The AMIGA sample of isolated galaxies XI. A First Look at Isolated Galaxy Colors

0.43 MB·English

by  Mirian Fernández Lorenzo

Astronomy&Astrophysicsmanuscriptno.AMIGA˙colors˙astroph (cid:13)c ESO2012
January30,2012
The AMIGA sample of isolated galaxies XI.
A First Look at Isolated Galaxy Colors
M.Ferna´ndezLorenzo1,J.Sulentic1,L.Verdes–Montenegro1,J.E.Ruiz1,J.Sabater2 andSa´nchez,S.1
1InstitutodeAstrof´ısicadeAndaluc´ıa,Granada,IAA-CSICApdo.3004,18080Granada,Spaine-mail:[email protected]
2InstituteforAstronomy,UniversityofEdinburgh,EdinburghEH93HJ,UK
Received.....;accepted.....
2
ABSTRACT
1
0
Context.Thebasicpropertiesofgalaxiescanbeaffectedbybothnature(internalprocesses) ornurture(interactionsandeffectsof
2
environment).Deconvolvingthetwoeffectsisanimportantcurrenteffortinastrophysics.Observedpropertiesofasampleofisolated

n galaxies should be largely the result of internal (natural) evolution. It follows that nurture–induced galaxy evolution can only be
a understoodthroughcomparitivestudyofgalaxiesindifferentenvironments.
J Aims.WetakeafirstlookatSDSS(g–r)colorsofgalaxiesintheAMIGAsampleinvolvingmanyofthemostisolatedgalaxiesinthe
7 localUniverse.ThisleadsustosimultaneouslyconsiderthepitfallsofusingautomatedSDSScolors.
2 Methods.WefocusonmedianvaluesfortheprincipalmorphologicalsubtypesfoundintheAMIGAsample(E/S0andSb–Sc)and
comparethemwithequivalentmeasuresobtainedforgalaxiesindenserenvironments.
] Results.WefindaweaktendencyforAMIGAspiralgalaxiestoberedderthanobjectsinclosepairs.Wefindnocleardifference
O whenwecomparewithgalaxiesinother(e.g.group)environments.However,the(g−r)colorofisolatedgalaxiesshowsaGaussian
distributionasmightbeexpectedassumingnurture–freeevolution.Wefindasmallermedianabsolutedeviationincolorsforisolated
C
galaxiescomparedtobothwideandclosepairs.Themajorityofthedeviationonmediancolorsforspiralsubtypesiscausedbya
h. color–luminositycorrelation.Surprisinglyisolatedandnon–isolated early–typegalaxiesshowsimilar(g−r).Weseelittleevidence
p foragreenvalleyinoursamplewithmostspiralsredderthan(g−r)=0.7havingspuriouscolors.
- Conclusions.ThereddercolorsofAMIGAspiralsandlowercolordispersionsforAMIGAsubtypes–comparedwithclosepairs–is
o likelyduetoamorepassivestarformationinveryisolatedgalaxies.
r
t Keywords.galaxies:general—galaxies:fundamentalparameters—galaxies:interactions—galaxies:evolution
s
a
[

1. Introduction flected by the morphology–density relation (Dressler 1980;
1
v vanderWeletal. 2010, and references therein). In dense envi-
Insomewaysourstudyofgalaxypropertiesisstillinitsinfancy.
4 ronmentsluminousredearly–typegalaxiespredominatewhilein
Wehaveaplethoraoftheoreticalideasbutwearestilltryingto
3 lowestdensityenvironmentbluelate–typespiralsarethedefin-
understandwhatbasic measurese.g.size, luminosityandcolor
8 ing population (Dressler 1980; Capaketal. 2007). While it is
5 are telling us. This is, in part, because galaxies are composite easytorecognizearichcluster,definitionsoflowdensityenvi-
1. structuresandinanotherpartbecausewecannoteasilyseparate ronmentscanbeconfusing.Inrecentyearstherehasbeenanin-
effects of nature (internalprocesses) from nurture(interactions
0 creased emphasison identifyinglow density or isolated galaxy
andeffectsofenvironment).
2 populations.One of the most useful samples remains the visu-
1 Theopticalcolorsofgalaxiesreflecttheirstellarpopulations ally selected Catalog of Isolated Galaxies (CIG) compiled by
: and these colors correlate with morphology and environment. Karachentseva(1973)morerecentlyvettedastheAMIGAsam-
v
The distribution of galaxy colors in the (g−r) vs. (u−g) plane ple(Sulentic2010,andreferencestherein).
i
X (Stratevaetal.2001)showsastrongbimodalitywithclearsep- Starformationisstronglydependentonenvironmentwithin-
r aration into red and blue sequences. Study of morphologyand creasedactivitytowardslowdensityenvironments(Lewisetal.
a spectral classification (Stratevaetal. 2001) for subsamples of 2002;Hoggetal.2003,2004;Baldryetal.2006).Inthissense,
287redand500bluegalaxiesshowthatthetwocolorpeakscor- Baloghetal. (1998) foundthat the mean star formationrate in
respondroughlytoearly–(E,S0,andSa)andlate–type(Sb,Sc, galaxies with similar bulge–to–total (B/T) luminosity ratios is
andIrr)galaxiesas expectedfromthe respectivedominanceof alwayslowerinclustersthaninthefield.HoweverPattonetal.
oldandyoungstellarpopulations.Colorsofgalaxiesalsodepend (2011)foundthattheoppositeishappeningingalaxypairswith
stronglyonluminosityinthesensethatmoreluminousgalaxies clear signs of star formation induced by interaction within the
ofthesamemorphologicaltypeareredder(Baldryetal.2004). bluegalaxies.Thisresultagreeswiththebluer(U−BandB−V)
Thecolor–magnituderelationismostobviousintherest–frame colorsfoundpreviouslybyLarson&Tinsley(1978)forpeculiar
(g−r)(correctedtoz=0.1),wheretheseparationbetweenthered galaxies.
andbluepopulationsisevident(Blantonetal.2003).
Approximately10%ofthelowdensityuniverseispopulated
Environment is also thought to play a role in the mix of bypairs(alsobytripletsanddensegroups)whereenvironmen-
morphological types for a sample of galaxies which is re- tal effects can reproducethe processes that happen in starburst
galaxies and clusters (e.g. Xu&Sulentic 1991; Iovino 2002).
Sendoffprintrequeststo:M.Ferna´ndezLorenzo What we are trying to say is that there are two sources of en-
1
Ferna´ndezLorenzoetal.:TheAMIGAsampleofisolatedgalaxiesXI
vironmentaleffects: 1) the morphology–densityrelation and 2) catalog (see details below). These workflows allow also com-
one–on–onegalaxy interactions which can be found in a wide parisonbetween valuesstored in the AMIGA databasecoming
range of density environments. In this sense, the AMIGA vet- fromdifferentreleases,registeringthenewvalueswhilekeeping
ting of the CIG (see below) is intended to produce an isolated aversionoftheoldones.Thereforethemethodologytocalculate
samplethatminimizesbotheffects. thesevaluesisstoredintheseworkflowsenablingreproducibil-
The AMIGA project (Analysis of the interstellar Medium ityandre–usability,eventhere–purposabilityforsimilarcross–
of Isolated GAlaxies) is producing and analyzing a mul- boundary use cases. Currently releases of data in HyperLeda
tiwavelength database for a refinement of the Catalog of are not registered, hence while the methodology, as explained
Isolated Galaxies (CIG, Karachentseva 1973, n=1050 galax- above, can be preserved, traceability of the HyperLeda data is
ies). We have evaluated and improved the sample in dif- notpossibleyet.TheseworkflowshavebeenbuiltintheTaverna
ferent ways: 1) Revision of all CIG positions in the sky Workflow Mamagement System2 and can be accessed in the
(Leon&Verdes-Montenegro 2003), 2) optical characterization MyExperimentportal3.ThedataforthefullAMIGAsampleare
of the sample including completeness, luminosities, and helio- listedinTable1,andarealsoavailableintheAMIGAVOcom-
centricvelocities(Verdes-Montenegroetal.2005,andsection2 pliant interface. We describe the details of the revision below.
ofthispaper),3)Morphologicalrefinementandidentificationof For completeness, we explain here all the revised parameters,
galaxieswithasymmetries(Sulenticetal.2006,andsection2.2 althoughopticalluminosityhasnotbeenusedinthispaper.
of this paper), and 4) quantification of the degree of isolation
includingthe numberdensityto the 5th neighbour(η ) and the
k
2.1.VelocitiesandDistances
estimationofthetidalforce(Q)(Verleyetal.2007a,b).
The multiwavelength analysis of our AMIGA sample has
We have searched for new velocitiesfor those CIG with helio-
shown that isolated galaxies have different properties than
centric velocities (V ) larger than 1000 km/s, since for lower
galaxies in higher density environments (even field samples). hel
values redshift–independent distance estimates have been pre-
Variables expectedto be enhancedby interactionsare lower in
ferred,andthesameasinVerdes-Montenegroetal.(2005)were
AMIGAthananyothersample,suchaslowerinfraredluminos-
kept.ThevalueofV foragalaxywithavailableredshiftdata
ity(L <10.5L⊙)andcolderdusttemperature(Lisenfeldetal. hel
FIR hasbeenupdatedwhentheerrorsquotedintherecentbibliogra-
2007), a low level of radio continuum emission dominated
phyweresmallerthaninourpreviouscompilation.Forasubset
by mild disk star formation (Leonetal. 2008), no radio ac-
ofgalaxieswefoundthatthesourceofthedataprovidedinNED
tive galactic nuclei (AGN) selected using the radio–FIR cor-
wereobtainedfromStockeetal.(2004)but,whilethepaperwas
relation (0%; Sabateretal. 2008) and a small number of opti-
providing galactocentric velocities, NED was quoting them as
cal AGN (22%; Sabateretal. 2012, submitted), a smaller frac-
heliocentric.ThiserrorwasreportedtoNEDteamandbothcor-
tionofasymmetricHIprofiles(<20%,Espadaetal.2011),and
rected in NED and in our database. Only for 40 CIG galaxies
less molecular gas (Lisenfeldetal. 2011). In addition, early–
velocitydatawerenotfoundinthebibliography,hence1010out
type galaxies in AMIGA are fainter than late types, and more
of1050CIGgalaxiescurrentlyhaveredshiftmeasures.
AMIGAspiralshostpseudo–bulgesratherthanclassicalbulges
Distanceswereobtainedfromvirgo–centricvelocities(V )
(Durbalaetal. 2008). The data are being released and periodi- vir
asD= V /H (usingH =75km/sMpc−1),whereV iscal-
callyupdatedathttp://amiga.iaa.es,whereaVirtualObservatory vir 0 0 vir
culated from the heliocentric velocityV and galactic coordi-
compliant web interface with different query modes has been hel
natesfollowingHyperLedaconvention.Virgo–centricvelocities
implemented.
were calculated as V = V + 208 cos(θ), where V is the
ThispaperpresentsafirstlookatcolorsfortheAMIGAsam- hel lg lg
radialvelocitywithrespectto theLocalGroupandθ isthean-
ple. It now becomes possible to analyze more than half of the
gulardistancebetweenthegalaxyandVirgocenter.Inorderto
AMIGA sample using uniform digital images, magnitudesand
transformtheV toV wetransformedαandδcoordinatesin
colorsofthesloan digitalskysurvey(SDSS,Yorketal. 2000). hel vir
Leon&Verdes-Montenegro(2003)tolandbvalues.
InSect.2,thedatarevisionoftheAMIGAsampleisprovided.
The sample selection is presented in Sect. 3, and the determi-
nation of the absolute magnitudes is described in Sect. 4. The
2.2.Morphologies
dependenceof the rest–framecoloras functionof the morpho-
logical type and environment is analyzed in Sect. 5 and 6, re- Sulenticetal. (2006) performed a careful revision of the mor-
spectively.Finally,theconclusionsarepresentedinSect.7. phologiesforthewholeCIGsamplebasedonPOSSII(Second
PalomarObservatorySkySurvey;Reidetal.1991)images.We
have recently revised those morphologies for all CIG galaxies
2. TheAMIGAdatarevision with V > 1000 km/s and CCD images available either from
hel
SDSSorourowndata(N=843).ForCIGgalaxieswithV <
Giventhat,sincetheprojectstarted,asignificantnumberofnew hel
1000km/s(N = 57),morphologicaltypeswere compiledfrom
data are available for the sample, we have revised the appar-
the bibliographyand the mean value used. For N = 134galax-
ent magnitudes, morphologicaltypes, distances and optical lu-
ieswithonlyPOSSIIdataavailable,asecondrevisionhasbeen
minositiesfor the CIG sample with respect to the onesused in
performed, with minor modifications to the values assigned in
Verdes-Montenegroetal. (2005) and Lisenfeldetal. (2007). In
theframeoftheWf4Everproject1,therevisionoftheseproper- Sulenticetal. (2006). For the remaininggalaxiesfor which we
wereunabletoperformanyclassification,weuseddatafoundin
tieshasbeenpartiallyautomatedbytheimplementationofsci-
NEDandHyperLedadatabase.
entific workflows which ask for and gather values, of some of
thepropertiesforalltheAMIGAgalaxies,fromtheHyperLeda Globallythereisashiftinthemorphologieswithrespectto
Sulenticetal.(2006)towardslatertypesby∆T=0.2,thatwein-
1 http://www.wf4ever-project.org terpretasduetothehigherresolutionprovidedbyCCDimages
2 http://www.taverna.org.uk/ revealingsmaller bulges. Types(T) havebeen codedfollowing
3 http://www.myexperiment.org/packs/231.html RC3 (seemorphologicalcodesinTab.2).Sulenticetal.(2006)
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Ferna´ndezLorenzoetal.:TheAMIGAsampleofisolatedgalaxiesXI
Table1.MainpropertiesoftheCIGsample1.
CIG V D T IA B A A A Bc L D d i Target
hel T g i K T B 25 25
(kms−1) (Mpc) (RC3) (mag) (mag) (mag) (mag) (mag) [L )] (′) (′) (o)
⊙
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15)
1 7299 96.926 5 1 14.167 0.173 0.571 0.040 13.383 10.570 1.393 0.640 65.094 0
2 6983 94.745 6 0 15.722 0.255 0.278 0.031 15.157 9.840 0.721 0.502 46.816 1
3 - - 4 0 16.057 0.246 0.354 - 15.457 - 0.402 0.242 55.052 0
4 2310 31.880 3 0 12.818 0.252 0.863 0.017 11.685 10.283 3.289 0.729 90.000 1
5 7865 105.907 0 0 15.602 0.225 0.131 0.118 15.128 9.949 0.726 0.318 75.468 1
6 4528 61.623 7 1 15.395 0.412 0.638 0.016 14.329 9.798 0.697 0.308 65.321 1
7 12752 169.896 4 0 15.662 0.100 0.338 0.083 15.141 10.354 0.692 0.427 53.958 1
8 6342 85.041 5 0 15.624 0.489 0.726 0.035 14.374 10.060 0.752 0.277 71.680 0
9 8474 113.035 5 1 15.537 0.111 0.637 0.047 14.742 10.160 0.910 0.380 68.066 1
10 4613 63.645 5 0 15.377 0.366 0.546 0.025 14.440 9.782 1.054 0.501 63.935 0
.. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
1 Thefulltableisavailableinelectronicformathttp://amiga.iaa.es.Thecolumns correspond to(1)Galaxyidentificationaccording toCIG
catalog; (2) Heliocentric velocity; (3) Distance; (4) Morphological type; (5): Degree of optical asymmetry, (6) B–band magnitude from
HyperLeda,(7):Galacticextinction,(8):Internalextinction;(9)KcorrectionintheB–band;(10):CorrectedmagnitudeintheB–band;(11)
logarithm of the optical luminosity in the B–band; (12): Major axis; (13) Minor axis; (14) Galaxy inclination, as described in Sect. 2. In
column(15)weflaggalaxieswichcode1whenthegalaxyispartofthestudiedinthispaper,and0otherwise,followingSect.3.
also flaggedgalaxiessuspectedto be interacting.We havenow 2.3.Opticalluminosity
replacedthiscodebyadescriptiveone,basedalsoonvisualin-
Theopticalluminositieshavebeenderivedas
spection of the optical images, as described next. Code IA=0
is assigned if no relevant signs of distortions are visible. Code
log(L /L )=11.95+2log[D(Mpc)]−0.4Bc (2)
IA=1 correspondsto galaxies seen in the images as asymmet- B ⊙ T
ric, lopsided, warped or distorted, with an integral sign shape
where the solar luminosity is given in units of the solar bolo-
or tidal feature (tail, bridge, shell). Those galaxies are always
metricluminosityasinLisenfeldetal.(2007).Themeanvalue
treatedseparatelyinouranalysis,inordertocheckwhetherthey
ofthedifferencebetweenournewvaluesforopticalluminosities
presenta differentbehaviourthantheonesclassified with code
withrespecttotheonesusedinLisenfeldetal.(2007)isassmall
0.CodeIA=2isassignedifthegalaxywasidentifiedaspairsin
as0.02±0.18magbuthastheadvantageofbeingderivedfrom
Verleyetal.(2007a)and/orinNED,orifthegalaxylookslikea
B magnitudescompiledfromHyperLedadatabase,soreducing
mergerorsuperpositionoftwogalaxies.Thesegalaxiesarenot T
theerrors.
consideredpartofAMIGAsampleandaremarkeddifferentlyin
theplots.ThenewdataarepresentedinTab.1andnowallCIG
galaxieshaveamorphologicalcode. 2.4.Opticaldiameterandaxisratio(D andR )
25 25
WehavemadeuseoftheHyperLedadatabaseinthecompilation
2.2.1. Apparentmagnitudes ofthemajoraxisD (isophotallevelat25mag/arcsec2intheB–
25
band)andaxisratiosR (R =D /d ,whered istheminor
BlueopticalmagnitudesB havebeenobtainedfromHyperLeda 25 25 25 25 25
T axis, at an isophotal level of 25 mag/arcsec2), as well as their
(Patureletal. 2003), instead of using the Catalog of Galaxies
errors(minorandmajoraxisaregiveninTab.1).
and Clusters of Galaxies (Zwickyetal. 1961-1968) as in
Verdes-Montenegroetal.(2005),andthecorrectedBc wascal-
T
culatedasfollows: 2.5.Inclinations
The inclination (i) was determined from the value of R in
Bc =B −A −A −A (1) 25
T T g i K HyperLeda database and our revised morphological type with
thefollowingequation(Heidmannetal.1972):
where A is the galactic dust extinction, A the internal ex-
g i
tinction correction and AK the K correction. Ag has been ob- 1−10−2log(R25)
tained from HyperLeda (Schlegeletal. 1998), except for CIG sin2(i)= (3)
447forwhichonlyNEDdatawereavailable.A wascalculated 1−10−2log(R0)
i
as in HyperLeda (Bottinellietal. 1995) using their values for
wherelog(R )=0.43+0.053×TforT≤7andlog(R )=0.38
log(R ) (axis ratio of the isophote 25 mag/arcsec2 in the B– 0 0
25 forT>7.
bandforgalaxies)butourownmorphologicaltypes.FinallyA
K
was obtained as defined in HyperLeda2 (A =ak(T)V /10000;
K hel
deVaucouleursetal. 1976), using our own morphologies and 3. Sampleselection
distances. Bothuncorrectedandcorrectedmagnitudesarelisted
inTab.1. Asstarting samplewe use thecatalogof 791AMIGA galaxies
selected by Verleyetal. (2007b), where the galaxies with iso-
2 http://leda.univ-lyon1.fr/leda/param/btc.html lation parameters Q>-2 and ηk>2.4 (the tidal strength created
3
Ferna´ndezLorenzoetal.:TheAMIGAsampleofisolatedgalaxiesXI
surprise underthe assumption thatisolated galaxiesare simply
theoutliersofloosegroupswheretheearly–typefractionis∼0.4
(vanderWeletal.2007).Wefind∼0.15inoursample,whichis
still largeenoughto be interesting.Other typesare represented
in such small numbers that we assume them to be simply ran-
dom galaxies that happen to be unusually isolated at this time.
Thisassumptionismotivatedbythestandardideathatalldisky
galaxies with a large bulge are products of nurture. The late–
type spiral population involves galaxies with small bulges (or
even pseudo–bulges, Durbalaetal. 2008) which, if interpreted
asa secularevolutiondiagnostic,cannothavespentmuchtime
inricherenvironments.
4. Derivingrest–framecolors
Fig.1.Distributionoftheheliocentricvelocitiesofthe466CIG A variety of magnitudeestimates are given for each galaxyin-
galaxiesusedinthiswork. cludedintheSDSScatalog.Wechosethemodelmagnitudesfor
derivingcolorsinoursamplebecausetheyarecalculatedusing
best–fitparametersinr–bandwhicharethenappliedtotheother
byall theneighbours, Q, ismorethan 1%ofthe internalbind- bands. Model magnitudes are therefore computed through the
ing forces; for the local numberdensity, η , this translates to a sameapertureforallbands.Inordertocomputeabsolutemag-
k
valueof2.4;Athanassoula1984),andwithrecessionvelocities nitudesineachbandthefollowingcorrectionswereapplied:
V <1500 km/s, were rejected. These conditions imply that all
r – A correction for Galactic dust extinction applying the
galaxies in our starting sample have their evolution dominated
reddening corrections computed by SDSS following
by their intrinsic properties (see Verleyetal. 2007b, for more
Schlegeletal.(1998).
details). This sample is complete up to Bc=15.3, where Bc is
T T – Thek–correctionineachbandwascalculatedusingthecode
themagnitudeintheB–bandfromHyperLedaaftercorrections.
kcorrect(Blanton&Roweis2007),whichdeterminesthe
ThecompletenesslimitwasdecidedinVerdes-Montenegroetal.
spectralenergydistribution(SED)ofthegalaxyusingSDSS
(2005)(Bc=15mag)afterapplyingthe<V/Vm>test(Schmidt
T photometry from a nonnegative linear combination of five
1968),andhasbeenrecentlyupdatedsinceB–bandmagnitudes
templatesbasedontheBruzual&Charlot(2003)stellarevo-
wererecalculatedfollowingHyperLedaexpressionsin2010(see
lutionsynthesiscodes.
section2).Thereare657objectsinthecompleteAMIGAsam-
– Absolutemagnitudeswerecalculatedusingtheupdateddis-
plethatalsofulfilltheaboveisolationcriteria.Photometricdata
tancesshowninTab.1.
used in this work come from the SDSS–III (Data Release 8,
DR8 Aiharaetal. 2011). The SDSS project used a 2.5 m tele- TheinternalextinctioncorrectioninB–bandwascalculated
scope(Gunnetal.2006)toobtainphotometricinformationfrom byVerdes-Montenegroetal.(2005)asafunctionofinclination
CCD imagesin u, g,r,i, andz passbands.A newapproachfor andmorphologicaltypefollowingdeVaucouleursetal.(1991).
backgroundsubtractionwasappliedinDR8thatfirstmodelsthe We used the Calzetti law (Calzettietal. 2000) for deriving the
brightestgalaxiesineachfieldinordernottoaffecttheestimated SDSS–band internal extinctions based on the B–band correc-
skybackground(Blantonetal.2011). tions. We represented the rest–frame color (g−r) versus incli-
Fromthe657galaxiesthatarepartofthecompleteAMIGA nationbeforeandaftertheextinctioncorrectionsandfoundthat
sample,wefound496objectsintheSDSSdatabase.We found thiscorrectionwasoverestimated(theslopeofthelinearregres-
and removed14 galaxies from the catalog involving imprecise sionchangesfrom0.17to−0.21forScgalaxiesandfrom0.16
identificationsofgalaxynucleiintheSDSSdatabaseorgalaxies to−0.13forSbgalaxies,aftercorrections).Mastersetal.(2010)
with a nearby bright star adversely affecting galaxy photome- studied the effect of this correction on the colors through its
try.We alsoremoved16galaxieswithunknownredshiftssince dependencyoninclination,spiraltypeandabsolutemagnitude.
thosewillbeneededforthefollowinganalysis.Thefinalsample Thebestresultforour(g−r)versusinclinationplotsisobtained
consists of 466isolated galaxieswith radialvelocitiesbetween usingalinearcombinationoftheirrelationsasdefinedinequa-
1500and24000kms−1.Hereafter,werefertoitastheAMIGA– tion3intheirpaper(theslopeofthe(g−r)versusinclinationre-
SDSS sample. We have represented its redshift distribution in lationafterthiscorrectionis0.025forScand0.023forSbgalax-
Fig.1.Thissampleincludes70galaxieswithasymmetriesthat ies),whiletheexpressionstheygiveforeachmorphologicaltype
aresuspectedofbeinginvolvedininteractionsorhavingnearby (bulge–diskratio)produceanovercorrectioninalloursubsam-
companions.Thesepropertiesarerepresentedinoursampleby ples.Wealsonotethatthedependenceoftheinternalextinction
the degree of asymmetry IA=1 (63) or IA=2 (7) (see Section correctionongalaxyluminosityderivedinMastersetal.(2010)
2.2),whereIA=2representsthemostasymmetricgalaxies.We isnotreproducedbyourdata.IfAMIGAspiralsarereallymore
do not rejectthese objects since we are tryingto see whatfea- dynamicallyquiescentsystems,itisperhapsnotsurprisingthat
turescanagalaxydevelopinisolation,but,throughoutthepaper, correctionsderivedfromalmostcertainlylessquiescentsamples
we check the effect of these galaxies in the median colors. We wouldyielddifferentcorrections.Moreover,thispreliminaryre-
focusourattentiononthetwomoststatisticallysignificantsub- sultoflowerextinctioninAMIGAspiralscanbeunderstoodas
samplesinvolvingSb–ScspiralsandE/S0early–types.Thesein- asignoflessdustduetoourassumptionthatthestarformation
volveapproximately68%and15%oftheAMIGA–SDSSsam- has been lower in our isolated galaxies for all or most of their
pleusedinthisworkrespectively.Theformerisinterpretedasa lives(Leonetal.2008).
kindof ”parentpopulation”ofisolated galaxiesbecauseit rep- Finally, we applied the correction of Mastersetal. (2010),
resents 2/3 of the total sample. The latter was somewhat of a based on their equation 3, to our Sa–Sc galaxies. We have not
4
Ferna´ndezLorenzoetal.:TheAMIGAsampleofisolatedgalaxiesXI
early–typegalaxiesalthoughmedian(g−r)valuesremainessen-
tiallyconstantouttoT=3(Sb).BeginningwithtypeSbweseea
decreaseinmedian(g−r)asexpectedifthissequencereflectsa
uniformlydecreasingcontributionfromanoldstellarpopulation
(Stratevaetal.2001;Blantonetal.2003).
Surprisingly the color distributions for our late–type spiral
Sb–Sc populationshow some galaxies with colors even redder
than the E/S0 subsample. Either AMIGA early–type galaxies
areextraordinarilyblueorthesespiralshaveanomalouscolors.
Careful examination of these objects using the SDSS naviga-
tiontoolshowsthatcolorsofthereddestSb–Scgalaxiesareun-
reliable and/or that the assigned galaxy types are incorrect. In
the case of our Sc subsample (which is perhaps the easiest to
classify) we find n=10 galaxies with (g−r)>0.7 (tipical colors
ofearly–types).In8casesthereisaproblemwiththecolor:1)
Fig.2.DistributionofHubbletypesintheAMIGA–SDSSsam- fiveareaffectedbyastarprojectedonorveryclosetothegalaxy
ple. (CIG261,304,649,716,1010),2)two(CIG349,946)belongto
the7galaxiespreviouslyidentifiedwithahighdegreeofasym-
metry(IA=2),3)one(CIG988)ishighlyinclinedandtheex-
tinctioncorrection(Mastersetal.2010)couldbemaximallyaf-
fectedbyuncertaintyoftheadoptedinclination.Oftheremain-
ing 2 red Sc spirals, one (CIG 709) shows among the highest
recession velocity in our sample (V>14000km/s). At this dis-
tance the number of resolution elements in the galaxy images
approachesthatofPOSSII.InthecaseofCIG709,theimageof
SDSSshowsacloseobjectwithunknownredshiftwhichcould
be a minor companioncausingsome kindof asymmetryin the
opticalbands.Finally,CIG807maywellbeanScspiralbutthe
blue disk is not resolved. The point of this exercise is to show
thatonecanidentifyremarkablypureisolated(local)spiralsub-
samplesbutonly if the abovepitfalls are taken intoaccount.If
theseeffectsarenottakenintoaccounttheaveragepropertiesof
theisolatedsubsamplescanbeblurredbeyondstatisticalutility.
Consideration of Sbc and Sb spirals reveal similar effects
amongthereddestgalaxiesthatonlydetailedsurfacephotometry
could correct. Naturally similar problems can afflict the bluest
galaxies in each spiral subtype. Colors for 2/4 of the bluest Sc
spirals((g−r)<0.4)arealsolikelyaffectedbytheirnearbybright
stars.Theseeffectscanbeasourceofseriousscatterincolordis-
Fig.3.Distributionoftherest–frame(g−r)colorasafunctionof tributionsforanygalaxysampleandillustratethecautionneeded
Hubble type. The yellow points are the median values of each inusingSDSScolors.Ontheotherhand,whiletheobjectswith
morphologicaltype. The blue triangles are objects with asym- IA=2areoutsidethenormaltrendofthemedianvalues,thecolor
metryindexIA=1whiletheredopenpointsrepresentthemost oftheAMIGAgalaxieswithasymmetryindexIA=1agreeswith
asymmetricobjects(IA=2)inoursample.Theerrorbarsrepre- thecolorofsymmetricgalaxies(IA=0).Inthefollowinganaly-
sentthemedianabsolutedeviation. sis, objectswith IA=2have been removedbutnotobjectswith
spuriouscolors,sincetheyalsoexistinthesamplesthatwehave
used as comparison.Nevertheless,we took accountof their ef-
correctedthemorphologicaltypesearlierthan0(E/S0)andlater fectsthroughtheerrormeasures.
than 6 (Scd/Sd/Irr) because their numbers are small and their
We expectto find a smaller color dispersionfor spiralsub-
(g−r)vs. inclinationplotsdo notshowany clear trendof color
types in the AMIGA sample because these galaxies are mini-
vs.i(theslopeofthefitsis∼0). mallyaffectedbyenvironmentaleffectswhichapparentlyinduce
alargercolordispersion.Thishasbeenknownsincethefirststa-
tisticalstudyofcolorsforgalaxiesininteractingpairsandmul-
5. (g–r)colorasfunctionofmorphologicaltype
tiplets (i.e. they evolve more passively, e.g. Larson&Tinsley
In Fig. 2 we presentedthe numberof galaxiesin the AMIGA– 1978). One of the goals of the AMIGA project is to provide a
SDSSsampleofeachmorphologicalsubtype,andFig.3shows samplethatcouldbettercharacterizeintrinsicgalaxyproperties
the distribution of SDSS (g−r) colors for the AMIGA sample andtheirdispersions.
as a function of the morphologicalsubtype. We calculated the What is the main source of color dispersion for spiral sub-
medianvaluesratherthanmeanvalues,sincetheyarelesssen- typesifwehaveachievedourgoalofminimizingeffectsofenvi-
sitivetooutliersproducedbyanerrorinthecolorforoneobject ronmentalnurturefromoursample?Spiralscontainaredbulge
or misclassification. We have used the median absolute devia- (rednessdependingon the nature of the bulge) and a blue disk
tionasascattermeasuresinceitrepresentsarobustestimatorof makingtheirglobal(g−r)colorsensitivetotheapertureusedin
dispersion for median values. Not surprisingly the reddest me- estimatingthe g and r magnitudes.We checkedthe (g−r)color
dianvaluesof(g−r)arefoundforthefirstfourbinsrepresenting versusabsolutemagnituderelationforScgalaxiesinthreesep-
5
Ferna´ndezLorenzoetal.:TheAMIGAsampleofisolatedgalaxiesXI
arate redshift ranges. The results are presented in Fig. 3. We
find a tendency for galaxies of fixed absolute magnitude to be
(g−r)∼0.08 redder at lower recession velocities implying that
colormeasuresinoursamplecouldbeincreasinglyaffectedby
bulgelightatlowerrecessionvelocities.Thisisaminorbutsys-
tematiceffect.However,anapertureeffectwillalsounderstimate
theabsolutemagnitudeofthegalaxy,makingitmoredifficultto
estimatetheamplitudeofthecolorbias.
Fig. 4 shows that the major source of color dispersion in
Fig. 3 is connected with the color–luminosity trend. Sb–Sc
color distributions show Gaussian distributions for each sub-
typewithFWHM=0.15–0.2,spanningalmost2dexinluminos-
ity(M =−19to−22.5).TheeffectislargestforScspiralsinour
r
sample where the color–luminositytrend appearsto be steeper
(ScspiralswithM =-22.5are∼0.25magredderthanSc spirals
r
with M =-19). Fig. 4 also shows the (g−r) vs. M density dia-
r r
gramobtainedfromtheNair&Abraham(2010) samplecover-
ing the range 0.01<z<0.05 (SDSS DR8). This sample applied
no morphology or environmental selections so we see the bi-
modality previouslyfoundfor SDSS data (Stratevaetal. 2001;
Blantonetal. 2003). The distribution of our Sc subsample fol-
lows the blue sequence with the recession velocity vs. color Fig.4.(g−r)color–magnitudediagramfortheScgalaxiesinthe
bias visible. The same bias in the color as function of redshift AMIGA sample. The blue diamondsare objectsat z<0.02,the
hasbeenfoundbyusingthesampleofNair&Abraham(2010). yellow triangles are galaxies at redshift 0.02<z<0.04, and the
Moreover,fora givenluminosityand morphologicaltype(Sc), pink squares are those objects at z>0.04. The grey–scale rep-
the petrosian radius R given in the SDSS database for the resentsthedensitydiagramobtainedfromtheNair&Abraham
90
Nair&Abraham(2010)sampledecreasesaswegoatlowerred- (2010)sampleat0.01<z<0.05,usingthedataofDR8.
shifts.Themaintrendofourdatainthefigure(andhencesource
ofcolordispersion)clearlyinvolvesthecolor–luminositycorre-
lation. The overlap (i.e. green valley) rather than being a class
ofgalaxieswithintermediatecolorsmaybeentirelyduetospi-
ralswithspuriousredcolorsduetotheeffectsdiscussedabove.
The(g−r)vs.M diagramforavettedsampleofisolatedgalax-
r
ies likely shows a much clearer dichotomythan othersamples.
Thereisnoevidenceforanastrophysicallysignificantgreenval-
leybutweneedmorereliablecolorstoconfirmthisresult.
Fig.5showsanequivalentdiagramfortheearly–type(E/S0)
part of the AMIGA sample. Despite their isolation they fall in
theredsequencedefinedbyearly–typesinricherenvironments
(e.g.Nair&Abraham(2010)).Theydonotprovideevidencefor
a greenvalley.Ourearly–typesubsampleshowsnocolortrend
with recession velocity. We notice only a slight trend between
colorandluminosity(galaxieswithM =-22.5are∼0.1magred-
r
der than galaxies with M =-19). In the case of early–typesthe
r
FWHM of the Gaussian fit to the color distribution is ∼0.14
(similar to Sb galaxies color distribution). The bluest galaxies
mightbemisclassifiedasE/S0althoughphotometricstudyofa
fewofthem(Marcumetal.2004)suggeststhattheymaynotbe
spirals.Inaddition,threeofthem(CIG264,981,and1025)hav-
ingHIemissionwererevisedinordertocheckforthepresence Fig.5.Same asFig. 4 butfortheE/S0 galaxiesinthe AMIGA
ofpeculiaritiesinthe morphologies,suchas dustlanes,optical sample.
shells,bluecoresorstarformation.Allofthemwereconfirmed
asearly–typegalaxies(Espada 2006).
colors(Pattonetal.2011).Larson&Tinsley(1978)foundlarger
colordispersioninanextremenurturesample,whoseevolution
6. Colordependenceonenvironment
iscompletelydominatedbyexternaleffects.Thekeywordhere
Some studies have shown that galaxies of a fixed morphol- isdispersion:colorsofgalaxiesinpairsandgroupsarenotsys-
ogyinhigherdensityenvironmentsareredder(Balletal.2008; tematically bluer but they show a larger color dispersion. The
Skibbaetal.2009)andthereasonmightbethatdenseenviron- AMIGAsample ofgalaxiesinvolvessomeofthe mostisolated
mentssuppressstarformation(Baloghetal.1998).Ontheother objectsin the localUniverseandare minimallyaffectedby ex-
handisolatedgalaxiesarelikelytoshowratherpassivestarfor- ternalprocesses,at leastduringthe pastfew Gyr. We therefore
mationleadingonetoexpectspiralsinricherenvironments(e.g. expectthatAMIGAgalaxiesofagivenmorphologicaltypewill
pairs, even the isolated pairs usually included in field galaxies showminimalcolordispersionandtheaboveresultssupportthat
samples) to show more active star formation and hence bluer expectation.
6
Ferna´ndezLorenzoetal.:TheAMIGAsampleofisolatedgalaxiesXI
Table2.Median(g−r)colorsasfunctionofmorphologicaltype.Theerrorsrepresentthemedianabsolutedeviation.
Type T AMIGA NAIR EFIGI CPG CPG
(WID) (CLO)
E -5 0.72±0.06 0.78±0.03 0.78±0.03 0.79±0.03 0.76±0.03
E -4 0.77±0.02 − 0.78±0.02 0.80±0.08 0.79±0.04
E/S0 -3 0.75±0.04 0.76±0.05 0.77±0.04 0.79±0.06 0.77±0.07
S0 -2 0.75±0.04 0.76±0.04 0.76±0.04 0.78±0.06 0.77±0.06
S0 -1 − − 0.78±0.06 0.72±0.05 0.73±0.09
S0/a 0 0.74±0.07 − 0.76±0.07 0.77±0.05 0.78±0.04
Sa 1 0.77±0.05 0.71±0.06 0.73±0.05 0.72±0.11 0.71±0.09
Sab 2 0.74±0.05 0.69±0.07 0.72±0.07 0.71±0.10 0.67±0.15
Sb 3 0.71±0.06 0.67±0.08 0.71±0.08 0.71±0.13 0.69±0.12
Sbc 4 0.65±0.09 0.61±0.08 0.66±0.07 0.63±0.12 0.59±0.14
Sc 5 0.57±0.08 0.56±0.08 0.62±0.09 0.69±0.12 0.51±0.15
Scd 6 0.49±0.06 0.46±0.07 0.58±0.09 0.55±0.11 0.51±0.17
Sd 7 0.42±0.06 0.42±0.06 0.47±0.08 0.34±0.17 0.43±0.10
Sdm 8 0.35±0.05 0.41±0.07 0.44±0.12 0.48±0.07 0.30±0.12
Sm 9 − 0.36±0.09 0.40±0.16 − 0.56±0.13
Im 10 0.24±0.03 0.33±0.10 0.29±0.09 − 0.29±0.12
Table 2 provides a quantitative comparison of (g−r) me-
dian colors in our sample and in samples involving denser en-
vironments. We used three catalogs for this comparison: 1)
Nair&Abraham(2010)whichincludesadetailedvisualclassi-
ficationsfor14,034galaxiesintheSDSSDR4.Weselectedonly
objectswith morphologicalclassification availableand redshift
0.01<z<0.05 (8976) to better match our AMIGA–SDSS sam-
ple ( 98%); 2) the EFIGI catalog (Baillardetal. 2011) which
provides detailed morphological information for a sample of
4458PGCgalaxiesalsousingSDSSDR4.Bothsamplesinclude
galaxiesin a wide range of environments;3) We also compare
withthecatalogofisolatedpairsofgalaxies(CPG,Karachentsev
1972),composedby1206objects.Itwasvisuallycompiled,like
CIG,usingPOSSIIandapplyinganisolationcriterion.
We used SDSS DR8 photometric data for all three sam-
ples and derived rest–frame colors in the same way as for
our sample. For the CPG sample, there are 916 galaxies with
SDSSphotometry.Wecalculatedtheprojecteddistancebetween
galaxies in each pair using redshifts taken from HyperLeda.
Following Xu&Sulentic (1991) we separated this sample into Fig.6. Distribution of absolute magnitudes in the r–band for
close–interacting(CLO–galaxieswithseparationSEP<2Mpc) thewholeAMIGA–SDSSsample,andfortheNair&Abraham
andwide(WID)pairs(SEP>2Mpc).Wecheckedthedistribution (2010),Efigi,andCPGsamplesdescribedinthetext.
ofredshiftandabsolutemagnitudesinther–bandforeachsam-
ple and found good agreementwith the whole AMIGA–SDSS
sample. In the cases of EFIGI and CPG catalogs, we removed the E/S0 population of AMIGA is fainter than any other sam-
theobjectswithrecessionvelocitieslowerthan1500km/saswe
ple (Sulenticetal. 2006). The median values of colors for the
didforourAMIGAsample,duetothedeterminationoftheiso-
Nair&Abraham(2010)andclosepairssamples,forthe(Sb–Sc)
lation parameters (Verleyetal. 2007b). We have also removed
spirals,areconsistentbutslightlybluerthanoursample.Inthe
objectsfainterthanMr >-17sincewedonothavecounterparts caseofthecomparisonwithNair&Abraham(2010),thediffer-
in the AMIGA–SDSS sample. The final samples of compari- encesin colormaybe producedbythe differentmorphological
son have 8879 (Nair), 3294 (EFIGI), and 839 (CPG) galaxies.
classificationsusedinbothsamples.Wefindtheirmorphologies
In Fig. 6 we present the absolute magnitudedistribution in the to be earlier than ours, with a mean deviationof ∼1.5 for each
r–bandforeachsample,as wellasthe probabilitygivenbythe
Hubbletype.Inordertotestthispossibility,weselectedasub-
Kolmogorov–Smirnov two sample test that these distributions
samplecomposedbythe142commonobjectsbetweenAMIGA
areindistinguishabletothe AMIGA–SDSSone.Thisprobabil-
andtheNair&Abraham(2010)sample,andcalculatedtheme-
ityislargerthan90%fortheCPGandNairsamples,whilethe dianvaluesof(g−r)obtainedusingeachmorphologicalclassifi-
lowestvalueisfoundinthecaseoftheEFIGIsample(63%). cation.Wefoundthatthedifferencebetweenbothmediancolors
Wefoundgoodagreementforthecolorsofearly–typegalax- inthecommonsamplewasconsistentwiththatfoundusingthe
ies in all samples. However, in all cases (from T=-5 to T=0), fullsamples.
the median values for the AMIGA sample are a little bluer Nevertheless,thedifferencesincolorofclosepairsseemto
(but within the errors) than the other samples. Because the be more robust because the colors of wide pairs are as red as
color–luminosityrelationhasatrend(brightergalaxiesarered- thecolorsofisolatedgalaxies.Thescatteris alsolargerforthe
der), this bluer color could be presumably due to the fact that closepairs,inagreementwithLarson&Tinsley(1978).InFig.7
7
Ferna´ndezLorenzoetal.:TheAMIGAsampleofisolatedgalaxiesXI
Fig.7.Distributionofabsolutemagnitudesintheg–band(left),r–band(centre)and(g−r)color(right)forallSb(top),Sbc(middle)
andSc(bottom)galaxies.ThesolidlinesrepresenttheAMIGA–SDSSsampleandthedashedlinesarethedistributionoftheCPG
closepairs.
we present the distribution of absolute magnitudes in r and g– We have also investigated the change in the median colors
bandsaswellas(g−r)colorforthreemorphologicaltypes(Sb, whenwerejectedobjectswithasymmetries(IA=1)andthedif-
Sbc and Sc) of the AMIGA–SDSS sample. We have also rep- ferencesarenegligible.
resented the same distributions for the close pairs of the CPG
sample.Whilethecolordistributionofeachmorphologicaltype
hasgaussiandistributionforoursample,thecolorhistogramfor 7. Conclusions
the CPG sample follows a non gaussian distribution. The loss
Wehavetakenafirstlookatthecolorsofisolatedgalaxiesusing
ofGaussianity in thedistributionofcolorcan beinterpretedas
SDSSgandrmagnitudes.Afirstlookisalsoinevitablyanintro-
aneffectoftheenvironmentalnurturethatoccursinasampleof
ductionintothepitfallsofusingtheSDSSautomatedmeasures
pairs.
of magnitudes. We find that the color distributions of morpho-
8
Ferna´ndezLorenzoetal.:TheAMIGAsampleofisolatedgalaxiesXI
logicalsubtypescanbewelldescribedasGaussiandistributions deVaucouleurs,G.,deVaucouleurs,A.,&Corwin,H.G.,Jr.1976,inSecond
withFWHM(g−r)=0.1–0.2.Thisisexpectedforsampleswhere referencecatalogueofbrightgalaxies,Austin:UniversityofTexasPress.,6
effects of environmental nurture have been minimized, and is +396p.
deVaucouleurs,G.,deVaucouleurs,A.,Corwin,H.G.,Jr.,Buta,R.J.,Paturel,
supportedbythe factthatthisGaussianity wasnotobservedin
G.,&Fouque,P.1991,Volume1-3,XII,2069pp.7figs.. Springer-Verlag
thesampleofgalaxypairs.Themajorityofthecolordispersion BerlinHeidelbergNewYork
forspiralsubtypesis caused bya color–luminositycorrelation, Dressler,A.1980,ApJ,236,351
with more massive spirals showing redder colors. In fact most Durbala,A.,Sulentic,J.W.,Buta,R.,&Verdes-Montenegro,L.2008,MNRAS,
390,881
of the Sb spirals in our sample concentrateat the upperregion
Espada,D.2006,Ph.D.Thesis
ofthebluecloud,belowtheredsequence.Weseelittleevidence
Espada,D.,Verdes-Montenegro,L.,Huchtmeier,W.K.,etal.2011,A&A,532,
for a green valley in our sample with most spirals redder than A117
(g−r)=0.7havingspuriouscolors(∼80%).Wefindapreliminary Fouque,P.,&Paturel,G.1985,A&A,150,192
difference in the color of the isolated and paired spiral galax- Gunn,J.E.,etal.2006,AJ,131,2332
Heidmann,J.,Heidmann,N.,&deVaucouleurs,G.1972,MmRAS,75,105
ies. The median value of (g−r) seems to be bluer when inter-
Hogg,D.W.,etal.2003,ApJ,585,L5
actions come into play. Nevertheless, no difference is found in Hogg,D.W.,etal.2004,ApJ,601,L29
the (g−r) color of early–type galaxies, which suggests that the Iovino,A.2002,AJ,124,2471
bluer color of spirals in pairs is presumably due to interaction Karachentsev, I. D. 1972, Soobshcheniya Spetsial’noj Astrofizicheskoj
Observatorii,7,1
enhancedstar formation.Our sample of isolated galaxiesgives
Karachentseva,V.E.1973,AstrofizicheskieIssledovaniiaIzvestiyaSpetsial’noj
amedianabsolutedeviationincolorwhichislowerthanthatin
AstrofizicheskojObservatorii,8,3
pairs of galaxies, where a more active star formation and, per- Larson,R.B.,&Tinsley,B.M.1978,ApJ,219,46
haps,ahigherdustdiffusioncausedbytheinteraction,are also Leon,S.,&Verdes-Montenegro,L.2003,A&A,411,391
sourcesofcolordispersion.Themeancolorsanddispersionsfor Leon,S.,Verdes-Montenegro,L.,Sabater,J.,etal.2008,A&A,485,475
Lewis,I.,etal.2002,MNRAS,334,673
isolatedgalaxysubtypes(especiallyE/S0andSb–Sc)arelikely
Lisenfeld,U.,Verdes-Montenegro,L.,Sulentic,J.,etal.2007,A&A,462,507
thebestnurture–freemeasuressofarobtained. Lisenfeld,U.,Espada,D.,Verdes-Montenegro,L.,etal.2011,arXiv:1108.2130
Marcum,P.M.,Aars,C.E.,&Fanelli,M.N.2004,AJ,127,3213
Acknowledgements. ThisworkhasbeensupportedbyGrantAYA2008-06181- Masters,K.L.,etal.2010,MNRAS,404,792
C02 co-financed by MICINN and FEDER funds, and the Junta de Andaluca Nair,P.B.,&Abraham,R.G.2010,ApJS,186,427
(Spain) grants P08-FQM-4205 and TIC-114. We are grateful to the AMIGA Patton,D.R.,Ellison,S.L.,Simard,L.,McConnachie,A.W.,&Mendel,J.T.
team for the great work they have done on improving the sample and to the 2011,MNRAS,412,591
anonymousrefereeforusefulcomments. Paturel,G.,Fouque,P.,Bottinelli,L.,&Gouguenheim,L.1989,A&AS,80,299
Wf4EverisfundedbytheSeventhFrameworkProgrammeoftheEuropean Paturel,G.,Theureau,G.,Bottinelli,L.,etal.2003,A&A,412,57
Commission (Digital Libraries and Digital Preservation area ICT-2009.4.1 Reid,I.N.,Brewer,C.,Brucato,R.J.,etal.1991,PASP,103,661
projectreference270192).Wearegratefultoallourcollaboratorsinthisproject. Sabater,J.,Leon,S.,Verdes-Montenegro,L.,etal.2008,A&A,486,73
Wethankthe SDSSgroupformakingtheir catalogues anddata publicly Sabater,J.,Verdes-Montenegro,L.,Leon,S.,etal.2012,TheAMIGAsampleof
available. Funding for SDSS-III has been provided by the Alfred P. Sloan isolatedgalaxies.X.Opticalcharacterisationofnuclearactivity,Submittedto
Foundation,theParticipatingInstitutions,theNationalScienceFoundation,and A&A
theU.S.DepartmentofEnergy.TheSDSS-IIIwebsiteishttp://www.sdss3.org/. Schlegel,D.J.,Finkbeiner,D.P.,&Davis,M.1998,ApJ,500,525
SDSS-III is managed by the Astrophysical Research Consortium for the Skibba,R.A.,etal.2009,MNRAS,399,966
ParticipatingInstitutionsoftheSDSS-IIICollaborationincludingtheUniversity Schmidt,M.1968,ApJ,151,393
ofArizona,theBrazilianParticipationGroup,BrookhavenNationalLaboratory, Stocke,J.T.,Keeney,B.A.,Lewis,A.D.,Epps,H.W.,&Schild,R.E.2004,
UniversityofCambridge,UniversityofFlorida,theFrenchParticipationGroup, AJ,127,1336
the German Participation Group, the Instituto de Astrofisica de Canarias, Strateva,I.,etal.2001,AJ,122,1861
the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins Sulentic,J.W.,etal.2006,A&A,449,937
University, Lawrence Berkeley National Laboratory, Max Planck Institute for Sulentic,J.2010,GalaxiesinIsolation:ExploringNatureVersusNurture,421,3
Astrophysics,NewMexicoStateUniversity,NewYorkUniversity, OhioState vanderWel,A.,Holden,B.P.,Franx,M.,etal.2007,ApJ,670,206
University,PennsylvaniaStateUniversity,UniversityofPortsmouth,Princeton vanderWel,A.,Bell,E.F.,Holden,B.P.,Skibba,R.A.,&Rix,H.-W.2010,
University,theSpanishParticipationGroup,UniversityofTokyo,Universityof ApJ,714,1779
Utah,VanderbiltUniversity, UniversityofVirginia,UniversityofWashington, Verdes-Montenegro,L.,Sulentic,J.,Lisenfeld,U.,Leon,S.,Espada,D.,Garcia,
andYaleUniversity. E.,Sabater,J.,&Verley,S.2005,A&A,436,443
WethanktheSAO/NASAAstrophysicsDataSystem(ADS)thatisalways Verley,S.,Odewahn,S.C.,Verdes-Montenegro,L.,etal.2007a,A&A,470,505
souseful. Verley,S.,etal.2007b,A&A,472,121
Xu,C.,&Sulentic,J.W.1991,ApJ,374,407
York,D.G.,etal.2000,AJ,120,1579
References Zwicky, F., Herzog, E., Karpowicz, M., Kowal, C., & Wild, P. 1961-1968,
Catalogue of Galaxies and of Cluster of Galaxies (Pasadena, California
Aihara,H.,etal.2011,ApJS,193,29 InstituteofTechnology,CGCG)
Athanassoula,E.1984,Phys.Rep.,114,321
Baillard,A.,etal.2011,arXiv:1103.5734
Baldry,I.K.,Glazebrook,K.,Brinkmann,J.,etal.2004,ApJ,600,681
Baldry, I. K., Balogh, M. L., Bower, R. G., Glazebrook, K., Nichol, R. C.,
Bamford,S.P.,&Budavari,T.2006,MNRAS,373,469
Balogh, M. L.,Schade, D., Morris, S. L.,Yee, H. K. C., Carlberg, R. G., &
Ellingson,E.1998,ApJ,504,L75
Ball,N.M.,Loveday,J.,&Brunner,R.J.2008,MNRAS,383,907
Blanton,M.R.,etal.2003,ApJ,594,186
Blanton,M.R.,&Roweis,S.2007,AJ,133,734
Blanton,M.R.,Kazin,E.,Muna,D.,Weaver,B.A.,&Price-Whelan,A.2011,
arXiv:1105.1960
Bottinelli,L.,Gouguenheim,L.,Paturel,G.,&Teerikorpi,P.1995,A&A,296,
64
Bruzual,G.,&Charlot,S.2003,MNRAS,344,1000
Calzetti,D.,Armus,L.,Bohlin,etal. 2000,ApJ,533,682
Capak,P.,Abraham,R.G.,Ellis,R.S.,Mobasher,B.,Scoville,N.,Sheth,K.,&
Koekemoer,A.2007,ApJS,172,284
9