Mon.Not.R.Astron.Soc.000,000–000 (0000) Printed1February2008 (MNLATEXstylefilev1.4) The evidence for jet-cloud interactions in a sample of high/intermediate-redshift radio galaxies C. Solórzano-Inãrrea1,2, C. N. Tadhunter1, D. J. Axon3 1Department of Physics and Astronomy, Universityof Sheffield, Sheffield, S3 7RH 2Department of Physics and Astronomy, Universityof Leeds, Leeds, LS29JT 3Department of Physical Sciences, Universityof Hertfordshire, Hatfield, AL10 9AB 1 0 0 1February2008 2 n a ABSTRACT J We present detailed long-slit spectroscopic observations of a sample of four powerful 5 radio galaxies, with intermediate/high redshifts (0.47 < z < 0.81). The observations 2 cover the rest-wavelength range 2600 ˚A- 6600 ˚A, chosen to include important diagnostic emission lines ([NeV]λ3426, [OII]λ3727, [NeIII]λ3869, Hβ, [OIII]λ5007), which 1 are also measured in optical observations of low-redshift radio galaxies. In two of v the galaxies (3C 352 and 3C 435A) the radio sources are of the same scale as the 7 emission-line regions, whereas in the other two (3C 34 and 3C 330) the radio sources 5 are extended on a larger scale than the emission-line structures. We find that the 4 extended regionsof all the galaxiespresenthighly disturbed kinematics,consisting of 1 0 line-splitting (∆v ∼ 1000 km s−1) and/or underlying broad components (FWHM = −1 1 1000— 1500km s ). These features aredifficult to explainin terms of gravitational 0 motioninthehaloesofthehostgalaxies.Rather,itislikelythattheyaretheresultof / strong shocks driven through the ISM/IGM by the radio sources. These observations h suggest that jet-induced shocks have an important effect on the emission-line proper- p ties even in sources in which the radio structures are on a much larger scale than the - o emission-line structures. r While the emission-line kinematics provide strong evidence for shock accelera- t s tion, the dominant ionization mechanism for the emission-line gas remains uncertain. a We have compared the optical diagnostic line ratios of the galaxies in our sample : v with various ionization models, including: pure shock ionization, shocks including i a photoionized precursor, power-law photoionization and photoionization including X matter-bounded clouds. We find that both pure-shock ionization and power-law pho- r toionization model predictions fail to provide good fits to the data. On the other a hand,onindividual diagnosticdiagrams,models forshockswhichinclude a photoionized precursor are consistent with the results for the majority of the EELR of the galaxies in our sample, and photoionization including matter-bounded clouds models also give reasonable fits to some of the EELR. However, in terms of the positions of the points relative to the model sequences on the diagnostic diagrams,there is a lack of consistency from diagram to diagram. The diagnostic diagram involving the line ratios [OIII](4959+5007)/4363and HeII(4686)/Hβ is particularly problematic in this regard. Overall, our results suggest that, if the EELR are shock-ionized, one or more of the assumptions implicit in the shock models may need to be reconsidered. In addition, we have investigated the nebular continuum contribution to the UV excess in the galaxiesin our sample.We find a substantialnebular emissioncontribu- tionto the UV continuuminallthe cases,inthe range∼ 10—40 per cent.However, after the subtraction of the nebular component, a significant UV excess remains in the extended nebulae of most of the objects. Key words: galaxies: active – galaxies:jets – galaxies:kinematics and dynamics. c 0000RAS (cid:13) 2 C. Solórzano-Inãrrea et al. 1 INTRODUCTION low-surface-brightness emission-line structures at large dis- tancesfromtheradiojetaxis.Thesestructuresareinconsis- Most powerful radio galaxies have extended emission-line tentwiththeilluminationmodel,sincepartsofthemlieout- regions (EELR) extendingto large distances from their nu- side the ionization cones predicted by the unified schemes, clei(5—100kpc)(Tadhunter1986).TheseEELRofferthe andrathersuggestthattheionizingeffectsoftheradiocom- possibility ofinvestigatingtheorigin oftheactivityandthe ponentscan extendfar from the radio jet axes. origin of the gas itself. However, if we are going to use the At higher redshifts (z > 0.5) there appears to be more EELRinthisway,weneedtoknowtheextenttowhichthe evidence for shocks than in the population of low-redshift emission-linemorphologiesandkinematicsreflecttheintrin- radiogalaxies.Atsuchredshiftspowerfulradiogalaxiesfre- sicpropertiesofthegaseoushaloes,andtheextendtowhich quentlyshowhighlycollimatedUVcontinuumandemission- they reflect the effects of the activity. Thus, it is crucial to linestructureswhicharecloselyaligned withtheradioaxes understand theionization mechanisms in these sources. (McCarthy et al. 1987; Chambers, Miley & van Breugel The nature of the mechanisms involved in producing 1987; Best, Longair & Röttgering 1996). Such collimated theobservedkinematicsandionizationoftheEELRremains structures are not what would be expected on the basis of highly uncertain. Currently, the two most accepted models illumination by the broad radiation cones predicted by the are photoionization by a central active nucleus, and shock- unifiedschemes.Inaddition,manyhigh-redshiftradiogalax- ionization by the interaction between the radio-emitting ies present highly disturbed emission-line kinematics along components and the ambient gas. In the latter model, the theradioaxis,whicharedifficulttoexplainintermsofpure so-called jet-cloud interaction model, the advancing radio gravitational motions (McCarthy, Baum & Spinrad 1996). jet drives strong shocks into the warm clouds of gas in the This suggests that processes other than AGN illumination haloes of the host galaxies. The regions directly behind the maybeatwork.Indeed,manyofthesefeaturesobservedin shocksarecompressedandheatedtoveryhightemperatures powerfulhigh-redshiftradiogalaxiesareconsistentwiththe and line emission is produced by two distinct mechanisms: jet-cloud interaction model described above and with the (a)asthepost-shockcloudscoolbyemittinglineradiation, results of detailed studies of jet-cloud interactions in low- and (b) photoionization of the cool, dense, post-shock gas redshift radio galaxies. andtheprecursorgasaheadoftheshockbythehotshocked Inaddition,recentworkbyBest,Röttgering&Longair gas. It is likely that no single mechanism, but a combina- (2000a),atredshiftsz 1,hasdemonstratedthatthereisa tion ofboth AGNphotoionization andjet-cloud interaction ≃ strong evolution of the emission-line properties of powerful is required to explain the kinematics and ionization of the radio galaxies with radio size. They find that radio sources EELR overthewhole range of redshifts. with small linear sizes have emission-line properties which Atlowredshifts(z<0.3),thepropertiesoftheEELRin are in agreement with the theoretical shock ionization pre- mostradiogalaxies appeartobeconsistent withtheillumi- dictions,andshowhighlydistortedvelocityprofiles.Incon- nationoftheambientgasbytheradiation fieldofanactive trast, the larger radio sources, where the shock fronts have nucleus(e.g. Fosbury1989), and theemission-line kinemat- passed beyond the emission-line regions, present emission- ics can be explained in terms of pure gravitational motion lineratiosconsistentwithAGNphotoionization,withhigher in the haloes of the galaxies (Tadhunter, Fosbury & Quinn ionization statesandnarrowerlinewidthsthanthoseofthe 1989b; Baum, Heckman & van Breugel 1990). This illumi- smaller radio sources. nation modelis inagreement with theunifiedschemes(e.g. However,inapparentcontradictionwiththeresultsob- Barthel 1989), in which it is proposed that all active galax- tained at z 1, Villar-Mart´ın, Tadhunter & Clark (1997), ies are intrinsically identical but, dueto orientation effects, ≃ basingtheirstudyontheUVlineratiosofasampleofradio their appearance varies. galaxies at z>2, found that theEELR appear to be mainly However, some nearby radio galaxies show clear ev- photoionized by the central AGN in the very high redshift idence for strong interactions between the radio-emitting regime. componentsandtheambientgas.Featuresobservedinthese One problem with comparing the results from samples galaxies include: atdifferentredshiftsisthatopticalobservationssampledif- close morphological association between radio and op- ferentrestwavelengthsastheredshiftvaries.Consequently, tic•al emission; the diagnostic diagrams used to determine the ionization complexkinematics(underlyingbroadcomponentsand mechanism involve lines of different ionization and excita- spl•it narrow components); tion as the redshift changes, and there is a danger that our large linewidths in the extendedgas; sensitivity to particular ionization mechanisms varies with • wavelength.Becauseofthisproblem,ithasbeendifficultto anticorrelationsbetweenlinewidthandionizationstate. • determinethebalancebetweenshocksandphotoioinization, Detailed studiesbyClark etal.(1997, 1998) andVillar- and how this balance varies with redshift. Mart´ın et al. (1999b) present direct evidence for the dra- Inthispaperwepresentdetailedlong-slitspectroscopic matic effect that shocks can have in the properties of the observationsoffourpowerfulhigh-redshift(0.47 0.7). ∼ It is noticeable that the [OII] emission is stronger than the [OIII] emission in both the nucleus and the western EELR. 4.1.5 The physical conditions This indicates a low-ionization state. Unfortunately, it was not possible to measure the electron temperaturefor3C34fromthe[OIII](4959+5007)/4363be- 4.1.3 The emission-line kinematics cause the[OIII]λ4363 emission line was not detected. Kinematic information was extracted from the one- dimensional spectra by fitting single Gaussians to the pro- 4.1.6 The continuum emission filesofthestrongemissionlines[OII]λ3727and[OIII]λ5007. Figure 2 (top) shows the variation in the velocity centroids Ithasbeendemonstrated(Dicksonetal.1995)thattheneb- of these emission lines along the radio axis. Both the [OII] ular continuum emission (a combination of free-free, free- and [OIII]velocities varyin asimilar manner,although the boundrecombination and two-photoncontinua,plushigher [OIII]lineemissiondoesnotextendtotheeastasfarasthe order Balmer lines) makes a major contribution to the UV [OII] line emission. A strong splitting ( 1000 km s−1) in continua of powerful radio galaxies wherever the emission both [OII] and [OIII] lines is observed a∼t a radial distance lines have large equivalent widths. However, there is still of 2 to 4.5 arcsec (16 to 36 kpc) on thewest side of the nu- some controversy about the relative importance of theneb- cleusalongtheradioaxis.Itcanbeseenthatthesplittingis ular component in the UV continuum emission. The theo- almost symmetric with respect tothenuclearvelocity,hav- reticalCaseBnebularcontinuumcanbegeneratedbyusing ing the two components relative shifts of + 500 and – the Hβ flux (e.g. Osterbrock 1989). This calculation is not 500kms−1.Theextractedspectrum(1.7x∼1.5arcsec2 ap∼er- particularlysensitivetodensityandtemperaturevariations, ture centred 3.7 arcsec west of the continuum centroid) onlytheintrinsicreddeningcouldgivesomeuncertainty;but showing the ∼high-velocity components to the [OII] line is thisisnotaproblemsincenosignificantreddeninghasbeen presented in Figure 3. measured in 3C 34. Thevariationsinthelinewidthsalongtheradioaxisfor The spatial profile of the nebular continuum was cal- the [OII] and [OIII] emission lines are shown in Figure 2 culated in the following way: a spatial slice, perpendicular (bottom). The linewidths are found to be moderate, about to thedispersion direction, containing theHβ emission line 400kms−1onaverage,forboth[OII]and[OIII]alongthedi- was extracted from the rest-frame 2-D spectrum. Then, an rectionoftheslit.Acrossmuchofthegalaxy,thelinewidths adjacent continuum slice of the same width was subtracted of [OII] and [OIII] are consistent, except for the small re- from the first one to obtain the continuum-free Hβ profile, gionsat 1arcsecdistancefrom thenucleusatbothsides, which was used to produce the nebular continuum profile where th∼ere are small but significant radial velocity differ- (byusing theNEBCONT routinein DIPSO). encesbetween[OII]and[OIII].Also,onthewestsideofthe Figure 1 (bottom) presents the spatial profile of the nucleus, at the location of the splitting, it can be seen that continuumemissionalongtheradioaxisof3C34.Thesolid the [OII] line tends to be slightly broader than the [OIII] line shows the UV continuum emission from 3400 ˚A – 3700 line; however, this could be due to the fact that the [OII] ˚A,thedashed lineshowstheblue-continuumemission after line is a doublet ([OII]λ3726.0 and [OII]λ3728.8). thesubtraction of thenebularcontinuumcontribution, and These results agree with those obtained by Neeser, the dotted line shows the continuum emission from 4500 Meisenheimer & Hippelein (1997), based on Fabry-Pérot ˚A – 4800 ˚A, scaled to the peak of the nebular-subtracted imaging. Althoughtheydonotdetectthelinesplitting,the blueprofile.Itisfoundthatthecontributionofthenebular large linewidths ( 1200 km s−1) they find in the western emission is 12 percent on the nucleusand 11 per cent EELRareconsiste∼ntwithunresolvedsplitting.Theyexplain on the east∼ern EELR, for the wavelength ran∼ge 3400 ˚A – thisasbeingtheoverlapoftwodistinctsources(thecentral 3700 ˚A. From Figure 1 (bottom), it can be seen that the one and thewestern extended region). nebular continuum cannot account for the UV continuum excess observed on both sides of the nucleus, especially on thewest side. 4.1.4 The emission-line spectra Integrated blue and red spectra of the eastern EELR, the 4.2 3C 330 centralnuclearregion andthewestern EELR of3C 34, and 4.2.1 Previous observations a 2-D spectrum showing the [OII]λ3727 emission line are presentedinFigure20.Theintegratedfluxesoftheobserved 3C 330, with a redshift z = 0.550, was first optically iden- emissionlinesinthesethreeregionsaregiveninTable3.The tified by Spinrad et al. (1976). It is a large 62 arcsec (458 c 0000RAS,MNRAS000,000–000 (cid:13) Jet-cloud interactions in high-z radio galaxies 5 kpc)doubleradiosource.Ground-based[OIII]λ5007andra- doubletcomponentsseparately;therefore,thiscouldslightly dio continuum images (McCarthy, van Breugel & Kapahi broadenthemeasured[OII]linewidths(FWHM).Inthenu- 1991)revealthat3C330hasasmalllobedistanceasymme- clear and northern extended region, both [OII] and [OIII] try, yet shows a large asymmetry in its extended emission linewidths follow smoooth curves, but they vary in a more lines,which arestrongeron thesideoftheradiolobecloser chaotic way along the southern EELR. The Hβ linewidth tothenucleus(North-East).MorerecentHSTnarrow-band couldonlybemeasuredinthecentralregionsofthegalaxy. images show a narrow cone-like structureon the north-east Inthenucleusandnorthernsideofthenucleus,thelinewidth side of the galaxy, which has been interpreted in terms of of Hβ varies in a similar manner as the [OIII] linewidth. illumination by a quasar hidden in the core of the galaxy However, on the southern side of the nucleus, it appears to (McCarthy 1997). However, the putative “ionization cone” beintermediate between thoseof the[OII]and [OIII]emis- is narrower than expected on the basis of the broad cones sion lines. predictedbytheunifiedschemesforpowerfulradiogalaxies High-resolution long-slit spectra, taken at the same (Barthel1989).ContinuumimagesbyMcCarthy,Spinrad& position angle (PA 230o) by McCarthy, Baum & Spinrad vanBreugel(1995) indicatethatthisobject liesinacluster (1996), reveal that the [OIII] line emission extends 17 ∼ andhasaclosecompaniontothenorth.Incontrast,ROSAT arcsec along the slit. The results they obtain in the kine- observations of 3C 330 reveal a relatively low X-ray lumi- matics are similar to ours, although they find a smooth ve- nosity (Crawford & Fabian 1996), which is not compatible locity curve for the [OIII] emission line. The amplitude of with the presence of a rich cluster in the environment of both the velocity gradient and the linewidths for [OIII] are 3C 330. Based on long-slit spectroscopy, McCarthy, Baum in agreement with what we obtain. & Spinrad (1996) carried out kinematic analysis of 3C 330, Figure 7 (top) shows the Hβ, [OIII]λ4959 and finding a large, smooth velocity gradient along PA 230o in [OIII]λ5007 emission-line profiles from the red spectrum of [OIII]λλ4959,5007. 3C330,correspondingtoa2.14x1.35arcsec2 aperturecen- tred at 3.39 arcsec south-west of the nucleus. Initially, a single Gaussian fit (dashed line) was considered, but it is 4.2.2 The emission-line structure clear that the [OIII]λ5007 profile cannot be reproduced by this simple fit. The broad wing seen in the [OIII]λ5007 line Figure 5 (top) shows the variation of the [OII]λ3727 (solid suggests theexistenceof abroad component,inaddition to line) and [OIII]λ5007 (dashed line) fluxes along the radio thenarrowcomponent,inthekinematicstructureof3C330. axis of 3C 330. Since the radio hot spots of 3C 330 are The two-component Gaussian fits (dot-dash-dot lines) and locatedoutsidetheEELR,theyarenotshowninthefigures. the total fit (dashed line) are presented in Figure 7 (bot- Lineemissionisseenextendingapproximately14arcsec tom).ItcanbenoticedthattheHβ profileisdominatedby (103 kpc) along the radio axis, with a central nuclear peak theemission of thebroad component. and aseparated peak at 2arcsec to thenorth-east of the ∼ The variation in the velocity centroids along the ra- continuum centroid. It can be noticed that the off-nucleus dio axis of 3C 330 for the narrow and broad components peak issignificantly larger for [OII]thanfor [OIII],indicat- seen in [OII]λ3727 and [OIII]λ5007 and the corresponding that the ionization state is much lower in the northern ing linewidths are shown in Figure 8. Because of the high- extendedregion than in thenucleus. resolution of the blue spectra, it was possible to fit each componentofthe[OII]doubletseparately,ineachkinematic component, assuming the low-density limit for the doublet 4.2.3 The emission-line kinematics ratio. A splitting in the [OII] emission line is detected at a In contrast to the other ojects in our sample, the radialdistanceof2.5to7arcsec(18to51kpc)south-westof intermediate-resolutionR300Bgratingwasusedfortheblue the nucleus. Note that the velocity centroids of the narrow observations of3C 330, and thelow-resolution R158R grat- componentsvaryinasimilarway,followingasmoothcurve, ingfortheredobservations,givinginstrumentalresolutions for [OII] and [OIII] in the southern region; in contrast, the of 4.3 ˚A and 7.4 ˚A, respectively. Figure 6 (top) shows the broad components have a more distorted behaviour, giving variation in the velocity centroids of [OII]λ3727, Hβ and theshift to thetotal velocities shown in Figure 6 (top). [OIII]λ5007 along the radio axis of 3C 330. The [OII], Hβ and [OIII] velocities vary in a similar manner along the 4.2.4 The emission-line spectra northernextendedregion, from 1to 5arcsec. However,a ∼ clear contrast in thevelocity centroidsof [OII]with respect Two-dimensionalspectrumshowingthe[OII]λ3727emission to [OIII] starts to appear in the nuclear region and reaches line, and integrated blue and red spectra of four spatial re- a maximum of 200 km s−1 of difference between both gions(southernEELR,nucleus,n1-andn2-northernEELR) ∼ velocities at the extreme of thesouthern EELR. Along this along the radio axis of 3C 330 are presented in Figure 21. extendedregion,the[OII]velocitycentroidsfollowasmooth Theintegratedfluxesoftheobservedemissionlinesinthese curve,butthe[OIII]velocitycentroidsvaryinachaoticway. regionsaregiveninTable4.Thefluxesarenormalisedtothe Figure 6 (bottom) shows how the linewidths of observed-frame Hβ flux for each region. Since the Balmer- [OII]λ3727, Hβ and [OIII]λ5007 vary along the radio axis line intensities (Hδ and Hγ) relative to Hβ are not signifi- of 3C 330. The low-ionization [OII] line is slightly broader cantlylowerthanexpectedinCaseBrecombination(Oster- thanthehigh-ionization[OIII]linealmosteverywherealong brock 1989) in the extended emission-line regions, the off- theradioaxis,exceptatbothextremesoftheslitwherethe nuclearlineratioswerenotcorrectedforintrinsicreddening. errors are bigger and it is not so clear. However, the [OII] However, there is evidence for significant reddening in the line was fitted with a single Gaussian, instead of fitting the nuclearaperturewithbothHδandHγsignificantlylessthan c 0000RAS,MNRAS000,000–000 (cid:13) 6 C. Solórzano-Inãrrea et al. expected for Case B recombination (EB−V = 0.59 0.13). interferometryof3C352,andconcludethatthemorphology ± The extinction implied by these results (A =2.4 0.5) is and velocity structure of the extended emission-line region B ± consistent with that inferred for the nuclear region of low- around3C352canbeexplainedintermsofcoolinggasion- redshift radio galaxies (Tadhunter, Metz & Robinson 1994; ized and accelerated by the bowshock associated with the Robinson et al. 2000). radio jet, while some ionization close to the centre could Figure 9 shows the variations in the also be due to radiative ionization. Based on long-slit spec- [OII]λ3727/[OIII]λ5007 and [OIII]λ5007/Hβ line ratios troscopy observations, Best, Röttgering & Longair (2000a) along the radio axis of 3C 330. It can be seen that the nu- study the UV emission-line ratios [CIII]λ2326/[CII]λ1909 clear region is of high ionization with 10 < [OIII]/Hβ < and[NeIII]λ3869/[NeV]λ3426of3C352,andcomparethem 13. The ionization state decreases to the northern side of with theoretical predictions of shock and photoionization the nucleus up to 1 arcsec, then rises up to 2 arcsec and models, finding that the line ratios are in agreement with ∼ decreasesagaintowardstheextremeofthenorthernEELR. shock models including a precursor region. OnthesouthernEELRthe[OII]/[OIII]lineratioshowslittle significant variation, but has a higher ionization state than thenorthernEELR.Unfortunately,onlyonepointcouldbe 4.3.2 The emission-line structure obtained along the southern region for the [OIII]/Hβ line ratio. Figure 10 (top) presents the [OII]λ3727 (solid line) and [OIII]λ5007(dashedline)spatialprofilesalongtheradioaxis of 3C 352. They were derived by extracting spatial slices, 4.2.5 The physical conditions following thesameprocedureoftheothergalaxies (seeSec- tion4.1.2).Itcanbeseenthatthe[OII]lineemissionextends The electron temperature T was measured for the e 10 arcsec (82 kpc) along the radio axis, while the [OIII] central region and the EELR of 3C 330, by using ∼ line emission only extends 6 – 7 arcsec (53 kpc) along the [OIII](4959+5007)/4363 line ratio. The [OIII]λ4363 ∼ thesamedirection.Theradiohotspotsinthisradiogalaxy linewidth was constrained to be the same as that of lie just outside the EELR, and they are not shown in the [OIII]λ5007. The values obtained from the red spectra are figures. [OIII](4959+5007)/4363 = 33 7 for the southern EELR, ± 51 4 for thenucleus (after reddeningcorrection), 66 8 for ± ± the n1-northern EELR and 44 7 for n2-northern EELR, which implies electron temperat±ures ofT = 23000+5000 K, 4.3.3 The emission-line kinematics e −3000 17600+500 K,15300+900 Kand19000+2000 K,respectively. A den−si1t0y00of n = 10−08c00m−3 was assum−e1d50.0 Figure 11 (top) shows how the velocity centroids of e [OII]λ3727 and [OIII]λ5007 vary along the radio axis of 3C 352. They follow a smooth rotation curve and both vary in 4.2.6 The continuum emission a similar manner. The variation in the linewidths of [OII]λ3727 and Figure 5 (bottom) shows spatial profile of the continuum [OIII]λ5007 is presented in Figure 11 (bottom). Both [OII] emission along the radio axis of 3C 330. The solid line rep- and[OIII]linewidthsvaryinasimilar way.However,in the resentstheprofileof theUVcontinuumemission (3200 ˚A– centralregionitappearsthatthelow-ionization [OII]lineis 3700˚A),thedashedlinerepresentstheUVcontinuumafter broader than the high-ionization [OIII] line. From this fig- the subtraction of the nebular continuum (calculated from ure,itcanalsobenoticedthatthe[OIII]lineemission does the rest-frame Hβ flux along the slit, in the same way as not extend as far as the [OII] line emission along the radio that of 3C 34, by using the NEBCONT routine in DIPSO axis. (seeSection4.1.6)),andthedottedlinerepresentsthegreen Figure 12 shows the Hβ, [OIII]λ4959 and [OIII]λ5007 continuum emission (5200 ˚A – 5700 ˚A), scaled to the peak emission-line profiles from thered spectrum of 3C352, cor- of the nebular-subtracted UV profile. A UV excess can be respondingtoa1.07x1.56arcsec2 aperturecentredat0.71 observed approximately between 2 and 4 arcsec north-east arcsec south-east of thenucleus. A single Gaussian fit,con- ofthenucleus.Itisfoundthatthecontributionofthenebu- sideringlineemissionfromonlyonekinematicalcomponent, laremission is 50percentoftheUVcontinuumemission isshownatthetop.However,thebroadwingsin[OIII]sug- ∼ inthenucleusof3C330, and 35percentinthenorthern gest the existence of a broad component in the kinematic ∼ EELR,forthewavelengthrange3200˚A–3700˚A.However, structure of 3C 352. The two-component fits (dot-dash-dot thenebularcontinuumcannotaccountfortheobservedUV lines)andtheresultingfit(dashedline)arepresentedatthe excessatthenorth-eastsideofthenucleus,sincethisexcess bottom of Figure 12. It can be seen that the broad compo- still remains after thenebularsubtraction. nent dominates theemission of Hβ. Figure13(top)showsthevariation ofthevelocity cen- troidsalongtheradioaxisof3C352forthebroad andnar- 4.3 3C 352 row components seen in [OII]λ3727 and [OIII]λ5007. The 4.3.1 Previous observations velocity centroids of Hβ are also plotted. The variation in the linewidth along the radio axis for the two kinematical 3C352isacompact10.2arcsec(84kpc)doubleradiosource componentsseenin [OII]λ3727 and[OIII]λ5007 isshown in at redshift z = 0.8067 (McCarthy, Spinrad & van Breugel Figure 13 (bottom) together with thelinewidth of Hβ. 1995). It was first studied optically by Smith et al. (1979) who found a low-ionization emission-line spectrum. Hip- pelein & Meisenheimer (1992) presentFabry-Pérot imaging c 0000RAS,MNRAS000,000–000 (cid:13) Jet-cloud interactions in high-z radio galaxies 7 4.3.4 The emission-line spectra 4.4.1 Previous observations Figure22 showsintegrated blueandred spectraof thecen- The radio source 3C 435A, at a redshift z = 0.471 and tral nuclear region, and the southern and northern EELR with an angular size of 14 arcsec (97 kpc), was discov- of 3C 352, a 2-D spectrum showing the [OII]λ3727 emis- ered at a small projected distance from the powerful radio sion line is also plotted. Fluxes of the emission lines in the source 3C 435B (McCarthy, van Breugel & Spinrad 1989), threeregionsarelistedinTable5,andarenormalisedtothe but the two objects are at different redshifts. Narrow-band observed-frame Hβ flux in each region. Given that the Hδ [OII] emission-line imaging shows presence of an extended andHγ fluxesrelativetoHβ areconsistent with Case Bre- emission-line nebula that extends well beyond the compact combination (Osterbrock 1989), no corrections for intrinsic radio source on both sides of the nucleus (van Breugel & reddeninghavebeen made tothe line fluxes. McCarthy 1989). Bidimensional spectroscopy hasbeen per- Thevariationinthe[OII]λ3727/[OIII]λ5007alongthe formedwiththeintegralfieldspectrographTIGER(Rocca- radio axis is shown in Figure 14 (top). It can be observed Volmerange et al. 1994), showing at least five components thattheionizationstatepeakswherethecontinuumcentroid around the central one. A scenario of gas being overpres- issituated,andthenfallsoneithersideofthenucleus,more suredbyradioplasmaexpansion,orbytheinteractionofrel- steeply towards thenorthern side, as theradius increases. ativisticelectronswiththeambientgas,wasfavoured.Kine- Figure 14 (bottom) shows the [OIII]λ5007 / Hβ line maticanalysisbyMcCarthy,Baum&Spinrad(1996),based ratio along theradio axis of 3C 352. Unfortunately,the Hβ on long-slit spectroscopy along PA 229o, shows a complex linecouldonlybemeasuredinthenuclearregion.However, velocity profile, with an overall amplitude of afew hundred fromthisfigureitcanbenoticedthatthenucleushasahigh km s−1, and apparent rotation in both the central galaxy ionization state ([OIII]/Hβ 10). and in thecomponent lying 4 arcsec north-east. ∼ ∼ 4.4.2 The emission-line structure 4.3.5 The physical conditions The spatial profiles of the [OII]λ3727 (solid line) and The electron temperature T was measured for the e [OIII]λ5007(dashedline)emissionlinesarepresentedinFig- central nuclear region of 3C 352 by using the ure15(top).Theseprofileswereobtainedinthesamewayas [OIII](4959+5007)/4363 line ratio; but this measurement those of the other four radio galaxies, by extracting spatial was not possible for the two EELR. The value obtained for slices through thelong-slit spectra (see Section 4.1.2). thenucleusfrom thered datais [OIII](4959+5007)/4363 = 46 7, which implies a temperature T = 18000+2000 K for The projected positions of the radio hot spots are in- the±nuclearregion.Adensityofn =10e0cm−3wa−s10a0s0sumed. dicated on the plots by dashed vertical lines. Line emission e extends approximately 24 arcsec (166 kpc) along the radio axis. In addition to the central galaxy, a companion can beseen located at 4–5arcsec (30kpc)north-east of the ∼ 4.3.6 The continuum emission continuumcentroidalongtheradioaxis(seealsoMcCarthy, vanBreugel&Spinrad1989). Thecompanion issituatedin The spatial profile of the continuum emission along the ra- the interaction zone of the radio jet with the intergalactic dioaxisof3C352isshowninFigure10(bottom).Thesolid medium (Rocca-Volmerange et al. 1994). The fact that the line shows theUV (2600 ˚A- 3700 ˚A) continuumprofile, the [OII] line is relatively stronger in this component indicates dashedlineshowstheUVcontinuumafterthesubtractionof that it has lower ionization state than the central compo- the nebular continuum contribution (derived from the rest- nent. frameHβfluxalongtheslit,byusingtheNEBCONTroutine inDIPSO(seeSection4.1.6)),andthedottedlineshowsthe 4400 ˚A – 4800 ˚A continuum profile, scaled to the peak of 4.4.3 The emission-line kinematics the nebular-subtracted UV profile. The emission from the starsituatedjustabout6.5arcsecnorth-westof3C352was Since the slit positions and the grating angles were coinci- subtracted before extracting the continuum profile of the dent for the red spectra taken on two different nights, the radio galaxy. It is found that the nebular emission contri- individualframeswerecoaddedtoproduceasinglelong-slit bution with respect to the continuum emission is 37 per spectra, and therefore increasing theS/N ratio. ∼ cent in the nucleus and in the southern EELR, and 28 Figure 16 (top) shows how the velocity centroids of ∼ per cent in the northern EELR, for the wavelength range [OII]λ3727 and [OIII]λ5007 vary along the radio axis of 3C 2600 ˚A – 3700 ˚A. There is no evidence for excess UV con- 435A. Both [OII] and [OIII] velocities are seen to vary in a tinuumfollowing thesubtraction ofthenebularcontinuum: similar manner, with rotation curve-like velocity variations the nebular-subtracted UV and longer wavelength contin- in both central and northern components. uum spatial profile are not significantly different (although The variation in the linewidths of [OII]λ3727 and thepresenceofthenearbybrightstarmakesthecomparison [OIII]λ5007 along the radio axis of 3C 435A is shown in difficult). This behaviour is similar to that observed in the Figure 16 (bottom). The low-ionization [OII] line tends to low-redshift jet-cloud interaction 3C 171 (Clark 1996). bebroaderthanthehigh-ionization[OIII]line,especiallyin the region between the nucleus and the northern radio hot spot. Also, in the northern EELR the [OIII] emission line seemstobemuchnarrowerthanthe[OII]emission line, be- 4.4 3C 435A yond the radio hot spot. In this case, the [OIII] linewidth c 0000RAS,MNRAS000,000–000 (cid:13) 8 C. Solórzano-Inãrrea et al. might have been affected by the subtraction of the night- 4.4.6 The continuum emission sky line that falls on it, since the S/N ratio in theEELR is The spatial profile of the continuum emission along the ra- muchlower than in thecentralregions. However, the[OIII] dio axis of 3C 435A is shown in Figure 15 (bottom). The linewidth results agree with those of McCarthy, Baum & solid line represents the UV (2600 ˚A – 3700 ˚A) continuum Spinrad (1996). emission,thedashedlinerepresentstheUVcontinuumafter Figure 17 shows the [OII]λ3727 emission-line profile of 3C 435A, corresponding to a 2.50 x 1.56 arcsec2 aperture thesubtractionofthenebularcontinuumcontribution(calculated from therest-frame Hβ fluxalong theslit, byusing centredat1.43arcsecnorth-eastofthecontinuumcentroid. the NEBCONT routine in DIPSO (see Section 4.1.6)), and Initially,aone-componentGaussianfitwasconsidered(top), thedottedlinerepresentsthegreen(5200 ˚A–6000 ˚A)con- butthissimplefitcannotreproducethebroadwingof[OII], tinuumprofile,scaledtothepeakofthenebular-subtracted whichcanbeseenasemission fromabroadkinematiccom- UV profile. It is found that the nebular emission with re- ponent. The plot at the bottom of Figure 17 presents the spect to the continuum emission is 10 per cent in the two-component (narrowand broad) Gaussian fit(dot-dash- ∼ nucleus, and 21 per cent at the location of the northern dot lines) and the total fit (dashed line), which reproduces ∼ component, for the wavelength range 2600 ˚A – 3700 ˚A. On the[OII] profile muchbetter than theone-component fit. thebasisofthecomparisonbetweenthenebular-subtracted Figure 18 (top) shows how the velocity centroids vary UVandtheredcontinuumslices,thereisevidenceforaUV along the radio axis of 3C 435A for the broad and narrow excessonbothsidesofthenucleus,especiallyatthelocation components seen in [OII]λ3727. The [OIII]λ5007 velocity ofthenorthernhotspot.Note that the extended UVcontin- centroidsarealsoplotted.Nobroadcomponentcouldbefit- uum emission (nebular-subtracted) extends over the entire tedtothe[OIII]λ5007 emission lineat anyspatial location. emission line nebula and well beyond the radio hot spot on Itcanbeseenthatthenarrowcomponentof[OII]variesina the north-east side of the galaxy. similar way as the [OIII]velocity centroids, consistent with rotation, while the broad component has a more distorted andchaoticbehaviour.Thevariationinthelinewidthsalong the radio axis for the two kinematic components seen in 5 DISCUSSION [OII] is presented in Figure 18 (bottom). The linewidth of the broad component varies between 800 – 1500 km s−1 5.1 Summary of results ∼ (FWHM), reaching the maximum values in the region be- We summarise below some results derived in the previous tween the continuum centroid and the northern radio hot section: spot. Extremekinematics: Allthesourcesshowdisturbedoff- • nuclear emission line kinematics, including: line splitting in 4.4.4 The emission-line spectra 3C34and3C330;andthedetectionofbothbroad(FWHM = 1000 – 1500 km s−1) and narrow (FWHM < 600 km Integrated blue and red spectra of the southern EELR, s−1) components in the extended emission line∼regions of thecentralnuclearregion,thenortherncomponent andthe 3C 330, 3C 352 and 3C 435A. We emphasise the disturbed northern EELR of 3C 435A, and a 2-D spectrum showing kinematicsaredetectedinallthesourcesinoursample,not the[OII]λ3727emissionlinearepresentedinFigure23.The just those in which the radio and emission line structures fluxes of the observed emission lines in the four regions are havea similar scale. listed in Table 6, and are normalised to theobserved-frame Relationshipbetweenlinewidthandionizationstate: Al- Hβ flux for each region. The line fluxes have not been cor- • though we do not see evidence for an anticorrelation be- rected for intrinsic reddening, given that the Hα/Hβ ratio tween ionization state and linewidth as strong as seen in is not significantly larger than the theoretical value corre- some low-redshift jet-cloud interaction sources (Clark et al. sponding to Case B recombination (Osterbrock 1989), sug- 1997, 1998; Villar-Mart´ın et al. 1999b), the low-ionization gesting that theintrinsic reddening is not large. [OII]λ3727 and Hβ emission lines tend to be broader than Figure 19 shows the [OII]λ3727/[OIII]λ5007 and the the high-ionization [OIII]λ5007 emission line in the regions [OIII]λ5007/Hβ lineratiosalongtheradioaxisof3C435A. wherethecomplexkinematicstructuresdescribedaboveare From these plots it can be noticed that the region between observed,especially in thecentral region of 3C 352. the nucleus and the northern radio hot spot has the lowest Overall ionization state: The ionization state peaks in ionizationstate,1<[OIII]/Hβ <2,although,theionization • the near-nucleus regions of the galaxies and decreases to- state is seen to be low everywhere. It can also be seen that wards the EELR. In particular, in 3C 435A a minimum in the nucleus has higher ionization state than the northern the ionization state is observed at 2 arcsec north-east of companion located 4 – 5 arcsec to thenorth. ∼ ∼ thenucleus, just behindthe radio hot spot. High electron temperatures: The high electron temper- • atures measured in the extended regions of 3C 330 and in 4.4.5 The physical conditions thecentralregion of3C352areinconsistentwithphotoion- For 3C 435A, the [OIII]λ4363 was not measured because izationbyacentralAGN(Tadhunter,Robinson&Morganti it was outside the wavelength range covered. Therefore, 1989a),buttheycanbeeasilyexplainedintermsofjet-cloud the temperature diagnostic could not be obtained for this interactions (Villar-Mart´ın et al. 1999b). galaxy. Extended UV continuum: The contribution of the neb- • ularcontinuumemission totheUVcontinuumissignificant inallcases,withthenebularcontributionrangingfrom 10 ∼ c 0000RAS,MNRAS000,000–000 (cid:13) Jet-cloud interactions in high-z radio galaxies 9 percentinthenucleiof3C34and3C435A,to 40percent 1994; Villar-Mart´ın et al. 1999b) and/or in the turbulent ∼ in the extended regions of 3C 330. However, following sub- boundary layers of the radio jets is required. Furthermore, traction of the nebular component, a significant UV excess fast winds from the quasars and starbursts associated with remains in theextended nebulaein most of theobjects. thehostgalaxiescouldalsocontributetothelargevelocities observedinthesesources(Heckman,Armus&Miley1990). Further evidence for jet-cloud interactions is provided 5.2 Kinematics: The evidence for shocks bytheexistenceofbroadkinematiccomponentsintheemis- Inprevioussectionswehavepresentedevidenceforextreme sion lines of some of the radio galaxies. We have detected emission-linekinematicsinalltheobjects.Belowwediscuss underlyingbroadcomponentswithlargelinewidths(FWHM theimplications of these results. 1000 – 1500 km s−1) in the line profiles of three galaxies ∼ Line splitting is observed in the western EELR of 3C inoursample(3C330,3C352and3C435A),inadditionto 34 and 3C 330 (∆v 1000 km s−1 and 500 km s−1, re- narrow components (FWHM < 600 km s−1). The large 62 spectively). These v∼elocity shifts are lar∼ger than what we arcsec (458 kpc) radio source∼3C 330 shows an underlying would expect from gravity of an isolated elliptical galaxy broad component in both southern and northern EELR, at (∆v < 400 km s−1) (e.g. Tadhunter, Fosbury & Quinn radial distances of 1.5 – 4 arcsec (11 – 30 kpc) from the ∼ 1989b, Baum, Heckman & van Breugel 1990). Previously, nucleus. Again, evidence for interaction between the radio high-velocitycomponentshavealsobeenobservedintheex- and optical structures can be detected in the EELR, even tendedregionsofpowerfulradiogalaxies (Tadhunter1991), when the major radio components have passed beyond the bothatlowredshifts(inCygnusA)andathighredshifts(in EELR. In the case of 3C 352, in which the peaks of the ra- 3C265).Suchsplittings,whicharecharacteristicofexpand- dio lobes are located just outside the EELR, an underlying ing shells of material, are most likely the result of interac- broadcomponenthasalsobeendetectedatbothsidesofthe tionsbetweentheradioplasmaandtheinterstellarmedium. nuclear region. 3C 435A is theonly object of our sample in 3C 34 is a large double radio source, which extends 46 arc- which the radio hot spots have not passed yet beyond the sec (365 kpc); however, the line splitting is detected at a EELR.Inthisobject, abroad kinematiccomponent canbe radial distance of 2 to 4.5 arcsec (16 to 36 kpc) from detected in [OII]λ3727 at both sides of the nucleus. In all ∼ ∼ thenucleus.Similarly,3C330 isalarge 62arcsec (458kpc) of these cases, the linewidths of the broad components are double radio source, but we detect a line splitting in [OII] largerthanwouldbeexpectedforgravitationalacceleration at a radial distance of 2.5 to 7 arcsec (18 to 51 kpc) in the potential of a giant elliptical galaxy. ∼ ∼ fromthenucleus.Thisindicatesthattheeffectsoftheinter- Similar kinematically disturbed components have also actionsbetweentheradiocomponentsandthecloudsofgas been observed at low redshifts in other powerful radio are also important in galaxies with extended radio sources, galaxies with jet-cloud interactions. High-dispersion long- in which the main radio emitting components have passed slit spectra of thelow-redshift radio galaxies 3C 171 (Clark beyond theEELR. et al. 1998) and PKS 2250-41 (Villar-Mart´ın et al. 1999b) As mentioned above, these splittings are too large to have revealed multi-component emission-line kinematics: beduetogravitationalmotionsofthehostgalaxies.Onthe narrow components, with high-ionization state, and broad other hand,it is not yet clear whether direct shock acceler- components, with low-ionization state. In the case of PKS ation associated with the radio components is sufficient to 2250-41, the narrow component extends beyond the radio accelerate the clouds to such high velocities (Villar-Mart´ın structure, while the broad component is found to be spa- et al. 1999b). Considering the warm clouds (T 104 K) to tially associated with the radio emitting structures and is beinequilibriumwithahotambientphase(T ∼107K),the believed to represent gas cooling behind the shock fronts. ∼ densitycontrast between thetwo phasesis 1000, and the As argued by Villar-Mart´ın et al. (1999b), it is likely that ∼ velocity of the clouds due to the advance of the radio jet is the gaseous component associated with the broad lines is vc ∼vspρρhc (vs:shockvelocity;ρh:densityofthehotphase; accelerated by entrainment in the faster moving hot ISM ρ :densityofthewarmclouds).Assumingthatthehotspot behind theshock front. c advancespeedis 0.01c—0.1c (Scheuer1995), theclouds However, we have to be cautious in interpreting the will beaccelerated∼tovelocities of 100 —1000 km s−1 in broadcomponentsolelyintermsofjet-inducedshocks,since ∼ the direction of the jet, but the velocities perpendicular to abroadcomponentisdetectedwellbeyondthenorthernra- theradioaxiswill bemuchsmaller. Bymeasuringtheratio diohotspotin3C435A.Thisissimilartothephenomenon betweenthelengthoftheradioarmsandtheextensionper- observed in the high-redshift radio galaxy MRC1558-003, pendiculartotheradioaxes,thelateralvelocitiescanbees- which presents high velocities and large linewidths in the timated.Weobtainlateralextensionsrelativetothelengths EELR beyond the radio structures (Villar-Mart´ın, Binette oftheradioarmsof 0.4inthecaseof3C34,and 0.15for & Fosbury 1999a). This suggests that another accelerating ∼ ∼ 3C330 (seeradiomapsinBest, Longair &Röttgering1997 mechanism, apart from jet-cloud interactions, may be at and McCarthy, van Breugel & Kapahi 1991, respectively), work.Nonetheless,eveninthecaseof3C435A,thebroadest implyinglateralvelocitiesof 15—400kms−1.Giventhat emissionlinesaremeasuredinaregionbehindtheradiohot ∼ the radio sources 3C 34 and 3C 330 are likely to be close spot. Another common characteristic in the kinematics of to edge-on and on much larger scale than the emission-line the galaxies in our sample is that the [OII]λ3727 emission structures,weexpectthehigh-velocitycomponentsobserved line tends to be broader than the [OIII]λ5007 emission line in these galaxies to be due to the lateral expansion of the intheregionswherethedisturbedkinematicsareobserved. cocoons. Therefore, the bowshock acceleration may not be This could bebecause the[OII]line is adoublet and it was sufficienttoexplainthelargevelocities.Someentrainmentof fitted with a single Gaussian. To quantify this broadening, the clouds in thepost-shock wind (Klein, McKee & Colella wesimulated[OII]emissionlinesofdifferentwidthsandfit- c 0000RAS,MNRAS000,000–000 (cid:13) 10 C. Solórzano-Inãrrea et al. tedthemwithbothsingleandtwoGaussians.Wefoundthat tios with the predictions of both AGN photoionization and fittingthetwocomponentsofthedoubletwithasingleGaus- shock-ionization models. sianmadethelineonly 50kms−1 broaderthanifthetwo Figure 24 shows the resulting diagnostic diagrams, ∼ componentswerefittedseparately.However,ithappensthat which involve the line pairs: [NeV]λ3426 & [NeIII]λ3869, [OII] is broader by approximately 300 km s−1 in 3C 34 at [OII]λ3727 & [OIII]λ5007, Hβ & [OIII]λ5007, HeII(4686) thelocation ofthesplitting,andin3C330wherethebroad & Hβ and the electron temperature diagnostic line ratio componentisdetected,correspondingalsotolow-ionization [OIII](4959+5007)/4363. Emission line pairs involving the regions (see Figures 4 and 9 (bottom), respectively). In the same element are particularly useful for the diagnostic di- case of 3C 352, the [OII] line is observed to be 200 km agrams because the dependence of the line ratios on the s−1 broader than [OIII] in the central region, w∼ithin 1 elementalabundancesisrelatively minor(Baldwin, Phillips ∼ arcsec distance on either side of the nucleus, corresponding &Terlevich1981).Also,ifthetwoemissionlinesinthepair with the region where the underlying broad component is arecloseinwavelength,thepossibleerrorsarisingfrom cal- detected.In 3C 435A, the[OII]emission lineis observed to ibration and reddening corrections are minimized. bemuchbroaderthan[OIII]intheregionbehindthenorth- To generate the AGN model predictions we used the ernhotspot,coincidentwithalow-ionizationstate(seeFig- multipurposephotoionizationcodeMAPPINGS.Theresults ure 19). In addition, at a radial distance of 6 – 12 arcsec areplottedassolidlines,whichrepresentthelineratiospro- ∼ northofthenucleusof3C435A,beyondthenorthernradio ducedbyoptically-thick,single-slab,power-lawphotoioniza- hot spot,and coincident with ahigh-ionization-state region tionmodels(F να)withspectralindicesofα=-1.0,-1.5 ν ∝ (see Figure 19 (top)), the [OII] line appears to be 500 and-2.0(fromtoptobottom),andasequenceintheioniza- kms−1 broaderthan[OIII].However,sincetheS/Nr∼atiois tion parameter covering the range 2.5 10−4 < U < 10−1. low in thisextended region, the linewidth of [OIII]λ5007 in Adensityof100cm−3 andsolarabund×anceswereassumed. this object is likely to be affected by the subtraction of the The shocks models are taken from Dopita & Suther- night-skyline that falls on the[OIII] emission line. land(1995,1996).Weincludegridsofsimpleshocks(dashed An anticorrelation between linewidth and ionization lines) and shocks with the photoionized precursor included state is a common feature of radio galaxies in which jet- (50percentshocks+ 50percentprecursor) (dottedlines). cloud interactions are taking place: low-ionization lines are The two main parameters for controlling the post-shock broader than high-ionization lines. This phenomenon has emission line spectrum are the velocity of the shock (150 beenobservedinthepowerfullow-redshiftradiogalaxies3C v 500kms−1)andthemagneticparameter(0 B/√n s 171(Clark etal.1998) andPKS2250-41 (Clark etal.1997, ≤ 4 µ≤Gcm−3/2). Each sequence in the Figures corr≤esponds ≤ Villar-Mart´ın et al. 1999b). This anticorrelation is difficult to a fixedB/√n valueand a changing v . s toexplainintermsoftheAGNilluminatingtheundisturbed In addition to the photoionization and shock models, ambientgasinthehostgalaxy,butitcanbeeasilyexplained we have also plotted mixed-medium photoionization mod- intermsofshocks.Thelineemission containscontributions els, including both matter-bounded and radiation-bounded from both high-ionization-state gas, with narrow velocity clouds (dot-dash-dot line) from Binette, Wilson & Storchi- dispersion, emitted in the undisturbed precursor zone, and Bergmann (1996). These combine an optically-thick zone low-ionization-state gas, with a much broader velocity dis- (ionization-bounded[IB]component),illuminatedbyapho- tribution, emitted by the disturbed cooling gas behind the ton spectrum that is initially filtered through an optically- shock. Given the similarity between the kinematical prop- thin zone (matter-bounded [MB] component). The se- erties of the objects in our sample and the low-redshift jet- quences of line ratios were derived by allowing the ratio cloud interaction objects, it is plausible that the broad and (A ) of the solid-angle subtended from the nuclear pho- M/I narrow components in our sample arise in a similar way at toionizing source by the MB clouds relative to that sub- all redshifts. tendedbytheIBcloudstovaryintherange10−4 A ≤ M/I ≤ Overall, the complex kinematics observed in the ex- 10. Since by definition the MB clouds lie somewhere in be- tended regions of the galaxies in our sample indicate that tween the central source and the IB clouds, strictly speak- the material has been highly perturbed and accelerated by ing, A cannot be lower than unity. However, based on M/I theinteraction between theradio emitting componentsand theunifiedschemesandduetoorientationeffects,somefrac- theambientgas.Weseeevidenceforthisshockacceleration tion of theMB clouds located in theinner regions could be eveninthosegalaxieswiththemoreextendedradiosources obscuredfromtheobserver(e.g.byadustytorus),therefore (3C34and3C330),inwhichtheradiohotspotshavepassed giving a physical meaning to an apparent A < 1. M/I well beyondthe EELR. Forcomparison,wehavealsoincludeddatacorrespond- ing to the EELR of low-redshift radio galaxies. The crosses represent objects in which strong jet-cloud interactions are 5.3 Ionization mechanism: AGN photoionization taking place: PKS 2250-41, 3C 171, 4C 29.30, Coma A or jet-induced shocks ? (Clark1996),andPKS1932-464(Villar-Mart´ınetal.1998). Although it is likely that acomponent of theISMhas been The open triangles represent the photoionized radio galaxy accelerated by jet-induced shocks in all the sources in our 3C321whichisconsistentwithmixed-mediumphotoioniza- sample, this does not necessary imply that the clouds are tion models (Robinson et al. 2000). shock-ionized.Forexample,cloudscouldbeacceleratedand Figure24(a)showsthe[OIII](5007)/Hβ lineratioplot- compressed by jet-induced shocks, but then photoionized ted against [OII](3727)/[OIII](5007). This combination of by an illuminating AGN in the core of the host galaxy af- emission line pairs was first used by Baldwin, Phillips & ter they have cooled. To address the issue of the ionization Terlevich (1981) to distinguish between the four predomi- mechanism,inthissectionwecomparethemeasuredlinera- nantionizationmechanisms(HIIregions,planetarynebulae, c 0000RAS,MNRAS000,000–000 (cid:13)

The evidence for jet-cloud interactions in a sample of high/intermediate-redshift radio galaxies

Similar The evidence for jet-cloud interactions in a sample of high/intermediate-redshift radio galaxies