Strong molecular hydrogen emission and kinematics of the multiphase gas in radio galaxies with fast jet-driven outflows

1.8 MB·English

by  Pierre Guillard

DRAFTVERSIONJANUARY10,2012
PreprinttypesetusingLATEXstyleemulateapjv.2/16/10
,,,,,,,,
STRONGMOLECULARHYDROGENEMISSIONANDKINEMATICSOFTHEMULTIPHASEGASINRADIO
GALAXIESWITHFASTJET-DRIVENOUTFLOWS
P.GUILLARD1,P.M.OGLE1,B.H.C.EMONTS2,P.N.APPLETON3,R.MORGANTI4,5,C.TADHUNTER6,T.OOSTERLOO4,5,D.A.
EVANS7,ANDA.EVANS8,9
DraftversionJanuary10,2012
ABSTRACT
2 Observationsofionizedandneutralgasoutflowsinradio-galaxies(RG)suggestthatAGNradiojetfeedback
1 has a galaxy-scale impact on the host ISM, but it is still unclear how the molecular gas is affected. Thus it
0 iscrucialto determinethe physicalconditionsof themoleculargasin powerfulRG to understandhowradio
2 sources may regulate the star formation in their host galaxies. We present deep Spitzer IRS high-resolution
n spectroscopyof 8 nearbyRG that show fast HI outflows. Strikingly, all of these HI-outflow RG have bright
a H2 mid-IRlines thatcannotbe accountedforby UV or X-rayheating. This stronglysuggeststhat the radio
J jet,whichdrivestheHIoutflow,isalsoresponsiblefortheshock-excitationofthewarmH2 gas. Inaddition,
thewarmH gasdoesnotsharethekinematicsoftheionized/neutralgas. Themid-IRionizedgaslines(with
6 2
FWHMupto1250kms- 1for[NeII]12.8µm)aresystematicallybroaderthantheH2 lines,whichareresolved
] by the IRS in ≈60% of the detected lines (with FWHM up to 900 km s- 1). In 5 sources, 3C 236, 3C 293,
O
3C 459, 4C 12.50 and PKS 1549-79, the [NeII]λ12.8µm line, and to a lesser extent the [NeIII]λ15.5µm
C and [NeV]λ14.3µmlines, clearly exhibitblue-shiftedwings(up to -900 km s- 1 with respectto the systemic
. velocity)thatmatchwellthekinematicsoftheoutflowingHI orionizedgas. TheH2 linesdonotshowthese
h broadwings,excepttentativedetectionsin4C12.50,3C459andPKS1549-79.Thisshowsthat,contrarytothe
p HIgas,theH2 gasisinefficientlycoupledtotheAGNjet-drivenoutflowofionizedgas. Whilethedissipation
-
ofasmallfraction(<10%)ofthejetkineticpowercanexplaintheturbulentheatingofthemoleculargas,our
o
r datashowthatthebulkofthewarmmoleculargasisnotexpelledfromthesegalaxies.
t
s Subjectheadings:galaxies:jets,galaxies:kinematicsanddynamics,galaxies:evolution,galaxies:ISM,shock
a waves,ISM:general,ISM:jetsandoutflows,molecularprocesses,turbulence
[

1
1. INTRODUCTION in galaxy evolution, such as what is the magnitude of AGN
v
feedback(e.g.gasoutflowrates)andwhatisthemaindriving
3 Active galactic nucleus (AGN) feedback is recognised to
mechanism of AGN feedback (e.g. quasar wind, radio jets,
0 have an importanteffect on galaxy evolution. Widely intro-
circum-nuclearstarbursts).
5 duced in numerical simulations of galaxy evolution to clear
Most of the existing evidence for AGN radio jet feed-
1 the circum-nucleargasandhaltthe growthof super-massive
back on the scales of galaxy bulges comes from obser-
. black holes (Silk&Rees 1998; DiMatteoetal. 2005), this
1 vations of outflows of neutral gas (Morgantietal. 2003,
mechanismwouldexplainthecorrelationsfoundbetweenthe
0 2005b; Emontsetal. 2005; Lehnertetal. 2011) and ionized
BH mass and e.g. the bulge mass (e.g. Ferrarese&Merritt
2
gas (Nesvadbaetal. 2006, 2008; Holtetal. 2008) in radio
1 2000),andpreventtheformationoftoomanymassivegalax-
galaxies. These observations suggest that radio jets are an
: iesintheearlyuniverse(e.g.Thomasetal.2005).
v The co-evolution of massive black holes and their efficientmechanismtoconverttheenergyoutputoftheAGN
i intoanenergyinputintotheISM,andthatradiosourcesmay
X host galaxies has been well established observationally
regulate gas cooling in early-type galaxies (Bestetal. 2005,
in samples at various redshifts (e.g. Tremaineetal. 2002;
r 2006;Donosoetal.2009).
a Alexanderetal.2005).Nevertheless,detailedobservationsof
One of major open questions about estimating mass out-
individualactivegalaxiesinthenearbyuniverse,wherephys-
icalprocessesinthecentralregioncanbestudiedindetail,are flowratesiswhethertheionizedandHIgastracesthedomi-
nantphaseofthewind. Thereforeitiscrucialtocomparethe
essentialforansweringkeyquestionsabouttheroleofAGN
massesandkinematicsofeachgasphase. Ithasonlyveryre-
1Spitzer Science Center (SSC), California Institute of Technology, centlybeenrecognizedthatstarburstandAGN-drivenwinds
Pasadena,USA alsoincludemolecularcomponents(e.g.Veilleuxetal.2009;
2Australia Telescope National Facility, CSIRO, POBox76, Epping Feruglioetal.2010;Alataloetal.2011).Fischeretal.(2010)
NSW,1710,AUSTRALIA
and Sturmetal. (2011) reported the discovery of molecular
3NASAHerschelScienceCenter(NHSC),CaliforniaInstituteofTech-
nology,Pasadena,USA outflows in nearby ULIRGs (e.g. Mrk 231) through the de-
4NetherlandsFoundationforResearchinAstronomy,Dwingeloo,The tection of a series of OH and H2O lines seen in absorption
Netherlands againstthebrightIRdustcontinuumwithHerschel/PACSin
5KapteynAstronomicalInstitute,UniversityofGroningen,TheNether- the λ78- 79µm and λ119- 121µm ranges. However, esti-
lands
6DepartmentofPhysics&Astronomy,UniversityofSheffield,UK matesofoutflowratesfromabsorptionlinessufferfrommajor
7Massachusetts Institute of Technology, Kavli Institute for Astro- uncertaintiesregardinge.g. thegeometry,andthedegeneracy
physics and Space Research, 77 Massachusetts Avenue, Cambridge, betweencoveringfractionsandcolumndensities. Moreover,
MA02139,USA most of these sources are composite: the co-existence of a
8UniversityofVirginia,Charlottesville,USA
starburst, quasar, and radio source makes it difficult to infer
9NationalRadioAstronomicalObservatory
2 P.Guillardetal.
whatisdrivingthewind.Starbursts(Rupkeetal.2005),radi- stellar masses are derived from the K-band luminosities ac-
ationpressurefromthequasar(Feruglioetal.2010),andeven cordingtoMarconi&Hunt(2003):
mechanicalinteractionswiththeradiosource(Reynoldsetal.
log (M )=- 2.3+1.21×log (L ), (1)
2009)haveallbeenproposed. 10 ⋆ 10 K
Spitzer IRS spectroscopy opened a new perspective from whereM isthebulgestellarmassinM andL theK-band
⋆ ⊙ K
which to study the impact of the injection of kinetic energy luminosity in L . The unabsorbed 2- 10 keV AGN X-ray
⊙
ontheformationofmoleculargasandregulationofstarfor- fluxesaretakenfromtheliterature,except3C236,3C459and
mationinnearbyradiogalaxies. Ogleetal.(2010)foundthat PKS 1549-79which were unpublished. For 3C 236, we re-
30%ofasampleof55nearby3Cradiogalaxieshaveunusu- processedandextractedtheChandraACISspectrum.Wefind
allybrightmid-IRlineemissionfromwarm(102- 3K)H2gas, thatthespectrumiswellfittedwithasinglepowerlawofpho-
with weak tracers of star formation (SF) (e.g. PAHs). The tonindex1.67,absorbedbyacolumnofN =2.3×1023cm- 2,
H
H2 toPAHluminosityratioismorethan10timeslargerthan consistent with the presence of a dust lane close to the nu-
whatisexpectedfromUVandX-rayphotonheating.Wepro- cleus (deKoffetal. 2000). The 3C 459 and PKS 1549-79
posethattheH2 luminosityisassociatedwiththedissipation X-rayfluxeswereprovidedbyP.O’BrienandM.Hardcastle
of a small fraction of the mechanicalenergyof the radio jet (privatecommunications). Thejetkineticpowerisestimated
(Nesvadbaetal.2010;Ogleetal.2010). TheseH2-luminous from the 178 MHz flux density, according to the formula10
galaxieslieofftheSchmidt-Kennicuttrelationship,indicating derivedinPunsly(2005).
thatstar-formationmaybesuppressedrelativetonearbynor- Thesegalaxiesallshowverybroad(upto1000kms- 1)HI
malstar-forminggalaxies(Nesvadbaetal.2010). Numerical absorption profiles, with highly blue-shifted HI gas with re-
simulationsalsosuggestthatradiojetsappeartobeefficientat spect to their optical systemic velocities, which indicates a
injectingkineticenergyintotheISM(e.g.Wagner&Bicknell fast outflow of neutral gas (e.g. Morgantietal. 2003). The
2011),possiblyinhibitingstarformation. associated HI mass outflow rates are up to ≈ 60M⊙ yr- 1,
Thispaperreportsonthemid-IRSpitzerIRS(Houcketal.
up to 2 orders of magnitude higher than the mass outflow
2004) spectroscopy of 8 nearby powerful radio galaxies in
of ionized gas (see e.g. Emontsetal. 2005). These outflow
which fast (≈1000 km s- 1) outflows of ionized and neutral rates are estimated from the gas column density, the out-
gashavebeendetected(Morgantietal.2005b). Thesegalax- flowvelocity,andtheradiuswithinwhichthefloworiginates
ies are ideal targets to study the impact of AGN feedback (see e.g. Heckman 2002, for a review). In some cases,
on the different phases of the ISM, and in particular on the like3C305(Morgantietal.2005a),IC5063(Oosterlooetal.
molecular gas, and thus on star-formation. They present an 2000;Morgantietal.2007)and3C293(Morgantietal.2003;
environmentwhere winds can clearly be associated with the Emontsetal. 2005), this radius is estimated from high-
mechanism driving them, namely the radio jet. How is the resolutionradioandopticalobservations,wheretheoutflowis
kinetic energy of the outflow dissipated? Is the molecular spatiallyresolvedagainsttheradiocontinuum,andco-spatial
gasentrainedintheionized/neutraloutflow? Ifyes,whatare withregionswheretheradioemissioninthepropagatingra-
thephysicalprocessesthatcontrolthedynamicalcouplingbe- diojetisenhanced. Fortheothersources,theradiiaremore
tweenthetenuousgasoutflowandthedensemoleculargas? uncertain. It isassumed thatthe outflowis comingfromthe
Sect. 2and3 presentthegalaxysample anddetailsonthe brightestradiocontinuumregion,whichinprincipleprovides
data reduction and spectral analysis. Then we discuss spec- onlyalowerlimitsincetheHI absorptioncanonlybetraced
troscopic diagnostics (sect. 4), focusing on the H2 gas, and in regions where the continuum is bright. We checked that
wecomparethekinematicsoftheionized,HI,andH2 gasin these radii are consistent with optical spectroscopy,but note
sect.5.Sect.6discussestheexcitationmechanismsandorigin thattheseradiiestimatesonlyprovideanorderofmagnitude.
oftheH2 gas,andproposesaninterpretationoftheobserved SomeofthemainradioandHIpropertiesaresummarizedin
gasheatingandkinematicsofthemultiphaseISMgasofthe Table 2. In sect. 5.4, we discuss in more detail the HI kine-
hostgalaxy. matics,andcomparethemtothekinematicsofthemolecular
2. THESAMPLEOFHI-OUTFLOWRADIOGALAXIES andionizedgasphases.
Except PKS 1549-79, all of the observed sources are part 3. SPITZEROBSERVATIONS,DATAREDUCTIONANDANALYSIS
oftheMorgantietal.(2005b)sample. Mostofthesesources
The IRS has two high-resolution modules, short high11
are bright compact radio sources, with sizes ranging from
(SH)andlong-high12(LH),andfourlow-resolutionmodules,
0.01 to 40 kpc. These HI-outflow objects appear to be-
long to the minority of powerful radio galaxies (≈ 35%) short-low(SL1&SL2)andlong-low(LL1&LL2),spanning
5.2- 38µm. Inlowresolutionmode(λ/∆λ≈57- 127),we
thatshowevidenceforrecentstarformationatopticalwave-
used publicly available archival data for 7 of the 8 sources.
lengths (Tadhunteretal. 2011, based on spectral synthesis
Only PKS 1549-79 was not previously observed at low res-
modelling) and/or mid-IR wavelengths (Dickenetal. 2011,
olution,henceweobservedthissourceaspartofourSpitzer
basedonPAHdetection). Mostsuchobjectsarecompactra-
Cycle4programp40453. Athighresolution(λ/∆λ≈600),
dio sources (e.g. CSS/GPS/CSO) or have unusually strong
weobserved5sources(3C236,3C305,3C459,PKS1549-
compact steep spectrum cores (Tadhunteretal. 2011). The
79,andIC5063)aspartofourprogramp40453,andweused
starformationintheseobjectsisprobablylinkedtothepres-
archivaldatafortheremaining3sources(3C293,4C12.50,
ence of an unusually rich ISM in the nuclear regions of the
andOQ208)(p30877).Theexposuretimesforeachmodeare
host galaxies, perhapsaccreted in gas-richmergers. In such
objects the radio jets are expected to interact particularly
10 Thisformulausesthe151MHzfluxdensity. Whenadirectmeasure-
strongly with the dense circumnuclear gas. Therefore these
mentat150MHzwasnotavailable,wederiveditfromthe178MHzmeasure-
arejustthetypeofobjectsinwhichwemightexpectthejets ment(takenfromNED)byfittingthemeasuredradioSEDwithapower-law.
tohaveadirectimpactonthemoleculargas. 114.7′′×11.3′′slit,observedwavelengthsfrom9.9to19.6µm
Some properties of the sample are listed in Table 1. The 1211.1′′×22.3′′slit,observedwavelengthsfrom18.7to37.2µm
SpitzerIRSspectroscopyofHI-outflowradiogalaxies 3
Table1
PropertiesofHI-outflowradio-galaxiesobservedwithSpitzerIRS
Object RAa Deca zb DLc K-mag M⋆d M(H2)e M(H2) L24µmf logLXg logLX L(H2)/LXh
J2000.0 J2000.0 [Mpc] [M⊙] [M⊙] ref. [L⊙] [ergs- 1] ref.
3C236 100601.7 +345410.4 0.1004 449 12.25 7.4E10 <8E9 (1) 1.94±0.15E10 43.0 0.054
3C293 135217.8 +312646.5 0.0448 195 10.84 4.6E10 1.5E10 (2) 6.26±0.75E09 42.8 (4) 0.063
3C305 144921.8 +631615.3 0.0418 178 10.64 4.8E10 2.0E9 (1) 7.13±0.45E09 41.2 (5) 1.78
3C459 231635.2 +040518.1 0.2199 1046 ··· ··· ··· ··· 5.36±0.32E11 43.2 0.13
4C+12.50 134733.4 +121724.2 0.1234 551 12.21 1.3E11 1.5E10 (3) 1.20±0.04E12 43.3 (6) 0.16
IC5063lobe 205202.1 -570406.6 0.0113 45.3 8.75 1.6E10 ··· ··· 3.74±0.08E10 42.9 (7) 0.008
OQ208 140700.4 +282714.7 0.0766 337 11.52 5.2E09 1.4E10 (1) 2.31±0.03E11 42.7 (8) 0.08
PKS1549-79 155658.9 -791404.3 0.1521 699 ··· ··· ··· ··· 1.31±0.04E12 44.7 0.005
References.—(1)OcañaFlaqueretal.(2010);(2)Evansetal.(1999);(3)Evansetal.(2002);(4)Ogleetal.(2010);(5)Massaroetal.(2009);(6)O’Deaetal.
(2000);(7)Lutzetal.(2004);(8)Guainazzietal.(2004)
aPositionsofthesourcesusedfortheSpitzerIRSobservations.Exceptfor3C305,IC5063and4C12.50,thepositionsoftheradionucleiaretakenfromNED
(seeSect.3fordetails).
bRedshiftderivedfromopticallinemeasurements(seereferencesforthesystemicvelocitiesinTable2).
cLuminositydistanceassumingH0=73kms- 1Mpc- 1andΩm=0.27.
dStellarmassderivedfromtheK-bandluminosity.
eH2gasmassesestimatedfromCO(1-0)measurements.For4C12.50,onlytheH2massinthewesternlobeisquoted.
fRest24µmluminositymeasuredwithSpitzerIRS.Weaveragedthefluxover23- 25µm,afterremovalofthe[NeV]24.31µmwhenpresent.
gUnabsorbed2- 10keVnuclearX-rayluminosityinergs- 1. For3C236forwhichweextractedtheX-rayspectrumfromtheChandraarchive(seesect.6.1).
ThePKS1549-79X-rayfluxisfromChandradata(PaulO’Brien,privatecommunication)andagreeswiththeSuzakuvalue(4.5×1044ergs- 1). The3C459
X-rayfluxisfromXMMdata(MartinHardcastle,privatecommunication).
hRatiooftheH2lineluminosity(summedovertheS(0)toS(3)rotationaltransitions)totheunabsorbed2- 10keVnuclearX-rayluminosity.
Table2
RadioandHIpropertiesofoutflowradio-galaxiesobservedwithSpitzerIRS
Object sizea size F178MHz Qjetb τ N(HI) M(HI)c vsysd vsys voute M˙ radius f
[kpc] ref. [Jy] [ergs- 1] [1021cm- 2] [M⊙] [kms- 1] ref. [kms- 1] [M⊙yr- 1] [kpc]
3C236 6.0 (1) 15.7 7.6×1045 0.0033 5.0 1.2E8 30129 (9) 750 47.0 0.5
3C293 5.0 (2,4) 17.1 5.1×1045 0.0038 6.0 1.0E8 13450 (2) 500 56.0 1.0
3C305 10.0 (3) 13.8 6.2×1045 0.0023 2.0 4.7E7 12550 (7) 250 12.0 1.0
3C459 39.0 (5) 30.8 2.5×1046 0.0005 0.75 1.8E7 65990 (10) 300 5.5 1.0
4C12.50 0.15 (6) 4.6 2.5×1045 0.0017 2.6 7.0E6 37027 (10) 600 21.0 0.02- 0.2
IC5063 8.0 (7) 6.3 2.0×1045 0.0120 10.0 2.4E8 3400 (11) 350 35.0 0.4
OQ208 0.01 (6) 0.12 5.2×1043 0.0057 8.3 2.0E4 22985 (12) 600 1.2 0.01
PKS1549-79 0.4 (8) 12.6 7.7×1045 0.02 40.0 1.0E8 45628 (10) 250 30.0 0.1- 1.0
References. — (1) deKoffetal. (2000); (2) Emontsetal. (2005); (3) Morgantietal. (2005a); (4) Zirbel&Baum (1998); (5) Nilssonetal. (1993);
(6) Xiangetal. (2002); (6) Heisler&Vader (1994); (7) Morgantietal. (2005b); (8) Holtetal. (2006); (9) Hilletal. (1996); (10) Holtetal. (2008); (11)
Morgantietal.(1998);(12)Marzianietal.(1993)
aSizeoftheradiosource.Notethatfor3C293,thisisthesizeoftheinnerradiosource.
bJetcavitykineticluminosityestimatedfromthe178MHzflux(seetext,Sect.2).
cMassofHIgasintheoutflowingcomponent(withintheradiusquotedinthetable).
dSystemicvelocityofthegalaxy(seetextfordetails).
eOutflowvelocity,estimatedashalfofthefullwidthatzerointensityoftheblue-shiftedpartofthebroadHIcomponent.
fRadiusoftheHIoutflowregion.ExceptforPKS1549-79,theradiivaluesarefrom Morgantietal.(2005b).
listed in Table 3, and were chosen to reach a signal-to-noise
ratioofatleast10fortheH S(1)17µmline. Table3
2 SpitzerIRSobservationlog
Eveniftheoutflowofneutralgasisoccurringatakpc-scale
distance from the nucleus, this is still spatially unresolved
Object SL LL SH LH
withtheIRSinhigh-resolutionmode. However,twosources
(3C 305 and IC 5063) exhibit a more extended inner radio 3C236 13×14 5×14 4×120 10×60
3C305 13×14 5×14 4×120 10×60
structure, and we placed the slit slightly off-nucleus, coinci-
3C293 3×120 3×120 3×120 10×60
dentwith abrightpeakintheradiocontinuum,atadistance 3C459 16×14 2×30 4×120 10×60
of2arcsecfromthecore. Notethatthecoreisstillincluded 4C+12.50 3×14 2×30 6×30 4×60
inalloftheIRSslits. TheslitpositionsaregiveninFigure1. OQ208 2×60 2×14 4×120 3×60
IC5063lobe 2×14 1×30 8×30 4×60
4C12.50isasystemoftwointeractinggalaxies(Axonetal.
PKS1549-79 2×60 3×30 4×120 5×60
2000),andtheSHslitwaspositionedonlytoincludethewest-
erncompanion. Forthe othersources, the slits were centred Note. —ExposuretimesfortheIRSmodulesgivenas
numberofcycles×rampdurationinseconds.
onthenucleus.
Thegalaxieswereobservedinstaringmode,andplacedat
3.1. Spitzerdatareduction
two nod positions along the slit (1/3 and 2/3 of the length
4 P.Guillardetal.
Figure1. Footprintsofthehigh-resolutionIRSslits(SHandLH)forthe3C305andIC5063galaxies.Forthesetwosources,theradioobservationsresolvethe
HIoutflowagainsttheradiojet,atadistanceofabout2arcsecfromthenucleus. Therefore,theslitswerecentredslightlyoff-nucleus,atthelocationofthe
broad,blue-shiftedHIabsorptionassociatedwiththeoutflow(indicatedbytheorangecircle).Thepositionoftheradiocoreismarkedwithagreencross.
of the slit). The data were processed by the Spitzer Science inIRSstaringmode,andtheSMARTpackage16wasusedto
Center S18.7 pipeline. We started the data reduction from performoptimalextraction. We checked on 3C 293that the
thebasic calibrateddataproducts,whichincludecorrections SPICEandSMARTextractionsgiveverysimilarresults.
forflat-fielding,straylightandnon-linearityofthepixelsre-
3.2. Spectralanalysis
sponse. All but one (4C 12.50) galaxies had dedicated sky
background (off) observations for all high-resolution mod- Tomeasurethefluxesandlinewidthsofemissionlines,we
ules.Whenavailable,the2Doff spectraweresubtractedfrom firstfittedthespectrawiththeIDLPAHFIT(Smithetal.2007)
the on observationfor each nod position. For 4C 12.50, the tool, which decomposes the spectra into starlight, thermal
LHmodulewasusedtoremovethebackgroundemission.For blackbody emission (extinguished by a uniform dust screen
theLHobservations,wecorrectedforthetime-andposition- ifspecified),resolvedPAHfeatures(fittedbyDrudeprofiles),
dependence of the dark current using the DARK_SETTLE andemissionlines. Originallydesignedto fit low-resolution
routine13. Spitzer IRS spectra, we adapted the routine to handle high-
The cleaning of rogue pixels was performed using the resolutiondata. In particular,we allow the emissionlinesto
IRSCLEANroutine14. Roguepixelmasksofthecorrespond- bespectrallyresolvedandwefitthembyGaussianprofiles.
ing IRS campaigns were used, and a further manual clean- We usethePAHFIT decompositionsto measurethefluxes
ingwasdoneforeachnodpositionandmodule. TheSpitzer ofthePAHcomplexes,andtoproducestarlight-freeanddust-
IRSCustom Extractor(SPICE) softwarewas usedto extract freespectra. ExceptforOQ208andPKS1549-79,wedonot
theone-dimensionalSHandLHspectra,withoptimalextrac- includeany extinctionin the fit. For OQ 208, 4C 12.50and
tion. The individual orders within the high-resolution mod- PKS1549-79,we introducedthe capabilityoffitting silicate
uleswereverywellalignedinfluxandnoscalingwasapplied absorptionfeaturesat9.7and18µm. ThenweranPAHFITa
between the orders. Then the orders were trimmed (by re- secondtime to fit accuratelythe emission lines. We also fit-
movingtheendofeachorder,wheretheresponsedrops)and tedthelineswithGaussianprofilesusingthenon-linearleast-
stitchedtogether. Finallya mediancombinationwasusedto squaresIDLfittingroutineMPFIT(Markwardt2009) onthe
producethefinalstackedspectra. continuum-freespectra.Thetwomethodsagreeverywelland
Forallbutonesource(4C12.50),thecontinuumlevelsof give similar line fluxes (within the uncertainties). We find
the SH and LH matched and no scaling was necessary. For significantdifferences(upto a factorof 3 in line flux)when
4C 12.50, we scaled the SH spectrum by a factor of 1.1 to tryingtomeasurethelinefluxesinonegowithPAHFIT,the
matchtheLHmodule,sinceitisthemostaccurateduetoits manyfreeparametersmakingthefitinaccurate.
backgroundsubtraction. For each of undetected emission lines, we computed the
The 3C236 and 3C305 low-resolution spectra were ex- fluxofanunresolvedGaussianlinewithapeakfluxequalto
tractedfromspectralmapswiththeCUBISM15software.For twicethermsnoiseina1µm-widebandcentredatthewave-
theothergalaxies,thelow-resolutionobservationsweredone lengthoftheline. Wetookthisfluxvalueasa2σupperlimit.
Wealsocomputethe24µmrest-framefluxesbyaveraging
the IRS line-freespectrum overa narrowband(23- 25µm).
13http://irsa.ipac.caltech.edu/data/SPITZER/docs/dataanalysistools/tools/dTahrkesseettnlea/rrowband24µmfluxesarelistedinTable1.
14http://irsa.ipac.caltech.edu/data/SPITZER/docs/dataanalysistools/tools/irsclean/
15http://irsa.ipac.caltech.edu/data/SPITZER/docs/dataanalysistools/tools/cub16ishmtt/p://isc.astro.cornell.edu/IRS/SmartRelease
SpitzerIRSspectroscopyofHI-outflowradiogalaxies 5
4. SPECTROSCOPICDIAGNOSTICS inFlower&PineauDesForêts(2010). Thegasisheatedtoa
rangeofpost-shocktemperaturesthatdependontheshockve-
The full high-resolution (SH+LH, i.e. observed wave-
lengths9.9- 37.2µm)spectraareshowninFigure2,andthe locity,thepre-shockdensity,andtheintensityofthemagnetic
field (which is perpendicularto the shock propagation). We
low-resolution spectra are presented on Figure 3. The loca-
useagridofshockmodels(varyingshockspeeds)similarto
tion of the detected PAH complexes and emission lines are
thatdescribedinGuillardetal.(2009),atpre-shockdensities
marked on each spectrum. Overall, the spectra are of very
good quality, with noise levels expected for such exposure nH =103 cm- 3 and 104 cm- 3. The initial ortho-to-pararatio
issetto3,andtheintensityofthepre-shockmagneticfieldis
times. Some minor spurious features still remain, in partic-
ular in the LH spectra (noisier than the SH), which are due 30µG.TheH2 linefluxesarecomputedwhenthepost-shock
to bad pixels or instrumental artefacts that were not cleaned gas has cooled down to a temperature of 100 K. At a given
pre-shock density, the shock velocity is the only parameter
duringthedatareduction. Inappendix,weprovidezoomson
theSHwavelengths(Figure9),andonallindividualdetected weallowtovary.
emissionlines(Figure10and11). Acombinationoftwoshockvelocitiesisrequiredtomatch
the observed H line fluxes. We show the best-fitting shock
2
4.1. Molecularhydrogen combinationinFigure13and14forthetwopre-shockdensi-
ties. Thesefitsarenotunique,buttheyprovideanestimateof
PowerfulemissionlinesfromH aredetectedinallofthe8
2 therangeofshockvelocitiesandpre-shockdensitiesneeded
high-resolutionspectra. TheH 0-0S(1)17µmand0-0S(3)
2 toreproducetheH excitation. Thisphase-spaceiswellcon-
9.7µm lines are detected in all radio-galaxies. The pure ro- 2
strainedwhensix or moreH linesare detected. Thelowest
tationalH linefluxes(ortheir2σ upperlimits)arelistedin 2
2 densityandshockvelocityisrequiredtofitthelow-excitation
Table4.Insomecases,like3C236,3C293,and4C12.50,the
lines S(0) and S(1), which probe the bulk of the warm H
H S(1)linedominatestheSHspectrum(Figure9). TheseH 2
2 2 mass,whereasthehighdensityandshockvelocityisneeded
strengthsarecomparableto thoseobservedinthe Ogleetal.
to fitthe high-excitationlines, aboveS(4). In reality, the H
(2010) sample of H -bright radio-galaxies, in some galaxy 2
2 emissionarisesfromadistributionofdensitiesandshockve-
collisions,likeStephan’sQuintet(Cluveretal.2010)andthe
locities.Withthepresentdatawecannotexcludethepresence
Taffygalaxies(Petersonetal. submitted).
ofveryhighdensitygas(n >105cm- 3).
Tocomputethemassesofthewarm(&100K)H ,wefol- H
2 As discussed in Guillardetal. (2009), the H masses are
lowtwodifferentapproaches. Thefirstoneissimilarto that 2
derivedbymultiplyingthegascoolingtime(downto100K)
described by Ogleetal. (2010) and consists of assuming a
bythegasmassflow(themassofgassweptbytheshockper
thermaldistributionoftheH levels. We constructedexcita-
2 unit time) required to match the H line fluxes. The shock
tiondiagrams,shownonFigure12,byplottingthelogarithm 2
modelparameters, gascoolingtimes, mass flows, and warm
ofthecolumndensitiesoftheupperH levelsdividedbytheir
2 H massesarequotedinTables6and7. ThewarmH masses
statistical weights, ln(N /g ), against their excitation ener- 2 2
vJ J derivedfromtheshockmodelingarelargerthanfromtheLTE
gies, E /k , expressed in K. For a uniform excitation tem-
vJ B model. Thisis mainly becauseof the differentvaluesof the
perature, the values ln(N /g ) should fall on a straight line
plotted versus E /k , wviJth aJslope proportional to T- 1. In H2ortho-to-pararatio,andbecauseatnH=103cm- 3,theS(0)
vJ B exc andS(1)linesarenotfullythermalized.
asituationoflocalthermalequilibrium(LTE),theexcitation
temperatureT equalsthatofthegas.Wefittedthedatawith
exc
twoorthreeexcitationtemperaturecomponents,althoughthe 4.2. Thermaldustcontinuumandaromaticfeatures(PAHs)
gasisatacontinuousrangeoftemperatures. Weconstrained Our sample reveal two types of spectra, those with a flat
thetemperaturerangetobe100<T <1500K.Ateachfitting thermaldustcontinuum(3C236,3C293,3C305),andthose
iteration, the statistical weights of the orthotransitions were with a steep rising continuum at long wavelengths(3C 459,
adjustedtomatchtheLTEvalue. 4C 12.50, IC 5063, OQ 208, and PKS 1549-79). There
TheresultsaregiveninTable5,wherewelistthefittedH2 is a remarkable similarity between the spectra of 3C 236,
excitation temperatures, ortho-to-para ratios, column densi- 3C293and3C305withthe3C326radio-galaxy(Ogleetal.
ties,masses,andtotalluminositiesforeachtemperaturecom- 2007), the Stephan’s Quintet (Cluveretal. 2010) and the
ponents.ThebulkofthewarmH2isconstrainedbythelowest Taffy galaxies (Peterson et al., submitted), where the dust
temperaturecomponent,i.e. bytheS(0)andS(1)lines. Thus, continuum is very weak compared to emission lines. The
iftheS(0)lineisnotdetected,weincludeitsupperlimitinthe narrow-band24µm luminosities (see sect. 3.2 and Table 1),
fitasa2σdetection(with1σ errorbar)andquotethemodel measuredontheLHspectra,spanthreeordersofmagnitude,
results as upperlimits. In all galaxieswhere the S(0) line is from 5.4×109 L⊙ (3C 305) to ULIRG-like luminosities of
detected,we measurewarmH2 masses, from≈3×108 M⊙ 1.1×1012 L⊙ (4C 12.50). For 4C 12.50 and OQ 208, our
in 3C 236, up to ≈3×1010 M⊙ in 4C 12.50. Similar ex- measurements are in agreement with those of Willettetal.
tremelylargewarm H2 masses were detected in 3C 433and (2010)onlow-resolutionIRSdata.
3C 436 (Ogleetal. 2010). The H2 column densities range Emission fromaromatic infraredbandsattributedto Poly-
from<4×1020to≈2×1022cm- 2. Thesecolumndensities cyclic Aromatic Hydrocarbons (PAHs) excited by UV pho-
dependontheassumedsizeoftheemissionregion. tons are detected in all galaxies. In general, in the high-
The second approach to fit the H line fluxes and derive resolutiondata, the11.3µmbandisthemostprominentfea-
2
the H physical parameters is similar to that described in ture. ThefluxesofthePAHcomplexes,giveninTable8,are
2
Guillardetal.(2009)andNesvadbaetal.(2010). Itassumes measuredwithPAHFITontheemissionline-freespectra(see
thattheH emissionispoweredbythedissipationofmechan- sect.3.2),bycombiningthefluxesoftheblendedfeaturesthat
2
icalenergyinthemoleculargas(seesect.6.1foradiscussion contribute to the main complexes (around 8, 11.3, 12.6 and
of the H excitation mechanisms). We model this dissipa- 17µm).
2
tion with magnetic shocks, using the MHD code described All of the radio-galaxies have a 11.3µm PAH to 24µm
6 P.Guillardetal.
Figure2. SpitzerIRShigh-resolution(SH+LH)spectraoftheHI-outflowradio-galaxies. ThelocationsofPAHfeaturesandemissionlinesaremarkedforeach
object.
SpitzerIRSspectroscopyofHI-outflowradiogalaxies 7
Figure3. SpitzerIRSlow-resolution(SL+LL)spectraoftheHI-outflowradio-galaxies. ThelocationsofPAHfeaturesandemissionlinesaremarkedforeach
object.Thelow-resolutionspectrafor3C293,OQ208andPKS1549-79werealreadypresentedby Ogleetal.(2010)and Willettetal.(2010).
8 P.Guillardetal.
Table4
H2linefluxesfromHI-outflowradiogalaxies
Source H2S(0) H2S(1) H2S(2) H2S(3) H2S(4) H2S(5) H2S(6) H2S(7)
28.22µm 17.03µm 12.28µm 9.66µm 8.03µm 6.91µm 6.11µm 5.51µm
3C236 0.20(0.03) 0.95(0.07) 0.32(0.05) 0.64(0.05) <1.04 <1.10 <0.23 <0.31
3C293 0.79(0.06) 3.46(0.29) 1.61(0.10) 2.50(0.16) 1.35(0.13) 2.84(0.14) 0.65(0.15) 1.35(0.19)
3C305 <0.31 3.82(0.42) 0.88(0.09) 1.89(0.12) 1.03(0.39) 2.93(0.69) 1.83(0.47) <1.40
3C459 <0.25 0.55(0.03) <0.36 0.37(0.02) <0.29 <1.04 <0.15 <0.49
4C12.50 2.31(0.13) 3.44(0.39) 0.96(0.09) 1.44(0.09) <0.72 <1.41 <0.93 <2.63
IC5063 4.63(0.24) 10.65(0.44) <1.8 3.86(0.49) <3.12 <5.10 <3.38 <5.20
OQ208 <0.38 1.11(0.09) <0.35 0.49(0.06) <0.75 <4.13 <2.14 <2.76
PKS1549-79 <0.46 1.45(0.12) 0.63(0.08) 0.95(0.09) <1.29 <2.23 <1.32 <3.36
Note. —H2 mid-IRlinefluxes(and1σerrorinparenthesis)inunitsof10- 17Wm- 2 measuredwithSpitzerIRS.Incaseof
non-detection, the2σupperlimitisindicated. TheH2 S(0)toS(3)linesaremeasuredinthehigh-resolution modules(except
forIC5063,wheretheS(3)linewasmeasuredintheSLmodulebecauseitfallsoutoftheSHwavelengthcoverage), andthe
S(4)toS(7)linesinthelow-resolutionmodules. NotethattheS(5)andS(6)linesareseverelyblendedwiththePAH6.2µmand
[ArII]λ6.98µmfeatures.
Table5
H2excitationdiagramfittingforathermaldistribution:results
Source Sizea T(K)b O/Pc N(H2)d M(H2)e L(H2)f
[”] [K] [cm- 2] [M⊙] [L⊙]
100(0) 1.587 3.3E+21 1.6E+09(0.5) 1.5E+07
3C236 3.0 241(27) 2.947 1.9E+20 9.5E+07(4.0) 8.2E+07
1045(80) 3.000 1.5E+18 7.3E+05(1.8) 1.8E+08
100(0) 1.587 6.1E+21 1.7E+09(0.2) 1.2E+07
3C293 4.7 285(14) 2.983 1.9E+20 5.3E+07(1.1) 7.4E+07
1048(47) 3.000 1.9E+18 5.2E+05(0.8) 1.1E+08
226(13) 2.922 <4.2E+20 <1.0E+08 5.3E+07
3C305 4.7
1253(93) 3.000 1.3E+18 3.1E+05(0.5) 1.2E+08
100(0) 1.587 <2.1E+22 <8.3E+09 1.1E+08
3C459 1.4 284(32) 2.983 1.5E+20 6.1E+07(3.0) 1.6E+08
1500(0) 3.000 1.6E+18 6.3E+05(1.1) 7.9E+08
100(0) 1.587 2.2E+22 3.8E+10(0.2) 3.7E+08
4C12.50 4.7 275(16) 2.978 1.6E+20 2.8E+08(0.9) 4.4E+08
1500(0) 3.000 5.5E+17 9.2E+05(1.5) 8.3E+08
100(0) 1.587 3.9E+22 7.3E+08(0.9) 4.7E+06
IC5063 4.7 210(34) 2.883 1.4E+21 2.6E+07(1.9) 8.8E+06
1251(103) 3.000 3.1E+18 5.9E+04(2.5) 1.9E+07
100(0) 1.587 <9.2E+21 <1.2E+09 1.0E+07
OQ208 2.0 186(29) 2.784 2.1E+21 2.8E+08(2.5) 7.1E+07
1500(0) 3.000 2.5E+18 3.4E+05(0.4) 2.6E+08
100(0) 1.587 <2.0E+22 <7.7E+09 8.4E+07
PKS1549-79 1.9 270(21) 2.975 5.1E+20 2.0E+08(0.7) 3.3E+08
1500(0) 3.000 3.6E+18 1.4E+06(0.2) 1.4E+09
aAssumedsize(diameter)oftheH2emittingsourceforthecalculationofthecolumndensities.
bFittedexcitationtemperatureassumingLTE(seetextfordetails).
cH2ortho-to-pararatio(fittedself-consistentlytofulfilltheLTEapproximation).
dH2modelcolumndensities.
e WarmH2 masses(and1σuncertainties) derivedfromthefit. Incaseofnon-detection oftheS(0)line,a2σupperlimitis
quoted.
fTotalH2luminosity,summedoverallrotationaltransitions(includingthosenotobservedwithSpitzer,whichincludesa≈40%
correctionat200K).
luminosity ratio that ranges from L /L =4×10- 2 cussionofthisclaim). AlthoughPAHemissionisexpectedto
PAH11.3 24µm
for 3C 293 to 8×10- 4 for 4C 12.50, which is similar to bediminishedbecauseofPAHdestructionbyhardUVorX-
the ratios observed in the Ogleetal. (2010) sample of 3C rayradiationclosetotheAGNVoit(1992),orbecauseofgas
radio-galaxies. This ratio is significantly lower than the suppressioncloseto thenuclei,itisunlikelythattheirabun-
SINGSstar-forminggalaxies,wherethemedianratiois≈0.1. dances are reduced significantly at galactic scales by AGN
3C459, PKS 1549-79 and 4C 12.50 are ULIRGs, but their effects(Ogleetal.2010).
L /L ratiosareatthelowerendoftheobservedval- Silicate absorptionat 9.7 and 18µm is presentin the low-
PAH11.3 24µm
ues(≈10- 3). Themid-IRcontinuumoftheseradio-galaxies resolution spectra of OQ 208 and 4C 12.50 (Willettetal.
2010), as well as PKS 1549-79. OQ 208 is the only galaxy
is therefore dominated by dust emission from the accretion
showingsilicateemission(Willettetal.2010).
diskorsynchrotronemissionfromthejet,butnotbystarfor-
mation. The weakness of the PAH emission relative to the
continuumemission is related to the weakness of the stellar
UVradiationfield(seeOgleetal.2010,andsect.6.1foradis- 4.3. Ionicfine-structurelines
SpitzerIRSspectroscopyofHI-outflowradiogalaxies 9
Figure4. Mid-infraredlinediagnosticdiagramsforthelogarithmofthemodellinefluxratios[NeV]/[NeII](left)and[OIV]/[NeII](right)against[NeIII]/[NeII].
Theobservedvaluesforthe8HI-outflowradio-galaxiesarecomparedtoshockandphotoionizationgridsofmodels.Theshockmodelgridisfromthe Allenetal.
(2008)MAPPINGSIIIshockcodeforcombinedprecursorandshockmodels. Thegasmetallicityissolarandthepre-shockgasdensityisnH=10cm- 3. The
orangelinesindicateconstantshockvelocities,from200(lightorange)to1000kms- 1(red),andthebluelinesconstantmagneticfieldstrengths,from10- 3(light
blue)to100µG(purple). Thedeeperthecolor,thelargeristheparameter. ThegridofphotoionizationNLRmodelswascomputedwiththeCLOUDYcode
(Ferlandetal.1998)withastandardpower-lawspectralindexα=- 1.5andvaryingionizationparameter(greenlines,U0=1- 10- 2)anddensitynH(pinklines,
nH=103- 106cm- 3).Ontherightplot,sincetheshockandphotoionizationmodelspartiallyoverlap,theconstantdensitylinesaredashedforclarity.
Table6 Table7
H2fluxesfittedwithshockmodels:resultsfornH=103cm- 3 H2fluxesfittedwithshockmodels:resultsfornH=104cm- 3
Source Vsa Massflowb tcool(50K)c M(H2)d Source Vsa Massflowb tcool(50K)c M(H2)d
[kms- 1] [M⊙yr- 1] [yrs] [M⊙] [kms- 1] [M⊙yr- 1] [yrs] [M⊙]
3 8.0E+04 1.5E+05 1.2E+10 4 2.2E+05 2.5E+04 5.6E+09
3C236 3C236
23 2.4E+03 1.8E+04 4.4E+07 29 2.8E+03 1.8E+03 5.0E+06
5 4.2E+04 8.1E+04 3.4E+09 8 4.0E+04 1.1E+04 4.4E+08
3C293 3C293
40 8.3E+02 7.8E+03 6.4E+06 29 1.5E+03 1.8E+03 2.7E+06
11 7.3E+03 4.4E+04 3.2E+08 5 5.5E+04 1.8E+04 1.0E+09
3C305 3C305
40 3.7E+02 7.8E+03 2.9E+06 32 1.3E+03 1.5E+03 1.9E+06
4 2.6E+05 1.1E+05 2.9E+10 8 8.3E+04 1.1E+04 9.2E+08
3C459 3C459
40 1.8E+03 7.8E+03 1.4E+07 36 6.2E+03 1.2E+03 7.5E+06
4 1.1E+06 1.1E+05 1.2E+11 4 1.8E+06 2.5E+04 4.4E+10
4C12.50 4C12.50
23 8.6E+03 1.8E+04 1.5E+08 13 3.2E+04 5.3E+03 1.7E+08
4 1.9E+04 1.1E+05 2.1E+09 4 3.1E+04 2.5E+04 7.8E+08
IC5063 IC5063
40 7.7E+01 7.8E+03 6.0E+05 38 1.5E+02 1.1E+03 1.6E+05
5 5.4E+04 8.1E+04 4.3E+09 3 1.6E+05 3.7E+04 5.7E+09
OQ208 OQ208
40 3.6E+02 7.8E+03 2.8E+06 40 1.6E+03 1.0E+03 1.7E+06
15 2.3E+04 2.9E+04 6.7E+08 8 1.7E+05 1.1E+04 1.8E+09
PKS1549-79 PKS1549-79
40 1.9E+03 7.8E+03 1.5E+07 40 1.1E+04 1.0E+03 1.2E+07
aShockvelocity. aShockvelocity.
bMassofgasthatistraversedbytheshockperunittimerequiredtomatch bMassofgasthatistraversedbytheshockperunittimerequiredtomatch
theobservedH2linefluxes. theobservedH2linefluxes.
cGascoolingtime,fromthepeakpost-shocktemperaturedownto100K. cGascoolingtime,fromthepeakpost-shocktemperaturedownto100K.
dWarmH2masses. dWarmH2masses.
andPKS1549-7917, andn <103 cm- 3 for3C305(see e.g.
e
Figure 3 of Alexanderetal. 1999). These densities are be-
The fluxes of the most commonly detected mid-IR ion- low the critical densities of both lines (see also Dudiketal.
ized gas lines are listed in Table 9. The [NeII]12.8µm 2009). Using the [SIII]18.71 and 33.48µm line ratios, we
and [NeIII]15.55µm are detected at high signal to noise ra- find n ≈2×102 cm- 3 for 3C 305 and n ≈3×103 cm- 3
e e
tio (> 6) in all 8 radio-galaxies. The [OIV]25.89µm and forIC5063. TheNeonandSulfurlineratiosgiveconsistent
[FeII]25.99µm pair is also very common, with at least one estimatesofelectrondensities,althoughstar-formingregions
lineofthedoubletdetectedin7/8galaxies. Thehighioniza- maycontributetothe[SIII]lineemission,whereasthe[NeV]
tion(Eion=97.12eV)[NeV]14.32µmlineisdetectedinhalf lineisprincipallyemittedbyAGN-heatedregions.
ofthesample.Althoughlistedasnon-detectedbyFarrahetal. Somemoreunusuallines,rarelyseeninAGN,andthatare
(2007)andWillettetal.(2010),wesecurelydetectthislinein not listed in Table 9, are detected in the high-quality spec-
4C12.50at3.2σ.
Three objects show detections in both [NeV]14.32 and 17 Holtetal. (2006) derive ne ≈430 cm- 3 for the NLR gas using the
24.32µmlines. Thefluxratiosofthesetwolinesareconsis- [SII](6731/6717Å) line ratio. Holtetal. (2011) derive ne =3×103 cm- 3
tentwithelectrondensitiesofn ≈3×103cm- 3 forIC5063 for4C12.50usingamoresophisticatedtechnique.
e
10 P.Guillardetal.
Table8
FluxesofthemainPAHcomplexesfromHI-outflowradiogalaxies
Source PAH6.2µm PAH7.7µm PAH11.3µm PAH12.6µm PAH17µm
3C236 <2.5 <4.5 3.7(0.1) 3.8(1.2) 3.2(1.3)
3C293 11.1(0.6) 55.7(2.5) 21.5(0.6) 10.4(0.4) 25.6(3.2)
3C305 15.1(3.4) 63.1(8.3) 19.2(0.1) 16.1(0.2) 11.2(2.6)
3C459 7.2(1.3) 22.5(1.3) 9.9(0.2) 9.7(0.2) 5.7(0.3)
4C12.50 9.8(2.3) 38.3(1.6) 10.2(0.2) 18.1(0.4) <9.5
IC5063 <43 189(1.9) 104.9(2.6) 230.6(0.8) 53.3(6.7)
OQ208 40.8(2.9) 51.5(1.4) 55.3(2.8) <61 101(8)
PKS1549-79 25(3.3) 187(5.3) 37.4(0.3) 31.7(0.7) 4.8(0.6)
Note. —PAHfluxes(and1σerrorinparentheses)inunitsof10- 17Wm- 2measuredwith
SpitzerIRS.Incaseofnon-detection,the2σupperlimitisindicated.
Table9
Fine-structurelinefluxesinHI-outflowradio-galaxies
Object [ArII] [ArIII] [SIV] [NeII] [NeIII] [SIII] [OIV] [FeII] [SIII] [SiII]
6.98µm 8.99µm 10.51µm 12.81µm 15.55µm 18.71µm 25.89µm 25.99µm 33.48µm 34.81µm
3C236 <1.6 <1.9 <0.13 0.92(0.06) 0.44(0.03) <0.14 <0.14 <0.13 <0.09 ··· a
3C293 2.6(0.3) 0.70(0.12) <0.18 4.07(0.29) 1.27(0.09) <0.42 0.27(0.02) 0.57(0.05) 1.32(0.12) 5.55(0.48)
3C305 2.8(0.4) <1.5 3.21(0.24) 4.15(0.29) 8.62(0.59) 4.11(0.33) 13.07(1.15) 0.90(0.07) 5.14(0.46) 11.24(0.97)
3C459 1.0(0.1) <0.15 0.11(0.01) 3.11(0.22) 1.00(0.07) 0.39(0.03) 0.46(0.04) 0.58(0.05) ··· a ··· a
4C12.50 <2.7 2.4(0.2) <0.7 5.45(0.39) 2.99(0.21) <0.83 2.88(0.25) <0.21 ··· a ··· a
IC5063 4.4(0.2) 9.5(0.3) 37.60(3.05) 22.83(1.62) 56.85(3.92) 23.88(1.93) 69.32(6.10) 3.97(0.33) 31.89(2.68) 28.3(1.1)b
OQ208 1.2(0.2) <1.8 <1.6 3.33(0.24) 2.60(0.18) <1.12 1.21(0.11) 0.45(0.04) <1.4b ··· a
PKS1549-79 3.2(0.3) 3.3(0.2) 1.45(0.12) 2.20(0.17) 5.45(0.39) <0.6 3.11(0.27) <0.8 ··· a ··· a
Note. —Ioniclinefluxes(and1σerrorinparentheses)inunitsof10- 17Wm- 2 measuredwithSpitzerIRS.Incaseofnon-detections, a2σupperlimitis
quoted.The[ArII]and[ArIII]linesaremeasuredinthelow-resolutionmodules.Alltheotherlinesaremeasuredinthehigh-resolutionmodules,exceptsomeof
the[SIII]and[SiII]linesmarkedwitha(b).
aObservedwavelengthnotvisibleintheIRSrange.
bMeasuredonthelow-resolutionLLmodule.
likely powered by shocks. Is it also the case for the ob-
Table10 served ionized line emission? In Figure 4, we compare the
High-ionizationforbiddenemissionlines
observedvalues of three fine-structure line flux ratios to the
predictionsof shock and photo-ionizationmodels. The grid
Object [NeVI]λ7.65µm [NeV]λ14.32µm [NeV]λ24.32µm of fast (&200 km s- 1) radiative shocks is from Allenetal.
3C236 <1.6 <0.06 <0.06 (2008). The pre-shock gas density is n = 10 cm- 3. Note
3C293 <0.53 <0.21 <0.17 H
thataugmentingthedensitybyafactor10reducestheseline
3C305 0.92(0.32) 1.42(0.12) 1.87(0.15)
3C459 <0.29 <0.16 <0.14 fluxratiosbyafactor2- 3onaverage,thusshiftingthemod-
4C12.50 2.66(0.18) 1.68(0.22) <1.1 els to the bottom left of Figure 4 by 0.3- 0.5 dex. The
IC5063 3.51(0.12) 22.70(1.86) 17.41(1.43)
photo-ionization models are computed with the CLOUDY
OQ208 <1.2 <0.8 <0.2
PKS1549-79 3.29(0.21) 3.35(0.27) 2.21(0.18) code(Ferlandetal.1998),withasetupupdatedfromthenar-
rowlineregion(NLR)modelspresentedinFerland&Netzer
Note.—Linefluxes(and1σerrorinparentheses)inunitsof10- 17Wm- 2
(1983).Weusedadustygasslabmodelatconstantpressure,a
measured with Spitzer IRS. In case of non-detection, a 2σ upper limit is
quoted. The[NeVI]λ7.65µmlineismeasuredintheSLmodule. Theother power-lawionizingcontinuumwith fν ∝ν- 1.5 andnocut-off
linesaremeasuredinthehigh-resolutionmodules. orextinction.Wevariedthehydrogendensityofthegasfrom
103to106cm- 3andtheionizationparameter18fromU =10- 2
0
trum of 3C 305. The low-ionization (Eion =7.9 eV) [FeII] to1.Notethatthesemodelsaresimplistic:theydonotinclude
17.94, 24.52, and 25.99µm lines are present, as well as the geometricalandinhomogeneityeffects,aswellasmetallicity
[FeIII]22.93µm(Eion=16.19eV).The[ArV]13.10µmlineis differences(assumed to be solar here). A detailed model of
alsoweaklydetected(seetheSHspectrumonFigure9). themid-IRemission ofthese sourcesisbeyondthescope of
In such objects, the excitation of the fine-structure thispaper.
lines can arise from photo-ionization by the AGN (e.g. The[NeIII]15.55µm/[NeII]12.8µmlinefluxratiosarein
Veilleux&Osterbrock 1987; Meijerinketal. 2007) or by the range of 0.3- 2.4, much higher than those observed in
shocks (e.g. Dopita&Sutherland 1996). In practice, dis- pure starburst galaxies (0.05-0.2, e.g. Bernard-Salasetal.
tinguishing between the two excitation mechanisms is diffi- 2009). Theseratiosareconsistentwithshockmodelsforv<
cult,sincethelinefluxratioscanbedifferentiallyaffectedby 250kms- 1 andnH<102 cm- 3,thehighervaluesof[NeIII]/
the structure (homogeneousor clumpy) of the emitting gas, [NeII] ≈2 requiring very low gas densities (nH <1 cm- 3).
andsincethemodelpredictionsforfine-structurelinefluxra-
tios are degenerateforboth excitationmechanisms(see also 18 U0 =S⋆/(nec) is a direct measure of the ionization state of the gas,
Grovesetal.2006). whereS⋆isthefluxofionizingphotons,netheelectrondensityattheinner
In Sect. 6.1, we will show that the warm H emission is faceoftheslabofgas,andcthespeedoflight.
2