BreakdownofKennicu0-SchmidtLawatGiantMolecularCloudScales

SachikoOnodera(MeiseiUniversity,Japan),NROMAGiCprojectteam,FUGINprojectteam

OutlineofToday’sTalk•  ResolvedKennicu0-Schmidtlawinnearbygalaxies– NROM33All-disksurveyofGiantMolecularCloudsproject(MAGiC)

–  BreakdownoftheK-SlawinM33atGMCscale–  Reasonforthebreakdown–  StarformaQonrelaQonderivedfromothertracersofstarformaQonrateandgas

•  ResolvedstarformaQonrelaQonintheMilkyWay–  PreliminaryresultfromNROgalacQc-planeCOsurveyproject(FUGIN)

IntroducQon:MolecularGasandStarFormaQoninNearbyGalaxies

•  Kennicu0-SchmidtlawGlobalcorrelaQonbetweengasmassandstarformaQonrate(SFR)ingalaxies（ΣSFR∝ΣgasN）N~1.4(Kennicu01998,Kennicu0&Evans2012)Large-scalestudiesprovideessenQalinformaQonontherelaQonbetweenlarge-scaleproperQesofgalaxiesandstarformaQon

Kennicu0&Evans2012

ResolvedKennicu0-SchmidtLawBigiel et al. 2008

TheprocessofconverQnggasintostarsoccursonasmallerscale,withinmolecularclouds.•  HowisthiscorrelaQon

connectedtoeachstar-formingregion?

•  TowhichscaledoesthiscorrelaQonhold?

ObservaQonalDifficultyMostgalaxiesaretoofartoresolveeachstar-formingregionbecauseofourresoluQonlimit→closegalaxies logΣHI+H2[Msun/pc2]

logΣ S

FR[M

sun/yr/kpc

2 ]

M33All-disksurveyofGiantMolecularClouds(NROMAGiC)

•  Localgroupgalaxy•  ClosetoourGalaxy

(D=840kpc)　 eachGMCcanbe

resolved　　(NRO45mresoluQon：20"~80pc)

ThebesttargetforstudyingGMCsandstarformaQoninawholegalaxyCO(1-0)surveywithNRO45m+BEARS+OTF

n Moderatelyface-onDistribuQonofGMCsinthewholedisk,inrelaQontoothercomponents(e.g.star-formingregions,arms)

(Arimotoetal.)

n Star-formingregionsexistoverthewholedisk

CO map Spitzer24um(starformaQonindicator)

等強度線: 分子ガス

VarietyofMolecularGasandStarFormaQon

CO(1-0)

Contour:CO

K-SlawisbrokenatsomescalesDatacubeavailableonNROwebsite!

CO map Spitzer24um(starformaQonindicator)

等強度線: 分子ガス

VarietyofMolecularGasandStarFormaQon

mostmassiveGMCbutweakSFacQvity

acQveSF(NGC595)butlessmassive　

CO(1-0)

Contour:CO

K-SlawisbrokenatsomescalesDatacubeavailableonNROwebsite!

TowhatscaleistheKennicu0-Schmidtlawvalid?

thesurfacedensityofmoleculargasmassvsSFRinahighresoluQon(~80pc)•  CorrelaQonsareevidentin

1kpc,500pc•  Becomelooserwithhigher

resoluQon,andfinallybreaksdown(dispersionover~fourordersofmagnigude)

Schruba+(2010),Boquien+(2015)whichusedUV,Hα,MIR,&FIRhaveshownthesimilarresults⇒GMCscale(~80pc)iswhere

theK-Slawbecomesinvalid

Σ(SFR)

Hα,corr[M

oyr-1pc

-2]

Onoderaetal.2010Σ(H2)[Msunpc-2]

ResoluQon~80pc ~250pc

~500pc ~1kpc

2σ

ReasonsforbreakdownoftheK-SlawatGMCscales

•  Drisofclustersfromtheirparentclouds•  StochasQcityeffectsontheesQmaQonofSFR•  DifferentevoluQonarystagesofGMCs

ReasonforbreakdownoftheK-SlawatGMCscales

•  Drisofclustersfromtheirparentclouds–  InMilkyWay,youngclustersrecedefromtheirparentGMCswithv>10km/s(Leisawitz+1989)

–  theseparaQonbetweenthemisexpectedtobe~100pcataclusterageof10Myr

⇒comparabletoourresoluQonof80pc　⇒　However,itcannotexplainsomestarformingregionswithoutassociatedGMCsnorGMCswithoutassociatedstarformingregions

ReasonforbreakdownoftheK-SlawatGMCscales

•  StochasQcityeffectsontheesQmaQonofSFR–  duetosmallsamplingathighspaQalresoluQons–  IMFisnotfullypopulatedwhensmallerregionsthatcontainonlyafewstarsinclustersaresampled.

–  Thus,inregionswithweakerexQncQon-correctedHαemission,thiseffectmayleadtosignificantsca0ersintheesQmatedΣ(SFR).

–  AssumingT〜104Kandne〜100cm−3inHIIregions,theionizingphotonfluxisQ(H0)=7.3×1011L(Hα)corrs−1(Kennicu01988;Brocklehurst1971).

–  Σ(SFR)=10−9Msunyr−1pc−2　　⇒L(Hα)corr=6.6×1035ergs−1withinthe80pcbeam　　⇒Totalionizingphotonflux： Q(H0)=4.9×1048s−1.

StochasQcityeffectsontheesQmaQonofSFR

–  TheraQooftheerrorinQ(H0)tothemeanvalue,σ[Q(H0)]/Q(H0),is∼10M−1/2(M:clustermass)(Cervinoetal.2002)

⇒theclustermassrequiredtoproducetheionizingfluxis50〜5×104Msun,whichresultsinσ[Q(H0)]/Q(H0)≈1to0.04.

•  Insummary,theerrorduetotheeffectofstochasQcityatΣ(SFR)=10−9Msunyr−1pc−2is0.04–1×10−9Msunyr−1pc−2inthe80pcscale.

•  TheerrordecreaseswithhigherΣ(SFR)andlowerspaQalresoluQons.

AlthoughtheerrorissignificantatsmallerΣ(SFR)atthe80pcresoluQon,itcannotexplainthesca0erofoverfourordersofmagnitudeinΣ(SFR).

EvoluQonsofGMCsinM33DifferentevoluQonarystagesinM33usingCO(3-2)•  TypeA：nosignofmassive

SF•  TypeB：onlywithrelaQvely

smallHIIregions•  TypeC:withbothHII

regions&young(<10Myr)stellargroups

•  TypeD:withbothHIIregions&relaQvelyold(10–30Myr)stellargroups

thedispersionintheK-SlawislargelyduetovariaQonsintheevoluQonarystageoftheGMCs

TypeA(1%)

TypeB(20%)

TypeC(45%)

TypeD(34%)

Miuraetal.2012

K-SlawatmatchedageinTaffyI

•  ThedispersionσofcorrelaQon:14%(constantconversionfactor)25%(differentconversionfactor)excludingregionD•  atthesameresoluQon(700pc)σ=50%(M51),27%(NGC3521)(Liuetal.2011)43%(M33:500pcresoluQon)(Onoderaetal.2010)thedispersionintheK-SlawislargelyduetovariaQonsintheevoluQonarystageofGMCs

•  TaffyI:interacQnggalaxythatexperiencedadirectcollisiononly~20Myrago

•  AgesoftheSFblobsesQmatedfromPaαEquivalentwidth•  AgesofallblobsexceptforregionBandregionD:∼7Myr

RegionD:<3.5Myr

Komugietal.2012

K-SlawusingYSOasSFRtracerinLargeMagellanicCloud

•  therelaQonbetweenΣ(SFR)&Σ(HI+H2)inLMCforsixGMCs

•  largesca0erinΣ(SFR)derivedfromHα+24um〜twoordersofmagnitude

•  theΣ(HI+H2)lieswithinafactoroftwo

•  sca0erinΣ(SFR)derivedfromYSO〜anorderofmagnitude

⇒YSO:abe0ertracerofSFR

Chenetal.2010

PreviousStudies:CO(3-2)-SFRcorrelaQonsinNearbyGalaxies(SeealsoMichiyama’sposter)

M83 disk&center

(Muraoka+ 2009)

In 500pc~kpc resolution CO(3-2) intensity: slightly better correlation with SFR than CO(1-0)

(Komugi＋ 2007) log I(CO)[K km/s]

Nearby galactic centers

I(CO(1-0)) I(CO(3-2))

CO(1-0) vs. SFR

CO(3-2) vs. SFR

CO(3-2)&CO(1-0)map

Color:CO(3-2)Grey:CO(1-0)

Miuraetal.2014

SimilardistribuQon

SFRvs.CO(1-0),CO(3-2)inGMCs

•  NocorrelaQonisfoundbetweenI(CO1-0)&Σ(SFR)inGMCscales•  I(CO3-2)-Σ(SFR)correlaQon(alreadyknowninkpc-scale)isvalid

downtoGMCscales⇒StarformaQoniscloselyassociatedwiththewarmanddense

regionstracedbyCO(3-2)line,alsoineachGMC

Onodera+2012

corr.coeff.=0.22 corr.coeff.=0.68

StarformaQonrelaQonsintheMilkyWay•  Spitzerc2d＆Gould’sBeltsurvey20low-massstar-formingmolecularclouds

•  Avmap→Σgas•  YSOnumberdensity→ΣSFR　•  resoluQon:sizeofmolecularclouds(〜3pconaverage)

•  indexissuperlinear:largelydifferentfromthatoftheextragalacQcK-Slaw（N=1〜1.4）

→star-formingthresholdingassurfacedensityof〜100Msunpc-2?

Heidermanetal.2010

StarformaQonrelaQonsintheMilkyWay

Sixhigh-massstar-formingmolecularclouds•  classIYSOnumber→ΣSFR•  HerschelFIR→Av→Σgas•  SinglepowerlawineachcloudbutNisdifferentamongclouds

•  NisalsosuperlineareveninΣgas>100Msunpc-2

5pc Willisetal.2015

FORESTUnbiasedGalacQcplaneImagingsurveywiththeNobeyama45mtelescope

(FUGINproject)

•  unbiasedCOlinemappingoftheGalacQcPlane(2014~2017)•  10°<l<50°,|b|<1°(80deg2)and198°<l<236°,|b|<1°(76deg2)•  spiralarms(Perseus,Sagi0arius,Scutum,andNormaarms),bar•  12CO,13CO,andC18O(J=1–0)lines,simultaneously•  newmulQ-beamreceiver,FOREST,ontheNobeyama45m

telescope•  angularresoluQonofthefinalmap:20″(12CO)，21″(13CO&C18O)

Redsquare:observaQonalregions,colormap:CfAsurveyCOmapbyDame+(2001)

FORESTUnbiasedGalacQcplaneImagingsurveywiththeNobeyama45mtelescope

(FUGINproject)

Umemotoetal.2017

12COtotalmoleculargas　diffuseregions〜102cm-3

13CO&C18OdenserandopQcallythinnermoleculargas〜103to104cm-3

PreliminaryResultsinM17Region

confidenQal

Comparisonwithpreviousresults

confidenQal

Summary•  The“classical”K-SrelaQonbetweenΣ(SFR)derivedfromHα,IRandUVandΣ(H2)derivedfromCObreaksdownattheGMCscale– DrisofnewbornstarsfromtheparentcloudsandstochasQcityeffectsontheesQmaQonofSFRarenotlargeenoughtoexplainthedispersion

– DifferentevoluQonarystagesofGMCsarethemainreason