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DRAFTVERSIONFEBRUARY1,2008 PreprinttypesetusingLATEXstyleemulateapjv.25/04/01 OBSERVATIONALEVIDENCEFORAMULTIPHASEOUTFLOWINQSOFIRSTJ1044+3656 JOHNEVERETT1,ARIEHKÖNIGL1,2,ANDNAHUMARAV3,4 AcceptedforpublicationinApJv569n2,April20,2002 ABSTRACT Spectral absorptionfeatures in active galactic nuclei (AGNs) have traditionallybeen attributed to outflowing photoionized gas located at a distance of order a parsec from the central continuum source. However, recent observationsofQSO FIRST J104459.6+365605by deKoolandcoworkers,whenintepretedinthe contextofa single-phasegasmodel,implythattheabsorptionoccursmuchfarther(≈700pc)fromthecenter.Wereinterpret theseobservationsintermsofashielded,multiphasegas,whichwerepresentasacontinuouslow-densitywind 2 0 with embeddedhigh-densityclouds. Ourmodelsatisfies alltheobservationalconstraintswithan absorbinggas 0 thatextendsonlyoutto∼4pcfromthecentralsource. Thedifferentdensitycomponentsinthismodelcoexist 2 in the same regionof space and havesimilar velocities, which makesit possible to accountforthe detectionin this source of absorptionfeatures that correspondto differentionization parameters but have a similar velocity n structure. This model also implies that only a small fraction of the gas along the line of sight to the center is a J outflowingattheobservedspeedsandthatthecloudsaredustywhereastheuniformgascomponentisdustfree. Wesuggestthatasimilarpicturemayapplytoothersourcesanddiscussadditionalpossiblecluestotheexistence 6 1 ofmultiphaseoutflowsinAGNs. Subjectheadings:galaxies:active—galaxies:Seyfert—quasars:absorptionlines—quasars:individual 1 (FIRSTJ104459.6+365605)—MHD v 8 6 1. INTRODUCTION (2000) explored radiatively-driven, continuous disk winds as 2 the origin of the BELR and the BALR. These models all in- Modelingactivegalacticnuclei(AGNs)isachallengingen- 1 volvedasingle-phasegasmedium. deavor in part because of the uncertain geometry of the gas 0 Recently, de Kool et al. (2001, hereafter dK01) analyzed 2 and dust within their cores. Our best understanding of the a Keck HIRES spectrum of the FIRST Bright Quasar Source 0 gas distribution comes from reverberation mappings (Bland- J104459.6+365605(hereafter,FBQS1044).Theyinferredthat / ford&McKee1982;Netzer&Peterson1997),whichindicate h excited Fe II levels are not populated according to local ther- that the broad emission-line region (BELR) lies at a distance p modynamicequilibrium. Thisobservationimpliesan electron o- RthBeElLuRm≈in0o.s0it1yLi14n4/2thpecsfpreocmtrathlebacnednt∼ral0.c1o-nt1inµumumin,wunhietsreofL14404is4 onbusmebrveerddbernosaitdyanbeso≈rp4ti×on1i0n3McmgI- I3,[qwuhailcifhy,intoggtehtihseorbwjeicthtatshae tr ergs s- 1. Based on observed absorption of BELR features by broadabsorption-linequasar(BALQSO)],theMgIabsorption s a broadabsorption-lineregion(BALR)gasandonopticalpolar- features, and single gas-phase photoionization models, place : ization measurements, it hasbeen inferredthatthe BALR lies thisBALRat∼700parsecsfromthecentralsource. v outsideoftheBELR;thebestestimateshaveplacedtheBALR Notonlydoesthissurprisingresultcontradictthepictureofa i X somewherebetweena fewtenthsandseveralparsecsfromthe close-inBALR,but,inaddition,dK01’sthoroughanalysissug- r centralsource(e.g.,Turnshek1988). geststhatthegasonlypartiallycoversthecontinuumsource.It a Velocities for these outflows are well determined from is not easy to understand how the absorbing gas could be ap- Dopplershifts: theBELRandBALRcomponentshavespeeds proximately1kpcfromthecenterandyetonlypartiallycover .5000to8000kms- 1and.30000kms- 1,respectively.Other theAGNcore. Additionally,theKeckspectraindicatedistinct outflow components have also been detected. Observations groupings of gas in velocity space; it is also difficult to ex- of the “warm absorber” (a partially ionized X-ray absorbing plain how these apparent clumps could move to such a large gas) in Seyfert galaxies and radio-quiet QSOs, and of a UV- distanceandstill remainbunchedup, retainingdistinctidenti- absorbingcomponentapparentlyassociatedwiththewarmab- ties. Even more striking is dK01’s observation that different sorber, indicategasoutflowingat .103 kms- 1. Furthermore, ionizationstateshaveasimilarkinematicstructure(i.e.,resid- spectrallinesclassifiedasbeingfromtheNarrowLineRegion ualintensityasafunctionofvelocity): inparticular,bothFeII (NLR)correspondtovelocitiesof.severalhundredkms- 1. andMgIexhibitabsorptiontroughsat-200,-1250,-3550,and Different theories have been proposed to explain some of -3800kms- 1. these outflows. Forexample,Emmering,Blandford,& Shlos- The700pcdistanceestimateresultsfromcombiningtheion- man (1992) considered a hydromagnetically-driven disk out- izationparameter5 impliedbytheobservedlow-ionizationMg flow of discrete, long-lived clouds as a model of the BELR, and Fe absorption lines with the inferred values of n and L e whereas Murray et al. (1995) and Proga, Stone, & Kallman (=1046ergss- 1).Onecanreducethisdistanceestimatebyatten- 1DepartmentofAstronomyandAstrophysics,UniversityofChicago,5640S.EllisAvenue,Chicago,IL60637,I:[email protected] 2EnricoFermiInstitute,UniversityofChicago,I:[email protected] 3AstronomyDepartment,UCBerkeley,Berkeley,CA94720,I:[email protected] 4PhysicsDepartment,UniversityofCalifornia,Davis,CA95616 5 TheionizationparameterU≡Q/4πnr2cisthedimensionlessratioofthehydrogen-ionizingphotondensitytothehydrogennumberdensityn: Qistherateof incidenthydrogen-ionizingphotons,risthedistancefromthecontinuumsource,andcisthespeedoflight. 1 2 Everett,Königl,&Arav uatingtheincidentcontinuumbyanintermediategas“shield.” uniform, this provides a good representation of magnetically Inthismodel,however,ionsatdifferentionizationstates(such confined constant-pressure clouds). In reality, the continuous astheFeIIandMgIcomponentsseeninFBQS1044)areex- outflowintheline-absorptionregioncanbeexpectedtoengulf pected to occupy different regions in space, with lower val- the clouds, but this simplified model should capture the basic ues of U corresponding to larger distances from the center physicaleffectsofatwo-phasemedium. (We verifiedthatour (e.g.,Voit,Weymann,&Korista1993). Thisstratificationwill results are independent of the cloud radial distribution within likelyleadtodisparatevelocitiesforthedifferentions: forex- theFeII/MgIabsorptionregion.) ample, models of self-similar MHD winds and of radiatively- Weobtaintheionizationstructureofthedifferentgasphases driven constant-U outflows predict that the terminal velocity, usingthe photoionizationcode Cloudy(Ferland2000),adopt- v ,variesasr- 1/2,wherer istheradiusatwhichthegasis ing the same source parameters as in dK01 and assuming (as ∞ inject inject theydoinmostoftheirmodels)aMathews& Ferland(1987) injectedintotheoutflow(e.g.,Blandford&Payne1982;Arav, spectrum. We take the scaling of the hydrogen number den- Li,&Begelman1994).Modelsthatrelysolelyonshieldingand sitywithsphericalradiustoben(r)∝r- 1,asintheAGNdisk- distancetoseparatethedifferentionizationcomponentsthere- wind modelsconsideredby Königl & Kartje (1994). In these forecannotexplaindK01’sobservations,inwhichdifferention- self-similarMHDoutflows,themagneticfieldB alsoscales izationstatesarefoundtohavesimilarvelocities. wind asr- 1, whichresultsinmagneticallyconfinedcloudshavinga We propose to explain the observations of FBQS 1044 by constantionizationparameter. generalizing the single-phase shielded-gas model, attributing Wefirstcalculatethephotoionizationofthecontinuouscom- the different ionization states to different density components ponent, stopping the computation when n drops to 4×103 inamultiphaseoutflow.Thesecomponentscoexistatthesame e cm- 3 (the value inferredfromthe observations). We then cal- distancefromthecenterandthushavedifferentionizationpa- culatehowtheradiationemergingthroughthecontinuousseg- rametersbutessentiallythesamevelocities.Inparticular,ifthe mentaffectscloudslocatedatthatdistance.Thetwoparameters high-andlow-ionizationlinesarise,respectively,inacontinu- weadjustinourmodelaren ,thewindhydrogennumberden- ouswindandindensecloudsthatareembeddedintheoutflow, w,i sity atr , andn , thehydrogennumberdensityofthe clouds. thenalltheabsorptioncomponentsproducedinagivenregion in c We explorea rangeofmodelstofind thevaluesofn andn ofthewindwillexhibitsimilarkinematicsignatures. w,i c thatbestreproducetheobservations. In our model, the continuous gas component extends from near the black hole’s event horizon out to the distance where 2.2. Results the observed Fe II absorption and electron density can be re- produced. The inner part of this component (interior to the Ourbest-fitvalueforthewinddensityisn ≈108.75 cm- 3. w,i BALR)isidentifiedasthe“shield.” Thisregioncouldbeasso- This yields the observed n in the region (at r≈4 pc) where e ciated with anMHD-driven(Königl& Kartje 1994),a Thom- theFeIIcolumndensityinthewindattainstheobservedvalue sonscattering-driven(e.g.,Blandford2001),ora“failed”line- of3×1015cm- 2,whichissignificantsincethen measurement e driven(e.g.,Murrayetal.1995;Proga,Stone,&Kallman2000) comesfromtheFeIIabsorptionlines. However,wedohaveto disk wind,orwitha diskcorona(e.g.,Emmeringetal. 1992). cutofftheoutflowveryclosetotheendofthehydrogenrecom- The outerregionof the continuousgascomponentis outflow- bination front so as not to exceed the observed Fe II column ingandaccountsfortheFeIIandMgIIabsorption,butisstill (seeFig. 1). Althoughtheabruptendoftheabsorbingcolumn too highlyionizedto containMg I absorbinggas. Within this couldbeanartifactcausedbyoursimplifiedtreatment,theoc- outflow are embedded higher-density clouds that account for currenceofastrongreductionintheabsorptionatthislocation thelower-ionizationMgIabsorption: theirhighdensityyields may have an actual physical basis. It may be a consequence a lower U in the clouds, allowing Mg I to exist. Such a two- of the decreasein the ionizationfractionin this region,which componentoutflowmayarisenaturallyinthecontextofacen- reducesthe efficiency with which the disk can drive an MHD trifugallydrivendiskwind,whichcouldupliftcloudsfromthe outflow,anditmayalsoreflectatransitionfromagaseoustoa disk surfacebyits rampressureandconfinethembyits inter- “clumpy”disk(see Shlosman& Begelman1987)orfromdif- nal magnetic pressure (e.g., Emmering et al. 1992; Kartje et ferential to solid-body disk rotation (see Bottorff, Korista, & al. 1999; Everett, Königl, & Kartje 2001). Alternatively, the Shlosman2000)onthatscale. clouds may represent transient density enhancements that are WealsonotefromFigure1thattheMgIIfrontoccurs∼2.5 produced by turbulence (e.g., Bottorff & Ferland 2001) or by timesclosertothecentralsourcethantheFe IIfront. (Thisis shocksinaradiativelydrivenwind(e.g.,Aravetal.1994).For duetotheformationofaHeIII→HeIIfrontinthewindthat illustration,weadoptherethe“cloudsupliftedandconfinedby absorbs photons with E > 54.4 eV, allowing Mg III, with an anMHDwind”picture. ionizationenergyof 80.1 eV, to recombineinto Mg II.) Since v ∝r- 1/2 in our chosen disk-wind model (see §1), the pre- 2. MULTIPHASEOUTFLOWMODEL ∞ inject dictedsmallerinitialradiusoftheMgIIfrontisconsistentwith 2.1. Setup thehigherMgIIvelocitiesobservedinFBQS1044. Our modelconsists oftwo segmentsthatrepresenttwo dis- Besides determining the measured values of the Fe II col- tinct gas phases. The first segment, which correspondsto the umn and of n , the continuouswind componentin our model e continuousphase,extendsfromr =10GM/c2=7.4×1013cm also exerts a strong influence on the cloud absorption proper- in (following dK01, we take the central black-hole mass to be ties throughits effecton the transmitted continuumspectrum. M = 5×108M ) out to just past the hydrogen recombina- Wefindthat,inorderforthecloudstoaccountfortheobserved ⊙ tion front, which corresponds to the Fe III → Fe II transi- MgIabsorptionwithoutalsodominatingtheFeIIabsorption, tion. The second segment, which models the confined dense theirirongas-phaseabundancemustbereduced,whichweat- clouds,isaconstant-densityzonelocatedjustbeyondthecon- tribute to depletion by dust. We assume an ISM dust compo- tinuous gas component(since the cloud temperature is nearly sition [the default Cloudy graphite and silicate grains with a MultiphaseOutflowinFBQS1044 3 Mathis, Rumpl, & Nordsieck (1977; hereafter MRN) power- f is the fraction of 4π steradians into which the wind flows, law size distribution]. The dust abundance is constrained by N is the total hydrogen column density of only the inferred H themeasuredextinction:A .1.0. Mg II and Fe II absorbing region (≈ 3.9×1023 cm- 2), v is 2500 Ourbest-fitvalueforthe typicalclouddensityis n ≈108.5 the observed outflow speed (∼ 108 cm s- 1), r (= 1.2×1019 c cm- 3. Thismeansthatthecloudsare∼104 timesdenser(and cm) is the inferred distance, and where we assume a verti- have a correspondingly lower ionization parameter) than the cally and azimuthally continuous wind. We take f ∼0.1 for surrounding continuous wind. Figure 2 shows the absorption BALQSOsources(Weymann1997). Fortheabovevalues,we column densities associated with a string of such clouds as a findM˙ ≈8M yr- 1. wind ⊙ functionofpathlengththroughtheclouds. Byequatingthethermalpressureintheclouds(≈2.7×10- 4 Ourmodelcanaccountfortheobservationswithcloudden- dynescm- 2)totheconfiningwindmagneticpressure,B2 /8π, wind sitiesthatrangebetween107.75 and109 cm- 3. Thisleewayre- we deduceB ≈8.2×10- 2 G. Itis encouragingthat, when wind flects the uncertainty in A2500. Whereas dK01 employ an ex- this value of Bwind is used in the n(r)∝r- 1 self-similar MHD tinctionof1.0magnitude,A2500 couldrangefrom∼1.0down wind model, it implies a local mass outflow rate that is com- to0.2magnitudesbasedonacomparisonbetweenthespectrum parabletothe aboveestimate ofM˙ , yielding∼4M yr- 1. wind ⊙ ofFBQS1044andthatofan“average”QSO(Weymannetal. If we instead choosen =109 cm- 3 (so as to satisfy the lower c 1991). If a population of lower-density clouds were present limitonthedustextinction,A =0.25)andrequirepressure with a significant fraction of the observed Mg I column, then balance,wefindM˙ ≈9M25y00r- 1. wind ⊙ the dusty cloudswould have A >1. On the other hand, if 2500 n ≫109 cm- 3, A woulddropbelow0.25. Withn =108.5 cmc - 3wepredictA2500≈0.5magnitudes,whichfitswecllwithin 3. CONCLUSION 2500 theinferredrange. Themostrobustresultofourstudyisthatashielded,multi- With the extinction already accounted for, the data require phase absorptionregionreproducesthe observationsof FBQS the continuousgas componentto be effectivelydust free. We 1044onaconventionalBALRscale(≈4pc).Inaddition,when testedthishypothesisbyincludingCloudy’sOrion-typedust(a one attributes the Fe II and Mg II absorptionto a low-density setofgraphiteandsilicategrainswithMRN’sminimumsizein- outflowcomponentandtheMgIabsorptiontoacospatialhigh- creasedfrom0.0025to0.03µm,appropriatetoaUV-irradiated density outflow component, it is possible to explain the simi- medium)inthewind,takingintoaccountdustsublimationand lar kinematic structure of the respective spectralfeatures. We sputtering. To include the effects of the latter process, we re- alsofindthatonlya smallfractionofthegasalongthelineof movedalldustgrainswhosesputteringtimescales(calculated sight can be outflowing at the observed speeds and that only following Tielens et al. 1994) do not exceed 1000 yr (the ap- thehigh-densitycomponentoftheoutflowisdusty.Wederived proximate time grains spend in the wind if they travel at the these results usinga “cloudsembeddedin a continuousMHD observed outflow velocity over a distance of 1 pc). Including diskwind”model,butourconclusionsalsoapplytootherplau- both of these effects, the predicteddustextinctionis overone siblescenariosthatincludeacontinuum-shieldinggascolumn order of magnitude greater than the maximum value allowed and an absorptionregion that contains distinct low- and high- by the observations. We also considered the effect of chang- densitycomponents. Ourbasicconclusionsappeartobequite ingthescalingofthewinddensitywithradiusfromn∝r- 1 to general,althoughtheprecisecompositionoftheabsorbinggas n∝r- 3/2(asinBlandford&Payne1982)andton∝r- 2. These and its detailed spatial and kinematic properties are not fully modelsagainoverestimatethe extinctionbyaboutanorderof constrainedbytheobservationsandremainmodeldependent. magnitudeafterdustsublimationandsputteringaretakeninto In addition to explainingthe FBQS 1044 observations, this account. Wethereforeconcludethat,ifthegascomprisingthe picturemayberelevanttotheinterpretationofabsorptionfea- shieldisassociatedwithadiskoutflow,thenitmustalreadybe turesinsimilarobjectswheresingle-phasemodelsimplyalarge dust free when it leaves the disk. Such a situation couldarise distance. Forinstance,inthecaseoftheradio-loudgalaxy3C ifthewindoriginatesinahotdiskcoronawherethematterre- 191,absorberdistancesof∼28kpcwereinferredbyHamann sideslongenoughforanydustgrainstobedestroyed. et al. (2001) using similar arguments to those employed by However,toprovidetherequisiteshielding,adust-freewind dK01. A multiple-phase model could place these absorbers requiresahighertotalgascolumnthanadustyoutflow,sothe muchclosertothecentralsource. inferred lack of dust in the wind implies a prohibitivelylarge ThisinterpretationmayalsobeapplicabletootherAGNob- mass outflow rate — much larger than could be launched by servations. As outlined in § 1, several distinct outflow com- themagneticfieldthatconfinesthecloudsinourmodel. Thus, ponents have been inferred in various types of AGNs. There only part of the shield can be outflowingat velocities that are is now growing evidence that these components may not be comparableto(orexceed)theobservedspeeds.Perhapsthein- single-phase. For the warm-absorber component, which has neroutflowhasa lowervelocitythanwe predict,orelse some been inferred to give rise to both X-ray and UV absorption oftheshieldmaynotevenbeoutflowing,asinadiskcoronaor (e.g.,Crenshaw1997;Mathuretal.1998;Monieretal.2001), a“failed”line-drivenwind(see§1). thereareindicationsinatleastsomesourcesthattheX-rayand All of these considerations yield our best model, which is UVabsorbingcomponentsarenotidentical(e.g.,theSeyfert1 comparedwiththeobservationalresultsinTable1. Thismodel galaxy NGC 3783 — Kaspi et al. 2000; Kraemer, Crenshaw, satisfies all the observational constraints and implies that the & Gabel 2001). Furthermore, it appears that the UV and X- absorbing gas lies over two orders of magnitude closer to the rayabsorbingcomponentsarethemselvesdividedintomultiple central source than the earlier estimate. The radius where the zones. IntheUVregime,thishasbeenestablishedinSeyfert1 observedgasleavesthedisksurfaceis,ingeneral,smalleryet. galaxieslikeNGC3783(Kraemer,etal.2001)andNGC3227 We can estimate the mass outflow rate associated with the (Crenshaw et al. 2001). In the X-ray regime, this is exempli- absorbinggasthroughtherelationM˙ ≈2πrfN m v,where fied by the Seyfert 1 galaxy MCG-6-30-15, which was mod- wind H p eled by Morales, Fabian, & Reynolds (2000) as an extended 4 Everett,Königl,&Arav multi-zone medium. These authors suggested that, in reality, phases, which we modeledas a continuouswindwith embed- these zones may correspond to a continuum of clouds at dif- deddense clouds, shieldedfromthe centralcontinuum. If the ferent radii and different densities, as in the BELR model of shieldisidentifiedwiththecontinuouscomponent,thenonlya Baldwinetal.(1995). Ahierarchical,turbulent-gasrealization fractionof it can be outflowingat a speed thatapproaches(or of this concept was recently presented by Bottorff & Ferland exceeds) the value in the Fe/Mg absorption region. We also (2001).Our“cloudsinacontinuouswind”scenarioisdesigned deduced that the clouds are dusty but that the shield is effec- toexplicitlyaddresstheoutflowingnatureoftheabsorbinggas tivelydustfree.Asfarasweareaware,thisisthefirstinstance but is otherwise similar to the above picture in its description of a BALR outflow in which the data provide direct evidence ofspatiallycoexistingmultiplephases.Forsimplicity,wehave fortheexistenceofamultiphasemedium. Togetherwithother treatedthecloudsaslong-lived,pressure-confinedentities,but piecesofevidence,thisresultlendssupporttotheviewthatall it is entirely conceivable that the clouds are transient features the majoroutflowcomponentsin AGNs maycontain multiple that arise in a turbulent outflow. The same basic picture of a phases. multiphasemediummaythusapplytothegasintheBELR,the BALR(e.g.,Aravetal.1999),thewarmabsorber,andeventhe NLR(e.g.,Komossa2001). Wegratefullyacknowledgetheinitialworkofandcontinued Inconclusion,wehavearguedthattheobservationsofFBQS discussionswithMartijndeKoolaswellashelpfulcomments 1044 can be interpreted in the context of the standard BALR from Mike Brotherton, Abraham Loeb, and the referee. J.E. pictureintermsofagasoutflowthatconsistsof(atleast)two andA.K.thankNASAforsupportthroughgrantNAG5-9063. 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ThecontinuouswindaccountsfortheFeIIaswellas thehigher-velocityMgIIabsorptionwithoutoverproducingthelow-ionizationMgIabsorption(whichisattributedtothedenseclouds). 6 Everett,Königl,&Arav FIG.2.—Columndensitiesindustycloudsofhydrogendensitync=108.5cm- 3thatareshieldedbythecontinuousdust-freewindofFig.1.Thecloudsaccount fortheMgIabsorptionwithoutoverproducingthehigher-ionizationFeIIabsorption(whichisattributedtothecontinuouswind).