Astronomy&Astrophysicsmanuscriptno.planck˙nearby˙galaxies˙aa6 (cid:13)c ESO2011 January12,2011 Planck Early Results: The Planck View of Nearby Galaxies PlanckCollaboration:P.A.R.Ade67,N.Aghanim44,M.Arnaud54,M.Ashdown52,72,J.Aumont44,C.Baccigalupi65,A.Balbi25, A.J.Banday70,6,59,R.B.Barreiro49,J.G.Bartlett3,50,E.Battaner74,K.Benabed45,A.Benoˆıt45,J.-P.Bernard70,6,M.Bersanelli23,38,R.Bhatia30, J.J.Bock50,7,A.Bonaldi34,J.R.Bond5,J.Borrill58,68,F.R.Bouchet45,M.Bucher3,C.Burigana37,P.Cabella25,J.-F.Cardoso55,3,45, A.Catalano3,53,L.Cayo´n16,A.Challinor73,52,8,A.Chamballu42,R.-R.Chary43,L.-YChiang46,P.R.Christensen62,26,D.L.Clements42⋆, S.Colombi45,F.Couchot57,A.Coulais53,B.P.Crill50,63,F.Cuttaia37,L.Danese65,R.D.Davies51,R.J.Davis51,P.deBernardis22,G.de Gasperis25,A.deRosa37,G.deZotti34,65,J.Delabrouille3,J.-M.Delouis45,F.-X.De´sert40,C.Dickinson51,H.Dole44,S.Donzelli38,47,O.Dore´50,7, U.Do¨rl59,M.Douspis44,X.Dupac29,G.Efstathiou73,T.A.Enßlin59,F.Finelli37,O.Forni70,6,M.Frailis36,E.Franceschi37,S.Galeotta36, K.Ganga3,43,M.Giard70,6,G.Giardino30,Y.Giraud-He´raud3,J.Gonza´lez-Nuevo65,K.M.Go´rski50,76,S.Gratton52,73,A.Gregorio24, A.Gruppuso37,F.K.Hansen47,D.Harrison73,52,G.Helou7,S.Henrot-Versille´57,D.Herranz49,S.R.Hildebrandt7,56,48,E.Hivon45,M.Hobson72, 1 W.A.Holmes50,W.Hovest59,R.J.Hoyland48,K.M.Huffenberger75,A.H.Jaffe42,W.C.Jones15,M.Juvela14,E.Keiha¨nen14,R.Keskitalo50,14, 1 0 T.S.Kisner58,R.Kneissl28,4,L.Knox18,H.Kurki-Suonio14,32,G.Lagache44,A.La¨hteenma¨ki1,32,J.-M.Lamarre53,A.Lasenby72,52, 2 R.J.Laureijs30,C.R.Lawrence50,S.Leach65,R.Leonardi29,30,19,M.Linden-Vørnle10,M.Lo´pez-Caniego49,P.M.Lubin19,J.F.Mac´ıas-Pe´rez56, C.J.MacTavish52,S.Madden54,B.Maffei51,D.Maino23,38,N.Mandolesi37,R.Mann66,M.Maris36,E.Mart´ınez-Gonza´lez49,S.Masi22, n S.Matarrese21,F.Matthai59,P.Mazzotta25,A.Melchiorri22,L.Mendes29,A.Mennella23,36,M.-A.Miville-Descheˆnes44,5,A.Moneti45, a J L.Montier70,6,G.Morgante37,D.Mortlock42,D.Munshi67,73,A.Murphy61,P.Naselsky62,26,P.Natoli25,2,37,C.B.Netterfield12, H.U.Nørgaard-Nielsen10,F.Noviello44,D.Novikov42,I.Novikov62,S.Osborne69,F.Pajot44,B.Partridge31,F.Pasian36,G.Patanchon3, 1 1 M.Peel51,O.Perdereau57,L.Perotto56,F.Perrotta65,F.Piacentini22,M.Piat3,S.Plaszczynski57,E.Pointecouteau70,6,G.Polenta2,35, N.Ponthieu44,T.Poutanen32,14,1,G.Pre´zeau7,50,S.Prunet45,J.-L.Puget44,W.T.Reach71,R.Rebolo48,27,M.Reinecke59,C.Renault56, ] S.Ricciardi37,T.Riller59,I.Ristorcelli70,6,G.Rocha50,7,C.Rosset3,M.Rowan-Robinson42,J.A.Rubin˜o-Mart´ın48,27,B.Rusholme43, O M.Sandri37,G.Savini64,D.Scott13,M.D.Seiffert50,7,P.Shellard8,G.F.Smoot17,58,3,J.-L.Starck54,9,F.Stivoli39,V.Stolyarov72,R.Sudiwala67, C J.-F.Sygnet45,J.A.Tauber30,L.Terenzi37,L.Toffolatti11,M.Tomasi23,38,J.-P.Torre44,M.Tristram57,J.Tuovinen60,M.Tu¨rler41,G.Umana33, . L.Valenziano37,J.Varis60,P.Vielva49,F.Villa37,N.Vittorio25,L.A.Wade50,B.D.Wandelt45,20,D.Yvon9,A.Zacchei36,andA.Zonca19 h p (Affiliationscanbefoundafterthereferences) - o r t s ABSTRACT a [ Theall-skycoverageofthePlanckEarlyReleaseCompactSourceCatalogue(ERCSC)providesanunsurpassedsurveyofgalaxiesatsubmillimetre (submm)wavelengths,representingamajorimprovementinthenumbersofgalaxiesdetected,aswellastherangeoffar-IR/submmwavelengths 1 overwhichtheyhavebeenobserved.Weherepresentthefirstresultsonthepropertiesofnearbygalaxiesusingthesedata.WematchtheERCSC v cataloguetoIRAS-detectedgalaxiesintheImperialIRASFaintSourceRedshiftCatalogue(IIFSCz),sothatwecanmeasurethespectralenergy 5 distributions(SEDs)oftheseobjectsfrom60to850µm.Thisproducesalistof1717galaxieswithreliableassociationsbetweenPlanckandIRAS, 4 fromwhichweselectasubsetof468forSEDstudies,namelythosewithstrongdetectionsinthethreehighestfrequencyPlanckbandsandno 0 evidenceofcirruscontamination.TheSEDsarefittedusingparametricdustmodelstodeterminetherangeofdusttemperaturesandemissivities. 2 Wefindevidence for colderdust thanhaspreviously beenfound inexternal galaxies,withT < 20K.Suchcoldtemperatures arefoundusing . 1 boththestandardsingletemperaturedustmodelwithvariableemissivityβ,oratwodusttemperaturemodelwithβfixedat2.Wealsocompare 0 ourresultstostudiesofdistantsubmmgalaxies(SMGs)whichhavebeenclaimedtocontaincooler dustthantheirlocalcounterparts. Wefind 1 thatincludingoursampleof468galaxiessignificantlyreducesthedistinctionbetweenthetwopopulations.FitstoSEDsofselectedobjectsusing 1 moresophisticatedtemplatesderivedfromradiativetransfermodelsconfirmthepresenceofthecolderdustfoundthroughparametricfitting.We : thusconcludethatcold(T <20K)dustisasignificantandlargelyunexploredcomponentofmanynearbygalaxies. v i Keywords.Infrared:galaxies–Submillimetre:galaxies–Galaxies:ISM X r a 1. Introduction tion(SED)ofdustemission,combinedwithlimitedwavelength coverage,meansthatIRASwasinsensitivetodustbelowatem- Dustisanimportantconstituentoftheinterstellarmedium(ISM) peratureof∼ 30K.ObservationsofdustinourownGalaxyby of galaxies. Whilst some properties of dust in our own and the FIRAS instrumenton COBE (Reach et al. 1995)foundev- very nearby galaxies can be studied through its absorption of idence for dust at several differenttemperatures. This included starlight, it was the IRAS satellite that first allowed dust emis- a widespread component at 16–21K, and another at 10–14K sionto be directlyobservedin largesamplesofexternalgalax- associated with molecular clouds in the inner Galaxy. A third ies (e.g., Devereux & Young 1990). The all-sky IRAS survey widespreadcoldercomponent,at4–7K,waslateridentifiedwith at 12, 25, 60 and 100µm in wavelength provided much new theCosmicInfraredBackground(CIB;Pugetetal.1996;Fixsen information on the properties of dust and how this relates to et al. 1998).None of these componentswould be detectable in other aspects of galaxies and galaxy evolution. However, the externalgalaxiesbyIRAS.COBE-DIRBEobservationsalsode- strong temperature dependenceof the spectral energy distribu- tected56externalgalaxies,findinganaveragedusttemperature of27.6K(Odenwaldetal.1996). ⋆ Correspondingauthor:D.L.Clements,[email protected] 1 PlanckCollaboration:ThePlanckViewofNearbyGalaxies Observations at longer far-infrared (FIR) or submillimetre comparisonoftheERCSCwithexistingdatafromground-based (submm)wavelengthsfromtheground(e.g.,Dunneetal.2000), observatories.Section4presentstheresultsoffittingparametric from space (e.g., Dale et al. 2005) or in combination (e.g., models to the dust SEDs of ERCSC galaxies, while Section 5 Willmeretal.2009),haveprovidedhintsthatcoolerdustplays discusses the results of physical template fitting. Finally, we asignificantroleinnearbygalaxies.ObservationswithHerschel draw conclusions in Section 6. Throughout this paper we as- ofpre-selectedobjects(e.g.,Bosellietal.2010)orofrelatively sume a concordance cosmology, with H = 70kms−1Mpc−1, 0 small fields (e.g., H-ATLAS Eales et al. 2010, covering up to Ω =0.7andΩ =0.3. Λ M 550deg2) provide valuable data at 250 to 500µm, which con- strain the long wavelength dust properties for specific popula- tions. However, the availability of the Planck1 Early Release 2. Planck ObservationsofNearbyGalaxies Compact Source Catalogue (ERCSC) provides a long wave- 2.1.ThePlanckMission length counterpart to IRAS, allowing us an unbiased view of theFIR-to-submmSEDsofa large,unbiasedsampleofnearby Planck (Tauberet al. 2010;Planck Collaboration2011a)is the (z<0.25)galaxies.Wearenow,forthefirsttime,abletoexam- thirdgenerationspacemissiontomeasuretheanisotropyofthe inetheroleofcolddustforawiderangeofobjectsinthelocal cosmic microwave background (CMB). It observes the sky in Universe. ninefrequencybandscovering30–857GHzwith highsensitiv- The discovery of the CIB (Puget et al. 1996; Fixsen et al. ity and angular resolution from 31′ to 5′. The Low Frequency 1998) has added to the importance of our understanding of InstrumentLFI; (Mandolesiet al. 2010;Bersanelli et al. 2010; dust in galaxies. The CIB demonstrates that roughly 50% of Mennellaetal.2011)coversthe28.5,44.1,and70.3GHzbands, all energy generated in the history of the Universe was ab- withamplifierscooledto20K.TheHighFrequencyInstrument sorbed by dust and reprocessed into the FIR/submm (Gispert (HFI;Lamarreetal.2010;PlanckHFI CoreTeam2011a)cov- etal. 2000).Deep surveysat850µmwith SCUBA (e.g.,Smail ers the 100, 143, 217, 353, 545, and 857 GHz bands, with etal.1997;Hughesetal.1998;Ealesetal.2000;Coppinetal. bolometerscooled to 0.1K. Polarization is measured in all but 2006) and at nearby wavelengths with other instruments (e.g., the highest two bands (Leahy et al. 2010; Rosset et al. 2010). MAMBO, AzTEC and LABOCA) have revealed much higher A combinationof radiative coolingand three mechanicalcool- number counts than would be predicted by a non-evolvingex- ers producesthe temperaturesneededfor the detectorsand op- trapolation of the local population. There must thus be very tics(PlanckCollaboration2011b).Twodataprocessingcenters rapidevolutionoftheFIR/submmgalaxypopulation,something (DPCs) checkandcalibratethedata andmakemapsof thesky confirmed by observations with ISO, (e.g., Dole et al. 2001) (Planck HFI Core Team 2011b; Zacchei et al. 2011). Planck’s Spitzer(e.g.,Frayeretal.2006;Be´therminetal.2010;Clements sensitivity,angularresolution,andfrequencycoveragemakeita et al. 2010a) and BLAST (Devlin et al. 2009). Herschel ob- powerfulinstrumentforGalacticandextragalacticastrophysics servations have now confirmed this rapid evolution through a as well as cosmology. Early astrophysics results are given in combination of number count (Clements et al. 2010c; Oliver PlanckCollaboration,2011h–z. et al. 2010) and luminosity function (Dye et al. 2010) studies. However,detailedinterpretationoftheseresultsishamperedby 2.2.ThePlanckEarlyReleaseCompactSourceCatalogue ourpoorknowledgeofgalaxySEDsinthe100–1000µmrange. Thisisdemonstrated,forexample,bytheapparentseparationin ThePlanckERCSC(PlanckCollaboration2011c)providespo- thetemperature-luminosityplaneoflocalIRAS-selectedgalaxies sitionsandfluxdensitiesofcompactsourcesfoundineachofthe andhighredshiftSCUBA-selectedSMGs(e.g.,Clementsetal. nine Planck frequency maps. The flux densities are calculated 2010b). The origin of this separation is unclear. It might rep- using aperture photometry, with careful modelling of Planck’s resent a genuine change in dust temperature with redshift, and elliptical beams. The colour corrections for sources with spec- selectionbiasesmaybepartlyinvolved,butitcouldalsoreflect tral index α = −0.5 (using the conventionSν ∝ να) are 1.017, ourignoranceofthefullFIR/submmSEDoflocalgalaxies.By 1.021and 1.030,respectively,forthe 28.5,44.1,and 70.3GHz properlyestablishingazeroredshiftbaselineforthedustSEDs LFI channels. Flux densities taken from the ERCSC should be oftypicalgalaxies,thePlanckERCSCwillallowtheoriginsof dividedby the appropriatecolourcorrectionto givethe correct theCIBandthenatureofthegalaxiesthatcontributetoittobe flux values for an assumed narrow band measurement at the muchbetterdetermined. centralfrequency.Forfrequenciesfrom28.5to143GHz,com- The central goals of this paper are thus twofold: to exam- pactsourceshavebeendetectedusinga versionofthe “Powell inethepropertiesofalargesampleoflocal(z < 0.25)galaxies Snakes”techniques(Carvalhoetal.2009);fordetailsseePlanck toestablish therangeofdusttemperaturesandotherproperties Collaboration (2011c). In the four higher frequency channels, found locally; and thus to set the local baseline against which sources were located using the SExtractor package (Bertin & higher redshift studies, and especially studies of the SMGs re- Arnouts1996).Sourcesdetectedinoneormoreofthefrequency sponsiblefortheCIB,canbecompared. mapswerethenputthroughafurthersetofsecondaryselection criteria; these are discussed in detail in Planck Collaboration The rest of this paper is organisedas follows. In Section 2 (2011c). The primary criterion utilized was a Monte Carlo as- we give details of Planck’s observations of local galaxies and sessment designed to ensure that ≥90% of the sources in the the ERCSC. We also discuss the results of matching ERCSC cataloguehaveafluxaccuracyofatleast30%. galaxiestosourcesobservedbyIRAS.InSection3wepresenta 1 Planck (http://www.esa.int/Planck) is a project of the European 2.3.MatchingTheERCSCtoIRASData SpaceAgency(ESA)withinstrumentsprovidedbytwoscientificcon- To understand the FIR Spectral SEDs we need a combination sortia funded by ESA member states (in particular the lead countries FranceandItaly),withcontributionsfromNASA(USA)andtelescope of data at long wavelengths, provided by the Planck ERCSC, reflectorsprovidedbyacollaborationbetweenESAandascientificcon- and data near the peak of a typical galaxy dust SED at about sortiumledandfundedbyDenmark. 100µm. The best source for the latter information is the IRAS 2 PlanckCollaboration:ThePlanckViewofNearbyGalaxies testthevalidityoftheassociationwiththeIRASsource.Thisin- cludedinspectionoftheSkySurveypostagestampsprovidedin NED.Associationswereacceptedasrealiftheassociatedgalaxy had a blue (g or B) magnitude brighter than 16. The surface- densityofsuchgalaxiesleadstotheprobabilityofachanceas- sociationbeing∼3%.ForsourceswheretherewasbothanIRAS anda 2MASSassociation,thislimitwasrelaxedto B = 17(or K ∼13).Ofthe88ERCSC-IIFSCzassociationswithpositional offsets 3–5′ (and with spectroscopic or photometric redshifts) 72 were associated with bright galaxies, two were associated withasecondFSCsourcehavingcirrus-likecoloursandarepre- sumed to be cirrus, and the remaining14 are classified as pos- sible galaxy associations (these are excluded from the reliable galaxycatalogueusedhereforfurtheranalysis). ThesecondcategoryofERCSC-IIFSCz associationswhich wescrutinisedindetailwerethoseforwhichthereisnoredshift in the IIFSCz. There were 165 of these and the NED associa- tionssuggestthat38arebrightgalaxies,sevenarecirrus,twoare brightplanetarynebulae,andtheremaining118areclassifiedas possible galaxyassociations (andexcludedhere). We were left with1717reliableERCSC-IIFSCzgalaxyassociationsofwhich Fig.1. Histogram of offsets between ERCSC and IIFSCz posi- 337areflaggedasextendedintheERCSC. 1597ofthese1717 objectshavespectroscopicredshifts. tions. all-sky FIR survey, and the most recent analysis of the IRAS 2.4.ERCSCSourcesnotassociatedwithIIFSCzSources Faint SourceCatalogue (FSC) is providedby Wang & Rowan- Fig.2showstheskydistributionofERCSCsourcesat|b|>20◦, Robinson (2009) in the Imperial IRAS FSC redshift survey with sourcesflagged as extendedin the ERCSC shownas blue (IIFSCz). This was constructed using IRAS FSC sources, all filledhexagons,andpoint-sourcesshowninblack.Associations of which are at |b| > 20◦, with IRAS colours used to exclude withtheIIFSCzareshownasredcircles.Theextendedsources stars and cirrus sources (with S(100)/S(60) > 8). The NASA not associated with IIFSCz sources have a strikingly clustered Extragalactic Database (NED) was then used to find spectro- distribution,whichmatchestheareasofourGalaxywithstrong scopic redshifts for the resulting FSC source list, and to asso- cirrusemission,asevidencedbyIRAS100µmmapsandbythe ciatethesourceswithSDSS(whereavailable;Yorketal.2000) ERCSCcirrusflag(values> 0.25).Wepresumethemajorityof and2MASS(Skrutskieetal.2006)galaxiestofindphotometry thesearecirrussourcesandnotextragalactic. at0.36–2.2µm.Thisphotometrywasthenusedtoestimatepho- To test this further, we looked for NED associations with tometricredshiftsforsourceswithoutspectroscopicredshifts. all444extendedERCSCsourceslackingIIFSCzassociationsat ThestartingpointformatchingtheERCSCtotheIIFSCzis |b| > 60◦. Only12 werefoundto haveassociationswith bright the 9042 sources detected at 857GHz by Planck. This is then restricted to the 5773 sourcesat |b| > 20◦ for which there will (b,g < 16)galaxies.Extrapolatingto|b|= 20–60◦,weestimate that a further ∼ 50 of these extended non-FSC sources will be beFSCdata.AssociationsofERCSCsourceswithIIFSCzwere looked for using a search radius of 5′. The histogram of posi- bright galaxies. The remainder of the 3431 extended non-FSC sourcesat|b|>20◦arepresumedtobeGalacticcirrus. tionaloffsets is shown in Fig. 1. The bulk of associations have offsetswithin2′.Evenat5′thereisnosteepincreaseinthenum- A ridge of non-FSC point sources can be seen in Fig. 2 berofassociationswhichwouldbeindicativeofalargefraction at b ∼ 70◦, l ∼ 120–230◦. These correspond to one of the of chance associations. On the basis of source surface-density, IRAScoveragegaps.WeexaminedNEDassociationsforall482 thechanceofarandomassociationwithanIIFSCzsourcewithin ERCSC point-sources not associated with IIFSCz sources. 32 3′is1.6%,andwithin5′itis4.5%.Atotalof1966associations were found to be associated with Local Group galaxies (M31, were found within 5′. There were 106 cases where an ERCSC SMCandWLM,with28intheLMC),123arebrightgalaxies, source picked up an association with more than one IIFSCz 27areassociatedwithIRASFSCorPSCGalacticcirrussources, source.Weexaminedthesecasescarefullytoensurethatonlya and10arebrightstarsorplanetarynebulae.Mostofthebright singleassociationwasaccepted.Generallythenearerassociation galaxies lie in the IRAS coveragegaps. The remaining289 are was preferred. Where the offsets of the two associations were classifiedaspossiblegalaxyassociations(andexcludedhere). comparable,the brighter IRAS source was preferred.There are To summarise, we have found a net total of 1884 definite 20caseswheretwobrightgalaxieslessthan5′aparthavegener- associations with galaxies. These constitute an ERCSC galaxy atedasingleERCSCsource,forwhichtheremaybeasignificant catalogue.A further419sourcesare notassociated with bright contributionfrombothgalaxiestotheERCSCflux.Thesecon- galaxies,buttherearegroundsforthinkingtheycouldbeextra- fused sources would benefit from additional observations with galactic sources. Some have IIFSCz associations, but there are ground-basedsubmminstrumentstodeterminethecontribution toomanypossiblefaintopticalornear-IRgalaxycounterpartsto ofeachcomponenttothesubmmemissiondetectedbyPlanck. beconfidentwhichmightbeassociatedwiththeERCSCsource. The remaining ERCSC-IIFSCz associations were further Someofthese419sourcesarealmostcertainlyfaintergalaxies, scrutinised as follows. Firstly, for sources with positional off- althoughmanycouldturnouttobecirrus.Improvedsubmmor sets between the two catalogues in the range 3–5′ all NED as- FIR positions are needed, either via Herschel or ground-based sociationswithin 5′ ofthe ERCSC positionswere examinedto telescopes,toidentifythesesourcesreliably. 3 PlanckCollaboration:ThePlanckViewofNearbyGalaxies Fig.2.SkyplotofERCSCsourcesingalacticcoordinates.BlackfilledhexagonsareERCSCpoint-sourcesandbluefilledhexagons areERCSC sourcesflaggedasextended.Red hexagonsaresourcesassociatedwith IIFSCz IRASFSC galaxies,afterscrutinising suspect categorieswith NED (and excludingsome, as described in the text). Green hexagonsare ERCSC sources notassociated withIIFSCz,butassociatedwithbrightgalaxiesinNED(onlyfor|b|>60◦forextendedsources). Followingthisidentificationanalysiswerestrictourselvesto are thosemostlikelyto cause problemsforpointsourcedetec- those galaxies with reliable IIFSCz associations and with de- tionintheERCSC.WemeasurethecirrusRMSina3×3array tections in the 857 and 545GHz bands at significance of 5σ of points, separated by 0.1◦ and centred on the position of the or greater, as well as detections in the 353GHz band of 3σ or ERCSC source. Since cirrus emission is likely to have cooler greater.Thisamountstoatotalsamplesizeof595galaxies. FIR-to-submmcoloursthantheintegratedemissionofanexter- nalgalaxy,wethenlookforanycorrelationbetweencirrusRMS andthe60µm-to-857GHzcolour.WeplotthisrelationinFig.3. 2.5.CirrusContamination Our analysis of the non-IIFSCz-identified ERCSC sources in As can be seem from Fig. 3, there appears to be a correla- Section 2.4 led us to the conclusion that sources which are tion between colour and cirrus RMS for the sources classified extended in the ERCSC are a result of cirrus structure in our asextendedintheERCSC.WeconcludethattheERCSCfluxes own Galaxy, or at best are a combination of cirrus structure forthesesourcesarepartiallycontaminatedwithcirrusemission with flux from a galaxy. Of the 595 reliably detected IIFSCz- fromourownGalaxy.We thusexcludethese127sourcesfrom identified ERCSC sources, 127 are listed as extended in the further analysis. Of the remaining 468 non-extended ERCSC ERCSC. We test these objectsfor the possibility of cirruscon- sources,fewerthan10lieintheregionofthiscorrelation.These taminationbyexaminingthe amplitudeof the localcirrusfluc- sourcesare retainedforthe followinganalysis,butanyconclu- tuationsinthe100µmcirrusmapsofSchlegeletal.(1998).We sionsthatcomesolelyfromthesespecificsourceswillbetreated adopt this approach since regions of greatest cirrus fluctuation withcaution. 4 PlanckCollaboration:ThePlanckViewofNearbyGalaxies FIR/submm colours than were found for the SLUGS objects, suggesting that the galaxies detected in the ERCSC contain coolerdustthanwasdetectedinthemajorityofSLUGSsources. 3.2.COContamination One factor that has complicated the interpretation of ground- basedsubmmobservationsofgalaxieshasbeenthepresenceof COemissionlineswithinthesubmmpassbandsthatmakeasig- nificantcontributiontothecontinuumflux.Seaquistetal.(2004) estimatedthattheCO(3-2)linecontributedanaverage25%of the flux received in the SCUBA 850µm continuum passband for galaxies observed in the SLUGS survey, with the range of fluxcontributionsgoingfrom10–45%forthesubsetofSLUGS galaxies for which CO(3-2) observations were available. The SCUBA850µmfilterhasabandwidthof∼30GHz.ThePlanck 353filterissignificantlybroader,at∼90GHz,sothelinecontri- Fig.3. 60µm to 857GHz (i.e., 350µm) colour plotted against butionwillbecorrespondinglysmallerat∼8%onaverage.This thecirrusRMSat100µminIRAS.ERCSCsourcesclassifiedas contaminationfractioncanbecheckedusingobservedvaluesof point-likeareshownasopendiamonds,whileextendedsources integratedCO3-2linefluxesforavarietyofobjectsfromBayet areshownassoliddots.Notethattheextendedsourcesshowa et al. (2006) and matching them to continuum observations of clearcorrelationbetweencolourandcirrusRMS,indicatingthat similarbeamsizetotheCOobservations.Wefindcontamination thesesourcesarelikelytobecontaminatedbycirrusemission. fractionsof2%forArp220,6%forMrk231andaworstcaseex- ampleinthecentralregionofNGC253,whereacontamination of11%iscalculated. Moregenerally,thisanalysishighlightsoneoftheissuesthat We can extend this analysis to other Planck bands using mustbefacedwhenusingtheERCSCcatalogue.Anyonewish- NGC 253 as a worst case since, unlike mostothers, thisobject ing to cross-matchPlanck sources, especially those detectedat has been observed over the full range of CO transitions acces- high frequencies, with sources at other wavelengths, needs to sible fromtheground.We findthatthehigherfrequencybands take greatcare in ensuringthat the ERCSC fluxes are not con- haveareducedlevelofcontaminationcomparedtothe353chan- taminatedbycirrusemission. nel, with <1% at 857 and 6% at 545 (assuming a flat spectral line energy distribution to estimate the contribution of the CO 5-4linethatisinaccessiblefromtheground).Morenormalob- 3. ComparisontoExistingSubmmData jectsthanNGC253,notdominatedbyanongoingstarburst,will 3.1.GalaxiesdetectedwithSCUBA have an even smaller level of CO copntaminationthan this. At lowerfrequencies,though,thecontaminationcanbecomemore Thelargeststudiesofcooldustinexternalgalaxiestodatehave serious. CO 2-1 could contribute as much as 21% of the con- beenassociatedwiththeSCUBALocalUniverseGalaxySurvey tinuum flux in the 217 band in the inner regions of NGC253. (SLUGS)anditsextensions(Dunneetal.2000;Dunne&Eales In the 100 band for this objectthe CO line could contributeas 2001; Vlahakis et al. 2005; Clements et al. 2010b). These en- muchas75%ofthefluxofthethermalcontinuum.NGC253is compass a total of about 250 objects that were observed with a worstcase scenario,so moretypicalsourceswouldof course SCUBA.ThetargetswereselectedonthebasisofIRASflux B- suffermuchlesscontamination.However,veryfewgalaxiesare band optical magnitudeor FIR luminosity.Most of the objects detectedbyPlancksolelyinthermalemissioninthisband,and weredetectedonlyat850µm(i.e.,notalsoat450µm),allowing, thefewthataredetectedarebrightnearbyobjectswithsubstan- with the IRAS data, only a single component(T,β) fit – where tial archival data that can allow a direct assessment of the CO the SED is describedas Sν ∝ νβB(ν,T),with B(ν,T)beingthe contribution. Planck function,andthe parametersT and βrepresentingtem- OurconclusionfromthisanalysisisthattheCOcontribution peratureanddustemissivityindex,respectively.Asmallfraction tothecontinuumfluxislikelytobesmallerthanothersourcesof of SLUGS galaxieswere also detected at 450µm,allowing for uncertaintyforgenericERCSC-detectedgalaxiesexceptforthe theexistenceofasecond,cooler,dustcomponenttobeassessed. smallnumberwhicharedetectedinthe217band.Fluxexcesses For these objects, and more recently for an ultra-luminous IR detectedinthisbandalonemightthusresultfromCOemission galaxy (ULIRG) sample, Dunne & Eales (2001) and Clements ratherthanfromanyputativeverycolddustcomponent. et al. (2010b)found some evidence for a colder dust contribu- tion. The presence of colder dust can be inferred from colour- 4. ParametricModelsofDustSEDs colour diagrams when two submm flux densities are available. We show the SLUGS sources and the ERCSC sources (after 4.1.FittingMethod colour corrections to the Planck flux densities and a suitable scaling has been applied to convert from Planck 857GHz flux GiventhePlanckandIRASfluxdatadescribedinSection2,with densitytothe SCUBA 450µmband)in Fig.4.Ascanbeseen, appropriatecolourcorrectionsappliedtothePlanckfluxdensi- the Planck galaxieslie on the same broadtrend as the SLUGS ties,wemodeltheunderlyingsignalinobservedfrequencyband galaxies(withtheexceptionofasmallnumberofobjectsdom- νasoneormoregrey-bodysourceswithfluxdensity inated by a non-thermal AGN component, such as 3C273 and 3C279).TheERCSCsources,though,extendthetrendtocooler G(ν;T,β)∝νβB (T), (1) ν 5 PlanckCollaboration:ThePlanckViewofNearbyGalaxies 0 ≤ β ≤ 3 and 3K ≤ T ≤ 100K with a uniformprior proba- bilitybetweenthoselimits(detectionsofverylowtemperatures, T <10K,areactuallydominatedbynon-thermalemission).We adoptauniformprioronlnA,asitrangesovermanyordersof i magnitude for sources of widely varying absolute luminosities anddistances. The MCMC engine first creates a 15,000-sample Markov chain, varying one parameter at a time, using this to find an approximately-orthogonal linear combination of parame- ters, with which a subsequent 100,000-sample chain is run. Convergenceisassessedbyre-runningasmallnumberofchains from a different starting point and checking for agreement to muchbetterthanonestandarddeviationinallparameters. WecalculateanapproximationtotheBayesianevidence,or modellikelihood(Jaffe1996;Jaynes2003)inordertocompare the two-temperature and one-temperature fits. The evidence is calculatedastheaverageofthelikelihoodfunctionovertheprior distribution; we approximate the likelihood as a multivariate Fig.4. Colours for the ERCSC galaxies (black dots) compared Gaussian function of the parameters centred at the maximum- tothosefoundforSLUGSgalaxies(red;Dunne& Eales2001; likelihoodMCMC sample with covariancegivenby the empir- Vlahakisetal.2005)andULIRGs(blue;Clementsetal.2010b). ical covariance of the samples (this approximation ignores the Afluxcorrectionfactorof0.506hasbeenappliedtothePlanck priorontheamplitudeoftheindividualgreybodies). 857GHz flux densities to extrapolate them to the SCUBA InFigures5,6weshowsampleoutputfromourMCMCruns 450µm band. Only sources detected at > 3σ in the 353GHz fordifferentobjectsandmodels,alongwiththemeasuredSEDs (850µm) band and at > 5σ in the 857GHz band (the require- andfits.ForobjectssuchasF01384-7515inFigure5,ifwein- ment for inclusion in our analysis) are shown. The four points stead performa two-temperaturefit, it prefersthe amplitudeof abovethegeneraltrendin thelowerleftofthe diagramare the thesecondtemperaturecomponenttobemanytensofordersof well-knownnon-thermaldominatedsources3C279,0537−441, magnitudebelowthefirst,andgivestemperaturevaluesconsis- OJ+287and3C273.TheSLUGSpointwiththelowest60µmto tent with the one-temperaturefit; this indicates, along with the SCUBAfluxratioscorrespondstothegalaxyIC979;itisoffset approximate evidence discussed above, that a one-temperature from the general correlation for SLUGS and ERCSC galaxies, modelisstronglypreferred. andVlahakisetal.(2005)notethatitsIRASfluxdensitiesshould betreatedwithcaution. 4.2.ResultsfromParametricFits where B (T) is the Planck functionfor blackbodyflux density. 4.2.1. SingleComponentFits ν Wefitthedatad toone-componentmodelsoftheform ν Figure7showstheT−βplaneforparametricfitstoall468reli- ablyidentifiednon-extendedsourceswithintheERCSC-IIFSCz d = AG[ν(1+z);T,β]+n , (2) ν ν crossmatchwhosefluxdensitiespassourS/N ratiocriteria for ortotwo-componentmodelswithafixedβ=2grey-bodyexpo- inclusion, together with similar single temperature parametric nent, fits from Dunne et al. (2000) and Clements et al. (2010b). As canbeseen,thePlanckERCSCsourcesoverlapwiththeSLUGS d = A G[ν(1+z);T ,2]+A G[ν(1+z);T ,2]+n . (3) galaxiesbutextendtocoolertemperaturesandflatter,i.e.,lower ν 1 1 2 2 ν β,SEDs.ThemedianparametersforthePlancksourcesareT = Intheseequations,AorA isanoverallamplitudeforeachcom- 26.3K with temperatures ranging from 15 to 50K, and β=1.2 i ponent, and the factor of (1+z) converts from rest-frame fre- compared to corresponding values from 104 SLUGS galaxies quency to observed frequency for an object at redshift z. The Dunneetal.(2000)ofT =35Kandβ=1.3andofT =41Kand noisecontributionisgivenbyn ,whichwemodelasaGaussian β=1.6for26ULIRGsClementsetal.(2010b).Thisconfirmsthe ν with variance σ2. For the Planck channels, the determination resultfromconsiderationofPlanck-IRAScoloursin Fig.4 that ν of the noise contribution is described in Planck Collaboration weareseeingcoolerdustintheERCSC-IIFSCzgalaxies. (2011c).ForIRAS,thedetectionsareclassifiedintheIIFSCZof TherearetensourcescommontotheERCSC-IIFSCzcross- Wang & Rowan-Robinson (2009) into (1) good detections, for matchedcatalogueandtheSLUGSstudies.ThefitsusingPlanck which we take σ = 0.1d ; (2) marginal detections, for which data and using SLUGS data for all but two of these sources ν ν we take σ = 0.5d ; and (3) upper limits, for which we take are in good agreement. The two exceptions are NGC7541 and ν ν σ to be the reported upper limit, and d = 0. As mentioned NGC5676.Thelikelycauseofthedisagreementsinthesecases, ν ν above,weonlyconsidersourceswithdetectionsinthe857and isthepresenceofaclosecompanionIRASsourcetoNGC7541 545bandsatsignificanceofatleast5σorgreaterandinthe353 (NGC7537 3.1′ separation, and thus only ∼0.7 beam FWHM bandofatleast3σ. away), so that the Planck flux density is likely over-estimated, Thus, the parameters of our model are some subset of the andextendedIRASemissioninNGC5676,makingtheIRASFSC A,T,β, dependingon which modelwe fit. We use a Bayesian fluxdensitiesusedinouranalysisunderestimates. i i Markov Chain Monte Carlo (MCMC) (e.g., Lewis & Bridle ThepositionofourgalaxiesintheLuminosity-Temperature 2002;Jaynes2003)techniquetoprobetheparameterspace;with planeis animportantquestionsince itrelatesto claimsof evo- ourGaussiannoise,thisisequivalenttoanexplorationoftheχ2 lution in the dust propertiesof galaxies. It has previouslybeen surface, albeit with a nonlinear parameterization.We require a suggestedthathighredshift,highluminositySMGshavelower 6 PlanckCollaboration:ThePlanckViewofNearbyGalaxies Fig.5.Leftpanel:SamplesfromtheSEDlikelihoodfunction(χ2)forF01384-7515andtheone-temperaturemodel.Thebottomrow showstheone-dimensional(marginalized)posteriorfortheparameters(logA,β,T),andtheotherpanelsshowalltwo-dimensional marginaldistributions.Rightpanel:thedatapointsforthisobject,alongwiththeone-temperaturemodelforthemaximumlikelihood sample (yellowcurve;T = 30,K, β = 1.7)and the modeldeterminedby the mean of the samples of each parameter(redcurve; T =(32±5)K,β=1.6±0.4wheretheerrorsarethevariances).Notethelogarithmicaxeswhichmakeinterpretationoftheerror barsdifficult. Fig.6.AsinFigure5,butforF00322-0840andthetwo-temperaturemodelwithfixedβ=2.Themaximum-likelihoodtemperatures are20Kand49Kthemeansandvariancesare(20±0.8)Kand(44±8)K. dusttemperaturesandhigherdustmassesthanmorenearbyob- localgalaxiesandtheSMGsisstartingtobefilledbythePlanck jects Yang et al. (2007). Comparison of SMGs from Chapman objects.ThePlanckfluxesforoneofthesesourcesmayinclude etal.(2005),Coppinetal.(2008)andKova´csetal.(2006)with somecontaminationfromcirrus,buttherestlieinareasofnor- morelocalgalaxiesfromDunneetal.(2000)andlocalULIRGs mal to low Galactic cirrus noise and should thus be fully reli- Clements et al. (2010b)confirms this effect. Claims have been able.ThelargeareacoverageofPlanckisparticularlyimportant madethatsourcesselectedatlongerwavelengthsthanthe60µm in this as it allows us to probe generic L/ULIRG-class objects typicalof IRASderivedsamples(e.g.,Symeonidisetal. 2009), (L > 1011L )ratherthanhavingtorelyonpre-selectedIRAS FIR ⊙ Patelet al. (in prep))showless ofa separationbetweenthe lo- brightsourcesasinClementsetal. (2010b).Herschelobserva- calsourcesandthehigherredshiftSMGs.Muchofthisworkis tions,whicharealsobeginningtoshowthegapbeingfilled,do hamperedbythepoorsamplingofthedustSEDsoflocalobjects notcoverenoughareatoincludemanysuchL/ULRGobjectsin at wavelengths between 100 and 850µm. Recent results from the local Universe Amblard et al. (2010). We find several cool Herschel Amblard et al. (2010) and BLAST Dye et al. (2009) (T < 30K) ULIRGs that have very similar characteristics to have begunto fill the gapbetween local IRAS galaxiesand the SMGs.Theissueoftheapparentdistinctionbetweenlocalgalax- SMGs,suggestingthatourviewofdusttemperaturesinlocalob- ies and high-z SMG population thus seems to be approaching jectsarebiasedtowarmertemperaturesthroughourdependence resolution. onIRASfluxdensities.InFig.8weshowthepositionsofPlanck While the temperaturedistributionof our objectsis consis- galaxiesontheL−T plane.Ascanbeseen,thegapbetweenthe tentwithwhathasbeenseenelsewhere,wefindthatsomeofour 7 PlanckCollaboration:ThePlanckViewofNearbyGalaxies Fig.7. Temperature-β correlation for ERCSC-IIFSCz matched Fig.8.TheTemperature-Luminosityplaneshowingavarietyof galaxies(soliddots)togetherwithdatafromDunneetal.(2000) FIRpopulations.Opensquaresare SMGsfromChapmanetal. and Clements et al. (2010b)for SCUBA observedsources(tri- (2005), open triangles are SMGs observed with SHARCII by anglesandsquaresrespectively).Thefoursourceswithβ=0and Coppin et al. (2008) and Kova´cs et al. (2006) . + signs are T < 10K at the left of the diagram are the non-thermaldomi- the SLUGS sources from Dunne et al. (2000), x are interme- natedsources3C279,0537-441,OJ+287and3C273. diate redshift ULIRGs from Yang et al. (2007), ULIRGs from Clementsetal.(2010b)areopencircles.Planck-ERCSC-IIFSCz galaxies are shown as solid dots. As can be seen the previous galaxieshaveβmorethan3σlessthan1.Onepossiblecausefor apparentdistinction between the local FIR populationsand the this mightbe the 353 flux density beingaffected by Eddington SMGsisweakenedbysourcesfromthisworklyinginthesame bias (see e.g., Teerikorpi (2004)),leading to ’flux-boosting’of regionastheSMGsandbyfillinginsomeofthegapbetweenthe lowersignificancedetections,sinceweacceptthesefluxesdown populations.ThefouraberrantsourceswithT <15KandhighL to 3σ. This is tested by repeating the fits using only the IRAS, in the bottom right of the plot are the non-thermal dominated 857and545fluxdensities.Whiletherearesmalldifferencesin sources3C279,0537-441,OJ+287and3C273. fitstoindividualobjectsresultingformtheexclusionofthe353 flux densities, the general distribution remains the same, com- pletewiththelowβsources.Wethusconcludethatthisisareal effectandnotduetoEddingtonbiasoranyotherissuerelatedto brightblazarsandarethusdominatedbynon-thermalemission, the353fluxdensities,suchascontaminationbyemissionfrom whileoneisasourcethatmightstillcontainsomecirruscontam- theCO3-2molecularline.Whilesuchlowβvaluesarenotex- ination.Wethusfindatleast13galaxieswhichappeartocontain pected in simple modelsof dust, it is suggestive that the SEDs verycolddust.Suchdusthaspreviouslybeenfoundinourown canbebetterfitbyaparameterizationthatusesamixtureofdust galaxy(e.g.Reach et al. 1995)buthas notbeenseen beforein attwotemperatures,assuggestedbyDunne&Eales(2001)and large scale extragalactic surveys. The small number of sources whichis a goodfitto ourown galaxyasseen by COBE Reach which have T lower than 7K are all dominated by nonther- etal.(1995).Weinvestigatethisbyapplyingtwocomponentfits cold malemission.Thedetailsofthetemperature-temperatureplotin tothedustSEDs. Fig. 9, with small scatter and the temperature of the hot com- ponentbeinglargelyindependentofthatofthecoldcomponent 4.2.2. TwoTemperatureFits uptoT ∼ 18Kwilllikelyhaveimplicationsconcerningthe cold relationshipbetweenhotandcolddustcomponents. Wecarryouttwotemperaturecomponentfitsonoursources,as- sumingβ=2forbothcomponents,andpresentthetemperature- temperature plot in Fig. 9. We also use the Baysian evidence 4.3.TheBroaderERCSC-IIFSCzSample calculated during the fitting process (Jaffe 1996; Jaynes 2003) todeterminehowmanyofoursourcesshowevidenceforatwo Theparametricfittingreportedhereonlyconcernsthe468non- componentfitabovethatofthesinglecomponent(T,β)fit. We extendedERCSC-IIFSCz matched galaxieswhich are detected find thatthe two componentfit is favoured in mostcases, with at 5σor greaterin the 857and 545bandsand at3σ or greater 425objectsgivingahigherevidenceforthismodelandonly43 at 353.This ensuresthat uncertaintiesin the fluxesdo notpre- preferringthesinglecomponentfit.Onceagainwetestthepos- cludeagoodfittotheSED,butbringstheriskthatwemightbe sibilitythatissueswiththelowersignificance353GHzfluxden- missingasignificantlydifferentsubclassofobjectintheremain- sities might bias these fits by repeating the analysis with these ing1122.Wehavethusappliedourfittingmethodstothiswhole fluxesexcluded.Whilethisincreasestheuncertaintiesinthefits, sample,regardlessofERCSCS/Nbeyondthebasicdetectionre- aswiththe(T,β)fitswefindthattheexclusionofthe353GHz quirementofa5σorgreaterdetectionat857GHz.Whilethere fluxesmakesnosystematicdifferencetothetemperaturesfound. arelargererrorsbarsonthefittedparameterswefindnoindica- We find 17 galaxies fit by models containing a dust com- tionthatgalaxiesinthislargersamplehaveadifferentrangeof ponentwith temperaturesas low as 10K. Fourof these are the dustpropertiestothosediscussedabove. 8 PlanckCollaboration:ThePlanckViewofNearbyGalaxies usetwofurthercirrustemplateswithφ=1and0.1,whichcor- respond to significantly cooler dust than in the standard cirrus template.Thestarting pointforthe presentanalysisisthe tem- plate fit for each object given in the IIFSCz Catalogue Wang & Rowan-Robinson (2009). This was done by fitting the op- tical and near-IR fluxes with an optical galaxy or QSO tem- plate. The IRAS data were then fitted with one of the original fourRowan-Robinsonetal.(2008)templates.Thismodelisthen comparedtothePlanckdata.Inalmostallcasesadditionalcom- ponentsareneeded,sincetheIRAS-basedpredictionsunderesti- matethesubmmfluxdensitiesprovidedbyPlanck.Moreweight isgivento857and545fluxdensitiesinthisprocesssincethey are generally at higher signal to noise and are thus less sub- jecttoEddingtonbiaseffects.The353GHzand,wheredetected, 217GHzfluxdensitiesarealsosubjecttocontaminationbyCO 3-2and2-1emission,respectively,whichmayalsocontributeto an excess flux in these bands beyond what might be expected fromthecontinuumfit. Fig.9. The Temperature-Temperature plane for two tempera- 5.1.ResultsfromTemplateFits ture component fits for ERCSC-IIFSCz matched galaxies. to- getherwithdatafromDunne&Eales(2001)andClementsetal. InFigure9weanalyzetheSEDsofthearchetypalnearbygalax- (2010b)forSCUBAobservedsources(trianglesandsquaresre- ies,M51,M100,M2andArp220.M51andM100aremodelled spectively). Only those ERCSC-IIFSCz sources where the two withtwocirrustemplateswithφ=1(solarneighbourhood)and5 temperature model is preferred and with a reliably determined (GalacticCentre),andwithamodestM82starburstcomponent. colddustcomponenttemperature(i.e.,T/σ(T)>4)areplotted. M82itselfneedsanadditionalcomponentofcoolcirrus(φ=1) The sourceswith the coldestTcold < 7K in this plot are domi- aswellastheM82templateofEfstathiouandRowan-Robinson. natedbynon-thermalemission. FinallyArp220ismodelledextremelywelloverallinfraredand submmwavelengthsbytheArp220templateusedbyEfstathiou and Rowan-Robinson. The models for these galaxies by Silva 5. PhysicalModels:TemplateFitting et al. (1998) are also shown and perform well, especially for M51andArp220. The FIR and submm spectral energy distributions of galaxies Fig. 10 shows fits to galaxies with detections in 16 photo- fromtheIRAS,ISOandSpitzer surveyshavebeensuccessfully metric bands: 5 optical bands (SDSS), 3 near infrared bands modelled with a small number of templates (Rowan-Robinson (2MASS), 4 mid and FIR bands (IRAS) and 4 submm bands (1992), Rowan-Robinson et al. (2005), Rowan-Robinson et al. (Planck).Thebluecurveisthesolarneighbourhoodcirrustem- (2008)). However the submm data available in such studies is plate(φ= 1)andcontributessignificantlytotheSEDsof7out quitelimitedandweexpecttogetamuchbetterunderstanding ofthe8galaxies.Dustgrainsinthiscomponentareintherange ofcooldustingalaxieswiththedatafromPlanck.Alreadywith 15–20K,dependingongrainradiusandtype(Rowan-Robinson Herschel,thereisevidenceforunexpectedquantitiesofcolddust 1992).Dustmassesareintherange107−3.108M . ⊙ insomegalaxiesRowan-Robinsonetal.(2010). Togetan overviewof the wholesample,Fig. 12showsthe The Rowan-Robinson et al. (2010). study of the SEDs of distributionof545GHz(550µm)fluxdensityversusredshiftfor Herschel-detected galaxies used SPIRE flux densities extend- galaxies well detected at 350–850µm, and with spectroscopic ing from 250 to 500µm combined with pre-existing data from redshifts. The loci of galaxies with an Arp 220 template at lu- SWIREatSpitzerandopticalwavelengths.Throughthecombi- minosity L = 1012 and 1013L are shown. With the restric- IR ⊙ nationofPlanckdatawiththeIIFSCz,thegalaxysampleconsid- tionsto point-sourceswith gooddetectionsinthe three highest eredhereincludesdatafromtheopticaltoIRASfluxes,andthen frequencyPlanckbands,andtogalaxieswithspectroscopicred- thePlanckdatahasfluxdensitiesat350,550and850µm(857, shifts,anumberofULIRGsarefoundintheERCSCsurvey,but 545and353GHz).Someofourobjectsarealsodetectedat1.4 noHLIRGs,apartfromthequasar3C273. mm(217GHz)whichisincludedinouranalysisifavailable.The Fig. 13 shows the colour-ratio S /S versus redshift. 857 545 rangeofwavelengthsavailablewiththeERCSC-IIFSCzsample Galaxies in the IRAS Bright Galaxy Sample are indicated as is thus broader than that available through Herschel. This en- red dots. Sources for which T < 10K in the 2-temperature 2 ablesustoplacebetterconstraintsontheroleandimportanceof fits discussed above are indicated as blue dots. Sources with colddustin these objects.Oursample isalso muchlargerthan log (S /S ) < 0.4 represent a new population of cooler 10 857 545 the 68 objects considered in Rowan-Robinsonet al. (2010), so submmsources.Wehavemodelledall17galaxieswithcool857 we can better determinethe varietyand overallstatistics of the GHz/545GHzcolours(log (S /S < 0.4),andgoodopti- 10 857 545 SEDsoflocalgalaxies. caldata(Fig.14).Almostallrequiretheverycoldcirrusmodel ThetemplatesusedinfittingIRAS,ISOandSpitzerdataare withT =10–13K,φ=0.1(greencurvesinFig.14).Table1 dust (1)acirrus(opticallythininterstellardust)modelcharacterised givesthepropertiesofthegalaxieswhoseSEDswehavemod- by a radiation intensity φ = I(galaxy)/I(ISRF) = 5, where elledindetail.Thecolumnsare:ERCSCRAandDec,IRASFSC I(ISRF)istheintensityoftheradiationfieldinthesolarneigh- name,separationbetweenERCSCandIIFSCzposition,spectro- bourhood,(2)a normalM82-likestarburst, (3)a higheroptical scopic redshift, luminosityin cirrus φ = 5, φ = 1 andφ = 0.1 depth Arp220-like starburst, (4) an AGN dust torus. In fitting components, luminosity in M82 and Arp220 starburst compo- the SEDs of Herschel galaxies, Rowan-Robinson et al. (2010) nents, optical luminosity, optical SED type, extinction, stellar 9 PlanckCollaboration:ThePlanckViewofNearbyGalaxies Fig.10. Templatefits for the fourarchetypalnearbygalaxies,M51,M100,M82 andArp 220.Black curves:fits with Efstathiou and Rowan-Robinson templates (black, separate components as dotted lines), blue curves: Silva et al. (1998) models. Planck ERCSCdatashownasredfilledhexagrams.ISO-SWSmid-infraredspectroscopydataforM82andSpitzer-IRSdataforArp220 (Siebenmorgen&Kru¨gel2007)areshowninmagenta. massanddustmass.Stellarmassanddustmassarecalculatedas foundinthe solarneighbourhood.We alsofindthatsomelocal inRowan-Robinsonetal.(2008),buttheremaybesomemodel- galaxiesare both luminousand cool, with propertiessimilar to dependenciesinthedustmassessincewehaveassumedthatthe those of the distant SMGs uncovered in deep submm surveys. cold dust in these galaxies is similar to Galactic dust. We can Thissuggeststhatpreviousstudiesofdustinlocalgalaxieshave summarizethe SED modellingshown in Figs 10,11 and14 as beenbiasedawayfromsuchluminouscoolobjects.Wealsofind follows:(1)mostnearbygalaxiesshowevidencefordustattem- thatthedustSEDsinmostgalaxiesarebetterdescribedbypara- peraturessimilartothatseeninthesolarneighbourhood(φ=1), metric modelscontainingtwo dustcomponents,one warm and aswellasthewarmerdustfoundinIRAS,ISOandSpitzerstud- onecold,withthecoldcomponentreachingtemperaturesaslow ies; (2) there is a new populationof coolsubmmgalaxieswith as10K.SomeobjectshaveSEDsdominatedbythiscoldmate- evencoolerdust(φ = 0.1,T = 10–13K).Thiscoolerdustis rial.Theseconclusionsarebasedonbothparametricfitsandby dust likelytohaveamoreextendedspatialdistributionthengenerally detailedfittingofradiativetransferderivedphysicaltemplatesto assumedforthegasanddustingalaxies. theSEDs.However,otherphysicalorparametricdescriptionsof dust, for example where β varies with wavelength, might lead todifferentresultsregardingthisverycoldcomponent.Thispa- 6. Conclusions perrepresentsthefirstexploitationofPlanckdataforthestudy of a large sample of galaxies in the local Universe. As such it Our studies of nearby galaxiesdetected by Planck have shown indicates both the benefits and hazards of the ERCSC for this evidenceforcolderdustthanhaspreviouslybeenfoundinlocal galaxies.Thetemperatureofthisdust,however,issimilartothat 10