Gemini GMOS and WHT SAURON integral-field spectrograph observations of the AGN driven ...

18 Pages·2012·1.57 MB·English

Mon.Not.R.Astron.Soc.000,1–18(2012) Printed26July2012 (MNLATEXstylefilev2.2)
Gemini GMOS and WHT SAURON integral-field spectrograph
observations of the AGN driven outflow in NGC1266
Timothy A. Davis,1⋆ Davor Krajnovic´,1 Richard M. McDermid,2 Martin Bureau,3
4 5 6 2 6
Marc Sarzi, Kristina Nyland, Katherine Alatalo, Estelle Bayet, Leo Blitz, Maxime
7 8 2 9 2
Bois, Fre´de´ric Bournaud, Michele Cappellari, Alison Crocker, Roger L. Davies,
P. T. de Zeeuw,1,10 Pierre-Alain Duc,8 Eric Emsellem,1,11 Sadegh Khochfar,12 Harald
2 Kuntschner,13 Pierre-Yves Lablanche,1,11 Raffaella Morganti,14,15 Thorsten Naab,16 Tom
1 Oosterloo,14,15 Nicholas Scott,17 Paolo Serra,14 Anne-Marie Weijmans,18† and Lisa M.
0
2 Young5‡

l
u 1EuropeanSouthernObservatory,Karl-Schwarzschild-Str.2,85748Garching,Germany
J 2GeminiObservatory,NorthernOperationsCentre,670N.A‘ohokuPlace,Hilo,HI96720,USA
3Sub-Dept.ofAstrophysics,Dept.ofPhysics,UniversityofOxford,DenysWilkinsonBuilding,KebleRoad,Oxford,OX13RH,UK
4
4CentreforAstrophysicsResearch,UniversityofHertfordshire,Hatfield,HertsAL19AB,UK
2
5PhysicsDepartment,NewMexicoInstituteofMiningandTechnology,Socorro,NM87801,USA

6DepartmentofAstronomy,CampbellHall,UniversityofCalifornia,Berkeley,CA94720,USA
]
O 7ObservatoiredeParis,LERMAandCNRS,61Av.del‘Observatoire,F-75014Paris,France
8LaboratoireAIMParis-Saclay,CEA/IRFU/SAp–CNRS–Universite´ParisDiderot,91191Gif-sur-YvetteCedex,France
C
9UniversityofMassachussets,Amherst,USA
. 10SterrewachtLeiden,LeidenUniversity,Postbus9513,2300RALeiden,theNetherlands
h
11Universite´ Lyon1,ObservatoiredeLyon,CentredeRechercheAstrophysiquedeLyonandEcoleNormaleSupe´rieuredeLyon,9avenueCharlesAndre´,
p
F-69230Saint-GenisLaval,France
-
o 12Max-PlanckInstitutfu¨rextraterrestrischePhysik,POBox1312,D-85478Garching,Germany
r 13SpaceTelescopeEuropeanCoordinatingFacility,EuropeanSouthernObservatory,Karl-Schwarzschild-Str.2,85748Garching,Germany
st 14NetherlandsInstituteforRadioAstronomy(ASTRON),Postbus2,7990AADwingeloo,TheNetherlands
a 15KapteynAstronomicalInstitute,UniversityofGroningen,Postbus800,9700AVGroningen,TheNetherlands
[ 16Max-Planck-Institutfu¨rAstrophysik,Karl-Schwarzschild-Str.1,85741Garching,Germany
17CentreforAstrophysics&Supercomputing,SwinburneUniversityofTechnology,POBox218,Hawthorn,VIC3122,Australia
1 18DunlapInstituteforAstronomy&Astrophysics,UniversityofToronto,50St.GeorgeStreet,Toronto,ONM5S3H4,Canada
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Accepted2012July23.Received2012July5;inoriginalform2012June13
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(cid:13)c 2012RAS
2 TimothyA. Daviset al.
ABSTRACT
WeusetheSAURONandGMOSintegralfieldspectrographstoobservetheactivegalactic
nucleus(AGN)poweredoutflowinNGC1266.Thisunusualgalaxyisrelativelynearby(D=30
Mpc),allowingustoinvestigatetheprocessofAGNfeedbackinaction.Wepresentmapsof
thekinematicsandlinestrengthsoftheionisedgasemissionlinesHα,Hβ,[OIII],[OI],[NII]
and[SII],andreportonthedetectionofSodiumDabsorption.Weusethesetracerstoexplore
the structure of the source,derive the ionised and atomic gas kinematics and investigatethe
gasexcitationandphysicalconditions.NGC1266containstwoionisedgascomponentsalong
mostlinesofsight,tracingtheongoingoutflowandacomponentclosertothegalaxysystemic,
the origin of which is unclear. This gas appears to be disturbed by a nascent AGN jet. We
confirm that the outflow in NGC1266 is truly multiphase, containing radio plasma, atomic,
molecularandionisedgasandX-rayemittingplasma.Theoutflowhasvelocitiesupto±900
kms−1awayfromthesystemicvelocity,andisverylikelytoberemovingsignificantamounts
of cold gas from the galaxy. The LINER-like line-emission in NGC1266 is extended, and
likely arises fromfast shockscaused by the interactionof the radio jet with the ISM. These
shockshavevelocitiesofupto800kms−1,whichmatchwellwiththeobservedvelocityof
the outflow. Sodium D equivalent width profiles are used to set constraints on the size and
orientationoftheoutflow.Theionisedgasmorphologycorrelateswith thenascentradiojets
observedin1.4Ghzand5Ghzcontinuumemission,supportingthesuggestionthatanAGN
jetisprovidingtheenergyrequiredtodrivetheoutflow.
Keywords: galaxies:individual:NGC1266–ISM:jetsandoutflows–galaxies:jets–galax-
ies:ellipticalandlenticular,cD–galaxies:evolution–galaxies:ISM
1 Introduction OurrecentCombinedArrayforResearchinMillimetre-wave
Astronomy (CARMA) and Sub-Millimetre Array (SMA) obser-
In recent years the idea feedback from an active galac-
vations of the nearby lenticular galaxy NGC1266 suggest that
tic nucleus (AGN; e.g. Springel,DiMatteo&Hernquist 2005;
it harbors a massive AGN-driven molecular outflow, providing
Crotonetal.2006) couldberesponsible for thequenching of star
an excellent local laboratory for studying AGN-driven quenching
formation has grown in popularity. Such quenching seems to be
(Alataloetal.2011,hearafterA2011). NGC1266isanearby(D=
required to create the red-sequence galaxies we observe today
29.9Mpc;derivedfromrecessionvelocityinCappellarietal.2011;
(e.g. Baldryetal. 2004). There is circumstantial evidence to sup-
hereafterATLAS3DPaperI),early-typegalaxy(ETG)inthesouth-
portAGN-drivenquenching,suchasthestudybySchawinskietal.
ern sky (δ = −2◦), which was studied as part of the ATLAS3D
(2007)suggestingthatAGNarepredominantlyfoundingreenval-
project.Athreecolourimageofthisgalaxy(fromKennicuttetal.
ley galaxies, but direct evidence for removal/heating of cold star-
2003) is presented in Figure 1. While typical CO spectra from
forminggasisrare.
early-type galaxies reveal the double-horned profile characteris-
The physical mechanism by which an AGN could drive
tic of gas in a relaxed disk with a flat rotation curve, the spec-
molecular gas out of a galaxy is still debated. Radiation pres-
trum of NGC1266 shows a narrow central peak (FWHM ≈120
sure is thought to be important in star formation-driven outflows
km s−1) with non-Gaussian wings out to at least ±400 km s−1
(e.g. Murray,Quataert&Thompson 2005), and is potentially im-
withrespecttothesystemicvelocity(Youngetal.2011).Imaging
plicatedinAGN-powered‘quasarmode’outflows(e.g.Aravetal.
of thehigh-velocity components usingtheSMA revealed thatthe
1999; Kurosawa&Proga 2009). Kinetic feedback from an AGN
wingsresolveintoredshiftedandblueshiftedlobes(A2011),coin-
jet can provide sufficient power todirectlypush through the ISM
cident withHαemission(Kennicuttetal.2003),1.4GHzcontin-
of a galaxy and entrain or destroy it (e.g. Rosarioetal. 2010;
uum (Baan&Klo¨ckner 2006), and thermal bremsstrahlung emis-
McNamara&Nulsen 2012), but it is unclear if the geometry of
sion (detected with Chandra; A2011; Fig. 3). Molecular gas ob-
a bipolar jet, which often emerges perpendicular to the nuclear
disk, will allow the jet to remove the ISM from an entire galac- servations suggest that 3×108 M⊙ of molecular gas is contained
within the central 100 pc of NGC1266, and that at least 5×107
ticdisk. Broad-linewinds candeposit significant momentum into
gas surrounding an AGN, which could also lead to large out- M⊙ofthisgasisinvolvedinamolecularoutflow(A2011).Thisis
thusthefirstobservedlarge-scaleexpulsionofmoleculargasfrom
flows (e.g. Ostrikeretal. 2010). Alternatively, heating by X-rays
a non-starbursting ETG in the local universe, and this presents a
and cosmicrayscould destroy/alter themolecular clouds close to
uniqueopportunitytostudythispowerfulprocessinaction.
an AGN, removing the need to expel them from the galaxy (e.g.
Begelman,deKool&Sikora1991;Ferlandetal.2009).Thesepro-
In this paper we present SAURON (Spectrographic Areal
cessesshouldbedistinguishableifwecanidentifyandstudylocal
Unit for Research on Optical Nebulae) and Gemini Multi-Object
galaxieswhereAGNfeedbackisongoing.
Spectrograph(GMOS)integral-fieldunit(IFU)observationsofthe
ionised gas in NGC1266. By investigating the ionised gas kine-
maticsandlineratioswehopetoconstraintheoutflowparameters
⋆ E-mail:[email protected]
† DunlapFellow andionisationmechanisms andthusshed lightonthemechanism
‡ AdjunctAstronomerwithNRAO drivinggasfromthegalaxy.InSection2wepresentthedata,and
(cid:13)c 2012RAS,MNRAS000,1–18
IFU observationsoftheAGNdrivenoutflowin NGC1266 3
izedpixelfittingroutine(Cappellari&Emsellem2004),providing
parametric estimates of the line-of-sight velocity distribution for
eachbin.Duringtheextractionofthestellarkinematics,theGAN-
DALFcode(Sarzietal.2006)wasusedtosimultaneouslyextract
theionisedgaslinefluxesandkinematics.ThestandardGANDALF
reductioncompletedinthepipeline(usingasinglegaussianforthe
lines)isinsufficientinthissource,duetothecomplexstructureof
theionisedgasoutflow(seeFigure2).Wehavereanalyzedthedat-
acubeusingamulti-gaussiantechnique(asdescribedbelow)after
thesubtractionofthestellarcontinuum.
2.1.1 Emissionlinefitting
TheSAURONspectraincludetheHβ,[OIII]and[NI]ionisedgas
spectrallines.AscanbeseeninFigure2someofthebinnedspax-
elsshow clear signs of havingtwoionised gascomponents along
thelineofsightwithdifferentvelocities.Inordertofitthesepro-
fileswecreatedanIDLprocedurebasedontheNon-LinearLeast
SquaresFittingcodempfit(Markwardt2009).Inthisprocedurewe
perform two fits, and compare the chi-square to determine if two
componentsareneededateachposition.
In the first fit, we assume a single ionised gas component is
present,andfittheHβ,[OIII]and[NI]lineswithsinglegaussians.
Figure1.SINGs(Kennicuttetal.2003)B,V andRbandcompositethree
Thesegaussiansareconstrained tohavethesamekinematics(ve-
colourimageofS0galaxyNGC1266.Thewhitebarshowsalinearscale
of1Kpc(6′.′94atanadopteddistance of29.9Mpc;ATLAS3D PaperI). locityandvelocitydispersion).Additionally,weconfinetheveloc-
OverlaidarethetotalfieldofviewofourSAURONIFU(red)andGMOS ity of the lines to be within 1000 km s−1 of the galaxy systemic
IFU(blue)observations. (2170kms−1;ATLAS3DPaperI),andtohaveavelocitydispersion
greaterthantheinstrumentalresolution,andlessthanaconvolved
velocitydispersionof≈200kms−1.Initialguessesattheionised
describeourreductionprocesses.Wethenpresentthederivedmaps
gaskinematicsweremadebyassumingtheionisedgasco-rotates
of thegaskinematicsandlinefluxes.InSection3wediscussthe withthestars,withavelocitydispersionof120kms−1.Wecon-
kinematicstructureof thesystem, gasexcitationmechanisms and
strainthefittingbyforcingeachgaussiantohaveapeakatleast3
thedrivingforcebehindtheoutflow.Finallyweconcludeanddis-
timeslargerthanthenoiseinthecontinuum,ortobezero.Anyflux
cussprospectsforthefutureinSection4.
whichhada1σerrorbarthatincludedzerowassettozero.Initial
guesses ofthelinefluxeswereestimatedbytakingthemaximum
2 DataReductionandResults
fluxwithintheallowedvelocityrangeofeachline.Thetwo[OIII]
2.1 SAURONdata
linesinourspectralrangehaveafixedlineratiodeterminedbythe
SAURONisanintegral-fieldspectrograph builtat LyonObserva- energy structure of theatom, and wefixed thelineratioassumed
toryandmountedattheCassegrainfocusoftheWilliamHerschel inourfittoagreewiththeobservedlineratio(F5007=2.99×F4959:
Telescope(WHT).ItisbasedontheTIGERconcept(Baconetal. Storey&Zeippen2000;Dimitrijevic´etal.2007).
1995), using a microlens array to sample the field of view. De- Inthesecondfitweassumetwo,independentionisedgascom-
tails of the instrument can be found in Baconetal. (2001). The ponentsarepresentineachbin,andfiteachcomponentwithitsown
SAURON data of NGC1266 was taken at the William Herschel setofindependentlinkedgaussians.Asbefore,itisassumedthatthe
Telescope(WHT),onthenight of 10-11 January 2008, aspartof linesineachcomponenttracethesamekinematics(velocityandve-
theATLAS3Dobservingcampaign(ATLAS3DPaperI).Thegalaxy locitydispersion).Onceagainweconfinethevelocityofeachofthe
wasobservedwiththelow-resolutionmodeofSAURON,covering componentstobewithin1000kms−1ofthegalaxysystemic,and
afieldofviewofabout33′′×41′′with0′′94×0′′94lenslets.The tohaveavelocitydispersiongreater thantheinstrumental resolu-
. .
fieldofview(FOV)ofourobservationsisshowninredonFigure tion.Weusedifferentupper bounds for thefirstand secondcom-
1.SAURONcoversthewavelengthrangefrom4810-5350A˚ witha ponentsofthegasdistribution.Componentoneisforcedtohavea
spectralresolutionof105kms−1. velocitydispersionlessthan200kms−1,asbefore.Ingeneralthe
ThebasicreductionoftheSAURONobservationwasaccom- second component is needed where the outflow is present, and is
plishedusingthestandardATLAS3D pipeline.Detailsofthispro- thusallowedtohaveahighervelocitydispersion.Weallowedthe
cess, including extraction of the stellar kinematics are presented linesinthesecondcomponenttohaveamaximumvelocitydisper-
in ATLAS3D Paper II (Krajnovic´etal. 2011). In brief, the two sionof360kms−1.Inpracticehowevergoodfitswerefoundwith
observed datacubes were merged and processed as described in velocity dispersions <300km s−1. The same limitswere used on
Emsellemetal. (2004), using the Voronoi binning scheme devel- thelinefluxesasdescribedabove.
oped by Cappellari&Copin (2003). This binning scheme max- Oncethetwofitsdescribedabovewerecompleteforeachbin,
imisesthe scientific potential of the data by ensuring a minimum we tested (using an F-test, as implemented in the mpfit package
signal-to-noiseratioof40perspatialandspectralpixel.Thisdoes Markwardt 2009) if adding the additional free parameters to our
however result in an non-uniform spatial resolution, here varying modeloftheemissionlinesproducedasignificantlybetterfit,over
from 0′.′8 × 0′.′8 for unbinned spaxels in the central regions, to and above the improvement expected when one adds free param-
10′′×7′′inthelargestouterbin. eters. The F-test can be used as an indicator of where fittingtwo
TheSAURONstellarkinematicswerederivedusingapenal- componentsproducesbettermodels,butthebestthresholdtotake
(cid:13)c 2012RAS,MNRAS000,1–18
4 TimothyA. Daviset al.
should be determined by visually inspecting the fits obtained (as
thevaluestestedforareattheextremeedgeofthepossibledistri-
bution).Inthisworkwevisuallychoseathresholdthatcorresponds
to an improvement in the chi-square of 60% when adding in the
additionalparameters.Whenaspaxeldidnotsatisfythiscriterion
thenthevaluesfromthesinglegaussianfitwereused,andthesec-
ondcomponentsettozero.Wheretwocomponentswerefoundto
benecessarywedenotedthecomponent closesttothegalaxysys-
temicascomponent one, and thefaster component as component
two.
Inanattempttoensurethatthefitswererobust,andspatially
continuous, we implemented an iterative fitting regime where the
fittingprocesses described above were performed for each spaxel
inturn.Thentheresultingtwodimensionalfluxandvelocitymaps
were smoothed using a gaussian kernel, and then these smoothed
values used as the initial guesses for the next iteration of the fit-
tingprocedure.Usingthisprocedurewefoundthattheparameters
usuallyconvergedwithinthreeiterations,withverylittlevariance
between fitting attempts. Figure 2 shows SAURON spectra from
a single bin, overlaid with the two component fit. The top panel
showsthespaxelwiththelargestlineflux,themiddlepanelshows
thespaxelwiththebiggestdifferenceinthefittedvelocitiesandthe
bottompanelshowsthelowestfluxregionwhereatwocomponent
fitcanbeconstrained.Clearlyinthelowfluxregionsofthecubethe
fittedvelocitiesaredrivenbythe[OIII]5007line,andtheparameters
havecorrespondinglyhigheruncertainties.
InFigure3weshowtheobservedkinematicsforcomponent
one(panelsa&b)andcomponenttwo(panelsc&d).Theveloc-
itydispersionmapshavehadtheinstrumentaldispersionquadrati-
callysubtracted.Wealsoshowthestellarvelocityfieldderivedfrom
theseSAURONobservations(panele)forreference,aspresentedin
PaperII.InFigure4weshowthefittedlinefluxes.
2.2 GeminiGMOSdata
InadditiontotheSAURONdata,weobtainedGeminiGMOS-IFU
observations of the central parts of NGC1266, providing higher
spatial resolution and a longer wavelength coverage. The GMOS
IFU uses a lenslet array of 1500 elements to feed individual po-
sitions on the sky to optical fibres (Allington-Smithetal. 2002;
Hooketal.2004).ThetotalfieldofviewoftheIFUis5′′×7′′,with
a spatial sampling of 0′.′2. The Gemini GMOS-IFU observations
ofNGC1266weretakenoverthenightsof24th,26thand27thof
January2009attheGeminiNorthtelescope(programGN-2008B-
DD-1).Weusedafourpointditherpatterntoextendourcoverage
to a total field of view of ≈9′.′1×12′.′5, around the optical centre
of the galaxy. The resultant field of view (FOV) of our observa-
tionsisshowninblueonFigure1.ThelowresolutionR150grat-
Figure2.StellaremissionsubtractedSAURONspectrumfromsinglebins ingwasused,resultinginaspectralresolutionof≈185kms−1(at
(blacksolidline)withlineidentifications.Thetoppanelshowsthespaxel 6500A˚)over thewavelengthrange5000-7300 A˚.Twodifferent
withthelargestlineflux(x=0′′,y=-4′′),themiddlepanelshowsthespaxel blazewavelengths(688and700nm)wereusedondifferentexpo-
withthebiggestdifferenceinthefittedvelocities(x=0′.′8y=-5′.′17)andthe surestoallowcontinuousspectralcoveragebyaveragingoverchip
bottompanelshowsthelowestfluxregionwhereatwocomponentfitcanbe gaps/bridges.
constrained(x=-4′.′0y=-5′.′17).Overlaidisthetwocomponentfitproduced
InordertoreducetheGMOSIFUdataweutilizedadatare-
byoutfittingroutine,asdescribedinSection2.1.1.Componentone(nearest
ductionpipeline,asusedinvandeVenetal.(2010).Thispipeline
thegalaxysystemic)isshowninorange,whilecomponenttwoisshownin
calibratesandflatfieldsthedata,before itistrimmedandresam-
blue.Thereddashedlineshowsthesumofcomponentoneandtwo,which
pledintoahomogeneousdatacube.Thiscubewasbinnedusingthe
closelymatchestheobserveddata.
VoronoibinningtechniqueofCappellari&Copin(2003),ensuring
asignal-to-noise ratioof 40per spatial and spectral pixel.Due to
thelow spectral resolutionand thedepthof theexposures wede-
tect lineemission to high significance over almost the entire IFU
cube, butwereunabletodetect stellarabsorption featurestohigh
significance.Asweareinterestedintheionisedgaskinematicsin
(cid:13)c 2012RAS,MNRAS000,1–18
IFU observationsoftheAGNdrivenoutflowin NGC1266 5
(a) (b)
(c) (d)
(e)
Figure3.IonisedgaskinematicsderivedfromtheSAURONIFUdatareductionprocessdiscussedinSection2.1.1.Inthetoprow(panelsaandb)wedisplay
thekinematicsofcomponentone(confinedtobeclosesttothegalaxysystemicvelocity).Binswhereonlyoneionisedgascomponentisrequiredarealsoshown
incomponentone.Thekinematicsofthefastercomponentisshowninthemiddlerow(panelscandd).Theionisedgasvelocityisdisplayedintheleftpanels
(a,c),andthevelocitydispersionintherightpanels(b,d).ThestellarvelocityfieldofthisgalaxyderivedfromthesesameobservationinATLAS3DPaperIIis
shownasacomparisoninpanele,withstellarcontinuumfluxcontoursoverlaid.TheseplotsarecentredaroundthegalaxypositiongiveninATLAS3DPaper
I.
this work we simply wish to remove the (relatively smooth) stel- kinematics when measuring the fluxes of weaker lines. Example
larcontinuum.Wedothisbyfittingthestellarcontinuumwiththe specta extracted from the cube are shown in Figure 5. We show
penalizedpixelfittingroutineofCappellari&Emsellem(2004),as here the region around the Hα, [NII] and [SII] lines only. These
usedforourSAURONdata.Wewereabletoconstrainthenumber specta wereselected tolieat thespatial positionwiththe highest
ofstellartemplatesrequiredusingourbestfittotheSAURONdata. lineflux(toppanel),thespaxelwiththelargestdifferencebetween
Oncethestellarcontinuumwassuccessfullyremovedwewereleft the two fitted velocities (middle panel) and at the lowest flux bin
withacubecontainingtheionisedgasemissiononly. in which we can constrain two components (bottom panel). With
thelowspectralresolutionofthisdatathelinesareblended,how-
The spectral range of our cube includes various ionised gas
everweclearlyrequiretwocomponentstofitthelineemission.We
emissionlines.The[OIII]and[NI]areincludedinourGMOSspec-
alsodetectSodiumD(NaD)absorptionagainstthestellarcontin-
trumintheregionwhichoverlapswiththeSAURONspectralrange.
uum(anexamplespectrumisshowninFigure6).Wedescribethe
Theselineshoweverappearveryweakbecausetheyareattheedge
fittingprocedureusedforthegasemissionlinesindetailinSection
of our band pass, where the throughput is low. The main strong
2.2.1,andtheprocedureusedtomeasuretheparametersoftheNaD
lineswedetectareHα,[NII]6548,6583 and[OI]6300,whileHeIand absorptioninSection2.2.2.
[NII]5754 aredetectedmoreweakly.Wechoosetofitthekinemat-
icsofthegasemissiononthestronglinesonly,andimposethese
(cid:13)c 2012RAS,MNRAS000,1–18
6 TimothyA. Daviset al.
(a) (b)
(c) (d)
(e) (f)
Figure4.IonisedgaslinefluxesderivedfromtheSAURONIFUdatareductionprocessdiscussedinSection2.1.1.Intheleftcolumnwedisplaythefluxof
componentone(confinedtobeclosesttothegalaxysystemic).Binswhereonlyoneionisedgascomponentisrequiredarealsoshownincomponentone.The
fluxofthefasterout-flowingcomponentisshownintherighthandcolumn.ThetoprowshowstheHβlinefluxes(panelsa&b),thesecondrowthe[OIII]
linefluxes(panelsc&d),andthethirdrowthe[NI]fluxes(panelse&f).Fluxesareinunitsof10−16ergs−1cm−2arcsec−2ineachSAURONbin.
2.2.1 Emissionlinefitting againnotethatgoodfitswerefoundinmostbinswithvelocitydis-
persions<300kms−1.
AsfortheSAURONdata,toensurethatthefitswererobust,
GMOSemissionlinefittingwascarriedoutasdescribedinSection andspatiallycontinuousweimplementedaniterativefittingregime
2.1.1, with some modifications, described below. We fit here the wherethefittingprocessesdescribedabovewereperformedmulti-
Hα, [NII], [SII] and [OI] lines with single and double gaussians. pletimes,usingasmoothedversionoftheoutputfromtheprevious
Initialguesses forthevelocityandvelocitydispersion weremade runastheinitialconditions.Herewefoundthattheparametersusu-
using the derived kinematics from the SAURON cube. The two allyconvergedwithinfouriterations,againwithverylittlevariance
[NII]linesintheHαregionofthespectrumhaveafixedlineratio betweenfittingattempts.Figure5showstheGMOSspectrafroma
determinedbytheenergystructureoftheatom,andweforcedthe singlebin(fromthesamespatialregionasselectedbefore),overlaid
line ratios to the theoretical line ratio (F6584=2.95×F6548: Acker withthetwocomponentfit,asfoundbythisprocedure.
1989). The [SII] doublet is an electron density tracer, with the InFigure7weshowtheobservedkinematicsforcomponent
lineratioF6731/F6717 varyingfrom0.459inthehighdensitylimit one(panelsa&b)andcomponenttwo(panelsc&d).Thevelocity
to 1.43 at the low density limit (e.g. DeRobertis,Dufour&Hunt dispersionmapshavehadtheinstrumentaldispersionquadratically
1987). Here we constrain the [SII] lines ratio to lie somewhere subtracted.InFigure8weshowthefittedlineequivalentwidthsfor
within this region. We here allowed the lines in the second com- thestronglines,withfittedcomponentoneinthetoprowandcom-
ponenttohaveamaximumvelocitydispersionof500kms−1,but ponenttwointhebottomrow.Wecalculatetheequivalentwidthin
(cid:13)c 2012RAS,MNRAS000,1–18
IFU observationsoftheAGNdrivenoutflowin NGC1266 7
Figure6.GMOSspectrumoftheNaDregionfromasinglebin(x=-1′.′0,
y=-1′.′8;blacksolidline).Overlaidisthetwocomponentfitproducedbyour
fittingroutinefortheemissionlines,asdescribedinSection2.2.Component
one(nearestthegalaxysystemic)isshowninorange,whiletheout-flowing
componenttwoisshowninblue.Theredlineshowsthesumofcomponent
oneandtwo(and ourfittotheNaIskyline), whichclosely matches the
observeddata.ShowningreenisourfittotheNaDabsorptiontrough.
thestandardwaybyfindingthewidthofarectangle,withaheight
whichisthesameastheaveragestellarcontinuumfluxintheregion
ofthelines,whichhasthesameareaastheobservedlines.Asthe
GMOSdataweretakeninnon-photometricconditions,wewilluse
onlyratiosofthelinefluxesfromthispointon.
2.2.2 Absorptionlinefitting
The sodium absorption lines at 5890 A˚ and 5896 A˚ are detected
in our GMOS IFU data (Figure 6). This feature is unlikely to be
duetoanimperfectstellartemplateleavingnegativeresidualsafter
subtractionfromtheGMOSspectrum,asthefittedvelocitiesofthe
absorptionfeaturedonotmatchthestellarvelocitiesassumedwhen
fittingthetemplate.
In order to extract the absorption depths, and determine the
neutralgaskinematicswejointlyfittheabsorptiondoublet,andthe
neighbouring HeI emission line(and NaIskyline). Wefixtheve-
locityandvelocitydispersionoftheHeIlineusingthebestsolution
for each bin derived fromthestronger lines(asdescribed inSec-
tion2.2.1).Wethenfitthislinewithtwogaussiancomponents,as
Figure5.StellarsubtractedGMOSspectrum(blacksolidlines)fromsingle before,todeterminethelinefluxes.
bins with line identifications. Shown in the top panel is the bin with the SimultaneouslywefittedtheNaDabsorptiondoublet(whichis
spaxelwiththepeaklineflux(x=0′.′91,y=-2′.′08),themiddlepanelisthe blendedinourdata),assumingagaussianprofileforbothlines.For-
spaxelwiththelargestdifferencebetweenthetwofittedvelocities(x=-0′.′2, mallyanabsorptionlineshouldbefittedwithaVoigtprofile,asthe
y=-4′.′29),andthebottompanelshowsthebinwiththelowesttotalfluxin absorptionhasanintrinsicLorentzianshape,whichhasbeencon-
whichweareabletofittwocomponents(x=-1′.′85,y=-5′.′73).Overlaidisthe
volvedwiththeinstrumentalgaussianresponse.Inthelowspectral
twocomponentfitproducedbyoutfittingroutine,asdescribedinSection
resolutiondatawepresentherehoweverwefitgaussianprofiles,as
2.2.Componentone(nearestthegalaxysystemic)isshowninorange,while
theinstrumentresponsefunctionismuchbroaderthantheintrinsic
thefastercomponenttwoisshowninblue.Thereddashedlineshowsthe
absorption.IfonefitsaVoigtprofiletoourdata,thebestfitprofiles
sumofcomponentoneandtwo,whichcloselymatchestheobserveddata.
alwaystendtowardsapuregaussian,withaLorentzianwidth(Γ)
ofzero,validatingsuchanapproach.WedonotfixtheNaDveloc-
ityandvelocitydispersion,astheabsorptionarisesfromadifferent
gasphase,whichmayhavedifferentkinematics(seeSection3.2).
ThevelocitiesoftheNaDhostinggasareconstrainedinourfitto
lie within 1000 km s−1of the systemic velocity, and the velocity
(cid:13)c 2012RAS,MNRAS000,1–18
8 TimothyA. Daviset al.
dispersionof thiscomponent isconstrainedtobegreaterthanthe deedobservingunrelatedcloudsalongthelineofsight,whichare
instrumental, but less than 500km s−1. At the spectral resolution not dynamically linked. A2011 estimate the age of the molecular
of our data weonly require asingle neutral gas component inall outflow in thisobject as ≈2.6Myr, so a recent cause of this fea-
spaxelsinordertofittheabsorptionprofileswell. tureisnotcompletelyruledout.Alternativelyiftheseareunrelated
InFigure9weshowtheobservedabsorptionequivalentwidth, cloudslongthelineofsight,thebluefeaturessouthofthenucleus
and the kinematics for the NaD absorbing gas. We calculate the may be directly related to the outflow. Close correlation between
equivalentwidthinthestandardway,asabove. someofthesefeaturesandtheradiojetsupportthisconclusion(see
Section3.5).Higherspatialresolutionobservationswouldallowus
3 Discussion todisentanglethesetwopossibilities.
Panel c of Figure 3 shows the global SAURON view of the
3.1 Ionisedgasemissionlinekinematics
gaskinematicswhereasecondcomponent wasrequired.Thisgas
Figures3and7showtheionisedgaskinematicsderivedfromour appears to be in a two lobed structure, orientated approximately
multi-gaussian fitting procedure. The SAURON data has a much North-South (misaligned from the kinematic axis of the stars by
widerfieldofview,providinginsightintothelargescalekinematics ≈70◦ (Krajnovic´etal.2011)).Thegasinthiscomponent hasve-
ofthisobject.TheGMOSIFUdatazoomsintothecentralportions locitiesup to≈800 kms−1 awayfromthesystemicvelocity. We
ofthisobjecttorevealtheinnerregions. denote this component as the outflow from this point. Panel c of
PanelaofFigure3showstheSAURONionisedgaskinemat- Figure7showsthiscomponent inmoredetail.Withthefinerspa-
icsforthecomponentnearestthegalaxysystemicvelocity(which tialsamplingoftheGMOS-IFUmapweareabletodetectgaswith
wewillhereaftercallthesystemiccomponent).Thiscomponentin- velocities up to ≈900km s−1away from the systemic. As argued
cludesgasouttoaradiusof≈10′′(1.5Kpc).A2011discussedthe inA2011theescapevelocityinthecentreofthisobjectisatmost
moleculargasdistribution,andfindevidenceforarotatingmolecu- ≈340km s−1 supporting the idea that the outflow in this system
lardisk,aswellasamolecularoutflow.Theoriginofthissystemic allowsmaterialtoescapethegalaxy.Themoleculargasintheout-
component, and itsrelation tothe molecular disk is unclear. This flowofthisobjectreachesvelocitiesofupto≈480kms−1,with
component could beduetounrelated gascomponents atdifferent aslightlysmallerspatialextent(seeFigure10).Thiscouldsuggest
locationsalongthelineofsight,oritmaybeacoherent structure moleculargasisdestroyedasitflowsoutofthegalaxy,orthatour
whichhasbeendisturbed. observationswerenotsensitivetodetectemissionfromthemolec-
Somedegreeofsymmetryappearstoexistinthegasdistribu- ulargasatthehighestvelocities.
tionaroundalineinclined≈20◦fromEast.Thismaysuggestsome Themolecular gasinNGC1266 dominatesthetotalmassof
bulkrotation,withakinematicpositionangleof≈30◦.Ifthiscom- theISM(withamassof≈2×109M⊙),andiscontainedwithinthe
ponentisrotating,thencomparisonwiththestellarrotation(shown innermost≈100pcofthegalaxy(A2011).Itisveryhardtoexplain
inthebottomrowofFigure3)showsthatitismisalignedfromthe how this gas lost its angular momentum if it was already present
stellarrotationby≈90◦,suggestingitcouldbeinthepolarplane. withinthegalaxy.Deepopticalimagingshowssomeminorsigna-
Intheinner≈6′′howeverthevelocityfieldchangessign,andisdis- turesthatcouldbeduetorecentdisturbances,butnosignaturesof
turbed. astellarbar(Ducetal.,inprep).Aminormergercouldexplainthe
Figure 7 shows the GMOS zoomed in view of the centre of compactnessofthegas,ifthemergerhappenedwiththecorrectini-
NGC1266. The same disturbed features present in the SAURON tialparameterstoleavethegaswithlittleornoangularmomentum.
data are observed in the GMOS velocity field (Panel a of Figure Thedynamicalmass(M1/2)ofNGC1266withinasphereofradius
7). Thesefeatures persist whatever our choice of initialvelocities r1/2(containinghalfofthegalaxylight)is1×1010M⊙(Cappellari
for thefittingprocedure, andarelocatedat thesamespatialloca- etal.,inprep).Aminormergerwithasmallergalaxycouldprovide
tionasthemostblue-andred-shiftedgasincomponenttwo.When thegaswesee,andwithastellarmassratioof≈5:1(assumingthe
fittingmultiplecomponentstoobservedvelocityprofilesitsalways smaller galaxy was gas rich, with a gas fraction of one) may not
possible that such reversed signvelocity structures arearesult of leavevisibletracesintheluminosityweightedgalaxykinematics.
amis-fittingorover-fittingof thelinecomponents. Herehowever InDavisetal.(2011)weanalyzedthekinematicmisalignment
wefindthesamestructurefromboththeSAURONandGMOSdata of the ionised gas in ATLAS3D galaxies (extending the work of
independently.OuriterativefittingproceduredescribedinSections Sarzietal.2006)inordertogaincluesabouttheoriginofthegas.
2.1.1and2.2.1isdesignedtoavoiddiscontinuousfits,andthustries Inthatworkwesuggested thatgaswithkinematicmisalignments
toremovesuchdisturbedstructures,butisunabletofindbetterfits >30◦almostcertainlyhaveexternallyaccretedgas.Ifthesystemic
in these spaxels. The middle panel of Figures 2 and 5 show the component is rotating (and its misalignment from the stellar ro-
emissionlinespectruminthebinwiththelargestblue-shiftedve- tation axis is not caused by orbit branching or similar; Pfenniger
locityineachdataset(wherethedisturbedsystemiccomponent is 1985;Contopoulos&Magnenat1985)thenthiswouldonceagain
alsodetected).Clearlytheouteredgesofeachblendedlineorline- argueforarecentminormerger/accretion.
complex(whichdriveourdeterminationoftherelativevelocitiesof
thetwocomponents)arewellfit,increasingourconfidencethatthis 3.2 NaDabsorption
structureisreal.
If the systemic component is a misaligned rotating structure Thesodiumabsorption doublet at5890 A˚ and 5896A˚ provides a
then we speculate that the disturbed structure visible in the inner goodprobeofthecoldISMintheoutflow.Theionisationpotential
partscouldbewherethemolecularoutflowdetectedinA2011has of NaI is lower than that of hydrogen, at only 5.1 eV. The pho-
punchedthrough,andmaterialisflowinginwardtofillthevacuum. tonsthationizeNaIarethusinthenear-UV(λ ≈2420A˚).These
Giventhedynamicaltimescaleofgasatthisradius(≈30-40Myr; linesprimarilyprobetheISMinthewarmatomicandcoldmolecu-
A2011) itisdifficulttoimaginethatthedisturbed gasinthecen- larphases,wherethereissufficientdustextinctiontoallowneutral
tre of this object could exist for long without being smeared out. sodium to survive (Spitzer 1978). For NaD lines to be observed,
This suggests that either this feature isvery young, or we are in- onlyrelativelymodest opticaldepthsandHIcolumndensitiesare
(cid:13)c 2012RAS,MNRAS000,1–18
IFU observationsoftheAGNdrivenoutflowin NGC1266 9
(a) (b)
(c) (d)
Figure7.Ionised gaskinematics derived fromtheGMOSIFU datareduction process discussed inSection 2.2.Inthe toprow(panels a&b)wedisplay
thekinematicsofcomponentone(confinedtobeclosesttothegalaxysystemic).Binswhereonlyoneionisedgascomponentisrequiredarealsoshownin
componentone.Thekinematicsofthefasterout-flowingcomponentareshowninthebottomrow(panelsc&d).Theionisedgasvelocityisdisplayedinthe
leftpanels,andthevelocitydispersionintherighthandpanels.
required,whichmakestheselinesasensitiveprobeoftheoutflow- 1989 extinction law) and to a HI column density of >∼8×1020
ing(orinflowing)neutralISM. cm−2.TheNaDlinesweobservearelikelytobeassociatedwith
As shown in Figure 9 we detect NaD only in the central re- the HI in this source, which is detected in absorption by A2011.
gions, and southern part of the galaxy. As absorption lines are TheyfindatotalHIcolumndensityofNHI =2.1×1021 cm−2 in
frontofthecontinuumsourceinNGC1266, andestimatethatthe
viewedagainstthestellarcontinuum, ifblueshiftedvelocitiesare
observed it is clear that the gas is outflowing, rather than inflow- HI column depth in the outflow is ≈ 8.9×1020 cm−2, consistent
withourdetectionofNaD.
ing.Thegaskinematicsshowthatitislikelycaughtintheoutflow,
withtypical blueshiftedvelocities of ≈-250km s−1 and extreme Our observations provide an alternative way to estimate the
velocitiesdetectedoutto−500kms−1(whichiswellbeyondthe reddening,andthustheatomicgascolumndensityineachspaxel.
Theequivalent width(EW)of theNaD absorption lineshas been
escapevelocity).ThepositionangleoftheoutflowtracedinNaD
shown to correlate with reddening. Here we use the relation of
(and molecular gas; see Figure 10) is slightly different than that
tracedbytheionisedgas,by≈35±5◦.Itisunclearifthedifference Turatto,Benetti&Cappellaro(2003),derivedfromlowresolution
spectroscopicobservationsofsupernovae:
betweenthetwogasphasesissignificant.Wediscussthisfurtherin
Section3.5. E(B−V)
=−0.01+0.16×EW(NaD), (1)
ThepresenceofNaDintheoutflowprovidesfurtherevidence mag
that NGC1266 hosts a multi-phase outflow, and that cold gas is
whereE(B-V)isthestandardcolourexcess.Thiscanbecombined
being removed from the galaxy. As discussed above, the outflow
withtherelationbetweenE(B-V)andHIcolumndensity,suchas
extendstohighervelocitieswhentracedbyionisedgasthanwhen
thatderivedbyBohlin,Savage&Drake(1978):
usingadensegastracer.Eitherthegasisdissociatedfurtheroutin
theoutflow,orwenolongerhavethesensitivitytodetectit. N(HI) E(B−V)
= . (2)
cm−2 0.2×10−21
ToobservetheNaDlines,theextinctionmustbesufficientfor
theoptical depth (τ)to be >∼ 1at 2420 A˚ whichcorresponds to UsingtheserelationswefindthattheaverageHIcolumndensityin
anAv>∼ 0.43magintheV-band(foraCardelli,Clayton&Mathis theoutflowofNGC1266,asderivedfromtheNaDEW(displayed
(cid:13)c 2012RAS,MNRAS000,1–18
10 TimothyA. Daviset al.
(a) (b) (c)
(d) (e) (f)
Figure8.IonisedgaslineequivalentwidthsderivedfromtheGMOSIFUdatareductionprocessdiscussedinSection2.2.InthefirstrowwedisplaytheEW
ofcomponentone(confinedtobeclosesttothegalaxysystemic).Binswhereonlyoneionisedgascomponentisrequiredarealsoshownincomponentone.
TheEWofthefasterout-flowingcomponentisshowninthesecondrow.TheHαlineEWsareshowninpanelsaandd,the[NII]lineEWsinpanelsbande,
andthe[SII]EWsincolumnscandf.
(a) (b) (c)
Figure9.NaDatomicgaskinematicsderivedfromtheGMOSIFUdatareductionprocessdiscussedinSection2.2.2.Inpanelawedisplaytheequivalent
widthoftheabsorptionline.Panelbshowsthederivedgaskinematics,andpanelcthederivedvelocitydispersion.
(cid:13)c 2012RAS,MNRAS000,1–18