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