstantof1houranddistanceof15◦),yield-
ingtheV2 measurementsindicatedbythegraycirclesinFig.1. 4 ThestarHD240991 wasexcluded fromthecalibration,sincetwo
sys observations showed systematically lower visibilities than other cali-
Averagesweretakenforthoseobjectswithtwocalibratedmea-
brators.
surementsadjacentintimethatwereconsistentwitheachother
5 http://nexsci.caltech.edu/software/V2calib/wbCalib/index.html
2
Kishimotoetal.:Theinnermostdustystructureinactivegalacticnuclei
We note that the exact inclination of the structure is not
known,thustheresultingpossibleelongationoftheringdueto
inclinationisstillgenerallyunknown.However,wenotethatwe
donotseeasignificantPAdependenceintheeffectiveringradii
in NGC4151 over the PA range from ∼10◦ to ∼50◦ (Paper I;
seealsoFig.3describedbelow),wheretheinnersystemaxisis
supposed to be at PA ∼90◦ (optical polarization, Martel 1998;
radio jet, Mundelletal. 2003), despite the object often being
thoughttobe relativelyinclinedatthenarrow-lineregionscale
(e.g.Dasetal.2005andreferencestherein).
Since the visibility measurements are affected by the host
galaxy flux fraction within the FOV of the KI, and also by the
flux contribution from the unresolved accretion disk (AD), we
estimatedthesetwoquantitiesusingourUKIRTimagingdatain
the same way as described in sect.3 of Paper I. For Mrk6, we
used the 2MASS images. In brief, we fitted each SED with a
power-lawform f ∝ν+1/3fortheAD(supportedbyboththeory
ν
andobservations;Kishimotoetal.2008)andablack-bodyform
forthedust(thebest-fittemperatureswere∼1200-1500K).The
resultsarestatedinTable2alongwiththeringradiicorrectedfor
Fig.2.FluxofthenuclearPSFcomponentinWFCAMimages(except these effects. We note that the effects are generally very small,
forMrk6,forwhichweused2MASSimages)derivedfrom2Dfits.The andthetwoeffectsalsotendtopartiallycanceleachother.
SEDsfittedwithablackbodyandapower-law f ∝ν+1/3(seesect.3.1)
ν
areshownbydottedlines.
3.2.NGC4151re-observation
We obtained quite extensive data for NGC4151 in May 2009
as described in Paper I. The wide FOV of WFCAM provided
(PaperI),butre-observedthetargetinMay2010tomeasurethe
simultaneous PSF measurements from stars in the same field.
visibility essentially at the shortest possible projected baseline
ThesePSFswereusedtodecomposeeachimageintothenuclear
under the current delay line restriction in the KI, and to check
PSF componentand host galaxy, leading to the SED measure-
for visibility variability. Pottetal. (2010) compared their data
ment of the nuclear point source in each AGN. The measured
onNGC4151withthatofSwainetal.(2003)andour2009data,
fluxesaresummarizedinTable2.TheSEDs,aftercorrectingfor
andreportedthattheobjecthasnotshownanysignificantvari-
reddeninginbothourGalaxyandforIC4329Ainthehostgalaxy
abilityintheK-bandvisibility.
(Table2),areshowninFig.2,togetherwiththefourSEDsfrom
Figure 3 shows our re-observations plotted over the May
PaperI.
2009 measurements. The previous data (squares) showed a
marginalV2 decreaseoverincreasingbaselines.Thisisnowap-
parentlysupportedbythehigherV2observedattheshorterpro-
3. Results
jected baseline of ∼72 m. We caution that, when we compare
3.1.Visibilitiesandringradii the data from different nights, we should take into account the
possible systematic uncertaintyin the absolute V2 calibrations,
For all of our targets, quite high visibilities were observed whileeachV2datapointinFig.3isshownwithonlyastatistical
(Table1), whichwasalsothe caseforthe previousfourtargets error,whichisadequateforcomparingdatawithinagivenstable
in Paper I. We interpret these high visibilities as an indication night.Thesystematicuncertaintycouldbeupto∼0.03(footnote
ofthepartialresolutionofthedustsublimationregionaswear- 6; indicatedas a dashedverticalbar in the left inset of Fig. 3),
guedinPaperIanddiscussedinsects.3.2and4below.Themost althoughthisnumberisprobablyconservativeforthewide-band
simplistic,physically-motivatedrepresentationofthedustsubli- side data thatwe use here. Thiswas deducedfromthe system-
mationregionseen face-onwouldbea ringgeometry.Tomea- atic differencein V2 betweenitsobservedandpredictedvalues
sure its effective radius regardless of the structure details (e.g. for known-orbit binaries where the difference was comparable
smooth versus clumpy distribution [Krolik&Begelman 1988], to or smaller than statistical errors. (From our data alone, we
thisinformationprobablynotbeingcontainedinthevisibilities estimate the systematic uncertaintyof ∼0.01 after the flux-bias
atlowspatialfrequencieswellbeforethefirstnull),wededucein correction,andthishasbeenincorporatedintheerrorsshownin
Table1athin-ringradiusRring thatcorrespondstotheobserved Table1,asdescribedinsect.2.1.)
visibilityattheprojectedbaselineforeachtargetobservation.
Havingtheseinmind,wecalculatedthePearson’slinearcor-
The fractional uncertainty in the ring radius σRring/Rring for relationcoefficientbetweentheprojectedbaselineandcalibrated
the data at the low spatial frequencieswell beforethe first null V2, by weighting the May 2010 data conservatively using the
can be estimated in the same way as in the Gaussian geometry uncertaintyof0.03(whenthestatisticalerrorissmallerthanthis
case,givenas value)whilekeepingthestatisticaluncertaintyforthe2009data
σRring = 1 σV2, asweights.Thecoefficientis−0.766,meaninginthiscaseof12
R −2lnV2 V2 data points that the confidence level for rejecting the null cor-
ring
relation is 99.6%, or 2.9σ. (Note that weighting the 2009 data
where σV2 is the total uncertaintyin V2. When we have multi- usingthe uncertaintyof 0.03as wellwouldin this case lead to
ple data at different baselines as in the case of NGC4151, we evenalargersignificance.)
estimate the overall fractional uncertainty in the same way by
replacingV2andσV2/V2withtheirmeanoverthedatapoints. 6 http://nexsci.caltech.edu/software/KISupport/dataMemos/kvis params.pdf
3
Kishimotoetal.:Theinnermostdustystructureinactivegalacticnuclei
Fig.3. Calibrated V2 for NGC4151 as afunction of projected baselines. Squares show our previous data taken in May 2009 (Paper I), while
crossesandtrianglearethenewdatatakenon2010May1and2,respectively,allbeingenlargedintheleftinset.TheabsoluteV2 calibrationis
saidtohaveapossiblesystematicerrorupto0.03(seesect.3.2),whichisshownasadashedverticalbarinthisinset.Thedottedlineineach
panel showsthebest-fitvisibilitycurveofathin-ringmodel witharadiusof0.45masforourprevious May2009 data.Intherightinset,ring
radiicorrespondingtoeachdatapointareplottedalongthePAofeachprojectedbaseline.Notethatthecorrectionfortheaccretiondiskandhost
galaxycontributionsisnotincorporatedinthisfigure,anddoesnotsignificantlychangetheringradius(seeTable2).
Theringradiusimpliedbythenewmeasurementsisconsis-
tentwith theradiusdeducedfromthedata inMay2009within
theerrorsevenwhenexcludingthesystematicuncertainty.Thus,
wedidnotdetectanysignificantvariabilityintheinterferometric
size. This is consistent with the result by Pottetal. (2010). On
thebasisofourquasi-simultaneousUKIRTSEDmeasurements,
the nuclear K-band flux has brightened by a factor of 1.5 over
theoneyearinterval.Onthistimescale,theoverallinnerradial
dust distribution does not seem to have changed significantly.
Thisconclusionremainsthesameevenafterthehostgalaxyand
accretiondiskfluxfractionsaretakenintoaccount.
4. Discussions
4.1.Radiusvsluminosity
Figure 4 shows the ring radii R derived from the visibility,
ring
afterthecorrectionforthehostgalaxyandunresolvedADcom-
ponent, as a function of the UV luminosity L, defined here as
a scaled optical luminosity of 6νL (5500Å) (Kishimotoetal. Fig.4. Ring radius derived for each KI target (filled circles) after
ν
2007). The flux at 5500Å is here extrapolated from the fitted thecorrection forhost galaxyandunresolved ADcomponent, plotted
SED at 0.8 µm by assuming the AD spectral shape of f ∝ againstUVluminosity,orscaledV-bandluminosity(extrapolatedfrom
ν the WFCAM SED; see sect. 4.1). The reverberation radii against the
ν0 (based on spectral index studies summarized in Fig. 2 of
samescaledV-bandluminosity(Suganumaetal.2006,andreferences
Kishimotoetal.2008)andshowninFig.2.
therein)arealsoindicatedbygrayplussignsinadditiontotheirfit(dot-
Wecandirectlycomparetheringradiuswiththenear-IRre-
tedline).
verberationradiusR ,whichisthelight-crossingdistanceover
τK
the time lag of the K-band flux variation relative to the opti-
cal flux variation(e.g.Glass 2004; Suganumaetal. 2006). The
time-lagradiiR ofasampleofgalaxieshavebeenshowntobe thattheinterferometricringradiialsoscaleapproximatelywith
τK
approximatelyproportionaltoL1/2 (Suganumaetal.2006;their L1/2,andtheyareofthesameorderasthereverberationradiifor
fitisshownasadottedlineinFig.4),andarelikelytobeprob- agivenluminosity.ThisiswhatwereportedinPaperI,butnow
ing the dust sublimation radius in each object. Figure 4 shows weconfirmthiswithalargersample.Thisfurthersupportsthat
4
Kishimotoetal.:Theinnermostdustystructureinactivegalacticnuclei
Table2.Point-sourcefluxfromUKIRTimagingdataandtheKIresultscorrectedforhostgalaxyandunresolvedADcomponent.
name date flux(mJy)a magnitude hostb AD V2corrected Rringcorr. RτK fitd
(UT) Z Y J H K J K (%) fractionc (pc) (pc)
AKN120 2009-12-13 11.7 11.8 16.4 26.6 60.7 12.4 10.1 0.6±0.1 0.17±0.05 0.822±0.117 0.38±0.14 0.15
IC4329A 2010-06-13 15.0 16.0 23.9 41.6 75.5 12.0 9.8 0.9±0.2 0.29±0.09 0.839±0.119 0.21±0.08 0.13
Mrk6e 1999-02-27 — — 16.3 29.1 53.6 12.4 10.2 0.2±0.1 0.21±0.05 0.890±0.061 0.18±0.05 0.097
3C273 2010-06-14 29.0 29.1 33.2 45.7 81.9 11.7 9.7 <0.1 0.28±0.09 0.942±0.047 0.81±0.34 1.1
NGC4151 2010-06-14 51.1 54.0 81.8 136. 264. 10.7 8.5 0.2±0.1 0.14±0.05 0.912±0.021f 0.037±0.007g 0.037
aFluxmeasurementuncertaintyis∼5%(seesect.3inPaperI).bHostgalaxyfluxfractionatK-bandestimatedfortheKI’s50masFOVintheAO-correctedimages.
cADfluxfractionofthepointsourceatK-band.dRτKfromUVluminosityusingthefitbySuganumaetal.(2006).eFrom2MASSimages.f Valuefortheshortest
baselinedata.gBest-fitvaluefor2010-05-01data.
theKIobservationsindeedpartiallyresolvethedustsublimation
region.
We note that all of our KI targets have similarly high vis-
ibilities, thus the inferred angular sizes are relatively similar
(Table1).Thisiswhatweexpectforthe L1/2 scaling,sincethe
angularsizesofthedustsublimationradiusscaleonlywiththe
apparentmagnitudesoftheilluminatingsource(forz≪1cases;
e.g. Kishimotoetal. 2007), which are within a relativelysmall
range.Conversely,thesimilarlyhighvisibilitiesobservedforthe
KItargetsimplythatthephysicalsizeofthecorresponding,par-
tiallyresolvedstructurescalesroughlywithL1/2.
4.2.Innerradialstructure
Furthermore, we confirm the tendency already seen in Paper I
for R to be either roughly equal to or slightly larger than
ring
R foragivenluminosity.AswedescribedinPaperI,thiscan
τK
beunderstoodinthepicturewhereR representsaradiusvery
τK
closetotheinnerboundaryofdustdistribution,whileR cor-
ring
responds to a brightness-weightedeffective radius. The former
Fig.5. Ratioof R toR fitplottedagainst theratioof luminosity
is based on the fact that the reverberation technique generally ring τK
L at 5.0 GHz to that at 0.55 µm. The former is calculated from the
ν
placesweightonthesmallrespondingradiiwhenthelagisde- radiofluxlistedinTable1,assumingS ∝ ν−0.8 forextrapolationand
ν
termined from the peak in the cross-correlation function (e.g. K-correction.
sect.3inKoratkar&Gaskell1991andreferencestherein).Itis
also based on the fact that the R fit actually is very close to
τK
thedustsublimationradiusatthelarge-grain(black-body)limit,
whichisthesmallestpossiblesublimationradiusforagivensub- 4.3.Radioconnection
limationtemperature(thistemperaturebeingconstrainedbythe
observed color temperature; Kishimotoetal. 2007; Fig. 2). In Intriguingly,objects with the ratio Rring/RτK close to unity, i.e.
thispicture,R closetoR meansasteepandcompactmass corresponding to the steepest and most compact distribution,
ring τK
distributionwhere mostdust sits close to the innermostradius. are those that are known to show linear radio jet structures
On the other hand, if R is observed to be much larger than (NGC4151,Mundelletal. 2003; Mrk231,Ulvestadetal. 1998,
ring
R ,thedustdistributionismuchshallowerandmoreextended. known as compact symmetric object; 3C273). Mrk6 is also
τK
Inthiscase,wecanusetheratioofR totheR fitasan knowntoexhibitalinearjetstructure(e.g.Kukulaetal.1996),
approximate probe for the radial distriburtiinogn of the τinKnermost, but our Rring measurement has a relatively large uncertainty.
likelyaccreting(e.g.Krolik&Begelman1988),dustymaterial. Figure 5 shows the Rring/RτK fit ratio plotted against the radio-
In practice, the real inner boundary radius of the dust distri- to-optical luminosity ratio. Here we might have started to see
bution is probably still slightly smaller than R . In addition, evidence of a correlation, suggesting that jet-launchingobjects
the measured individual R has on average anτKuncertainty of possessaverysteepandcompactdistributionofinneraccreting
the orderof the scatter fromτK the fit (Fig. 30 in Suganumaetal. material. We regardthis possible correlation as tentative, since
2006). Takingthe ratio with respectto the R fit, however,we thesamplesizeissmallandthestatisticalsignificanceisstillnot
can take out the relativelyrobust L1/2 dependτKencefromthe in- very high (e.g. the Spearman’s rank correlation analysis gives
terferometricringradii,quiteinsensitivelyto theuncertaintyin 91%confidence,or1.7σ).
the reverberationmeasurements. The resulting ratio, at least in One possible remaining ambiguity concerns the UV lumi-
a relative sense over the sample, has a physically interpretable nosity L. Here we have adopted the scaled optical luminosity
meaningdescribed above,and can be used to exploreany pos- forL.ItmightbebettertouseanobservedUVluminosity,per-
sible relations between the inner radial structure and the prop- hapsaveragedoveralongtimescaleifsublimationradiusisnot
erty of the central engine in each AGN. In this way, we can changing quickly. However, uncertainties from foreground ab-
exploit the power of the interferometry, which can easily dis- sorptionintheUVcanbesignificant.Inaddition,theobserved
tinguishasizedifferenceofafactoroffew,asdemonstratede.g. L1/2 scalingofR seemstoimplythattheopticalluminosityis
τK
inKishimotoetal.(2007). atleastapproximatelyproportionaltothe(dust-heating)UVlu-
5
Kishimotoetal.:Theinnermostdustystructureinactivegalacticnuclei
minosity.Wewillhavetoseewhetherfurtherstudyofthemost adirectprobeofthephysicalstructureoftheaccretingmaterial
relevantluminositystrengthensorweakensthecorrelation. at the best possible spatial resolution available so far. We plan
Anothersourceofambiguityistheinclination,althoughwe tofurtherexploretheregionwithmoreinterferometricmeasure-
focusintentionallyonType1objects,whichshouldlargelyavoid ments.
thisproblem.Inthesimplestpictureofaninclinedcircularring,
Acknowledgements. The data presented herein were obtained at the W.M.
the projection correction would make the ring radii systemati-
Keck Observatory, which is operated as a scientific partnership among the
callylarger,butwouldnotnecessarilyweakentheobservedten- CaliforniaInstituteofTechnology,theUniversityofCaliforniaandtheNational
tativerelationship.Withmoremeasurements,wehopetopursue AeronauticsandSpaceAdministration(NASA).TheObservatorywasmadepos-
thePAdependencyineachobjectaswehavedoneforNGC4151 siblebythegenerousfinancialsupportoftheW.M.KeckFoundation.TheKeck
InterferometerisfundedbyNASAaspartofitsExoplanetExplorationprogram.
(sect.3.2;Fig.3).
The United Kingdom Infrared Telescope is operated by the Joint Astronomy
Finally we note that the effect of the synchrotronemission CentreonbehalfoftheScienceandTechnologyFacilitiesCounciloftheU.K.
contribution to the deduced ring size is considered to be very WethankN.TeamoandJ.C.Pelleforkindlyprovidingthepre-imagingdata.
small,ifatallpresent,aswediscussbelow. ThisworkhasmadeuseofservicesproducedbytheNASAExoplanetScience
InstituteattheCaliforniaInstituteofTechnology.Thisresearchhasalsomade
useoftheNASA/IPACExtragalacticDatabase(NED)whichisoperatedbythe
4.4.Synchrotroncontributionand3C273 Jet Propulsion Laboratory, California Institute of Technology, under contract
with NASA.SH acknowledges support by Deutsche Forschungsgemeinschaft
For radio-loud objects, the synchrotron contribution at K-band (DFG)intheframeworkofaresearchfellowship(“Auslandsstipendium”).
can potentially make the apparent ring size smaller than it ac-
tually is, just as the unresolved AD contribution does. Based References
on the radio to infrared SEDs (Sandersetal. 1989; Elvisetal.
1994; those from NED), the only objectfor which this issue is Beckert,T.,Driebe,T.,Ho¨nig,S.F.,&Weigelt,G.2008,A&A,486,L17
Burtscher,L.,Jaffe,W.,Raban,D.,etal.2009,ApJ,705,L53
relevantinourpresentsampleis3C273.Inaquiescentstate,the
Colavita,M.M.&Wizinowich,P.L.2003,inPresentedattheSocietyofPhoto-
objectisknowntohaveonlylowpolarizationthroughtheoptical Optical Instrumentation Engineers (SPIE) Conference, Vol. 4838, Society
(<∼0.5%;e.g.Impeyetal.1989)tonear-IR(<1%;Smithetal. of Photo-Optical Instrumentation Engineers (SPIE)Conference Series, ed.
1987; Sitko&Zhu 1991), while a flaring state is accompa- W.A.Traub,79–88
Condon,J.J.,Yin,Q.F.,Thuan,T.X.,&Boller,T.1998,AJ,116,2682
niedbymuchhigherpolarization(Courvoisieretal.1988;Wills
Courvoisier,T.,Robson,E.I.,Hughes,D.H.,etal.1988,Nature,335,330
1989;Crossetal.2001).TheadditionalemergingfluxintheK- Cross,L.L.,Wills,B.J.,Hough,J.H.,&Bailey,J.A.2001,inAstronomical
bandinthelatterstatecanbeattributedtosynchrotroncontribu- SocietyofthePacificConferenceSeries,Vol.227,BlazarDemographicsand
tion(Courvoisieretal.1988). Physics,ed.P.Padovani&C.M.Urry,140–+
However, the object was in a quiescent state at the time Das,V.,Crenshaw,D.M.,Hutchings,J.B.,etal.2005,AJ,130,945
Elvis,M.,Wilkes,B.J.,McDowell,J.C.,etal.1994,ApJS,95,1
of both the KI and UKIRT runs, judging from the public light
Glass,I.S.2004,MNRAS,350,1049
curve7andtheobservedflux.WethereforeinferthattheK-band Impey,C.D.,Malkan,M.A.,&Tapia,S.1989,ApJ,347,96
synchrotroncontribution,ifpresentatall,wassmallatthetime Jaffe,W.,Meisenheimer,K.,Ro¨ttgering,H.J.A.,etal.2004,Nature,429,47
of our observations. Even if all the possible K-band polarized Kishimoto,M.,Antonucci,R.,Blaes,O.,etal.2008,Nature,454,492
Kishimoto,M.,Hoenig,S.F.,Antonucci,R.,etal.2009a,A&A,507,L57
fluxinaquiescentstate,.0.8mJy,originatesfromsynchrotron
Kishimoto,M.,Ho¨nig,S.F.,Beckert,T.,&Weigelt,G.2007,A&A,476,713
emission with an intrinsic polarization of ∼10% (Impeyetal. Kishimoto,M.,Ho¨nig,S.F.,Tristram,K.R.W.,&Weigelt,G.2009b,A&A,
1989),thecontributionis.8mJy.Oureffectiveradiusestimate 493,L57
forthedustdistributionwouldbecomelargerby.10%afterthe Koratkar,A.P.&Gaskell,C.M.1991,ApJS,75,719
potentialcorrectionforthesynchrotroncomponent.Thisiswell Krolik,J.H.&Begelman,M.C.1988,ApJ,329,702
Kukula,M.J.,Holloway,A.J.,Pedlar,A.,etal.1996,MNRAS,280,1283
withintheerrorbarshowninFigs.4and5.
Martel,A.R.1998,ApJ,508,657
Meisenheimer,K.,Tristram,K.R.W.,Jaffe,W.,etal.2007,A&A,471,453
Mundell,C.G.,Wrobel,J.M.,Pedlar,A.,&Gallimore,J.F.2003,ApJ,583,
5. Conclusions 192
Nagar,N.M.,Wilson,A.S.,Mulchaey, J.S.,&Gallimore,J.F.1999,ApJS,
WehavepresentedKeckinterferometermeasurementsat2.2µm 120,209
for4newType1AGNs,aswellasre-observationsofNGC4151. Pott,J.,Malkan,M.A.,Elitzur,M.,etal.2010,ApJ,715,736
Putting these together with the results from our previous tar- Sanders,D.B.,Phinney,E.S.,Neugebauer,G.,Soifer,B.T.,&Matthews,K.
1989,ApJ,347,29
getsandcomparingthesewiththeoptical-infraredreverberation
Schlegel,D.J.,Finkbeiner,D.P.,&Davis,M.1998,ApJ,500,525
measurements,wehaveinterpretedtheobservedhighvisibilities Schmitt,H.R.,Ulvestad,J.S.,Antonucci,R.R.J.,&Kinney,A.L.2001,ApJS,
asanindicationofthepartialresolutionofthedustsublimation 132,199
regionineachobject. Sitko,M.L.&Zhu,Y.1991,ApJ,369,106
Smith,P.S.,Balonek,T.J.,Elston,R.,&Heckert,P.A.1987,ApJS,64,459
Wehavearguedthatwecaninterprettheratiooftheinterfer-
Suganuma,M.,Yoshii,Y.,Kobayashi,Y.,etal.2006,ApJ,639,46
ometriceffectiveringradiusoftheinnerdustyregiontothere-
Swain,M.,Vasisht,G.,Akeson,R.,etal.2003,ApJ,596,L163
verberationL1/2-fitradiusasanapproximateprobeofthesteep- Tingay,S.J.,Jauncey,D.L.,King,E.A.,etal.2003,PASJ,55,351
ness/flatnessoftheinnerradialstructure.Ithasbeententatively Tristram,K.R.W.,Meisenheimer,K.,Jaffe,W.,etal.2007,A&A,474,837
shown that this inner structuremightpossibly be related to the Tristram,K.R.W.,Raban,D.,Meisenheimer,K.,etal.2009,A&A,502,67
Ulvestad,J.S.&Wilson,A.S.1984,ApJ,285,439
radio-loudnessofthecentralengine.
Ulvestad, J. S., Wrobel, J. M., & Carilli, C. L. 1998, in Astronomical
The possibleradioconnectionatleastillustratesthe impor- SocietyofthePacificConferenceSeries,Vol.144,IAUColloq.164:Radio
tantpotentialofthisnewexplorationoftheinnerregion.Weare EmissionfromGalacticandExtragalacticCompactSources,ed.J.A.Zensus,
stilllimitedintermsoftheproximitytothecentralengine,since G.B.Taylor,&J.M.Wrobel,199–+
Ulvestad,J.S.,Wrobel,J.M.,&Carilli,C.L.1999,ApJ,516,127
we are using the emission from dust grains which cannot sur-
White,R.L.,Becker,R.H.,Helfand,D.J.,&Gregg,M.D.1997,ApJ,475,479
vive at distances too close to the central UV source. However,
Wills,B.J.1989,inLectureNotesinPhysics,BerlinSpringerVerlag,Vol.334,
the dustdistributionin or aroundthe sublimationregionis still BLLacObjects,ed.L.Maraschi,T.Maccacaro,&M.-H.Ulrich,109–+
Winkler,H.,Glass,I.S.,vanWyk,F.,etal.1992,MNRAS,257,659
7 http://www.aavso.org Wittkowski,M.,Kervella,P.,Arsenault,R.,etal.2004,A&A,418,L39
6