活动星系核中的尘埃

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1、AbstractDustisthecornerstoneoftheunificationtheoryofactivegalacticnuclei(AGNs).ThistheoryproposesthatallAGNsareessentially―bornequal‖:alltypesofAGNsaresurroundedbyanopticallythickdusttorusandarebasicallythesameobjectbutviewedfromdifferentlinesofsight.Thelargediversityintheobservationalpropert

2、iesofAGNsissimplycausedbytheviewing-angle-dependentobscurationofthenucleus:thoseviewedface-onareunobscured(allowingforadirectviewoftheirnuclei)andrecognizedas―type1‖AGNs,whilethoseviewededge-onare―type2‖AGNswithmostoftheircentralengineandbroadlineregionsbeinghiddenbytheobscuringdust.Itisthisc

3、rucialroleplayedbydustintheunifiedmodelofAGNsthatmakesunderstandingdustpropertiesveryimportantinunderstandingAGNs.However,littleisknownaboutthedustinthecircumnucleartorusofAGNs.ThereisevidencesuggestingthatthesizeandcompositionofthedustinAGNsmaydiffersubstantiallyfromthatoftheGalacticinterste

4、llardust,asreflectedbytheflat/―gray‖extinctioncurves,the2175Åextinctionbumpisnot(oratleastrarely)seeninAGNs,andtheanomaloussilicateemissionorabsorptionfeaturesobservedrespectivelyintype1andtype2AGNs.InthisthesiswetookacomparativestudyoftheextinctionandIRemissionaswellastheUV/IRspectroscopicpr

5、opertiesandtheinferredcompositon,sizeandmorphologyofthedustinAGNsandthedustintheinterstellarmediumoftheMilkyWayandothergalaxies.ThenwesummarizedourcurrentunderstandingoftheextinctionandinfraredemissionpropertiesofthecircumnucleardustinAGNsaswellastheinferreddustcompositionandsizedistribution.

6、Themainresultsarethefollowing:1.LittleisknownaboutthewavelengthdependenceoftheextionctioncausedbythecircumnucleardustofAGNs.Sofar,theAGNextinctioncurvesaremainlyinferredfromcompositequasarspectraandindividualreddenedAGNs.Thesetwoapproachesderivecontradictingresults:theformerofternrevealsa―gra

7、y‖extinction,implyingthatthesizedistributionofthedustintheAGNcircumnuclearenvironmentsisskewedtowardssubstantiallylargegrains;thelaterofternsuggestsasteep–risingSMC-likeextinction,indicatingapreponderanceofsmallgrainsnearthenucleus.2.The2175Å