ANewStudyofRadioSNRSinM33

KnoxS.Long,RichardL.White,RobertH.BeckerWilliamP.Blair,DavidJ.Helfand,&FrankWinkler

AbstractWe have carried out new 6 and 20 cm observations of M33 with the Jansky Very Large Array, primarily to study the properties of supernova remnants in the galaxy. Our scaled array observations have a limiting sensitivity of about 25 uJy (5 sigma) and a resolution of 5” (FWHM), corresponding to a spatial resolution of 20 pc at the distance of M33. We detect about 85 of the SNRs contained in the list of 137 optically identified SNRs described by Long et al. (2010), and a few additional objects from the survey of Lee & Lee (2014). A substantial fraction of the optical SNRs not detected are in regions where emission from H II recombination makes identification of non-thermal emission from the SNR difficult. We also discuss a blind search for SNRs based on the radio emission alone. Of the SNRs we detect in this search at radio wavelengths, 53 have also been detected at X-ray wavelengths. Thus we are able to make a direct comparison of the X-ray, optical, and radio properties of the SNRs in M33, the first time that has been possible to a significant extent in an external spiral galaxy.

SNRaremulJ-wavelengthobjects•  SNRappearancedependsonSNandthesurroundingmediumandage–  SNRdiameterisnotaproxyforage

•  X-rayàprimaryshockphysics,thermalcontent,ISMdensity,ejectaabundances

•  OpJcalàsecondaryshockphysics,densiJesand(occasionally)shockspeedandabundances

•  RadioàparJcleacceleraJon•  àTounderstandSNRsasaclass,highqualitydataarerequiredatmulJplewavelengths

SNRsamples

Galac%c•  294SNRsintheGalaxy(Green

14)•  Wherearetheydetected?

–  Radio–nearlyall–  OpJcal–30%–  X-ray–40%

•  Advantages–  SpaJallyresolved–  Detailedstudiesofindividual

objectspossible•  Disadvantages

–  Distancesarepoorlyknown–  VariableabsorpJon

Extragalac%c•  1400SNRsandSNRcandidates

(beyondMC)•  Wherearetheydetected

–  Radio10%–  OpJcal95%–  X-ray15%

•  Advantages–  Distanceisknown–  AbsorpJonislessofaproblem

•  Disadvantages–  NotspaJallyresolvedinall

bands–  Photonsarefew

Magellanic Cloud samples are important, but not today’s talk

DetecJonsofSNRsinNearbyGalaxies

•  SNRsinnearbygalaxiesidenJfiedprimarilyfrom[SII]:HαraJos>0.4.HIIregions~0.1

•  X-rayonlyIDshaveusuallynotbeenmadethoughsomesourcescanberecognizedasSNRsinM31&M33–  SensiJvityisthelimiJngfactor

•  Radio-onlyIDsusuallybasedanon-thermalradiosourceataposiJonwherethereisdiffuseHαemission.–  Inafewgalaxies,notablyNGC6946,thenon-thermalradiosources

lineupalongthespiralarmsandsoidenJficaJonsseemfirm•  Lacey+01idenJfied35non-thermalradiosourcesinNGC6946allinthespiral

armsofthegalaxy,fewofwhichwereintheopJcalcatalogofMatonic+97–  Elsewhere,backgroundradiosourcesareaconcern,especiallyif

samplesizeissmall•  Consequently,mostradiodetecJonsofSNRsaredetecJonsof

radiosourcesattheposiJonsofopJcalSNRs

X-ray Hα [S II] V

M33isobvious•  Nearby•  LowexJncJon•  Reasonablesize•  Well-studied

–  OpJcal–Hodge’sLocalGroupGalaxySurvey

–  X-ray-Chandra1.4Msec•  LotsofSNRsknown

– OpJcal137(Long+10)+199(Lee+14)à217

–  X-ray–82(of137)

Hα

X-ray

Radio-Gordon+99

•  ObservaJonswiththeVLAandWSRT@6&20cmwithalimiJngsensiJvityof~300µJy

•  Detectedemissionat20cmfrom53opJcallyidenJfiedSNRs–  Chomiuk&Wilcots1995arguethatthereareactually77radioSNRsinM33(non-

thermal+Hα)–  Gordon+99assumedthesewerebackgroundsources

•  Widerangeoffluxesatagivendiameter–  ConsistentwithresultsfromLMCandSMCthatradio Σ-DrelaJonsarenotveryreliable

esJmatesofdistance

AnewEVLAradiosurvey

•  1.4GHz(20cm)–  C–12hr–  B–32hr(7fields)–  (A–16hr)

•  5GHz(6cm)–  C–48hrs(41fields)

•  Goals–  10xthesensiJvityofGordon+99

–  Berermeasurementofspectralindices

Today’s talk is a progress report on the results

Hαand20cm(Lowν)

Most of the matching sources are HII regions

Hα 20 cm (Low ν)

20cm(Hiν)and6cm

20 cm (Hi ν) 6 cm

RadiodetectedSNRs•  217opJcalSNRs,13outside

fieldofbothradioimages•  VisualinspecJonshows104

radio-detectedSNRs–  94from137inL10–  10morefromnewLL14

objects•  Radiodetectedobjectsare

skewedslightlytowardsmallerD–  OpJcalmediandiameter–50

pc–  Radiodetected–44pc

Examples–SNRs

20 cm

Hα

6 cm X-ray

[SII] V

20 - 6

Hα-0.1[SII]

X-raySources

•  Tuellmann+11found662X-raysourcesinM33ACISsurvey•  ThevastmajorityofthesesourcesarebackgroundAGNbased

onesJmatesofthenumberofAGNseeninfield•  ~100X-raysourceshaveradiocounterpartswithnon-thermal

radioindices•  Most,butnotall,arenotassociatedwithHαemissionsoare

unlikelytobeSNRs

Todate–nonewSNRs•  T11-318isagoodexampleofthe

issues•  WhyinteresJng

–  Non-thermalradiosourceinnebulositywithsomeevidenceofexcess[SII]

•  WhylikelynotaSNR–  X-raysourcehashardnessraJo(H-S)/

Tot0.45,mostSNRs-0.5–  Spectrumcanbefitwithapowerlaw

•  TentaJveconclusion–brightAGNwhichhappenstobebehindanHII

•  ButunusualtoseeasourcethisbrightfromanAGN

•  SystemaJcsearchforSNRsfromnon-thermalradiosourcesongoing

LuminosityFuncJon

Fluxvs.diameter

X-rayradiocomparison

Summary

•  IdenJficaJonofradiocounterpartstoknownSNRsandinindependentsurveyforradioSNRsisnecessarytounderstandSNRSasagroup

•  EVLAM33surveyisastepinthisdirecJonfillingintheradioproperJesofthesample

•  SofarthemainresultisthatwehaveexpandedthesampleofradioSNRsbyaboutafactorof2

•  Thereareprobablynotlargenumbersofradio-onlySNRinM33butthatpartoftheprogramissJllon-goingasisanydetailedinterpretaJon

2010 2016

38

17 29

45

8 0 0

Optical

Radio X-Ray

87

42 62

20

6 0 0

Optical

Radio X-Ray