Radio jet interactions in the radio galaxy PKS 2152-699

8 Pages·0.3 MB·English

by  R. A. E. Fosbury

Mon.Not.R.Astron.Soc.000,000–000 (0000) Printed1February2008 (MNLATEXstylefilev1.4)
Radio jet interactions in the radio galaxy PKS 2152-699
⋆
R.A.E. Fosbury1 , R. Morganti2,3, W. Wilson2, R.D. Ekers2,
S. di Serego Alighieri4, C.N. Tadhunter5
1 Space Telescope-European Coordinating Facility, D-85748 Garching bei Mu¨nchen, Germany
2 CSIRO, Australia Telescope National Facility, PO Box 76, Epping, NSW 2121, Australia
3 Istituto di Radioastronomia, CNR, via Gobetti 101, 40129 Bologna, Italy
4 Osservatorio Astrofisico di Arcetri, largo E.Fermi 5, I-50125, Firenze, Italy
5 Department of Physics, University of Sheffield, Sheffield S3 7RH, England
8
9
9
1
Accepted ,Received
n
a
J
ABSTRACT
6
We present radio observations of the radio galaxy PKS 2152-699 obtained with the
2
Australia Telescope Compact Array (ATCA). The much higher resolution and s/n of

the new radio maps reveals the presence of a bright radio component about 10 arcsec
1
v NEofthe nucleus.Thislies closeto the highlyionizedcloudpreviouslystudiedinthe
9 optical and here shown in a broadband red snapshot image with the HST PC 2. It
4 suggests that PKS 2152-699 may be a jet/cloud interaction similar to 3C277.3. This
2 couldcausethe changein the positionangle (of∼20◦) ofthe radioemissionfromthe
1 inner to the outer regions.Onthe largescale, the source has Fanaroff& Riley type II
0 morphology although the presence of the two hot-spots in the centres of the lobes is
8 unusual. The northern lobe shows a particularly relaxedstructure while the southern
9
one has an edge-brightened, arc-like structure.
/
h
Key words: galaxies: active – galaxies:interactions – galaxies: radio continuum
p
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o
r
t
s
a 1 INTRODUCTION found coincident or close to a radio feature — either jet or
: lobe — are known and, in some cases, well studied (e.g.,
v Extended-emission line regions (EELR) are a common fea-
NGC 7385, Simkin & Ekers 1979; 3C171, Heckman, van
i tureofpowerfulradiogalaxies. Inthehigh-redshiftobjects,
X Breugel & Miley 1984; 3C277.3, van Breugel et al. 1985a;
theseregionsdisplayaparticularrangeofphenomenawhich
r Minkowski’sobject,vanBreugeletal.1985b;4C29.30, van
are of especial interest for studies of theproperties of AGN
a Breugel et al. 1986; Centaurus A, Morganti et al. 1990;
and the formation and evolution of their host galaxies. Ex-
3C285, van Breugel & Dey 1993; PKS 2250-41, Clark et al.
tended line and rest-frame ultraviolet continuum emission
1997 and PKS 1932-43, Villar-Martin et al. in prep.).Some
appears, above reshifts of around 0.8, to be aligned with
ofthemarebelievedtorepresentaninteractionbetweenthe
theextendeddoubleradiostructures(McCarthyetal.1987,
radio plasma and theISM: a ‘jet/cloud’ interaction.
Chambers, Miley & van Breugel 1987) although the radio
andopticalemittingregionsarenotnecessarilyco-extensive. PKS 2152-699 is a powerful, nearby radio galaxy (z =
In some cases, however,thereis a close correlation between 0.0282, 1 arcsec = 0.8 kpc for H◦=50 km s−1 Mpc−1) with
the radio emission and the EELR over distances of tens of a cloud of highly ionized gas observed at about 10 arcsec
kiloparsecsandextremekinematiccomponentsareobserved (∼8 kpc) from the nucleus. The very highly ionized cloud
associated with the radio emission (e.g., McCarthy et al. (HIC), with ions up to Fe9+ and a blue optical continuum,
1987, McCarthy 1993), suggesting a continuing interaction was first studied in detail by Tadhunteret al. (1987, 1988).
between theradio plasma and the ISM. Although the HIC has a velocity very similar to systemic,
Inanefforttounderstandthehighredshiftphenomena broad, blue wings in the [O III] emission lines (up to 3000
inmoredetail,wearestudyingselectedlowredshiftobjects km/sfromthesystemicvelocityoftheHICandgalaxy)have
which exhibit some of these characteristics. The correlation been observed. The presence of some gas at high velocities
betweenEELRandradioemission isnotsocommon atlow ledTadhunteretal.(1988)toconcludethatthecloudcould
z. Nevertheless, a number of cases of regions of ionized gas possibly berelated to interaction between theradio plasma
and theISM.
However, later work (di Serego Alighieri et al. 1988;
⋆
Email:[email protected] Fosbury et al. 1990) showed that the HIC has a very blue
(cid:13)c 0000RAS
2 R.A.E. Fosbury et al.
opticaltonear-UVcontinuumwith10%linearopticalpolar-
izationandtheE-vectorperpendiculartothepositionangle
ofthenucleus-HICaxis.Theexistenceoftheblue,polarized
continuum led di Serego Alighieri et al. (1988) to suggest
that this resulted from the scattering by dust in the cloud
of beamed radiation from the nucleus. In this picture, the
source of ionization for the cloud is UV radiation from the
nucleus.Thepresenceoftransverseionizationgradientsalso
lent support to the beamed illumination model (Tadhunter
et al. 1988).
The quality of the radio maps available until now
(Christiansen et al. 1977, Tadhunter et al. 1988, Jones &
McAdam 1992, Fosbury et al. 1990) does not allow a de-
tailedinvestigationoftheradioemissionintheregionofthe
HIC. To search for clear evidence of a jet/cloud interaction
inPKS2152-699,wehavemadenewradioobservationswith
the Australia Telescope Compact Array (ATCA) at both 3
and6cmwavelength.Inpresentingtheradiodataandcom-
paringwiththeopticalmorphology,weuseabroadbandred
imageofthegalaxytakenwiththeHSTPC2availablefrom
the publicarchive. VLBI observations of thenuclear region
were presented by Tingay et al. (1996).
Subsequent papers will report a series of infrared, op-
tical, ultraviolet and X-ray observations which allow us to
studythebroad-bandspectralenergydistributionofthenu-
cleus and separate components within theinteraction site.
Figure 1.ATCA4.8GHzimageofPKS2152-699. Thecontour
levelsare–1,1,2,3,4,5,6,8,10,12,16,20,30,40,80,160×3
mJybeam−1.
2 OBSERVATIONS
The observations reported in this paper were made on the
19and23January,21Marchand1April1992usingthefour Table 1.RadioPropertiesofPKS2152-699
6-kmconfigurationsavailablewith ATCAandthestandard
continuum correlator setup with a bandwidth of 128 MHz
Region Ia ma Ib α4.7
and 32 channels. The two simultanous frequencies were set 4.7GHz 4.7GHz 8.6GHz 8.6
Jy % Jy
to 4.74 and 8.64 GHz. The source was observed for 12h in
Total 9.94 24.0 3.80 –
each configuration. The data were calibrated by using the Core 0.77 2.0 0.81 +0.10
MIRIAD package (Sault, Teuben & Wright 1995), which is HIC 0.04 21.9 0.017 −1.10
necessary for the calibration of the polarization of ATCA Nlobe 3.61 26.4 – –
data. The flux scale is based on the recent compilation of Nhotspot 0.21 14.6 0.09 −0.87
mesurements of the primary calibrator PKS 1934-638 by Slobe 5.41 21.2 2.30 –
Reynolds (1996) which corresponds to 5.91 Jy at 4.7 GHz Shotspot 0.56 13.8 0.25 −0.92
and2.84 at 8.6 GHz.This differsfrom thepreviouscalibra- a)beamsize2.1×2.3arcsec
tioninuseattheCompact Arrayby(new-old)-8.1%at4.7 b)beamsize1.5×1.6arcsec
GHz and +9.8% at 8.6 GHz.
At 4.7 GHz we have made images with both uniform
weight and using the “robust” parameter equal to 0.5. The
former gives the full resolution of 1.39×1.44 (PA = 11.7◦) WehavealsoobtainedtheimagesoftheStokesparame-
whilethelattergivesabeamof2.3×2.1arcsec(PA=58◦). ters(Q,U),thepolarizedintensityimage(P =(Q2+U2)1/2)
Using the “robust” parameter we were able to give more and position-angle image (χ = 0.5arctan(U/Q)). Here we
weight to the short baselines and therefore the extended present these images only for the data at 4.7 GHz because
low-brightnessemissionisbetterimaged.Thetotalintensity at 8.6 GHz the polarization maps are not completely reli-
map at 4.7 GHz at lower resolution is shown in Fig. 1. At able,probablyduetoinstrumentalpolarizationaffectingthe
8.6 GHz, the data have a full resolution of 0.8×0.9 arcsec datain theearliest daysof ATCA when thedata presented
(PA = −26◦). The rms noise of the total intensity maps is herewere collected. The rms noise of the Q and U maps at
about 0.80 mJy beam−1 in the4.7 GHz map and 0.65 mJy 4.7 GHz is about 0.17 mJy beam−1.
beam−1 in the8.6 GHz map. The polarized intensity and the fractional polarization
The total fluxes derived from these synthesis observa- (m = P/I) were estimated only for the pixels for which
tions are given in Table 1. At 8.6 GHz, it appears to be P >5σ . Fig. 2 shows a greyscale image of the polarized
QU
lowerthansingledishobservations(6.22Jyat8.4GHzfrom intensity while Fig. 3 shows contours of the total intensity
Wright & Otrupcek 1990), most likely dueto missing short with superimposed vectors whose length is proportional to
spacings. the fractional polarization and whose position angle is that
(cid:13)c 0000RAS,MNRAS000,000–000
Radio jet interactions in the radio galaxy PKS 2152-699 3
theobservationswerenotmadewithmatchedarrays:amore
completestudyofbothpolarization andspectralindexisin
progress and will be presented in a forthcoming paper.
2.1 Results
Compared to the previous observations from the Molonglo
SynthesisTelescope(Tadhunteretal.1988)andfromATCA
(Fosburyetal.1990),theradiostructureisnowshownmore
clearly.Animportantfeatureisthebrightsource∼10arcsec
NE of the nucleus, i.e., at the same distance and similar—
but not identical—position angle from the nucleus as the
HIC. This component, which we call RC, was not visible
in the previous low resolution radio images available for
PKS2152-699althoughitwasseenwithalowersignificance
in the early ATCA image byFosbury et al. (1990).
The new radio images show that PKS 2152-699, al-
thoughstrictlyclassifiedasaFanaroff&RileytypeIIsource
on the basis of the ratio of hot-spot separation to total
source length, it is unusual in showing the hot-spots near
the centres of the lobes. This behaviour, which is interme-
diate between FR I and II types, has been observed before
(e.g. Capetti, Fanti & Parma 1995) in objects with radio
Figure2.GreyscaleimageofthepolarizedintensityofPKS2152- power on the border between the two classes (logP ∼ 25.5
69at6cm.Therangeisbetween 0and10mJy. WHz−1at4.7GHz).ThetotalradiopowerofPKS2152-699
(logP=25.61 W Hz−1 at 4.7 GHz) is indeed typical of the
transition region between FR I and II galaxies. For the ob-
jectsstudiedbyCapettietal.(1995),thepeculiarmorphol-
ogy could beduetoprecession of thecentralengine or per-
haps by an externally-induced change in jet direction. The
southern lobe of PKS 2152-699 shows an edge-brightened,
arc-like structure which suggests jet precession. The bright
spot then represents the primary hot-spot and the current
point of impact of the jet with the ISM while the arc-like
brightemissionrepresentsthepreviousimpactpointsduring
the change of direction of the jet (see also the simulations
inCox,Gull&Scheuer1991). Somethingsimilar could also
occur in the northern lobe with the radio plasma far away
from the hot-spot could represent the backflow from pre-
vious, more distant, fading hot spots. A similar scenario,
with the lobe considered as a relic from earlier jet activ-
ity, has been suggested for 3C111 (Linfield & Perley 1984).
Hot-spots in the middle of the lobe can also be due to pro-
jection effects or theresult of an interaction movingthe jet
direction.Thespectralindicesobservedinthehot-spotsare
unusuallysteep(α4.7 ∼−0.9)whichcouldbeduetothere-
8.6
sultofaspectralbreak betweenthesetwofrequencies.This
has been observed in the knots of 3C277.3, an object with
many characteristics in common with PKS 2152-69.
Figure3.Contours(asinFig.1)ofthetotalintensityat4.8GHz TheradioemissioninPKS2152-699isasymmetricboth
imageofPKS2152-699 withsuperimposedvectors whoselength influxandcore/lobedistance.Thesouthernlobeextendsfor
isproportional tothe fractional polarization andwhose position
approximately30arcsec(24kpc)whilethenorthernextends
angleisthatoftheelectricfield.
to45arcsec(36kpc).Wedonotfindclearevidenceforajet,
but a thin, low brightness emission bridge between the nu-
of theelectric field.Themean fractional polarization of the cleus and thenorthern lobe is visible at 4.7 GHz. Although
different regions is given in Table 1. veryweak, thetotal emission from thenorthern lobe shows
In order to estimate thespectral index in some regions substructure. This substructure can be seen very clearly in
wehaveproducedan8.6GHzmapdegradingtheresolution polarizedemission(Fig.2).Twoarm-likestructuresarevis-
tomatchthatofthe4.7GHz(uniformweight).Thespectral ible along its southern and northern edges. The northern
indexα4.7 (definedasS ∝να)was estimated onlyfrom the lobe shows a somewhat higher fractional polarization while
8.6
regions with signal above 5σ in both maps. The values of thehotspotsappeartobelesspolarizedthantherestofthe
I
thespectralindexmustbeinterpretedwithcautionbecause lobes. In the southern lobe, the polarization vectors follow
(cid:13)c 0000RAS,MNRAS000,000–000
4 R.A.E. Fosbury et al.
the edge-brightened arc-like structure (see Fig. 3), typical
of such sources. The fractional polarization in the lobes is
quitehigh although not exceptional.
PKS2152-699hasaprominentcore(seeTable1).High
resolution observations made in 1988-89 with the Parkes-
TidbinbillainterferometerbyJonesetal.(1994) giveacore
flux of 784 mJy at 2.3GHz while more recent observations
obtainedin1994 withthesameinstrumentgive583mJyat
thesamefrequency(Morgantietal.1997).Thismayindicate
some variability of the flux density of the nucleus although
newobservationswillbenecessarytoconfirmthis.Thecore
has an invertedspectral index,α∼0.10.
The ratio R between the core flux density and the ex-
tendedfluxdensityderivedat4.7GHzisR∼0.06.Thisisa
typicalvalueforbroad-linegalaxiesasPKS2152-699isclas-
sified by Tadhunter et al. (1988) while it is large compared
to typical FR II narrow-line radio galaxies as discussed in
Morganti et al. (1997) for datacollected at 2.3 GHz.
2.2 The nearby galaxy 2153-699
PKS2152-699isknowntobesituatedinagalaxy-poorenvi-
ronment(Tadhunteretal.1988).However,thepresenceofa
nearby (∼3.8 arcmin east) strong radio source, PKS 2153- Figure 4. Contours of the total intensity at 4.8 GHz image of
69, was already known from the model fitting to low res- thenearbygalaxyPKS2153-699.Thecontourlevelsare-1,1,2,
olution data carried out by Ekers (1969). This source is 4,6,8,10,12,14,16,20,30 ×2mJybeam−1
unresolved in the maps of Christiansen et al. (1977) and
Tadhunter et al. (1988) and has been identified by Jones VLBIobservationsrevealacore-jetmorphology onthepar-
& McAdam (1992) with a 20th magnitude galaxy with un- secscaleandthePAofthisstructureis∼44◦±5◦,closeto
known redshift but likely to be in the background given its that of the centroid of the optical HIC. The overlay shows
magnitude. With the new data we have mapped the region that the HIC is situated to the east of RC which itself is
correspondingtoPKS2153-699andresolvedthesourceinto coincident with aprominent part of thesubstructureof the
twolobesortails.Sometrailofradioemissiontothewestis cloud. This latter component was identified as a red stellar
also observed. More faint structure may be missed because object (C) in theline-free continuum observations reported
of the attenuation of the primary beam. In Fig. 4 the con- bydiSeregoAlighierietal.(1988)andisthereforepredom-
tours of the radio emission are shown. The cross indicates inantly continuum rather than line emission with a colour
the position of the optical identification, situated between verydifferentfromtherestoftheHIC.Thedustbandcross-
thetwo lobes. ing the galaxy in PA∼ 110◦ was inferred from the ground-
based images from the colour gradient measured across the
galaxy (diSerego Alighieri et al. 1988).
2.3 Correlation with the optical image In addition to the emission components to the NE of
thenucleus,whichextendtogreaterdistancethanshownin
A broad-band HST PC 2 image (F606W filter, single 500s
Fig. 5 (Tadhunter et al. 1988), the HST image shows two
exposure) of PKS 2152-699 was retrieved from the pub-
faintregionstotheSWatradialdistancesofapproximately
lic archive. After interactively cleaning cosmic-ray events, ◦
11and16arcsecinPA237 .Thesewerenotdetectedinthe
we have used this image to produce an overlay with the
groundbased images.
new radio image at 4.7GHz. The registration between the
There is also a bright ‘bow’ structure, convex to the
two images was carried out by aligning the radio nucleus nucleus, approximately 3 arcsec along PA∼57◦ to the NE.
(RA(J2000) = 2157 06.0, DEC(J2000) =-69 41 24.0) with
Thisisdiametrically oppositethefaintSWstructures.This
the peak of the optical image (σ ∼ 0.2 arcsec). The over-
bowwasseenasanuclearextensioninthegroudbasedemis-
lay isshown in Fig. 5while Fig. 6presentsacartoon which
sion line imaging (see Fig. 5).
shows more clearly the spatial relationship between the ra-
dio, optical emission and dust absorption components. The
HSTimage, which includes line(predominantly [O III], Hα
and[NII])emissionandcontinuum,clearlyshowsstructural 3 DISCUSSION
detailsoftheHICandseveraladditionalcomponentswhich
The combination of radio and optical images of PKS 2152-
fallalongthesameaxis.Thepositionanglebetweenthenu-
699 allow usto make thefollowing statements:
cleus andtheobserved radio component,RC, neartheHIC
◦
is 34 . This is intermediate between that of the large-scale (i) ThereisaradiocomponentassociatedwiththeHIC—
radio structure (PA∼ 23◦ defined from the low resolution although it is not situated at thebrightest optical location.
MOST radio image, Tadhunter et al. 1988) and that from The optical emission coincident with this is red in colour
VLBI observations presented by Tingay et al. (1996). The and probably continuum rather than line emission.
(cid:13)c 0000RAS,MNRAS000,000–000
Radio jet interactions in the radio galaxy PKS 2152-699 5
Figure 5HSTF606Wimagewithradio6cmcontourssuperimposed.TheHSTimagehasbeenmanuallycleanedofcosmicrayevents
andisshownonalogarithmicscale.Theradiocontours arealsologarithmic,rangingfrom3to700mJybeam−1.Theradioand
opticalnucleihavebeenforcedtocoincide.Theregionscontainingsomeofthefaintfeaturesareshownwithastretched intensityscale.
(ii) Thereisa progression in PA from theVLBI axis( = ence of the blue optical continuum and the offset between
thenucleus–HICaxis)tothenucleus–innerradiocompo- thecloud/nucleusaxisandtheradioaxis.Theyalsopointed
◦
nent to thelarge-scale radio double axis (44 – 34 – 23 ). out,however,thatthecloudofionizedgasin3C277.3shows
(iii) Thereareanumberof distinct opticalstructures(of a large velocity gradient while the HIC in PKS 2152-699
whichtheHICisthemostprominent)lyingclosetothe44◦ showsbroad,lowintensitywingsonthe[OIII]linesextend-
PA axis. These exist on both sides of the nucleus although ingtotheblue.Thepresenceofextensive,chaoticdustlanes
they are more numerousand brighterto the NE. intheinnerregionsofthegalaxysuggeststhatthetheradio
(iv) A dust lane crosses the nucleus in PA∼ 110◦ with jet is interacting with a fragment of a merging galaxy.
emission alongitsnorthernedge.Thiscouldbethelowion- We have estimated for PKS 2152-699 the minimum
izationlineemissionreportedbyTadhunteretal.(1988)but pressure associated with the bright radio component to be
we cannot excludea continuum contribution. ∼3×10−10 dynescm−2.Wedonothaveagoodmeasureof
(v) Thenorthernandsouthernlobeshaveaverydifferent the density of the warm line-emitting gas but if we assume
morphologies — the northern being diffuse with a central T≈15000 K (Tadhunter et al.1988) and n ∼ 200 cm−3 (a
e
hotspot, thesouthern brighterwith a ‘trailed’ hotspot. typical value for a bright extranuclear cloud) we find that,
as in thecase of other jet/cloud interactions, the radio and
The discovery of the bright radio component next to line-emitting gas pressures are quite comparable (Clark &
the HIC supports the hypothesis of a jet/cloud interac- Tadhunter 1996) suggesting that the region of high ioniza-
tion in PKS 2152-699 and it reinforces the similarity be- tion has been compressed by the interaction with the radio
tween this object and 3C277.3, one of the best examples of plasma.
jet/cloud interaction (vanBreugelet al. 1985a). Aspointed The presence of EELR in high and intermediate red-
out by Tadhunter et al. (1988), comparison of the two ob- shift radio galaxies is often associated with asymmetries in
jectsshowsasimilarityintheemission-linespectra,thepres- theradiomorphology andpolarization (Pedeltyet al.1989,
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themselves. We are currently persuing such studies using
theseand othernew observational data on this source.
ACKNOWLEDGEMENTS
ThisworkisbasedonobservationswiththeAustraliaTele-
scope Compact Array (ATCA), which is operated by the
CSIRO Australia Telescope National Facility. It also uses
observationsmadewiththeNASA/ESAHubbleSpaceTele-
scopeobtainedfromthedataarchiveattheST-ECF.RAEF
isaffiliated totheAstrophysicsDivision,Space ScienceDe-
partment, European Space Agency. RM acknowledges sup-
port from the DITAC International Science & Technology
Program.
REFERENCES
Capetti A.,FantiR.,ParmaP.1995,A&A300,643
Chambers K.C., Miley G.K., van Breugel W. 1987 Nature 329,
604
Christiansen W.N., Frater R.H., Watkinson A., O’SullivanJ.D.,
LockhartI.A.&GossW.M.1977,MNRAS181,183
ClarkN.E.,TadhunterC.N.1996,inCygnusA–StudyofaRadio
Galaxyeds.C.L.Carilli&D.E.Harris,CUP,p.15
ClarkN.E.,Tadhunter C.N.,Morganti R.,KilleenN.E.B.,Hook
R.N.,FosburyR.A.E.,SiebertJ.&Shaw M.1997, MNRAS,
286,558
CoxC.I.,GullS.F.,Scheuer P.A.G.1991,MNRAS252,558
di Serego Alighieri S., Binette L., Courvoisier T. J.-L., Fosbury
R.A.E.&Tadhunter C.N.1988,Nature,334,591
EkersR.D.1969,AuJPS7,1
FanaroffB.L.&RileyJ.M.1974MNRAS167,31p
Fosbury R.A.E., di Serego AlighieriS., Courvoisier T.J.-L., Sni-
Figure6Cartoonshowingthedifferentabsorptionandemission jders M.A.J., Tadhunter C.N., Walsh J. & Wilson W. 1990,
components inPKS2152-699. The VLBIimage isrepresented to in“IUEAstronomyinthe EraofNew Space Missions”ESA
adifferentscaleatthelowerleft. SP310,513
Heckman T.M., van Breugel W.J.M. & Miley G.K. 1984, ApJ
286,509
Liu & Pooley 1991, Clark et al. 1997). In PKS 2152-699,
JonesP.A.,McAdamW.B.1992, ApJS80,137
however,thereisnostrongpolarization asymmetryandthe Jones P.A.,McAdamW.B.&Reynolds J.E.1994, MNRAS268,
stronger, closer (in the sky plane) radio lobe is on the side 602
opposite to the jet/cloud interaction. In contrast with the LinfieldR.&PerleyR.1984,ApJ279,60
more powerful radio galaxies at higher redshifts, where the LiuR.&PooleyG.,1991,MNRAS253,669
polarization and structural asymmetries appear to be due McCarthyP.J.,vanBreugelW.,SpinradH.,DjorgovskiS.1987,
to large-scale ISM density variations across the source, the ApJ321,L29
McCarthyP.J.1993,ARAA31,639
interactionseenheremaybeatransitoryphenomenonwith-
Morganti R., Robinson A., Fosbury R.A.E., di Serego Alighieri
out a major influenceon the main radio lobe structure.
S.,Tadhunter C.N.,MalinD.F.,1990,MNRAS249,91
Morganti R., Oosterloo T.A., Reynolds J.E., Tadhunter C.N. &
MigenesV.1997,MNRAS284,541
Pedelty J.A., Rudnick L., McCarthy P.J., Spinrad H., 1989, AJ
4 CONCLUSIONS 97,647
Reynolds J.E. 1996 in “Australia Telescope Compact Array,
We have presented new radio maps of the radio galaxy Users’sGuide”eds.W.M.Walsh&D.J.McKay
PKS 2152-699 obtained with the ATCA. These reveal a Sault,R.J.,Teuben,P.J.,Wright,M.C.H.1995in“Astronomical
brightradiocomponentnexttothecloudofveryhighlyion- DataAnalysisSoftwareandSystemsIV”,eds.R.Shaw,H.E.
ized gas, situated about 8 kpc from the nucleus. The radio Payne and J.J.E. Hayes, Astronomical Society of the Pacific
ConferenceSeries,77,433
componentisseparatedfrom thebrightestregion oftheop-
SimkinS.M.&EkersR.D.1979ApJ84,56
ticalcloudbutcoincideswithsourceofredcontinuumemis-
Tadhunter, C.N., Fosbury, R.A.E.,Binette, L.A., Danziger, I.J.,
sion. This structure, togetherwith theunusualmorphology
Robinson,A.:1987,Nature325,504
ofthenorthernradiolobe,suggeststhatajet/cloudinterac-
TadhunterC.N.,FosburyR.A.E.,diSeregoAlighieriS.,BlandJ.,
tionhastakenplace.Suchinteractionsarerelativelyrareat DanzigerI.J.,GossW.M.,McAdamW.B.&SnijdersM.A.J.
low redshift but,when they occur, dooffer theopportunity 1988,MNRAS235,403
for quantitative investigation of the properties of the jets TingayS.J.etal.1996, AJ111,718
(cid:13)c 0000RAS,MNRAS000,000–000
Radio jet interactions in the radio galaxy PKS 2152-699 7
vanBreugelW.J.M.,DeyA.1993,ApJ414,563
vanBreugelW.,MileyG.,HeckmanT.,Butcher H.& BridleA.
1985a, ApJ290,496
van Breugel W., Filippenko A.V.,Heckman T.,MileyG. 1985b,
ApJ293,83
vanBreugelW.,HeckmanT.M.,MileyG.,FilippenkoA.V.1986,
ApJ311,58
Wright A.E. & Otrupcek R. 1990, Parkes Catalogue 1990, Aus-
traliaTelescopeNationalFacility
(cid:13)c 0000RAS,MNRAS000,000–000
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