First results from the CALYPSO IRAM-PdBI survey. I. Kinematics of the inner envelope of NGC1333-IRAS2A

0.23 MB·

by  S. Maret

Astronomy&Astrophysicsmanuscriptno.iras2-kinematics cESO2014
(cid:13)
February3,2014
LettertotheEditor
⋆ ⋆⋆
First results from the CALYPSO IRAM-PdBI survey
I. Kinematics of the inner envelope of NGC1333-IRAS2A
S.Maret1,A.Belloche2,A.J.Maury3,F.Gueth4,Ph.André5,S.Cabrit6,1,C.Codella7,andS.Bontemps8,9
1 UJF-Grenoble1/CNRS-INSU,InstitutdePlanétologieetd’AstrophysiquedeGrenoble,UMR5274,Grenoble,F-38041,France
2 Max-Planck-InstitutfürRadioastronomie,AufdemHügel69,53121Bonn,Germany
3 Harvard-SmithsonianCenterforAstrophysics,60Gardenstreet,Cambridge,MA02138,USA
4 4 IRAM,300ruedelapiscine,38406SaintMartind’Hères,France
1 5 LaboratoireAIM-Paris-Saclay,CEA/DSM/Irfu-CNRS-UniversitéParisDiderot,CE-Saclay,F-91191Gif-sur-Yvette,France
0 6 LERMA,ObservatoiredeParis,CNRS,ENS,UPMC,UCP,61Avdel’Observatoire,F-75014Paris,France
2 7 INAF-OsservatorioAstrofisicodiArcetri,LargoE.Fermi5,I-50125Firenze,Italy
8 UniversitédeBordeaux,LAB,UMR5804,F-33270Floirac,France
n
9 CNRS,LAB,UMR5804,F-33270Floirac,France
a
J
Received...;accepted...

1
3
ABSTRACT

]
A ThestructureandkinematicsofClass0protostarsonscalesofafewhundredAUispoorlyknown.Recentobservationshaverevealed
thepresenceofKepleriandiskswithadiameterof150-180AUinL1527-IRSandVLA1623A,butitisnotclearifsuchdisksare
G
commoninClass0protostars.Herewepresenthigh-angular-resolution observationsoftwomethanollinesinNGC1333-IRAS2A.
. Wearguethattheselinesprobetheinnerenvelope,andweusethemtostudythekinematicsofthisregion.Ourobservationssuggest
h
thepresence ofamarginalvelocitygradientnormal tothedirectionoftheoutflow. However,thepositionvelocitydiagramsalong
p
thegradientdirectionappearinconsistentwithaKepleriandisk.Instead,wesuggestthattheemissionoriginatesfromtheinfalling
-
o andperhapsslowlyrotatingenvelope,aroundacentralprotostarof0.1 0.2M .Ifadiskispresent,itissmallerthanthediskof
r L1527-IRS,perhapssuggestingthatNGC1333-IRAS2Aisyounger. − ⊙
t
s
Keywords. ISMindividualobjects:NGC1333-IRAS2A–ISM:kinematicsanddynamics–ISM:molecules–Stars:formation
a
[

2
1. Introduction structures are slowly rotating infalling envelopes rather than
v
centrifugallysupporteddisks(Bellocheetal.2002;Chiangetal.
6
Understanding the first steps of the formation of protostars
8 2010). On smaller scales (severalhundredAU), little is known
9and protoplanetarydisks is a major unsolvedproblem of mod- on the envelope/disk structure and kinematics. Only two Class
ern astrophysics. Observationally, the key to constraining pro-
6 0 protostars,L1527-IRSand VLA1623A,show an evidenceof
tostar formation models lies in high-resolution studies of the
. a compact (150 AU to 180 AU in diameter) Keplerian disk
1youngest protostars. Because their lifetime is only t 105 yr
(Tobinetal. 2012; Murilloetal. 2013). Studying these regions
0 ∼
and most of their mass is still in the form of a dense en-
requires observations of specific (optically thin) tracers of the
4
velope (M << M ), Class 0 protostars are likely to re-
1 env innerregionto avoid contaminationby the outflow and the ex-
tain detaile∗d information on the initial conditions and detailed
: tended envelope. Methanol lines are good specific probes of
vphysicsofthecollapsephase(Andréetal.2000).However,the
theseregions,aswediscussbelow.
iphysics of Class 0 protostars is still surprisingly poorly under-
X
stood, due to the paucity of the sub-arcsecond (sub)mm ob- Inthisletter,wepresentobservationsoftwomethanollines
rservations required to probe their innermost (100 AU) regions. intheNGC1333-IRAS2AClass0protostar(hereafterIRAS2A)
a
Several basic questions thus remain open, such as the mere locatedinthePerseusmolecularcomplexat235pc(Hirotaetal.
existence of accretion disks during the Class 0 phase, or the 2008). These observations are part of the CALYPSO (Con-
structure of the velocity field in Class 0 envelopes (e.g., rela- tinuum And Line in Young Proto-Stellar Objects) survey1, an
tive importance of inflow, rotation and outflow). On the large IRAM Plateau de Bure Interferometer (hereafter PdBI) large
scales, some of the Class 0 sources show evidence of flat- programthat aims at studyinga largesample of Class 0 proto-
tenedstructures,extendingroughlyperpendiculartotheoutflow starsatsub-arcsecondresolution.Weusetheselinestoprobethe
over 10,000 AU (Bellocheetal. 2002; Looneyetal. 2007; kinematicsoftheprotostellarenvelopeon 200AUscales,and
Tobin≥etal.2010).However,lineobservationsindicatethatthese todetermineifadiskispresent.Twocomp∼anionletterspresent
the complex organic molecule (COM) emission (Mauryetal.
⋆ BasedonobservationscarriedoutwiththeIRAMPlateaudeBure 2014)andthejetproperties(Codellaetal.2014).
interferometer. IRAM is supported by INSU/CNRS (France), MPG
(Germany),andIGN(Spain).
⋆⋆ Table 1 is only available in electronic form via
http://www.edpsciences.org 1 http://irfu.cea.fr/Projets/Calypso/
Articlenumber,page1of7
A&Aproofs:manuscriptno.iras2-kinematics
Fig.1.ContinuumandlineemissionsobservedtowardsIRAS2AwiththePdBI.Theleftpanel showsthe1mmcontinuumemission. Contour
spacingis10mJybeam 1 (6.6σ).Theotherpanelsshowthevelocityintegratedintensitiesofthe1mmand3mmmethanollines(blueandred
−
contours) together withthecontinuum (grayscale image). Theblueand redcontours correspond tovelocities< 6.5kms 1 and> 6.5kms 1,
− −
respectively.Inthecenterpanel,theblueandredcontoursarealmostcoincident.Thecontourspacingsare100mJybeam 1 kms 1 (3.2σ)and
− −
30mJybeam 1kms 1(2.1σ)forthe1mmand3mmlines,respectively.Ineachpanelthedashedellipseindicatesthesizeandorientationofthe
− −
synthesizedbeam.Thedashedlineshowstheorientationoftheoutflow(whichhasaP.A.of25 ; Codellaetal.2014).
◦
Fig.2. Realpartofthevisibilityofthe1mm
(left panel) and 3 mm (right panel) methanol
lines as a function of the UV radius (black
points with error bars). The visibilities have
been averaged over the line profile, and then
averaged circularly. The red solid line in each
panelshowstheresultofaGaussiansourcefit,
while the red dotted line shows the result of
apoint source fit.Thedashed lineintheright
panelshowstheresultofaGaussiansourcefit
with a FWHM size fixed to that of the 1 mm
line(0.44 ).Theblackdottedlineineachpanel
′′
indicatesthezerolevel.
2. Observations naturalweighting,anddeconvolvedusingthestandardCLEAN
algorithm in the MAPPING program. The synthesized beam is
Observations of IRAS2A were carried out with the PdBI be-
0.79 0.76 (P.A. 70 ) and 1.71 1.31 (P.A. 54 ) for the
tween November 2010 and February 2011 using the A and C ′′ × ′′ ◦ ′′ × ′′ ◦
1mmand3mmlines,respectively.TheRMSnoiseperchannel
configurations of the array. The CH OH (5 4 3 = 0 E )
3 1 − 2 t 1 in the final datacubes is 21 mJy/beam and 5 mJy/beam for the
lineat216.945600GHz(1mm)wasobservedusingthenarrow-
1mmand3mmlines,respectively.
bandbackend,providingabandwidthof512channelsof39kHz
(0.05 km s 1) each. The CH OH (1 2 3 = 1 E ) line at
− 3 0 1 t 1
−
93.196670 GHz (3 mm) was also observed using the narrow-
band backend, but with 256 channelsof 312 kHz (1.0 km s 1)
−
each. Calibration was done using CLIC, which is part of the
GILDAS software suite2. For the 1 mm observations, the phase
RMS was < 80◦, with precipitable water vapor (PWV) be- 3. Resultsandanalysis
tween 0.5 mm and 2 mm, and system temperatures (T ) be-
sys
tween 100K and250K.For the3 mm observations,the phase
Figure1showsthe1mmcontinuumemissiontogetherwithve-
RMS was < 40 , with PWV of 2-3 mm and T of 70-80 K.
◦ sys locityintegratedintensitymapsofthe1mmand3mmmethanol
The continuum emission was removed from the visibility ta-
lines.Continuumemissionisdetectedinthreesources,whichare
bles to produce continuum-free line tables. The visibilities of
labeledMM1,MM2,andMM3inCodellaetal.(2014).Wede-
the 1 mm methanol line were resampled at a spectral resolu-
tect1mmand3mmmethanollineemissiontowardsthebright-
tion of 0.5 km s 1 to improve the signal-to-noise ratio. Spec-
− estcontinuumpeak(MM1)withasignal-to-noiseratioattheline
tral datacubes were produced from the visibility tables using a
peaksof21and8forthe1mmand3mmmethanollines,respec-
2 http://www.iram.fr/IRAMFR/GILDAS/ tively.Emissionfromtheselinesiscompact.Inaddition,noclear
Articlenumber,page2of7
S.Maret etal.:KinematicsoftheinnerenvelopeofNGC1333-IRAS2A
Fig.3. First-ordermomentmapsofthe1mm
(left panel) and 3 mm (right panel) methanol
lines. In each panel the solid contours show
the velocity integrated lineintensity. The con-
tour spacingsare200mJybeam 1 kms 1 and
− −
20mJybeam 1kms 1forthe1mmand3mm
− −
methanol lines, respectively. The dashed line
showstheorientationoftheoutflow,whilethe
dashed arrow indicates the orientation of the
velocity gradient as determined from thefirst-
ordermomentfit(seeSect.3).Thelineandar-
rowintersectatthepositionofMM1.
differencebetweentheblue-shiftedandred-shiftedemission(at respectively), the amplitude and orientation obtained for each
velocities<6.5kms 1and>6.5kms 1,respectively3)isseen. lineareconsistent.Thegradientorientationsareindicatedbyar-
− −
Todeterminethesizeofthelineemission,wefittedthevis- rows in Fig. 3. Interestingly, they are roughly perpendicularto
ibilitiesassumingthattheemissionfollowsaGaussiandistribu- the outfloworientation,as onewouldexpectfor rotationof the
tion.Weaveragedthevisibilitiesovertheentirevelocityrangeof protostellarenvelopeordisk.
theline,andweperformedafitofthevelocityaveragedvisibili- Figure 4 shows the position-velocity (hereafter P.V.) dia-
tiesintheUVplane.Figure2showstheresultofthefit,together gramsforbothlines.ThecutsweredonealonganaxiswithP.A.
withtherealpartofthevisibilities(averagedasafunctionofthe of 107 , and centered on the peak of the 1 mm line. Figure 4
◦
UV radius for clarity). The fit parametersare given in Table 1. also shows the first-order moment measured along the cut. No
AsseeninFig.2,the1mmmethanollineemissionisspatially clearsignatureofrotationisapparentintheP.V.diagram.Both
resolved, and it is reasonably well fitted by a Gaussian source diagrams are almost symmetric with respect to the cut center
withaFWHMsizeof0.44 0.03 .Ontheotherhand,the3mm position. However, the first-order moment measured along the
′′
methanolline is only marg±inallyresolved; the emission is best cutincreasesfromnegativetopositiveoffsets.Thisisconsistent
fittedbyaGaussianof0.59 0.11 FWHM,butitssizeisalso withthepresenceofagradientalongthisaxis.Thisincreasein
′′
±
consistent(ata2σlevel)withthatofthe1mmline.Thisisalso the first-order moment along the cut is also marginal (see the
apparentintherightpanelofFig.2, whichshowstheexpected errorbarsinFig.4),butthesametrendisseenforbothlines.
realpartofthevisibilityforthe3mmline,assumingaGaussian
sourceof0.44 .Thepositionofthe1mmmethanollinepeakis,
′′
withintheuncertainties,consistentwiththepositionoftheMM1 4. Discussionandconclusions
continuumsource.Althoughthepositionofthe3mmmethanol
Our observations reveal compact methanol emission (0.4
line appears slightly offset, it is also consistent (at a 5σ level) ′′
FWHM, i.e., 90 AU in diameter) centered on the position of
with the position of MM1. Table 1 also gives the linewidths at ∼
theMM1continuumsource.Theobservedemissionhasseveral
the position of the 1 mm line emission peak. Both the 1 mm
possibleorigins.First,methanolemissioncanarisefromshocks,
and3mmlineshaveGaussianshapes,withaFWHMof3.3and
as a result of ice sputtering; indeed, methanol emission is ob-
4.1kms 1,respectively.
− served towards the end points of the large scale east-west out-
Figure3showsthefirst-ordermoment(meanvelocity)maps
flow of IRAS2A (Bachilleretal. 1998). It is thereforepossible
for both lines. From visual inspectionof the momentmaps, no
thattheemissionobservedhereiscausedbyshocksonsmaller
clearvelocitygradientisapparent.Wehavethereforeattempted
scales.However,thelineGaussianshapesandsmalllinewidths,
to fit the first order moment maps with a linear function of
togetherwiththestrikingcontrastbetweenthemethanolandthe
the R.A. and Dec. offsets. This linear gradient is expected if
SO and SiO emission (which are associated with the shocked
the emitting region is rotating as a solid body (Goodmanetal.
gas;seeCodellaetal.2014),donotfavorthishypothesis.
1993).Althoughsolidbodyrotationisnotrealistic,itprovidesa
Second,theemissionmayarisefromtheinnerregionofthe
firstindicationofwhetherornotrotationispresent.Becausethe
envelopewherethetemperatureisgreaterthan 100K(theso-
mapsshownin Fig.3 areoversampled,we havefitted thefirst- ∼
called hot corino). Maretetal. (2005) did a single-dish survey
order momentmeasured every half synthesized beam (Nyquist
of the methanol emission from a sample of six Class 0 proto-
sampling).Thesepixelswereweightedby1/σ2,whereσisthe
stars,andfoundabundancejumps(byabout2ordersofmagni-
1σ noise on the first-order moment, computed from the noise
tude)intheinnerenvelopesoffourofthem(includingIRAS2A).
per channel in the data cubes (see Belloche 2013, Eq. (2.3)).
They interpreted these abundance jumps as due to the thermal
Results of the fit are given in Table 1. For the 1 mm line, we
evaporationof grain mantles in the hot corino. Several COMs,
find a gradient with a P.A. α = 107 27 and an amplitude
G = 0.23 0.11kms 1/ (202 97k±ms 1◦/pcat235pc).For such as acetonitrile, methyl formate, or dimethyl ether, have
the3mm,±wefindα=−13′1′ 36±andG =0−.47 0.29kms 1/ alsobeendetectedinIRAS2Awithsingle-dish(Bottinellietal.
(413 255kms 1/pc).Alt±houg◦hthegradientd±etectionis−onl′y′ 2007)andinterferometric(Mauryetal.2014)observations.The
± − similar COM (Mauryetal. 2014) and methanol emission sizes
marginal(2.1σand1.6σforthevaluesofGat1mmand3mm,
(this study) strongly suggest a common origin. Compact water
(H18O) emission has also been detected in IRAS2A with the
3 In thepresent study, we adopt av of 6.5 km s 1, as determined 2
LSR − PdBI(Perssonetal.2012).ThesizeoftheH18Oemission(0.8 )
fromafitofthefirst-ordermomentmapofthe1mmmethanolline(see 2 ′′
below). is twice as large as the methanolemission. However,the H18O
2
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A&Aproofs:manuscriptno.iras2-kinematics
Fig.4. Position-velocitydiagramsforthe1mm
(left panel) and 3 mm (right panel) methanol
lines. The contour spacing is 50 mJy beam 1
−
(2.4σ) and10mJybeam 1 (2σ) forthe1mm
−
and 3 mm methanol lines, respectively. The
red points with error bars show the first order
moment measured at each position offset.The
horizontal dashed line shows the source v
LSR
(6.5kms 1).Theverticaldashedlinesindicate
−
thecenterofthecut.
mapsshowsomeemissionassociatedwiththeoutflow.Thiscon- M . 0.1 0.2 M . This estimate is in reasonable agreement
tamination by the outflow may explain the larger extension of wi∗ththeva−lueof0.2⊙5M obtainedbyBrinchetal.(2009).
the H18O emission with respect to the methanol and the COM The1mmlineP.V.d⊙iagramcanbeusedtotestthedisksce-
2
emission. Dust continuum observations and modeling indicate nario.WehavecomputedsyntheticP.V.diagramsforaKeplerian
that the radiusat which the dust temperatureexceeds100K in diskwithvariousvaluesofM (seeAppendixAfordetails).We
IRAS2Aisabout50AU(Jørgensenetal.2002)4.Thisradiusis findthattheobservedP.V.dia∗gramisinconsistentwithaKeple-
in goodagreementwith the size of the methanolemission,and riandisk,regardlessofthemassofthecentralobject.Inparticu-
thereforefavorsthehotcorinoscenario. lar,aKepleriandiskwithM =0.1M wouldproducetwopeaks
Athirdscenarioisthattheemissionoriginatesfromthesur- intheP.V.diagram,whicha∗renotob⊙served.Ontheotherhand,
face of a disk. From SMA observationsof the dustcontinuum, a Kepleriandisk M = 0.01 M would have a single peak P.V.
Jørgensenetal. (2005) suggested that IRAS2A harbors a cir- diagram,butthepre∗dictedlinew⊙idthwouldbe2-3timessmaller
cumstellardiskof200-300AUindiameter,withamassbetween thanobserved,evenforaveryturbulentdisk.
0.01M and0.1M .Theysuggestedthatthediskcouldbethe To summarize, we favor a scenario in which the methanol
major r⊙eservoir of t⊙he COMs and other molecules observed in emission observed in IRAS2A originates in the inner envelope
that source. Brinchetal. (2009) modeled the HCN and H13CN ofthe protostar,whichisinfallingandperhapsslowly rotating.
(4-3) emission observedwith the SMA towards IRAS2A at 1 Ifadiskispresentandisemittinginmethanol,itisspatiallyun-
′′
resolution,andfoundthatthevelocityfieldwasdominatedbyin- resolvedso its radiusis smaller than45 AU (0.4′′), i.e. smaller
fall,withlittlerotation.Aflatteneddisk-likestructuredominated thanthediskofL1527-IRS.Sincethemassofthecentralobject
byinwardmotionsisalsofavoredbyPerssonetal.(2012)toex- inL1527-IRS(0.2M ;Tobinetal.2012)iscomparabletothat
plaintheH18OemissionobservedinIRAS2A.Ourmethanolob- of IRAS2A, this may⊙suggest that IRAS2A is younger.Higher
2
servationssuggest the presence of a marginalvelocity gradient angularresolutionobservationsare neededto confirmthe pres-
orientedroughlyinadirectionperpendiculartothenorth-south ence of rotation in the inner parts of IRAS2A and to measure
outflow. The orientation of the gradient is similar to that of a the rotation profile precisely. In addition,observationsof other
secondeast-westoutflowdetectedinthissource.However,this Class 0 protostars are needed to obtain more statistics on the
second outflow is probably driven by the MM2 source and its presenceofrotationalysupporteddisksinthisphase,andtoes-
axis does notpass throughthe position of MM1 (Codellaetal. tablishwhendisksappearduringtheevolutionofprotostars.
2014), while the methanol emission is clearly associated with
Acknowledgements. Theresearchleadingtotheseresultshasreceivedfunding
MM1.Therefore,the gradientismostlikelycausedbyrotation fromtheEuropeanCommunity’sSeventhFrameworkProgramme(/FP7/2007-
oftheinnerenvelopeoradiskabouttheoutflowaxis. 2013/) under grant agreements No 229517 (ESO COFUND) and No 291294
(ORISTARS),andfromtheFrenchAgenceNationaledelaRecherche(ANR),
Regardlessof the origin of the emission (i.e., hot corino or
underreferenceANR-12-JS05-0005.
disk),ifthematerialtracedbythemethanollinesisboundtothe
protostellarsystem(asopposedtounboundoutflowmaterialfor
example),the linewidthcanbeusedtoestimate thedynamical
massofthesystem,M (1 2) rv2/G,wherevistheveloc- References
dyn
∼ −
ityobservedataradiir,andGisthegravitationalconstant.This
André,P.,Ward-Thompson,D.,&Barsony,M.2000,ProtostarsandPlanetsIV,
expressionholdsifthelinebroadeningisduetoinfallmotions, 59+
orKeplerianrotationaboutanaxisclosetotheplane-of-the-sky Bachiller, R.,Codella, C.,Colomer,F.,Liechti, S.,&Walmsley,C.M.1998,
(see,e.g.,Terebeyetal.1992).Ifweassumethatthevelocityat A&A,335,266
r = 45 AU is 1.65 km/s (i.e., the 1 mm line HWHM), we ob- Belloche,A.2013,inEASPublicationsSeries,Vol.62,25–66
Belloche,A.,André,P.,Despois,D.,&Blinder,S.2002,A&A,393,927
tain M 0.1 0.2 M (to be compared to a total envelope
mass Mdyn ≃= 1.7−M ;Jør⊙gensenetal. 2002). Strictly speaking, Bottinelli,S.,Ceccarelli,C.,Williams,J.P.,&Lefloch,B.2007,A&A,463,601
env Brinch,C.,Jørgensen,J.K.,&Hogerheijde,M.R.2009,A&A,502,199
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Codella,C.,Maury,A.J.,Gueth,F.,etal.2014,acceptedtoA&A
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4 A more recent analysis suggests a larger value (90 AU; 528
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A&A–iras2-kinematics,OnlineMaterialp6
AppendixA: Syntheticpositionvelocitydiagrams Table1.Linespectroscopicparameters,resultsofthevisibilityfits,and
resultsofthefirst-ordermomentfits.
foraKepleriandisk
TotesttheKepleriandiskscenario,wehavecomputedsynthetic Line 51 423t =0E1 10 213t =1E1
P.V.diagramsforthe1mmmethanolline.Wehaveassumedthat νa(GHz) 2−16.945600 −93.196670
the emissionfollowsa Gaussiandistribution,with a FWHM of Eup(K) 55.9 309.9
0.44′′ (as determined from the visibility fit). The line-of-sight R.A.offsetb(′′) −0.06±0.02 −0.27±0.05
velocity is assumed to be given by (see, e.g., Guilloteauetal. Dec.offset(′′) 0.00 0.02 0.06 0.05
2012) Sizec(′′) 0.44±0.03 0.59±0.11
± ±
I d(mJybeam 1) 457 21 24 5
peak −
± ±
Linewidthe(kms 1) 3.30 0.04 4.10 0.07
−
v(r,θ)=sin(i) cos(θ) v (r)+v (A.1) ± ±
kep LSR I dvf(Jybeam 1kms 1) 1.61 0.02 0.11 0.01
− −
± ±
where r and θ are the cylindricalcoordinatesin the disk plane, Rv0g(kms−1) 6.54 0.03 6.76 0.15
± ±
i is the inclination of the disk rotation axis with respect to the αh(◦) 107 27 131 36
± ±
lineofsight(i.e.,i=90◦foranedge-ondisk),vLSRisthesource Gi(kms−1/′′) 0.23±0.11 0.47±0.29
velocityinthelocalstandardofrest,andv (r)istheKeplerian
kep
velocity Notes. (a) Frequencies are from the CDMS catalog (Mülleretal.
2001) (b) Position of the emission peak, as determined from the vis-
ibility fit. Offsets are relative to the continuum position of MM1
GM (03h28m55s.58;31◦14′37′.′057;J2000; Codellaetal. 2014) (c) Decon-
vkep(r)= r r ∗ (A.2) v(do)lLveindesopuerackeiFnWtenHsiMtysaitzet,heasspuomsiitniognaocfir1cumlamr Glianuesseiamnisbsrioignhtpneeasks..
(e)LineFWHM.(f)Lineintegratedintensity.(g)Velocityattheposition
with G the gravitational constant and M the mass of the
central protostar. The line is assumed to∗ have a Gaussian of MM1, obtained from a fit of the first-order moment map. (h) Posi-
tion angle of the velocity gradient, from N to E. (i) Velocity gradient
shape,withalocallinewidth∆v(r)(FWHM/√8ln(2))equalto
amplitude.
0.1v (r), in agreementwith the valuedeterminedin DM Tau
kep
by Guilloteauetal. (2012). Although this value is uncertain, it
cannotexceedv (r)becauseadiskwithalarger∆v(r)would
kep
be unstable. We assume that the disk is rotating about an axis
withi = 60 .Thisisconsistentwiththediskrotatingaboutthe
◦
outflowaxis,whichhasi 45 (Codellaetal.2014).Finally,we
◦
≥
assumeav of6.5km/s,asourcedistanceof235pc,and M
LSR
isleftasafreeparameter.Thediskisnottruncatedinradius;we∗
merelyassumethatitslineemissiondecreasesasaGaussian,as
mentionedabove.Wecomputeasyntheticdatacubewithapixel
size of 0.1 , and a channelwidth of 0.5 km/s. The intensity of
′′
theemissionasafunctionofchanneliscomputedassumingthat
theline-of-sightvelocityvariesasafunctionofr andθ follow-
ingEq.(A.1).Thisdatacubeisthenconvolvedwiththesynthe-
sized beam, assumed to be a Gaussian with a FWHM of 0.8 .
′′
The convolveddata cube is then scaled so that the peak inten-
sity matches the observations (453 mJy/beam). Finally, Gaus-
sian noise is added in each channel so that the signal-to-noise
ratioalsocorrespondstotheobservations( 21).
∼
Figure A.1 shows the synthetic position velocity diagrams
we obtainfordifferentvaluesof M . We find thatourobserva-
tions are inconsistent with a Keple∗rian disk, regardless of the
mass of the centralobject. For M = 0.05M and 0.1M , the
syntheticP.V.diagramshavetwop∗eaks,while⊙theobserved⊙P.V.
diagramhasonepeak(seeFig.4).For M = 0.01M ,thesyn-
theticP.V.diagramissinglepeaked,andth∗epredicted⊙first-order
momentalongthecutisconstant,withintheerrorbars.However,
thepredictedlinewidthismuchsmallerthanobserved(compare
the size of the P.V. contours along the vertical axis in Fig. 4
and A.1). A broader linewidth would require a larger value of
∆v(r).However,wefindthatevenforaveryturbulentdiskwith
∆v(r) = 0.9v (r),thepredictedlinewidthis2-3timessmaller
kep
than observed. We conclude that the observed methanol emis-
sion can notarise from a Kepleriandisk, and mustoriginatein
theinfallingandperhapsslowlyrotatinginnerenvelope.Amore
detailed modeling of the methanol line emission is needed to
determine the precise velocity field of the inner region of the
protostarenvelope.
A&A–iras2-kinematics,OnlineMaterialp7
Fig.A.1.Syntheticposition-velocitydiagramsforthe1mmmethanolline(graycontours).Thecontourlevelsandaxisrangesarethesameasin
Fig.4.Theredpointswitherrorbarsshowthelinecentroidalongthecut.Thediagramshavebeencomputedassumingthattheemissionoriginates
inaKepleriandiskwithdifferentmassesofthecentralprotostar(seetext).