Table Of ContentAstronomy&Astrophysicsmanuscriptno.20111211 c ESO2012
(cid:13)
January31,2012
⋆
Planetary nebula kinematics in NGC 1316: a young Sombrero
E.K.McNeil-Moylan1,2,3,K.C.Freeman1,M.Arnaboldi2,andO.E.Gerhard3
1 Mt Stromlo Observatory, Australian National University, Cotter Road, Weston Creek, ACT 2611, Australia; E-mail: emc-
[email protected]
2 EuropeanSouthernObservatory,Karl-Schwarzschild-Str.2,D-85748Garching,Germany;
3 MaxPlanckInstituteforExtraterrestrialPhysics,Karl-Schwarzschild-Str.1,85741Garching,Germany;
Receiveddate:/Accepteddate:
2
ABSTRACT
1
0
Aims.Wepresentpositionsandvelocitiesfor796planetarynebulae(PNe)intheFornaxBrightestClusterGalaxyNGC1316(Fornax
2
A).Theplanetarynebulaeandexistingkinematicsareusedtoexploretherotationofthismergerremnantandconstraindynamical
n models.
a Methods.UsingFORS2ontheVLT,thePNvelocitiesweremeasuredusingacounter-dispersedslitless-spectroscopytechniquethat
J producedthelargest-to-datesampleoutsideoftheLocalGroup.Spherical,non-rotating,constant-anisotropyJeansmodelswerecon-
9 strainedbyobservationsoftheplanetarynebulaeandexistingintegratedlightspectra.
2 Results.Thetwo-dimensionalvelocityfieldindicatesdynamically-importantrotationthatrisesintheouterparts,possiblyduetothe
outwardtransferofangularmomentumduringthemerger.Themodelingindicatesahighdarkmattercontent,particularlyintheouter
] parts,thatisconsistentwithpreviousestimatesfromdynamicalmodels,lensingandstellarpopulationmodels.
O Conclusions.TheexceptionallylargesampleofPNvelocitiesmakes itpossibletoexplore thekinematicsofNGC1316indetail.
C Comparingtheresultstootherearly-typegalaxieslikeNGC1399andNGC4594(M104,Sombrero),NGC1316representsatransi-
tionphasefromamajor-mergereventtoabulge-dominatedgalaxylikeNGC4594.
.
h
Keywords.Galaxies:individual:NGC1316–Galaxies:ellipticalandlenticular–Techniques:spectroscopic
p
-
o
r
t 1. Introduction NGC 1316 is a radio source (Fornax A) with some similari-
s ties (Schweizer 1980) to NGC 5128 (Cen A), the subject of
a Early-typegalaxiesholdan importantplace in the evolutionof
[ one of the earliest and most successful planetary-nebula sur-
structure in the Universe, but their formation and development veys(Huietal. 1995). PreviousworkonNGC 1316includesa
1 arenotwellunderstood.Thehalosareofparticularinterestbe- survey(Arnaboldietal. 1998) whichdetected 43PNe. Itis the
v cause of the high dark-mattercontentandthe link between the
brightest cluster galaxy (BCG) in Fornax and the dominantel-
0 orbital structure and the formation history. However, these re-
lipticalintheinfallingsubclusterdescribedbyDrinkwateretal.
1 gions are difficult to observe because integrated light spectra
(2001).Itisassumedtobetheremnantofamergeroftwodisk
0 fail to reach sufficient signal-to-noise at large radii. This chal-
galaxies based on the intermediate age globular cluster system
6 lenge has been addressed using novel techniques on increas-
. (Goudfrooijetal.2001)anditsdusty,unsettledappearance.
1 ingly large telescopes (Proctoretal. 2009), IFU spectroscopy
We present PN observations of the galaxy in Sect. 2. Sect.
0 (Weijmansetal.2009),anddiscretetracerslikeglobularclusters
3 covers the creation of the PN catalog including the separa-
2 (Spitleretal. 2006; Schuberthetal. 2010) and planetary nebu-
tionoftheoverlappingNGC1316andNGC1317populations.
1 lae.
: The results are presented in Sect. 4, and our analysis, discus-
v Planetary nebulae (PNe) provide a powerful tool for ex- sion of the implicationsand future work are are found in Sect.
Xi ploringellipticalstellarsystemsbeyond2-3Re (Huietal.1995; 5. Throughout this work, we adopt the measured distance of
Arnaboldietal. 1998; Pengetal. 2004; Me´ndezetal. 2001,
21.5MpcforNGC1316(Tonryetal.2001),so1 =6.25kpc.
r 2008; Dohertyetal. 2009; Coccatoetal. 2009; McNeiletal. ′
a
2010). Theyare brightenoughto be detected as individualob-
jectsbecausetheyemitupto15%oftheirlightat[OIII]5007Å
2. Planetarynebulaobservations
(Dopitaetal. 1992; Scho¨nberneretal. 2010). Moreover, their
spatialdistributionfollowsthestars,sotheirmeasuredkinemat-
The planetary nebula kinematics were measured using
icscanbecombinedwithintegrated-lightspectroscopyfromthe
counter-dispersed spectroscopy with FORS2 on the VLT
innerregions(Coccatoetal.2009).Usingcurrent8m-classtele-
(Appenzelleretal. 1998). As shown in Fig. 1, NGC 1316 was
scopes,itispossibletogeneratelargeenoughcatalogsofplan-
observed with 7 fields on 3-5 November 2002. The observing
etarynebulavelocitiestoconstraindynamicalmodelsofnearby
conditionsaresummarizedinTable1.
galaxiesathaloradii.
TheFORSfield-of-viewis6.8 6.8or42.5kpconeachside
We present a planetary-nebula survey of the galaxy NGC ′ × ′
at21.5Mpc(Tonryetal.2001).Thespatialscaleis0 .25/pixel.
1316. It was selected as a nearby, merger-remnant archetype. ′′
We used the 1400V grating with a measured mean disper-
⋆ BasedonobservationsmadewiththeVLTatParanalObservatory sionof0.63Åpix−1.ThemeasuredFWHMofthearclinesinthe
underprogramIDs070.B-0089A calibrationframewas3.8pixels.
2 McNeil-Moylanetal.:PlanetaryNebulaKinematicsinNGC1316
intheP.A.=0andP.A.=180framesisafunctionoftheobject’s
velocity.
The direction of dispersion is along the horizontal axis (x-
axis).Boththe x-andy-axescontainspatialinformationdueto
the slitless technique. The grism causes an anamorphic distor-
tion in the focalplane including contractionin the directionof
dispersion.
Althoughthe reduction and calibration techniquesused for
this data are detailed in Sect. 2.3 of McNeiletal. (2010), we
summarizethembrieflyhere.Thegeometryofthefieldofview
ismappedusingasetofthreedaytimecalibrationframesbased
onadrilledmaskwithagridofholes.Themaskisimagedwith
whitelightinthefirstcalibrationframe.Inthesecondandthird
frames, the light from the mask is dispersed using white and
HeArlampsrespectively.Incombination,thethreeframesallow
us to measure the local dispersion, the local bandpass (which
shiftsacrossthefieldduetotheconvergingbeamandtheinter-
ferencefilter)andtheanamorphicdistortion.
3. Catalogingandisolatingtheplanetarynebulae
Fig.1. DSSimageofNGC1316showingtheapproximatepo-
sitionsofthesevenfieldsobserved.NGC1316sitsatthecenter Theobservationswerereducedandregisteredusingsimilartech-
of Field 1 and NGC 1317 is visible in Field 7. The dispersion niques to those detailed in McNeiletal. (2010). Using regis-
direction is oriented along the major axis of NGC 1316. The tered images, PNe were detected by blinking the two counter-
actualobservedareaisslightlysmallerbecausethetwocounter- dispersedexposures.Adetectioniscomprisedofapairof[OIII]
dispersedexposuresofeachfielddonotoverlapcompletely.
5007Åemission-linesources(oneineachexposure)ofapproxi-
matelythesamebrightnessandatthesamey-position.Thesepa-
Table1.ObservinglogforNGC1316 . rationbetweentheobjectsmustbeconsistentwiththetransmis-
∗
sion limits of the filter. To estimate and improvethe complete-
Field P.A.Label Exp.Time Seeing ness of the catalog, two independentattempts at the detections
(s) (FWHM) areundertakenafewdaysorweeksapart.
NGC1316-1 W140 4 1080 1.16 The observations for NGC 1316 were done using FORS2
′′
×
NGC1316-1 E320 4 1080 1.26′′ insteadofFORS1.Thisenabledamoreeffectivecalibrationset-
×
NGC1316-2 W140 4 1080 1.01′′ upwithadrilledmaskinsteadoftheseriesofcalibrationslitlets
×
NGC1316-2 E320 4 1080 1.13
′′ usedbyMcNeiletal.(2010).Thedistortioncorrectionandreg-
×
NGC1316-3 W140 4 1080 0.98
× ′′ istrationisthesameastheonedescribedin 2.3ofMcNeiletal.
NGC1316-3 E320 4×1080 1.16′′ (2010),butthecalibrationpositionsappear§lessextendedinthe
NGC1316-4 W140 4 1080 0.93
× ′′ verticaldirection,whichmakesthemeasiertomeasure.
NGC1316-4 E320 4 1080 0.95
′′
NGC1316-5 W140 4×1080 1.10 Theastrometrywasperformedfollowingthestepsdescribed
′′
×
NGC1316-5 E320 4 1080 1.10 inMcNeiletal.(2010).ThepositionofeachPNeistakentobe
′′
×
NGC1316-6 W140 4 1080 1.16′′ the mean of the detections in the two counter-dispersed expo-
×
NGC1316-6 E320 4 1080 1.11′′ sures. The astrometric solution is based on the measured posi-
×
NGC1316-7 W140 4 1080 0.81′′ tions of the stars and the coordinatesof the correspondingob-
×
NGC1316-7 E320 4 1080 0.92
× ′′ jectsintheUSNO-Bcatalog(Monetetal.2003).Ourmeasured
uncertainty(rms error of the solution) is about0. 3, which in-
EachfieldisobservedatP.A.=140 and320 , labeledW140and ′′
∗ ◦ ◦
E230respectively. cludes the difficulty of measuring bandpass-shifted continuum
sources.
3.1.Velocitycalibration
An interference filter, FILT 503 5+86, was used to select
emissionatthewavelengthoftheredshifted[OIII]line.Thefil- The drilled-mask calibrations used in these observations are
ter prevents spectra of continuum sources from overwhelming moreaccuratethantheslitletsusedforFORS1data.Thereisno
thefield,anditallows> 50%-transmissiondetectionofPNein reasontosuspectthattheNGC1316PNvelocitiesareincorrect
the rangeof -720to 2280kms 1. A plotof the filter bandpass ineitherarelativeoranabsolutesense.
−
andadiscussionofhowwellitisapproximatedbyaGaussianis To check the agreement between the 7 fields, we matched
availableinSect.4.4.2ofMcNeiletal.(2010). duplicatedetectionsin the areas of overlap.Therewere 78 du-
In counter-dispersedspectroscopy, the field is imaged with plicatedPNeconcentratedinfieldsthatwereverticallyadjacent
a grism in the light path. This causes continuum sources such (Fields 1 & 2, Fields 1 & 3, Fields 4 & 5, and Fields 6 & 7).
as stars to appear as streaks in the direction of dispersion. Inthesefourcases,themeasuredshiftbetweenthefieldswasof
Emission-lineobjectssuchasplanetarynebulaeappearasdots. thesameorderastheerrorintheshift,soitwasnotapplied.The
Anotherexposureistakenwiththepositionangle(P.A.)rotated rmsof the differencesin the pairs was 42 km s−1. We estimate
180 . The distance between the emission line objects detected theinstrumentalerrorofthissampletobe42/√2 30kms 1.
◦ −
≈
McNeil-Moylanetal.:PlanetaryNebulaKinematicsinNGC1316 3
40
e
N
P
30
f
o
r
e
b 20
m
u
N 10
0
1000 1200 1400 1600 1800 2000 2200 2400
Velocity Hkm s^-1L
Fig.3. VelocitydistributionandhistogramofthePNefromthe
F7observations.Thevelocitiesarerepresentedinthehistogram.
The smooth function represents the maximum-likelihoodfit to
thedistribution—itisparametrizedasthesumoftwoGaussians
multipliedbyaGaussianrepresentingthefilter.
3.2.1. Velocitycriterion
Fig.2. Comparisonofthevelocitiesinthiscatalogandthesam-
plefromArnaboldietal.(1998)forthe23PNeincommon.The Thefirstcriterionformembershipisbasedonvelocity.Because
previousmeasurementhasbeensubtractedfromthe newerone thevelocityseparationissosmall,andNGC1317’ssystemicve-
ontheverticalaxisandtheerrorshavebeencombinedinquadra- locityissoneartheedgeofthefilter,weconsideredtheshapeof
ture. The median difference is 1.08 km s 1. The scatter in the the filter to be significantin shaping the overallvelocitydistri-
−
differences (70.7 km s 1) is explained by the combined instru- bution.Usingamaximum-likelihoodtechnique,wefittheField
−
mentalerrorsofthetwosamples.Thisindicatesthattheabsolute 7velocitydistributionwitha sumoftwoGaussians(represent-
velocitycalibrationofthissampleisaccurate. ingthetwogalaxies)multipliedbyaGaussian(representingthe
filter).ThefittothevelocitydistributionisshowninFig.3.The
fittedmeansofthetwogalaxiesarefoundat1826.86kms 1and
−
We comparedthe measuredPN velocitiesfromthissample 1936.08 km s 1 compared to the observed values of 1760 km
−
tothosepreviouslymeasuredbyArnaboldietal.(1998).23PNe s 1and1941kms 1(Longhettietal.1998;deVaucouleursetal.
− −
areincommonbetweenthetwosamples.Themediandifference 1991).AccountingforrotationintheouterpartsofNGC1316,
betweenthetwomeasurementsis1.08kms 1.Thescatterinthe wefindthisfitisconsistentwithourphysicalunderstandingof
−
difference is 70.7 km s 1, which is roughly expected from the thesystem.
−
combination of the instrumental errors of each sample (30 km Wethenreversethetechniquetocalculatetheprobabilityof
s 1 and 60 km s 1). The differences are plotted in Fig. 2. We membership of each velocity in the NGC 1316 Gaussian mul-
− −
concludethatourabsolutevelocitycalibrationisreliable. tiplied by the filter versus the NGC 1317 Gaussian multiplied
by the filter. The probabilities were normalized such that each
PNe must either be a member of one galaxy or the other. The
3.2.DecomposingtheNGC1316andNGC1317
probability of membership in NGC 1316 defines our velocity
populations
membershipcriterion.
TheNGC1316PNsampleshowslocalizedcontaminationfrom
the nearbyFornaxgalaxyNGC 1317.It is an SABa galaxyal-
3.2.2. Spatialcriterion
most directly North of NGC 1316. Their projected separation
is377 , andtheirsystemic velocitiesareonly181kms 1 apart Forthespatialcriterion,weprojectourPNeontothemajoraxes
′′ −
(NGC1316at1760kms 1fromLonghettietal.1998andNGC of the two galaxies and estimate the light contributions from
−
1317 at 1941 kms 1 from deVaucouleurset al. 1991). Due to each galaxy at the location of each PN. We can use this selec-
−
NGC1316’srotation,thevelocityseparationnearNGC1317is tion method because PNe trace the stellar light (Coccatoetal.
evenless.Althoughitisamuchsmallergalaxy,weexpectthere 2009).
tobecontaminationfromNGC1317inthefield thatcoversits We estimate the major-axis radius of each PN assuming a
nucleus,Field7.ThedecompositionwasappliedtoField7alone fixed ellipticity of ǫ = 0.33 based on isophotes from the DSS
becauseitistheonlyfieldsignificantlyinfluencedbyNGC1317. imageofNGC1316andǫ =0.17forNGC1317basedonmea-
ThedecompositionoftheNGC1316andNGC1317PNsamples surements by Wozniaketal. (1995). The position angle of the
followsasimilartwo-foldmembership-assignmenttechniqueto photometricmajoraxisofNGC1316isassumedtobeconstant
the one described in McNeiletal. (2010) for NGC 1399 and at 50 . For NGC 1317,we estimate P.A.=150 based on Fig. 2
◦ ◦
NGC 1404. Each PN is assigned a probability of membership in Wozniaketal. (1995), but this is only valid because we are
in NGC 1316 based on its velocity and the surface brightness interestedinvaluesoutside 16 .
′′
∼
of the galaxyat that position. The probabilitiesare normalized Wecomparedthelightcontributionfromeachgalaxybyus-
suchthatallobjectsinthecatalogbelongtoeitherNGC1316or ing the B-band light profiles from Schweizer (1980) for NGC
NGC 1317,butmembershipis assignedonlyif thereis greater 1316andWozniaketal.(1995)forNGC1317.Toestimatethe
than90%confidence. surface brightness profile beyond the limits of these observa-
4 McNeil-Moylanetal.:PlanetaryNebulaKinematicsinNGC1316
tions,wefittheoutermost14observationsfromSchweizerwith
aSersicprofileandtheoutermost15observationsfromWozniak
etal.withanexponentialprofile.Theprobabilityofmembership
basedon positionis theratio of the surfacebrightnessofNGC
1316tothesurfacebrightnessofNGC1317.
3.2.3. SelectionoftheNGC1316sample
ToselectthefinalsampleforNGC1316,wemultipliedtheve-
locityandspatialcriteria.Thefinalprobabilitiesarenormalized
sothatthetotalprobabilityofmembershipforeachobjectisone.
However, objects are only assigned membership in a galaxy if
theyhave morethan90%probabilityofbelonging.Thisyields
acatalogof796PNeboundtoNGC1316.69PNearemembers
ofNGC1317and43areambiguous.
3.3.Contaminationfromothersources
Basedonthetwo-folddecompositiontechniqueinSect.3.2,we
areabletoidentifyandremovePNethatbelongtonearbygalax-
ies. Our observationsalso includepossible contaminationfrom
other sources. Most background galaxies can be identified as
Fig.4. VelocityhistogramofthePNedetectedintheNGC1316
non-planetarynebulaebecausetheyareassociatedwith contin-
observations. This includes objects associated with NGC 1316
uum, they are spatially extended or they have double emission
andNGC1317.TheredGaussianrepresentsNGC1316andthe
lines.Thesecontaminantsareremovedbeforethesampleisas-
blackcurveindicatesthetransmissionofthefilterintherelevant
sembled.
velocityrange. Some low-velocityobjectsare skewing the dis-
However, some emission-line sources cannot be distin-
tribution, and we see the suggestion of a second peak near the
guished from PNe—they are most likely unresolved Lyman-α
systemic velocityof NGC 1317.(1941km s 1 accordingto de
galaxies at z = 3.1. These background objects show a veloc- −
Vaucouleursetal.1991)
itydistributioncenteredonthefilterinsteadofthegalaxy’ssys-
temicvelocityenablingustoestimatehowmuchcontamination
ispresentinthecatalog.InthecaseofNGC1316,theseobjects Table2.CatalogofPNeinNGC1316
would have lower velocities on average than the PNe from the
galaxy.However,theyareextremelydifficulttoremovebecause
their spatial distribution is approximately flat over the field of ID RA Dec wavelength v
helio
view. Contamination from these background galaxies is mini- J2000 J2000 Å kms 1
−
mizedbyavoidingfaintobjectsintheselectionprocessbecause
their equivalent widths are low and they are less likely to be NGC13161 50.47341 -37.21804 5039.0 1924
continuum-free(Arnaboldietal.2002).InthecaseoftheNGC NGC13162 50.47824 -37.23466 5033.4 1587
1316sample,contaminationislimited(seetheexcessinthehis- NGC13163 50.47914 -37.21044 5038.7 1901
togramatlowvelocitiesinFig.4)andweareabletoeffectively NGC13164 50.48403 -37.22564 5035.3 1700
NGC13165 50.48860 -37.24886 5031.5 1472
analyzeoursamplewithmethodsthatarerobusttooutliers.
NGC13166 50.48942 -37.21301 5036.9 1798
NGC13167 50.49080 -37.24301 5036.4 1764
3.4.PNcatalogs NGC13168 50.49086 -37.20056 5033.6 1598
NGC13169 50.49483 -37.20033 5035.5 1713
3.4.1. Finalizingthecatalogs NGC131610 50.49716 -37.23789 5033.2 1572
. . . . .
Thevelocityhistogramof 908PNe observedin the NGC1316 .. .. .. .. ..
fieldsisshowninFig.4.Thisisanexceptionallylargecatalog. NGC1316794 50.86464 -37.18436 5038.1 1868
796 of these objectsare boundto NGC 1316with greaterthan NGC1316795 50.86579 -37.18282 5039.4 1947
90%probability.Thesamplealsoincludes69membersofNGC NGC1316796 50.87387 -37.21063 5038.2 1876
1317’sPN populationand 43 ambiguousobjects. The catalogs
for NGC 1316 and NGC 1317are presented in Tables 2 and 3
NOTES - Details on the astrometry are in Sect. 3. Velocities,
respectively.
measuredfromthe[OIII]5007Åline,arecorrectedtoheliocen-
tric.Thevelocityerroris30kms 1.Thefullcatalogisavailable
−
3.4.2. Comparingtheefficiencyofourdetections intheassociatedelectronicmaterial.
Theexpectednumberofdetectionsforoursampleisdetermined
by the observationsandthe intrinsic propertiesof the galaxies. commondistanceandcomputethesizeofahypotheticalsample
Wecanjudgetheefficiencyofeachobservingrunbyscalingthe forcomparison.
sizeofthesamplesbythesefactors. Beginning with the 146 PNe detected in NGC 1399, we
This sample is comprised of nearly 5.5 times as many ob- add 55 objects based on symmetry arguments to account for
jectsastheNGC1399catalogpresentedinMcNeiletal.(2010). the 4 of 9 fields that were not observed. We scale by 2.42
SincetheyarebothmembersoftheFornaxcluster,weassumea to account for the difference in brightness. For this we used
McNeil-Moylanetal.:PlanetaryNebulaKinematicsinNGC1316 5
Table3.CatalogofPNeinNGC1317
ID RA Dec wavelength v
helio
J2000 J2000 Å kms 1
−
NGC13171 50.65941 -37.09871 5039.8 1970
NGC13172 50.66192 -37.09394 5040.7 2026
NGC13173 50.66277 -37.10502 5040.3 1998
NGC13174 50.66303 -37.10728 5041.5 2072
NGC13175 50.66341 -37.10949 5040.1 1989
NGC13176 50.66537 -37.08525 5039.6 1956
NGC13177 50.66625 -37.09976 5041.6 2081
NGC13178 50.66925 -37.10303 5039.5 1951
NGC13179 50.66943 -37.08724 5039.1 1927
NGC131710 50.66995 -37.10643 5039.5 1954
. . . . .
. . . . .
. . . . .
NGC131767 50.71118 -37.09235 5039.2 1933
NGC131768 50.71183 -37.09738 5039.3 1938
NGC131769 50.72124 -37.10676 5039.1 1926
NOTES - Details on the astrometry are in Sect. 3. Velocities,
Fig.5. Spatialdistributionofthe908objectsintheNGC1316
measuredfromthe[OIII]5007Åline,arecorrectedtoheliocen-
observations. North is up and East is left. The centers of the
tric.Thevelocityerroris30kms 1.Thefullcatalogisavailable
− two galaxiesare markedwith blackcrosses. SurroundingNGC
intheassociatedelectronicmaterial.
1317, the solid, black dots representPNe bound to NGC 1317
with >90%probability. The colored dots indicate membership
2MASS (Skrutskieetal. 2006) K magnitudes adjusted accord- in NGC 1316. If a PN cannot be assigned membership with
ing to Kormendy&Tremaine (2011). Finally, we consider the >90% probability, it is marked as ambiguous (hollow black
relationfromBuzzonietal.(2006)relatingthePNnumberden- dots). Ignoring the structure from this companion galaxy, this
sity to the color of the galaxies. The overall trend implies that figureshowsNGC1316’srotationorientedalongP.A.=64 (see
◦
reddergalaxieshavea higherspecificfrequency.Despite being Sect. 4.2). The north-east is rotating away from the observer
reddenedbydust,NGC1316isbluerthanNGC1399implying whilethesouth-westismovingtowardsusrelativetothemean.
anincreasein ourpredictedsample.Thereissignificantscatter
in the Buzzoniet al. relation, accountedfor by variation in the
lifetimesofPNpopulations,andamuchsteeperrelationforex-
ternalellipticalsthanforLocalGroupgalaxies.Theadjustment Thefirstbinisincompletebecauseofthevoidinthecenter
where PNe are not detectable. The surface brightness profiles
forourpredictedsampleisbetween1.2and2.5.
Adjustingforthesedifferences,wecancompareoursample are in goodagreementuntil 250′′ where the influenceof the
∼
of796PNeinNGC1316toapredictedsamplebetween588and dustbecomesapparent.Duststronglyaffectstheintegratedlight
observations in the outer parts. The NE major axis is the least
1216PNe.Weconcludethat,althoughNGC1316hasaremark-
affected, and, therefore,is the best pointof comparisonfor the
ablylargesample,itisnotunexpected.
PNe.
IntheregionwherethePNsampleiscompleteanddustdoes
4. Results notobscuretheB-bandintegratedlight,thePNnumberdensity
shadowstheNEmajor-axissurfacedensityofthestars.Wecon-
4.1.Thespatialdistribution
cludethatthePNe andtheintegratedlightare compatibletrac-
The spatial distribution of the PNe in NGC 1316 is shown in ers of the underlying stellar mass. We will use the two tracers
Fig. 5. The overall shape is determined by the layout of the 7 togethertoconstraindynamicalmodelsofNGC1316in 5.2.
§
observed fields in Fig. 1, and we see rotation along the major
axis(P.A.=64 ,seeSect.4.2).
◦ 4.2.Thekinematics
The analysis of the PN kinematics and their use as trac-
ers in dynamical models are dependent upon the consistency Aphase-spaceprojectionofline-of-sightvelocityagainstradius
of PNe and stars. Coccatoetal. (2009) showed this for a sam- isshowninFig.7.Therearesomehigh-andlow-velocityobjects
ple of elliptical galaxies observed with the Planetary Nebulae thatmaybecontaminants,buttheywillnotaffecttherobustdis-
Spectrograph. In Fig. 6, we show a comparison of the stellar persionmeasurementsdiscussedinSect.5.1.
surface brightness and the PN number density. The PNe were
We quantifythe rotationof the sample by modelingthe to-
dividedintoannularbinsandthelogarithmicprojectednumber
talrotationandtherotationinannularbins.S0galaxiesusually
densityineachbinwascalculatedas
displayrotation,andweareinterestedtolearntowhatextentthe
flatteningisrotationallysupported.Thefittedrotationforthefull
µ = 2.5log(N /A)+c,
PNe PNe
− sampleofPNeisshowninFig.8.
whereN isthenumberofPNeinthebin,Aistheareaofthe Forthefit,weassumethatthegalaxyissphericallysymmet-
PNe
annulusandcisanarbitraryconstantselectedforthegalaxy(but ric,theamplitudeofrotationisonlyafunctionofradiusandthat
remainingconstantforallthebins). the axis of rotation is in the plane of the sky (Coˆte´etal. 2001;
6 McNeil-Moylanetal.:PlanetaryNebulaKinematicsinNGC1316
NED
1760km/s
Fig.6. Surface density profiles for the PNe and stars in NGC Fig.7. Line-of-sight velocity against projected radius. The
1316.RedandblackcrossesmarktheNEandSWmajor-axisB- sample is centered on the systemic velocity of 1760km/s
bandsurfacebrightnessprofilesrespectively(Caonetal.1994). (Longhettietal. 1998). Solid red objects have been assigned
The hollow squares show the measurements from Schweizer membership in NGC 1317 with >90% probability. The hol-
(1980). The agreement with the NE major axis between 200 low red dots are ambiguous– they could not be assigned to ei-
′′
and500 indicatesthatthePNedotracethelight,exceptwhere ther galaxy with more than >90% probability. There are some
′′
dustobscurestheobservations. extreme-velocityobjectsnearthecenterofthefilter(779kms 1)
−
andaround2700kms 1thatmaybebackgroundgalaxies.
−
Woodleyetal.2010).Thevelocityasafunctionofpositionan- 2500
gle,Θ,isparametrizedas
L
s
(cid:144)m 2000
vp[Θ]=Vsys+Acos(Θ Θ0), Hk
− y
cit 1500
o
where Vsys is the systemic velocity, A is the amplitude of rota- Vel
tion,andΘ istheP.A.ofthekinematicmajoraxis.Wealsocon-
0 1000
sidered adding a sin(3Θ) term, but the simpler modelwas pre-
ferredbyaBayesianInformationCriteriontest(Schwarz1978).
500
Becausewesuspectafitincludingafreesystemicvelocityto -3 -2 -1 0 1 2 3
beinfluencedbythecontaminationfromthecenterofthefilter, PositionAngleHRadiansL
weholdV constantat1760kms 1(Longhettietal.1998).The
sys −
resultisakinematicmajoraxisatP.A.=64 8 andanamplitude Fig.8. The line-of-sightvelocities of the NGC 1316 PNe as a
◦
of rotation of 85 11 kms 1. The photom±etric major axis is at functionof position angle. The grey dots representthe decom-
−
P.A.=50 . ± posedPNesample.Theblackfitrepresentsrotationofaspheri-
◦
callysymmetricsystemwiththeaxisofrotationintheplaneof
Using the rotation fitted to the entire sample as an initial
the sky. It indicates an amplitude of 85kms 1 and a kinematic
guess, we divided the PNe into five radial bins. The P.A. and −
majoraxisatP.A.=64 (1.11radians).
amplitudeofrotationaremodelledforeachbin,andtheresults ◦
areinFig.9andFig.10respectively.Thepositionangleofthe
kinematic major axis is offset from the photometricmajor axis
by1.6σ,butstillconsistent(seeFig.9).Theamplitudeofrota-
5. Discussion
tion rises in the outer parts. Thiscould indicate thatsome PNe
bound to NGC 1317 with a systemic velocity of 1941 km s 1
− 5.1.Line-of-sightvelocitydispersion
(deVaucouleursetal.1991)havestayedinoursample.Thissce-
narioisnotsupportedbythedistributionofthePNeinFig.8nor The line-of-sight velocity dispersion profile is a useful tool to
the consistency of bin 5’s position angle with the inner bins in illustratethemassdistributionanddynamicsofellipticalgalax-
Fig.9.Therisecouldalsobearealdescriptionofthekinemat- ies. For ourmeasurements,we use a robusttechniqueformea-
ics of NGC 1316. This phenomenon could be evidence of the suring the dispersion of discrete tracers that is described in
outwardtransferofangularmomentumresultingfromamerger McNeiletal. (2010). Because the calculation is only based on
(Quinn&Zurek1988). objectslyingwithin2σofthemean,outliersdonothaveastrong
McNeil-Moylanetal.:PlanetaryNebulaKinematicsinNGC1316 7
L
s 120
e
e
r
g
De 100
H
s
xi 80
A
aj.
M 60
c
ati 40
m
e
n
Ki 20
f
o
A 0
P 0 100 200 300 400 500
ProjectedRadiusH''L
Fig.9. Fittedvaluesforthepositionangleofthekinematicma-
jor axis of NGC 1316. The connected black points show the
kinematic major axis’s P.A. known from fitting the rotation in
five radial bins. The P.A. fitted to the entire sample is 64 8
◦
±
(shownasgreydottedline).Thedashedgreylineshowsthepho-
tometricmajoraxisat50 .
◦
Fig.11. Line-of-sightvelocitydispersionprofileforNGC1316.
200
The hollow circles representthe integrated lightmeasurements
L
H(cid:144)Rotationkms 110500 ææææææææææææææææææææææææææææææææ daofsriginoosapnmtihnesersBs(trhieoeoodsnulriltedoligisuweaarsllsussebtatoatnrafrdsalt).chdt(eaee2rds0Nec0irGnc6iboC)qemfu1otpah3rude1ttrh6eraadetrunomurdtesaoa.itmjniToogrhnmeatfihoxrtetie.isos.TrunoThlbtiehsnueisanNtPrseGttNerCurcedhmsi1nisel3ipinq1eetun6are-tl.
of ææææ Thetwotracersinterfacewellat∼150′′.
ude 50 ææææ 1.0
plit ææææ
m 0ææ
A 0.8
0 100 200 300 400 500
e
ProjectedRadiusH''L N 0.6
P
or
Fig.10. The rotation curve of the PNe in the outer parts of Σf
NGC1316.Theblacklinetracestheamplitudeofrotationofthe (cid:144)V 0.4
PNeinannularbins.Atsmallradii,thegraydotsshowpositive
major-axis rotation measurements from Bedregaletal. (2006), 0.2
andtheblackdotsshowmajor-axisrotationmeasurementsfrom
Arnaboldietal.(1998).
0.0
0 1 2 3 4 5
R(cid:144)Re
Fig.12. V/σprofileofNGC1316.ThefittedrotationofthePNe
effect.Thismethodisresilientagainstanylingeringcontamina-
is dividedby the robustdispersionmeasurementshown in Fig.
tionfrombackgroundgalaxies.
11toillustratetherelativedynamicalimportanceofrotationand
In the case of NGC 1316, we measure the dispersion after
randommotions.For NGC 1316,rotationis more importantin
accountingfortherotation.Therobusttechniquewasappliedto
theouterpartsthanitisintheinnerparts.1R =109 =11.4kpc
theresidualsoftherotationfitineachofthefiveannularbins. e ′′
(Caonetal.1994).
The random-motion profile of NGC 1316 is shown in Fig.
11. At small radii, the integrated-light measurements from
Bedregaletal. (2006) show a falling dispersion profile. As we 5.2.JeansModels
moveintothehalo,theplanetarynebulaeindicatethattheveloc-
To better understand the meaning of the kinematics of the
itydispersioncontinuestofalloffuntilatleast 500 .
∼ ′′ PN sample in NGC 1316, we construct a simple dynami-
V/σ is used to quantify the relative importance of rotation
cal model of the galaxy. We begin with the Jeans equations
and random motions in the dynamics of the galaxy. We divide
(Binney&Tremaine1987),assumingsphericalsymmetry:
the amplitude of rotation for the PNe by the robust dispersion
shown in Fig. 11. The V/σ profile for the planetarynebulae in 1d(ρσ2(r)) β σ2(r) dΦ
NGC1316isshowninFig.12.Rotationismoreimportantinthe r +2 0 r = , (1)
ρ dr r −dr
outerpartsthanitisintheinnerpartsofNGC1316,suggesting
thatangularmomentumtransferredoutwardsduringthemerger whereρisthespatialdensity,σ istheradialcomponentofthe
r
(Quinn&Zurek1988). velocitydispersion,β istheanisotropyofthevelocitydistribu-
0
8 McNeil-Moylanetal.:PlanetaryNebulaKinematicsinNGC1316
σ2
tion(β 1 θ),whichisassumedtobeindependentofradius 300
≡ − σ2r
here, and Φ is the total potential. The expressions on the left-
L
s
hand side of Eq. 1 can be related to observationallyaccessible (cid:144)m
quantities.Inthiscase,wesolveforthevelocitydispersionand Hk 250
correctfortheprojectionontotheplaneofthesky.Theprojected on
velocitydispersionofthemodelisgivenas rsi
pe 200
σ2(R)= 2 ∞ 1 β R2 j(r)σ2r(r)rdr, (2) Dis
p I(R)ZR − 0r2! √r2−R2 ocity 150
where I(R)istheobservedsurfacebrightnessprofileandj(r)is el
V
the light density which is calculated from the mass density, ρ,
dividedbyaconstantmass-to-lightratio,Γ. 100 0.5 1.0 5.0 10.0 50.0 100.0
Thevelocitydispersionofthemodel,σr dependsontheto- RadiusHkpcL
tal mass of the system. As a first attempt, we assume a model
where mass traces the light with a constantmass-to-lightratio. Fig.13. Self-consistentJeansmodelofNGC1316.Bluepoints
We comparedthe model’s projected velocity dispersion profile are integrated-lightdispersionsfromBedregaletal. (2006) and
totheobservationsofintegratedlight(Bedregaletal.2006)and the red points show the dispersions of PNe in annular bins.
the robust dispersion measurementsof the PN sample. The in- Thebluecurverepresentsamodelwithamass-to-lightratioof
tegratedlightpositionswereadjustedby-0.32kpcto maximize 4.0M /L andaconstantanisotropyof0.44.Thedisagreement
thesymmetryofthedispersionprofile1.Sincethisnon-rotating betwe⊙ent⊙hemodelandtheobservationsintheouterpartunder-
modeldoesnototherwiseaccountfortheenergyassociatedwith linestheimportanceofDMinthedynamicsofNGC1316.
rotation,weconstrainourmodelwiththeobservationalquantity
σ . In the case of the integrated light, this is the line-of-sight
tot
velocityandthevelocitydispersionaddedinquadrature.Inthe 300
case of the PNe, it is the robust dispersion of the binned PNe
velocitieswithoutadjustingfortherotation.Thegoodness-of-fit
wasquantifiedwithareducedχ2-stylemeritfunction 250
L
s
1 N (σ (R) σ (R))2 (cid:144)m
χ2 = tot i − p i , (3) k 200
N n σ2 (i) H
− Xi=1 error Σtot
e
where N is the number of data points constraining the fit and
150
n is the number of free parameters, σ is the observed value
tot
of sigma at a radius, R, σ (R) is the projected dispersion of
i p i
the model at Ri and σerror is the uncertainty of the observation 100
0.5 1.0 5.0 10.0 50.0 100.0
belongingtothatradius.
RadiusHkpcL
Thebestfittingself-consistentmodelisshowninFig.13.We
assumethatthetotalmasstracesthelightwithaconstantmass-
Fig.14. Dynamical model of NGC 1316 including dark
to-lightratio.Thismodelhasamass-to-lightratioof4.0M /L
matter. The blue points are integrated-light dispersions from
andananisotropyof0.44.Thedisagreementbetweenthem⊙ode⊙l
Bedregaletal.(2006)andtheredpointsaremeasuredfromPNe.
andtheobservationsintheouterpartsindicatesthenecessityof
Themodel(bluecurve)hasaconstantmass-to-lightratioof2.8
adarkmattercomponent,inthiscaseparameterizedasapseudo-
M /L andaconstantanisotropyof0.50.Thedarkmatterdistri-
isothermaldistributionsuchthat
bu⊙tion⊙ischaracterizedbyσ = 289kms 1 andacoreradius
DM −
σ2 of5kpc.Thismodeldoesnotrotate.
ρ (r)= DM , (4)
DM 2πG(a2+r2)
where σ is a velocity dispersion representing the total mass
DM
oftheDMhaloandaisacoreradius. ThemodelingofNGC1316islimitedbythesimplifications
Addinginthedarkmattercomponent,weexploredagridof inthemodelingtechnique.Theoutcomewouldbeimprovedby
modelsvaryingoverthefourparametersβ ,Γ,σ ,anda.We assuminganaxisymmetricdistributionthatisflattenedbyrota-
0 DM
resolved the anisotropy (β) to 0.01, the mass-to-light ratio (Γ) tion. The mass-to-lightratio might well change over the radial
to 0.1M /L , the core radius (a) to 1 kpc and the dark matter range of our models. Allowing the anisotropy to change as a
dispersio⊙n(σ⊙ )to1kms 1. functionof radiuswill add flexibility to the fitting andcreate a
DM −
The best value for our merit function corresponded to a moreaccuratemodelofNGC1316.
modelwithβ0 =0.50,Γ=2.8M /L ,a=5kpc,andσDM =289 Despite the inherent assumptions in this model, it presents
kms−1.Thebestmodelisshown⊙in⊙Fig.14. a realistic physical description that is consistent with observa-
tions and theory. Our mass-to-light ratio of 2.8 M /L lands
1 Bedregaletal.(2006)selectedthepeakofthedispersionprofileas at the low end of values measured for other galaxi⊙es (⊙see Fig
theirpositionzero-point.Uponcloserinspection,thehighestdispersion
4.25inBinney&Tremaine(2008)).Thedarkmattercontentof
valuewasananomalyinanotherwisesymmetricalprofile.Weremoved
NGC 1316 shown in Fig. 15 is towards the high end of esti-
theanomalouspointandfittedtheprofilewithasymmetricalfunction
findingashiftof-0.32kpcrelativetotheirsystem.Thefitsharedthe matesof5-65%within1Re (11.4kpc= 109′′,Caonetal.1994)
samepeakasthemeasurements(withtheobjectrepresentingtheprevi- (Gerhardetal. 2001; Treu&Koopmans 2004; Cappellarietal.
ouszero-pointremoved). 2006;Thomasetal.2007;Barnabe`etal.2009).
McNeil-Moylanetal.:PlanetaryNebulaKinematicsinNGC1316 9
1.0
Barnabe`,M.,Czoske,O.,Koopmans,L.V.E.,etal.2009,MNRAS,399,21
Bedregal,A.G.,Arago´n-Salamanca,A.,Merrifield,M.R.,&Milvang-Jensen,
B.2006,MNRAS,371,1912
0.8
n Binney,J.&Tremaine,S.1987,GalacticDynamics(PrincetonUniversityPress)
actio0.6 BinUnenyiv,eJr.s&ityTPrreemssa)ine,S.2008,GalacticDynamics:SecondEdition(Princeton
Fr Buzzoni,A.,Arnaboldi,M.,&Corradi,R.L.M.2006,MNRAS,368,877
s Caon,N.,Capaccioli,M.,&D’Onofrio,M.1994,A&AS,106,199
s
Ma0.4 Cappellari,M.,Bacon,R.,Bureau,M.,etal.2006,MNRAS,366,1126
Coccato,L.,Gerhard,O.,Arnaboldi,M.,etal.2009,MNRAS,394,1249
M
Coˆte´,P.,McLaughlin,D.E.,Hanes,D.A.,etal.2001,ApJ,559,828
D
0.2 deLorenzi,F.,Gerhard,O.,Saglia,R.P.,etal.2008,MNRAS,385,1729
deVaucouleurs,G.,deVaucouleurs,A.,Corwin,Jr.,H.G.,etal.1991,S&T,82,
621
0.0 Doherty,M.,Arnaboldi,M.,Das,P.,etal.2009,A&A,502,771
0 20 40 60 80 100
Dopita,M.A.,Jacoby,G.H.,&Vassiliadis,E.1992,ApJ,389,27
RadiusHkpcL Drinkwater,M.J.,Gregg,M.D.,&Colless,M.2001,ApJ,548,L139
Gerhard,O.,Kronawitter,A.,Saglia,R.P.,&Bender,R.2001,AJ,121,1936
Fig.15. Dark matter mass fraction of NGC 1316. By consid- Goudfrooij, P., Mack, J., Kissler-Patig, M., Meylan, G., & Minniti, D. 2001,
eringthe darkandluminouscomponentsourmodelseparately, MNRAS,322,643
Hui,X.,Ford,H.C.,Freeman,K.C.,&Dopita,M.A.1995,ApJ,449,592
we can assess what fraction of the mass at each radius is DM.
Kormendy,J.&Tremaine,S.2011,ARA&A,inprep.
Thisplotismadeforthemodelthatbestfitsthekinematicdata: Longhetti,M.,Rampazzo,R.,Bressan,A.,&Chiosi,C.1998,A&AS,130,267
β =0.50,Γ=2.8M /L ,a=5kpc,andσ =289kms 1. McNeil,E.,Arnaboldi,M.,Freeman,K.,etal.2010,A&A,518,A44+
0 DM −
⊙ ⊙ Me´ndez,R.H.,Riffeser,A.,Kudritzki,R.-P.,etal.2001,ApJ,563,135
Me´ndez,R.H.,Teodorescu,A.M.,&Kudritzki,R.-P.2008,ApJS,175,522
Monet,D.G.,Levine,S.E.,Canzian,B.,etal.2003,AJ,125,984
5.3.Implicationsfortheassemblyofearly-typegalaxies
Peng,E.W.,Ford,H.C.,&Freeman,K.C.2004,ApJ,602,685
Evidence from the globular cluster system (Goudfrooijetal. Proctor,R.N.,Forbes,D.A.,Romanowsky,A.J.,etal.2009,MNRAS,398,91
Quinn,P.J.&Zurek,W.H.1988,ApJ,331,1
2001) indicates that the last major merger occured 3 Gyr ago.
Scho¨nberner,D.,Jacob,R.,Sandin,C.,&Steffen,M.2010,A&A,523,A86+
The resulting galaxyis dusty with dynamicallyimportantrota- Schuberth,Y.,Richtler,T.,Hilker,M.,etal.2010,A&A,513,A52+
tion.ProjectingtheevolutionofNGC1316forwardintime,the Schwarz,G.1978,TheAnnalsofStatistics,6,461
dustwill settle intoa disk (vanderKruit&Freeman2011, and Schweizer,F.1980,ApJ,237,303
Skrutskie,M.F.,Cutri,R.M.,Stiening,R.,etal.2006,AJ,131,1163
referencestherein).A system likethiscouldevolveintoan ob-
Spitler,L.R.,Larsen,S.S.,Strader,J.,etal.2006,AJ,132,1593
jectliketheSombreroGalaxy(NGC4594,M104).
Thomas,J.,Saglia,R.P.,Bender,R.,etal.2007,MNRAS,382,657
NGC 1316 provides a lower limit for the time between a Tonry,J.L.,Dressler,A.,Blakeslee,J.P.,etal.2001,ApJ,546,681
major merger and a galaxy like NGC 4594 to form. Likewise, Treu,T.&Koopmans,L.V.E.2004,ApJ,611,739
vanderKruit,P.C.&Freeman,K.C.2011,ARA&A,49,301
it constrains the time since NGC 4594 last underwenta major
Weijmans,A.-M.,Cappellari,M.,Bacon,R.,etal.2009,MNRAS,1006
mergertobegreaterthan3Gyr.Inthecontextofmassassembly
Woodley,K.A.,Go´mez,M.,Harris,W.E.,Geisler,D.,&Harris,G.L.H.2010,
withinclusters,NGC1316tellsadifferentstorytotheFornaxcD AJ,139,1871
galaxy,NGC1399.NGC1399isaslowrotating,possiblytriax- Wozniak,H.,Friedli,D.,Martinet,L.,Martin,P.,&Bratschi,P.1995,A&AS,
ial,dominantgalaxy.ThecDenvelopeimpliesthataccretionis 111,115
currentlydominatingitsmassassembly.Incontrast,NGC1316
is in a phase where it has recently undergone a major merger
andwouldneedtobeinvolvedinseveralmoretoresembleNGC
1399. As shown in Fig. 10 and 11, NGC 1316’s rotation stays
constant in the outer parts, but the random motions decrease.
Despitedominatingitssubcluster,NGC1316illustratesanear-
lierphaseinmassassemblywithinclusters.
5.4.Futurework
The ultimate goal of these observations is to constrain the
outer parts of dynamical models. We have presented spher-
ical, non-rotating Jeans models. Future work will focus on
more sophisticated models including NMAGIC modeling (see
deLorenzietal.2008).
Acknowledgements. Wethank A. Bedregal for generously sharing the major-
axiskinematicsofNGC1316.WethankW.Harrisfordiscussionsregardingthe
rotationofNGC1316.ThisworkhasmadeuseoftheNASA/IPACExtragalactic
Database(NED)whichisoperatedbytheJetPropulsionLaboratory,California
InstituteofTechnology,undercontractwiththeNationalAeronauticsandSpace
Administration.
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