Search for Compact Extragalactic Radio Sources Near Massive Star Forming Regions

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

6

002 nJu 61 1v8936060/hp-ortsa:viXraRevised:31May2006

Searchforcompactextragalacticradiosourcesnearmassivestar

formingregions

Y.Xu1,2,M.J.Reid3,K.M.Menten2,

andX.W.Zheng4ABSTRACT

WehaveusedtheVeryLargeArraytosearchforcompactmilliarcsecond-sizeradiosourcesnearmethanolmasersinhigh-massstar-formingregions.SuchsourcesarerequiredforVeryLongBaselineInterferometryphase-referencingob-servations.Weconductedpointedobservationsof234compactsourcesfoundintheNVSSsurveyand nd92sourceswithunresolvedcomponentsandsyn-chrotronspectralindexes.ThesesourcesarelikelythecoresofAGNsand,thus,goodcandidatesforastrometriccalibrators.

Subjectheadings:galaxies—radiocontinuum—astrometry

1.Introduction

Phase-referencedVeryLongBaselineInterferometry(VLBI)observationscanmeasureaccuratelythepositionofatargetsourcerelativetoareferencesource.This,forexample,permitsonetomeasurethetrigonometricparallaxandpropermotionsofsourcesinourgalaxyrelativetoextragalacticsources.WearenowcarryingoutalargeprogramtodothisformethanolmasersinregionsofhighmassstarformationthroughouttheMilkyWay.Table1contains38sourcesshowingmaseremissionin12.2GHz20 3 1Elineofmethanolthatweultimatelyintendtoobserve.

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

VLBIphase-referencedobservationsinvolveaphasecalibratorandatargetsource.How-ever,thedistributionofknowncalibratorsisnotsu cientlydenseenoughto ndonewithin≈2 ofanygivenmasersource,whichisnecessaryforhighprecisionastrometry:Systematicerrorsareusuallythelimitingfactorinphase-referencedpositionmeasurements,andtheseerrorsscalewiththeangularseparationbetweenthesources.Therefore, ndingcalibratorsascloseaspossibletothemasertargetsourcesismandatory.

Forthispurpose,wehaveconductedasurveyofNRAOVLASkySurvey(NVSS;Condonetal.1998)sourcesnearourmethanolmasertargets.Wechosesourceswhose1.4GHz uxdensitiesaregreaterthan20mJyandthatareunresolved(<20′′)attheNVSSresolution.TheNVSSsurveytypicallyyieldsabout15suchcompactsourceswithin1 ofanytargetposition.SinceourmasersourcesareintheGalacticplanemanyoftheseNVSSsourcesarecompactHIIregions,planetarynebulae(PNe),and,perhaps,compactsupernovaremnants(SNRs),and,thus,unsuitableforVLBIobservations.However,someoftheunresolvedsourcesarelikelyextragalacticsynchrotronsources.

InadditiontotheNVSSsources,weaugmentedourcandidatelistwithsourcesfromtheliterature(Gregory&Condon1991;Maetal.1998)andincludedknowncompactsourcesasacheckonourprocedures.Intotal,weobserved234compactsourceswithin1 ofthemasersources.

2.ObservationsandDatareductions

On2004April2wemadesnap-shotobservationsofour234sourcesusingtheNRAO1VLAinitsC-con gurationatC-band(4.885GHz)andU-band(14.939GHz).Bandwidthswere50MHz,observationswereindualcircularpolarization,andon-sourcetimeswerebetween30and70seconds.Theabsolute uxdensityscalewasdeterminedfromobservationsof3C286and3C48.Occasionallywemissedobservationsowingtoelectronicproblemsand,thus,forsomesourcesnodatacouldbeobtained(seeTable4).ThedatawerereducedwiththeNRAOAstronomicalImageProcessingSystem(AIPS)usingstandardprocedures.Weachievedrmsnoiselevelsofabout0.3mJyat4.885GHzand0.8mJyat14.939GHz,respectively.

Inordertoobtainbetterpositionalaccuracyandcheckoncompactness,were-observed53sourcesthathad uxdensitieshigherthan5mJyinboth,theC-andU-bandsandwere

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

unresolvedinC-band.Theseobservationsweredoneaslow-priorityobservationsinsmallgapsintheVLAscheduleintheA-orB-arrayatU-bandon2004September26,27,28,October29,and2005May1,10,and26,respectively.WechoseU-bandasitistheVLAfrequencythatisclosesttothatofthe12.2GHzmasers.Theobservationsofeachobjectinvolved6short(1minduration)scans,spreadoverarangeintimeforbetteruv-coverage.Tominimizethephaseerrorsarisingfromtemporalchangesintheatmosphericphasepaths,weobservedastandardVLAcalibratorbeforeandaftereachtargetsource.Typicalmaprmsnoiselevelswereabout0.2mJy.Thisallowedusdeterminepositionsaccuratetobetterthan0.1arcsec.ItisimportanttoreachthatprecisionforVLBIastrometryinordertominimizesecond-orderpositionalerrorsandimproveimagequality.

3.Results

Wedetectedabout92ofthe234candidatesourceswith uxdensitiesof5mJyatC-bandwith attishorfallingspectralindexes.ThesearelikelycompactextragalacticsourcesassociatedwithAGNactivity.

InTable2welistweaksources<5mJyatC-bandobservedintheC-con guration.Thesearetooweakforcurrentastrometricobservations.

InTable3welistthesourcesthatwereclearlyresolved.ThesesourcesareprobablymostlyHIIregions,PNe,andSNRs.Whilesomeultra-andhyper-compactHIIregionsmaynotberesolvedbytheVLA,theyshouldhave atorrisingspectraatcentimeterwavelengths(Wood&Churchwell1989;Kurtzetal.1994),thatcanbeeasilyrecognizedinourdual-frequencyobservations.AlthoughSNRshavefallingspectra,theyshouldberesolvedduetotheirlargersize(Green2004).ThesourcesdetectedaC-band,butnotatU-band,mightbeusedascalibratorsatlowerfrequency,e.g.,forVLBIobservationsof6.7GHzCH3OHmasers,and/or1.6and6.0GHzOHmasers.

Table4liststheparametersofthe92sourcesthatareunresolvedatC-band,have atorfallingspectralindexes,andarepotentiallystrongenoughtobecalibrationsourcesforVLBIphase-referencedobservations.TheirimagesareshowninFigure1whichisavailableintheelectronicversionofthispaper.Exceptforafewsources,consistingoftwocomponents,mostofthesourcesappeardominatedbyasinglecompactcomponent.Mostofthemcontainover85%oftheir uxdensityinanunresolvedcomponentatC-and/orU-bandandarelikelycompactextragalacticsources.EventhoughweselectedsourceswithourC-con gurationobservationsthatwerenearlyunresolvedandhad>5mJyatC-band,whenobservedwiththemoreextendedA-orB-con gurationssomewerenotdetected.Sincethesemightcontain

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

acompactcomponentthatcouldbeusedasaphase-referencecalibratoratlowerfrequencies,wealsoretaintheminTable4.

Already,source023016+620937inTable4hasproventobeagoodcalibratorforVeryLongBaselineArrayobservations(VLBA;Xuetal.2006).Thissourceprobablyhasapositionuncertaintyofaboutafewmilliarcseconds(mas).Usingthisandtwoothersourceswehavemeasuredaparallax(totheW3OHmasers)withanaccuracyof0.007mas.ThreeofoursourcesareinclucedinthethirdextensiontotheVeryLongBaselineArray(VLBI)CalibratorSurvey(VCS3;Petrovetal.2005)listedtherewith(sub)masaccuracies.Bycomparingtheresultsfromdi erentobservationslistedinTable5we ndthatourC-arraypositionsdeviatefromtheVCS3positionsby0.25,0.91,and0.14arcsecandourA-arraypositionsby51and11mas.We,thus,estimatethatthepositionuncertaintyisabout0.5′′insnap-shotC-con gurationobservationsand0.05′′–0.15′′inVLAA-andB-con gurationobservations,respectively,forhighdeclinationsources.Positionalaccuracyislikelytodegradeconsiderablyatlowdeclinationsandforweaksources(lessthan10mJy).Wecalculatedthetwo-pointspectralindexfrom5to15GHzfromC-con gurationobservations.MostofthesourcesinTable4haveasteep-spectrumwithanaveragespectralindexofα=0.96(Sν～ν α).OnemustkeepinmindthatsincethesewereoftenmeasuredwithobservationswithinoneVLAcon guration,the5GHzbeamsizewasaboutafactorof10largerinsolidanglethanthe15GHzbeamsize.Thus,ifasourceisunresolvedat5GHz,butpartiallyresolvedat15GHz,thespectralindexmayappearoverlysteep.Ulvestadetal.(1981)foundamedianspectralindexofα=0.09between1.4and5GHzforunresolvedsourcesina ux-limitedsample.Zhang&Fan(2003)classi edthissamplebypropertiesofgalaxies.Theyfoundanaveragespectralindexof0.22forblazers,0.28forQSOs,and1.01forgalaxies,respectively.Asacomparison,weobtainedanaveragespectralindexofα=0.83between1.4and5GHz.Ofcourse,sincebothobservationsspannedmanyyears,timevariabilitycould,inprinciple,a ectspectralindexresults.Howevergeneralspeaking,mostofsourcesarelikelytoberadiogalaxies.

4.Conclusions

AVLAsearchhasresultedintheidenti cationof92compactsourcesmostlikelyofextragalacticnature.Thesesourcesarelikelytobesuitablecalibratorsforphase-referencingVLBIobservationsof12.2GHzCH3OHor/andlowerfrequencymasers.

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

REFERENCES

Condon,J.J.,Cotton,W.D.,Greisen,E.W.etal.1998,AJ,115,1693

Green,D.A.2004,ACatalogueofGalacticSupernovaRemnants,MullardRadioAstronomy

Observatory,CavendishLaboratory.Gregory,P.C.,&Condon,J.J.1991,ApJS,91,1011

Kurtz,S.,Churchwell,E.,&Wood,D.O.S.1994,ApJS,91,659Ma,C.,Arias,E.F.,Eubanks,T.M.,etal.1998,AJ,116,516

Petrov,L.,Kovalev,Y.Y.,Fomalont,E.,&Gordon,D.,2005,AJ,129,1163Ulvestad,J.,Johnston,K.,Perley,R.,&Fomalont,E.1981,AJ,86,1010Wood,D.O.S.,&Churchwell,E.1989,ApJS,69,831

Xu,Y.,Reid,M.J.,Zheng,X.W.,&Menten,K.M.2006,Science,311,54Zhang,J.S.,&Fan,J.,H.2003,ChJAA,3,415

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

Table1.12.2GHzMethanolMaserSourcesConsidered

a

Nodetectedcompactextragalacticradiosourceswithin1 ofthissource.

Table2.SourceswithC-bandFluxDensities<5mJyObservedinC-Con guration

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

Table3.SourcesResolvedinC-orU-BandObservations

KnownHIIregionaccordingtoSIMBADAstronomicalDatabaseand/orsourcewithrisingspectrum.

b

a

PlanetarynebulaaccordingtoSIMBADAstronomicalDatabase.

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

Table4.ParametersofPossibleCalibrators

SourceName

SourcePositionα(2000)δ(2000)

1.4GHz

(mJy)

5GHz(mJy)

15GHz(mJy)

SpectralIndex

θ(′′)

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

Table4—Continued

SourceName

SourcePositionα(2000)δ(2000)

1.4GHz

(mJy)

5GHz(mJy)

15GHz(mJy)

SpectralIndex

θ(′′)

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

Table4—Continued

SourceName

SourcePositionα(2000)δ(2000)

1.4GHz

(mJy)

5GHz(mJy)

15GHz(mJy)

SpectralIndex

θ(′′)

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

Table4—Continued

SourceName

SourcePositionα(2000)δ(2000)

1.4GHz

(mJy)

5GHz(mJy)

15GHz(mJy)

SpectralIndex

θ(′′)

Note.—The rstcolumnpresentssourcenameforthemasers(boldface)andtheextragalacticradiosources.ThenexttwocolumnslisttheirJ2000equatorialcoordinates.Forthemasersourcesthenextcolumngivesacommonname(ifavailable).Forthecalibratorsourcescolumns4to6givetheintegrated uxdensityatL-(fromNVSS),peak uxdensityatC-andU-bands,respectively.Column7isthespectralindexbetweenC-andU-bands(Sν～ν α).Column8istheupperlimitsofsourcesizes(FWHMofthemaximummajoraxesofthesourcesasdeterminedfromtheGaussian tsusingAIPStaskJMFIT).ThedatacomefromC-bandobservedwithC-con guration,exceptthosemarkedbysigns.Thelastcolumngivestheseparationbetweenmasersandcalibrators.Somesourceshavenodataduetofailureofthetelescope.

aU-bandbU-bandcU-banddSourceeSource

dataobservedwithCcon guration.dataobservedwithAcon guration.dataobservedwithBcon guration.listedinGregory&Condon(1991).

listedinVLBAcalibratorsource(Petrovetal.2005).

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

parisonofCalibratorPositionErrorsDerivedfromVLAandVLBIData

SourceName

VLA-CPositionα(2000)δ(2000)

(Y/C VLBI)

(arcsec)

VLA-APositionα(2000)δ(2000)

(Y/A VLBI)

(arcsec)

VLBI

α(2000)δ(2000)

Error

(mas)

Note.—-Listedare,lefttoright,sourcename,positionderivedfromVLAC-arrayobservations,di erencebetweenthelatterandtheVLBIposition(easto setandnortho set),positionderivedfromVLAA-arrayobservations,di erencebetweenthelatterandtheVLBIposition,andtheVLBIpositionanditsuncertainties.Ofthecoordinatesforthelattertwopositionsonlysecondsoftimeandarcsecondsaregiven.

a

FromourVLBAobservations(Xuetal.2006).

bFromVCS3(Petrovetal.2005).

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

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55.1

RIGHT ASCENSION (J2000)

C array-17 03 35

180929 170352

40

45

)

0002J( NO50ITANILCED55

04 00

05

18 09 30.5

1030.0

29.529.0

28.5

28.0

RIGHT ASCENSION (J2000)

2 cm

A array

180650 202742

-20 27 40.0

)

0040.5

02J( NOITANILC41.0

ED41.5

42.0

18 06 50.3450.3250.30

50.2850.2650.2450.22

50.2050.18

RIGHT ASCENSION (J2000)

C array-21 24 25

180806 212445

30

35

)

00040

2J( NOIT45

ANILCED50

55

25 0005

18 08 08.0

07.5

07.006.5

06.0

05.5

RIGHT ASCENSION (J2000)

-18 04 30

180927 180451

35

40

)

000245

J( NOITA50

NILCED55

05 00

05

10

18 09 29.0

28.5

28.027.5

27.0

26.5

RIGHT ASCENSION (J2000)

2 cm

B array

-18 13 28.5

181007 181331

29.0

29.5

)

0030.0

02J( NO30.5

ITANILC31.0

ED31.5

32.0

32.5

33.018 10 08.15

08.10

08.05

08.0007.9507.9007.85

RIGHT ASCENSION (J2000)

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

-18 13 15

181007 181331

20

25

)

0002J( 30

NOITANILC35ED40

45

50

18 10 09.0

08.5

08.007.5

07.0

RIGHT ASCENSION (J2000)

B array-18 11 36.0

181401 181142

36.2

)

036.4

002J( NOITA36.6

NILCED36.8

37.0

37.218 14 02.04

02.03

02.02

02.0102.0001.9901.9801.97

01.96

01.95

RIGHT ASCENSION (J2000)

-19 13 56

5758)

590002J( 14 00NOITAN01ILCED020304

05

06

18 14 45.5

45.4

45.3

45.245.145.044.944.8

RIGHT ASCENSION (J2000)

C array181723 161442

-16 14 30

35

)

0002J(40

NOITANILC45

ED50

55

15 00

18 17 24.023.5

23.022.5

22.0

RIGHT ASCENSION (J2000)

-20 55 02.6

J1811 2055

02.8

03.0

)

0002J( N03.2

OITANILC03.4

ED03.6

03.8

04.0

18 11 06.84

06.82

06.8006.7806.76

06.74

RIGHT ASCENSION (J2000)

C array-18 11 20

25

30

)

0002J( NO35

ITANILCED40

45

50

18 14 03.0

02.5

02.001.5

01.0

RIGHT ASCENSION (J2000)

-18 36 12.6

181530 183614

12.8

13.0

)

0002J13.2

( NOITANIL13.4

CED13.613.8

14.018 15 30.42

30.40

30.3830.36

30.34

30.32

RIGHT ASCENSION (J2000)

C array-16 14 36

181723 161442

38

)

0002J( N40

OITANILCED42

44

46

18 17 23.3

23.223.1

23.022.922.822.722.6RIGHT ASCENSION (J2000)

-17 03 15

181134 170325

20

)

0025

02J( NOITA30

NILCED35

40

4518 11 36.0

35.5

35.034.534.0

RIGHT ASCENSION (J2000)

C array-19 13 45

181445 191400

50

55

)

0002J( N14 00

OITANILC05

ED10

15

2018 14 46.5

46.0

45.545.044.544.0

RIGHT ASCENSION (J2000)

-18 35 55

181530 183614

36 00

05

)

010

002J( NO15

ITANILCE20

D25

30

35

18 15 32.0

31.5

31.0

30.530.0

29.5

29.0

RIGHT ASCENSION (J2000)

C array-07 25 35

183124 072551

40

45

)

0002J( NO50

ITANILCED55

26 00

05

18 31 26.025.5

25.024.524.0

RIGHT ASCENSION (J2000)

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

-07 25 44

183124 072551

46

)

00048

2J( NOITANIL50

CED52

54

18 31 25.1

25.0

24.9

24.824.724.624.5

24.4

RIGHT ASCENSION (J2000)

C array-08 55 05

183319 085527

10

)

15

0002J( NOI20

TANILCED25

30

35

18 33 20.5

20.019.5

19.0

18.5

RIGHT ASCENSION (J2000)

-09 53 05

183424 095319

1015

)

000220

J( NOITANI25

LCED30

354018 34 25.5

25.0

24.524.0

23.5

23.0

RIGHT ASCENSION (J2000)

C array-06 53 20

183758 065330

25

)

00030

2J( NOITA35

NILCED40

45

50

18 37 59.0

58.558.0

57.5

57.0

RIGHT ASCENSION (J2000)

-07 06 30

183214 070643

35

)

040002J( NOIT45

ANILCED50

55

07 00

18 32 16.0

15.5

15.014.514.0

RIGHT ASCENSION (J2000)

B array

-07 11 08.8

183354 071106

09.0

09.2

)

0002J( N09.4OITANILC09.6

ED09.8

10.0

10.2

18 33 54.04

54.0254.0053.98

53.96

RIGHT ASCENSION (J2000)

-09 53 17

183424 095319

18

19

20

)

0002J(21

NOITAN22

ILCED23

24

25

26

18 34 24.6

2724.5

24.4

24.324.224.124.0

23.9

RIGHT ASCENSION (J2000)

C array-06 53 27

183758 065330

28

29)

300002J(31 NOITA32NILCE33D343536

3718 37 58.4

58.3

58.2

58.158.057.957.8

57.7

RIGHT ASCENSION (J2000)

-08 55 26.4

183319 085527

26.6

26.8

)

027.0

002J( NOI27.2

TANILCE27.4

D27.6

27.8

28.0

18 33 19.64

19.62

19.6019.5819.56

19.54

RIGHT ASCENSION (J2000)

C array183354 071106

-07 11 00

05

)

0002J( N10

OITANILCE15

D20

2518 33 55.0

54.554.0

53.5

RIGHT ASCENSION (J2000)

-09 37 10

183558 093724

15

20

)

0002J( N25

OITANILCE30

D35

40

18 35 59.5

59.0

58.558.0

57.5

RIGHT ASCENSION (J2000)

C array-08 40 30

183809 084048

35

40

)

0002J( NO45

ITANILCED50

5541 0018 38 10.5

10.009.5

09.0

08.5

RIGHT ASCENSION (J2000)

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

-03 10 55

184236 031108

11 00

)

0005

02J( NOIT10

ANILCED15

20

25

30

18 42 37.036.5

36.035.5

35.0

RIGHT ASCENSION (J2000)

C array-01 34 00

184353 013415

05

10

)

0002J( NO15

ITANILCED20

25

30

18 43 54.0

53.553.0

52.5

52.0

RIGHT ASCENSION (J2000)

-01 19 25

184614 011942

30

)

35

0002J( NOI40

TANILCED45

50

55

18 46 16.0

15.5

15.014.5

14.0

13.5

RIGHT ASCENSION (J2000)

C array184700 022751

-02 27 48

50

)

0002J( NOIT52

ANILCED54

56

58

18 47 00.8

00.7

00.6

00.500.400.300.2

00.1

RIGHT ASCENSION (J2000)

-03 11 04

184236 031108

06

)

0002J( NO08

ITANILCED10

12

18 42 36.3

14

36.236.1

36.035.935.835.735.6

RIGHT ASCENSION (J2000)

C array-04 54 10

184445 045425

15

)

20

0002J( NOIT25

ANILCED30

35

40

18 44 47.0

46.5

46.045.5

45.0

RIGHT ASCENSION (J2000)

-04 08 35

184626 040853

40

45

)

0002J50( NOITANIL55CED09 00

05

10

18 46 28.0

27.5

27.026.5

26.0

RIGHT ASCENSION (J2000)

C array00 11 06

184821+001108

05

04

)

000203

J( NOITA02

NILCED01

00

10 59

58

18 48 21.5

21.4

21.321.221.121.0

RIGHT ASCENSION (J2000)

-01 28 55

184351 012914

29 00

05

)

0002J( 10

NOITANILC15

ED20

25

30

18 43 52.5

52.0

51.551.0

50.5

RIGHT ASCENSION (J2000)

A array

-01 19 40.0

184614 011942

40.2

40.4

)

0002J( N40.6

OITANILCE40.8

D41.0

41.2

41.4

18 46 14.73

14.72

14.71

14.7014.6914.6814.6714.66

14.65

14.64

RIGHT ASCENSION (J2000)

-02 27 35

184700 022751

40

45

)

0002J50

( NOITANIL55

CED28 00

05

10

18 47 01.5

01.0

00.500.0

46 59.5

RIGHT ASCENSION (J2000)

B array-02 17 11.4

184936 021629

11.6

)

011.8

002J( NOITA12.0

NILCED12.2

12.4

12.618 49 35.21

35.20

35.19

35.1835.1735.1635.1535.14

35.13

RIGHT ASCENSION (J2000)

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

C array-02 17 00

184936 021629

05

)

000210

J( NOITANILC15

ED20

2518 49 36.0

35.8

35.6

35.435.235.034.834.6

34.4

RIGHT ASCENSION (J2000)

C array05 01 30

185124+050118

25

)

0002J( NO20

ITANILCED15

10

0518 51 25.8

25.6

25.4

25.225.024.824.624.4

24.2

24.0

RIGHT ASCENSION (J2000)

C array-00 39 57

185152 004000

58

59

)

00040 00

2J( NOITA01

NILCED02

03

04

0518 51 53.2

53.1

53.052.9

52.8

52.7

RIGHT ASCENSION (J2000)

00 19 58.0

A array185343+001957

57.8

)

57.6

0002J( NOITAN57.4

ILCED57.2

57.0

18 53 43.8943.8843.87

43.8643.8543.8443.8343.82RIGHT ASCENSION (J2000)

B array

-01 32 56.4

184959 013256

56.6

56.8

)

0002J( N57.0

OITANILC57.2

ED57.4

57.6

57.8

18 49 59.38

59.36

59.3459.32

59.30

59.28

RIGHT ASCENSION (J2000)

A array00 35 33.0

185146+003532

32.8

)

032.6

002J( NOIT32.4

ANILCED32.2

32.0

31.8

18 51 46.77

46.76

46.75

46.7446.7346.7246.7146.70

46.69

46.68

RIGHT ASCENSION (J2000)

C array185244+053534

05 35 45

40

)

0002J( NOIT35

ANILCED30

25

20

18 52 45.6

45.445.2

45.044.844.644.444.244.043.8RIGHT ASCENSION (J2000)

C array185343+001957

00 20 10

05

)

0002J( N00

OITANILCE19 55

D50

45

18 53 45.044.5

44.043.5

43.0RIGHT ASCENSION (J2000)

C array05 02 40

35

)

0002J( NOIT30

ANILCED25

20

18 51 21.8

21.6

21.4

21.221.020.820.620.4

20.2

20.0

RIGHT ASCENSION (J2000)

C array185146+003532

00 35 45

40

)

0002J35

( NOITANIL30

CED25

20

1518 51 48.0

47.5

47.046.5

46.0

RIGHT ASCENSION (J2000)

03 52 35

C array185319+035218

30

25

)

0002J( N20

OITANILCE15

D10

0518 53 20.5

20.019.5

19.0

RIGHT ASCENSION (J2000)

2 cm

B array

04 01 00.0185407+040059

00 59.8

)

00059.6

2J( NOITANIL59.4

CED59.2

59.0

18 54 07.9507.9407.93

07.9207.9107.9007.8907.88

RIGHT ASCENSION (J2000)

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for Very Long Baseline Interferometry phase-referencing observations. We conducted p

04 01 15

185407+040059

1005

)

0002J( 00

NOITANILC00 55

ED50

45

40

18 54 09.0

08.5

08.007.5

07.0

RIGHT ASCENSION (J2000)

C array05 22 10

185513+052158

05)

0000

02J( NOITAN21 55ILCED50

45

18 55 14.5

14.0

13.5

13.0

12.5

RIGHT ASCENSION (J2000)

05 09 29.2

185521+050927

29.0

28.8

)

0002J28.6

( NOITANI28.4

LCED28.2

28.0

27.8

18 55 21.9621.9521.94

21.9321.9221.9121.9021.89

21.8821.87RIGHT ASCENSION (J2000)

C array04 14 35

185618+041420

30

)

0025

02J( NOITAN20

ILCED15

10

18 56 19.5

19.018.518.0

RIGHT ASCENSION (J2000)

185500+021544

02 15 50

45

)

0002J( NOIT40

ANILCED35

30

25

18 55 01.2

01.0

00.8

00.6

00.400.200.054 59.859.6

59.4

RIGHT ASCENSION (J2000)

05 22 01

C array00

185513+052158

21 59

58

)

0002J57

( NOITAN56

ILCED55

54

53

52

18 55 13.7

13.6

13.513.413.313.2

RIGHT ASCENSION (J2000)

05 09 40

185521+050927

35

)

0002J(30

NOITANILC25

ED20

15

18 55 23.022.5

22.021.521.0RIGHT ASCENSION (J2000)

C array04 15 30

185650+041520

25

)

0002J(20

NOITANILCED1510

05

18 56 51.2

51.0

50.8

50.650.450.250.049.8

49.6

49.4

RIGHT ASCENSION (J2000)

02 15 44

185500+021544

43

42

)

000241

J( NOITA40

NILCED39

38

37

36

18 55 00.4

00.3

00.200.100.0

54 59.9

RIGHT ASCENSION (J2000)

C array185515+021054

02 11 0010 55)

0002J( NO50

ITANILCED45

40

35

18 55 16.4

16.2

16.0

15.815.615.415.215.0

14.8

14.6

RIGHT ASCENSION (J2000)

185618+041420

04 14 23.0

22.8

)

0002J( NOIT22.6

ANILCED22.4

22.2

18 56 18.80

22.0

18.7918.78

18.7718.7618.7518.7418.73

RIGHT ASCENSION (J2000)

C array00 51 35

185749+005119

30

25

)

0002J( NO20

ITANILCED15

10

05

00

18 57 50.5

50.049.5

49.0

48.5

RIGHT ASCENSION (J2000)

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