document: in the unification scheme of agn the difference between type 1 and type 2 agn is explained by angle - dependent circumnuclear obscuration of the accretion disk and broad - line region @xcite . this obscuring dusty medium 
   commonly referred to as `` dust torus ''  is optically and geometrically thick and probably extends from sub - parsec scales outward to several 10s of parsecs , or beyond for high luminosity objects . 
   the dust in the torus absorbs the incident uv / optical radiation an re - emits the received energy in the infrared 
   .    observations have shown that type 1 agn show significantly more emission in the near - ir than type 2 agn for the same given intrinsic luminosity ( e.g. * ? ? ? 
   this is consistent with the picture where the face - on view onto the torus in type 1 agn exposes the innermost hot dust to the observer . on the other hand in type 2 agn the torus 
   is seen edge - on so that internal obscuration blocks the line - of - sight to the hot dust . owing to this effect 
   , it is expected that for a given agn luminosity the infrared emission of type 1 agn is generally stronger than from type 2s .    in the light of attempts at forming isotropic agn samples based on ir fluxes it seems important to know exactly how strong of a bias towards type 1s over type 2s 
   may occur when invoking flux limits . 
   moreover , probing the wavelength dependence of this anisotropy in the infrared has some constraining power on our understanding of how the torus obscures the agn . it may be possible to distinguish torus models where the dust is smoothly distributed from those where the dust is arranged in clouds ( e.g. * ? ? ? 
   * ) : if the dust is smoothly distributed within the torus , a large degree of anisotropy is expected . 
   if , however , the dust is arranged in clouds the anisotropy is expected to be smaller . 
   a problem commonly encountered when studying agn samples in the local universe is a significant contribution of the host galaxy to the ir . 
   this is related to the typical lower luminosity seyfert galaxies which dominate the nearby agn population . 
   one way around this problem is the use of high - spatial resolution observations , as possible with the largest ground - based telescopes or interferometers , which are able to resolve out the host and isolate the agn emission ( for details see * ? ? ? 
   * ) . however , it is difficult to set up representative samples owing to the observational limitations . 
   another possibility is the use of high luminosity objects  typically at higher redshift  where the agn outshines the host galaxy by a large factor in the optical and near - ir . 
   if pah features are absent , the agn most likely dominates the mid - ir wavelength region as well ( in our sample : host @xmath4 for wavelengths @xmath5 17@xmath2 ) .    in this paper 
   we aim at quantifying the wavelength dependence of the anisotropy of the agn emission in the infrared from @xmath1 . for that we use a ( nearly ) isotropically selected and complete sample of quasars and radio galaxies with hidden quasars at @xmath0 as recently presented in @xcite and described in sect . 
   [ sec : sample ] . 
   here we improve the analysis by using host - galaxy subtraction for the radio galaxies and use clumpy torus models for interpretation . in sect . 
   [ sec : results ] we show the average seds of each of the subsamples which are representing obscured ( type 2 ) and unobscured ( type 1 ) agn . 
   we further analyze the origin of the anisotropy by fitting extinction models and clumpy torus models to the observations in sect . 
   [ sec : analysis ] . in sect . 
   [ sec : obsaniso ] we discuss our results by comparing them to previous ir anisotropy estimates in literature . 
   the results are summarized in sect . 
   [ sec : summary ] . 
   the object sample for this paper comprises all 3crr @xcite radio galaxies and quasars with @xmath6 this lobe dominated sample presents a well matched set of radio galaxies and quasars in terms of their intrinsic luminosity ( @xmath7erg / s for the quasars and @xmath8erg / s for the radio galaxies ; errors indicate standard deviation of the sample ) . 
   the data used here have been presented previously in @xcite and @xcite and we refer the reader to these papers for further details on the source selection , data reduction , and building of the average seds . to summarize briefly , we obtained mid - ir photometry in all six filters from 3.6@xmath2 to 24@xmath2 and spectroscopy from 19@xmath2 to 38@xmath2 utilizing all three instruments onboard the _ spitzer _ 
   space telescope @xcite . 
   after the data reduction in a standard manner , the individual source seds were interpolated onto a common rest frame wavelength grid . 
   the quasars and radio galaxies were then averaged into a mean sed for each class of objects . 
   the individual seds ( including observed and interpolated photometry ) as well as the the average seds are presented in ( * ? ? ? 
   * their figs.1 & 2 ) .    for this paper , additional corrections have been applied to the radio galaxy data before the averaging process outlined above : at the shortest wavelengths considered here ( @xmath9@xmath10 m , rest frame ) the radio galaxy seds show contributions from the host galaxy . 
   since we want to isolate the emission coming from the active nucleus , we have to correct for the stellar emission in these cases . 
   this correction was performed by fitting the observed irac photometry with a combination of a moderately old ( 5 - 10gyr ) elliptical galaxy sed to represent the stellar emission ( taken from the grasil webpage ; @xcite ) and a hot black body for the agn dust whose temperature we allowed to vary ( see e.g. * ? ? ? 
   * ; * ? ? ? 
   the resulting black body temperatures in the radio galaxies range from 600 to 970k , with a median value of 860k . 
   the fraction of host galaxy light contributing to the flux measured at the observed frame wavelengths 3.6 , 4.5 , 5.8 , and 8.0@xmath10 m was found to be 0.9 , 0.6 , 0.3 , and 0.1 , respectively . despite a negligible contribution from the host galaxy 
   , we performed similar fits to the quasar sample as well to obtain characteristics of the hot dust emission and compare it to the radio galaxies . 
   for the quasars we find notably hotter temperatures in the range from 8801250k ( median 1020k ) . 
   this is consistent with the idea that the hottest dust is obscured in radio galaxies , while directly seen in quasars . in the radio galaxies we then subtracted the estimated host galaxy contribution from the observed irac photometry using the scaled template sed . 
   for the irs and mips measurements the host galaxy contributions were considered negligible at restframe wavelength @xmath11 and no corrections have been applied . 
   we refrain from further corrections related to possible starformation . 
   as pointed out in @xcite neither the individual seds nor the averages showed any pah features ( see also fig . 
   [ fig : aver_sed ] ) , which indicates that any contribution from starformation to the mid - ir is probably negligible . 
   the radio galaxy 3c368 has a galactic m - star superimposed close to the position of the radio galaxy nucleus ( e.g. * ? ? ? 
   * ; * ? ? ? 
   both sources are partly blended even at the shortest irac wavelengths which makes the correction for the host galaxy emission in this source quite uncertain . 
   consequently , we removed this source from the sample considered here . 
   this leaves us with 11 quasars and 8 radio galaxies from which the average seds have been calculated . 
   in fig .  [ fig : aver_sed ] we show the average sed of @xmath13 quasars ( red ) and radio galaxies ( blue ) respectively . 
   the error bars reflect the mean absolute deviation while the shaded areas show the range of the respective subsample at each wavelength point of the interpolated data ( see sect . 
   [ sec : sample ] ) . for each of the object types we calculated a spline fit through the mean data points in order to guide the eye . 
   it is obvious that the radio galaxies are systematically lower in infrared emission than the quasars . 
   the discrepancy is largest in the near - ir and flattens out towards longer wavelengths . 
   @xcite showed similar average seds . 
   here we used additional host galaxy subtraction , which isolates the agn light much better ( see sect .  [ 
   sec : sample ] ) . 
   this is most obvious in the near - ir part of the radio galaxies shortward of 5@xmath2 . 
   the sed keeps on falling toward shorter wavelengths consistent with the wien tail from hot dust emission , instead of making an upward turn ( see * ? ? ? 
   since both types have the same radio luminosities due to our selection , this difference between quasars (= type 1 agn ) and radio galaxies (= type 2 agn ) is a generic property of the sample . 
   it either reflects a difference in line - of - sight extinction ( e.g. by cold dust in the host galaxy ) , or traces the anisotropy in re - emission of the agn - heated dust . 
   @xcite tested the former possibility and found a surprisingly good match of the difference between radio galaxies and quasars in the mid - ir by a single extinction law . 
   this , however , breaks down in the near - ir . in this paper 
   we will test if , instead , a single absorber and emitter (= the dust torus ) may be responsible for the radio galaxy / quasar anisotropy ( see sect . 
   [ sec : modcomp ] ) .    to quantify the wavelength dependence of the anisotropy we plot the quasar / radio galaxy ratio in fig . 
   [ fig : ratio ] . also shown is the mean absolute deviation of the ratio calculated by propagating the standard deviations of each subsample . from 2 to 8@xmath2 the emission ratio gradually decreases from 20 to 2 . in the silicate feature 
   this ratio increases again up to about 3 and flattens out towards 15@xmath2 at a value of @xmath14 . 
   our sample comprises a range of sed shapes , meaning that a range of ratios is observed . 
   most of this sample range comes from the radio galaxies which show much less uniformity than the quasars ( see fig . 
   [ sec : sample ] ) . 
   we illustrated the range of ratios covered by the radio galaxies in fig . 
   [ fig : range ] where we plot the wavelength dependence of the ratio of each radio galaxy using the average quasar sed and normalize it to 15@xmath2 .    at around 10@xmath2 
   the radio galaxies show the silicate feature in absorption while quasars display a weak silicate emission feature . 
   we used the spline fits described above ( see fig . 
   [ fig : aver_sed ] ) to locate the centers of the silicate features following the method outlined by @xcite . 
   the silicate absorption feature center is found to be at @xmath15 while the peak of the silicate emission feature was measured at @xmath16 . 
   this difference in central wavelength is similar to the ones observed in local galaxies . 
   as recent high spatial resolution studies of seyferts suggest , the `` shift '' in wavelength is not a pure radiative transfer effect due to the location or distribution of the dust , but implies a change of dust chemistry within the torus @xcite . 
   as demonstrated by @xcite the silicate emission feature may be located at around 10.5@xmath2 if a fraction of the hot silicate dust consists of porous silicate grains . 
   we note that the transition from quasars to radio galaxies is not as smooth as one may expect . in spite of some overlap in the range of seds of both types in the near - ir part in fig . 
   [ fig : aver_sed ] , quasars generally show infrared emission characteristics expected for a type 1 agn ( blue ir color ; silicate emission feature ) and radio galaxies have ir seds with type 2 emission properties ( redder sed ; silicate absorption feature ) . 
   in this section we analyze the scenarios that can lead to the observed anisotropy in radio galaxies and quasars . 
   there are two possibilities : ( 1 ) extinction by a cold dust screen and ( 2 ) absorption and emission in a warm dusty medium . 
   the former possibility may be associated with cold dust in the host galaxy while the latter one is equivalent to the dust torus in the agn unification scheme ( which we may call `` intrinsic anisotropy '' ) . 
   we will first discuss the plausibility and consequences of a cold dust screen on the seds . if the ir anisotropy is dominated by cold host galaxy dust 
   , then we have a situation where the ir emission originates from the torus while the absorption is coming from a different component ( i.e. dust in the host ) . 
   this means that we require an additional component outside the agn to model the data ( e.g. as used for a significant minority of high-@xmath17 type 2 qsos in @xcite ) . 
   however , the objects suffering extinction ( here : radio galaxies ) would be offset from quasars by only a single extinction law . 
   this has been tested and ruled out by @xcite for the same set of objects as presented here . in fig . 
   [ fig : ratio ] we show the anisotropy ratio between quasars and radio galaxies ( black circles with error bars ) . 
   we overplot a standard ism extinction curve , resembling cold screen extinction , scaled to the observed 15@xmath2 anisotropy ( dark - blue dotted line ; using a mixture of 53% silicates and 47% graphite , based on updated dust opacity cuves by @xcite , and a grain size distribution according to @xcite ) . 
   the extinction curve significantly overpredicts the anistropy in the silicate feature with better agreement in the near - ir . for reference we also plot the extinction curve based on ( 
   * light - blue dotted line ;  pixie dust  ) , as used in @xcite , which results in better agreement within the silicate feature but significant offsets in the near - ir . 
   in fact , @xcite pointed out that a good correspondence of quasars and radio galaxies can be achieved only if the quasar sed is attenuated by at least _ two _ instead of one extinction components  which is reminiscent of radiative transfer (= absorption _ and _ emission ) within the torus rather than a cold screen 
   .    moreover , we found a mean anisotropy of about 1.4 at 15@xmath2 ( see sect .  [ sec : results ] ) . 
   dust opacity curves typically have opacity ratios @xmath18 . in order to obtain the observed anisotropy 
   , the dust screen would have to have @xmath19 . 
   while such optical depth values are in reach for galactic dust lanes ( e.g. extinction towards our own galactic center ) , it requires very edge - on views onto disk galaxies since the scale height of galactic disks is small . on statistical grounds 
   this possibility may be viable for a minority of all radio galaxies , but it is unlikely that the whole population is dominated by host extinction . 
   we note that the same line of argument can be made using the near - ir anisotropy leading to even higher @xmath20 and illustrating the need for more then just one cold extinction screen in this scenario . 
   we use our clumpy torus models _ cat3d _ 
   @xcite to test if the observed anisotropy ratio can be explained by the intrinsic anisotropy as predicted in the unification scheme . 
   generally smooth dust torus models predict stronger anisotropy than clumpy models @xcite . 
   @xcite argue that the observed small anisotropy in the mid - ir / x - ray correlation ( see sect . 
   [ sec : obsaniso ] ) is qualitatively in agreement with a clumpy torus . 
   here we aim at being more quantitative and show consistency of the observed anisotropy with torus orientation .    in fig . 
   [ fig : ratio ] we overplot the observed ratio with predicted ratios of a clumpy torus model ( red dashed line ) . as mean torus inclination in quasars 
   we assumed 39@xmath21 while the mean radio galaxy inclination is set to 75@xmath21 . 
   this corresponds to a mean opening angle of the torus of 60@xmath21 or a type 1/type 2 ratio of 1:1 , which is consistent with the number statistics of our complete and isotropic sample @xcite . 
   [ fig : ratio ] shows that the model is following the continuum anisotropy curve quite well . 
   there is , however , a slight deviation within the silicate feature where in the center of the feature the model curve predicts slightly lower anisotropy than shown by the observed curve . 
   this may be indicative of additional , off - torus obscuration in some objects ( e.g. from the host galaxy ) , which effectively deepens silicate absorption features in radio galaxies ( the denominator of the plot in fig . 
   [ fig : ratio ] ) and , to a lesser degree , changes the spectral slope . 
   if this happens in individual objects , the average curve and scatter will tend to be slightly more anisotropic . 
   some local examples of host obscuration are centaurus a , ngc  5506 , or the nucleus of the circinus galaxy where host - galactic dust lanes are projected onto the nucleus producing deep silicate features . 
   in fact the silicate absorption feature in the average radio galaxy sed seems to be deeper than in typical local seyfert 2 galaxies without host obscuration @xcite . 
   note that this requires a statistical alignment of cold host dust with that of the torus ( see sect . 
   [ sec : extinct ] ) . 
   the model used for reproducing the ratio uses a dust cloud distribution with radial power law @xmath22 and 5 clouds along the line - of - sight in equatorial direction ( for details see * ? ? ? 
   * ) . in comparison 
   to models for seds and mid - ir interferometry of local seyfert galaxies , these parameters suggest only a slightly more centrally condensed and transparent torus @xcite , while the half - opening angle may be wider ( 60@xmath21 instead of 45@xmath21 ) . 
   in fact a range of torus model parameters satisfies the observed type 1/type 2 anisotropy spectrum within the error bars of the sample ( e.g. various steeper and shallower dust distributions ) . from bayesian inference analysis we found that the torus model parameters are generally poorly constrained ( broad posterior distributions for individual parameters ) . 
   a weakness is certainly that modeling the flux ratio is not very constraining for model parameters since it does only take relative fluxes into account , while absolute fluxes ( e.g. actual silicate strength of type 1s or type 2s ) are not included . on the other hand , what the modeling shows is that the observed small ratios at long wavelengths and the change of anisotropy from the near- to the mid - ir are in agreement with expectations from clumpy torus models without fine - tuning parameters .    in summary , the torus model seems to reproduce the observed anisotropy reasonably well over most of the wavelength range , while single extinction laws result in much worse fits . 
   the model parameters used in the clumpy torus model fit are reasonable in comparison to fits to local agn . 
   it demonstrates plausibility of the scenario that the anisotropy is related to torus orientation . 
   this strongly suggests that the observed anisotropy is a measure for the intrinsic anisotropy of luminous type 1 and type 2 agn at @xmath12 . 
   in sect .  [ sec : analysis ] we argued that the observed ir anisotropy is probably reflecting the `` intrinsic anisotropy '' as caused by the dust torus . 
   the isotropic and complete selection of the sample helps to minimize any biasing effects on the anisotropy . on the other hand , optically- and 
   x - ray - selected samples often suffer from missing some of the most obscured objects . 
   moreover , since the ratio is @xmath23 at 15@xmath2 , flux - limited mid - ir selected samples are potentially biased towards type 1 agn as well . 
   thus , even using 12@xmath2-selected agn samples will slightly suffer from the assumption of isotropy . 
   one popular way of comparing type 1s and type 2s is the correlation between x - ray and mid - ir luminosity . in case 
   the x - luminosity is emitted isotropically ( and traces the dust - heating emission ) , and the mid - ir emission is radiated very anisotropically , this correlation is expected to be different for type 1 and type 2 agn . however , using high spatial resolution observations @xcite showed that local seyfert 1 and seyfert 2 galaxies , up to column densities of few @xmath24 @xmath25 , essentially follow the same correlation . 
   a conservative estimate suggests that at 12@xmath2 the difference between both types is smaller than a factor of 3 . despite including some `` mildly '' compton - thick objects in this study 
   , the most obscured objects are still missing due to the lack of intrinsic x - ray data . 
   this essentially makes anisotropy estimates from the mid - ir / x - ray - correlation a lower limit on the `` true '' anisotropy . 
   nevertheless this result is fully consistent with our finding for powerful @xmath12 agn . at 12@xmath2 
   we find a type 1/type 2 ratio of @xmath26 . assuming that x - ray selection misses the highest - inclination objects our result would predict that the anisotropy in the mid - ir / x - ray correlation is @xmath27 , at least for powerful agn as presented here . 
   @xcite used a sample of local seyfert galaxies and compared the average 535@xmath2 sed of type 1s and type 2s , scaled to their respective 8.4ghz emission . 
   however since the sources have been selected according to a flux limit at 12@xmath2 , the sample can not be considered isotropic . 
   @xcite report generally higher fluxes for type seyfert 1 agn as compared to seyfert 2s . 
   the anisotropy decreases from a factor of about 8 to @xmath32.5 from 5 to 8@xmath2 . 
   this is significantly larger than what we find for our isotropically selected radio - loud sample . at longer wavelengths the seyfert 1/seyfert 2 ratio of @xcite flattens to about a factor of 23 ( with no convergence to unity as expected at long wavelengths ) which is , again , larger than what we found . 
   the discrepancy between our results and @xcite may be either due to ( 1 ) the different selection criteria chosen , ( 2 ) a difference between low and high luminosity agn , or ( 3 ) a difference between radio - quiet and radio - loud agn . while the data in @xcite has not been corrected for host galaxy , the contribution by starformation should not be significant given the lack of pah features in the average spectrum . 
   if a host - correction were applied , it would predominantly affect type 2 agn , thus making the anisotropy even larger . 
   furthermore , if the mid - ir selection had any effect , then the sample would miss out agn at highest obscuration , so that the real type 1/type 2 anisotropy would again be larger . in conclusion 
   , possible selection effects and host contamination in the @xcite study would tend to result in an underestimated anisotropy , making the difference to our findings even stronger . 
   it is well possible that the difference in anisotropy between our high - luminosity radio - loud sample and the low - luminosity radio - quiet sample is real . 
   this would imply that either luminosity or radio power are the drivers for the observed characteristics . 
   radio jets are highly collimated so that any influence of the jet can be expected perpendicular to the torus plane and just in a very small solid angle . 
   it is , therefore , more reasonable to assume that the higher agn luminosity would cause the lower anisotropy than the jet . 
   the classical receding torus picture changes the opening angle of the torus for higher luminosity ( e.g. * ? ? ? 
   * ; * ? ? ? 
   this mainly affects the relative number of type 1s and type 2s in a sample . 
   the relatively high fraction of about 50% unobscured agn in our sample would support this scenario . 
   however , to change the anisotropy between both types , it would be necessary to also change the obscuration properties ( i.e. type 2s must on average look more like type 1s ) . 
   such a scenario of `` radiation - limited obscuration '' has been proposed by @xcite and supported by observations of @xcite . in this case about the same effect is expected for radio - quiet and radio - loud agn . 
   we use the sample of quasars and radio galaxies at @xmath12 recently presented in @xcite . since the sample was selected isotropically 
   , it should cover all torus inclination angles ( weighted by solid angle ) . 
   for these objects an infrared 117@xmath2 restframe sed has been constructed . 
   average seds were calculated for the quasar (= type 1 agn ) and radio galaxy (= type 2 agn ) samples , respectively , in order to study the intrinsic anisotropy of the ir emission of the dust torus . 
   it is shown that the ratio between type 1 and type 2 agn in our parameter space of very luminous radio galaxies , the value gradually decreases from 20 to 2 at wavelengths 2 to 8@xmath2 . within the 10@xmath2 silicate feature the ratio raises slightly . at longer wavelength 
   the mid - ir emission becomes more isotropic . 
   the intrinsic ratio between our type 1 and type 2 agn is @xmath14 at 15@xmath2 . when using ir - selected flux - limited samples this anisotropy has to be taken into account . 
   by analyzing the silicate feature in the sample averages we find the well - established `` shift '' of the central peak of the silicate emission feature with respect to the center of the absorption feature . 
   the resulting central wavelengths at @xmath15 for the absorption and @xmath16 for the emission feature are in agreement with previous reports ( e.g. * ? ? ? 
   * ; * ? ? ? 
   we discussed our results in the frame of other anisotropy estimators . 
   our findings are consistent with upper limits derived from the x - ray / mid - ir correlation of local seyfert galaxies @xcite . 
   some discrepancy exists with respect to a similar study of @xcite for nearby seyferts . 
   if real it would imply that nearby , radio - quiet lower - luminosity agn show a higher degree of anisotropy in the ir than higher luminosity , radio - loud sources . 
   this may be explained by a receding torus model with luminosity - dependent obscuration . 
   we also show that the overall relatively small degree of anisotropy is consistent with the torus being clumpy rather than smooth . 
   our clumpy torus model reproduces the observed type 1/type 2 ratio reasonably well . 
   we would like to thank our referee prof . 
   andy lawrence for helpful and constructive comments which significantly improved the paper , as well as poshak gandhi who also commented on this manuscript . 
   the paper was made possible by deutsche forschungsgemeinschaft ( dfg ) in the framework of a research fellowship ( `` auslandsstipendium '' ) for sh . 
   mh is supported by the nordrhein - westflische akademie der wissenschaften und der knste . 
   this work is based on observations made with the spitzer space telescope , which is operated by the jet propulsion laboratory , california institute of technology under a contract with nasa . 
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summary: we use restframe near- and mid - ir data of an isotropically selected sample of quasars and radio galaxies at @xmath0 , which have been published previously , to study the wavelength - dependent anisotropy of the ir emission . for 
   that we build average seds of the quasar subsample (= type 1 agn ) and radio galaxies (= type 2 agn ) from @xmath1 and plot the ratio of both average samples . from 2 to 8@xmath2 restframe wavelength 
   the ratio gradually decreases from 20 to 2 with values around 3 in the 10@xmath2 silicate feature . 
   longward of 12@xmath2 the ratio decreases further and shows some high degree of isotropy at 15@xmath2 ( ratio @xmath31.4 ) . 
   the results are consistent with upper limits derived from the x - ray / mid - ir correlation of local seyfert galaxies . 
   we find that the anisotropy in our high - luminosity radio - loud sample is smaller than in radio - quiet lower - luminosity agn which may be interpreted in the framework of a receding torus model with luminosity - dependent obscuration properties . 
   it is also shown that the relatively small degree of anisotropy is consistent with clumpy torus models .