Protostellar Interferometric Line Survey of the Cygnus X ...

Astronomy & Astrophysics manuscript no. main_arxiv ©ESO 2021September 9, 2021

Protostellar Interferometric Line Survey of the Cygnus X region(PILS-Cygnus)

First results: observations of CygX-N30

S. J. van der Walt1, L. E. Kristensen1, J. K. Jørgensen1, H. Calcutt2,3, S. Manigand1, M. el Akel4, 1, R. T. Garrod5, andK. Qiu6, 7

1 Niels Bohr Institute & Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K.,Denmarke-mail: [email protected]

2 Department of Space, Earth and Environment, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden3 Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100

Torun, Poland4 CY University, Observatoire de Paris, CNRS, LERMA, F-95000 Cergy, France5 Departments of Astronomy and Chemistry, University of Virginia, Charlottesville, VA 22904 USA6 School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023, People’s Republic of China7 Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210023, People’s

Republic of China

Received . . . ; accepted . . .

ABSTRACT

Context. Complex organic molecules (COMs) are commonly detected in and near star-forming regions. However, the dominantprocess in the release of these COMs from the icy grains —where they predominately form— to the gas phase is still an openquestion.Aims. We investigate the origin of COM emission in a high-mass protostellar source, CygX-N30 MM1, through high-angular-resolution interferometric observations over a continuous broad frequency range.Methods. We used 32 GHz Submillimeter Array (SMA) observations with continuous frequency coverage from 329 to 361 GHz at anangular resolution of ∼ 1′′ to do a line survey and obtain a chemical inventory of the source. The line emission in the frequency rangewas used to determine column densities and excitation temperatures for the COMs. We also mapped out the intensity distribution ofthe different species.Results. We identified approximately 400 lines that can be attributed to 29 different molecular species and their isotopologues. We findthat the molecular peak emission is along a linear gradient, and coincides with the axis of red- and blueshifted H2CO and CS emission.Chemical differentiation is detected along this gradient, with the O-bearing molecular species peaking towards one component of thesystem and the N- and S-bearing species peaking towards the other. The chemical gradient is offset from but parallel to the axisthrough the two continuum sources. The inferred column densities and excitation temperatures are compared to other sources whereCOMs are abundant. Only one deuterated molecule is detected, HDO, while an upper limit for CH2DOH is derived, leading to a D/Hratio of <0.1%.Conclusions. We conclude that the origin of the observed COM emission is probably a combination of the young stellar sourcesalong with accretion of infalling material onto a disc-like structure surrounding a young protostar and located close to one of thecontinuum sources. This disc and protostar are associated with the O-bearing molecular species, while the S- and N- bearing specieson the other hand are associated with the other continuum core, which is probably a protostar that is slightly more evolved than theother component of the system. The low D/H ratio likely reflects a pre-stellar phase where the COMs formed on the ices at warmtemperatures (∼ 30 K), where the deuterium fractionation would have been inefficient. The observations and results presented heredemonstrate the importance of good frequency coverage and high angular resolution when disentangling the origin of COM emission.

Key words. Astrochemistry; Stars: formation; Stars: protostars; ISM: molecules; ISM: individual objects: W75N(B); Submillimeter:ISM.

1. Introduction

Complex organic molecules (COMs; molecules with at least sixatoms, of which at least one is carbon; Herbst & van Dishoeck2009) are found everywhere in and near star-forming regions(e.g. Caselli & Ceccarelli 2012; Ceccarelli et al. 2014; Jørgensenet al. 2020). Our current understanding is that most COMs formon the surfaces of ice-covered dust grains, either from simplevolatile gas species frozen out onto the grains, or from rad-

icals in the ice (Öberg 2016). Near the forming stars, whereTdust & 100 K, the water-rich ice mantels sublimate off the dustgrains, releasing COMs into the gas phase, where they can be di-rectly observed at submillimetre (submm) wavelengths (the so-called hot cores; e.g. Kurtz et al. 2000; Cesaroni et al. 2010;Jørgensen et al. 2016). However, other non-thermal mechanismscan be efficient at desorbing COMs into the gas phase, and havebeen proposed in the literature. These include sputtering of the

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ices in shocks, where the shocks are generated by jets and out-flows (e.g. Avery & Chiao 1996; Jørgensen et al. 2004; Arceet al. 2008; Sugimura et al. 2011; Lefloch et al. 2017), accretionshocks from the envelope onto the disc (e.g. Podio et al. 2015;Artur de la Villarmois et al. 2018; Csengeri et al. 2018, 2019),explosive events near forming stars (e.g. Orion KL; Zapata et al.2011; Orozco-Aguilera et al. 2017), and UV irradiation of theoutflow cavity walls (e.g. Drozdovskaya et al. 2015). Which ofthese processes dominate in releasing the molecules from the iceto the gas phase is in many cases unclear, as is the impact on theobserved chemistry.

Recently, Belloche et al. (2020) presented observations ofa sample of 26 solar-type protostars as part of the CALYPSOsurvey performed with the NOrthern Extended Millimeter Array(NOEMA). COM emission from methanol, CH3OH, the ‘sim-plest COM’ was detected towards 12 of the sources, with 8 ofthese sources having detections of at least three COMs. Theselatter authors found that a canonical hot-corino origin may ac-count for only four of the sources with COM emission, whilean accretion-shock origin fits best with two or possibly threesources, and an outflow origin fits three others. It is therefore be-coming increasingly clear that the origin of COMs in scenariosother than the canonical hot-corino (and hot cores) are relativelycommon, and through large surveys like CALYPSO we may geta better understanding of how these COMs form.

The work presented here is part of a large-frequency-rangeline survey of ten intermediate- to high-mass protostellar sourcesin the Cygnus X molecular cloud, which forms part of theGreat Cygnus Rift in the Galactic plane. Cygnus X is a prolificstar-forming region, with many newly formed stars of variousmasses, and has been the focus of numerous studies (for a fullreview of the region, see Reipurth & Schneider 2008, and refer-ences therein). Given its location in the Perseus Galactic spiralarm, the distance to Cygnus X is uncertain, with values in the lit-erature ranging between 1.3 and 3 kpc (e.g. Campbell et al. 1982;Odenwald & Schwartz 1993; Rygl et al. 2012). We assume thedistance of ∼1.3 kpc obtained by Rygl et al. (2012) from maserparallax measurements. It is home to one of the most massiveOB associations known in the Galaxy, Cyg OB2, with hundredsof young O-type stars and perhaps thousands of B-type stars(Knödlseder 2000). These massive stars provide a huge amountof ionising radiation to the region, making it an ideal target forthe study of how the external environment created by these mas-sive stars affects the chemistry of the surrounding star formingregions. To this end, full chemical inventories of a large sampleof surrounding protostars are required.

This kind of survey has historically been observationallyvery expensive, because it requires high angular resolution andmany hours of observation time to obtain the wide frequencyrange needed. However, in recent years it has become muchcheaper thanks to the upgraded receivers on the SubmillimeterArray (SMA), and its new SWARM1 correlator. It is now possi-ble to obtain 32 GHz of continuous frequency coverage in a frac-tion of the time required in the past. Taking advantage of thesenew capabilities of the SMA, we obtained data from ten newlyformed sources surrounding the Cyg OB2 association in order tostudy how the chemistry of these young stars is affected by theenvironment in which they form. Together, these observationsform the Protostellar Interferometric Line Survey of Cygnus-X(PILS-Cygnus).

1 SWARM is an acronym for SMA Wideband Astronomical ROACH2(second generation Reconfigurable Open Architecture ComputingHardware) Machine.

The focus of this paper is one of the most studied sources inthe Cygnus X cloud, W75N (B) (e.g. Haschick et al. 1981; Persiet al. 2006), or CygX-N30 (N30 hereafter, using the designationby Motte et al. 2007). This source contains three mm contin-uum cores, MM1, MM2, and MM3, where MM1 is the bright-est source and is composed of MM1a and MM1b (e.g. Shep-herd 2001; Minh et al. 2010). Three radio continuum sourceswere also detected towards MM1 (VLA1, VLA2 and VLA3),which have been identified as ultra-compact HII (UC HII) re-gions or thermal jets (Hunter et al. 1994; Torrelles et al. 1997;Shepherd et al. 2003; Carrasco-González et al. 2010; Rodríguez-Kamenetzky et al. 2020). Shepherd et al. (2004) found that theVLA sources drive high-velocity molecular outflows traced bySiO (2−1 and 1−0) emission. VLA1 and VLA2 were associ-ated with OH, H2O, and CH3OH masers (Torrelles et al. 1997;Minier et al. 2001; Hutawarakorn et al. 2002; Fish et al. 2005;Surcis et al. 2009), while VLA3 was found to be associatedwith one H2O maser (Shepherd 2001) with a radio jet and SiO(1−0) emission (Carrasco-González et al. 2010). A large-scaleCO outflow has been observed and found to originate from MM1and extending ∼1 pc in both directions (see Fischer et al. 1985;Hutawarakorn et al. 2002; Shepherd et al. 2003; Gibb et al. 2003;Birks et al. 2006; Surcis et al. 2009, 2011). Through MERLIN2

measurements of OH masers, Hutawarakorn et al. (2002) foundthat N30 hosts a rotating molecular disc with a radius of 3000AU, a rotation velocity of 6 km.s−1, and a mass of 120 M�.These latter authors found that this disc has a position angle of155◦ (measured from north), which is orthogonal to the large-scale molecular outflow seen in CO and H2 (PA ∼ 65◦). Theauthors note that the compact cluster of high-velocity OH andH2O masers coinciding with VLA2 appears to mark the centreof the outflow.

Minh et al. (2010) observed N30 with the SMA in the 215and 345 GHz spectral windows with 8 GHz frequency coverage,which indicated that a hot core is located at MM1b and is asso-ciated with a thermal jet from VLA1. These authors also founda chemical difference between the continuum cores MM1a andMM1b, which they suggest is the result of the evolution of amassive star-forming core. They argue that VLA1 is the heatingsource of the hot core, which suggests that the region associatedwith VLA1 is the site of recent star formation. Minh et al. (2010)observed SiO emission at the position of VLA2, which they in-terpret as a spherical shock driven by the recent star formation atthe site of VLA1.

In this paper we present new SMA observations of N30, pro-viding 32 GHz of continuous frequency coverage in the 345 GHzatmospheric window. This large frequency coverage makes itpossible to perform an unbiased survey of the spectroscopic sig-natures of the different components in the region and establishtheir molecular inventories. The paper is laid out as follows: adetailed description of the observational setup and data reduc-tion is given in Section 2. In Section 3 we present the results ofour analysis and then discuss them in Section 4. We end with asummary and conclusions in Section 5.

2. Observations

The SMA observations of N30 form part of the PILS-Cygnusprogramme (PI: Kristensen, project ID 2017A-S028), which inturn is an extension of the PILS programme (Jørgensen et al.2016), in which 34 GHz continuous frequency coverage ob-servations of the low-mass protostar, IRAS 16293–2422, ob-

2 Multi-Element Radio Linked Interferometer Network


S. J. van der Walt et al.: Protostellar Interferometric Line Survey of the Cygnus X region (PILS-Cygnus)

tained from the Atacama Large Millimeter/Submillimeter Ar-ray (ALMA) were studied. The ten intermediate- to high-massprotostars of PILS-Cygnus were selected because they are all lo-cated in the same molecular cloud structure, and because of theirproximity to the Cyg-OB2 association, which provides an oppor-tunity to study the role of the external environment in setting thechemistry of newly formed stars. This paper presents the firstresults of the PILS-Cygnus programme.

2.1. Calibration

The observations were performed using the SMA in a combi-nation of the compact and extended configurations, that is, withprojected baselines ranging from 7 to 211 m. The full surveycovered ten sources and every source was observed for approxi-mately an equal amount of time over ten tracks: five tracks in thecompact configuration and five tracks in the extended configu-ration. This was done to ensure approximately equal sensitiv-ity for all observed sources. The compact-configuration trackswere executed between 27 June 2017 and 7 Aug 2017, whilethe extended-configuration tracks were observed between 20 Oct2017 and 10 Nov 2017. The number of antennas available in thearray was between six and eight.

MWC349A was used as the complex gain calibrator for allobservations, while the quasars 3c273, 3c454.3, and 3c84 wereused for bandpass calibration depending on the time of the obser-vations. Neptune, Titan, Callisto, and Uranus were used for fluxcalibration, again depending on the time of the observations. Adetailed observing log is presented in Appendix A, which alsoincludes information on the weather at the time of the observa-tions.

The receivers at the SMA were tuned such that they coveredthe entire frequency range from 329 to 361 GHz continuously.Specifically, the 345 GHz receivers were tuned to cover the spec-tral range from 329.2 to 337.2 GHz in the lower sideband and therange from 345.2 to 353.2 GHz in the upper sideband. The 400GHz receivers filled in the 8 GHz gaps, and covered the ranges of337.2–345.2 GHz and 353.2–361.2 GHz in the lower and uppersidebands, respectively. Each sideband consists of four chunks,and each chunk covers 2 GHz. The SWARM correlator providesa uniform spectral channel size of 140 kHz across the spectrum,corresponding to 0.12 km s−1 at 345 GHz. Prior to calibration,all spectral data were rebinned by a factor of four to a spectralresolution of 560 kHz, or 0.48 km s−1 at 345 GHz to improve thenoise level.

All data were calibrated in CASA 4.7 (Common AstronomySoftware Applications, McMullin et al. 2007). Calibration con-sisted first of flagging the channels at the edges and any anoma-lously high intensity spikes. The bandpass calibrator was thenphase-calibrated with a 30 sec solution interval before the com-plex gains and absolute flux were calibrated.

2.2. Imaging

Self-calibration and imaging were performed using CASA 4.7.Two rounds of phase self-calibration were performed on the con-tinuum, the first with a solution interval of 240 sec, followed by asecond round with a smaller solution interval of 60 sec. This re-sulted in a reduction in rms level of more than 30%. Only phaseself-calibration was performed.

Cleaning and imaging of the data set proceeded along twoaxes. First, the continuum data were cleaned in order to achievehigh angular resolution. This was done by setting the ‘robust’

Table 1. Properties of the N30-MM1 continuum cores.

Name Right Ascension Declination S 850 µm[Jy beam−1]

MM1a 20h 38m 36s.51 42◦ 37′ 33′′.48 0.53MM1b 20h 38m 36s.42 42◦ 37′ 34′′.58 0.48

parameter to −0.5, where robust= 2 gives natural weighting,and robust= −2 gives uniform weighting. This was an afford-able solution, because the continuum data had very high signal-to-noise ratio. The resulting beam size of the continuum datais 0′′.85 × 0′′.66 (PA = 12.1◦). The continuum rms sensitivity ofthe final line-free and self-calibrated image (Fig. 1) is 0.008 Jybeam−1.

In a second step, the line data were first continuum-subtracted using line-free channels. This was done by taking aspectrum towards MM1a in the image plane and going throughthe spectrum by hand to identify all the line-free channels. Thesefrequency ranges were then used throughout the cube, with thecontinuum subtraction done in the uv-plane. This exercise wasthen repeated to ensure that all the line-free channels remainedline-free. The obtained self-calibration solution was then appliedto the line data. To clean the line data, natural weighting wasused in order to get the highest possible line sensitivity. For thefull data cube, non-interactive cleaning was used with a circu-lar cleaning mask centred at coordinates R. A. = 20h38m 36s.62and Dec. = 42◦37′31′′.81, with a radius of 24′′, and includingthe MM1, MM2, and MM3 cores. The resulting beam size is∼ 1′′.65 × 1′′.55 (PA = 11◦). The noise level varies across thespectrum from ∼ 0.2 − 0.7 Jy beam−1 as a function of receiver,as is clearly visible in Fig. 2, particularly around a frequency of353.2 GHz. The noise level also varies as a function of the Inter-mediate Frequency (IF) performance of the receiver, as can beseen from the edge effects. A typical value of the rms is ∼0.5 Jybeam−1 in 0.48 km s−1 channels. The blanked channels in Fig. 2are high-amplitude edge channels.

3. Results

3.1. Continuum emission

The 345 GHz (850 µm) continuum image is shown in Fig. 1. Thefour previously identified sources are marked as MM1a, MM1b,MM2, and MM3 (e.g. Shepherd 2001; Minh et al. 2010). MM1aand MM1b are considerably brighter than MM2 and MM3,peaking at 0.53 and 0.48 Jy beam−1, respectively. All sourcesshow extended emission, with large-scale structure visible to thewest of the MM1 region, as well as northwest of MM1b. Thereis some extended emission to the east of MM2, and some faintstructure just visible to the south of MM1. As with previous stud-ies (e.g. Minh et al. 2010), we detect no COM emission fromthe continuum cores MM2 and MM3, and this paper thereforefocuses on emission towards MM1a and MM1b. The positionsof the peak continuum emission for MM1a and MM1b werederived using 2D Gaussian fits, and are shown in Table 1 andmarked with plus symbols in Fig. 1, with the dashed line repre-senting the axis going through these two positions. MM1a andMM1b are separated by ∼1′′, or ∼1300 AU, at a distance of 1.3kpc.

In addition to the 345 GHz continuum cores, Fig. 1 alsoshows the positions of the three radio continuum sources VLA1,VLA2, and VLA3, which were identified previously (Hunteret al. 1994; Torrelles et al. 1997; Shepherd et al. 2003) using



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Fig. 1. Observed continuum emission at a frequency of 345 GHz,showing the four continuum sources MM1a, MM1b, MM2, and MM3.The beam is shown in the bottom-left corner, and has dimensions0′′.85 × 0′′.66, with position angle 12.1◦. The VLA radio sources VLA1,VLA2, and VLA3 are labelled and marked with black crosses, with theemission peak positions of MM1a and MM1b shown by plus symbols,and the dashed line representing the axis through these positions. Alsoshown are the large-scale CO emission (red and blue arrows) and thedisc-like structure (dotted line) identified by Hutawarakorn et al. (2002)

.

mm and centimetre (cm) observations from the Very Large Ar-ray (VLA) telescope. VLA1 is located to the west and slightlyto the north of the MM1b submm peak, while VLA2 is to thenorth of the MM1a peak (southwest of MM1b). VLA3 is lo-cated very close to but slightly to the east of MM1a (see alsoRodríguez-Kamenetzky et al. 2020, for recent high-resolutionVLA observations of the region). The red and blue arrows repre-sent the large-scale CO emission (PA ∼65◦ from north) centredat VLA2, with the dotted line representing the disc-like structure(PA ∼155◦) traced by OH masers, as identified by Hutawarakornet al. (2002).

To check whether the dust is optically thick or not, the firststep is to calculate the dust mass. Here, this is only done towardsthe MM1a source, which is the brightest continuum source inthe field. The total mass (gas + dust) can be calculated using thefollowing relation (e.g. Artur de la Villarmois et al. 2018):

M =S νd2

κνBν(T ), (1)

where S ν = 0.53 Jy beam−1 is the peak intensity of MM1a,d = 1.3 kpc, and Bν(T ) is the Planck function at the specific fre-quency and temperature. κν is the dust opacity (at ν = 345 GHz,κν = 0.0175 cm2 per gram of gas for a gas-to-dust ratio of 100;Ossenkopf & Henning 1994). For a beam size of 0′′.85 × 0′′.66,and taking T = 30 K, we get M = 3.0M� of gas and dust. Ifthis mass is spread evenly over the beam, this corresponds to anH2 column density of 5.3 × 1024 cm−2, where a mean molecularweight of µ = 2.8 was used to account for Helium (Kauffmannet al. 2008). This may be converted to optical depth using thefollowing expression (e.g. Schöier et al. 2002):

τν = κνµmHNH2 . (2)

We note that Schöier et al. (2002) includes a dust-to-gas ratio,δ = 0.01, and κ is their dust opacity (dust only). As we have

folded the dust-to-gas ratio into κν above (gas + dust), this pa-rameter is not needed in the expression for the dust optical depth.Furthermore, we correct a typo in Schöier et al. (2002) and useµmH instead of mH2 , again with µ = 2.8. This yields a dustopacity of 0.43. We conclude that the dust emission is at leastmarginally optically thin for a gas-to-dust ratio of 100.

3.2. Molecular line emission

Figure 2 shows a spectrum from the data taken at the positionof peak continuum emission of MM1a. The 32 GHz continu-ous frequency coverage of the data (329 – 361 GHz) includedapproximately 400 molecular lines detected above 3σ towardsthe MM1 source, or a line temperature sensitivity of ∼ 10 K.Line identification was done by covering the points as describedin Snyder et al. (2005) and using the software package CAS-SIS3 (Centre d’Analyse Scientifique de Spectres Instrumentauxet Synthetiques; Vastel et al. 2015), in which the CDMS4 (Mülleret al. 2001, 2005; Endres et al. 2016) and JPL5 (Pickett et al.1998) molecular spectroscopy databases were used to construct asynthetic spectrum. Previously identified molecules were addedto the synthetic spectrum first, which was then compared to theobserved spectrum in order to find and identify the remaininglines above 3σ. From the observed lines, we identified 29 dif-ferent molecules and their isotopologues, including five COMs,(CH3OH, C2H5OH, CH3OCH3, CH3OCHO, and CH3CN).

The molecular transitions detected at > 3σ are listed be-low, with the oxygen-bearing species in Table 2, sulphur-bearingspecies in Table 3, and nitrogen-bearing species shown in Table4, together with SiO, HDO, CO, and HCO+. There are approx-imately 40 lines that remain unidentified, including two brightlines (at frequencies not corrected for the systemic velocity of354.44896 GHz and 356.24131 GHz, and labelled ‘U’ in Fig.2). A full list of detected molecules above 3σ are listed in Table8.

3.3. Integrated molecular intensity maps

The molecular peak positions were found by making integratedintensity emission maps of each molecule. Where a moleculehad more than one line, the lines were stacked using a 1/σ2

weighting scheme —where σ is the RMS measured on anemission-free region for each channel map— in order to in-crease the intensity and determine an average peak position ofthe molecule. Only unblended lines were used.

In the cases where red- and blueshifted components arepresent, the components were separated with integrated mapsmade for each component. A map of blue- and redshifted H2COemission is shown in Fig 3 as an example (frequency = 351.77GHz, J = 51,5 − 41,4, and Eup = 62.45 K). In this figure, thecontinuum emission is depicted in colour, with the red- andblueshifted integrated intensity maps shown in red and blue con-tours, respectively.

The maximum intensity for the components were found atpositions offset from the MM1a continuum peak: (−0′′.83, 1′′.72)for the blueshifted components and (−0′′.03, 0′′.52) for the red-shifted ones. The line plots for the blue- and redshifted compo-nents are shown in Figs. 4 and 5, respectively.

As can be seen from Fig. 3, the blue- and redshifted compo-nents of H2CO emission falls on an axis —marked with a dotted

3 http://cassis.irap.omp.eu4 https://cdms.astro.uni-koeln.de/5 http://spec.jpl.nasa.gov/



330 331 332 333

0

20 C18O SO

HNCOCH3OH

HNCO

13CH3OH 13CO CH3OH CH3CN C2H5OH CH3OHSO2

C2H5OH SO2 SO234SO2

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334 335 336 337 338

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C2H5OH

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343 344 345 346 347

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34SO2 34SO2

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34SO2 SO234SO2 SO2 HCOOH SO2 HCOOH

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Fig. 2. Spectrum towards N30 at the continuum peak of MM1a. The spectrum shows many molecular lines, with the identified lines markedand labelled. Some abbreviations are used where space is limited; ‘MF’ and ‘DME’ refer to methyl formate (CH3OCHO) and dimethyl ether(CH3OCH3), respectively, while ‘U’ stands for ‘unidentified’.

line— that runs parallel to the axis drawn between the positionsof the MM1a and MM1b peak continuum emission marked withplus signs and represented with a dashed line. The blue contoursare more collimated along the axis, but extend further out than

the red contours, while the red contours have some extendedemission to the west of MM1b, and north of the MM2 core.Similarly, the red- and blueshifted 342.88 GHz CS J = 7 − 6



20h38m37.0s36.8s 36.6s 36.4s 36.2s 36.0s 35.8s

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Fig. 3. Continuum image of N30, with the red and blueshifted 351.77GHz H2CO, J = 51,5−41,4, transition shown in contours. The blueshiftedcomponent shows more concentrated emission along the outflow axis(represented with a dotted line, running nearly parallel to the axisthrough the continuum peaks, represented with a dashed line), whilethe redshifted emission is slightly more extended perpendicular to theoutflow axis, with some emission to the north of the MM2 continuumcore. The velocity ranges extend to ± 14.25 km s−1 from the systemicvelocity of 9.5 km s−1. Beam sizes are shown in the bottom left cor-ner, and are 0′′.85 × 0′′.66, with PA = 12.1◦, for the continuum, and1′′.61× 1′′.51, PA = 162.24◦, for the molecular emission. Contour levelsare at 3σ, 6σ, and 12σ. The blue and red arrows represent the large-scale CO emission.

10 5 0 5 10 15 20 25 30Velocity [km s 1]

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Fig. 4. Blueshifted peak of the 351.77 GHz H2CO, J = 51,5 − 41,4 line,which peaks at an offset of (−0.075, 1.72) arcseconds from the MM1acontinuum peak (see Table 2).

transition is shown in Fig. 7. Other molecules that exhibit red-and blueshifted components are CO, 13CO, HCN, and HCO+.

In order to investigate this large-scale velocity gradient, Figs.6 and 10 show position–velocity maps of the H2CO and CSemission, respectively. The high-velocity emission of H2CO andCS is close to the centre (at 0′′ offset, between the red- andblueshifted emission peaks), whereas the emission at a larger off-set from the centre shows a velocity closer to the systemic veloc-ity of the protostar. This could trace an infall motion coupled to arotation pattern, which might be due to a disc-like structure (e.g.Zhu et al. 2011). A comprehensive study of the kinematics of thesystem is beyond the scope of this paper, but position–velocity

10 5 0 5 10 15 20 25 30Velocity [km s 1]

2

0

2

4

6

8

10

12

14

Flux

[Jy

beam

1 ]

Fig. 5. Redshifted peak of the 351.77 GHz H2CO, J = 51,5 − 41,4 line,which peaks at an offset of (−0.003, 0.52) arcseconds from the MM1acontinuum peak (see Table 2)

6 4 2 0 2 4 6Offset ["]

0.0

2.5

5.0

7.5

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12.5

15.0

17.5Ve

locit

y [k

m.s

1 ]

0

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4

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8

Jy.b

eam

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Fig. 6. Position–velocity map of the 351.77 GHz H2CO, J = 51,5 −

41,4 line. The high-velocity emission is located close to the position ofzero offset (located between the red- and blueshifted emission peaks),whereas the emission at larger offsets from the centre has velocity closerto the systemic velocity.

maps of a selection of other transitions are shown in AppendixC.

The panels in Fig. 11 show the molecular peaks of eachmolecule; these peaks are concentrated along the axis of the red-and blueshifted components of H2CO and CS emission. Eachpanel shows a contour map of the integrated molecular line emis-sion of a different molecule. In the case of molecules with morethan one unblended line, such as for example CH3OH, the im-ages show stacked emission for better S/N. The peak for eachmolecule was found using 2D Gaussian fits to the integrated (andagain stacked where more than one unblended line was detected)molecular line emission, and is indicated with a plus symbolof the same colour as the contour for that molecule. To verifythese fit results for the peak positions, an independent fit of thestrongest unblended CH3OH and SO2 lines was performed inuv-space prior to cleaning the data. These fits confirm the resultsfrom the image plane, and typical differences are less than 0′′.2,the adopted pixel size, and one-fifth of the beam. We thereforeadopt a typical uncertainty on the peak locations as 0′′.2 through-out. However, we note that the formal uncertainties on the peak



20h38m37.0s36.8s 36.6s 36.4s 36.2s 36.0s 35.8s

42°37'42"

39"

36"

33"

30"

R. A. (J2000)

Dec.

(J20

00)

MM1a

MM1b

MM2

VLA1VLA1VLA2VLA2

VLA3VLA3

0.0

0.1

0.2

0.3

0.4

0.5

Jy b

eam

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Fig. 7. Continuum image of N30, with the red- and blueshifted 342.88GHz CS line transition J = 7− 6 shown in contours. As with the H2COline, CS shows red- and blueshifted emission along the same outflowaxis. The blueshifted emission shows some extended emission furtherout to the northeast, while the redshifted emission is slightly more con-centrated than for H2CO. Here, the velocity ranges extend to ± 15.6 kms−1 from the systemic velocity of 8.75 km s−1. Beam sizes and contourlevels are as in Fig. 3.

10 5 0 5 10 15 20 25 30Velocity [km s 1]

0

2

4

6

8

10

Flux

[Jy

beam

1 ]

Fig. 8. Blueshifted peak of the 342.88 GHz CS J = 7 − 6 line, whichpeaks at an offset of (−0.094, 1.92) arcseconds from the MM1a contin-uum peak (see Table 3).

locations from the fits in the uv-plane and image plane, respec-tively, yield uncertainties of typically 0′′.01–0′′.02.

The full width at half maximum (FWHM) and source veloc-ities (3source) of the lines were determined by making 1D Gaus-sian fits to the respective lines. The detailed values obtained foreach line are shown in Table 2 for the oxygen-, Table 3 for thesulphur-, and Table 4 for the nitrogen-bearing species, with thistable also showing SiO, HDO, CO, and HCO+.

3.4. Molecular gradient

We find that all molecules that do not show significant extendedemission peak along a linear gradient coinciding with the axismarked by the red- and blueshifted components of the H2COand CS emission. This axis runs parallel to but is offset from theaxis drawn between the continuum peaks of MM1a and MM1b,as shown in Fig. 12. To investigate whether or not this observed

10 5 0 5 10 15 20 25 30Velocity [km s 1]

0

2

4

6

8

10

12

14

Flux

[Jy

beam

1 ]

Fig. 9. Redshifted peak of the 342.88 GHz CS J = 7 − 6 line, whichpeaks at an offset of (0.015, 0.72) arcseconds from the MM1a contin-uum peak (see Table 3)

6 4 2 0 2 4Offset ["]

0.0

2.5

5.0

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10.0

12.5

15.0

17.5Ve

locit

y [k

m.s

1 ]

0

2

4

6

Jy.b

eam

1

Fig. 10. Position–velocity map of the 342.88 GHz CS J = 7 − 6 line.As with the H2CO map, the emission at larger velocity is concentratedclose to the centre of the emission (between the red- and blueshiftedpeaks), whereas the emission close to the systemic velocity extends outto larger spacial scales.

molecular gradient is the result of a difference in upper-level en-ergy of the molecular transitions, that is, a temperature gradient,the peak positions of different transitions of CH3OH and SO2are represented in Figs. 13 and 14, where the upper-level ener-gies are represented in different colours. As can be seen fromthe plot, there does not seem to be any pattern, and the positionsof the respective lines seem to be distributed randomly. Morespecifically, the peaks are distributed within less than one-thirdof the beam, that is, the spread is over ∼0′′.4, whereas the beamsize is ∼1′′.5. A similar exercise was performed for the criticaldensities (ncrit), where ncrit = Aij/Kij, with Aij the Einstein A co-efficient for spontaneous emission, and Kij the rate coefficientof the transition from the upper level i to the lower level j, fortemperatures of 100 K (rate coefficients were obtained from theLeiden Atomic and Molecular Database; Schöier et al. 2005)6.Figures 15 and 16 again show the peak positions of the differenttransitions of CH3OH and SO2, with the critical densities of dif-ferent transitions represented in colours. As with the upper-levelenergies, there does not seem to be any density gradient, and the

6 https://home.strw.leidenuniv.nl/∼moldata/



42°37'37"

36"

35"

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33"

32"

CH3OCHOCH3OCHO

MM1aMM1a

MM1bMM1bVLA1VLA1

VLA2VLA2

VLA3VLA3

H2CSH2CS

MM1aMM1a

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CH3OCH3CH3OCH3

MM1aMM1a

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VLA2VLA2

VLA3VLA3

42°37'37"

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34"

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C34SC34S

MM1aMM1a

MM1bMM1bVLA1VLA1

VLA2VLA2

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13CH3OH13CH3OH

MM1aMM1a

MM1bMM1bVLA1VLA1

VLA2VLA2

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CH3OHCH3OH

MM1aMM1a

MM1bMM1bVLA1VLA1

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42°37'37"

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33"

32"

Dec.

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OCSOCS

MM1aMM1a

MM1bMM1bVLA1VLA1

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HC15NHC15N

MM1aMM1a

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CH3CNCH3CN

MM1aMM1a

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42°37'37"

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SiOSiO

MM1aMM1a

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VLA3VLA3

HC3NHC3N

MM1aMM1a

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HCOOH

MM1aMM1a

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VLA2VLA2

VLA3VLA3

20h38m36.7s 36.5s 36.4s 36.3s

42°37'37"

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HNCO

MM1aMM1a

MM1bMM1bVLA1VLA1

VLA2VLA2

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20h38m36.7s 36.5s 36.4s 36.3s

R. A. (J2000)

34SO234SO2

MM1aMM1a

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20h38m36.7s 36.5s 36.4s 36.3s

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VLA2VLA2

VLA3VLA3MM1aMM1a

MM1bMM1bVLA1VLA1

VLA2VLA2

VLA3VLA3

Fig. 11. N30 molecules in contours over continuum in grey-scale. The peak positions of the 2D Gaussian fits to the continuum cores, MM1a andMM1b, are represented with black stars, while the VLA sources are shown with crosses. The molecular peak positions are marked with colouredplus symbols of the same colour as the respective molecule contour plot. The contour levels are 3σ, 6σ, 12σ, and 24σ. The beam sizes arerepresented by the inner and outer ellipses, with inner representing the continuum, with dimensions as in Fig. 1, and the outer, the beam size ofthe molecular emission map, which have dimensions of ∼1′′.65× 1′′.55, and position angle of ∼11◦ for all molecules. The dotted line represents thered- and blueshifted H2CO emission, while the arrows represent large-scale CO emission. The panels are sorted according to position of the peakemission, from top to bottom, and left to right.



Table 2. Gaussian fits for molecular transitions of COMs, including t-HCOOH and H2CO.a

Molecule Frequency Transition Position Ipeakb Iint

b FWHMb 3sourceb

[GHz] [′′,′′] [Jy beam−1] [Jy beam−1 km s−1] [km s−1] [km s−1]A-CH3OH 331.5023 111,−0 − 110,+0 (−0.31, 0.70) 16.0 123.0 8.5 9.9

336.8651 121,−0 − 120,+0 (−0.33, 0.82) 14.9 112.4 8.2 10.2338.4087 70,+0 − 60,+0 (−0.48, 0.85) 14.7 124.6 10.4 9.9341.4156 71,−0 − 61,−0 (−0.29, 0.86) 12.6 87.7 8.0 8.7342.7298 131,−0 − 130,+0 (−0.27, 0.75) 14.9 109.5 8.3 9.1349.1070 141,−0 − 110,+0 (−0.40, 0.76) 15.7 120.4 8.3 11.0355.6029 130,+0 − 111,+0 (−0.41, 1.03) 13.9 99.5 7.5 10.4356.0072 151,−0 − 150,+0 (−0.37, 0.82) 17.1 134.4 8.5 10.8360.6616 31,+1 − 42,+1 (−0.45, 0.98) 10.6 76.1 7.4 9.5

E-CH3OH 338.1244 70,0 − 60,0 (−0.45, 0.87) 14.8 102.8 7.4 9.8338.3446 7−1,0 − 6−1,0 (−0.50, 0.90) 14.5 104.9 8.2 9.8360.8489 110,0 − 101,0 (−0.41, 0.93) 13.6 100.9 7.8 10.0

13CH3OH 330.0018 70,7,0 − 60,6,0 (−0.59, 0.99) 3.5 18.8 5.8 7.9330.2528 70,7,+0 − 60,6,+0 (−0.55, 1.07) 3.8 24.6 8.0 8.3330.4424 71,6,0 − 61,5,0 (−0.51, 0.93) 3.5 16.7 5.5 8.0330.4639 111,10,−0 − 110,11,+0 (−0.52, 0.94) 6.1 32.1 6.1 7.7330.5352 72,5,0 − 62,4,0 (−0.53, 1.02) 4.9 26.6 6.1 7.6333.1148 71,6,−0 − 61,5,−0 (−0.61, 0.98) 3.5 22.6 6.6 8.8335.5602 121,11,−0 − 120,12,+0 (−0.57, 1.05) 4.0 22.8 5.8 9.2

C2H5OH 338.8862 157,8,2 − 156,9,2 (−0.94, 1.45) 1.9 11.1 8.4 7.6339.3126 127,5,2 − 126,6,2 (−1.09, 1.67) 1.1 7.8 7.6 9.1339.3984 117,4,2 − 116,5,2 (−1.12, 1.63) 1.0 6.4 7.8 8.4

CH3OCH3 339.4916 191,18,5 − 182,17,5 (−0.54, 1.04) 3.5 18.6 5.2 9.4340.6126 103,7,1 − 92,8,1 (−0.89, 1.21) 2.9 16.2 6.6 7.7342.6080 190,19,0 − 181,18,0 (−0.57, 1.22) 4.7 27.7 5.7 9.4344.3578 191,19,3 − 180,18,3 (−0.64, 1.15) 4.4 27.3 6.6 8.8357.4602 182,17,1 − 171,16,1 (−0.69, 1.08) 4.8 28.3 7.0 8.0358.4541 55,1,1 − 44,1,1 (−0.76, 1.17) 7.3 63.0 10.6 10.2360.4660 201,19,0 − 192,18,0 (−0.79, 1.22) 4.0 25.9 6.1 10.9360.5847 200,20,0 − 191,19,0 (−0.80, 1.23) 5.3 35.8 6.9 10.1

CH3OCHO 333.4494 311,31,0 − 300,30,0 (−0.69, 1.14) 4.0 23.5 6.0 8.9336.3514 276,22,1 − 266,21,1 (−0.82, 1.24) 2.2 15.6 7.0 10.3344.0296 191,18,5 − 182,17,5 (−0.52, 1.08) 4.4 29.4 7.1 10.1354.6081 191,18,5 − 182,17,5 (−0.65, 1.23) 4.0 24.4 6.7 9.5

t-HCOOH 334.2658 152,14 − 142,13 (−0.03, 0.46) 2.5 15.8 6.9 10.2343.9523 151,14 − 141,13 (0.03, 0.37) 2.4 17.1 7.8 11.2

H2COc 351.7686 51,5 − 41,4 (−0.03, 0.52) 13.1 88.0 6.3 13.951,5 − 41,4 (−0.83, 1.72) 11.0 47.1 3.7 6.5

Notes. (a) The transitions listed here, as well as the transitions listed in Tables 3 and 4, were relatively isolated and unblended, and were used tomake the emission maps shown in Fig. 11. (b) Typical uncertainties on the Gaussian centroid fits are (0′′.2, 0′′.2) for the position, 0.3 Jy beam−1 forIpeak, Jy beam−1 km s−1 for Iint, and 0.4 km s−1 for the FWHM and 3source. (c) The two entries for H2CO are red- and blueshifted lines, respectively.See also entries for CS.

peaks are localised within a fraction of a beam (0′′.4 – 0′′.6 vs. the1′′.5 beam), which leads us to conclude that the observed gradientis not an excitation gradient.

Figure 12 illustrates the observed molecular gradient, wherethe molecular peak emission is represented in three groups.The O-bearing COMs peak closer to MM1b, between VLA1and VLA2 (positions 1 and 2), with CH3OH peaking close toVLA2, and the more complex species (C2H5OH, CH3OCHO,and CH3OCH3) peaking closer to VLA1. The exceptions hereare the S-bearing species, CS, OCS, and H2CS, which peak be-tween VLA1 and VLA2, while the other S-bearing species peakbetween VLA2 and VLA3 (position 3). This is also where theN-bearing species peak. Moreover, HCOOH peaks close to theVLA3/MM1a positions, but shows more extended emission in

the northwest direction, along the blueshifted outflow axis (seeFig. 11).

3.5. Other molecules

The 347.33 GHz SiO, J = 8−7, transition has a weak blueshiftedcomponent at −6 km s−1 (or perhaps a neighbouring unidentifiedline, see Fig. 17), which was included in the integrated line map,with the velocity range of the integrated map from −10 km s−1

to 20 km s−1. The source velocity and FWHM listed in Table 4are for the component centred around 10 km s−1. The molecularpeak for SiO is at position 3 in Fig. 12, together with the S- andN-bearing species.

Only one deuterated molecule is detected, the 335.395 GHzHDO, J = 33,1 − 42,2 transition. This is shown in contours over



Table 3. Gaussian fits for molecular transitions of S-bearing species.

Molecule Frequency Transition Position Ipeak Iint FWHM 3source[GHz] [′′,′′] [Jy beam−1] [Jy beam−1 km s−1] [km s−1] [km s−1]

CS 342.8828 70 − 60 (0.17, 0.72) 11.1 69.7 8.5 9.7342.8828 70 − 60 (−1.03, 1.92) 9.2 47.3 4.2 7.9

C34S 337.3965 70 − 60 (−0.54, 1.08) 8.3 49.1 6.0 9.0SO 340.7141 87 − 66 (0.13, 0.24) 16.3 84.9 9.5 5.4

334.4311 88 − 77 (0.14, 0.25) 17.7 98.5 10.6 5.2346.5281 89 − 78 (0.06, 0.25) 19.4 140.0 11.1 6.7

34SO 333.9010 87 − 76 (−0.07, 0.22) 8.1 57.4 7.5 9.9337.5801 88 − 77 (−0.22, 0.29) 10.7 80.9 9.0 8.7339.8573 89 − 78 (−0.16, 0.18) 9.0 64.1 7.5 10.5

SO2 332.0914 212,20 − 211,21 (−0.14, 0.17) 11.4 86.6 8.0 10.8332.5052 43,1 − 32,2 (−0.06, 0.30) 12.9 95.7 8.3 9.9334.6733 82,6 − 71,7 (−0.09, 0.23) 12.0 85.6 7.8 9.5336.0892 233,21 − 232,22 (−0.15, 0.29) 10.1 76.5 8.2 10.9336.6695 167,9 − 176,12 (0.03, 0.14) 4.8 35.2 7.6 10.8338.3060 184,14 − 183,15 (−0.06, 0.23) 14.3 107.0 8.3 10.0340.3164 282,26 − 281,27 (−0.05, 0.27) 8.0 58.5 7.9 10.6345.3385 132,12 − 121,11 (−0.15, 0.33) 16.7 137.2 10.6 10.4346.6522 191,19 − 180,18 (−0.09, 0.27) 17.4 133.7 9.1 9.4350.8628 106,4 − 115,7 (0.01, 0.07) 5.6 41.7 8.1 9.8351.8739 144,10 − 143,11 (−0.11, 0.19) 15.2 116.2 8.7 9.9355.0455 124,8 − 123,9 (−0.09, 0.27) 16.2 122.4 8.5 9.7357.1654 134,10 − 133,11 (−0.21, 0.37) 16.1 124.4 9.2 11.6357.2412 154,12 − 153,13 (−0.19, 0.29) 17.0 129.7 8.7 10.3357.3876 114,8 − 113,9 (−0.15, 0.27) 16.4 129.2 9.1 10.2357.5814 84,4 − 83,5 (−0.14, 0.22) 17.0 131.8 9.0 10.2357.8924 74,4 − 73,5 (−0.11, 0.27) 15.7 123.6 9.2 10.2357.9258 64,2 − 63,3 (−0.15, 0.29) 15.6 121.3 9.1 10.5357.9629 174,14 − 173,15 (−0.09, 0.26) 15.7 126.6 9.4 10.0358.0131 54,2 − 53,3 (−0.27, 0.37) 13.6 105.0 8.9 10.1358.2156 200,20 − 191,19 (−0.17, 0.25) 19.0 150.8 9.5 10.4359.7707 194,16 − 193,17 (−0.16, 0.29) 15.5 113.7 8.9 12.0

34SO2 342.2089 53,3 − 42,2 (−0.03, 0.37) 2.4 15.4 7.2 9.7342.3320 124,8 − 123,9 (0.08, 0.29) 2.8 19.7 7.2 10.5344.2453 104,6 − 103,7 (−0.02, 0.25) 2.3 17.7 9.1 10.5344.5810 191,19 − 180,18 (−0.06, 0.20) 4.5 35.3 8.3 11.0344.8079 134,10 − 133,11 (−0.05, 0.21) 2.7 20.0 8.3 11.0

OCS 340.4493 28 − 27 (−0.45, 0.79) 8.2 55.4 6.8 9.8352.5996 29 − 28 (−0.48, 0.70) 9.4 70.8 7.7 10.2

OC34S 332.1297 28 − 27 (−1.04, 1.44) 1.1 6.0 7.8 10.9343.9833 29 − 28 (−1.04, 1.49) 2.0 11.7 5.4 9.6

H2CS 338.0832 101,10 − 91,9 (−0.67, 1.16) 7.7 47.4 6.8 8.4342.9464 100,10 − 90,9 (−0.72, 1.22) 4.4 26.6 6.6 8.3343.4141 103,7 − 93,6 (−0.64, 1.00) 4.3 23.0 5.1 9.0343.8132 102,8 − 92,7 (−0.73, 1.23) 7.1 46.1 6.8 9.7

Notes. Uncertainties are as in Table 2.

the continuum in Fig. 18. HDO shows extended emission, alsofollowing the red- and blueshifted H2CO and CS axes, but withsome elongated structure to the north of VLA1 and MM1b. Theline peaks at 2.39 Jy beam−1, or about 6σ, and with the peakposition located between the VLA1 and VLA2 peaks.

3.6. Column densities

As we observe such a strong chemical gradient in the positionsof the molecular peak emission, we derived column densitiesfor the respective molecules at the three positions shown in Fig.12. A synthetic spectrum was constructed with CASSIS using

only line emission, assuming local thermodynamic equilibrium(LTE). The inbuilt regular grid function was used to cover a largeparameter space and compute the reduced χ2 minimum in orderto determine the best-fit spectral model. Four parameters wereused as variables for fitting of the observed spectra. These werethe source velocity (3source), FWHM, the column density (N), andexcitation temperature (Tex). Estimates for the FWHM and 3sourcewere first obtained by looking at a few individual lines and fittingGaussian profiles to these lines. These estimates were then usedwith a parameter space of 4 km s−1 around the lines, in steps of0.5 km s−1 , which is equivalent to the channel width. The initialparameter space for N was Nmin = 1014 and Nmax = 1019, with



Table 4. Gaussian fits for molecular transitions of N-bearing species, CO, HCO+, SiO and HDO.

Molecule Frequency Transition Position Ipeak Iint FWHM 3source[GHz] [′′,′′] [Jy beam−1] [Jy beam−1 km s−1] [km s−1] [km s−1]

N-bearing speciesCH3CN 330.7603 187 − 177 (−0.22, 0.50) 6.1 46.2 7.4 10.0

330.9126 185 − 175 (−0.18, 0.47) 7.8 56.2 7.1 9.5330.9698 184 − 174 (−0.22, 0.51) 11.4 82.3 7.5 9.2331.0143 183 − 173 (−0.24, 0.55) 10.0 72.6 7.2 9.2331.0461 182 − 172 (−0.35, 0.57) 7.5 55.3 7.4 9.5349.3933 193 − 183 (−0.20, 0.56) 11.7 88.8 8.1 9.7349.4268 192 − 182 (−0.20, 0.60) 9.8 73.0 7.7 10.1

HNCO 329.6644 150,15 − 140,14 (−0.14, 0.42) 8.8 66.9 8.3 9.2350.3330 161,16 − 151,15 (−0.05, 0.35) 7.6 61.4 8.4 10.2

HCNa 354.5055 4 - 3 (0.17, 0.52) 17.8 127.2 6.3 14.2HC15N 344.2001 4 − 3 (−0.19, 0.59) 10.2 78.7 8.6 9.9HC3N 336.5201 37 − 36 (−0.14, 0.53) 5.6 44.2 7.9 10.7

345.6090 38 − 37 (−0.15, 0.47) 6.5 51.8 8.6 10.1354.6975 39 − 38 (−0.18, 0.39) 6.7 53.8 8.7 10.6

CN 340.2478 30,3.5 - 20,2.5 (−0.49, 1.41) 1.4 11.3 9.8 9.4SiO and HDO

SiO 347.3306 80 − 70 (−0.07, 0.47) 2.8 33.6 11.7 11.2HDOb 335.39550 33,1 − 42,2 (−0.43, 0.92) 1.6 11.5 2.1 10.8

CO and HCO+

COa 345.7960 3 − 2 (0.35, 0.68) 18.2 156.0 10.1 11.613CO 330.5880 3 − 2 (0.57,−0.12) 10.7 51.9 4.5 10.6C18O 329.3305 3 − 2 (−0.64, 0.37) 3.5 25.2 8.2 9.1H13CO+ 346.9983 4 - 3 (−1.45, 0.50) 3.74 – 4.31 9.20

Notes. Uncertainties are as in Table 2. (a) For the HCN and CO lines, only the brightest, redshifted components are listed. (b) HDO emission isextended, so the peak position is of the maximum flux position, not derived from a 2D Gaussian fit.

Fig. 12. Representation of the observed molecular gradient towards theMM1 source. The molecules are separated into three groups, with theO-bearing COMs in the first and second groups, with group 1 includingH2CS, and group 2 including CS and OCS. Group 3 includes all thesulphur- and nitrogen-bearing species, as well as SiO and HCOOH.

ten steps in the range, and for Tex the range was 90 to 300 K,also with ten steps in this range. A few iterations were then runto decrease the ranges, but keeping the step size larger than theuncertainties. The source size was assumed to be 1.5′′, or slightlylarger than the beam size. Only line data were used in the mod-elling process. The values obtained for each molecule are shown

20h38m36.47s 36.46s 36.45s

42°37'34.8"

34.6"

34.4"

R. A. (J2000)

Dec.

(J20

00)

0 K < Eup <= 50 K50 K < Eup <= 100 K100 K < Eup <= 150 K100 K < Eup <= 150 K150 K < Eup <= 200 K150 K < Eup <= 200 K200 K < Eup <= 250 K200 K < Eup <= 250 K250 K < Eup <= 300 K300 K < Eup <= 350 K300 K < Eup <= 350 K

Fig. 13. Peak positions of CH3OH line transitions, with the upper-levelenergy of each transition represented in colour. The data points do notfollow a systematic pattern.

in Tables 5, 6, and 7. Table 5 shows the values obtained from fitsto the spectrum taken at position 1 (see Fig. 12), where the O-bearing species peak around VLA1. Table 6 in turn shows valuesobtained at peak position 2, between VLA1 and VLA2. Finally,Table 7 shows the values obtained at position 3, where the N- andS-bearing species peak (between VLA2 and VLA3). The uncer-tainties for N and Tex are mainly a result of how well the spectralmodel fits the data. This in turn depends on our assumptions ofLTE (if the level populations are not in LTE, this will introducea systematic error), optically thin emission (if emission is op-tically thick, column densities will be underestimated), and the



20h38m36.51s 36.50s 36.49s 36.48s 36.47s

42°37'34.2"

34.0"

33.8"

R. A. (J2000)

Dec.

(J20

00)

0 K < Eup <= 50 K50 K < Eup <= 100 K100 K < Eup <= 150 K150 K < Eup <= 200 K200 K < Eup <= 250 K250 K < Eup <= 300 K300 K < Eup <= 350 K300 K < Eup <= 350 K

Fig. 14. Peak positions of SO2 line transitions, with the upper-level en-ergy of each transition represented in colour. As with the CH3OH linetransitions, there does not seem to be any pattern with upper-level en-ergy.

20h38m36.47s 36.46s 36.45s

42°37'34.8"

34.6"

34.4"

R. A. (J2000)

Dec.

(J20

00)

1x105 < ncrit <= 1x106

1x106 < ncrit <= 1x1071x106 < ncrit <= 1x107

1x107 < ncrit <= 1x1081x107 < ncrit <= 1x108

1x108 < ncrit <= 1x109

1x109 < ncrit <= 1x10101x109 < ncrit <= 1x1010

Fig. 15. Peak positions of the CH3OH line transitions, with the criticaldensity now represented in colour. As with the upper-level energy, theredoes not seem to be a pattern depending on critical density.

20h38m36.51s 36.50s 36.49s 36.48s 36.47s

42°37'34.2"

34.0"

33.8"

R. A. (J2000)

Dec.

(J20

00)

1x105 < ncrit <= 1x1061x105 < ncrit <= 1x106

1x106 < ncrit <= 1x1071x106 < ncrit <= 1x107

1x107 < ncrit <= 1x1081x107 < ncrit <= 1x108

1x108 < ncrit <= 1x109

1x109 < ncrit <= 1x10101x109 < ncrit <= 1x1010

Fig. 16. Peak positions of SO2 line transitions, with the critical densityrepresented in colour. Again, no systematic pattern is seen.

line shape (we assume Gaussian line profiles). For species withmany optically thick lines, this becomes especially problematicbecause fewer lines can be used in the fit. The optical depth ofeach line was checked, and only lines with τ . 0.8 were usedin the modelling. The uncertainties on N and Tex were obtainedby fixing N (or Tex), and then changing Tex (or N) until we wereable to observe the impact of the change on the resulting fit, fol-

30 20 10 0 10 20 30Velocity [km s 1]

0

1

2

3

Flux

[Jy

beam

1 ]

Fig. 17. The 347.33 GHz SiO, J = 8 − 7 line, showing broad emission,with a weak blueshifted component at −6km s−1. The horizontal redline represents the baseline, while the vertical line is the source velocityderived for MM1a from the line modelling in CASSIS, at 9.5 km s−1.

20h38m37.0s36.8s 36.6s 36.4s 36.2s 36.0s 35.8s

42°37'42"

39"

36"

33"

30"

R. A. (J2000)

Dec.

(J20

00)

MM1a

MM1b

MM2

VLA1VLA1VLA2VLA2

VLA3VLA3

0.0

0.1

0.2

0.3

0.4

0.5

Jy b

eam

1

Fig. 18. Continuum image of CygX-N30, with contours showing the335.395 GHz HDO line emission (transition J = 33,1−42,2). The contourlevels are at 3σ, 4σ, 5σ and 6σ.

lowing the method outlined in Calcutt et al. (2018). Figures ofeach of the fitted lines for the molecules at position 2 are shownin Appendix D, with the synthetic spectra shown in red and over-plotted on the observed spectra in black.

In the case of molecules with many optically thick lines, suchas CH3OH and SO2, the column densities were obtained fromoptically thin isotopologue emission. The isotopologue columndensity was then multiplied by the ISM isotope ratio. As an ex-ample, the modelled column density of 13CH3OH was multipliedby the 12C/13C ratio, which we took to be ∼ 77 (Wilson & Rood1994). Similarly, column densities for optically thick sulphur-bearing molecular lines were obtained using the ISM isotopo-logue ratio 32S/34S ∼ 22 (Wilson 1999). In the case of CH3CN,we did not detect its isotopologue 13CH3CN, and so we used thehigher energy transition, CH3CN, v8=1, for the fitting.

Apart from HDO, no other deuterated molecules were de-tected. Upper limits for the column densities of CH2DOH werefound to be 4.6 ×1016 cm−2, 6.8×1016 cm−2, and 8.9×1016 cm−2

at positions 1, 2, and 3, respectively. These values were obtainedby assuming Tex, 3source, and FWHM of 13CH3OH, and then in-creasing the column density of the synthetic spectrum until some



lines have a strength of & 3σ of the observed spectrum. The ob-tained upper limits correspond to a D/H ratio of ∼0.1%. Thisvalue includes statistical correction for the three possible sym-metries of the CH2DOH molecule, which will give an observedNCH2DOH/NCH3OH ratio a factor of three higher than the actualratio (see e.g. Jørgensen et al. 2018; Manigand et al. 2019).

A number of more complex species have been de-tected towards high-mass star-forming regions; for exampleSgr(B2) near the Galactic centre. One of the more abundantmolecules detected towards this source is acetone (CH3COCH3)with a relative molecular abundance of X, corresponding toN(CH3COCH3) / N(CH3OH) ∼ 0.1 (Belloche et al. 2016). Whenadopting the same column-density ratio and physical conditions,we find that the non-detection towards N30 is consistent with thenoise level.

Relative abundances of the modelled molecules are shownin Figs. 19 and 20, with Fig. 19, showing the column densitiesof each molecule with respect to the column density of CH3OH,at each respective position, whereas Fig. 20 shows the columndensities with respect to the column density of CH3CN. As withthe integrated intensity maps, we see how the O-bearing speciespeak towards position 1, while the N- and S- bearing speciespeak towards position 3.

4. Discussion

In this section, we discuss our results in more detail, startingwith a comparison of the abundances towards N30 with othersources, followed by discussions on excitation temperatures andthe D/H ratio observed towards N30. We end the section with adiscussion of the continuum cores, and the observed moleculargradient.

4.1. Abundances compared to other sources

To put the inferred abundances into a broader context, we com-pare them to those observed towards different sources, lookingat the differences and similarities. An example of such a com-parison is presented by Drozdovskaya et al. (2019), in whichabundances towards the low-mass protostar IRAS 16293B arecompared with those measured towards Comet 67P/C-G, withthe cometary data used as a representation of the initial ingredi-ents that formed the Earth and the other Solar System planets.From their results, the authors concluded that the volatile com-position of cometesimals and planetesimals is partially inheritedfrom the pre- and protostellar phases of the evolution. Jørgensenet al. (2020) extended this comparison to include sources of dif-ferent masses and located in different environments. They com-pared, for example, IRAS 16293B and HH212 (both low-masssources located relatively close to the Sun), AFGL 4176 (a high-mass sources also in our Galactic neighbourhood), and Sgr B2(N2), a high-mass source located close to the Galactic centre.They also included the shocked regions L1157 B1 and Orion KLas well as Comet 67P/C-G in their comparison. The result of thiscomparison was that the abundances towards these sources arein general very similar, which is an indication that the underly-ing chemistry is relatively independent of the differences in theirphysical conditions. There are some differences, however. Theselatter authors found, for example, that abundances observed to-wards the protostellar sources tend to agree better with one an-other than with those towards Comet 67P/C-G, which suggeststhat some chemical processing occurs between the protostellarand cometary stages (see also Drozdovskaya et al. 2019). In this

section, we compare the available column densities observed to-wards the sources from Jørgensen et al. (2020) to the those weobserve towards N30. The column densities taken are relativeto CH3OH, CH3CN, and SO2, representing COM, N-, and S-bearing species, respectively. These sources were selected sim-ply because of the amount of data available in the literature foreach of them. While there are many sources in the literature withavailable column densities, it is rare to find sources observedwith wide enough frequency coverage so that column densitiescan be found for a large amount of molecules. We therefore com-pare N30 to these sources. As N30 shows a strong chemical gra-dient, it is important to place the column densities measured to-wards this source in context with those of the sources from thesestudies, and in this way achieve a better understanding of thephysical nature of the observed chemical gradient.

Figure 21 shows the column density ratios observed towardsN30 compared with those observed towards the sources dis-cussed above. The figure shows the column density ratios to-wards position 2 (see Fig. 12). Similar figures are provided forpositions 1 and 3 in Appendix B. The panels in the figure showthe column densities of each molecule with respect to CH3OH,with N30 represented on the y-axis, and each respective sourcerepresented on the x-axis. The upper-left panel shows the Galac-tic centre source, Sgr B2 (N2), which is part of the Sgr B2 molec-ular cloud, one of the most active high-mass star forming re-gions in the Galaxy; it was part of the high-resolution EMoCAsurvey (Exploring Molecular Complexity with ALMA Bellocheet al. 2016, 2017; Müller et al. 2016; Bonfand et al. 2019). Forthis source, the O-bearing species show similar abundances (dif-ferences within one order of magnitude), while the N-bearingspecies observed towards N30 have lower ratios compared toCH3OH (typically by a factor 10).

The upper-right panel shows abundances measured by theROSINA instrument of the Rosetta mission towards Comet67P/C-G, as presented by Drozdovskaya et al. (2019) in theircomparison to the low-mass source IRAS 16293B which wasthe target of the PILS program by Jørgensen et al. (2016). Abun-dances towards Comet 67P/C-G are in general higher than thatobserved towards N30, with no real differences between O- andN-bearing species. However, for IRAS 16293B, the O-bearingspecies are very similar to N30, while the N- and S-bearingspecies are in general higher towards N30. This is in contrastto the Galactic centre source Sgr B2 (N2), which also showssimilar O-bearing species, but with higher abundances in N-bearing species. This would suggest that N30 has abundancesin N-bearing species somewhere in between the Galactic cen-tre (high-mass) source, and the solar neighbourhood (low-mass)source IRAS 16293B.

Orion KL, which is not a ‘traditional’ hot core but is believedto be the result of an explosive event where a pre-existing denseregion is heated from the outside (Friedel & Snyder 2008; Zap-ata et al. 2011; Crockett et al. 2015; Pagani et al. 2017), shows,in general, similar abundances to those observed towards N30.The high-mass source AFGL 4176 (Bøgelund et al. 2019) showsabundances in even better agreement to N30. HH212 is a low-mass source, with COMs observed in its disc atmosphere, thatis, above and below the disc (Lee et al. 2019). This source alsoshows similarities to N30, although the available data in the lit-erature for this source are still limited. L1157-B1 (Arce et al.2008; Sugimura et al. 2011; Lefloch et al. 2017) on the otherhand is a shocked region, with the available column densitiesfor this source suggesting that the O-bearing species are a littleless abundant in N30, while the only N-bearing species avail-able for comparison, CH3CN, is significantly more abundant in



CH3O

H13

CH3O

H

CH318

OHCH

2DOH

C 2H 5

OH

CH3O

CHO

CH3O

CH3

H 2CO

H 213

CO

t-HCO

OH

c-HC

OOH

HDO

H 2CS SO

2

33SO

2

34SO

2

OCS

OC34

S

HNCO

HC3N

CH3C

N,v 8

=113

CH3C

N

10 4

10 3

10 2

10 1

100

Rela

tive

abun

danc

e to

CH 3

OHPos. 1 - COMs peakPos. 2 - CentrePos. 3 - N and S peak

Fig. 19. Relative abundances of each molecule relative to the column density of CH3OH at each respective position. The white arrows representupper limits, whereas the black bars represent the uncertainties (see Tables 5, 6 and 7).

CH3O

H13

CH3O

H

CH318

OHCH

2DOH

C 2H 5

OH

CH3O

CHO

CH3O

CH3

H 2CO

H 213

CO

t-HCO

OH

c-HC

OOH

HDO

H 2CS SO

2

33SO

2

34SO

2

OCS

OC34

S

HNCO

HC3N

CH3C

N,v 8

=113

CH3C

N

10 2

10 1

100

101

102

103

Rela

tive

abun

danc

e to

CH 3

CN

Pos. 1 - COMs peakPos. 2 - CentrePos. 3 - N and S peak

Fig. 20. Relative abundances of each molecule relative to the column density of CH3CN at each respective position. The white arrows and blackbars are as in Fig. 19.



Table 5. Column densities, excitation temperatures, FWHM and 3peak derived at the peak positions of H2CS and other COMs, excluding CH3OH(position 1 in Fig. 12).a

Molecule Column density Tex FWHM 3peak Peak positionb

[cm−2] [K] [km s−1] [km s−1]COMs and O-bearing species

CH3OHc 1.3 (0.2) ×1019 140 (25) 5.0 8.5 213CH3OH 1.7 (0.2) ×1017 140 (25) 5.0 8.5 1/2CH3

18OHd <3.9 ×1016 140 5.0 8.5 -CH2DOHd <5.2 ×1016 140 5.0 8.5 -C2H5OH 7.2 (2.0) ×1016 120 (60) 4.5 9.0 1CH3OCHO 1.9 (0.2) ×1017 110 (20) 4.5 8.5 1CH3OCH3 2.9 (0.2) ×1017 100 (20) 4.0 8.5 1H2COc 9.2 (1.5) ×1017 190 (40) 7.5 8.0 1H2

13CO 1.2 (0.2) ×1016 190 (40) 7.5 8.0 1t-HCOOH 2.8 (0.5) ×1016 190 (50) 7.0 11.0 3c-HCOOHd <2.3 ×1015 190 7.0 11.0 3HDOe 4.6 (2.0) ×1016 140 (25) 4.0 10.5 -

S-bearing speciesH2CS 3.3 (0.5) ×1016 170 (50) 5.5 9.0 133SOf 4.0 (2.0) ×1015 180 (40) 6.5 10.0 3SO2

c 5.9 (0.2) ×1017 180 (40) 6.5 10.0 333SO2

d <6.1 ×1015 180 (40) 6.5 10.0 -34SO2 2.7 (1.0) ×1016 180 (40) 6.5 10.0 3OCSc 3.1 (0.4) ×1017 170 (50) 5.5 9.5 2OC34S 1.4 (0.2)×1016 170 (50) 5.5 9.5 1

N-bearing speciesHNCO 4.0 (1.0)×1016 120 (20) 6.5 9.5 3HC3N 3.0 (1.0)×1015 200 (40) 7.0 9.5 3CH3CN, v8=1g 3.6 (2.0)×1016 140 (15) 7.0 10.5 2/313CH3CNd < 6.0 ×1014 140 7.0 10.5 -

Notes. (a) Values are derived from synthetic spectrum fitting with CASSIS, with the assumption of LTE. (b) Positions of peak molecular emissionare as represented in Fig. 12. (c) Column densities for optically thick lines derived using ISM ratios from Wilson & Rood (1994). (d) Upper limitswere determined by setting Tex, FWHM, and 3peak, equal to that of a detected isotopologue. (e) To estimate a column density for HDO, the excitationtemperature of methanol was assumed. (f) Both SO and 34SO had optically thick lines, so only the column density of 33SO could be derived, usingTex of 34SO2. (g) CH3CN, v8=1, was used for the model fit of CH3CN because it is optically thick, and 13CH3CN was not detected.

N30. Nevertheless, when all the sources are compared, the abun-dances observed towards AFGL 4176 agree best with those to-wards N30. At a distance of ∼ 3.7 kpc, this source is more dis-tant than N30 (d ∼ 1.3 kpc), and more luminous, with an up-per limit of 2 × 105 L� (compared to N30, with a luminosity of∼ 2.04 × 104 L�; Cao et al. 2019). It also has a large disc-likestructure, as was found by Johnston et al. (2015) using ALMAobservations of CH3CN on scales of ∼ 1200 AU. Furthermore,Bøgelund et al. (2019) found (also from ALMA observations, ata resolution of ∼ 1285 AU) that the O- and N-bearing speciesin this source also peak in slightly different locations, with N-bearing species peaking slightly closer to the continuum peakthan the O-bearing species. This would suggest that a combina-tion of processes could be causing the sublimation of the COMsfrom the dust grains rather than the traditional hot core model.The agreement with Orion KL also strengthens the case that it isa combination of processes that result in the COMs we observe.

It therefore seems that, when comparing the abundancesobserved towards N30, they agree more with other high-masssources, such as AFGL 4176 (a more traditional hot core, butwith some chemical differentiation) and Orion KL (a high-mass,shocked region), than with the abundances observed towardslow-mass sources, such as IRAS 16293B, or the outflow region,L1157-B1. The agreement is also better with these high-mass

sources than compared to high-mass sources in the Galactic cen-tre. The environment here, which has a cosmic ray ionisationrate of a factor of 50 higher than usually assumed for the Galac-tic disc (Guzmán et al. 2015; Bonfand et al. 2019), resulting ina higher dust temperature. This presents some challenges forour understanding of the formation of COMs (Jørgensen et al.2020), which are believed to form primarily on grain surfaces atlow temperatures. However, it might explain the high abundanceof N-bearing species in the Galactic centre, which evolves overlonger timescales in the gas phase (Garrod et al. 2017; Bøgelundet al. 2019). It might also explain the low abundance of S- andN-bearing species in low-mass sources, where the temperaturesare lower than in their high-mass counterparts. Bøgelund et al.(2019) suggest that AFGL 4176 is a very young source, wherelittle processing of the chemical inventory by the protostar hasoccurred, which is why they observe N-bearing species to below in abundance compared to Sgr B2. For the shocked regionL1157-B1, the O-bearing species are sputtered off of the dustgrains, but there is not sufficient time for the nitrogen chem-istry to evolve in the gas phase (see chemical models by e.g.Garrod 2013; Barone et al. 2015; Garrod et al. 2017; Codellaet al. 2017). The agreement between the abundances towardsN30 MM1 and AFGL 4176 would suggest that the sources areat a similar stage of evolution, although at scales of ∼ 1200 AU,



Table 6. Column densities, excitation temperatures, FWHM and 3peak derived at the peak positions of CH3OH (position 2 in Fig. 12)a

.



CH3OHc 1.0 (0.2) ×1019 120 (25) 4.5 9.0 213CH3OH 1.3 (0.2) ×1017 120 (25) 4.5 9.0 1/2CH3

18OHd <3.0 ×1016 100 4.5 9.0 -CH2DOHd <4.0 ×1016 100 4.5 9.0 -C2H5OH 6.7 (2.0) ×1016 130 (60) 5.0 9.5 1CH3OCHO 1.4 (0.2) ×1017 110 (20) 4.5 9.0 1CH3OCH3 2.4 (0.2) ×1017 110 (20) 5.0 9.0 1H2COc 5.9 (1.5) ×1017 160 (40) 8.0 9.0 1H2

13CO 7.6 (2.0) ×1015 160 (40) 8.0 9.0 1t-HCOOH 4.0 (0.5) ×1016 190 (50) 7.0 11.0 3c-HCOOHd <3.3 ×1015 190 7.0 11.0 -HDOd 6.8 (2.0) ×1016 120 (25) 4.0 10.5 -


c 7.3 (0.2) ×1017 130 (40) 6.0 10.0 333SO2

d <8.1 ×1015 130 (40) 6.0 10.0 -34SO2 3.3 (1.0)×1016 130 (40) 6.0 10.0 3OCS b 2.4 (0.4) ×1017 170 (50) 5.0 10.0 2OC34S 1.1 (0.2) ×1016 170 (50) 5.0 10.0 1

N-bearing speciesHNCO 5.0 (1.0)×1016 150 (20) 6.5 10.5 3HC3N 4.0 (1.0)×1015 210 (40) 7.0 10.0 3CH3CN, v8=1g 5.5 (2.0)×1016 140 (10) 7.0 10.5 2/313CH3CNd <9.1 ×1014 140 7.0 10.5 -


AFGL 4176 appears to be a single source, as opposed to N30,which is at least a binary source at scales of ∼ 1300 AU, with theMM1b/VLA1 core probably less evolved than the MM1a/VLA3core.

Figure 22 shows the abundances of O-bearing species nor-malised to CH3OH, with N30 on the x-axis and the respectivesources depicted with different symbols on the y-axis. Figure 23shows the N and S-bearing species normalised to CH3CN andSO2, respectively. Some trends that can be seen in Fig. 22 are thatthe abundances of O-bearing species in Comet 67P and L1157-B1 are in general higher than the protostellar sources (aroundone order of magnitude), while the shocked region Orion KLshows higher relative abundances in CH3OCHO and CH3OCH3(5–10 times higher), but with H2CO and C2H5OH comparableto N30. IRAS 16293B has abundances in O-bearing species thatare a little higher than N30 (around five times), while Sgr B2(N2) has a higher abundance in C2H5OH and (five to ten times),and with abundances of CH3OCHO, CH3OCH3, and H2CO sim-ilar to those for N30. As discussed above for Fig. 21, we also seefrom this figure that the best agreement is with the high-masssource AFGL 4176. This can also be seen in the abundances withrespect to CH3CN and SO2 in Fig. 23, with AFGL 4176 show-ing similar abundances, while Orion KL has higher abundancesin N-bearing species but a similar abundance of H2CS. How-

ever, for the N- and S-bearing species, the number of molecularspecies available for comparison is limited.

Therefore, while N30 clearly shows a strong chemical gra-dient with different species peaking in different locations, theinferred abundances are typical of what is seen towards otherintermediate- and high-mass protostars. This suggests that, nomatter the physical origin of the chemical gradient, the chem-istry does not change significantly between different sources.

4.2. Excitation temperatures

We find some differences when comparing the excitation tem-peratures of different molecular species. The N- and S-bearingspecies seem to be slightly warmer than the O-bearing species,with ranges from 130 to 200 K and 100 to 140 K, respectively.HC3N seems to be warmer than other molecular species, witha range of 200 − 240 K between the three positions in Fig. 12.t-HCOOH also seems to be warmer (170− 190 K) than other O-bearing species, but considering that it peaks at the position withthe N-bearing species, this might not be strange, because it doesnot seem to be connected with the other O-bearing molecules.H2

13CO also has a warmer excitation temperature, in the rangeof 150 − 190 K.

Other authors have found more significant differences in theexcitation temperatures of N- and O-bearing species towards



Table 7. Column densities, excitation temperatures, FWHM, and 3peak derived at the peak positions of the N- and S- bearing species peak (position3 in Fig. 12).a



CH3OHc 5.7 (1.5) ×1018 100 (25) 5.0 9.5 213CH3OH 7.4 (2.0) ×1016 100 (25) 5.0 9.5 1/2CH3

18OHd <1.7 ×1016 100 5.0 9.5 -CH2DOHd <2.3 ×1016 100 5.0 9.5 -C2H5OH 5.5 (2.0) ×1016 140 (60) 5.5 10.5 1CH3OCHO 9.6 (2.0) ×1016 110 (20) 5.0 9.0 1CH3OCH3 1.5 (0.2) ×1017 100 (20) 4.5 9.5 1H2COc 4.3 (1.5) ×1017 150 (40) 8.5 9.5 1/2H2

13CO 5.6 (2.0) ×1015 150 (40) 8.5 9.5 1t-HCOOH 4.8 (0.5) ×1016 170 (50) 7.0 11.0 3c-HCOOH <4.0 ×1015 170 (50) 7.0 11.0 3HDOe 8.9 (2.0) ×1016 100 (25) 4.0 11.0 -


c 1.1 (0.2) ×1018 130 (40) 6.5 10.0 333SO2

d <1.2 ×1016 130 6.5 10.0 -34SO2 4.8 (1.0) ×1016 130 (40) 6.5 10.0 3OCSb 1.4 (0.4) ×1017 150 (50) 5.0 10.0 2OC34S 6.5 (2.0)×1015 170 (50) 5.0 10.0 1

N-bearing speciesHNCO 5.9 (1.0) ×1016 160 (40) 6.5 10.5 3HC3N 4.0 (1.0) ×1015 240 (40) 7.0 10.0 3CH3CN, v8=1g 6.0 (2.0) ×1016 140 (10) 7.0 10.5 2/313CH3CNd <1.0 ×1015 140 7.0 10.5 -


other sources. An example is Orion KL, in which the O-bearingspecies trace gas of lower temperatures —ranging between 100and 150 K— than the N-bearing species, which trace gas of200 − 300 K (Bell et al. 2014; Crockett et al. 2015). Jørgensenet al. (2018) also found a range of 80 − 300 K in excitation tem-peratures of different molecular species in IRAS 16293, and sug-gested that the differences observed could be attributed to bind-ing energy. van ’t Hoff et al. (2020) argues that the so-called ‘sootline’ located close to the protostar at a temperature of ∼ 300 Kis marked by an excess of hydrocarbons and nitriles sublimatedfrom of carbon grains inside this line. The O-bearing COMs onthe other hand desorb around the water snowline, which is lo-cated further out from the protostar at a temperature of ∼ 100 K.However, in the case of N30, we do not observe the COMs con-centrated at a central position, but rather spread out in a chemicalgradient, which suggest that it is probably not a traditional hotcore(s) but rather a combination of factors causing the chemi-cal gradient and the difference in excitation temperature that weobserve, including two or more protostars (see Section 4.4).

4.3. D/H ratio

We find an upper limit on the D/H ratio derived forN(CH2DOH)/N(CH3OH) of about 0.1%. Compared to IRAS

16293B, which has values of 2%-3%, this is very low. It isalso lower than values reported by Neill et al. (2013) for OrionKL, in which they found similar D/H ratios for water, formalde-hyde, and methanol, 0.2%-0.8%. However, for Sgr B2 (N2), Bel-loche et al. (2016) reported a XD/XH ratio for CH2DOH of0.12%, which they argue might be because of the higher kinetictemperatures in the Galactic centre region compared to nearbystar-forming regions. Bøgelund et al. (2019) do not detect anydeuterated species towards AFGL 4176, which further strength-ens the agreement between this source and N30, as discussed inthe abundance comparison above. Other high-mass sources havealso shown low D/H ratios (e.g. Ratajczak et al. 2011; Bøgelundet al. 2018). Bøgelund et al. (2018) conclude that warm forma-tion temperatures of ∼ 30 K could account for the low deutera-tion in the NGC 6334I regions, with the pre-stellar cloud heatedby a nearby O-type star and associated HII region. In the caseof N30, the presence of the strong radiation field caused by thenearby Cyg–OB2 association (projected distance of ∼23 pc ata distance of 1.3 kpc; Reipurth & Schneider 2008) may haveheated the pre-stellar cloud and resulted in the low levels ofdeuteration we observe.

An alternative is that the prestellar phase is cold but short, asis expected for higher mass sources. In this scenario, time is thebottleneck in setting the deuteration, as opposed to above where



0.0 0.2 0.4 0.6 0.8 1.0N(X) / N(CH3OH)

0.0

0.2

0.4

0.6

0.8

1.0N

(X) /

N(C

H 3OH

) (N3

0 - P

ositi

on 2

)

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 Sgr B2 (N2)

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 Comet 67P

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 IRAS 16293B

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 Orion KL

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 AFGL 4176

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 HH212

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 L1157 B1 H2COC2H5OHCH3OCH3CH3OCHOCH3CNHNCOHC3Nt-HCOOHSO2H2CS

Fig. 21. Column densities towards N30, position 2, with respect to CH3OH on the y-axis compared to different sources plotted on the x-axis. Thesolid line represents equal abundances, whereas the dotted lines represent an order of magnitude difference.

temperature is the limiting factor. Either way, the low degree ofdeuteration in sources such as this one is not unexpected.

4.4. Continuum cores, and the observed molecular gradient

We find that the O-bearing species have their peak emission con-centrated towards the radio (cm) continuum source, VLA1, closeto but to the west of the MM1b submm continuum core. S- andN-bearing species on the other hand peak between VLA2 and



10 3 10 2 10 1 100

N(X) / N(CH3OH) (N30 - Position 2)10 3

10 2

10 1

100

N(X

) / N

(CH 3

OH)

H 2CO

C 2H 5

OH

CH3O

CH3

CH3O

CHO

t-HCO

OH

AFGL 4176Sgr B2 (N2)Orion KLIRAS 16293BComet67PHH212L1157 B1

Fig. 22. Column densities with respect to CH3OH towards N30, position2, on the x-axis compared to different sources plotted on the y-axis.Each source is marked with a different marker. The solid and dottedlines are as in Fig. 21

10 2 10 1 100 101

N(X) / N(CH3CN, SO2) (N30 - Position 2)10 3

10 2

10 1

100

101

102

N(X

) / N

(CH 3

CN,S

O 2)

HNCO

HC3N

H 2CS


Fig. 23. Column densities towards N30, position 2 (on the x-axis), withrespect to CH3CN for the N-bearing species and SO2 for H2CS, com-pared to different sources plotted on the y-axis. Each source is markedwith a different marker. The solid and dotted lines are as in Fig. 21

VLA3 to the north of MM1a. All molecules peak on a gradi-ent traced by the red- and blueshifted axis of H2CO and CSemission. This axis is nearly perpendicular to the larger scale(∼1 pc; Fischer et al. 1985) bipolar outflow axis seen in COemission, which might indicate that the observed submm and ra-dio continuum sources are located in a disc-like structure (seeHutawarakorn et al. 2002). It is important to note here thatthis disc-like structure is more akin to a pseudo-disc that is notrotation-supported, but just a rotating structure around the pro-tostars. Looking at the H2CO and CS maps in Figs. 3 and 7,it is also clear that this structure is very large, with a radiusof around 3000 AU, and encompass all the continuum sources(see also Hutawarakorn et al. 2002). Similar disc-like struc-tures are also observed in other sources, such as G35.20-0.74N,in which Hutawarakorn & Cohen (1999) observed a large-scaleoutflow structure seen in CO emission perpendicular to a disc-like structure containing four hot cores. Chemical differentiation

between the different cores was also observed for this source(with separation between the cores of 1000 − 2000 AU; Allenet al. 2017), with O- and S-bearing species detected towards theinner two cores (B1 and B2), but few N-bearing species, whilethe outer two cores (B3 and A) have strong detections of N-, S-, and O-bearing species. Another source is G328.2551−0.5321,for which Csengeri et al. (2018) found N-bearing COMs peak-ing towards the protostar, while the O-bearing COMs peak to-wards two spots, offset from the protostar (see also Csengeriet al. 2019). The authors interpreted the two spots as accretionshocks onto a disc with an estimated distance of 200 − 800 AUfrom the central protostar. These large disc-like structures aretherefore not uncommon in high-mass protostars, and chemicaldifferentiation also seems to be a common feature. Furthermore,with the high angular resolution provided by interferometric ob-servations, more and more examples of sources are identified inwhich the observed COM emission cannot be explained by thecanonical hot-core scenario in which COMs sublimate from theheated dust grains close to the protostar. This was also seen byBelloche et al. (2020) for low-mass protostars in the CALYPSOsurvey.

For N30, we observe chemical differentiation between S- andN-bearing species associated with the VLA2 and VLA3/MM1acores on the one hand, and COMs and O-bearing species associ-ated with the VLA1/MM1b core on the other. Molecules that donot follow this differentiation in O- and S-/N-bearing species aret-HCOOH, observed to peak towards position 3 at the N- andS-bearing species position, and CS, OCS, and H2CS that peaktowards the O-bearing species position.

Our results therefore suggest that N30 is not a purely tradi-tional hot core in which ice-covered dust grains collapse towardsa warm protostar and are heated to temperatures & 100 K as theyget closer, where the ices sublimate and we see a peak of COMemission (see e.g. Herbst & van Dishoeck 2009, and referencestherein). The release of the COMs into the gas phase may thenlead to further reactions in the dense warm gas, but this is stillcentred on the region where the dust temperature exceeds ∼ 100K. Instead, the O-bearing COM emission is likely caused by acombination of processes, including accretion of infalling mate-rial onto the disc surface —which is similar to what was foundby Csengeri et al. (2018) for G328.2551–0.5321—,while the N-and S- bearing species towards VLA3/MM1a might be a slightlymore evolved source where the gas-phase chemistry had moretime to evolve.

5. Summary and Conclusions

We observed CygX-N30 and MM1 with the SMA in the 345GHz frequency window at a resolution of ∼1′′ and with 32GHz of continuous frequency coverage. About 400 lines weredetected from 29 different molecular species and their isotopo-logues.

We observe a chemical gradient of molecules along the axisof a disc-like structure perpendicular to the large-scale bi-polarCO emission observed in previous studies. This disc is parallelto but offset from the axis connecting the mm continuum cores(by ∼1′′). The O-bearing molecular emission peaks are close tobut offset to the west of the MM1b continuum core and are be-tween the VLA1 and VLA2 radio continuum cores, which fall onthe molecular gradient–disc axis. The N- and S-bearing specieson the other hand are concentrated closer to the MM1a core,between the VLA2 and VLA3 radio continuum cores. The disc-like structure is observed from the red- blueshifted H2CO andCS emission, which signifies infalling gas onto the surface of



the disc-like structure. This implies that the COMs observed to-wards MM1 are not purely the result of a traditional hot core,but are rather caused by a combination of processes, includingaccretion. In order to test this hypothesis, it will be useful to re-observe this source in a few years to check for time variability.

Comparing the abundances observed towards N30 MM1with other sources, we find that it is similar to the high-massprotostar AFGL 4176, and to a lesser extent to the shocked re-gion Orion KL, and to the Galactic centre source Sgr B2 (N2).The O-bearing species show similar abundances with respect toCH3OH towards these sources, whereas for Sgr B2 (N2), the N-bearing species are less abundant in N30, while the low-masssource IRAS 16293B has lower abundances in N- and S-bearingspecies; the O-bearing species are similar. The agreement withAFGL 4176 seems to suggest that N30 MM1 is at a similar stageof evolution to this source, but with the MM1b/VLA1/VLA2source at the centre of the disc-like structure probably at an ear-lier stage than the MM1a/VLA3 core, where the N- and S- bear-ing species had more time to evolve.

We observe a small difference in excitation temperature be-tween the O-bearing species and the S- and N- bearing species. Alarger difference is observed for HC3N, H13

2 CO, and t-HCOOH,which seem to trace warmer gas than the other species. Thelow levels of deuteration in N30 MM1 suggest that the grain-surface formation temperature of COMs in the pre-stellar cloudwas warm, that is, ∼30 K, probably the result of radiation fromthe nearby Cyg-OB2 association.

In conclusion, these observations highlight the benefit of be-ing able to observe large frequency ranges simultaneously andat high angular resolution in order to shed light on the phys-ical origin of COMs. Particularly, the frequency coverage en-sures that a large number of species from different chemicalfamilies are covered simultaneously, and the high angular res-olution allows spatial correlations between species to be closelyexamined. This is especially important for the physically com-plex structure of sources such as N30, which complicates ourunderstanding of the origin of COMs. It is therefore importantto study such sources with multiple chemical tracers, and at suf-ficient angular resolution to be able to disentangle the variousphysical and chemical processes taking place. Further analysisof the remaining nine sources in the PILS-Cygnus survey willclearly continue to shed light on their origin.

Acknowledgements. We acknowledge and thank the staff of the SMA for theirassistance and continued support. The authors wish to recognise and acknowl-edge the very significant cultural role and reverence that the summit of MaunaKea has always had within the indigenous Hawaiian community. We are mostfortunate to have had the opportunity to conduct observations from this moun-tain. The SMA is a joint project between the Smithsonian Astrophysical Obser-vatory and the Academia Sinica Institute of Astronomy and Astrophysics andis funded by the Smithsonian Institution and the Academia Sinica. The researchof SJvdW, LEK and MeA is supported by a research grant (19127) from VIL-LUM FONDEN. JKJ and SM acknowledge support by the European ResearchCouncil (ERC) under the European Union’s Horizon 2020 research and innova-tion programme through ERC Consolidator Grant “S4F” (grant agreement No646908). Finally, we would like to thank the anonymous referee, who providedconstructive comments that helped improve the clarity of the paper.

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Appendix A: Observing log

The full observing log is provided in Table A.1. Specifically, thisincludes the observing dates and calibrators used for each nightof the observations. The observing strategy was to observe twoscience targets between a pair of gain observations, and to loopover all ten targets in each track. This ensured uniform sensitiv-ity. Furthermore, a random source was chosen to start each track,to ensure near uniform uv coverage for all sources, and thus sim-ilar image fidelity.

Appendix B: Column density comparison

The column density comparisons with other sources at positions1 and 3 (see Fig. 12) are provided here, with the comparisonat position 2 shown and discussed in the text. There is a slightdifference, as expected from the difference in column densitiesof the different positions, with a slightly better agreement withOrion KL and AFGL 4176 at position 3.

Appendix C: Position–velocity maps

Position–velocity maps of selected molecular lines are presentedin Fig. C.1, with the maps of H2CO and CS shown (Figs. 6and 10 respectively) and discussed in the text. A full kinemat-ics study of the source is beyond the scope of this work, but itis clear from Fig. C.1 that different molecules trace different re-gions in the system, which is also seen in the molecular gradientthat we observe.

Appendix D: Molecular line plots

In this Appendix we present plots of all the lines for each ofthe molecules listed in Table 6, taken at position 2 in Fig. 12,for which we made a model fit. In all the plots, the model isoverplotted in red over the observed spectrum in black. Onlylines detected above 3σ ∼10 K intensity are shown.



Table A.1. Observing log.

Observing date No of antennas Configuration Bandpass Flux Gain τ(225 GHz)21/06/2017 7 COM 3c454.3 Titan, Neptune mwc349a 0.05–0.0722/06/2017 7 COM 3c273, 3c454.3 Titan, Neptune mwc349a 0.1027/06/2017 7 COM 3c454.3 Callisto mwc349a 0.0810/07/2017 7 COM 3c454.3 Callisto mwc349a 0.05–0.0607/08/2017 6 COM 3c84 Titan, Uranus mwc349a 0.0520/10/2017 8 EXT 3c84 Uranus mwc349a 0.02–0.0322/10/2017 7 EXT 3c84 Uranus mwc349a 0.08–0.1008/11/2017 8 EXT 3c84 Uranus mwc349a 0.0709/11/2017 7 EXT 3c84 Uranus mwc349a 0.0710/11/2017 8 EXT 3c84 Uranus mwc349a 0.07



0.0 0.2 0.4 0.6 0.8 1.0N(X) / N(CH3OH)

0.0

0.2

0.4

0.6

0.8

1.0N

(X) /

N(C

H 3OH

) (N3

0 - P

ositi

on 1

)

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 Sgr B2 (N2)

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 Comet 67P

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 IRAS 16293B

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 Orion KL

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 AFGL 4176

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 HH212

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1


Fig. B.1. Column densities towards N30, position 1, with respect to CH3OH, on the y-axis, compared to different sources plotted on the x-axis.The solid line represents equal abundances, whereas the dotted lines represent an order of magnitude difference.



0.0 0.2 0.4 0.6 0.8 1.0N(X) / N(CH3OH)

0.0

0.2

0.4

0.6

0.8

1.0N

(X) /

N(C

H 3OH

) (N3

0 - P

ositi

on 3

)

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 Sgr B2 (N2)

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 Comet 67P

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 IRAS 16293B

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 Orion KL

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 AFGL 4176

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1

100 HH212

10 5 10 4 10 3 10 2 10 1 10010 5

10 4

10 3

10 2

10 1


Fig. B.2. Column densities towards N30, position 3, with respect to CH3OH, on the y-axis, compared to different sources plotted on the x-axis.The solid line represents equal abundances, whereas the dotted lines represent an order of magnitude difference.



10 3 10 2 10 1 100


10 2

10 1

100

N(X

) / N

(CH 3

OH)

H 2CO

C 2H 5

OH

CH3O

CH3

CH3O

CHO

t-HCO

OH


Fig. B.3. Column densities with respect to CH3OH towards N30, po-sition 1, on the x-axis, compared to different sources plotted on they-axis. Each source is marked with a different marker. The solid anddotted lines are as in Fig. 21

10 3 10 2 10 1 100


10 2

10 1

100

N(X

) / N

(CH 3

OH)

H 2CO

C 2H 5

OH

CH3O

CH3

CH3O

CHO

t-HCO

OH


Fig. B.4. Column densities with respect to CH3OH towards N30, po-sition 3, on the x-axis, compared to different sources plotted on they-axis. Each source is marked with a different marker. The solid anddotted lines are as in Fig. B.1

10 2 10 1 100 101


10 2

10 1

100

101

102

N(X

) / N

(CH 3

CN,S

O 2)

HNCO

HC3N

H 2CS


Fig. B.5. Column densities towards N30 position 1 (on the x-axis), withrespect to CH3CN, for the N-bearing species, and SO2 for H2CS, com-pared to different sources plotted on the y-axis. Each source is markedwith a different marker. The solid and dotted lines are as in Fig. B.1

10 2 10 1 100 101


10 2

10 1

100

101

102

N(X

) / N

(CH 3

CN,S

O 2)

HNCO

HC3N

H 2CS


Fig. B.6. Column densities towards N30 position 3 (on the x-axis), withrespect to CH3CN, for the N-bearing species, and SO2 for H2CS, com-pared to different sources plotted on the y-axis. Each source is markedwith a different marker. The solid and dotted lines are as in Fig. B.1



0.0 0.2 0.4 0.6 0.8 1.0Offset ["]

0.0

0.2

0.4

0.6

0.8

1.0

Velo

city

[km

s1 ]

5.0 2.5 0.0 2.5 5.00.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5SO 344.311 GHz

0

2

4

6

8

10

12

14

Jy.b

eam

1

5.0 2.5 0.0 2.5 5.00.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5 SO2 351.874 GHz

0

2

4

6

8

10

Jy.b

eam

1

5.0 2.5 0.0 2.5 5.00.0

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5.0

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20.0 CH3OH 331.502 GHz

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17.5CH3OH 338.615 GHz

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5.0 2.5 0.0 2.5 5.00.0

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17.5CH3OCH3 342.608 GHz

0.50.00.51.01.52.02.53.03.5

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5.0 2.5 0.0 2.5 5.00.0

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17.5 CH3OCHO 360.466 GHz

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20.0 CH3CN 331.014 GHz

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20.0 HNCO 329.664 GHz

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Fig. C.1. Position–velocity maps of selected molecular lines. The red vertical line represents the position of 0 ′′ offset from the centre positionbetween the peak red- and blueshifted H2CO emission (see 6). The horizontal line represents the systemic velocity, also for H2CO.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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1.0Br

ight

ness

tem

pera

ture

[K]

10 0 10 20 3010

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40 Frequency = 330.0018 GHz, Eup = 76.499 K

10 0 10 20 30

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Frequency = 330.194 GHz, Eup = 69.013 K

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30Frequency = 330.3191 GHz, Eup = 202.002 K

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Fig. D.1. 13CH3OH synthetic spectrum overplotted on the observed spectrum. The fitted values obtained were column density = 1.3 ×1016cm−2,excitation temperature (Tex) = 120.0 K, line width (FWHM) = 4.5 km s−1, and source velocity (3source) = 9.0 km s−1.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

0.0

0.2

0.4

0.6

0.8

1.0Br

ight

ness

tem

pera

ture

[K]

10 0 10 20 3010

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Fig. D.2. 13CH3OH synthetic spectrum overplotted on the observed spectrum. The fitted values obtained were column density = 1.3×1016cm−2,excitation temperature (Tex) = 120.0 K, line width (FWHM) = 4.5 km s−1, and source velocity (3source) = 9.00 km s−1.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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1.0Br

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[K]

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75

100


Fig. D.3. CH3OH observed spectral lines. In this case the column density was obtained by multiplying the fitted column density of 13CH3OH withthe ISM isotopologue ratio of 12C/13C = 77. The obtained column density was 1.0×1019cm−2.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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[K]

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0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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[K]

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0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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[K]

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0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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1.0Br

ight

ness

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pera

ture

[K]

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Fig. D.8. C2H5OH model lines and synthetic spectrum. The model fitted values obtained were column density = 6.7×1016cm−2, excitation temper-ature (Tex) = 130.0 K, line width (FWHM) = 5.0 km s−1, and source velocity (3source) = 9.5.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

0.0

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1.0Br

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ture

[K]

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Fig. D.9. CH3OCHO model lines and synthetic spectrum. The model fitted values obtained were column density = 1.4×1017cm−2, excitationtemperature (Tex) = 110.0 K, line width (FWHM) = 4.5 km s−1, and source velocity (3source) = 9.0 km s−1.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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ture

[K]

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0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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40


Fig. D.14. CH3OCH3 model lines and synthetic spectrum. The model fitted values obtained were column density = 2.4×1017cm−2, excitationtemperature (Tex) = 110.0 K, line width (FWHM) = 5.0 km s−1, and source velocity (3source) = 9.0 km s−1.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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]

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Fig. D.17. H213CO model lines and synthetic spectrum. The model fitted values obtained were column density = 7.6×1015cm−2, excitation tem-

perature (Tex) = 160.0 K, line width (FWHM) = 8.0 km s−1, and source velocity (3source) = 9.0 km s−1.



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Fig. D.18. t-HCOOH model lines and synthetic spectrum. The model fitted values obtained were column density = 4.0×1016cm−2, excitationtemperature (Tex) = 190.0 K, line width (FWHM) = 7.0 km s−1, and source velocity (3source) = 11.0 km s−1.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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20


Fig. D.19. t-HCOOH model lines and synthetic spectrum. The model fitted values obtained were column density = 4.0×1016cm−2, excitationtemperature (Tex) = 190.0 K, line width (FWHM) = 7.0 km s−1, and source velocity (3source) = 11.0 km s−1.

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Fig. D.20. 33SO model lines and synthetic spectrum. The model fitted values obtained were column density = 5.0×1015cm−2, excitation temperature(Tex) = 140.0 K, line width (FWHM) = 6.5 km s−1, and source velocity (3source) = 10.0 km s−1.



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Fig. D.21. 34SO2 model lines and synthetic spectrum. The model fitted values obtained were column density = 3.3×1016cm−2, excitation tempera-ture (Tex) = 130.0 K, line width (FWHM) = 6.0 km s−1, and source velocity (3source) = 10.0 km s−1.



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Fig. D.22. SO2 observed spectral lines. In this case the column density was obtained by multiplying the fitted column density of 34SO2 with theISM isotopologue ratio of 34S/32S = 22. The obtained column density was 7.3×1017cm−2.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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Fig. D.23. SO2 observed spectral lines. In this case the column density was obtained by multiplying the fitted column density of 34SO2 with theISM isotopologue ratio of 34S/32S = 22. The obtained column density was 7.3×1017cm−2.



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Fig. D.24. H2CS model lines and synthetic spectrum. The model fitted values obtained were column density = 3.3×1016cm−2, excitation tempera-ture (Tex) = 140.0 K, line width (FWHM) = 5.5 km s−1, and source velocity (3source) = 9.0 km s−1.

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Fig. D.25. OC34S model lines and synthetic spectrum. The model fitted values obtained were column density = 1.1×1016cm−2, excitation temper-ature (Tex) = 170.0 K, line width (FWHM) = 5.0 km s−1, and source velocity (3source) = 10.0 km s−1

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Fig. D.26. OCS observed spectral lines. In this case the column density was obtained by multiplying the fitted column density of OC34S with theISM isotopologue ratio of 34S/32S = 22. The obtained column density was 2.4×1017cm−2.



0.0 0.2 0.4 0.6 0.8 1.0Velocity [km s 1]

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Fig. D.27. HNCO model lines and synthetic spectrum. The model fitted values obtained were column density = 5.0×1016cm−2, excitation temper-ature (Tex) = 150.0 K, line width (FWHM) = 6.5 km s−1, and source velocity (3source) = 10.5 km s−1.

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Fig. D.28. HC3N model lines and synthetic spectrum. The model fitted values obtained were column density = 4.0×1016cm−2, excitation tempera-ture (Tex) = 210.0 K, line width (FWHM) = 7.0 km s−1, and source velocity (3source) = 10.0 km s−1.



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Fig. D.29. CH3CN, v8=1 model lines and synthetic spectrum. The model fitted values obtained were column density = 5.5×1016cm−2, excitationtemperature (Tex) = 140.0 K, line width (FWHM) = 7.0 km s−1, and source velocity (3source) = 10.5 km s−1.



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Fig. D.30. CH3CN, v=0 observed spectral lines. In this case the column density was obtained using the higher energy v = 1 transition. The obtainedcolumn density was 5.5×1016cm−2.



Table 8. Detected molecular transitions. The listed line transitions are from bestfit line models obtained using the software package CASSIS, on the spectrumtaken at the position of peak emission of CH3OH (position 2 in Fig. 12). Themodel parameters are listed in Table 6. Only transitions above 10 K are listed(∼ 3σ), corresponding to about 1.0 Jy beam−1.

Frequency Molecule Transition Eup/kB Aij Opacity (τ)[GHz] [K] ×10−4[s−1]329.330552 C18O 3 − 2 31.61 0.02 1.39329.385477 SO 21 − 10 15.81 0.14 0.64329.459589 HNCO 153,13 − 143,12 501.48 4.34 0.13329.459599 HNCO 153,12 − 143,11 501.48 4.34 0.13329.573452 HNCO 152,14 − 142,13 296.83 4.72 0.62329.584800 HNCO 152,13 − 142,12 296.83 4.72 0.62329.632881 CH3OH 122,10,0 − 113,9,0 218.80 0.60 61.09329.664367 HNCO 150,15 − 140,14 126.58 5.04 2.24329.861407 CH3OCHO 275,23,1 − 265,22,1 241.00 5.23 0.24329.874892 CH3OCHO 275,23,0 − 265,22,0 241.00 5.23 0.24330.001752 13CH3OH 70,7,0 − 60,6,0 76.50 1.58 0.84330.194042 13CH3OH 7−1,7,0 − 6−1,6,0 69.01 1.55 0.88330.252798 13CH3OH 70,7,+0 − 60,6,+0 63.41 1.58 0.94330.289345 13CH3OH 7−5,2,0 − 6−5,1,0 188.13 0.77 0.16330.309191 13CH3OH 75,3,0 − 65,2,0 200.19 0.77 0.15330.319110 13CH3OH 75,2,−0 − 65,1,−0 202.00 0.78 0.14330.336917 13CH3OH 7−4,4,0 − 6−4,3,0 151.77 1.06 0.30330.342534 13CH3OH 74,4,−0 − 64,3,−0 144.21 1.07 0.32330.349987 13CH3OH 72,6,−0 − 62,5,−0 101.23 1.46 0.63330.355512 CH3OH 203,17,0 − 194,16,0 537.04 0.64 4.41330.362042 13CH3OH 74,3,0 − 64,2,0 159.85 1.07 0.28330.371293 13CH3OH 73,5,+0 − 63,4,+0 113.47 1.29 0.50330.373443 13CH3OH 73,4,−0 − 63,3,−0 113.47 1.29 0.50330.391188 13CH3OH 7−3,5,0 − 6−3,4,0 126.37 1.30 0.45330.405456 CH3OCH3 162,15,3 − 151,14,3 128.46 1.65 0.10330.406503 CH3OCH3 162,15,1 − 151,14,1 128.46 1.65 0.41330.407549 CH3OCH3 162,15,0 − 151,14,0 128.46 1.65 0.26330.408395 13CH3OH 73,4,0 − 63,3,0 111.39 1.29 0.51330.442421 13CH3OH 71,6,0 − 61,5,0 84.49 1.59 0.79330.463873 13CH3OH 111,10,−0 − 110,11,+0 165.27 3.90 1.51330.464947 13CH3OH 72,5,+0 − 62,4,+0 101.24 1.46 0.63330.535222 13CH3OH 72,5,0 − 62,4,0 85.80 1.44 0.71330.535890 13CH3OH 7−2,6,0 − 6−2,5,0 89.45 1.46 0.69330.557569 CH3CN, v=0 189,0 − 17−9,0 728.67 23.60 0.08330.587965 13CO 3 − 2 31.73 0.02 1.45330.760284 CH3CN, v=0 187,0 − 177,0 500.65 26.80 0.41330.793887 CH3OH 83,5,2 − 92,7,2 146.28 0.54 76.08330.842762 CH3CN, v=0 186,0 − 17−6,0 407.94 28.00 0.80330.848569 HNCO 151,14 − 141,13 170.31 5.01 1.62330.912608 CH3CN, v=0 185,0 − 175,0 329.46 29.10 1.41330.969794 CH3CN, v=0 184,0 − 174,0 265.22 30.00 2.22331.014296 CH3CN, v=0 183,0 − 17−3,0 215.24 30.70 3.17331.046096 CH3CN, v=0 182,0 − 172,0 179.53 31.20 4.09331.065182 CH3CN, v=0 181,0 − 171,0 158.11 31.50 4.76331.071544 CH3CN, v=0 180,0 − 170,0 150.96 31.60 5.01331.149215 CH3OCHO 284,25,1 − 274,24,1 247.76 5.34 0.23331.159562 CH3OCHO 284,25,0 − 274,24,0 247.76 5.34 0.23331.160928 CH3OCHO 2711,17,3 − 2611,16,3 490.18 4.62 0.02331.459814 CH3OCHO 283,25,2 − 273,24,2 247.74 5.36 0.23331.469465 CH3OCHO 283,25,0 − 273,24,0 247.74 5.36 0.23331.469664 CH3OCHO 96,4,0 − 85,4,1 138.16 1.61 0.04331.502319 CH3OH 111,10,0 − 110,11,0 169.01 3.93 595.50331.580244 SO2 116,6 − 125,7 148.95 0.43 0.80331.748518 CH3CN, v8=1 18−1,3 − 171,3 670.28 31.40 0.15331.755099 CH3OH 155,10,5 − 166,11,5 823.92 1.27 0.37



Table 8. continued.

Frequency Molecule Transition Eup/kB Aij Opacity (τ)[GHz] [K] ×10−4[s−1]331.784009 CH3OCHO 293,27,1 − 283,26,1 253.07 5.43 0.23331.788199 CH3OCHO 311,31,4 − 301,30,4 445.37 6.26 0.05331.792159 CH3OCHO 293,27,0 − 283,26,0 253.06 5.43 0.23331.795710 CH3OCHO 292,27,2 − 282,26,2 253.07 5.43 0.23331.803922 CH3OCHO 292,27,0 − 282,26,0 253.06 5.43 0.23331.992354 CH3CN, v8=1 182,2 − 17−2,2 731.74 31.20 0.09332.015818 CH3CN, v8=1 180,2 − 170,2 676.58 31.60 0.14332.017856 CH3CN, v8=1 181,2 − 171,2 697.02 31.50 0.12332.028758 CH3CN, v8=1 184,3 − 17−4,3 737.59 30.00 0.09332.091431 SO2 212,20 − 211,21 219.53 1.51 3.00332.120135 CH3OCHO 231,22,1 − 222,20,0 292.14 0.34 0.01332.129700 OC34S 28 − 27 231.16 1.07 0.15332.173573 34SO2 233,21 − 232,22 274.74 2.54 0.16332.387753 CH3CN, v8=1 181,3 − 17−1,3 670.57 31.60 0.15332.505242 SO2 43,1 − 32,2 31.29 3.29 5.82332.570617 CH3OCHO 301,29,2 − 292,28,1 256.98 0.80 0.03332.570888 CH3OCHO 302,29,1 − 292,28,1 256.98 5.53 0.23332.571107 CH3OCHO 301,29,2 − 291,28,2 256.98 5.53 0.23332.571378 CH3OCHO 302,29,1 − 291,28,2 256.98 0.80 0.03332.575715 CH3OCHO 301,29,0 − 292,28,0 256.96 0.80 0.03332.575985 CH3OCHO 302,29,0 − 292,28,0 256.96 5.53 0.23332.576202 CH3OCHO 301,29,0 − 291,28,0 256.96 5.53 0.23332.576472 CH3OCHO 302,29,0 − 291,28,0 256.96 0.80 0.03332.603808 CH3OCHO 2714,13,2 − 2614,12,2 353.08 4.11 0.07332.604456 CH3OCHO 2714,13,0 − 2614,12,0 353.08 4.11 0.07332.836225 34SO2 164,12 − 163,13 162.90 3.02 0.32332.958301 CH3OCHO 2713,15,0 − 2613,14,0 335.28 4.33 0.08332.996563 CH3OH 222,20,2 − 213,18,2 614.49 0.63 2.16333.114779 13CH3OH 71,6,−0 − 61,5,−0 78.52 1.59 0.82333.419204 CH3OCHO 2712,16,0 − 2612,15,0 318.83 4.54 0.10333.448976 CH3OCHO 311,31,1 − 301,30,1 259.59 5.73 0.24333.449419 CH3OCHO 311,31,0 − 301,30,0 259.57 5.64 0.24333.593050 CH3OCHO 274,23,2 − 264,22,2 240.60 5.42 0.24333.601947 CH3OCHO 274,23,0 − 264,22,0 240.60 5.42 0.24333.864722 CH3OH 91,8,1 − 82,6,2 125.52 0.01 1.53333.900983 34SO 87 − 76 79.86 4.69 1.81334.031781 CH3OCHO 2711,17,0 − 2611,16,0 303.76 4.74 0.12334.265833 t-HCOOH 152,14 − 142,13 141.58 4.17 0.18334.426571 CH3OH 30,3,4 − 21,2,4 314.47 0.56 5.88334.673353 SO2 82,6 − 71,7 43.15 1.27 3.83335.133570 CH3OH 22,1,0 − 31,2,0 44.67 0.27 30.12335.395500 HDO 33,1 − 42,2 335.27 0.26 0.19335.560207 13CH3OH 121,11,−0 − 120,12,+0 192.66 4.04 1.32335.582017 CH3OH 71,7,0 − 61,6,0 78.97 1.63 386.60336.028165 CH3OCHO 279,19,0 − 269,18,0 277.85 5.14 0.16336.032357 CH3OCHO 279,19,1 − 269,18,1 277.85 4.90 0.15336.089228 SO2 233,21 − 232,22 276.02 2.67 3.68336.351390 CH3OCHO 276,22,1 − 266,21,1 249.36 5.49 0.22336.354829 CH3OCHO 265,21,2 − 255,20,2 230.58 5.57 0.26336.365317 CH3OCHO 156,9,5 − 145,9,5 282.13 0.37 0.01336.368224 CH3OCHO 276,22,0 − 266,21,0 249.36 5.49 0.22336.373878 CH3OCHO 265,21,0 − 255,20,0 230.58 5.57 0.26336.438224 CH3OH 147,7,0 − 156,9,0 488.22 0.36 2.76336.520084 HC3N 37 − 36 306.91 30.50 0.56336.553811 SO 1110 − 1010 142.88 0.06 0.70336.605889 CH3OH 71,7,6 − 61,6,6 747.41 1.64 0.48336.669581 SO2 167,9 − 176,12 245.12 0.58 0.71336.865149 CH3OH 121,11,0 − 120,12,0 197.07 4.07 491.30336.918184 CH3OCHO 266,20,0 − 256,19,0 235.47 5.53 0.24



Table 8. continued.

Frequency Molecule Transition Eup/kB Aij Opacity (τ)[GHz] [K] ×10−4[s−1]337.060513 C17O 31.5 − 22.5 32.35 0.00 0.00337.060709 C17O 30.5 − 21.5 32.35 0.01 0.00337.060831 C17O 32.5 − 23.5 32.35 0.00 0.00337.060936 C17O 32.5 − 22.5 32.35 0.01 0.01337.060988 C17O 34.5 − 23.5 32.35 0.02 0.04337.060988 C17O 35.5 − 24.5 32.35 0.02 0.06337.061050 C17O 31.5 − 21.5 32.35 0.01 0.01337.061123 C17O 33.5 − 23.5 32.35 0.01 0.01337.061214 C17O 30.5 − 20.5 32.35 0.02 0.01337.061226 C17O 33.5 − 22.5 32.35 0.01 0.02337.061471 C17O 32.5 − 21.5 32.35 0.01 0.01337.061553 C17O 31.5 − 20.5 32.35 0.01 0.01337.061951 C17O 34.5 − 24.5 32.35 0.00 0.01337.062093 C17O 33.5 − 24.5 32.35 0.00 0.00337.135853 CH3OH 33,1,1 − 42,3,1 61.64 0.16 20.65337.186488 CH3OH 70,7,7 − 60,6,7 798.97 1.68 0.30337.197845 33SO 87,7.5 − 76,6.5 80.53 4.70 0.07337.198488 CH3OH 75,3,8 − 65,2,8 698.08 0.83 0.40337.198620 33SO 87,8.5 − 76,7.5 80.53 4.83 0.08337.199371 33SO 87,5.5 − 76,4.5 80.54 4.65 0.05337.252172 CH3OH 73,5,6 − 63,4,6 722.84 1.39 0.52337.273561 CH3OH 74,4,6 − 64,3,6 679.25 1.13 0.66337.279180 CH3OH 72,5,8 − 62,4,8 709.70 1.54 0.66337.284320 CH3OH 70,7,6 − 60,6,6 572.96 1.68 2.84337.295913 CH3OH 73,5,7 − 63,4,7 686.20 1.37 0.74337.297484 CH3OH 71,7,3 − 61,6,3 390.02 1.65 17.36337.302644 CH3OH 72,6,7 − 62,5,7 650.99 1.55 1.20337.312360 CH3OH 71,7,8 − 61,6,8 596.79 1.65 2.19337.337010 CH3OH 234,20,4 − 222,20,4 1001.45 0.00 0.00337.396459 C34S 70 − 60 64.77 8.00 0.48337.420459 CH3OCH3 212,19,0 − 203,18,0 220.14 1.11 0.09337.421003 CH3OCH3 212,19,1 − 203,18,1 220.14 1.11 0.15337.421547 CH3OCH3 212,19,5 − 203,18,5 220.14 1.11 0.06337.429366 t-HCOOH 159,6 − 149,5 386.63 2.80 0.03337.444214 t-HCOOH 158,7 − 148,6 332.76 3.13 0.05337.463703 CH3OH 76,1,3 − 66,0,3 533.02 0.45 1.13337.490562 CH3OH 76,2,5 − 66,1,5 558.25 0.44 0.86337.491036 t-HCOOH 157,9 − 147,8 285.19 3.42 0.07337.519138 CH3OH 73,4,4 − 63,3,4 482.23 1.38 5.77337.546116 CH3OH 75,2,3 − 65,1,3 485.37 0.82 3.31337.580147 34SO 88 − 77 86.07 4.89 1.99337.581680 CH3OH 74,4,4 − 64,3,4 428.20 1.13 8.09337.587936 t-HCOOH 1514,1 − 1414,0 749.92 0.56 0.00337.590319 t-HCOOH 156,9 − 146,8 243.95 3.68 0.09337.605288 CH3OH 72,6,5 − 62,5,5 429.43 1.56 11.02337.610661 CH3OH 73,5,5 − 63,4,5 387.45 1.37 14.77337.625753 CH3OH 72,6,3 − 62,5,3 363.50 1.55 21.13337.635754 CH3OH 72,5,3 − 62,4,3 363.50 1.55 21.13337.642478 CH3OH 71,7,4 − 61,6,4 356.30 1.65 24.26337.643915 CH3OH 70,7,4 − 60,6,4 365.40 1.69 22.64337.646042 CH3OH 74,3,5 − 64,2,5 470.22 1.14 5.33337.648209 CH3OH 75,2,5 − 65,1,5 610.96 0.83 0.95337.655199 CH3OH 73,5,3 − 63,4,3 460.94 1.38 7.09337.671238 CH3OH 72,5,4 − 62,4,4 464.72 1.55 7.70337.685248 CH3OH 75,3,4 − 65,2,4 493.95 0.83 3.07337.707568 CH3OH 71,6,5 − 61,5,5 478.21 1.65 7.16337.722348 CH3OCH3 74,4,1 − 63,3,1 47.98 0.96 0.22337.723002 CH3OCH3 74,4,5 − 63,3,5 47.98 1.94 0.05337.723390 CH3OCH3 312,30,0 − 311,31,0 447.56 0.61 0.01



Table 8. continued.

Frequency Molecule Transition Eup/kB Aij Opacity (τ)[GHz] [K] ×10−4[s−1]337.730739 CH3OCH3 74,4,0 − 63,3,0 47.98 1.94 0.16337.731869 CH3OCH3 74,4,3 − 63,3,3 47.98 1.22 0.07337.732193 CH3OCH3 74,3,1 − 63,3,1 47.98 0.98 0.22337.748830 CH3OH 70,7,3 − 60,6,3 488.49 1.69 6.61337.778023 CH3OCH3 74,4,1 − 63,4,1 47.98 0.98 0.22337.779477 CH3OCH3 74,3,5 − 63,4,5 47.98 1.94 0.16337.785430 t-HCOOH 155,11 − 145,10 209.05 3.90 0.12337.787213 CH3OCH3 74,3,0 − 63,4,0 47.98 1.94 0.27337.787868 CH3OCH3 74,3,1 − 63,4,1 47.98 0.96 0.22337.787949 t-HCOOH 155,10 − 145,9 209.05 3.90 0.12337.790087 CH3OCH3 74,4,3 − 63,4,3 47.98 0.72 0.04337.837801 CH3OH 206,14,2 − 215,17,2 675.95 0.60 0.99337.877550 CH3OH 71,6,6 − 61,5,6 747.65 1.65 0.48337.969438 CH3OH 71,6,3 − 61,5,3 390.15 1.66 17.37338.083195 H2CS 101,10 − 91,9 102.43 5.77 1.73338.124488 CH3OH 70,7,1 − 60,6,1 78.08 1.70 400.70338.201860 t-HCOOH 153,13 − 143,12 158.34 4.23 0.17338.248816 t-HCOOH 154,11 − 144,10 180.54 4.09 0.14338.305993 SO2 184,14 − 183,15 196.80 3.27 6.43338.320356 34SO2 132,12 − 121,11 92.45 2.27 0.33338.344588 CH3OH 71,7,2 − 61,6,2 70.55 1.67 424.10338.404610 CH3OH 76,2,1 − 66,1,1 243.79 0.45 20.32338.408698 CH3OH 70,7,0 − 60,6,0 64.98 1.70 457.60338.430975 CH3OH 76,1,2 − 66,0,2 253.95 0.45 18.46338.442367 CH3OH 76,1,0 − 66,0,0 258.70 0.45 17.56338.456536 CH3OH 75,3,2 − 65,2,2 189.00 0.83 64.94338.475226 CH3OH 75,2,1 − 65,1,1 201.06 0.83 57.59338.486322 CH3OH 75,2,0 − 65,1,0 202.88 0.84 56.78338.504065 CH3OH 74,4,2 − 64,3,2 152.89 1.15 128.00338.512632 CH3OH 74,4,0 − 64,3,0 145.33 1.15 138.20338.530257 CH3OH 74,3,1 − 64,2,1 160.99 1.15 118.70338.540826 CH3OH 73,5,0 − 63,4,0 114.79 1.39 226.80338.543152 CH3OH 73,4,0 − 63,3,0 114.79 1.39 226.80338.559963 CH3OH 73,4,2 − 63,3,2 127.71 1.40 200.70338.583216 CH3OH 73,5,1 − 63,4,1 112.71 1.39 232.30338.611810 SO2 201,19 − 192,18 198.88 2.87 6.15338.614936 CH3OH 71,6,1 − 61,5,1 86.05 1.71 372.40338.639802 CH3OH 72,5,0 − 62,4,0 102.72 1.58 290.30338.721693 CH3OH 72,6,1 − 62,5,1 87.26 1.55 333.20338.722898 CH3OH 72,5,2 − 62,4,2 90.91 1.57 325.00338.759948 13CH3OH 130,13,+0 − 121,12,+0 205.95 2.18 0.67338.785687 34SO2 144,10 − 143,11 134.34 3.08 0.34339.341459 SO 33 − 23 25.51 0.14 1.34339.398442 CH3OCHO 117,4,2 − 116,5,2 116.89 1.71 0.06339.398465 CH3OCHO 117,5,2 − 116,6,2 116.89 1.71 0.06339.491473 CH3OCH3 191,18,0 − 182,17,0 176.10 2.03 0.23339.491586 CH3OCH3 191,18,5 − 182,17,5 176.10 2.03 0.14339.857269 34SO 89 − 78 77.34 5.08 2.44339.978923 CH3OCHO 94,6,2 − 83,5,2 57.90 2.11 0.10340.052575 C33S 70 − 60 65.28 8.19 0.27340.141143 CH3OH 22,0,0 − 31,3,0 44.67 0.28 30.23340.189247 CH3OCHO 65,2,2 − 54,1,2 49.00 3.42 0.12340.229102 t-HCOOH 153,12 − 143,11 158.64 4.30 0.17340.316406 SO2 282,26 − 281,27 391.80 2.58 1.73340.393659 CH3OH 166,11,0 − 175,12,0 509.17 0.50 3.41340.449273 OCS 28 − 27 236.95 1.15 1.79340.612619 CH3OCH3 103,7,1 − 92,8,1 62.81 1.23 0.34340.683969 CH3OH 111,11,4 − 100,10,4 444.25 1.10 10.10340.714155 SO 87 − 76 81.25 4.99 63.85340.741990 CH3OCHO 285,24,1 − 275,23,1 257.35 5.78 0.22



Table 8. continued.

Frequency Molecule Transition Eup/kB Aij Opacity (τ)[GHz] [K] ×10−4[s−1]340.754756 CH3OCHO 285,24,0 − 275,23,0 257.35 5.78 0.22340.837357 33SO 88,6.5 − 77,5.5 86.75 4.89 0.06340.838679 33SO 88,8.5 − 77,7.5 86.75 4.92 0.07340.839639 33SO 88,9.5 − 77,8.5 86.75 5.03 0.08341.131665 13CH3OH 131,12,−0 − 130,13,+0 222.32 4.19 1.12341.275524 SO2 218,14 − 227,15 369.13 0.69 0.41341.403068 SO2 404,36 − 403,37 808.37 4.11 0.16341.415615 CH3OH 71,6,0 − 61,5,0 80.09 1.71 389.60341.673961 SO2 365,31 − 364,32 678.52 4.34 0.41341.722187 CH3OCHO 294,26,1 − 284,25,1 264.17 5.88 0.21341.732284 CH3OCHO 294,26,0 − 284,25,0 264.16 5.88 0.21341.917897 CH3OCHO 293,26,2 − 283,25,2 264.15 5.89 0.22341.927501 CH3OCHO 293,26,0 − 283,25,0 264.15 5.89 0.22342.208857 34SO2 53,3 − 42,2 35.10 3.10 0.28342.231633 34SO2 201,19 − 192,18 198.24 3.06 0.29342.332013 34SO2 124,8 − 123,9 109.51 3.06 0.35342.350119 CH3OCHO 302,28,0 − 293,27,0 269.49 0.77 0.03342.351420 CH3OCHO 303,28,1 − 293,27,1 269.50 5.98 0.21342.358225 CH3OCHO 302,28,2 − 292,27,2 269.50 5.98 0.21342.359508 CH3OCHO 303,28,0 − 293,27,0 269.49 5.98 0.21342.366296 CH3OCHO 302,28,0 − 292,27,0 269.49 5.98 0.21342.367680 CH3OCHO 303,28,1 − 292,27,2 269.50 0.77 0.03342.521194 t-HCOOH 161,16 − 151,15 143.59 4.56 0.20342.607898 CH3OCH3 190,19,5 − 181,18,5 167.14 3.30 0.24342.726474 CH3OH 206,15,5 − 197,13,5 978.98 0.68 0.05342.729796 CH3OH 131,12,0 − 130,13,0 227.47 4.23 393.60342.761625 SO2 343,31 − 342,32 581.92 3.45 0.64342.882850 CS 70 − 60 65.83 8.40 7.64342.941346 H2CS 107,3 − 97,2 733.25 3.10 0.01342.946424 H2CS 100,10 − 90,9 90.59 6.08 0.65343.086102 33SO 89,7.5 − 78,6.5 78.03 5.11 0.07343.087298 33SO 89,8.5 − 78,7.5 78.03 5.09 0.08343.088078 33SO 89,9.5 − 78,8.5 78.03 5.13 0.09343.147898 CH3OCHO 311,30,2 − 302,29,1 273.44 0.89 0.03343.149303 CH3OCHO 175,12,0 − 164,13,0 107.81 0.25 0.02343.153227 CH3OCHO 311,30,0 − 301,29,0 273.43 6.08 0.22343.309830 H2CS 104,7 − 94,6 301.07 5.12 0.12343.322082 H2CS 102,9 − 92,8 143.31 5.86 0.43343.325713 H2

13CO 51,5 − 41,4 61.28 11.20 0.55343.409963 H2CS 103,8 − 93,7 209.10 5.56 0.76343.414146 H2CS 103,7 − 93,6 209.10 5.56 0.76343.435260 CH3OCHO 284,24,2 − 274,23,2 257.08 5.92 0.22343.443944 CH3OCHO 284,24,0 − 274,23,0 257.08 5.92 0.22343.599019 CH3OH 131,12,5 − 142,13,5 624.04 0.36 0.63343.731783 CH3OCHO 277,20,2 − 267,19,2 258.47 5.77 0.20343.753320 CH3OCH3 172,16,3 − 161,15,3 143.70 1.96 0.10343.754216 CH3OCH3 172,16,1 − 161,15,1 143.70 1.96 0.42343.755112 CH3OCH3 172,16,0 − 161,15,0 143.70 1.96 0.16343.813168 H2CS 102,8 − 92,7 143.38 5.88 0.43343.952343 t-HCOOH 151,14 − 141,13 136.28 4.60 0.20343.983268 OC34S 29 − 28 247.67 1.19 0.15344.029259 CH3OCHO 320,32,2 − 311,31,1 276.10 0.77 0.03344.040629 13CH3OH 8−3,6,0 − 9−2,8,0 144.49 0.61 0.19344.109039 CH3OH 182,17,1 − 173,15,1 419.40 0.68 12.63344.200109 HC15N 4 − 3 41.30 18.80 1.34344.245346 34SO2 104,6 − 103,7 88.38 2.96 0.33344.310612 SO 88 − 77 87.48 5.19 70.30344.312267 CH3OH 102,9,5 − 113,9,5 491.91 1.77 9.01344.357816 CH3OCH3 191,19,3 − 180,18,3 167.18 3.36 0.16



Table 8. continued.

Frequency Molecule Transition Eup/kB Aij Opacity (τ)[GHz] [K] ×10−4[s−1]344.358041 CH3OCH3 191,19,0 − 180,18,0 167.18 3.36 0.24344.443433 CH3OH 191,19,0 − 182,16,0 451.23 0.73 10.38344.515385 CH3OCH3 113,9,1 − 102,8,1 72.78 1.30 0.35344.518572 CH3OCH3 113,9,0 − 102,8,0 72.78 1.30 0.13344.581045 34SO2 191,19 − 180,18 167.41 5.16 0.58344.807915 34SO2 134,10 − 133,11 121.46 3.17 0.35344.970808 CH3OH 127,5,4 − 116,5,4 761.59 0.89 0.36344.987585 34SO2 154,12 − 153,13 148.13 3.27 0.34344.998160 34SO2 114,8 − 113,9 98.48 3.05 0.34345.030561 t-HCOOH 160,16 − 150,15 143.05 4.66 0.20345.067795 CH3OCHO 2814,14,2 − 2714,13,2 369.64 4.71 0.06345.069059 CH3OCHO 2814,15,0 − 2714,14,0 369.64 4.71 0.06345.132599 13CH3OH 40,4,0 − 3−1,3,0 35.76 0.82 0.34345.285620 34SO2 94,6 − 93,7 79.20 2.88 0.31345.338538 SO2 132,12 − 121,11 92.98 2.38 7.31345.448984 SO2 269,17 − 278,20 521.00 0.76 0.17345.466962 CH3OCHO 2813,16,0 − 2713,15,0 351.86 4.94 0.08345.519656 34SO2 74,4 − 73,5 63.61 2.59 0.25345.553093 34SO2 64,2 − 63,3 57.19 2.35 0.20345.609010 HC3N 38 − 37 323.49 33.00 0.55345.795990 CO 3 − 2 33.19 0.03 -345.903916 CH3OH 161,15,0 − 152,14,0 332.65 1.04 40.61345.919260 CH3OH 183,15,2 − 174,14,2 459.43 0.73 8.98345.929349 34SO2 174,14 − 173,15 178.51 3.37 0.31345.985381 CH3OCHO 2812,17,0 − 2712,16,0 335.44 5.16 0.09346.202719 CH3OH 54,2,0 − 63,3,0 115.16 0.22 24.87346.204271 CH3OH 54,1,0 − 63,4,0 115.16 0.22 24.87346.523878 SO2 164,12 − 163,13 164.47 3.39 7.29346.528481 SO 89 − 78 78.78 5.38 86.10346.652169 SO2 191,19 − 180,18 168.14 5.22 12.89346.718858 t-HCOOH 152,13 − 142,12 144.46 4.66 0.19346.998344 H13CO+ 4 − 3 41.63 32.90 0.12347.188283 13CH3OH 141,13,−0 − 140,14,+0 254.25 4.36 0.92347.330581 SiO 80 − 70 75.02 22.00 0.15347.478251 CH3OCHO 275,22,2 − 265,21,2 247.25 6.14 0.24347.493965 CH3OCHO 275,22,0 − 265,21,0 247.26 6.14 0.24347.628340 CH3OCHO 2810,19,1 − 2710,18,1 306.77 5.49 0.13347.887461 CH3OCHO 205,15,0 − 195,14,0 262.21 3.68 0.08348.049886 CH3OCHO 286,23,1 − 276,22,1 266.06 6.10 0.20348.065967 CH3OCHO 286,23,0 − 276,22,0 266.06 6.10 0.20348.100194 13CH3OH 110,11,0 − 101,9,0 162.36 1.08 0.39348.117469 34SO2 194,16 − 193,17 212.61 3.50 0.27348.387800 SO2 242,22 − 233,21 292.74 1.91 2.25348.534365 H2CS 101,9 − 91,8 105.19 6.32 1.76348.786868 CH3OCHO 73,5,1 − 62,5,0 95.90 1.29 0.03348.911401 CH3CN, v=0 199,0 − 18−9,0 745.42 28.70 0.08349.024971 CH3CN, v=0 198,0 − 188,0 624.32 30.50 0.20349.106997 CH3OH 141,13,0 − 140,14,0 260.20 4.41 306.30349.125287 CH3CN, v=0 197,0 − 187,0 517.41 32.10 0.42349.286006 CH3CN, v=0 195,0 − 185,0 346.22 34.60 1.42349.346343 CH3CN, v=0 194,0 − 184,0 281.99 35.50 2.23349.393297 CH3CN, v=0 193,0 − 18−3,0 232.01 36.30 3.18349.426850 CH3CN, v=0 192,0 − 182,0 196.30 36.80 4.09349.446987 CH3CN, v=0 191,0 − 181,0 174.88 37.10 4.76349.453700 CH3CN, v=0 190,0 − 180,0 167.74 37.20 5.01349.806179 CH3OCH3 112,9,1 − 101,10,1 66.48 0.42 0.11350.103118 13CH3OH 11,1,+0 − 00,0,+0 16.80 3.29 0.51350.168100 CH3CN, v8=1 191,3 − 18−1,3 687.09 37.00 0.14350.286493 CH3OH 153,12,4 − 164,13,4 694.83 2.09 2.00



Table 8. continued.

Frequency Molecule Transition Eup/kB Aij Opacity (τ)[GHz] [K] ×10−4[s−1]350.333059 HNCO 161,16 − 151,15 186.20 5.97 1.64350.421585 13CH3OH 81,7,0 − 72,5,0 102.62 0.70 0.30350.423619 CH3CN, v8=1 19−2,2 − 182,2 748.55 36.80 0.09350.444906 CH3CN, v8=1 190,2 − 180,2 693.40 37.20 0.14350.449631 CH3CN, v8=1 191,2 − 181,2 713.84 37.10 0.12350.457580 CH3OCHO 288,21,0 − 278,20,0 283.91 6.03 0.17350.465645 CH3CN, v8=1 194,3 − 18−4,3 754.41 35.60 0.09350.507127 CH3CN, v8=1 193,3 − 183,3 717.75 36.30 0.11350.552359 CH3CN, v8=1 192,3 − 182,3 695.38 36.80 0.14350.687662 CH3OH 40,4,1 − 31,3,2 36.34 0.87 174.00350.842670 CH3CN, v8=1 19−1,3 − 181,3 687.41 37.20 0.14350.862756 SO2 106,4 − 115,7 138.84 0.44 0.72350.905100 CH3OH 11,1,0 − 00,0,0 16.84 3.32 269.20350.919517 CH3OCHO 276,21,2 − 266,20,2 252.31 6.29 0.23350.947331 CH3OCHO 276,21,0 − 266,20,0 252.31 6.29 0.23350.947970 CH3OCHO 304,27,4 − 293,26,5 466.76 0.69 0.00350.998044 CH3OCHO 287,22,1 − 277,21,1 274.59 6.17 0.19351.236479 CH3OH 95,4,1 − 104,6,1 240.51 0.36 20.00351.257223 SO2 53,3 − 42,2 35.89 3.36 6.30351.416798 HNCO 163,14 − 153,13 518.35 5.31 0.14351.416812 HNCO 163,13 − 153,12 518.35 5.31 0.14351.537795 HNCO 162,15 − 152,14 313.70 5.75 0.63351.551573 HNCO 162,14 − 152,13 313.70 5.75 0.63351.633257 HNCO 160,16 − 150,15 143.46 6.13 2.27351.768645 H2CO 51,5 − 41,4 62.45 12.00 -351.873873 SO2 144,10 − 143,11 135.87 3.43 7.85351.994870 HNCO 231,23 − 240,24 333.30 2.31 0.31352.082921 34SO2 214,18 − 213,19 250.41 3.65 0.23352.599570 OCS 29 − 28 253.88 1.28 1.75352.897581 HNCO 161,15 − 151,14 187.25 6.10 1.64352.917739 CH3OCHO 313,29,1 − 303,28,1 286.44 6.56 0.20352.920275 CH3OCHO 312,29,0 − 303,28,0 286.43 0.85 0.03352.921697 CH3OCHO 312,29,2 − 302,28,2 286.44 6.56 0.20352.925693 CH3OCHO 313,29,0 − 303,28,0 286.43 6.56 0.20352.927094 CH3OCHO 313,29,1 − 302,28,2 286.44 0.85 0.03352.929508 CH3OCHO 312,29,0 − 302,28,0 286.43 6.56 0.20353.401848 CH3OCHO 294,25,2 − 284,24,2 274.04 6.46 0.20353.410588 CH3OCHO 294,25,0 − 284,24,0 274.04 6.46 0.20353.552866 CH3OH 173,14,4 − 172,15,4 770.97 0.43 0.21353.723522 CH3OCHO 321,31,2 − 312,30,1 290.42 0.97 0.03353.728572 CH3OCHO 321,31,0 − 312,30,0 290.41 0.98 0.03353.739964 13CH3OH 151,14,−0 − 150,15,+0 288.46 4.54 0.75353.811872 H13

2 CO 50,5 − 40,4 51.02 12.70 0.21354.127629 CH3OH 192,17,3 − 181,17,3 738.20 1.43 1.09354.131005 CH3OH 261,26,0 − 253,23,0 820.37 0.00 0.00354.445952 13CH3OH 41,3,0 − 30,3,0 43.71 1.27 0.47354.505477 HCN 4 − 3 42.53 20.50 -354.607764 CH3OCHO 330,33,2 − 321,32,1 293.12 0.70 0.02354.697463 HC3N 39 − 38 340.52 35.70 0.54354.898595 H13

2 CO 52,4 − 42,3 98.41 10.80 0.13355.045517 SO2 124,8 − 123,9 111.00 3.40 7.96355.190900 H2

13CO 53,3 − 43,2 157.52 8.25 0.21355.602945 CH3OH 130,13,0 − 121,12,0 211.03 2.53 258.70355.835971 OC34S 30 − 29 264.75 1.32 0.14355.964812 CH3OH 163,13,4 − 162,14,4 731.75 0.44 0.30356.007235 CH3OH 151,14,0 − 150,15,0 295.26 4.60 231.90356.040644 SO2 157,9 − 166,10 230.41 0.64 0.74356.137265 t-HCOOH 162,15 − 152,14 158.67 5.07 0.19356.176243 H2

13CO 52,3 − 42,2 98.52 10.90 0.13



Table 8. continued.

Frequency Molecule Transition Eup/kB Aij Opacity (τ)[GHz] [K] ×10−4[s−1]356.442778 CH3OCH3 253,22,1 − 244,21,1 313.48 0.91 0.06356.575254 CH3OCH3 84,5,5 − 73,4,5 55.27 2.09 0.17356.576016 CH3OCH3 84,5,1 − 73,4,1 55.27 1.47 0.32356.582852 CH3OCH3 84,5,0 − 73,4,0 55.27 2.09 0.28356.586761 CH3OCH3 84,4,1 − 73,4,1 55.27 0.62 0.14356.626667 CH3OH 234,20,2 − 225,18,2 727.83 0.80 0.81356.723697 CH3OCH3 84,4,1 − 73,5,1 55.27 1.47 0.32356.724457 CH3OCH3 84,4,0 − 73,5,0 55.27 2.10 0.17356.724864 CH3OCH3 84,5,3 − 73,5,3 55.27 1.17 0.06356.734223 HCO+ 4 − 3 42.80 35.70 1.50356.755190 SO2 104,6 − 103,7 89.83 3.28 7.54356.873814 13CH3OH 132,12,−0 − 123,9,−0 243.84 0.79 0.16356.874537 CH3OH 188,11,2 − 197,12,2 717.88 0.49 0.43357.102182 34SO2 200,20 − 191,19 184.55 5.81 0.56357.165390 SO2 134,10 − 133,11 122.97 3.51 8.02357.241193 SO2 154,12 − 153,13 149.68 3.62 7.72357.338598 13CH3OH 54,2,−0 − 63,3,−0 114.77 0.24 0.06357.339947 13CH3OH 54,1,+0 − 63,4,+0 114.77 0.24 0.06357.387579 SO2 114,8 − 113,9 99.95 3.38 7.84357.459408 CH3OCH3 182,17,3 − 171,16,3 159.81 2.31 0.10357.460164 CH3OCH3 182,17,1 − 171,16,1 159.81 2.31 0.42357.460920 CH3OCH3 182,17,0 − 171,16,0 159.81 2.31 0.26357.581449 SO2 84,4 − 83,5 72.36 3.06 6.47357.657954 13CH3OH 72,5,0 − 61,5,0 85.80 1.63 0.69357.671821 SO2 94,6 − 93,7 80.64 3.20 7.09357.892442 SO2 74,4 − 73,5 65.01 2.87 5.67357.925848 SO2 64,2 − 63,3 58.58 2.60 4.68357.962905 SO2 174,14 − 173,15 180.11 3.73 7.08357.984520 CH3OCHO 109,1,0 − 98,2,0 86.21 0.99 0.06357.994262 CH3OH 153,12,4 − 152,13,4 694.83 0.44 0.41357.995629 CH3OCHO 285,23,2 − 275,22,2 264.44 6.71 0.22358.013154 SO2 54,2 − 53,3 53.07 2.18 3.46358.037887 SO2 44,0 − 43,1 48.48 1.45 1.95358.215633 SO2 200,20 − 191,19 185.33 5.83 12.44358.347316 34SO2 234,20 − 233,21 291.93 3.86 0.19358.354940 CH3OH 184,15,3 − 195,14,3 877.17 1.44 0.25358.364215 CH3OCHO 287,21,2 − 277,20,2 275.67 6.59 0.19358.399594 CH3OH 142,13,1 − 141,14,2 266.13 0.01 0.60358.414648 CH3OH 106,5,1 − 115,6,1 306.43 0.34 10.37358.449468 CH3OCH3 55,1,5 − 44,0,5 48.80 3.71 0.07358.451541 CH3OCH3 55,0,3 − 44,0,3 48.80 3.71 0.14358.452015 CH3OCH3 55,0,1 − 44,0,1 48.80 3.71 0.55358.454082 CH3OCH3 55,1,1 − 44,1,1 48.80 3.71 0.55358.456618 CH3OCH3 55,1,0 − 44,0,0 48.80 3.71 0.20358.605799 CH3OH 41,3,1 − 30,3,1 44.26 1.32 234.40358.987971 34SO2 152,14 − 141,13 118.72 2.92 0.35359.151158 SO2 253,23 − 252,24 320.93 3.10 2.89359.350585 CH3OCHO 2911,19,0 − 2811,18,0 337.64 6.07 0.10359.351992 CH3OCHO 2911,18,0 − 2811,17,0 337.64 6.07 0.10359.381524 CH3OCH3 123,10,3 − 112,9,3 83.73 1.43 0.09359.384589 CH3OCH3 123,10,1 − 112,9,1 83.73 1.43 0.35359.387642 CH3OCH3 123,10,0 − 112,9,0 83.73 1.43 0.22359.542805 CH3OCHO 296,24,1 − 286,23,1 283.31 6.75 0.19359.558047 CH3OCHO 296,24,0 − 286,23,0 283.32 6.75 0.19359.677119 CH3OH 143,11,4 − 142,12,4 660.20 0.45 0.54359.678517 CH3OH 333,31,1 − 332,31,2 1349.89 1.37 0.00359.770685 SO2 194,16 − 193,17 214.26 3.85 6.20359.936339 t-HCOOH 169,7 − 159,6 403.91 3.64 0.04359.937371 t-HCOOH 1610,6 − 1510,5 464.07 3.24 0.02



Table 8. continued.

Frequency Molecule Transition Eup/kB Aij Opacity (τ)[GHz] [K] ×10−4[s−1]359.956533 t-HCOOH 1611,5 − 1511,4 530.50 2.80 0.01359.960609 t-HCOOH 168,8 − 158,7 350.03 3.99 0.05360.022974 t-HCOOH 167,10 − 157,9 302.47 4.30 0.07360.148273 t-HCOOH 166,11 − 156,10 261.23 4.58 0.10360.290404 SO2 345,29 − 344,30 611.96 4.80 0.64360.388616 t-HCOOH 165,12 − 155,11 226.35 4.82 0.12360.393461 t-HCOOH 165,11 − 155,10 226.35 4.82 0.12360.408817 CH3OCHO 2910,20,0 − 2810,19,0 324.07 6.30 0.12360.409986 CH3OCHO 2910,19,2 − 2810,18,2 324.07 5.65 0.11360.465944 CH3OCH3 201,19,3 − 192,18,3 194.09 2.55 0.09360.584554 CH3OCH3 200,20,5 − 191,19,5 184.48 3.89 0.08360.584633 CH3OCH3 200,20,1 − 191,19,1 184.48 3.89 0.61360.661633 CH3OH 31,3,3 − 42,3,3 339.14 2.64 18.91360.721829 SO2 208,12 − 217,15 349.82 0.77 0.46360.763437 t-HCOOH 163,14 − 153,13 175.65 5.16 0.17360.796220 13CH3OH 161,15,−0 − 160,16,+0 324.94 4.74 0.59360.811283 t-HCOOH 164,13 − 154,12 197.84 5.02 0.15360.848946 CH3OH 110,11,1 − 101,9,1 166.05 1.21 160.20360.976377 t-HCOOH 164,12 − 154,11 197.86 5.03 0.15


Protostellar Interferometric Line Survey of the Cygnus X ...

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