Complex organic molecules in organic-poor massive young stellar objects

1.7 MB·English

by  Edith C. Fayolle

Astronomy&Astrophysicsmanuscriptno. ms_icegas_1col (cid:13)cESO2015
January15,2015
Complex organic molecules in organic-poor
massive young stellar objects.
EdithC.Fayolle1,2,KarinI.Öberg2,RobinT.Garrod3,EwineF.vanDishoeck1,
andSuzanneE.Bisschop4,5
5
1 1 LeidenObservatory,LeidenUniversity,P.O.Box9513,2300RALeiden,TheNether-
0
2 lands

n e-mail:[email protected]
a
J 2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA

3
02138,USA
1
3 Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853-

]
R 6801,USA
S
4 TheCentreforStarandPlanetFormation,NaturalHistoryMuseumofDenmark,Uni-
.
h
versityofCopenhagen,ØsterVoldgade5-7,CopenhagenK.,DenmarkDK-1350
p
- 5 TheCentreforStarandPlanetFormation,NielsBohrInstitute,JulianeMariesvej30,
o
r
CopenhagenØ.,Denmark,DK-2100
t
s
a
[

1 ABSTRACT
v
8
Context. Massive young stellar objects (MYSOs) with hot cores are classic sources of
6
1
complexorganicmolecules.Theoriginsofthesemoleculesinsuchsources,aswellasthe
3
0 small- and large-scale differentiation between nitrogen- and oxygen-bearing complex
.
1 species,arepoorlyunderstood.
0
5 Aims. Weaimtousecomplexmoleculeabundancestowardachemicallylessexplored
1
class of MYSOs with weak hot organic emission lines to constrain the impact of hot
:
v
molecularcoresandinitialiceconditionsonthechemicalcompositiontowardMYSOs.
i
X
Methods. WeusetheIRAM30mandtheSubmillimeterArraytosearchforcomplexor-
r
a
ganicmoleculesover8-16GHzinthe1mmatmosphericwindowtowardthreeMYSOs
withknowniceabundances,butwithoutluminousmolecularhotcores.
Results. Complexmoleculesaredetectedtowardallthreesourcesatcomparableabun-
danceswithrespecttoCH OHtoclassicalhotcoresources. Therelativeimportanceof
3
CH CHO,CH CCH,CH OCH ,CH CN,andHNCOdifferbetweentheorganic-poor
3 3 3 3 3
MYSOs and hot cores, however. Furthermore, the N-bearing molecules are generally
concentrated toward the source centers, while most O- and C-bearing molecules are
presentbothinthecenterandinthecolderenvelope.Gas-phaseHNCO/CH OHratios
3
Articlenumber,page1of28
EdithC.Fayolle etal.:Newconstraintsontheoriginsoforganics
aretentativelycorrelatedwiththeratiosofNH iceoverCH OHiceinthesamelines
3 3
ofsight,whichisconsistentwithnewgas-grainmodelpredictions.
Conclusions. Hotcoresarenotrequiredtoformcomplexorganicmolecules,andsource
temperature and initial ice composition both seem to affect complex organic distribu-
tionstowardMYSOs. Toquantifytherelativeimpactoftemperatureandinitialcondi-
tionsrequires,however,alargerspatiallyresolvedsurveyofMYSOswithicedetections.
Key words. Astrochemistry,ISM:molecules,ISM:abundances
1. Introduction
Organicmoleculescontainingmorethansixatoms,theso-calledcomplexorganics(Herbst
&vanDishoeck2009),arecommonlyfoundinthewarmanddensegas(T ą100K,ną
106 cm´3 )aroundyoungstellarobjects(YSOs),so-calledmolecularhotcores(e.g.,Blake
et al. 1987; Cazaux et al. 2003; Fuente et al. 2005). Abundances and abundance ratios of
complexorganicsarefoundtovarysubstantiallybetween(Helmich&vanDishoeck1997)
andwithinYSOs(e.g.,Wyrowskietal.1999). Thissuggeststhatformationanddestruc-
tion routes are highly environment specific and that there is a sensitive dependence of
the complex organic chemistry on chemical and physical initial conditions. In addition,
different filling factors of the warm gas should play a role if there the complex organic
productsofcoldandhotchemistrydifferthere.
The potential environmental dependencies and chemical memories lead to complex
organicshavingagreatpotentialasprobesofthecurrentandpastphysicalandchemical
conditionswheretheyarefound(Nomura&Millar2004).Theirpotentialutilityisfurther
increasedbythefactthatmostcomplexorganicmoleculespresentlargenumbersoflines,
spanningmostexcitationconditionsfoundinspace. Complexmoleculesarealsoofhigh
interest for origins of life theories since they are the precursors of even more complex
prebioticmaterial(Ehrenfreund&Charnley2000). Usingmoleculesasprobesofphysical
conditionsandadvancementsinprebioticevolutionfromorganicsbothrelyonadetailed
understandingofcomplexorganicchemistry.Theformationanddestructionmechanisms
andratesofmostcomplexorganicsare,however,poorlyconstrained.
TheformationoforganicmoleculesaroundmassiveYSOs(MYSOs)wasfirstthought
to proceed through gas phase reactions in dense hot cores, following evaporation of ice
grain mantles (e.g., Charnley et al. 1992). Recent laboratory experiments and modeling
efforts point now toward a more complicated sequential scenario that relies to a greater
extent on surface formation routes on submicron-sized dust particles. Herbst & van
Dishoeck(2009)classifycomplexorganicmoleculesintermsofgenerationsaccordingto
thefollowingscenario. Ininterstellarcloudsandinthedeeplyembeddedearlyphasesof
starformation,atomsandmoleculesaccreteorformonthesurfaceofdustgrains,building
Articlenumber,page2of28
EdithC.Fayolle etal.:Newconstraintsontheoriginsoforganics
upanicymantleofsimplespecieslikeH O,CH ,andNH (Tielens&Hagen1982). This
2 4 3
icymantleisprocessedatlowtemperaturebyatoms, whichcandiffuseevenatthelow
temperaturesincloudcores,creatingthezerothgenerationoforganicmolecules. Agood
example of these species is CH OH, which is efficiently formed at low temperature by
3
thehydrogenationofCOice(Watanabe&Kouchi2002;Watanabeetal.2003,2004;Fuchs
etal.2009;Cuppenetal.2009). First-generationcomplexorganicsformwhenheatingthe
coldenvelopeupbytheincreasingluminosityofacentralYSOandisduetoacombina-
tion of photoprocessing of the ice resulting in radical production and a warming up (20
to 100 K) of the grains, thereby enhancing the mobility of radicals and molecules (Gar-
rod et al. 2008; Öberg et al. 2010). When the icy grains move inward and reach a region
warmer than 100 K, the icy mantle evaporates, bringing the zeroth- and first-generation
organicsintothegasphase,whereadditionalchemicalreactionsgiverisetotheformation
ofthesecond-generationcomplexorganics(e.g.,Charnleyetal.1992;Dotyetal.2002;Viti
etal.2004).
In the proposed scenario of complex molecule formation, the initial ice mantle plays
a critical role. The exact composition of this ice may therefore have a strong effect both
ontheproductcompositionofformedorganicsandontheiroverallformationefficiency.
Garrod et al. (2008) and Öberg et al. (2009) find, for example, that CH OH ice is a key
3
startingpointformostcomplexorganicformation. Rodgers&Charnley(2001)usedahot
corechemistrymodeltoshowthattherelativeamountofNH intheicehasalargeimpact
3
ontheCH CN/CH OHprotostellarabundanceratio. Observationallytestingtheserela-
3 3
tionshipswouldprovidekeyconstraintsontheformationpathwaysofcomplexorganic
molecules.
IsolatedMYSOswithwarminnerenvelopesaregoodlaboratoriesfortestingthishy-
pothesis as these sources are bright enough to observe a wide variety of organics and
some of them present ice features from the cold outer protostellar envelope (Gibb et al.
2004). Sources presenting both complex gas and ice features are, however, rare as the
sources need to be evolved to possibly display a bright hot core chemistry accessible to
currentobservationalfacilitiesandyoungenoughsuchthattheicematerialhasnotbeen
completely consumed by accretion, warm up, and envelope dispersal. In the massive
YSOsamplestudiedbyBisschopetal.(2007),onlythreehotcorespresenticespectra(see
Table 1). Such a small number prevents any analysis of the correlation between ice and
gascontentandjustifiesoursearchforotherobjectsthatdisplaybothicefeaturesandgas
phaseorganics.
Toextendthesampleofsourceswithbothcomplexorganicsandiceobservations,we
lookforgasphaseorganicsspeciesaroundnon-hotcoreMYSOs(absenceorlow-levelof
hotCH OHemission)thatalsohaveiceobservationsavailablefromtheliterature. These
3
sourcesarecalledfromnowonorganic-poorMYSOs(poorinlinesoforganicmolecules).
Articlenumber,page3of28
EdithC.Fayolle etal.:Newconstraintsontheoriginsoforganics
Complex molecule observations in such objects may additionally shed light on the con-
ditionsunderwhichdifferentkindsofcomplexmoleculescanform,i.e. whichmolecules
requirethepresenceofahotcoretobeabundant.
Massive objects NGC7538 IRS9, W3 IRS5 , and AFGL490 have been observed in the
mid-infraredbytheInfraredSpaceObservatory(ISO)andanalyzedsystematicallyforice
abundancesbyGibbetal.(2004)andreferencestherin. NGC7538IRS9isa6ˆ104Ld lu-
minousobjectlocatedinPerseus.ItisclosetohotcoresourceNGC7538IRS1anddisplays
atleastthreebipolaroutflows,evidenceforaccretion(Sandelletal.2005),andahotcom-
ponentclosetothecentralobject. W3IRS5isassociatedwithfiveYSOs,twoofwhichare
massive (van der Tak et al. 2005; Megeath et al. 2005; Rodón et al. 2008; Chavarría et al.
2010). It has a luminosity of 17ˆ104Ld and presents strong S-bearing molecular lines
(Helmich et al. 1994). AFGL490 is a very young medium-mass YSO of 4.6ˆ103Ld, in
transitiontoaHerbigBestar, whichdrivesahigh-velocityoutflow(Mitchelletal.1995)
andshowsevidenceofarotatingdisk(Schreyeretal.2006). Sincethesesourcesarecon-
sideredtopotentallybeatanearlierevolutionarystagethantypicalhot-coresources,itis
difficulttopredictthechemicalcomplexityandthespatialemissionoftheorganicsthat
couldbeobservedinthesesources.
In this study we use a combination of single-dish IRAM 30m data and spatially re-
solvedobservationsfromtheSubmillimeterArray1(SMA)tosearchfororganicmolecules
around these three MYSOs and report on their complex organic abundances in the cool
protostellar envelope and in a warmer region closer to the star. A subset of these data
wasusedintheÖbergetal.(2013)tostudythedetailedradialdistributionofmolecules
inNGC7538IRS9,whilethepresentstudyfocusesontheoveralldetectionrateoforgan-
ics in these organic-poor sources, and on how they compare with ice abundances and
traditional hot core chemistry. The paper is organized as follows. The observations are
described in Section 2, and the results of the line analysis are shown in Sections 3.1, 3.2,
and3.3. Thechemistryinoursampleiscomparedtothechemistryintraditionalhot-core
sourcesinSection3.4.Section3.5presentscorrelationstudiesbetweeniceandgascolumn
densities and abundances, testing the impact of initial ice compositions on the complex
chemistry. A discussion of the use of these line-poor sources to underpin the origins of
complexchemistryispresentedinSection4,whichisfollowedbytheconclusionsofthis
study.
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EdithC.Fayolle etal.:Newconstraintsontheoriginsoforganics
Table1:Sourcecharacteristicsandiceabundances. Thesourcesobservedinthisstudyare
inboldface,theothersarefromBisschopetal.(2007).
Source α(2000) δ(2000) d L N X[%](/N )
H2O H2O
kpc 104Ld 1017cm´2 CH3OH CH4 NH3 OCN´
NGC7538IRS9 23:14:01.6 +61:27:20.4 2.7 3.5 70 4.3˘0.6 2˘0.4 15˘2.7 1.7˘0.5
W3IRS5 02:25:40.5 +62:05:51.3 2.0 17 51 ă3.3 ă1.3 ă5.7 ă0.23
AFGL490 03:27:38.7 +58:47:01.1 1.4 0.46 6.2 11˘4 ă2.4 ă16 ă1.2
W33A 18:14:38.9 -17:52:04.0 3.8 5.3 110 15˘5 1.5˘0.2 15˘4 6.3˘1.9
AFGL2591 20:29:24.6 +40:11:19.0 3.3 18 12 14˘2 ă2.7 ă2.3 –
NGC7538IRS1 23:13:45.4 +61:28:12.0 2.4 15 22 ă4 1.5˘0.5 ă17 ă0.5
OrionIRc2 05:35:14.3 -05:22:31.6 0.4 1.0 24.5 10˘3 – – 2˘0.6
G24.78 18:36:12.6 -07:12:11.0 7.7 1.2 – – – – –
G75.78 20:21:44.1 +37:26:40.0 1.9 19 – – – – –
NGC6334IRS1 17:20:53.0 -35:47:02.0 1.7 11 – – – – –
2. Observations and analysis
2.1. Observations
TheMYSOsNGC7538IRS9, W3IRS5, andAFGL490locatedinPerseusNGC7538at2.7
kpc,inPerseusW3at2.0kpc,andinCamelopardalisOB1at1.4kpcrespectively(seeTable
1) were observed with the IRAM 30m and the Submillimeter Array. The three sources
were observed with the IRAM 30m telescope on February 19–20, 2012 using the EMIR
230GHzreceiverandthenewFTSbackend. AtthesefrequenciestheIRAM30mbeamis
„102. Thetwosidebandscover223–231GHzand239–247GHzataspectralresolutionof
„0.2kms´1 andwithasidebandrejectionof-15dB(Carter, M.etal.2012). Wechecked
thepointingeveryonetotwohoursandfoundtobeaccuratewithin22to32.
Focus was checked every four hours and generally remained stable through most of
the observations; i.e., corrections in the range of 0.2–0.4 were common, but a correction
of 0.7 was required once. We acquired spectra in both position-switching and wobbler-
switchingmodes. Theresultingspectrahadsimilarrelativelineintensities,indicativeof
noemissioninthewobbler-offposition. Thewobbler-switchingmodewasconsiderably
more stable, and we used these data alone for the quantitative analysis. The weather
during the observations was excellent and the τ varied between 0.05 and 0.15.
225GHz
We converted the raw IRAM spectra to main beam temperatures and fluxes using for-
ward and beam efficiencies and antenna temperature to flux conversion values listed at
www.iram.es/IRAMES/mainWiki/Iram30mEfficiencies. The spectra were reduced us-
ingCLASS2.Alinearbaselinewasfittedtoeach4GHzspectralchunkusingfourtoseven
windows. The individual scans were baseline-subtracted and averaged3. The absolute
flux scale of the lines were then set using calibrated SMA data as outlined in detail by
Öbergetal.(2013).
1 TheSubmillimeterArrayisajointprojectbetweentheSmithsonianAstrophysicalObservatory
andtheAcademiaSinicaInstitueofAstronomyandAstrophysics. ItisfundedbytheSmithsonian
InstituteandtheAcademiaSinica.
2 CLASSwebsite:http://www.iram.fr/IRAMFR/GILDAS
3 Reduceddataareavailablethroughthedataversenetworkathttp://dx.doi.org/10.7910/DVN/
26562
Articlenumber,page5of28
EdithC.Fayolle etal.:Newconstraintsontheoriginsoforganics
Fig.1: ImageoftheCH CNemissionusingthe13 -12 at239.138GHzlineacquiredby
3 0 0
theSMAforthemassiveyoungstellarobjectsNGC7538IRS9,W3IRS5,andAFGL490tar-
getedinthisstudy.Theblackcontourpresentsthe50%lineintensity,andthesynthesized
beamisshowninwhiteatthebottomleft. A2”radiusmaskusedtoextractthespectrais
overplottedindashedredline. ImagesforthehotcoresourceNGC7538IRS1ispresented
aswell. Thelattersourcehasbeenthroughthesameprogramasthethreeothersources.
SMA observations were acquired in the compact and extended array configurations.
Thedatainthecompactconfigurationweretakenon15October2011forallsourcesand
with seven antennas, resulting in baselines between 16 m and 77 m. The data in the
extended configuration were obtained using eight antennas, resulting in 44 m to 226 m
baselinesandwereacquiredon29July2011forW3IRS5andAFGL490andonthe15th
ofAugust2011forNGC7538IRS9. Weset-uptheSMAcorrelatortoobtainaspectralres-
olutionof„1kms´1 using128channelsforeachofthe46chunkscovering227-231GHz
inthelowersidebandand239–243GHzintheuppersideband. Theτ was0.09on
225GHz
29July,0.1on15August,and0.07on15October20114.
We used the MIR package5 to perform the first data reduction steps (flux calibration
and continuum subtraction). Absolute flux calibration is done with Callisto. The band-
pass calibrators 1924-292 and 3c84 were used for the compact observations, and 3c454.3
and 3c279 were used to calibrate 29 July and 15 July observations, respectively. The
quasars 0014+612 and 0102+584 were used as gain calibrators for NGC7538 IRS9, and
0244+624, 0359+509, and we used 0102+584 for W3 IRS5 and AFGL490. The compact
andextendeddatawerecombinedforeachsourcewithMIRIAD5usingnaturalorrobust
weighting, depending on the data quality, which resulted in synthesized beam sizes of
2.0”ˆ1.7”forNGC7538IRS9,2.2”ˆ2.8”forW3IRS5,and2.3”ˆ2.9”forAFGL490.
2.2. Spectral extraction and rms
Both the IRAM and SMA data were frequency-calibrated using the bright 5-4 CH OH
3
ladderaround241.7GHz,correctingfortheintrinsicvelocityofthedifferentsources. We
extractedtheSMAspectrausinga22-radiusmaskaroundthecontinuumphasecenterof
eachsource.ThemaskdimensionwaschosentoencompassamajorityoftheCH CNline
3
4 Observations are available on the SMA archive website herhttp://www.cfa.harvard.edu/cgi-
bin/sma/smaarch.pl
5 MIRwebsite:http://www.cfa.harvard.edu/~cqi/mircook.html
Articlenumber,page6of28
EdithC.Fayolle etal.:Newconstraintsontheoriginsoforganics
emissionat239.318GHzthatcanbeassociatedwithacorecomponent,asshowninFigure
1. Weselecteda22 masksizebasedonacombinationoftheoryanddatainspection, i.e.
theoptimalmasksizeshouldincludeallthehotemissionandexcludeasmuchaspossible
ofthecoldenvelopeemission. Inallsources,theselectedmasksizeshouldbebiggerthan
the 100 K radius and thus incorporate all emission associated with a potential hot core.
TowardNGC7538IRS9andAFGL490,wherethe100Kradiusshouldbesmallerthan22
,smallermaskswerealsoexploredtomoreexclusivelytracetheT ą100Kregion,butthe
resultingspectrahadgenerallytoolowsignal-to-noiseratiotobeusefulforaquantitative
analysis. SomecolderchemistrycontributiontotheSMAspectrainthesesourcescannot,
thus,beexcludedapriori,butthesucceedinganalysis(seebelow)demonstratedthatthe
emissionisindeeddominatedbyhotgas.
The rms for the IRAM and SMA observations of each source was derived in a line
free region of several hundred channels: the 229.37-229.445 GHz region for the lower
side band and the 240.7 - 240.75 GHz region for the upper side band. The rms derived
for the IRAM observations is between 15 and 20 mK, which is lower than any previous
millimeter observations for these sources. For the SMA data, the rms for the lower side
bandis„70mK,and„100mKfortheuppersideband.
3. Results
3.1. Line identification and characterization
Figure2showstheIRAM30m239-243GHzspectraforthethreetargetedline-poorMYSOs
and the hot-core source NGC7538 IRS1. The organic-poor MYSOs have, as expected, a
lower line density, but also many line coincidences with the hot core. Of the lines from
complexorganicslistedbyBisschopetal.(2007)foundintheirsamplehot-coresources,
CH OH,CH CN,CH CCH,HNCO,CH OCH ,andCH CHOlineswereidentifiedinat
3 3 3 3 3 3
leastoneoftheorganic-poorMYSOsusingthesplataloguecatalogtool6 andtheCDMS7
andtheJPL8 spectraldatabases(Mülleretal.2001;Pickettetal.1998). Allavailablelines
intheobservedspectralrangewereusedforthequantitativeanalysisexceptforCH OH
3
whereweonlyusedthelinesfromthe5-4laddertosimplifytheexcitationanalysis.
WefittedtheidentifiedlineswithaGaussianfunctioninIDLusingtheroutine’gauss-
fit’ for isolated lines and ’mpfitfun’ when a multiple Gaussian fit was required because
of overlapping lines. A local baseline component was added to the fits when needed,
andthepresenteduncertaintieswereoutputbythefittingroutines. Wecalculated3σup-
perlimitsusinganaverageFWHMforthedifferentsources. Unresolvedmultipletswere
treatedinoneoutthreewaysdependingonthenatureoftheoverlappinglines: 1)Ifone
6 Splataloguewebsite:http://www.cv.nrao.edu/php/splat/
7 CDMSwebsite:http://www.astro.uni-koeln.de/cdms
8 JPLdatabasewebsite:http://spec.jpl.nasa.gov/
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EdithC.Fayolle etal.:Newconstraintsontheoriginsoforganics
Fig. 2: 239-243 GHz spectral window from the IRAM 30m displaying emission lines for
typical hot core source NGC 7538 IRS 1and weak line MYSOs NGC7538 IRS9, W3IRS5,
AFGL490.Thestar-markedlinesareCOghostlinesconsistentwiththesidebandrejection
foreachsource.
of the possible contributing lines had a very low Einstein coefficient or high upper en-
ergyleveland/orisnotlikelytobedetectedbasedonnon-detectionsofthesamespecies
in other frequency ranges, then it was assumed to not contribute significantly and was
not included in the fit. 2) If the lines came from the same species and the upper energy
level and Einstein coefficients were identical or close to identical, then the degeneracies
were added and the feature was treated as a single line, 3) if none of the two previous
conditionsweremet,wedidnotincludethemultipletintheanalysis.
Line upper energy levels, Einstein coefficients, degeneracies, and quantum numbers
from the Splatalogue are listed with the derived line fluxes and FWHM in Table 2 for
CH OHfromthesingle-dishobservations,inTable3forCH OHfromtheSMAspectra,
3 3
in Table 4 for CH CN from IRAM, in Table 5 for CH CN from the SMA, in Table 6 for
3 3
CH CCHfromIRAM,inTable7forCH CCHfromtheSMA,andinTable8forHNCO,
3 3
CH OCH , and CH CHO. Only the lines with an Einstein coefficient logarithm higher
3 3 3
than ´4.5 and their upper level energy below 400 K are displayed in the tables. Due to
the high line density for CH OCH and CH CHO, only the lines with an upper energy
3 3 3
levelbelow200Kareshownforthesespecies. Noothercomplexmoleculesweredetected
towardanyofthesources. Formoleculeswithweaklines,weonlyusedtheIRAMdata
sincetheSMAobservationshavelowerspectralresolutionandsignal-to-noiseratio.
3.2. Spatial origin of the line emission
Figures3,4,and5presentthelinefluxesofkeymoleculesfromboththesingle-dishand
SMA observations toward the three MYSOs. The IRAM beam is 6.2 to 7.2 times larger
than the SMA mask ((IRAM radius at 227-243 GHz: 5–5.42)2/(SMA mask radius: 22)2).
Articlenumber,page8of28
EdithC.Fayolle etal.:Newconstraintsontheoriginsoforganics
Table2: CH OHlinesdatafromIRAM30mspectra.
3
Freq Eup logA gu Transition ş NGC7538IRS9 ş W3IRS5 ş AFGL490
FdV FHWM FdV FHWM FdV FHWM
(GHz) (K) (Jykms´1) (kms´1) (Jykms´1) (kms´1) (Jykms´1) (kms´1)
239.746 49.1 -4.25 11 5 -4 A` 20.7˘2.3 3.70˘0.03 6.1˘0.8 2.32˘0.04 4.6˘0.7 4.4˘0.2
1,5 1,4
241.700 47.9 -4.22 11 5 -4 E 30.8˘3.3 3.47˘0.02 7.1˘0.9 2.43˘0.04 6.7˘0.9 3.53˘0.07
0,5 0,4
241.767 40.4 -4.24 11 5 -4 E 60.7˘6.3 3.37˘0.01 11.2˘1.3 2.98˘0.03 16.7˘1.9 3.11˘0.02
-1,5 -1,4
241.791 34.8 -4.22 11 5 -4 A 69.2˘7.1 3.37˘0.01 12.6˘1.5 2.91˘0.03 20.3˘2.2 3.09˘0.02
0,5 0,4
241.807 115.2 -4.66 22 5 -4 A˘ 2.3˘0.5 4.5˘0.4 1.6˘0.3 1.58˘0.09 ă1.4 -
4 4
241.813 122.7 -4.66 11 5 -4 E 1.1˘0.4 3.6˘0.6 1.2˘0.3 1.7˘0.2 ă1.4 -
-4,2 -4,1
241.830 130.8 -4.66 11 5 -4 E ă1.1 - 1.3˘0.3 2.0˘0.2 ă1.4 -
4,1 4,0
241.833 84.6 -4.41 22 5 -4 A˘ 13.3˘1.6 4.61˘0.06 5.5˘0.7 2.18˘0.04 3.6˘0.6 4.9˘0.2
3 3
241.842 72.5 -4.29 11 5 -4 A´ 10.1˘1.4 5.5˘0.1 3.2˘0.5 1.90˘0.08 2.6˘0.6 6.8˘0.5
2,4 2,3
241.844 82.5 -4.41 11 5 -4 E 2.4˘0.5 3.3˘0.3 3.2˘0.5 2.2˘0.1 1.5˘0.3 3.50˘0.02
3,2 3,1
241.852 97.5 -4.41 11 5 -4 E 3.2˘0.6 5.5˘0.4 2.2˘0.4 2.1˘0.1 1.5˘0.4 6.5˘0.8
-3,3 -3,2
241.879 55.9 -4.22 11 5 -4 E 23.5˘2.6 3.64˘0.02 6.7˘0.9 2.58˘0.05 5.2˘0.7 4.1˘0.1
1,4 1,3
241.888 72.5 -4.29 11 5 -4 A` 8.5˘1.1 4.28˘0.09 3.8˘0.5 2.04˘0.06 2.5˘0.5 5.2˘0.3
2,3 2,2
241.904 60.7 -4.29 11 5 -4 E 15.9˘1.7 3.66˘0.02 5.0˘0.6 2.57˘0.03 3.9˘0.5 3.85˘0.07
-2,4 -2,3
241.905 57.1 -4.30 11 5 -4 E 15.9˘1.7 3.66˘0.02 5.0˘0.6 2.57˘0.03 3.9˘0.5 3.85˘0.07
2,3 2,2
Table3: CH OHlinesextractedfromSMAobservationswitha22-radiusmask.
3
Freq Eup logA gu Transition ş NGC7538IRS9 ş W3IRS5 ş AFGL490
(GHz) (K) FdV FHWM FdV FHWM FdV FHWM
(Jykms´1) (kms´1) (Jykms´1) (kms´1) (Jykms´1) (kms´1)
239.746 49.1 -4.25 11 5 -4 A` 7.6˘1.1 4.6˘0.2 2.3˘0.5 1.9˘0.2 3.0˘0.7 4.6˘0.5
1,5 1,4
241.700 47.9 -4.22 11 5 -4 E 7.3˘1.0 4.1˘0.2 2.8˘0.6 2.4˘0.2 3.7˘0.8 5.9˘0.5
0,5 0,4
241.767 40.4 -4.24 11 5 -4 E 8.2˘1.1 3.5˘0.1 3.2˘0.6 2.3˘0.2 1.8˘0.5 2.6˘0.3
-1,5 -1,4
241.791 34.8 -4.22 11 5 -4 A 7.1˘1.0 3.16˘0.09 3.5˘0.7 2.9˘0.2 2.4˘0.6 4.9˘0.7
0,5 0,4
241.807 115.2 -4.66 22 5 -4 A˘ 2.1˘0.7 6˘1 1.4˘0.5 2.4˘0.5 ă1.1 -
4 4
241.813 122.7 -4.66 11 5 -4 E 1.0˘0.4 3.6˘0.9 1.0˘0.5 2.8˘0.8 ă1.1 -
-4,2 -4,1
241.830 130.8 -4.66 11 5 -4 E ă0.8 - ă1.1 - ă1.1 -
4,1 4,0
241.833 84.6 -4.41 22 5 -4 A˘ 6.4˘1.1 4.7˘0.3 3.1˘0.7 2.9˘0.3 1.8˘0.6 4.6˘0.8
3 3
241.852 97.5 -4.41 11 5 -4 E 1.9˘0.6 3.4˘0.5 1.4˘0.5 1.5˘0.4 ă1.1 -
-3,3 -3,2
241.879 55.9 -4.22 11 5 -4 E 5.5˘0.9 3.4˘0.2 2.6˘0.6 2.3˘0.2 1.9˘0.6 4.7˘0.7
1,4 1,3
241.888 72.5 -4.29 11 5 -4 A` 4.6˘0.8 5.2˘0.3 1.6˘0.5 1.6˘0.2 1.8˘0.7 7˘2
2,3 2,2
241.904 60.7 -4.29 11 5 -4 E 5.3˘0.8 4.5˘0.1 1.7˘0.3 2.2˘0.2 1.7˘0.4 5.2˘0.5
-2,4 -2,3
241.905 57.1 -4.30 11 5 -4 E 5.3˘0.8 4.5˘0.1 1.7˘0.3 2.2˘0.2 1.7˘0.4 5.2˘0.5
2,3 2,2
Table4: CH CNlinesdatafromIRAM30mspectra.
3
Freq Eup logA gu Transition şNGC7538IRS9 ş W3IRS5 ş AFGL490
(GHz) (K) FdV FHWM FdV FHWM FdV FHWM
(Jykms´1) (kms´1) (Jykms´1) (kms´1) (Jykms´1) (kms´1)
239.023 258.9 -3.00 54 13 -12 1.6˘0.5 9˘2 ă1.0 - ă1.5 -
5 5
239.064 194.6 -2.97 54 13 -12 2.0˘0.7 9˘2 0.9˘0.3 6˘2 1.2˘0.4 6˘2
4 4
239.096 144.6 -2.95 108 13 -12 5.3˘0.8 6.0˘0.3 2.2˘0.4 2.2˘0.2 2.4˘0.6 8˘1
3 3
239.120 108.9 -2.94 54 13 -12 4.5˘0.7 5.7˘0.3 1.7˘0.4 2.8˘0.3 1.5˘0.5 6˘2
2 2
239.133 87.5 -2.93 54 13 -12 5.8˘0.8 4.6˘0.2 2.4˘0.4 2.4˘0.2 2.1˘0.5 4.9˘0.5
1 1
239.138 80.3 -2.93 54 13 -12 7.4˘1.0 5.2˘0.2 2.6˘0.4 2.1˘0.2 2.4˘0.5 5.4˘0.5
0 0
Thatmostemissionlinesinthesefiguresdonotdisplayafactorofsixorsevendifference
between the IRAM 30m and SMA spectra demonstrates a non-uniform emission across
the object. Some emission line fluxes, most notably CH CN, are similar (within a factor
3
oftwo)betweentheIRAM30mandSMAspectra,indicatingofalargecontributionfrom
unresolvedemissionatthesourcecenter. Incontrast,littleornoCH CCHfluxfromthe
3
IRAM is recovered by the SMA, which indicates extended emission. The fact that some
CH CCHIRAM30mfluxesaremorethan6.2–7.2ˆhigherthanthecorrespondingSMA
3
fluxes is explained by spatial filtering of large-scale emission and/or off-centered emis-
Articlenumber,page9of28
EdithC.Fayolle etal.:Newconstraintsontheoriginsoforganics
Table5: CH CNlinesdatafromSMAspectra.
3
Freq Eup logA gu Transition şNGC7538IRS9 ş W3IRS5 ş AFGL490
(GHz) (K) FdV FHWM FdV FHWM FdV FHWM
(Jykms´1) (kms´1) (Jykms´1) (kms´1) (Jykms´1) (kms´1)
239.064 194.6 -2.97 54 13 -12 2.9˘0.9 7.6˘1.2 ă0.8 - ă1.9 -
4 4
239.096 144.6 -2.95 108 13 -12 5.1˘1.0 5.6˘0.4 2.9˘0.9 6.8˘1.2 ă1.9 -
3 3
239.120 108.9 -2.94 54 13 -12 4.4˘1.1 9.6˘1.0 1.2˘0.5 2.9˘0.9 1.8˘0.8 6˘2
2 2
239.133 87.5 -2.93 54 13 -12 5.6˘1.3 6.9˘0.7 3.1˘0.6 4.4˘0.4 1.8˘0.9 6˘2
1 1
239.138 80.3 -2.93 54 13 -12 5.2˘1.2 6.3˘0.6 2.1˘0.5 2.7˘0.4 1.8˘0.9 6˘2
0 0
Table6: CH CCHlinesdatafromIRAM30mspectra.
3
Freq Eup logA gu Transition ş NGC7538IRS9 ş W3IRS5 ş AFGL490
(GHz) (K) FdV FHWM FdV FHWM FdV FHWM
(Jykms´1) (kms´1) (Jykms´1) (kms´1) (Jykms´1) (kms´1)
239.088 346.1 -4.07 16 14 -13 ă1.1 - ă0.7 - ă1.0 -
6 6
239.179 201.7 -4.88 58 14 -13 1.0˘0.3 3.4˘0.6 0.9˘0.3 2.5˘0.6 ă1.0 -
4 4
239.211 151.1 -4.00 16 14 -13 4.7˘0.7 3.1˘0.2 4.0˘0.5 2.00˘0.06 1.5˘0.3 3.5˘0.4
3 3
239.234 115.0 -4.85 58 14 -13 5.1˘0.7 2.71˘0.08 3.6˘0.5 1.98˘0.07 1.5˘0.4 3.0˘0.3
2 2
239.248 93.3 -4.84 58 14 -13 9.0˘1.1 2.92˘0.05 5.8˘0.7 2.2˘0.05 2.7˘0.4 2.3˘0.1
1 1
239.252 86.1 -4.84 58 14 -13 10.2˘1.2 2.74˘0.04 6.4˘0.8 2.12˘0.04 3.7˘0.5 2.9˘0.1
0 0
Table7: CH CCHlinesdatafromSMAspectra.
3
Freq Eup logA gu Transition şNGC7538IRS9 ş W3IRS5 ş AFGL490
(GHz) (K) FdV FHWM FdV FHWM FdV FHWM
(Jykms´1) (kms´1) (Jykms´1) (kms´1) (Jykms´1) (kms´1)
239.088 346.1 -4.07 16 14 -13 ă0.9 - ă0.7 - ă1.0 -
6 6
239.179 201.7 -4.88 58 14 -13 ă0.9 - 0.9˘0.3 2.5˘0.6 ă1.0 -
4 4
239.211 151.1 -4.00 16 14 -13 1.8˘0.6 3.2˘0.5 ă1.1 - 1.0˘0.6 4.2˘1.5
3 3
239.234 115.0 -4.85 58 14 -13 1.3˘0.5 3.5˘0.7 ă1.1 - ă1.0 -
2 2
239.248 93.3 -4.84 58 14 -13 2.3˘0.7 3.5˘0.5 ă1.1 - ă1.0 -
1 1
239.252 86.1 -4.84 58 14 -13 2.4˘0.7 2.9˘0.4 ă1.1 - 1.6˘0.8 5.9˘1.9
0 0
sion. CH OH lines display a mixed behavior: lines with higher upper energies show
3
moreoverlapbetweentheIRAM30mandSMAspectrathanthecolderlines. TheIRAM
30m and SMA line fluxes for the 11 - 10 HNCO line at 241.774 GHz are close for
0,11 0,10
NGC7538IRS9andsimilarforW3IRS5,butnoneoftheIRAM30mfluxisrecoveredbythe
AFGL490SMAobservations. Basedontheselines,HNCOemissionappearstobecoming
from both the core and the envelope of NGC7538 IRS9, from the core of W3 IRS5 alone,
andfromtheenvelopeofAFGL490.Thissource-to-sourcedifferencecouldpartiallycome
from different excitation conditions in the three sources, and the excitation-abundance
structure degeneracy can only be strictly broken by observation of additional lines. The
simplestscenarioforexplainingourdetectionisforHNCOtohavebothanextendedand
acompactorigin, however, andthisisalsosupportedbythereportedexcitationcharac-
teristicsandemissionprofileofHNCOinothersources(Bisschopetal.2007).
In Fig. 5 the signal-to-noise ratio is lower, but it is still clear that CH CHO toward
3
NGC7538 IRS9 only has extended emission since none of the IRAM 30m line flux is re-
coveredintheSMAspectra. NoCH CHOlinesaredetectedintheothertwoMYSOsin
3
the spectral range where IRAM 30m and SMA observations overlap. CH OCH is de-
3 3
tectedtowardNGC7538IRS9andAFGL490,andinbothcasestentativeSMAdetections
suggestthattheemissionoriginatesinthesourcecenters. Basedonthedifferentemission
Articlenumber,page10of28