the kinematic morphology–density relation in Abell 85, Abell 168 and Abell 2399

19 Pages·2014·3.11 MB·English

MNRAS443,485–503(2014) doi:10.1093/mnras/stu1165
The SAMI Pilot Survey: the kinematic morphology–density relation
in Abell 85, Abell 168 and Abell 2399
L. M. R. Fogarty,1,2‹ Nicholas Scott,1,2 Matt S. Owers,3 S. Brough,3
Scott M. Croom,1,2 Michael B. Pracy,1 R. C. W. Houghton,4 Joss Bland-Hawthorn,1
Matthew Colless,5 Roger L. Davies,4 D. Heath Jones,6 J. T. Allen,1,2
Julia J. Bryant,1,2,3 Michael Goodwin,3 Andrew W. Green,3
Iraklis S. Konstantopoulos,3 J. S. Lawrence,3 Samuel Richards,1,2,3 Luca Cortese7
and Rob Sharp5 Do
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1SydneyInstituteforAstronomy,SchoolofPhysics,UniversityofSydney,NSW2006,Australia lo
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2ARCCentreofExcellenceforAll-SkyAstrophysics(CAASTRO) de
34AAustsrtorpahliyasnicAss,tDroenpoamrtimcaelnOtobfsPerhvyastiocrsy,,UPnOivBerosxit9y1o5f,ONxofrotrhd,RDydeenyNsSWWil1ki6n7s0o,nABuustirldailniag,KebleRd.,OxfordOX13RH,UK d from
5ResearchSchoolofAstronomyandAstrophysics,AustralianNationalUniversity,CanberraACT2611,Australia h
6SchoolofPhysics,MonashUniversity,ClaytonVIC3800,Australia ttp
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7CentreforAstrophysicsandSupercomputing,SwinburneUniversityofTechnology,HawthornVIC3122,Australia ://a
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Accepted2014June9.Received2014June2;inoriginalform2014April14 ic
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ABSTRACT m
/m
Weexaminethekinematicmorphologyofearly-typegalaxies(ETGs)inthreegalaxyclusters n
ra
Abell85,168and2399.UsingdatafromtheSydney-AAOMulti-objectIntegralfieldspectro- s
/a
graphwemeasurespatiallyresolvedkinematicsfor79ETGsintheseclusters.Wecalculate rtic
λ ,aproxyfortheprojectedspecificstellarangularmomentum,foreachgalaxyandclassify le
R /4
the79ETGsinoursamplesasfastorslowrotators.Wecalculatethefractionofslowrotators 43
intheETGpopulations(fSR)oftheclusterstobe0.21±0.08,0.08±0.08and0.12±0.06for /1/4
Abell85,168and2399,respectively,withanoverallfractionof0.15±0.04.Thesenumbers 85
/1
arebroadlyconsistentwiththevaluesfoundintheliterature,confirmingrecentworkasserting 4
8
7
that the fraction of slow rotators in the ETG population is constant across many orders of 5
2
4
magnitude in global environment. We examine the distribution of kinematic classes in each b
y
cluster as a function of environment using the projected density of galaxies: the kinematic g
u
bmuotrpinhoAlobgeyll–1d6e8nsaitnydre2l3a9ti9ont.hWisetrfiennddtihsantointAsebeenl.l8W5efeSxRaimncinreeastheesidnifhfiegrheenrcedsenbseittwyereegniothnes est on
1
individualclusterstoexplainthis.Inaddition,wefindslowrotatorsontheoutskirtsoftwoof 0
M
theclustersstudied,Abell85and2399.Thesegalaxiesresideinintermediatetolowdensity a
rc
regions and have clearly not formed at the centre of a cluster environment. We hypothesize h
2
thattheyformedatthecentresofgroupsandarefallingintotheclustersforthefirsttime. 0
2
3
Keywords: techniques:imagingspectroscopy–galaxies:clusters:individualAbell85,Abell
168,Abell2399–galaxies:ellipticalandlenticular,cD–galaxies:kinematicsanddynamics.
symmetriclightprofilethatdoesnotexhibitspiralstructure.Within
1 INTRODUCTION
thisdefinitionETGsaretraditionallyclassifiedmorphologicallyas
Early-typegalaxies(ETGs)havebeenstudiedextensivelysincethe ellipticalandS0galaxies.However,thisclassificationdoesnotnec-
questtounderstandgalaxyformationbegan.Exactlywhatdefines essarilyreflectphysicalprocesseswithinthegalaxiesthemselves.
anETG,however,canbesubtlydifferentdependingonmanycon- TounderstandtheformationofETGswewishtoprobethesepro-
textualfactors.HerewedefineanETGtobeagalaxywithasmooth cessesandinterprettheirimpactonETGsandtheirformationhisto-
ries.OnewaytodothisistoprobetheangularmomentumofETGs
throughtheirmeasuredkinematicsandinsteadclassifythembased
(cid:3) onakinematicmorphology.TheSAURONandATLAS3Dsurveys
E-mail:[email protected]
(cid:2)C 2014TheAuthors
PublishedbyOxfordUniversityPressonbehalfoftheRoyalAstronomicalSociety
486 L.M.R.Fogartyetal.
introducedthistechnique(Cappellarietal.2007;Emsellemetal. thekinematicmorphology–densityrelationinAbell1689,amuch
2007,2011)andanewclassificationsystemforETGs.Inthissys- highermassanddenserclusterthanVirgo.Insteadofglobalgalaxy
tem,highangularmomentumETGsareclassifiedasfastrotators fractions they used the metric of SR fraction, f , defined as the
SR
(FRs)andlowangularmomentumETGsasslowrotators(SRs). fractionofSRsintheETGpopulation.Theyfoundatrendofin-
Inthisnewframework,mostETGs(∼86percent)arefoundto creasing f with increasing local density, analogous to the trend
SR
exhibitregularrotation,whereasacomparativelysmallerfraction in the fraction of SRs in the total population seen in ATLAS3D.
ofobjectsshownoorweaksignsofrotation.Many(50percent) This work was then followed by a study of the Coma cluster by
elliptical and most (90 percent) S0 galaxies turn out to be FRs. Houghtonetal.(2013)whosawthesametrendofincreasingf
SR
Thesegalaxiesareaxisymmetricoblatespheroidsandarethought withincreasinglocaldensity,butalsonotedthattheglobalvalue
toharbourstellardiscs(Krajnovic´etal.2011).SRsontheotherhand forf wasconstantacrossallsamples.Thatistosaythatacross
SR
arethoughttomostlybetruedispersiondominatedsystems,which many types of global host environment (GHE; such as low-mass
maybemildlytriaxial(Emsellemetal.2007).Giventhedifference cluster, high mass cluster, field, etc.) the relative number of SRs
intheirdynamics,theformationmechanismsresponsibleforFRs andFRsisconstant.Thisimpliesthattheformationmechanismfor
and SRs must be different. However, the dominant factor in the SRs must be equally efficient across a wide range of GHEs, i.e.
D
formationofSRsandFRsisstillopenfordebate. SRsarenotonlyformedinclusters.However,withinaparticular o
w
SinglemergingeventmodelsbyBoisetal.(2011)showthatitis GHE, Houghton et al. (2013) did confirm the strong dependence n
lo
possibletocreateFRsandSRsinmajormergerscenarios.However, of f on local point environment (LPE; defined as the local en- a
SR d
thecreationofanSRbyasinglemajormergerreliesontheorbits vironment of the galaxy) suggesting that perhaps SRs migrate to ed
of the two progenitor galaxies being exactly retrograde, and this thecentreoftheirhostclustersthroughdynamicalfriction,despite fro
m
scenariocreatesanSRwithmanysignaturesofbeingadoublesigma forming elsewhere. Scott et al. (2014) investigated the kinematic h
galaxy(i.e.twocounter-rotatingdiscs),thusnotatruedispersion- morphology–densityrelationinthelow-massFornaxcluster,find- ttp
s
dominatedsystem.Investigatingapopulationofgalaxies,Khochfar ing that fSR increases towards the centre of the cluster. The trend ://a
et al. (2011) use semi-analytic models to show that in merging seen is weaker in Fornax than the more massive clusters studied c
a
scenariosanFRistheusualproduct,eitherthroughmaintaininga (Virgo, Coma and Abell 1689). Scott et al. (2014) also find that de
m
smallamountofstarsinastellardiscorregrowingthediscafterthe eveninmass-matchedsamplesofSRsandFRstheSRsaremore ic
mergerevent.Conversely,theyfindthatalthoughSRsarelikelyto likelytoliveindenserLPEs.Thisimpliesthatdynamicalfriction .o
u
haveundergonemoremajormergerstheirrecentpastwasdominated alonecannotberesponsibleforthekinematicmorphology–density p.c
o
bymultipleminormergerswithrandomtrajectories.Theseminor relation. m
events do not allow a stellar disc to build up in the remnant and Thecausesandnatureofthekinematicmorphology–densityre- /m
n
canthereforeleadtotheformationoftrueSRs.Naabetal.(2013) lation,anditsimportanceinrelationtotheformationofETGs,are ra
s
addressedtheformationofFRsandSRsbystudyingcosmological still not well understood. Outstanding questions include, what is /a
hydrodynamical simulations of 44 central galaxies and satellites, thedominantformationmechanismforSRsandFRs,ifany?Are rtic
withtheuniqueabilitytolinkthekinematicfeaturesintheirz=0 SRsmostlyformedinsituatthecentreoftheirGHEsordothey le/4
4
galaxies with the formation histories of individual objects. They migrate there through mass segregation by dynamical friction, or 3
/1
concluded that it is not possible to single out individual FR and both?Whatrolesdotheprocessesofmajorandminormergingplay /4
SR formation scenarios, instead finding it possible to make both in the creation of FRs and SRs and their observed distributions? 85
classes of ETGs by several means. Factors like the mass ratio in These questions can only be answered by increasing the number /14
8
mergingevents,theamountofgaspresent,andwheninthehistory ofETGsobservedwithspatiallyresolvedspectroscopyandcom- 7
5
ofaparticulargalaxymajormergereventsoccurred,canallimpact paringtheseobservationstoavarietyofsimulationssuchasthose 24
thetypeofETGformed. showninBoisetal.(2011),Khochfaretal.(2011)andNaabetal. by
IthasbeenshowninworkbyOemler(1974)andDavis&Geller (2013).Sincethecollectionofintegralfieldspectroscopy(IFS)data gu
e
(1976)thattherelativefractionofdifferentgalaxymorphological tendstobetimeconsumingtheseobservationscanbedifficultto s
typesvarieswithenvironment,suchthatETGsaremoreprevalent accomplishquickly.However,theintroductionofnewmulti-object t on
ingalaxyclustersattheexpenseoflate-typegalaxies(LTGs,here IFSinstrumentsmeansthatsoonlargesamplesofgalaxieswillbe 10
includingbothspiralandirregulargalaxies).Usingthelocalgalaxy availableforstudyinthisway. M
a
density as an independent variable to study this effect, Dressler The Sydney-AAO Multi-object Integral field spectrograph rc
h
(1980)foundaverycleartrendwithdensity,suchthatthepopula- (SAMI; Croom et al. 2012) is one such multi-object IFS. SAMI 2
0
tionfractionofETGsincreased,withacorrespondingdecreasein was commissioned at the Anglo-Australian Telescope (AAT) in 23
theLTGfraction,athigherlocaldensity.Thisisthemorphology– 2011andcomprises13fibrebundleintegralfieldunits(IFUs)de-
density relation. Crucially, this relation was found to hold for all ployable across a 1◦ diameter field of view. SAMI can target 13
typesofclustersstudied–hightolowmass,regularandirregular, galaxiesinasingleobservation(ormoreusually12galaxiesand
andsomestrongX-raysources. one calibration star), significantly decreasing the amount of time
TheimportanceofenvironmentintheformationofFRsandSRs neededtobuildalargesampleofgalaxieswithIFSdata.Alarge-
has been investigated in several recent studies. Cappellari et al. scalegalaxysurveyusingSAMIiscurrentlyunderway(theSAMI
(2011),usingtheATLAS3Dsampleof260ETGsina42Mpcvol- GalaxySurvey1)withmanyscientificaimssurroundingthenature
ume,showedthatthefractionofSRsintheiroverallparentgalaxy ofgalaxyformationandevolution.
sample(includingETGsandLTGs),increasessharplyinthecentre TheSAMIPilotSurveyisaprecursortotheSAMIGalaxySurvey,
of the Virgo cluster. Analogous to the morphology–density rela- comprisingobservationsofthreegalaxyclusters,Abell85,168and
tion,thisisknownasthekinematicmorphology–densityrelation. 2399.TheSAMIPilotSurveywascarriedoutinordertoanswer
TheincreaseinthefractionofSRsatthecentreoftheVirgocluster
suggeststhatSRsmaybeformedmoreefficientlyindenserenviron-
ments.D’Eugenioetal.(2013)followedthisworkbyinvestigating 1http://sami-survey.org
MNRAS443,485–503(2014)
SAMIkinematicmorphology–density relation 487
Table1. InformationaboutthethreeclustersobservedaspartoftheSAMIPilotSurvey.Notethatthethreeclustershave
arangeinmassandX-rayluminosity(columns5and6).TheX-rayluminositiesarefromPiffarettietal.(2011).Roughly
halftheobservedsampleispartoftheAbell2399selectionandthisistheonlyclustersamplewithcontaminationfrom
non-memberETGs.
Cluster RA(J2000) Dec.(J2000) Redshift M200virial LX,500 Numberof Numberof
(×1014M(cid:5)) (×1044ergs−1) ETGs clusterETGs
Abell85 10.46021 −9.30318 0.0549 11.9±1.4 5.10 28 28
Abell168 18.73997 0.40807 0.0451 2.4±0.3 0.47 12 12
Abell2399 329.38949 −7.79424 0.0583 5.3±0.7 0.45 39 33
All – – – – – 79 73
some of the specific questions about ETGs in clusters mentioned coveredbythebluearmofAAOmega.Wethereforeanalyseonly D
o
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above.Thispaperfocussesononeaspectofthis,investigatingthe thebluearmSAMIdata. n
kinematicmorphology–densityrelationinthethreeclusters.This loa
d
workalmostdoublesthenumberofclusterspreviouslyexamined e
d
inthisway. 2.1.1 TheSAMIPilotSurveyETGs fro
andThHr0ou=gh7o0uktmwse−a1dMopptc−a1.cosmology with (cid:4)m=0.3, (cid:4)(cid:5) = 0.7 TSAheMoIbPseilrovtaStiuornvseyp,reasesmntaeldlear,nmdoarnealtyarsgeedteidnpthreiscuwrsoorrktofotrhmeftuhlel m http
s
SAMI Galaxy Survey. The SAMI Pilot Survey was focused on ://a
observationsofgalaxiesinclusterenvironments. c
a
2 OBSERVATIONS AND DATA Aparentsampleofclusterswasidentifiedfromthecatalogueof de
We use data from SAMI on the AAT, along with archival data Wangetal.(2011),constrainedtohavez<0.06andtobeobservable mic
attheAAT (i.e.Dec. <10◦).Galaxies werethenincludedinthe .o
from the Sloan Digital Sky Survey (SDSS) and the Chandra and u
XMM–Newtontelescopes. sample if they were within 1◦ radius of the cluster centre and a p.c
redshiftrangeof0.025<z<0.085andhadMr <−20.25.This om
selectionincludesforegroundandbackgroundobjectsinthegalaxy /m
n
sampleforeachcluster.Sevenclusterswereincludedintheparent ra
2.1 SAMIData s
sampleandthreeofthesewereobserved:Abell85,168and2399. /a
SAMI(Croometal.2012)isamulti-objectintegralfieldspectro- Table1givessomedetailsabouteachofthethreeclusters. rtic
le
graph mounted at the prime focus of the AAT. SAMI’s 13 IFUs FortheSAMIPilotSurveyatotalof14galaxyfieldswereob- /4
4
(called hexabundles, Bland-Hawthorn et al. 2011; Bryant et al. servedon10nightsacrosstwoseparaterunsin2012Septemberand 3
2011, 2014) are deployable across the 1◦ diameter field of view October.Duetohardwareproblemswhichhavesincebeensolved, /1/4
provided by the AAT triplet corrector. Each hexabundle subtends weusedonlyninehexabundlesperfield,observingeightgalaxies 85
∼15arcsecindiameteronthesky,andcomprises61individualfi- andonecalibrationstarineach.Weobservedatotalof112galax- /14
8
breseachwithacorediameterof1.6arcsec.Thecircularfibresare ies. However, data for six of the galaxies proved to be unusable 7
5
arrangedinacircularpattern,soinevitablythespatialcoverageof duetoastrometricerrorsduringtheSeptember2012 run.Thefinal 24
ahexabundleisnotcontiguous.However,theSAMIhexabundles observedsamplecontains106galaxies,ofallmorphologicaltypes, by
have a high fill factor, with a mean of 73 percent. As well as 13 inthreeclusterfields. gu
e
hexabundles, SAMI also has 26 individual sky fibres, deployable For this work, we are primarily interested in the ETGs so be- s
acrossthefieldofview.Thisenablesaccurateskysubtractionfor fore performing our analysis we morphologically classified each t on
allIFUobservationswithouttheneedtoobserveseparateblanksky galaxybyeye.Thepurposeofthisstepisnottogeneratedetailed 10
frames.SinceanindividualSAMIfibreundersamplestheseeingat classificationsbutonlytorejectspiralandirregulargalaxiesfrom M
a
SidingSpring(1.9–3.0arcsecduringourobservations)weadopta oursample.Forthatreason,ourclassificationsystemcontainsonly rc
h
ditheringstrategytoregainspatialresolutioninourfinalcombined twocategories,ETGsandLTGs.WedefineanETGtobeagalaxy 2
0
datacubes. whichhasasmoothandsymmetriclightprofileanddoesnotexhibit 23
From the AAT prime focus unit, SAMI’s 819 fibres (includ- spiral structure. We attempt to match the ATLAS3D classification
ing both the hexabundle fibres and the dedicated sky fibres) feed criteriaasmuchaspossible,butthisisinevitablyimperfectsince
the double-beamed AAOmega spectrograph (Sharp et al. 2006). oursampleismuchmoredistant.WeusedSDSSDR8r-bandim-
AAOmega is a fully configurable spectrograph with multiple ages,consultingSDSScolour(gri)imagesinborderlinecases.All
dichroicsanddiffractiongratingstochoosefrom.Thestandardcon- galaxies with obvious spiral arms were excluded but if a galaxy
figurationforSAMIusesthe580Vgratinginthebluearm,giving wasborderlineitwasincludedinthesample.Thisyielded79ETGs
R ∼ 1700 over the wavelength range 3700–5700 Å. This config- and27LTGsinoursampleof106galaxies.Wefocusonlyonthe
uration was chosen to cover a broad range of important stellar ETGsinthispaper,andwilldealwiththeLTGsinFogartyetal.,in
absorptionfeatures,includingtheCaII H+K,Hβ andMgblinesin preparation(hereafterPaperI).
galaxiesuptoaredshiftof0.1.IntheredarmSAMIusesthe1000R ThefinalsampleofETGsincludesfivegalaxieswhicharenot
grating,givingR∼4500overthewavelengthrange6250–7350Å. cluster members, but foreground or background interlopers. The
This configuration was chosen to allow high-resolution observa- criteria by which we allocate cluster members is discussed in
tionsoftheHα and[NII] emissionlinecomplex.Forthiswork Section 3.3. The five non-members in our sample are included
weareprimarilyinterestedinfittingthestellarabsorptionfeatures in our analysis, but left out of any cluster-related statistics or
MNRAS443,485–503(2014)
488 L.M.R.Fogartyetal.
measurements. This leaves us with a sample of 74 cluster mem- spectraarealsopropagatedthroughthisprocess.Thisprocessyields
berETGs.ThedistributionoftheETGsbyclusterissummarized two data cubes for each galaxy, one each for the blue and red
inTable1. spectrographarms,alongwithtwocorrespondingvariancecubes.
Itisimportanttonotethatthisresamplingschemegeneratesdata
and variance cubes in which individual spaxels are not indepen-
2.1.2 SAMIdatareduction
dent.Theindividualvariancespectragivethecorrectuncertainties
ThedatareductionprocedurefortheSAMIGalaxySurveyisde- forindividualdataspectra,butsincelightfromasingleobserved
scribedindetailintwoforthcomingpapersAllenetal.,inprepara- spectrum may contribute to more than one output spectrum, the
tionandSharpetal.,inpreparation.ThedatafromtheSAMIPilot uncertaintiesinadjacentoutputspaxelsarecorrelated.Thishasim-
Survey are similar but not identical to the SAMI Galaxy Survey plications when measuring uncertainties on integrated properties
data.Wefollowthesamedatareductionprocedureforbothcam- (such as λ ) or when calculating the true variance on composite
R
paigns except when performing telluric correction (which is not spectraformedbysummingtwoormoredifferentspaxels.Inasin-
relevant for this work, which is confined to the blue SAMI data glewavelengthslice,eachspaxeliscorrelatedwithsomenumber
cubes) and with one minor difference when combining dithers to ofitsnearestneighbours.Thestrengthofthiscorrelationdepends
D
createthefinaldatacubes.Theprocedureisdescribedindetailin onthepositionoftheoriginalfibresinrelationtotheoutputspaxel o
w
the two papers mentioned above and is therefore described only grid.Thecorrelationinformationforeachspaxelisrecordedfora n
lo
brieflybelow. 5×5gridofitssurroundingspaxelsonly.Thisinformationiscar- a
d
AllSAMIdataarereducedfromrawfilestorow-stackedspec- riedforeachspaxelineachwavelengthslice,yieldingathirdsetof ed
trum(RSS)formatusingthe2DFDR datareductionpackage(Sharp ‘cubes’(thesehavetwoextradimensionscoveringthe5×5grid) fro
m
&Birchall2010).2DFDR wasinitiallywrittentoprocessdatafrom of correlation information for each galaxy. These cubes must be h
the2dFspectrographandhasbeenupdatedtoprocessallAAOmega multipliedbythevarianceinthespaxel(s)ofinteresttoreconstruct ttp
s
data, including SAMI data. 2DFDR performs bias subtraction and the true variance. For example, consider the case where we wish ://a
pixel-to-pixelflat-fieldingbeforeextractingindividualfibrespectra to sum the spectra in two neighbouring spaxels and estimate the c
a
fromarawframe.Theextractedspectraarethenwavelengthcal- trueuncertainlyintheresultingspectrum.Wemustfirstisolatethe de
ibrated,skysubtractedandcorrectedforfibre-to-fibrethroughput spaxelsofinterestinbothrelevant5×5correlationfactorgrids, mic
variations,beforebeingreformattedintoanRSSfile,consistingof multiplybytheappropriatevariancespectraandthensumtheresult .o
u
all819extractedSAMIspectra.Varianceinformationisalsoprop- inordertoreconstructthecomplete,truevariancespectrum(includ- p.c
o
agatedby2DFDR sooutputfibrespectraeachhavecorresponding ingthecovariancebetweencontributingspaxels)appropriatetothe m
variancespectra.AftertheRSSfilesareproducedanobservation newcompositespectrum. /m
n
ofaspectrophotometricstandardstarisusedforfluxcalibration.A Themethodweusetoaccountforthiseffectwhenwecalculate ra
sfieepldariasteusceadlibtoractioornrescttarf,orobteslelruvreicdaabtstohreptsiaomn.eFtoimrteheasStAheMgIaPlailxoyt theuncertaintyinλRisdetailedinSection5. s/artic
le
Surveythecalibrationstarhadlow-qualitydataandsothesedata /4
2.2 Archivaldata 4
were treated differently to the data in the SAMI Galaxy Survey. 3
/1
However,thisisnotrelevanttotheresultspresentedinthispaper 2.2.1 X-rayimaging /4
asthetelluriccorrectionaffectstheredarmdatacubesonlyandso 85
adescriptionisomittedhere. BothAbell85and168haveextensiveX-raydataavailableinthe /14
8
SincetheSAMIhexabundleshavenon-uniformspatialcoverage, Chandra archives. The data for Abell 85 consists of nine point- 7
5
all galaxy fields are observed multiple times with a small dither ingsusingtheACIS-Ichiparray:one∼38ksexposurecentredon 24
betweenexposures.Thepurposeofthisobservingstrategyistofillin theBCG(ObsID904;Kempner,Sarazin&Ricker2002)andeight by
thegapsbetweenfibresandregainspatialresolution.FortheSAMI ∼10ksexposuresintheperipheralclusterregions(ObsIDs4881, gu
e
GalaxySurveyafixedseven-pointhexagonalditherpatternwithan 4882,4883,4884,4885,4886,4887,4888;Sivakoffetal.2008). s
offsetof60percentofacorediameterbetweendithersisused(see For Abell 168, there are two ACIS-I Chandra observations with t on
Sharpetal.,inpreparationfordetails).However,duringtheSAMI ∼37 and ∼40ks exposures (ObsIDs 3203 and 3204; Hallman & 10
Pilot Survey the dither pattern was not set and the step between Markevitch 2004). The Chandra data were reprocessed using the M
a
dithers was larger. This impacts the chosen ‘drizzle’ parameters CHANDRA_REPROscriptwithintheCIAOsoftwarepackage(ver- rch
applied to this data set which do not match those chosen for the sion4.4;Fruscioneetal.2006).Thescriptappliesthelatestcali- 2
0
SAMIGalaxySurvey. brationstothedata(CALDB4.5.1),createsanobservation-specific 23
Oncetheflux-calibratedRSSframes(containingbothdataand badpixelfilebyidentifyinghotpixelsandeventsassociatedwith
variancespectra)foreachditherareinhand,thesearecombinedto cosmicrays(utilizingVFAINTobservationmodewhereavailable),
formdataandvariancecubesforeachgalaxyintheobservedfield. andfilterstheeventlisttoincludeonlyeventswithASCAgrades0,
ThisstepisperformedusingcustomPYTHONcodedevelopedbythe 2,3,4,and6.TheDEFLAREscriptisthenusedtoidentifyperiods
SAMIGalaxySurveyteamandthereaderisreferredtoSharpetal., contaminated by background flares. No significant contamination
inpreparationforadetaileddiscussionofhowthisisachieved.In was found in either data set. For the imaging analyses, exposure
short,theroundSAMIfibres(1.6arcsecdiameter)areresampled mapswhichaccountfortheeffectsofvignetting,quantumefficiency
on to a regular grid of square output spaxels using an algorithm (QE),QEnon-uniformity,badpixels,dithering,andeffectivearea
similartoDrizzle(Fruchter&Hook2002).Thefibresareshrunk wereproducedusingstandardCIAOprocedures.2Theenergydepen-
by some user-chosen drop factor and ‘drizzled’ on to the regular denceoftheeffectiveareaisaccountedforbycomputingaweighted
outputgrid.FortheSAMIPilotSurveythedropfactoris0.75and instrument map with the SHERPA make instmap weights script
theoutputspaxelsare0.5arcseconeachside.Allditherpositionsare
resampledinthiswayandcombinedateachwavelengthslice,with
a correction for differential atmospheric refraction. The variance 2cxc.harvard.edu/ciao/threads/expmap_acis_multi/
MNRAS443,485–503(2014)
SAMIkinematicmorphology–density relation 489
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o
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Figure1. ThestellarkinematicmapsforJ004001.68−095252.5,amemberofAbell85.ThemapswerederivedusingpPXF(Cappellari&Emsellem2004) n
lo
usingthe985MILESstellartemplates(Sa´nchez-Bla´zquezetal.2006)asreferencespectra.Thetoprowshows,fromlefttoright,summedfluxinarbitrary a
units,Vinkms−1andσ inkms−1.Thebottomrowshows,lefttoright,S/Nmeasuredacross200wavelengthslicesofthedatacube,uncertaintyonVin de
d
kms−1anduncertaintyinσ inkms−1.TheblackcontoursindicatemeasuredfluxfromtheSAMIcube,i.e.thatshowninthetop-leftpanel.Eachpanelis fro
10arcseconaside.Theivorycolouredellipserepresentsoneeffectiveradius. m
h
ttp
usinganabsorbedMEKALspectralmodelwithtemperature,abun- classify our sample. The r-band postage stamps are also used to s
dance and neutral hydrogen density appropriate for each clus- derive photometric parameters, such as effective radius, for each ://a
c
a
ter. Background subtraction was performed using the blank sky object.TheprocedurefollowedisdescribedinSection3.2. d
e
backgrounds3,4 which were processed in the same manner as the Inaddition,three-colourmosaicswerecreatedfromSDSSDR7 m
ic
observations.Theblankskybackgroundswerereprojectedtomatch griimagesofeachclusterusingMONTAGE.Themosaicscoverthe .o
u
thetangentpointoftheobservations,andwerenormalizedtomatch centralpartsofeachclusterandarepresentedinSection6. p
.c
the9–12keVcountsintheobservations.Thisyieldedclean,cali- o
m
bratedX-rayimagesforAbell85and168. /m
Abell 2399 has three archival XMM–Newton observations 3 DERIVED PARAMETERS nra
(ObsIDs0201902801,0404910701and0654440101).Here,weuse s
/a
onlythe2010June(0654440101)observationasithasthelongest 3.1 Stellarkinematics rtic
exposure(∼93ks).TherawdataareprocessedfollowingtheXMM– le
We fit stellar kinematic fields for each of our 79 ETGs using the /4
NewtonExtendedSourceAnalysisSoftware(XMM-ESAS)package5 penalizedpixel-fittingroutine,pPXF,createdbyCappellari&Em- 43
(seealsoSnowdenetal.2008)withintheScienceAnalysisSystem /1
(SAS).6ThetasksemchainandepchainarerunontheMetalOxide stoellfietmst(e2l0la0r4t)e.mpPpXlaFteusspeescatrpaencoalnivzoedlvmedaxwimithumanliakpeplirhoopordiamteeltihnoed- /485
Semi-conductor(MOS)andPNdatatoproduceeventlistsfilteredof of-sightvelocitydistribution(LOSVD)toobservedgalaxyspectra. /14
badpixelsandwiththelatestcalibrationsapplied.Thepn-filterand 8
TheLOSVDisparametrizedbyatruncatedGauss–Hermiteexpan- 7
5
mos-filtertasksareusedtoidentifyandremoveperiodsofincreased sion,allowinghigherordersoftheLOSVDtobefit,beyondvelocity 24
backgroundduetoflareactivity.Thedataweremoderatelyaffected (V)andvelocitydispersion(σ).HerewefitfourLOSVDmoments: by
bthyeflMaOreSs1a,nMdOthSe2calenadnPeNdedxepteocstuorres,triemsepsecatrieve5ly4.,I6m0aagnedsa2n6dkesxpfoo-r V,σ,h3andh4,thoughinpracticeweuseonlythefirsttwoofthese gue
forouranalysis.Weusethe985MILES(Sa´nchez-Bla´zquezetal. s
suremapsweregeneratedbythemos-spectraandpn-spectratasks 2006)stellartemplatesasreferencespectra. t on
usingthecleanedeventlistsinthe0.4–1.25keVand2.0–7.2keV For each of our galaxies the procedure is as follows. First a 10
bands(toavoidthestronginstrumentallines).Correspondingmaps highsignal-to-noiseratio(S/N)spectrumisextractedfromtheblue M
a
ofthequiescentparticlebackgroundwereproducedwiththemos- data cube in a 2 arcsec circular aperture centred on the galaxy. rc
backandpn-backtasks.Thesebackgroundmapsarerecasttothe The pPXF routine is run on this spectrum to find the best-fitting h 2
source image coordinates using the rot-img-det-sky task. Source, templates for that galaxy. This reduced set of templates are then 023
backgroundandexposureimagesforallbandsanddetectorswere
fit to individual spaxels within the data cube, with the weights
combinedwiththecombtask,yieldingafinalX-rayimageofAbell
giventoeachtemplateallowedtovary.Anadditionalfourth-order
2399.TheresultingX-rayimagesarediscussedinSection6.
polynomial was fitted with the templates in order to account for
anyresidualfluxcalibrationerrorsinourSAMIdata.Onlyspaxels
2.2.2 SDSSopticalimaging for which the S/N was greater than 5 per spectral pixel were fit.
ThisproducesmapsofV,σ,h andh foreachgalaxy,alongwith
3 4
AsdiscussedinSection2.1.1,weuseSDSSDR8r-bandpostage maps of the uncertainties on these quantities. The uncertainties
stamps and gri colour images of each galaxy to morphologically calculatedfromthepPXFfitsarecorrectforindividualspaxelsbut
arecorrelatedwithadjacentspaxels,aneffectwhichimpactsany
integratedparametersderivedfromthekinematicmaps.
3cxc.harvard.edu/contrib/maxim/acisbg/
4cxc.harvard.edu/caldb/downloads/Release_notes/supporting/ An example set of kinematic maps for J004001.68−095252.5,
README_ACIS_BKGRND_GROUPF.txt amemberofAbell85,areshowninFig.1.Thetopthreepanels
5ftp://xmm.esac.esa.int/pub/xmm-esas/xmm-esas.pdf show the flux, V and σ maps generated by pPXF. The bottom-
6http://xmm.esac.esa.int/sas/ leftpanelshowsanS/Nmapandthebottom-centreandright-hand
MNRAS443,485–503(2014)
490 L.M.R.Fogartyetal.
panelsshowtheuncertaintiesonVandσ,respectively(eachpanelis (cid:10)v , which is taken to be the velocity dispersion within the
thresh
10arcseconaside).Kinematicmapsforallgalaxiesinthesample, annularbinofinterest.Thislocalvelocitydispersionisestimated
includingthe27LTGs,willbepresentedinPaperI. fromthemedianabsolutedeviationwhichisarobust,outlierresis-
tantmeasureofthescaleofadistribution(Beers,Flynn&Gebhardt
1990).Galaxieswhichhavegapvaluesexceeding(cid:10)v ,aswell
3.2 Photometricfitting thresh
ashaving|v |>σ ,whereσ istheclustervelocitydispersion,
pec v v
We derive several photometric parameters for each galaxy in our marktheouterlimitsoftheclusterintheannularradialbinofin-
sampleusingtheSDSSDR8r-bandimages.Fortheanalysispre- terest. Galaxies with larger velocities are removed as interlopers.
sentedhereweareparticularlyinterestedinaccuratevaluesforthe Theprocedureisiterateduntilthenumberofmembersstabilizes.
effectiveradius,R ,andtheellipticity((cid:9))andpositionangle(PA) Galaxiesidentifiedasnon-membersusingthismethodareshown
e
foreachgalaxy. inFig.2asblackopensquares.
UsingtheapproachdescribedinCappellarietal.(2007)wecon- Inafewcases,structurewhichisnearbyinredshift,butisun-
structaMultiGaussianExpansion(MGE)model(Emsellem,Mon- likelytobewithinthecluster,causestheshifting-gappermethodto
net&Bacon1994)ofthesurfacebrightnessprofilefromtheSDSS fail(e.g.,inFig.2,∼2.8MpcfromtheBCGinA2399).Toaddress
D
image of each galaxy. The surface brightness profile is described this,weusetheadaptivelysmootheddistributionofgalaxiesinv – o
pec w
as the sum of a set of two-dimensional Gaussians with varying radiusspacetolocatetheclustercaustics(Diaferioetal.1999).The n
lo
normalization,widthandaxialratio.Thisformalismisextremely caustics,shownasgreensolidlinesinFig.2,tracetheescapeveloc- a
d
flexibleandprovidesagooddescriptionofthesurfacebrightness ityoftheclusterasafunctionofcluster-centricradiusand,therefore, ed
profilesofawidevarietyofgalaxymorphologies(Scottetal.2013). robustlyidentifytheboundaryinvpec radiusspacebetweenbona- from
FromtheMGEmodelwedeterminetheeffectiveradiusfollowing fide cluster members and line-of-sight interlopers (e.g. Serra & h
themethodofCappellarietal.(2009).TheMGEmodeliscircular- Diaferio2013;Owersetal.2013).Twomeasuresoftheuncertainty ttp
s
ipzreeds,ersveitntigngthtehepeaaxkiaslurraftaiocesobfriegahcthneGssauosfseiaanchcocmompopnoennetntto,t1hewnhtihlee odansthh–edocattuesdtilcinbeoiunnFdiagr.y2,arisetmheeaasnuarleydti.caTlhaeppfirrostx,imshaotwionnatostahebl1uσe ://ac
a
radiuswhichenclosesexactlyhalfthetotalluminosityofthemodel uncertaintyandismeasuredasdescribedbyDiaferioetal.(1999). de
m
isdeterminedbyinterpolatingoveragridofradialvalues. Thesecond,shownasreddashedlinesinFig.2showsthe68thper- ic
WedetermineellipticityandPAprofilesdirectlyfromtheSDSS centilelimitsderivedfromadistributionofcausticmeasurements .o
u
imagesusingtheIDLroutinefind_galaxy.pro(Krajnovic´etal.2011). determinedfrom1000boostrapresamplingsoftheclustermember p.c
o
The ellipticity and PA at a given radius are determined from the phase-spacedistribution.Onlygalaxieswhichliewithintheouter m
second moments of the luminosity distribution of all connected 68thpercentilelimitareretainedinthefinalclustermembersam- /m
n
pixels above a given flux level. For example, (cid:9)e and PAe are the ple.Thosegalaxiesrejectedusingthismethodareshownasblack ras
values of the ellipticity and PA determined at the isophote that opencirclesinFig.2.Usingthesample√ofspectroscopicallycon- /a
enclosesanareaequaltoπRe2. firmed cluster members within R200 (cid:6) (3)σv/10H(z), the virial rticle
masseslistedinTable1weredeterminedusingthemethodoutlined /4
4
inOwersetal.(2009). 3
3.3 Clustermembership /1
/4
Tclousstteurdsyinthoeurdsiasmtripbluet,iwonemofukstineenmsuarteicwmeohrapvheoalnogaicecsurfaotretdheetetrhmreie- 3.4 Galaxyenvironment 85/14
8
nationofclustermembershipforall79ETGs.Ifwedonotreliably In any discussion of the influence or importance of galaxy en- 7
5
determinewhichgalaxiesareclustermemberswewillbiasouranal- vironment one must first think carefully about the meaning and 24
ysisbyincludingline-of-sightinterlopers.Thethreeclustersfrom quantificationof‘environment’.Hereweconsidertwotypesof‘en- by
theSAMIPilotSurveyareincludedintheSAMIClusterRedshift vironment’.FollowingHoughtonetal.(2013)wedefinetheGHE gu
e
Survey(Owersetal.,inpreparation).Thesurveywascarriedout torefertotheglobalenvironmentofagalaxy–i.e.doesitresidein s
usingthe2dF/AAOmegamulti-objectfibrespectrograph,capable acluster,group,orinthefield?Anotherconsiderationhereisthe t on
of targeting ∼392 galaxies in one exposure. The survey provides overallmassanddensityofindividualclusterswhencomparedto 10
deeper spectroscopy and therefore greater completeness than that oneanother. M
a
availablefromSDSS.Therefore,weusethecataloguederivedfrom WealsousetheLPEasperHoughtonetal.(2013)tomeanthe rc
h
theSAMIClusterRedshiftSurveytodetermineclustermembership localprojectedsurfacedensityatthepositionofagalaxy. Inthis 2
0
foroursample. paper,wewillfocusmoreonthismeasureofenvironment,sincethe 23
Theallocationofclustermembersisaniterativeprocesswhich GHEforallofourgalaxiesissimilar–theyallresideinclusters,
willbedescribedindetailinaforthcomingpaper(Owersetal.,in albeitoneswithdifferingoverallclusterproperties.
preparation).Briefly,aninitialcullofnon-membersisachievedby These two definitions are helpful when considering the overall
rejecting those galaxies which have |v | < 5000km s−1, where positionofindividualgalaxies.Asanexample,dogalaxieswiththe
pec
v isthepeculiarvelocitymeasuredwithrespecttotheredshift samemeasuredprojectedenvironment(i.e.LPE)behavethesame
pec
oftheBCG.Followingthisinitialrejection,theprocessentersan regardless of whether they are central in a group GHE or on the
iterative phase where a modified version of the ‘shifting-gapper’ outskirtsofaclusterGHE?Thisquestionisbeyondthescopeofthis
method(Faddaetal.1996;Owersetal.2009)isusedtorefinethe paperbutitconciselyillustratestheneedtothinkof‘environment’
membershipselection.Thegalaxiesaresortedbyprojecteddistance inseveralcomplexandpossiblyinterdependentways.
fromtheBCGandsplitintoannularradialbins.Thewidthofthe
annularbinsissetsuchthateachbincontains40-50galaxies.Within
3.4.1 Localpointenvironmentmeasurements
eachradialbin,thegalaxiesaresortedbyv ,andthevelocitygap,
pec
(cid:10)v , between consecutive galaxies is determined. The distribu- Wederiveavalueforthenearest-neighboursurfacedensities((cid:11) )
pec N
tionof(cid:10)v issearchedforvalueswhichexceedathresholdvalue, forallgalaxiesintheSDSSStripe82observationsthatcoverthese
pec
MNRAS443,485–503(2014)
SAMIkinematicmorphology–density relation 491
clusters. The surface density is defined using the projected co-
movingdistancetotheNthnearestneighbour(d )withvelocity=
N
±2000kms−1withinavolumelimiteddensity-definingpopulation:
(cid:11)N =N/πdN2.Thedensity-definingpopulationhasabsoluteSDSS
Petrosian magnitudes M < M − Qz, k-corrected to z = 0,
r r,limit
whereM =−19.0magandQdefinestheexpectedevolution
r,limit
of M as a function of redshift (Q = 0.87; Loveday et al. 2012).
r
WethencalculatedensitiesforN=3,5and10.Toaidcomparison
with ATLAS3D we have used the same N, velocity and absolute
magnitudelimits.
4 KINEMATIC CLASSIFICATION
D
We wish to classify our sample of 79 ETGs as SR/FR. In this ow
section, we examine several methods of kinematic classification, nlo
a
bothquantitativeandqualitative. d
e
d
fro
m
h
4.1 Apertureeffects ttp
s
dTeorqivueadntkiitnateimvealtyicclmasaspisfy.λouringaalpaxroiexsywfoerfitrhsetlmumeaisnuorseitλyR-wfreoimghoteudr ://aca
R d
specificstellarangularmomentumforeachgalaxywithinafiducial em
radiusandisdefinedasfollows(Emsellemetal.2007): ic
.o
u
λR ≡ (cid:9)R√(cid:9)RV|2V+|(cid:10)σ2(cid:10) = (cid:11)iN=(cid:11)0FiN=iR0Fi(cid:2)iRVi|iV2i+| σi2, (1) p.com/m
n
whereFi,Ri,Vi,σi aretheflux,radius,velocityandvelocitydis- ras
persionoftheithofNspaxelsincludedinthesum. /a
ReI,dfeoarllayl,lw7e9wEoTuGldsliikneotuormseaamspulree.λARlwthiothuignhthoeurefsfaemctpivleercaodvieurss, rticle/4
a range in angular size, the majority of galaxies have 2arcsec≤ 43
Re≤7arcsec and fit comfortably within the SAMI hexabundles /1/4
withsufficientspatialresolution.Forthese70objectswecalculate 85
λRTwhiethsiinxRlae.rgest galaxies in the sample have R >7 arcsec and /1487
e 5
RoSvueer/vr2fielyilnssthatemeaSpdAl.eEM,mthIsahetelilxteaimsbrueantrdealfle.os(r.2Fa0og0ra7lt)ahxeshyseotwoobecjdhe,acnutsgsiewnigetsmthcleeaasSssuAifirUecRaλtORioNant 24 by gu
basedonλ betweenR /2andR . es
ConverseRly, three gaelaxies in oeur sample are quite small, such t on
IthnatthRiseccaosev,earsmoenalysuorenmeeonrttowfoλinwdeitpheinndRentwreilslobluetiboinaseeldemtoelnotws. 10 M
R e a
values.Thisisbecauseavelocitygradientacrossasingleresolution rc
h
elementwillbeunresolvedandmeasuredasdispersion.Toavoid 2
0
thiseffect,wemeasureλR within2Re forthethreegalaxieswith 23
R <2arcsec.Unlikemeasurementsofλ withinR /2andR ,the
e R e e
propertiesofthisparameterhavenotbeenfullyinvestigatedatlarge
Figure2. Thephase-spacedistributionofgalaxiesineachofthethreeclus- radii. However, the compact galaxies in our sample display very
tersintheSAMIPilotSurvey.Thefilledcirclesshowthespectroscopically orderlyvelocitymapsandgoodS/Nouttolargeradii.Theyareall
confirmedclustermembers.Theblackopensquaresshowthenon-members veryclearFRswithnoambiguityintheirclassifications,sowefeel
identifiedbytheshifting-gappermethod.Theblackopencirclesshowthe justifiedinextendingtheλ measurementsoftheseobjectsto2R .
R e
non-membersidentifiedasbeingbeyondthelimitsdefinedbythevelocity
Despitethefactthatweusethreefiducialradiiforoursample,
caustics(greensolidline).Thereddashedlineshowsthe68thpercentile
Fig. 3 clearly demonstrates that for our purposes this does not
uncertaintiesonthecaustics.Thebluedot–dashedlineshowsthestandard
influence our classifications. The galaxies with λ measurements
analyticestimateoftheuncertaintyinthecausticmeasurement.Thelarger R
withinasmaller(R /2)andlarger(2R )radiithanoriginallyused
blueandredcircularpoints(bothopenandclosed)aretheETGsobservedin e e
theSAMIPilotSurvey,withcoloursindicatingtheirkinematicclassification todefinetheclassificationsystemareallunambiguouslypositioned
(seeSection4).TheverticaldashedblacklinesshowR200andthevertical inλR−(cid:9)space.Thatistosaytheyfallawayfromthedividingline
reddottedlinesshowtheSAMIfieldofview. andthereisnodoubtthatthesystemadoptedhereworkswellfor
thissample.
MNRAS443,485–503(2014)
492 L.M.R.Fogartyetal.
D
o
w
n
lo
a
d
e
d
Figure3. λR plottedagainst(cid:9)forall79ETGsintheSAMIPilotSurveysample.Theleft-handpanelshowsthosegalaxiesclassifiedatRe/2,themiddle from
showsthoseclassifiedatReandtheright-handpanelshowsthoseclassifiedat2Re.InallpanelstheblacklineshowsthedivisionbetweenFRsandSRsas h
definedbyequation(2).ThebluepointsareFRsandtheredareSRs.ThesquareturquoisecolouredpointinthecentrepanelisJ215634.45−075217.5.This ttp
s
isadoublesigmagalaxy(notatrueSR)andisdiscussedinSection4.3. ://a
c
a
d
e
4.2 ClassificationusingλR mic
.o
Themeasuredflux,Vandσmapsareusedtocalculateλ parameter u
R p
attheappropriatefiducialradiusforeachgalaxy.Thecalculation .co
usestheR ,(cid:9) andPAmeasurementsfromtheMGEfitsdescribed m
e /m
inSection3.2.The(cid:9)andPAvaluesusedarethosemeasuredatthe n
correctfiducialradiusforeachgalaxy.Theresultsarepresentedin ras
/a
TabTloedAis1c.riminatebetweenFRsandSRsweusetheλR−(cid:9) space. rticle
SincewehaveusedthreefiducialradiitomeasureλRforoursample, /44
3
weneedthreedifferentcriteriatodivideFRsandSRs.Weusethe /1
criteriondefinedbyEmsellemetal.(2011),whichisdependenton /4
8
5
ellipticity: /1
√ 48
λR <k (cid:9), (2) 75
2
4
wgahlaexreyλaRnadntdhe(cid:9)avraelumeeoafsukreidswdeitpheinndtehnetsoanmethfiedcuhcoiaicleraodfiufisdinuctihael by gu
e
radiusforaparticulargalaxy.Assumingalinearscalingfromthe s
aavndaldoup2etsRko,=frke0sa.pt2eR6c5et/i,v2kela=yn.d0R.3e10puabnldish0e.3d6i3nfEomrvsealllueemsoetfakl.a(t2R01e/12),,wRee FlJi2nig1eu5s6rie3n4d4.i.4c5aTt−eh0eF7Rr5as2d1iaa7nl.dp5r,thotefihelreedsdoolufibnλleResfsionigrdmaiclalat7ge9aSlEaRxTsyG.dTsihisnecuobsulsarecsdkamilninpSeleeh.ciTtgihohenlibg4lh.u3tes. t on 10 M
e a
Fig.3showsλR−(cid:9)forall79ETGsintheSAMIPilotSurvey.The The x-axis shows galaxy radius in units of effective radius, Re, clearly rch
threepanelscorrespondtothethreefiducialradiiusedtomeasureλ illustratingthedifferingspatialcoverageofourdata. 2
R 0
and(cid:9).Theleft-handpanelshowsthegalaxiesclassifiedatRe/2,the 23
centrepanelshowsthoseclassifiedatR andtheright-handpanel
e
showsthoseclassifiedat2R .Inallthreepanelstheblacksolidline
e
marksthedivisionbetweenFRsandSRs,suchthatSRsliebelow slowincreaseinλ .Thelattercouldbecausedbyincreasednoise
R
thelineandFRsaboveit.Thus,thebluepointsareclassifiedasFRs athigherradiiwhichcanbiasmeasurementsofλ tolargervalues.
R
andtheredasSRs. Inoursamplearangeofprofileshapescanbeseen,withnoclear
Wealsocalculateresolvedradialprofilesofλ foreachgalaxy. gap between the two populations of objects. The SRs tend have
R
TheseareshowninFig.4whereFRsareshowninblueandSRs shallowerslopesthantheFRsbutthereissomeclearoverlapinthe
inred,asclassifiedusingtheλR−(cid:9) space.Ofcourse,sinceλR is twoclassesofobjects.TheoverlapiscausedbythefactthatλRisa
aprojectedparameter,andtheradialprofiledoesnotincludeany projectedquantityandthereforeinformationabouttheellipticityof
information about the ellipticity of the galaxies, these profiles do individualgalaxiesisneededtofullyclassifythemasSRsorFRs.
notgivethewholepicture.However,theoverallshapesofprofiles Galaxiesinthisoverlapregionmayhavesimilarvaluesforλ at
R
can be helpful as a check on other methods of classification. We aparticularradiusbutdifferencesinellipticitywillmeantheycan
expect that for FRs λ will increase rapidly with radius, perhaps havedifferentkinematicclassifications.Thisillustratestheneedto
R
withaplateauatlargeradii.ForSRsweexpectadecreaseoravery considermorethanonemethodofkinematicclassificationofETGs.
MNRAS443,485–503(2014)
SAMIkinematicmorphology–density relation 493
Figure5. ThederivedstellarkinematicsforJ215634.45−075217.5,withpanelsasperthetoprowinFig.1.Eachpanelis10arcseconaside.Thisgalaxyisa
doublesigmagalaxy,thoughttoconsistoftworoughlyequalmasscounter-rotatingdiscs.Thecharacteristicdouble-peakedσ map(right-handpanel)betrays
thetruenatureofthisgalaxy.
4.3 Visualclassifications 5 ERROR ANALYSIS
D
WealsoclassifygalaxiesasFRsandSRsbasedonvisualinspec- AsdiscussedinSection2.1.2,SAMIdatacubesaregeneratedfrom o
w
tionofthekinematicfields.Severalauthorsexaminedthekinematic raw, dithered, fibre spectra using a drizzle-like algorithm (Sharp n
lo
mapsforall79ETGsinthesample.Thiswasdoneinisolationand etal.,inpreparation).Thisresultsindatacubesinwhichthespaxels ad
withoutpriorknowledgeoftheλR−(cid:9)classifications.Thekinematic arenotindependent:boththedataandnoiseareinasinglespaxel ed
mapsinspectedwereidenticaltothoseinthetoprowofFig.1.The are correlated with surrounding spaxels. The variance in a single fro
m
errormapswerenotprovided.Thevisualclassificationswerecar- spaxel is, by definition, correct for that spaxel. However, blindly h
ried out using a scheme of five classes designed to incorporate combiningspectraandtheircorrespondingvariancespectraneglects ttp
s
some uncertainty. The classifications were: definite FR, probable thecovariancebetweenspaxelsandresultsinanoverestimateofthe ://a
FR,unknown,probableSR,definiteSR.Theresultswerecollated S/Nforthecombinedspectrum.Thiscomplicatestheerroranalysis c
a
d
andcomparedafterallauthorscompletedtheirindividualclassifi- for integrated parameters derived from higher order SAMI data e
m
cations.Formostgalaxiesalloramajorityofauthorsagreeonthe products, such as kinematic maps. In this section, we discuss in ic
visual classification. In most of these cases the visual and λR−(cid:9) detailhowwedealwiththisproblem,particularlywithrespectto .ou
classificationsalsoagree. ourcalculationofλRandtheassociateduncertainty. p.c
IncaseswherethevisualandλR−(cid:9)classificationsdonotagree om
thegalaxyinquestionisusuallyclosetothedividinglineinλR−(cid:9) 5.1 Scaledkinematicuncertainties /mn
space.Forourstatisticalanalysis,weadopttheλR−(cid:9)classification ra
s
inallsuchcases,ofwhichthereareonlyahandful.However,there WeusepPXF(Cappellari&Emsellem2004)toderivethestellar /a
aresomegalaxiesofinterestforwhichitisusefultodiscussboth kinematicsfortheSAMIPilotSurveygalaxies(seeSection3.1and rtic
the quantitative λR−(cid:9) classifications and the contradicting visual Paper I). This produces spatially resolved maps of flux, V and σ le/4
4
classification.OnesuchgalaxyisdiscussedinSection6.4. along with corresponding uncertainty maps. As discussed above, 3
There is one clear misclassification using the λR−(cid:9) di- the error on any individual spaxel in these maps is correct (see /1/4
agram which is resolved using the visual classifications. Sharpetal.,inpreparationformoredetails),butcombiningthese 85
J215634.45−075217.5isclassifiedasanSRbutinhabitsaregion errors directly is invalid since this neglects covariance between /14
8
of the λR−(cid:9) not typically populated by true SRs. The kinemat- spaxels. When calculating uncertainties on integrated properties 75
ischsowfonrtihnisblgaaclkaxiynaFrieg.sh4o.wItnisinvFisiuga.l5lyacnldasistsifireaddiaaslλanR pFrRofifloerias dneerigivhebdoufrroinmgtshpeasxeemls.apswemustaccountforcovariancebetween 24 by
variety of reasons. It is a very oblate system, with an ellipticity Toachievethiswewishtoscaletheuncertaintiesonflux,Vandσ gu
e
of 0.504, the velocity map shows more than one set of alternat- bysomeappropriatefactorthataccountsforthemissingcovariance s
ingregionsofapproachingandrecedingvelocityandthevelocity whencombiningspaxels.Toestimatetheappropriatescalingfactor t on
dispersionmapexhibitstwopeaksoneithersideofacentraldepres- weusethecovariance‘cube’createdbytheSAMIcubingcode(see 10
sion.Thesekinematicfeaturesareindicativeofaso-calleddouble Section2.1.2).Foreachspaxelineachwavelengthslicethiscube M
a
sigmagalaxy,initiallydiscoveredbyKrajnovic´etal.(2011)inthe containsa5×5gridofvaluesshowinghowcorrelatedthespaxel rc
h
ATLAS3D sample. They are called double sigma galaxies due to iswithitsneighbouringspaxels.Thecentralvalueinthis5×5grid 2
0
thetwocharacteristicspeaksinthevelocitydispersionmap.These correspondstothespaxelitselfandthereforealwayshasavalueof 23
galaxiesarethoughttoconsistoftworoughlyequal-masscounter- 1. The sum over this grid shows how correlated the pixel is with
rotatingdiscs(Emsellemetal.2011)andarethereforenottrueSRs. allofitsneighbours.Thistotalcorrelationvalue,whenmultiplied
Thestructureoftheirstellarkinematicfields,beingcomplex,mimic bythecorrectvariancevalue,isthesimplestwaytoaccountforthe
thelowλ ofSRs.Fortherestofouranalysiswerejectthisgalaxy trueuncertainty(varianceandcovariance)inasinglespaxel,when
R
fromoursample,butshowitspositioninplotsforcompleteness. combiningthatspaxelwithallofitsneighbours.
Amapofthesevaluescanbegeneratedateachwavelengthslice,
creatingafullcubeoftotalcorrelationmaps.Thecubecanthenbe
averagedacrossawavelengthrangeofinterest.Theleft-handpanel
4.4 Overallclassifications
of Fig. 6 shows the total correlation map for one of the galaxies
For the remainder of this paper, we will use the λR−(cid:9) kinematic inoursample,averagedacross200wavelengthslicesinthecentre
classificationsforallgalaxies.Thismeansthatinoursampleof78 ofthedatacube.Thetotalcorrelationfactorcanvaryquitesharply
galaxies(exceptJ215634.45−075217.5whichwenowrejectfrom fromspaxeltospaxel.Thisisexplainedbythewayweresampleour
oursample)wefind13SRsand65FRs.Ofthese11SRsand62 data.Insomecasesanoutputspaxelwillfallontheouteredgeofthe
FRsareclustermembers. footprintofaninputfibre.Thisspaxelmayreceivelittleornoflux
MNRAS443,485–503(2014)
494 L.M.R.Fogartyetal.
D
o
w
n
Figure6. Theleft-handpanelshowsthetotalcorrelationmapforJ004001.68−095252.5averagedacross200wavelengthslicesofthetotaldatacubewiththe lo
a
blueellipserepresentingtheeffectiveradiusofthegalaxyinquestion.Theaxesareinpixelswitheachpixel0.5arcseconasideandsothemapis25arcsec de
oringhat-shiadned.Tphaneecletnhtereunacnedrtraiignhtite-hsaonndσp.anelshowthetrendofthekinematicuncertaintieswithS/N.ThecentrepanelshowstheuncertaintiesonVandthe d fro
m
h
fromotheradjacentfibresandwillthereforebestronglycorrelated ttp
s
with its neighbouring spaxels, leading to a high total correlation ://a
c
factor. In other cases, an output spaxel may fall in the centre of a
d
thefootprintofaninputfibre.Mostofthefluxintheinputfibreis em
contributedtothatspaxelandsoitisonlyweaklycorrelatedwith ic
.o
adjacentspaxels,yieldingalowtotalcorrelationfactor. u
p
Toscaletheuncertaintiesonthefluxthemediantotalcorrelation .c
o
factor, F , is computed within the fiducial radius at which λ is m
measuredc.ThismethodoverestimatesthetruevalueofFcbysoRme /mn
negligibleamountasitincludescorrelationbetweenspaxelsonthe ras
eTdhgisegoefntheeraatpeseratusriengalnedfnacetaorresstuniteaibglhebfoourrsscjaulsitnogutthseidveatrhiaenacpeeirntutrhee. /article
fluxatthesamewavelengthslice(s)atwhichthecorrelationfactor /4
4
wasmeasured.Wemeasurethefluxover200wavelengthslicesand 3/1
thereforetakethemedianof200wavelengthslicestocalculatethe /4
8
correlation factor. The square root of Fc can be used to scale the 5/1
uncertainties(sigma)onthefluxmeasurements. 48
ToscaletheuncertaintiesonVandσwefirstconsidertherelation 75
2
bheigtwheveanluthesesoefquSa/NntiotineesaenxdpethcetsSt/hNeinunecaecrhtasipnatxieesl.oFnorVreaansdonσabtloy uFsiginugraeM7.oAntecoCmarploarcisaolcnuolafttihoen.uTnhceerbtaluinetipeosinotnsλshRodwerFivResdaanndatlhyeticreadllyshaonwd 4 by g
scalelinearlywithS/N.However,forlowerS/Nthisrelationbreaks SRs.Theturquoisesquarerepresentsthedoublesigmagalaxydiscussedin ue
s
down, with a trend towards increasingly large uncertainties. The Section4.3.Thesolidblacklineillustratesaone-to-onecorrelationandthe t o
centre and right-hand panels in Fig. 6 illustrates this. The centre dashedblacklineisafittothepoints.Theanalyticuncertaintiesareon n 1
panelshowstheuncertaintiesonVinthespaxelsusedtocalculate average25percentlargerthantheMCuncertaintiesandtheformervalues 0 M
tλhReassaamfeunpclotitofnorofthSe/Nunicnetrhtaoisnetisepsaoxnelσs..TInheearicghhct-ahsaen,dthpeagnreelesnholiwnes areadoptedfortheremainderofouranalysis. arch
2
indicatesalinearfittothepoints.Itisclearthatthelinearfitsdo 0
notdescribethedataperfectly,andinfactasecond-orderfitmay their appendix A [unlike Houghton et al. (2013) we neglect the 23
covariance between V and σ, which is very small]. The resulting
doabetterjob.However,thelinearfitdescribesthemajorityofthe
analyticuncertaintiesonλ areshowninTableA1,inthecolumn
data points well enough, so we adopt linear scaling between the R
marked(cid:10)λ .
flux uncertainties and the kinematic uncertainties. The reason for R
In addition to the analytic calculation, we calculate the uncer-
this is to enable us to scale the kinematic uncertainties using the
taintyinλ usingaMonteCarlo(MC)approach.Weusethescaled
samefactorasthefluxuncertainties,simplifyingourcalculationof R
theuncertaintiesonλ .Thuswescaleallthreeuncertaintymaps uncertaintymapsforeachparametertogenerate1000instancesof
(flux,V,andσ)usingtRhesquarerootofF . theflux,V,andσmaps,calculatingλRforeachiteration.Thespread
c intheresultsisameasureoftheuncertaintyinλ .Theresulting
R
uncertaintyvaluesforeachgalaxyarepresentedinTableA1inthe
columnmarked(cid:10)λ (MC).Fig.7showsthecomparisonbetween
5.2 Uncertaintiesonλ R
R the analytic and MC uncertainties on λ . There is a systematic
R
We use the scaled uncertainty maps for flux, V and σ to calcu- difference between the two measurements such that the analytic
late the uncertainty in λ for each galaxy in two ways. First, we uncertaintiesareanaverageof25percentlargerthantheMCun-
R
use the analytic method described by Houghton et al. (2013) in certainties,thoughthediscrepancyissmallerforsmalleruncertainty
MNRAS443,485–503(2014)