# Revealing the Physical Conditions around Sgr A* using Bayesian Inference -
I. Observations and Radiative Transfer

Tomas A. James Department of Physics and Astronomy, University College London,
Gower Street, London WC1E 6BT, UK  Serena Viti Leiden Observatory, Leiden
University, PO Box 9513, NL-2300RA, Leiden, The Netherlands  Department of
Physics and Astronomy, University College London, Gower Street, London WC1E
6BT, UK  Farhad Yusef-Zadeh  Department of Physics and Astronomy and CIERA,
Northwestern University, Evanston, IL 60208, USA  Marc Royster  Department of
Physics and Astronomy and CIERA, Northwestern University, Evanston, IL 60208,
USA  Mark Wardle Department of Physics and Astronomy and Research Centre for
Astronomy, Astrophysics and Astrophotonics, Macquarie University, Sydney, NSW
2109, Australia

###### Abstract

We report sub-arcsecond ALMA observations between 272 - 375 $\mathrm{GHz}$
towards Sgr A*’s Circumnuclear disk (CND). Our data comprises 8 individual
pointings, with significant SiO (8_7 - 7_6) and SO (7 - 6) emission detected
towards 98 positions within these pointings. Additionally, we identify H_2CS
(9_1,9 - 8_1,8), OCS (25 - 24) and CH_3OH (2_1,1 - 2_0,2) towards a smaller
subset of positions. By using the observed peak line flux density together
with a Bayesian Inference technique informed by radiative transfer models, we
systematically recover the physical gas conditions towards each of these
positions. We estimate that the bulk of the surveyed gas has temperature
$\mathrm{T_{kin}}<500$ $\mathrm{K}$ and density
$\mathrm{n}_{\mathrm{H}}\lessapprox 10^{6}$ ${\mathrm{cm}}^{-3}$, consistent
with previous studies of similar positions as traced by HCN clumps. However,
we identify an uncharacteristically hot ($\mathrm{T_{kin}}\approx 600$
$\mathrm{K}$) and dense ($\mathrm{n}_{\mathrm{H}}\approx 10^{6}$
${\mathrm{cm}}^{-3}$) source in the Northeastern Arm. This position is found
to be approximately consistent with a gravitationally bound region dominated
by turbulence. We also identify a nearby cold ($\mathrm{T_{kin}}\approx 60$
$\mathrm{K}$) and extremely dense ($\mathrm{n}_{\mathrm{H}}\approx 10^{7}$
${\mathrm{cm}}^{-3}$) position that is again potentially bound and dominated
by turbulence. We also determine that the total gas mass contained within the
CND is $M_{\mathrm{CND}}\approx 4\times 10^{4}$ $M_{\odot}$. Furthermore, we
qualitatively note that the observed chemical enrichment across large scales
within the CND is consistent with bulk grain processing, though multiple
desorption mechanisms are plausibly responsible. Further chemical modelling is
required to identify the physical origin of the grain-processing, as well as
the localised H_2CS and OCS emission.

astrochemistry, galaxies: ISM, ISM: clouds, ISM: kinematics and dynamics,
methods: observational, methods: statistical

††software: emcee (Foreman-Mackey et al., 2013), ChainConsumer (Hinton, 2016),
RADEX (Van Der Tak et al., 2007), CASA (4.7.0; McMullin et al., 2007)

tablenum SIXtablenum

##  1 Introduction

The Galactic Center, and within it the Central Molecular Zone, has long been
identified as a uniquely extreme environment within the Milky Way owing to the
$(4.154\pm 0.014)\times 10^{6}$ M⊙ supermassive black hole known as Sgr A*
that resides there (Gillessen et al., 2009; Abuter et al., 2019). Such an
environment has important consequences for theories of galactic evolution and
dynamics, as the Galactic Center can be used as a high-resolution laboratory
for studying the nuclei of external galaxies. However, it also has a profound
impact on theories of both ISM physics and chemistry under extreme conditions,
especially when considering dense molecular gas as precursors to star
formation.

Morphologically, the inner few $\mathrm{p}\mathrm{c}$ of the Galactic Center
is chaotic and multifaceted. Centrally, Sgr A* is situated within a trifecta
of ionised gas streams known as the Galactic Center Mini Spiral, or GCMS (Lacy
et al., 1980; Ekers et al., 1983). Surrounding the GCMS is an extensive torus
or ring like structure of turbulent molecular gas known as the Circumnuclear
ring or Circumnuclear disk, herein referred to as the CND (e.g. Christopher et
al., 2005). The diffuse region between Sgr A* and the CND - known as the
Central Cavity - is home to a collection of young and evolved stellar objects,
including $\approx 100$ OB stars (Eckart et al., 2004; Paumard et al., 2006;
Lu et al., 2008; Mauerhan et al., 2010) that are thought to considerably
increase the photoionisation rate within and around Sgr A* (Genzel et al.,
1996; Paumard et al., 2006).

Studies of the CND are complicated by a degree of uncertainty surrounding its
exact morphology and kinematics. The extent of the CND is easily identified in
low $J$-transitions of molecules such as CS, H_2CO and SiO (Martin et al.,
2012; Tsuboi et al., 2018) as well as dust continuum emission (Lau et al.,
2013) and high $J$-transitions of molecules like ^12CO (Goto et al., 2013).
Such observations identify the CND as extending radially from $\sim$1.6 pc
outwards to $\sim$5–7 pc from Sgr A* (Smith & Mac Low, 2014), rotating at
$\sim$110 $\mathrm{km}\text{\,}{\mathrm{s}}^{-1}$ between 2–5 pc (Ghez et al.,
2005; Genzel et al., 2010).

However, the CND is not continuous or indeed uniform as occasional regions
devoid of emission known as ‘gaps’ are observed, in turn indicating that
different molecules are mapping different regions of the CND. Notable amongst
these gaps is that seen in HCN (1-0) towards the North of Sgr A*. Wright et
al. (2001) propose that this gap is caused by an infalling arm of the Galactic
Center Mini Spiral pushing through the CND as it falls towards Sgr A* proper,
producing OH maser emission (Yusef-Zadeh et al., 1999) in the process. It is
therefore clear that the gas conditions within the CND are highly non-uniform
and position dependent.

In addition, the interior of the CND is highly irregular and inhomogeneous,
exhibiting clump like structures of size $0.14-0.43$ $\mathrm{p}\mathrm{c}$
distributed throughout when viewed in the near-IR HCN (1-0) transition
(Guesten et al., 1987; Jackson et al., 1993; Christopher et al., 2005). A
number of theories regarding the physical conditions within these clumps
exist, and Genzel et al. (2010) extensively summarises the two prevailing
theories as the ‘transient’ and ‘virial’ scenarios. In summary, the transient
scenario suggests that the clumps are typically warm ($>100$ $\mathrm{K}$),
less dense ($<10^{6}$ ${\mathrm{cm}}^{-3}$) and tidally unstable with
transient lifetimes $\approx 10^{5}$ $\mathrm{y}\mathrm{r}\mathrm{s}$.
Conversely, the virial scenario states that these clumps are cooler ($<100$
$\mathrm{K}$), dense ($10^{7}-10^{8}$ ${\mathrm{cm}}^{-3}$) and tidally stable
with lifetimes $>10^{7}$ $\mathrm{y}\mathrm{r}\mathrm{s}$. Crucially, this
stability affords these clumps the opportunity to begin in-situ star
formation. The tidal instability, and therefore shorter lifetime estimate in
the transient scenario, would not permit any gravitationally bound object
formation.

Within the detected clumps, Tsuboi et al. (2018) estimate that some of the
relatively low density regions have gas densities in the range $0.9-6\times
10^{4}$ ${\mathrm{cm}}^{-3}$. Smith & Wardle (2014) estimate denser HCN bright
cores to have densities in the range $0.1-2\times 10^{6}$
${\mathrm{cm}}^{-3}$. Smith & Wardle (2014), and independently Mills et al.
(2013), find that the HCN clumps have conditions consistent with that outlined
in the transient scenario. Crucially, such studies have not explored kinetic
gas temperatures $>250$ $\mathrm{K}$ and thus could fail to highlight hot and
dense embedded sources. However, Smith & Wardle (2014) theorise that the CND
is subject to such large tidal shear that local star formation is unlikely to
occur within the CND in the absence of some triggering event. This tidal shear
condition could be overcome should self-gravity dominate according to $\sim
10^{7}(r/\mathrm{pc})^{-3}$ ${\mathrm{cm}}^{-3}$ (Yusef-Zadeh et al., 2017).
Assuming that the bulk of the CND is found between 1.5 – 2 pc from Sgr A* as
traced by HCN (Christopher et al., 2005), then exceeding the tidal shear
condition would require gas density between $\approx 2\times 10^{6}$
${\mathrm{cm}}^{-3}$ at $\mathrm{r}\approx 1.5$ pc, dropping to $\approx
2\times 10^{5}$ ${\mathrm{cm}}^{-3}$ at $\mathrm{r}\approx 2$ pc. Satisfying
this criterion is essential for in-situ star formation to occur within these
clumps.

C-type shocks originating from clump-clump collisions have been proposed as an
efficient heating mechanism within the CND owing to the high observed
temperatures of $\mathrm{T_{kin}}>200$ $\mathrm{K}$ (Bradford et al., 2005;
Harada et al., 2015). However, star formation as a process also presents
multiple opportunities to drive C-type shocks in to the surrounding gas, in
turn chemically enriching the surrounding ISM in a similar manner to clump-
clump collisions. SiO and SO - as well as other S-bearing species such as H_2S
- are all known shock tracers (Martin-Pintado et al., 1992; des Forêts et al.,
1993) as a result of shock-driven evaporation of grain surface and/or mantle.
Subsequent reaction of the evaporated species in the gas-phase, for example Si
and S with O, can produce molecules such as SiO and SO. Previous simulations
(Martin-Pintado et al., 1992; Flower et al., 2003; Holdship et al., 2017;
James et al., 2020) have used these molecules to great effect when tracing
star formation related shocks under standard interstellar conditions. However,
as already demonstrated the CND and its surroundings represent extreme
departures from standard interstellar conditions. For example, the OB star
population in the Central Cavity could increase the photoionisation rate
substantially. In addition to this, the cosmic-ray ionisation rate within the
Central Molecular Zone is much larger than in other regions of the galaxy.
Both Yusef-Zadeh et al. (2007) and Goto et al. (2013) estimate this could
extend to an upper limit of between $10-10^{4}\zeta$ ${\mathrm{s}}^{-1}$
assuming a standard galactic ionisation rate of $\zeta\approx 3\times
10^{-17}$ ${\mathrm{s}}^{-1}$.

Additionally, the Central Molecular Zone and its immediate surroundings are
known to exhibit large scale distributions of molecules such as CH_3OH
(Gottlieb et al., 1979) as well as HCN, HNC and HCO+ emission (Jones et al.,
2011). Detection of these molecules, specifically CH_3OH, in abundance is
again typical of regions that have undergone grain processing. As noted by
Turner (1998), the gas-phase formation routes and efficiencies of CH_3OH in
particular cannot account for its measured abundance within the ISM. Instead,
Turner (1998) found that CH_3OH forms readily via successive Hydrogenation of
CO on the grain surface. Subsequent desorption - UV photodesorption being the
dominant mechanism in translucent clouds - then releases CH_3OH in to the gas-
phase (Turner, 1998). Crucially, these formation and desorption pathways are
consistent with measured gas-phase abundances of CH_3OH. Yusef-Zadeh et al.
(2013) also investigated this phenomenon by comparing chemical models to
CH_3OH observations to constrain the mechanism responsible for its gas-phase
existence. As Molinari et al. (2011) highlight, the dust temperature
$\mathrm{T_{dust}}\leq 40$ $\mathrm{K}$ within the Central Molecular Zone is
too low for thermal desorption to be significant. They therefore conclude that
cosmic-ray desorption represents the dominant desorption mechanism of CH_3OH
within the Central Molecular Zone. However, on smaller scales applied to the
CND both Latvakoski et al. (1999) and Lau et al. (2013) find that the dust
temperature can vary positionally from 40 $\mathrm{K}$ – 200 $\mathrm{K}$, in
turn showing that thermal desorption could become significant in sub-regions
of the CND where the dust temperature exceeds $\approx$ 100 $\mathrm{K}$.
Consequently, detections of molecules such as SiO, SO and CH_3OH are direct
tracers of underlying physical events such as shocks, and/or regions that have
undergone grain processing.

Broadly, the detected emission intensity of these molecules is a function of
the region’s physical gas conditions which are, in turn, a function of the
physical processes occurring within the gas. One may derive estimates of the
kinetic gas temperature Tkin, Hydrogen number density nH and molecular column
densities Nspec using radiative transfer codes such as RADEX (Van Der Tak et
al., 2007) in order to understand these processes in more detail. Crucially,
repeating this procedure for each position within and throughout a sample of
beam pointings allows mapping of the gas conditions across those pointings,
permitting a larger scale understanding of the physics and chemistry driving
an object’s evolution.

Within this paper we present 0.38” $\times$ 0.31” spectral observations of Sgr
A*’s Circumnuclear Disk, and apply the aforementioned radiative transfer
methodology to this data. We present these observations in Section 2 before
discussing their implications in Section 3. In Section 4 we outline our
statistical process coupled to radiative transfer that infers the physical gas
conditions towards each position. Sections 5 and 6 presents the results of our
modelling for each considered parameter, before Section 7 discusses the
possible emission mechanisms responsible for the observed complexity as well
as our mass estimates.

##  2 Observations

Table 1: Details of the observational pointings used to collect data for this study. Shown are the Field ID for each pointing, alongside its central RA and Dec and the associated sensitivity. To assist future reference, Field IDs are prepended to numerical positions where molecular emission is identified, e.g. N1, N2 etc. Each pointing has size $\sim$ 21′′ at 300 $\mathrm{GHz}$. Spatial coverage for each pointing is shown in Figure 1.  Field | Pointing Center | Sensitivity
---|---|---
ID |  $\alpha$, $\delta$ (J2000) | (mJy beam-1 chan-1)
N |  $17^{h}45^{m}40.60^{s}$, $-29^{\circ}00^{\prime}20.00^{\prime\prime}$ | 4.98
G |  $17^{h}45^{m}43.80^{s}$, $-29^{\circ}00^{\prime}20.00^{\prime\prime}$ | 5.24
D |  $17^{h}45^{m}41.75^{s}$, $-28^{\circ}59^{\prime}47.69^{\prime\prime}$ | 5.34
H |  $17^{h}45^{m}39.49^{s}$, $-28^{\circ}59^{\prime}51.02^{\prime\prime}$ | 5.02
J |  $17^{h}45^{m}38.00^{s}$, $-29^{\circ}00^{\prime}01.00^{\prime\prime}$ | 5.24
K |  $17^{h}45^{m}38.30^{s}$, $-29^{\circ}00^{\prime}40.00^{\prime\prime}$ | 5.35
L |  $17^{h}45^{m}39.95^{s}$, $-29^{\circ}01^{\prime}03.50^{\prime\prime}$ | 5.46
M |  $17^{h}45^{m}41.32^{s}$, $-29^{\circ}01^{\prime}01.63^{\prime\prime}$ | 5.39
Figure 1: The 8 ALMA pointings of size 21′′ at 300 $\mathrm{GHz}$ that
comprise our data, overplotted on an HCN emission map of Sgr A* and its
surrounding Circumnuclear disk (CND). Details of the individual pointings can
be found in Table 1. We follow the naming convention in Christopher et al.
(2005), as well as Figure 2 of Montero-Castaño et al. (2009), for referring to
regions within and around the CND, e.g. pointing G targets the Northeastern
Arm whilst pointings M and L target the Southern Extension. Note: the G
pointing is distinct and separate from the dust enshrouded sources of G1 and
G2 in Ciurlo et al. (2020).

ALMA Cycle 2 Band 7 (272 - 375 $\mathrm{GHz}$) observations (Project Code
2013.1.01242.S) that target various SiO transitions towards the CND are
utilized for this investigation. The data presented in Figure 1 and Table 1
was obtained on 2015 June 8 and consists of 8 pointings with the 12m array.
Each pointing has a total field of view of 19.608′′ and a synthesized beam of
0.38′′ $\times$ 0.31′′ with PA$=-72^{\circ}$ corresponding to an on sky
spatial scale of approximately $0.014\times 0.012$ pc. We thus assume a beam
filling factor of unity. The total integration time for each source is 151
$\mathrm{s}$ with the relevant baseline tuned at the rest frequency of SiO (7
- 6) (303.926809 $\mathrm{GHz}$) along with a total bandwidth of 937.5
$\mathrm{MHz}$ corresponding to $\sim$ 900 km s-1. The raw data product has a
velocity resolution of $\sim$ 0.5 $\mathrm{km}\text{\,}{\mathrm{s}}^{-1}$
(3840 channels).

The data was calibrated with the assistance of standard observatory scripts
using CASA 4.7.0 (McMullin et al., 2007). CASA was also used to image the data
with a 0.05′′ pixel size and 2 $\mathrm{km}\text{\,}{\mathrm{s}}^{-1}$ (2.03
Hz) channel width. A Brigg’s robustness parameter of 0.5 was utilized. The
result achieved a sensitivity of $\sim$5 mJy, as shown in Table 1. Integrated
and peak intensity maps were used to visually identify molecular line emission
in the data cubes, and these identified lines are listed in Table 3 within
Appendix B.

###  2.1 CND spectra

Spatial representations of the 8 pointings that comprise our observations are
shown in Figure 1. The spectra for each of the 99 positions is shown in
Appendix A, whilst the spectra derived quantities are shown in Table 3 of
Appendix B. The circular regions shown in Figure 1 represent the approximate
field of view of each pointing corresponding to 21′′ at 300 $\mathrm{GHz}$.
Within this, we follow the naming convention adopted in Christopher et al.
(2005) as well as Montero-Castaño et al. (2009) for surveying regions of the
CND. As such, the G pointing surveys the Northeastern Arm of Sgr A*, whilst
all other pointings survey the interior of the CND. We note that the
G-pointing and its sources within are distinct and separate from the dust
enshrouded sources G1 and G2 highlighted by Ciurlo et al. (2020). Within these
pointings, each position contains at least either an SiO (7 - 6) or SO (8_7 -
7_6) line. Only 2 observations - N3, IRS7 - contain only SiO (7 - 6) and SO
(8_7 - 7_6) respectively. 96 observations within the data contain both SiO (7
- 6) and SO (8_7 - 7_6) transitions; the exception is the M4 source in which
we do not detect SiO (7 - 6) but do detect both SO (8_7 - 7_6) and CH_3OH
(2_1,1 - 1_0,2) transitions.

Whilst SiO and SO are the most commonly detected molecules, CH_3OH forms the
third most commonly detected species, being present towards 16 different
positions. CH_3OH (2_1,1 - 1_0,2) is not detected in any L pointing. In fact,
it is most commonly observed within the N pointing. Additionally, our
detections of H_2CS (9_1,9 - 8_1,8) are only found within a small grouping of
observations within the G pointing. Furthermore, we find OCS (25 - 24) to have
even further localisation, being present in only two sources: G2 and K13a.
Curiously, G2 and K13a are located in two opposite, distinct regions within
the CND and do not appear to be causally or spatially related to one another.

##  3 Qualitative gas characteristics

Given the commonality of SiO and SO emission, the ratio
$\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ is a useful diagnostic of the
most intense emission regions. Figure 2 shows this ratio as a function of each
position’s location and extent. Each aperture within this plot represents the
on-sky location of a detection described in Section 2, with the size of the
aperture being approximately equivalent to the total extent in beams as given
in Appendix B. The colour scale employed to fill these apertures is
representative of the $\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ ratio as
indicated by the vertical colour bar. The underlying image represents HCN
emission of the CND. It’s flux density is defined according to the horizontal
colour bar.

Figure 2: The ratio of observed SiO to SO flux densities
$\mathrm{I_{SiO}/I_{SO}}$ for each position within the 8 pointings where SiO
and SO are conclusively identified. Each circle represents the extent of each
position in approximate synthesised beam sizes, and its colour denotes the
ratio $\mathrm{I_{\ce{SiO}}/I_{\ce{SO}}}$ towards that region as per the
vertical colour bar. Inset plots are labelled as Panel 1 – 3 and show
groupings of observations and their observational designations. Key here is
the uniformity in $\mathrm{I_{\ce{SiO}}/I_{\ce{SO}}}$ throughout the dataset;
most positions show $\mathrm{I_{\ce{SiO}}/I_{\ce{SO}}}<1.5$.

Within Panel 1, the observations G1, G2, G3a and G3b sit along a filament of
HCN emission, whilst G4 and G5 are situated outside of this structure. As
noted previously, we highlight that these positions and separate and distinct
from the G1 and G2 sources identified in Ciurlo et al. (2020). However, the
presence of the filament appears to have negligible effect on the
$\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ ratio as all sources $<1$. G1 is
found to have a low $\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ ratio of
$\approx 0.8$, whilst G2 is observed to be slightly lower at $\approx 0.75$.
The ratio at G3a is consistent with G1, whilst G3b is found to be slightly
lower again at $\approx 0.7$. However, G4 has a ratio approximately consistent
with G2, whilst G5 has ratio consistent with that of G1. Nevertheless, the
$\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ ratio implies that the gas in
this region has marginally greater SO emission than SiO, in turn indicating a
higher density of SO than SiO within this region.

When considering Panel 2, it is immediately evident that there is again very
little variation in the $\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ ratio
across the area covered. With the exception of K15a and K17, every other
observation in this inset plot shows
$\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}\lessapprox 1$. Interestingly, K12,
K13a and K13b sit along a ridge that demarcates a bright HCN emission cloud
from its surrounding background. It is this region that is subject to close
interaction between the Galactic Center Mini Spiral and the molecular gas
within the CND. From the $\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ ratio,
it would appear that this ridge shows stronger SO emission than SiO emission.

Panel 3, much like Panel 2, shows very little variation in ratio. The only
exception to this uniformity is the multi-component gas at L19 and L30. L19’s
surrounding gas shows only single component behaviour, making the multi-
component nature of L19 puzzling. Unfortunately, L30 does not have any nearby
observation to compare with, though it is worth noting than the
$\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ ratio for the second component
here is the largest ratio seen in the data at $\approx 12$. This stands in
stark contrast to the rest of the observations in Panel 3 whose ratios are
significantly lower and much more uniform at $\lessapprox 1$.

Moreover, in addition to L19 and L30 we find 2 further sources in our
observations - D3, and K8b - that exhibit multi-component behaviour.
Curiously, each of these sources contains only SiO and SO lines.

Broadly, Figure 2 seemingly indicates that the energetics of the CND do not
vary significantly throughout its extent, or from region to region. However,
$\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ is inherently degenerate as the
ratio when $\mathrm{I}_{\ce{SO}}<<1$ can also be the same as when
$\mathrm{I}_{\ce{SiO}}>>1$. We therefore utilise a quantitative approach to
deriving the gas conditions within each observation.

##  4 Gas condition inference procedure

Both the physics and chemistry of interstellar gas are entangled and thus form
a system that is extremely non-linear and non-trivial to model. We simplify
this modelling challenge by approaching the problem with non-LTE radiative
transfer in RADEX (Van Der Tak et al., 2007) coupled to a Bayesian inference
procedure. Within this scheme we may inform the radiative transfer with a set
of independent random variables that define the physical gas conditions. Monte
Carlo methods can then be used to explore the physical condition parameter
space, in turn converging on the most likely gas conditions for each region.
Additionally, this approach minimises the number of variables required to
model the CND gas, in turn allowing us to determine the physical gas
conditions with a minimal number of assumptions. A key assumption for applying
RADEX is, however, that the transitions under consideration are optically
thin, as is likely the case.

###  4.1 Radiative transfer

Using this approach, we utilise the radiative transfer code RADEX (Van Der Tak
et al., 2007) to compute the emitted line flux density of the relevant
transition for a parcel of gas with physical conditions described by the set
of parameters
$\mathcal{S}=\\{\mathrm{T}_{\mathrm{kin}},\>n_{\mathrm{H}},\>N_{\mathrm{spec}}\\}$.
Tkin is the gas temperature, nH is the molecular Hydrogen gas number density
and Nspec is the column density of the relevant species under consideration.
Owing to the strong UV heating supplied by the OB star population, as well as
the high temperatures inf erred in the CND from previous observations, we
explore temperatures up to 1000 $\mathrm{K}$. We used RADEX owing to its non-
LTE molecular excitation capabilities, as well as its widespread use in
studies that model interstellar spectra (e.g. Beuther et al., 2008; Lique et
al., 2009; Van Dishoeck et al., 2021), including towards the Galactic Center
(e.g. Wirström et al., 2010; Amo-Baladrón et al., 2011; Armĳos-Abendaño et
al., 2020). We intend to apply more detailed chemical modelling to these
regions in future in order to further understand their phenomenology. All
species within this study utilise temperature dependent collisional data from
the LAMDA database (Schöier et al., 2010). For temperatures outside of the
calculated temperature range that LAMDA reports, RADEX fixes the collisional
rate constant to the rate constant at the nearest temperature. For SiO, the
collisional data has been calculated up to and including collisional
temperatures of 1000 $\mathrm{K}$. Inspecting the rate constants for SiO (8_7
- 7_6) reveals relatively uniform (within a factor of 2) behaviour across the
a-priori temperature range. Considering a similar process for SO (7 - 6) we
note that the collisional rates have been determined up to 300 $\mathrm{K}$.
Much like SiO, the collisional data for SO is similarly constant within the
calculated temperature range. We therefore assume that, given the similar
chemical compositions and masses of SiO and SO, the same uniformity in
collisional rates is evident beyond 300 $\mathrm{K}$. We note similar
behaviour within the collisional data for the other molecular transitions
detected in our data, and we therefore apply the same assumption to all
molecules and transitions detected in our observations.

Additionally, each observation presented in Section 2 has been normalised to
units of mJy$/$beam and thus assumes that each observation fills the beam.
This renders RADEX computed flux densities, as RADEX assumes a beam filling
factor of $1$, directly comparable to the observational flux densities
presented. The assumption of a beam filling factor of unity is further
justified as the linear scale of our observations is sufficient to guarantee
that the only emission within the beam is from the targeted gas. Each source
is also fully resolved, in turn ensuring they fill each beam.

Repeating this procedure for each species and each transition in a given
observation allows us to construct a model $\boldsymbol{\theta}$ that
represents the synthetic flux density emitted from a region of gas at
temperature Tkin and gas density nH comprising species column densities Nspec.
Constructing the model in this manner assumes that all emission lines
contained within it originate from the same thermal component. As Section 2
showed, our observations are consistent with a single component. Where not, it
is clear and distinct that $2$ components are present, either through
distinctly different linewidths or bi-modal line profiles, and they are thus
treated as essentially two separate sources, in turn being analysed with $2$
distinct models.

However, given the complexity of the underlying physics and chemistry, and
indeed their associated degeneracy, it is useful to statistically survey the
entire parameter space across each dimension in order to better understand and
identify the probable conditions within each observation. An ideal process
with which to do this utilises Bayesian Inference.

###  4.2 Bayesian Inference

Bayesian Inference is a method of using conditional probability to build
statistical parameter distributions for multi-dimensional data.
Unsurprisingly, it utilises Bayes’ Theorem, defined in Equation 1.

$P(\boldsymbol{\theta}|\boldsymbol{d})=\frac{P(\boldsymbol{d}|\boldsymbol{\theta})P(\boldsymbol{\theta})}{P(\boldsymbol{d})}$
(1)

$P(\boldsymbol{\theta}|\boldsymbol{d})$ is defined as the probability of the
model $\boldsymbol{\theta}$ fitting the data $\boldsymbol{d}$ given that the
data is correct (known as “the posterior probability”).
$P(\boldsymbol{d}|\boldsymbol{\theta})$ is the probability of having obtained
the data $\boldsymbol{d}$ given a particular model $\boldsymbol{\theta}$
(known as “the likelihood”). $P(\boldsymbol{\theta})$ is defined as the
probability of the model $\boldsymbol{\theta}$ being correct (“the prior”) and
$P(\boldsymbol{d})$ is the probability that the data is correct (“the
evidence”). We define the data as being the observed flux densities, whilst
the model is the equivalent line flux density determined from RADEX as defined
in Section 4.1.

We assume flat priors in log space such that within each dimension, any value
is equally as likely as any other providing that such a value falls within the
non-zero prior range. The non-zero ranges used for these priors, and in turn
the extent of parameter spaces explored, are shown in Table 2.

Table 2: The pre-constrained parameter spaces surveyed in this preliminary study for each explored dimension. Tkin represents the gas kinetic temperature, nH is the Hydrogen gas number density and Nspec is the species column density corresponding to the species $\mathrm{spec}$.  Parameter | Range | Unit
---|---|---
Tkin |  $60$-$1000$ | $\mathrm{K}$
nH |  $10^{3}$-$10^{7}$ | ${\mathrm{cm}}^{-3}$
NSiO |  $10^{12}$-$10^{16}$ | ${\mathrm{cm}}^{-2}$
NSO |  $10^{12}$-$10^{16}$ | ${\mathrm{cm}}^{-2}$
N${}_{\mathrm{CH_{3}OH}}$ |  $10^{14}$-$10^{17}$ | ${\mathrm{cm}}^{-2}$
N${}_{\mathrm{H_{2}CS}}$ |  $10^{12}$-$10^{15}$ | ${\mathrm{cm}}^{-2}$
NOCS |  $10^{12}$-$10^{15}$ | ${\mathrm{cm}}^{-2}$

We constrain the upper and lower limits of column density for each molecule to
explore by estimating the LTE derived column density for the upper and lower
limits of temperature shown in Table 2. This makes use of molecular data
provided by Splatalogue (Remijan et al., 2007).

We compute the likelihood using the likelihood function defined in Equation 2.

$P(\boldsymbol{d}|\boldsymbol{\theta})=\exp\Bigg{(}-\frac{1}{2}\sum_{i}\frac{(d_{i}-\theta_{i})^{2}}{\sigma_{i}^{2}}\Bigg{)}$
(2)

Where the summation term represents the Chi-squared statistic. Within Equation
2, $d_{i}$ is the ith value of the data, $\theta_{i}$ is the ith value of the
model corresponding to $d_{i}$ and $\sigma_{i}$ is the error associated with
$d_{i}$.

By implementing this Bayesian procedure we sample from the underlying
posterior distribution using randomly sampled variables that define the gas
condition. These variables thus form the set $\mathcal{S}$. To perform this
sampling we use the affine-invariant MCMC sampler emcee (Foreman-Mackey et
al., 2013). emcee uses a numbers of “walkers” to systematically sample the
parameter space across a number of steps, in turn constructing a series of
Markov Chains. All walkers therefore define a representation of the underlying
posterior distribution, allowing us to identify statistically informed
estimates of the most likely gas condition towards each observation. We use an
ensemble of $500$ walkers and we run each walker for a maximum of $1\times
10^{4}$ steps. Every $100$ steps we assess convergence in each dimension using
the Gelman-Rubin statistic (Gelman & Rubin, 1991). We halt our sampling if
convergence is judged to have been achieved across all dimensions. We follow
Brooks & Gelman (1998) in judging successful convergence when the Gelman-Rubin
diagnostic for each dimension $<1.2$. For additional confidence, we select a
cut-off of $1.15$ for achieving sample convergence. In addition and where
relevant we also visualise our chains using ChainConsumer (Hinton, 2016).

This approach has a number of distinct advantages when deriving physical gas
conditions. Firstly, the number of variables required to define the gas is
limited to those required by RADEX, resulting in a relatively low number of
dimensions overall. Additionally, within this scheme each dimension is
entirely free and is not causally related to any other. As such, we derive the
gas conditions with almost no a-priori knowledge of the local chemistry. The
affine-invariant nature of the emcee sampler thus allows convergence to be
achieved independently of the underlying physics and/or chemistry beyond
radiative transfer, thus reducing uncertainty and bias.

##  5 Inference results: corner plots for individual sources

Figure 3 shows an example of the corner plot for the G2 source. G2 contains
the largest number of lines in our sample that our detected towards one
region.

Figure 3: An example corner plot for the G2 source that shows the sampled
distributions for each parameter, known as dimensions, in the model. Each
dimension is shown on the $x$ axis; the distributions on the diagonal
represents the posterior distributions for the relevant dimension e.g. the
posterior on the top left is the $\mathrm{T}$ posterior. All other plots in
the matrix show the joint distributions of parameters as per their $x$ and $y$
axes that contribute to the associated posterior. Tight constraints are
observed in the joint distributions within all dimensions except $\mathrm{T}$
which exhibits broad behaviour along its domain and highlights the broad
errors associated with this dimension.

Within this matrix, the marginalised posterior distributions for each
parameter are found on the diagonal. The peak of each of these distributions
represents the point of highest posterior density (HPD) and it this value that
is taken to be the most likely model given the data. The plots found within
the remaining cells represent the joint distributions for the parameters
defined by their relevant $x$ and $y$ axes. Any pair of parameters that are
bounded by a dark blue region is within $2\sigma$ of the HPD, whilst
everything bounded within the light blue region is within $3\sigma$ of the
HPD.

Considering the marginalised posterior distributions we see that each
dimension peaks to a maximum, though not without a degree of skewness in the
case of $\mathrm{T}$. Inspecting the joint distributions of all dimensions
except $\mathrm{T}$ shows roughly symmetrical, tight groupings that in general
extend to $\pm 0.5$ orders of magnitude. This produces posteriors that peak
strongly, though both SiO and OCS peak towards the lower boundary of the
distributions in this case.

Whilst estimates of $\mathrm{T}$ are broad, its HPD is reliably constrained in
the case of G2. However, the skewness in this distribution does serve to
highlight the assymetrical errors that we find are often associated with this
dimension. In this instance, the possible values $\mathrm{T}<350$ $\mathrm{K}$
become exponentially less likely. At $\mathrm{T}>350$ $\mathrm{K}$ we observe
a small plateau of equal likelihood until $\mathrm{T}\approx 600$
$\mathrm{K}$, whereby an approximately linear decrease in likelihood until
$\mathrm{T}\approx 1000$ $\mathrm{K}$ is encountered.

Figure 4: Corner plot for the K1 source as per Figure 3. This shows much
broader spread in all dimensions owing to the limited number of data points
available.

Unfortunately, the large errors and associated systematic uncertainties in
temperature are a consequence of the limited number of spectral lines detected
and used in this analysis. In the majority of cases within this study we
require fitting for at least 4 different dimensions using just 2 spectral
lines. An example corner plot for this scheme is shown in Figure 4, which
exhibits only SiO and SO lines. As a result, Figure 4 shows broader
constraints in all dimensions and less symmetry in the posterior distributions
therein, though $\mathrm{T}$ does peak despite $3\sigma$ errors spanning the
entire parameter space. Subsequent inspection of the temperature column of
Table 9 shows wide, asymmetrical errors on almost every constrained
temperature, serving to highlight the challenge in drawing a discrete
conclusion from a continuous, asymmetrical and weakly peaked distribution. The
errors on each parameter become both smaller and more symmetrical in nature,
when afforded more line detections, though the effect on constraining
$\mathrm{T}$ is slight. Additionally, the broad temperature distributions may
be reflective of the weak temperature dependence that is observed in the LAMDA
collisional data for the detected molecular transitions. Further constraints
could be applied if additional observations of molecular transitions that
exhibit strong temperature dependent behaviour are incorporated.

##  6 Inference results: Gas conditions in the CND

The derived HPD of the physical parameters for each position are shown in
Figures 5 \- 8. These plots are similar to that in Figure 2, however the
colour scale employed to fill the apertures here is indicative of the HPD of
the relevant dimension under consideration as computed from our inference
routine. For instance, Figure 5 shows the HPD of gas temperature Tkin towards
each observation. Similarly, Figures 6, 7 and 8 show the HPDs of nH, NSiO and
NSO respectively. Semi-transparent, hatched apertures represent sources that
have not achieved reliable convergence within the maximum number of steps
available. We define non-reliable convergence as any source that has converged
to an HPD but without an associated $1\sigma$ error range. Table 9 within
Appendix C shows the HPD for each source and each dimension therein together
with their associated error ranges. Thus considering each image allows the
dataset wide distribution of physical conditions to be investigated and
quantified.

###  6.1 Temperature

Figure 5: The points of highest posterior density (HPD) of the kinetic gas
temperature THPD towards each position outlined in Section 2. Semi-
transparent, hatched circular regions indicate a position whose chain has not
reliably converged. G2 (in Panel 1) is noticeably warmer than its
surroundings, which are much lower in their recovered temperatures. Panels 2
and 3 show more agreement between neighbouring positions.

The distribution of HPD temperatures THPD across the entirety of Figure 5
shows minor correlation on a local level; as expected, sources in close
proximity to one another have broadly similar temperatures. In general, this
behaviour manifests as $\pm 50$ $\mathrm{K}$ between neighbouring sources. An
example of this is found in Panel 1 which shows that G3a and G3b are almost
identical in temperature of $\approx 100$ $\mathrm{K}$. Both G3a and G3b, as
well as G1 and G2, are found within a long filamentary structure of HCN
emission that extends along the left vertical edge of Panel 1. This structure
can be regarded as sitting outside of the main CND structure, and represents
the 50 $\mathrm{km}\text{\,}{\mathrm{s}}^{-1}$ molecular cloud identified in
previous studies. However, both G1 and G2 are warmer than G3a and G3b with
T${}_{\mathrm{G1}}\approx 350$ $\mathrm{K}$ and T${}_{\mathrm{G2}}\approx 600$
$\mathrm{K}$. Additionally, Panel 1 also shows G5, which is external to the
HCN filament. G5 is similar in temperature to G3a and G3b with
T${}_{\mathrm{G5}}\approx 100$ $\mathrm{K}$. There is also an unconstrained
source on the boundary of the filament that is of similar temperature to G3a,
G3b and G5, though this source’s temperature estimate is likely unreliable.
Nevertheless, it would appear that the G3a and G3b observations capture the
same gas component, whilst G1 and G2 capture colder and warmer extremes of the
filament respectively.

When considering Panel 2, we see that the main grouping of observations in the
centre of the panel are consistent with temperatures
$400<\mathrm{T_{{HPD}}}<700$ $\mathrm{K}$, though there is a significant
number of positions that have not achieved reliable temperature convergence.
Additionally, $5$ of the converged positions are identified as having
T${}_{\mathrm{HPD}}\approx 500$ $\mathrm{K}$. Interestingly, this is
consistent with the bulk of the gas being close to the upper limit of the CND
clump temperature as identified by Requena-Torres et al. (2012). There are,
however, 2 constrained “hot” sources within Panel 2 that exceed this limit:
K15b and K24. Of these, K24 is the hottest at T${}_{\mathrm{K24}}\approx 800$
$\mathrm{K}$, whilst K15b is moderately cooler at T${}_{\mathrm{K15b}}\approx
700$ $\mathrm{K}$. K24 is isolated and much further North than K15b, and does
not appear to correlate with the underlying HCN emission. Conversely, K15b
sits embedded within the CND and is much closer to cooler sources. This
therefore indicates that in general the gas temperature is increasing towards
the South of Panel 2 and, in turn, to the South of the CND. This is also
consistent with the underlying HCN emission becoming brighter towards the
South of Panel 2.

Panel 3 shows a similar trend to that observed in the main grouping of Panel 2
in that almost every source in Panel 3 has temperature within the range
$350<\mathrm{T_{{HPD}}}<550$ $\mathrm{K}$. In this instance there are only 2
sources - L15 and L25 - that deviate significantly from $\approx 550$
$\mathrm{K}$. L25 sits at the furthest extremity of the observation grouping,
whilst L15 sits centrally within that grouping. However, we observe that THPD
increases from L15 along and down the line of observations towards L6, with L3
and L6 being of comparable temperature. The $2$ sources either side of L6 -
L10a and L1 - are again of comparable temperatures to L3 and L6. Continuing
along and up from L15 towards L20 shows that the tight grouping of
observations in L20, L21 and L24 are all of similar temperature, again
T${}_{\mathrm{HPD}}\approx 550$ $\mathrm{K}$. However, L25’s temperature of
T${}_{\mathrm{HPD}}\approx 350$ $\mathrm{K}$ stands in contrast to its warmer
surroundings.

Additionally, L19 is the observation that showed the largest
$\mathrm{I}_{\ce{SiO}}/\mathrm{I}_{\ce{SO}}$ ratio in Panel 3 as well as
globally across all observations. Panel 3 shows that its temperature is
unconstrained, though if we consider the estimate in relation to its
surroundings then we see no significant deviation from the average THPD of its
surrounding observations.

###  6.2 Gas density

Figure 6: As per Figure 5, but here the colour of the circular regions
represents Hydrogen gas density nH towards each position outlined in Section
2. Again, semi-transparent, hatched circular regions indicate a source whose
chain has not reliably converged.

When considering the distribution of HPD densities nHPD in Figure 6, we see a
similar local trend to that observed in temperature in Figure 5 such that
neighbouring sources are within $0.2$ orders of magnitude of one another.
Additionally, we also observe far fewer unconstrained sources than were noted
in Figure 5. However, more uniformity is seen in the determined values of nHPD
throughout the CND as a whole, with less than $2$ orders of magnitude
variation throughout.

Panel 1 shows that, in general, colder sources are found to be at higher
density. For example, G5 was identified as being $\approx 100$ $\mathrm{K}$
and is, in turn, here noted to have density n${}_{\mathrm{G5}}\approx 10^{7}$
${\mathrm{cm}}^{-3}$ \- the most dense of any position in our sample. Whilst
G1 and G2 were noted for their different temperatures (G1 becoming cooler than
G2), Panel 1 shows that they are broadly similar in density within their
associated error ranges. Furthermore the same density behaviour is seen in
G3a, G3b and G4 which were all identified as having similar temperatures.

When considering Panel 2, almost every source sits within the range
$10^{5.6}<\mathrm{n_{HPD}}<10^{6.2}$ ${\mathrm{cm}}^{-3}$, even those outside
of the main grouping identified in Panel 2 of Figure 5. The main grouping is
found within an HCN bright region that defines the Southern extent of the CND.
We note that the density range derived here is consistent with the density of
HCN bright cores estimated by Smith & Wardle (2014). Additionally, the hot
sources identified in K15b and K24 sit within this range and have densities
n${}_{\mathrm{K15b}}\approx 10^{6.2}$ ${\mathrm{cm}}^{-3}$ and
n${}_{\mathrm{K24}}\approx 10^{5.8}$ ${\mathrm{cm}}^{-3}$ respectively. K13a
is identified as having a density towards the upper limit, i.e.
$\mathrm{n_{HPD}}\approx 10^{6.2}$ ${\mathrm{cm}}^{-3}$, though its
surroundings are of lesser density. When considered in conjunction with K9 and
K10, it would appear that this region is tracing the dense inner-most ridge of
the CND.

Outside of this grouping we identify that K18 exhibits a large density of
$\mathrm{n_{HPD}}\approx 10^{6.4}$ ${\mathrm{cm}}^{-3}$. This is not
consistent with the underlying HCN emission and is not reflected in the
density of its nearest neighbour K19 whose density is $\mathrm{n_{HPD}}\approx
10^{5.8}$ ${\mathrm{cm}}^{-3}$. K18 is therefore regarding as an anomalous
position.

Within Panel 3 we observe that the L16 source acts as a dividing boundary such
that everything North of L16 - and thus the Northern-most cluster of
observations - all exist at almost exactly the same density of
n${}_{\mathrm{HPD}}\approx 10^{6.0}$ ${\mathrm{cm}}^{-3}$. South of L16 we
note that the sources show slightly more variety, with L3 being more dense
than the average of n${}_{\mathrm{HPD}}>10^{5.8}$ ${\mathrm{cm}}^{-3}$ and L16
being less dense at n${}_{\mathrm{HPD}}>10^{5.5}$ ${\mathrm{cm}}^{-3}$. L12 is
a unique outlier in that its density is significantly larger than any other
source in Panel 3 at n${}_{\mathrm{HPD}}>10^{6.4}$ ${\mathrm{cm}}^{-3}$.
Within Figure 5, L12 does not have a reliable temperature estimate. However,
if we consider the temperature identified we observe that it is $>800$
$\mathrm{K}$, thus potentially forming another non-quiescent region.

Additionally, observations that sit within HCN regions or filaments are found
to broadly exhibit higher densities than those observations outside of these
locations. Given that HCN emission traces dense gas this is unsurprising,
though it does lend additional weight to the hot, dense sources being embedded
non-quiescent regions such as a YSO.

###  6.3 Column density

Figure 7: As per Figure 6, but here the colour of the circular regions
represents SiO column density NSiO towards each observation outlined in
Section 2.

Much like Figure 6, the SiO column density in Figure 7 shows little variance
across the dataset. Figure 7 shows just over an order of magnitude’s
variation. The effects of temperature and density also appear to be negligible
in this case as the regional and local variation seen in Figures 5 and 6 are
not observed, or indeed reflected, here. For example, Panel 1 in Figure 7
shows almost uniform NSiO in the range $10^{13.4}>N_{\mathrm{SiO}}<10^{13.8}$
${\mathrm{cm}}^{-2}$ despite the temperature and density varying widely. A
noticeable feature of Panel 1 is the additional uniformity in NSiO for sources
within the HCN filament. Sources outside of this filament, e.g. G5, are found
to exhibit a different, larger column density.

Notable features within Panel 2 show that a tentative trend indicating the
brighter the underlying HCN emission then the larger the SiO column density.
For example, the upper half of the panel, where HCN emission is less intense,
showing marginally lower column densities than the lower half where HCN
emission is more intense. Curiously, K5a, K5b and K5c are observed to have
lower column density of N${}_{\mathrm{SiO}}\approx 10^{13.3}$
${\mathrm{cm}}^{-2}$ than their surrounding observations. This could indicate
that the surrounding gas acts to shield the K5 sources and thereby inhibit the
emission of SiO. This is further confirmed when noting that the gas density of
K5a, K5b and K5c are consistent with their surroundings. The lower half of
Panel 2 is much more uniform of N${}_{\mathrm{SiO}}\approx 10^{13.6}$
${\mathrm{cm}}^{-2}$ with the exception of K8a which has column density
N${}_{\mathrm{SiO}}\approx 10^{14.0}$ ${\mathrm{cm}}^{-2}$. The inner CND
ridge (K9 to K13b) all show uniform and consistent column density of
N${}_{\mathrm{SiO}}\approx 10^{13.6}$ ${\mathrm{cm}}^{-2}$ with this agreement
extending behind the ridge until K8a. Uniquely, the previously identified
ridge indicated by K12, K13a and K13b shows no distinct SiO behaviour relative
to its surroundings, thus indicating that any interaction between the Galactic
Centre Mini Spiral and the CND towards this region is not having an effect on
the SiO chemistry.

Panel 3 is not dissimilar in broad trend to Panel 2 in that it shows the same
agreement trends. The larger NSiO is located towards the observation’s
Northernmost tip, with the column density decreasing towards the South of this
complex. Interestingly, this region of relatively large NSiO sits within an
HCN dark region. By application, HCN traces dense molecular gas and thus shows
that, at least in this region, that regions of large SiO column density are
found in dense regions of gas.

Directly North of Panel 2 is another grouping of observations that houses the
largest derived value of NSiO at $\approx 10^{14.2}$ ${\mathrm{cm}}^{-2}$. The
surrounding observations are also observed to have NSiO towards the upper-half
of the derived scale, though these observations are consistent with the values
of NSiO derived towards the series of observations in Panels 2 and 3. This is
again consistent with the underlying HCN emission tracing dense regions within
the CND, ergo grain-processing as described in Section 1.

Figure 8: As per Figure 7, but here the colour of the circular regions
represents SO column density NSO towards each observation outlined in Section
2.

Figure 8 shows that almost all sources can be considered to have
N${}_{\mathrm{SO}}>10^{14}$ ${\mathrm{cm}}^{-2}$. A grouping of $3$
observations immediately south of Sgr A* houses the lowest value of NSO within
our data at $\approx 10^{14}$ ${\mathrm{cm}}^{-2}$.

Panel 1 echoes a similar trend to its SiO column densities, with the largest
column density in this Panel - G5 - residing outside of the main HCN filament.
Interestingly, G3b is here shown to be N${}_{\mathrm{SO}}\approx 10^{15}$
${\mathrm{cm}}^{-2}$, larger than it’s surroundings in G1 and G2 that show
consistent column densities of N${}_{\mathrm{SO}}>10^{14.5}$
${\mathrm{cm}}^{-2}$. G3a and G4 are also consistent, with
N${}_{\mathrm{SO}}>10^{14.7}$ ${\mathrm{cm}}^{-2}$.

Panel 2 again shows a number of interesting trends, specifically a degree of
non-uniformity throughout the derived values in the main grouping. We observe
that whilst the local agreement between neighbouring observations is again
evident here, it is more evident in the upper half of the panel than in the
lower half. For instance, the collection of sources from K1 to K6b all show
N${}_{\mathrm{SO}}\approx 10^{14.8}$ ${\mathrm{cm}}^{-2}$. To the South of
this complex we find that the observations along the inner boundary ridge (K9
to K13b) of the CND show large column densities towards K9 and K13b, with the
column density in general decreasing towards the centre of this line towards
K11. K8a also stands out as a high column density source, especially in
relation to its lesser column density neighbours. However, the derived column
densities for these sources span around $1$ order of magnitude, making the
individual variation from observation to observation slight. This is also true
when applied to the interaction ridge, which is here observed to be less
uniform than in SiO. However, this behaviour is consistent with the
$\mathrm{I_{\ce{SiO}}/I_{\ce{SO}}}$ ratio being consistent across the ridge.

Panel 3 again exhibits a similar trend to that seen in Figure 7, though there
is even less variation in NSO throughout this region. The HCN dark region
towards the Northernmost tip of this grouping may again be considered to house
the largest values of N${}_{\mathrm{SO}}\approx 10^{15}$ ${\mathrm{cm}}^{-2}$.

The dense NSiO observation to the North of Panel 2 in Figure 7 now shows
almost unanimous agreement in NSO with its neighbours indicating that whatever
mechanism is driving its excess SiO chemistry - relative to its surroundings -
is not reflected in its SO chemistry.

When considering the trends in both Figures 7 and 8, we see variation in both
NSiO and NSO throughout the data, though this variation is slight in both
dimensions and likely not large enough to indicate any localised energetic
events acting as vectors for excess emission in the vast majority of cases.
Importantly, the derived SiO and SO column densities are larger than the
expected quiescent column densities. The CND wide nature of this enhancement
suggests that the mechanism driving this excess is universal, and likely
grain-processing and/or desorption.

##  7 Formation mechanisms

It is clear that all sources in our data show enhancement of SO and SiO. As
already discussed, each of these molecules is a known tracer of grain-
processing activity, owing to both Si and S being far more abundant on the
grain surfaces than they are in the gas-phase. Indeed, SiO and SO do not form
readily in the gas-phase without Si or S trapped in/on the grains being
released in to the gas phase for subsequent reaction with O e.g. Si + O -¿
SiO. Conversely, CH_3OH is thought to form readily on grain surfaces via
successive hydrogenation of CO, where it is subsequently desorbed in to the
gas-phase by an energetic mechanism such as shock activity (e.g. James et al.
(2020)) or photodesorption (e.g. Bertin et al. (2016)).

Previous studies of the Galactic Center on large scales such as those by
Molinari et al. (2011) and Yusef-Zadeh et al. (2013) have shown that the gas
and dust are uncoupled and that the dust temperature $\mathrm{T_{dust}}\leq
40$ $\mathrm{K}$, well below the temperature at which thermal desorption
becomes significant. When considering smaller scales such as the CND,
Latvakoski et al. (1999) theorise that the dust temperature varies
positionally from 40 $\mathrm{K}$ to 200 $\mathrm{K}$, with the variation
likely a result of heating by the OB star population. Furthermore, our
analysis has also shown that the density of the most dense clumps to be
$\mathrm{n_{H}}\approx 10^{7}$ ${\mathrm{cm}}^{-3}$, a density at which the
gas and dust are likely coupled, either fully or partially (Goldsmith, 2001).
As a result, thermal desorption could also be dominant within sub-regions of
the CND. This naturally poses the question: what physical event(s) are
dominant in driving this grain-processing, and are these events associated
with specific events such as star formation, or is it instead energetic
activity associated with Sgr A* and its surroundings?

In the context of star formation, driven shock action is an efficient and
ubiquitous processor of grains, so much so that molecules like SiO and SO are
often used exclusively as tracers of shocks in star forming regions (Martin-
Pintado et al., 1992; des Forêts et al., 1993). As already noted, the OB star
population in the Central Cavity could raise the photoionisation rate towards
the inner edge of the disc, making photodesorption of grain mantle species an
efficient desorption mechanism here. Dense regions further in to the disc may
also be subject to photodesorption via secondary photons. Crucially, such
widespread desorption activity could act to pre-process the grain mantles,
rendering molecules such as SiO and SO unreliable shock tracers in the CND.

Furthermore, the uniform enhancement of SiO and SO observed throughout our
observations is indicative of a large scale process driving this desorption.
Star formation would be expected to occur in a structured manner, to the
extent that its signatures would be concentrated to relatively small regions
of the CND. These signatures are dependent on the evolutionary state of the
object; they could manifest as cold and dense self-gravitating regions, or hot
and dense gas swept up in outflows.

K13a is, however, one of only 2 observations in our sample that shows
significant OCS emission. K13a’s surroundings do not exhibit similar OCS
lines, indicating highly localised phenomena to the K13a locale. The only
other OCS positive source is G2 which, unlike K13a, exhibits CH_3OH and H_2CS
emission. Within K13a we note that the measured linewidth of the OCS line is a
factor of 2 less than the measured linewidths of the SiO and SO lines. This is
in spite of all lines towards K13a having consistent measured velocities. Such
behaviour could indicate that the SiO and SO lines are tracing a different
thermal component to the OCS line, hence we disregard the OCS line towards the
position when fitting for K13a. As a result, the assumption of LTE should be
cautioned towards this region.

Interestingly, when considering the G-pointing we find that G2 does not
exhibit similar behaviour, though there is minor variation in measured
linewidth across the detected lines. CH_3OH and H_2CS emission are widespread
throughout the G pointing, creating a unique subset of observations within our
sample. Unfortunately, the temperature towards K13a remains unconstrained.
However, if we consider the point of highest posterior density towards K13a as
absolute then $\mathrm{T_{K13a}}\approx 500$ $\mathrm{K}$. G2 has temperature
$\mathrm{T_{G2}}\approx 600$ $\mathrm{K}$. As such, the presence of OCS could
indicate high-temperature chemistry occurring within these regions. The non-
detections of CH_3OH and H_2CS in K13a is puzzling, though K13a is known to
sit along the Galactic Center Mini Spiral - CND ridge and thus could be
indicative of locally different chemistry. Conversely, OCS tracing a separate
thermal component towards K13a, and the absence of this towards G2,
potentially alludes to this interaction. Nevertheless, both of these regions
require further chemical follow up study to confirm.

One may broadly estimate whether the derived conditions towards the positions
in this study are indicative of star formation by considering density, mass
and pressure estimates. Considering G2 we note that the Roche Density
(Chandrasekhar, 1987), assuming an approximate distance from Sgr A* of 3.0 pc,
is $\approx 6\times 10^{6}$ ${\mathrm{cm}}^{-3}$, which is marginally smaller
than the derived gas density towards G2 thus implying tidal stability.
Considering an estimate of the mass, assuming that G2 is spherical and uniform
with average density $n_{\mathrm{H}}\approx 10^{6}$ ${\mathrm{cm}}^{-3}$ and
radius equivalent to $\sim$ 3 beams we find its mass
$M_{\mathrm{uniform}}\approx 22\times 10^{3}$ $M_{\odot}$. For G2 to be
gravitationally bound with linewidth $\Delta v\approx 20$
$\mathrm{km}\text{\,}{\mathrm{s}}^{-1}$ then its mass would need to exceed the
virial mass $M_{\mathrm{vir}}$. Using the same process as Christopher et al.
(2005), we find that $M_{\mathrm{vir}}$ towards G2 is $M_{\mathrm{vir}}\approx
40\times 10^{3}$ $M_{\odot}$, only marginally larger than
$M_{\mathrm{uniform}}$. As a result, G2 could very well be gravitationally
bound within the limits of the assumptions applied. Additionally, another
potentially bound source is L28 within the L pointing. L28 has uniform mass
$M_{\mathrm{uniform}}\approx 40\times 10^{3}$ $M_{\odot}$ and virial mass
$M_{\mathrm{vir}}\approx 48\times 10^{3}$ $M_{\odot}$, and shows the closest
agreement between uniform and virial masses within our sample. For G5, we note
$M_{\mathrm{uniform}}\approx 1\times 10^{3}$ $M_{\odot}$ and virial mass
$M_{\mathrm{vir}}\approx 4\times 10^{3}$ $M_{\odot}$. However, the recovered
gas density for G5 of $\mathrm{n_{H}}\approx 10^{7}$ ${\mathrm{cm}}^{-3}$ is
therefore larger than the equivalent Roche Density at 3.0 pc, implying that G5
could be able to overcome the tidal barrier to bind itself gravitationally.
This assumes that G5 is one discrete, monolithic clump. Given that G5’s
physical conditions render it such an outlier amongst our observed regions, it
is possible that this region is actually multiple clumps along the line of
sight whose spectra sum to produce a single spectra, in turn creating the
illusion of a spectra consistent with one unified clump.

We apply a similar process in order to estimate the total molecular gas mass
contained within the CND. This can be expressed as
$M_{\mathrm{CND}}\approx\pi(R_{\mathrm{out}}^{2}-R_{\mathrm{in}}^{2})h\rho$
where $h$ represents the height of the CND. Based on the underlying HCN maps
in Figure 2 we assume that this is, on average, $\approx 0.5$ pc. For
comparison, we utilise the same CND radii reported in Tsuboi et al. (2018):
$R_{in}\approx 1.5$ pc and $R_{out}\approx 2.0$ pc. Additionally, we assume
that the average CND density is equivalent to the modal density determined
previously: $\approx 5\times 10^{5}$ ${\mathrm{cm}}^{-3}$. This yields a total
mass of $M_{\mathrm{CND}}\approx 4\times 10^{4}$ $M_{\odot}$. Tsuboi et al.
(2018) estimate the molecular gas mass of the CND based on LTE assumptions to
be $3\times 10^{4}$ $M_{\odot}$, marginally smaller than our estimate.
However, we caution that our observations do not sample the full extent of the
CND, especially towards HCN faint regions such as those to the North of Sgr
A*. In this instance, the use of the modal density derived from our
observations - which deliberately target dense gas - could result in us
overestimating the mean density of the CND, in turn biasing our mass estimate.

When considering both thermal and turbulent pressure, one may express the
thermal pressure as $p_{\mathrm{therm}}/k_{B}\approx nT$ and the turbulent
pressure as $p_{\mathrm{turb}}/k_{B}\approx\rho\Delta v^{2}/k_{B}$. For
$\mathrm{T}\approx 600$ $\mathrm{K}$, $n_{\mathrm{H}}\approx 10^{6}$
${\mathrm{cm}}^{-3}$ and $\Delta v\approx 20$
$\mathrm{km}\text{\,}{\mathrm{s}}^{-1}$ then $p_{\mathrm{therm}}/k_{B}\approx
10^{9}$ ${\mathrm{cm}}^{-3}\text{\,}\mathrm{K}$ and
$p_{\mathrm{turb}}/k_{B}\approx 10^{11}$
${\mathrm{cm}}^{-3}\text{\,}\mathrm{K}$. Therefore, for G2 the turbulent
pressure dominates over the thermal pressure in spite of the high estimated
temperature towards this region. In fact, all positions within the G, K and L
pointings are dominated by turbulence, despite their wide range of estimated
temperatures. Additionally, this is seemingly independent of their potentially
bound states, though a more rigorous determination of mass based on LTE
assumptions and chemical abundances is required to identify more accurate
clump masses to compare to their virial counterparts.

##  8 Conclusions

In this paper, we have presented sub-arcsecond observations from 8 ALMA Band 7
(272 – 375 $\mathrm{GHz}$) pointings towards the Circumnuclear disk (CND) of
Sgr A*. We detect clear and distinct SiO (8_7 - 7_6) and SO (7 - 6) emission
towards 98 positions within these pointings. Additionally, we observe
widespread CH_3OH (2_1,1 - 2_0,2) emission as well as more localised emission
of H_2CS (9_1,9 - 8_1,8) and OCS (25 - 24) towards a subset of these 98
positions.

We have used a Bayesian Inference routine coupled to radiative transfer to
infer the physical conditions towards each observation based on the detected
line fluxes. Based on these results, we find the following:

  * •

The temperature of the regions probed by the observations is in general
$\mathrm{T}<500$ $\mathrm{K}$, approximately consistent with that derived
previously towards similar clumps. Most of the estimated densities within this
work are in good agreement with the previously reported values towards clumps
within the CND at $\mathrm{n_{H}}\lessapprox 10^{6}$ ${\mathrm{cm}}^{-3}$.

  * •

The ubiquity of SiO and SO detections, including their large derived column
densities, is consistent with large scale grain-processing occurring within
the CND. However, we find that multiple desorption mechanisms, both thermal
and non-thermal (e.g. UV or cosmic-ray photodesorption), are plausible engines
with which to drive grain-processing in the CND. Further chemical modelling is
required to identify which processes are efficient towards the CND.

  * •

The G2 source within the Northeastern Arm is identified as being hot
($\mathrm{T_{kin}}\approx 600$ $\mathrm{K}$) and dense ($\mathrm{n_{H}}\approx
10^{6}$ ${\mathrm{cm}}^{-3}$). SiO (8_7 - 7_6) and SO (7 - 6) emission is
identified towards it, as well as CH_3OH (2_1,1 - 2_0,2), H_2CS (9_1,9 -
8_1,8) and OCS (25 - 24) lines. Basic calculations indicate that this region
is potentially gravitationally bound and is turbulent pressure dominated. It
is therefore a source of immense interest for follow up observations and
study.

  * •

L28 is identified as having mass almost exactly consistent with that required
for binding to occur, though turbulence dominates here as well. L28 does not
show any outstanding feature in terms of its line detections or its recovered
physical quantities, rendering it somewhat of an outlier amongst the
potentially bound sources identified. Nevertheless, more accurate mass
estimates in follow up studies based on complex chemistry can help constrain
whether this region is indeed bound or not.

  * •

Similarly, G5 is found to have the largest recovered density within our data
of $\mathrm{n_{H}}\approx 10^{7}$ ${\mathrm{cm}}^{-3}$ whilst also exhibiting
one of the lowest recovered temperatures at $\mathrm{T_{kin}}\approx 60$
$\mathrm{K}$. G5’s high density is sufficient to overcome tidal effects
prohibiting the object from being gravitational bound. Basic mass estimates
also support this finding.

  * •

Another position of chemical interest is K13a. K13a shows detections of SiO
(8_7 - 7_6) and SO (7 - 6) as well as OCS (25 - 24) - the only other position
other than G2 to exhibit the OCS line. K13a is located along a ridge of the
CND that is interacting with the Galactic Centre Mini Spiral. Further follow
up study is required to understand the role that the ionised gas within the
Galactic Centre Mini Spiral plays in the chemistry of this ridge.

  * •

Using a similar mass derivation approach, we find that the total molecular gas
mass contained within the CND between 1.5 - 2.0 pc is $M_{\mathrm{CND}}\approx
4\times 10^{4}$ $M_{\odot}$.

## Acknowledgments

TAJ is funded by an STFC studentship, and thanks the STFC accordingly. SV
acknowledges the European Research Council (ERC) Advanced Grant MOPPEX 833460
as well as the European Union’s Horizon 2020 research and innovation program
under the Marie Skodowska-Curie grant agreement No. 811312 for the project
“Astro-Chemical Origins” (ACO). We thank J. Holdship for their discussion,
opinions and associated improvements on aspects of this work. We also thank
the anonymous referee and editors for their comments, suggestions and
improvements that have enriched and clarified this work. This paper makes use
of the following ALMA data: ADS/JAO.ALMA#2013.1.01242.S. ALMA is a partnership
of ESO (representing its member states), NSF (USA) and NINS (Japan), together
with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in
cooperation with the Republic of Chile. The Joint ALMA Observatory is operated
by ESO, AUI/NRAO and NAOJ.

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##  Appendix A Individual spectra

Fig. Set9. Individual spectra

Figure 9: An example individual spectra for position D1. Spectra for each
position in which at least one line was identified are available in the online
journal.

##  Appendix B Tabulated spectral data

Table 3: Tabulated summary of observations including the source designation, it’s RA and Dec, extent in beam sizes, the emission line detected, its peak line flux density, the local standard of rest velocity, the linewidth and the ratio of SiO to SO flux densities where relevant. Source | $\alpha$ | $\delta$ | Extent | Emission | Flux density | v | $\Delta v$ | $\mathrm{I}_{\mathrm{SiO}}/\mathrm{I}_{\mathrm{SO}}$
---|---|---|---|---|---|---|---|---
| (J2000) | (J2000) | (beam) | Line | (mJy/beam) | (km s-1) | (km s-1) |
N3 | $17^{h}45^{m}40.62^{s}$ | $-29^{\circ}00^{\prime}24.05^{\prime\prime}$ | 1.00 | SiO 7–6 | 58.6 $\pm$ 3.6 | -25.56 | 27.6 |
IRS7 | $17^{h}45^{m}40.04^{s}$ | $-29^{\circ}00^{\prime}22.76^{\prime\prime}$ | 1.00 | SO 8(7)–7(6) | 8.34 $\pm$ 2.6 | 32.80 | 20.9 |
N8 | $17^{h}45^{m}40.85^{s}$ | $-29^{\circ}00^{\prime}12.88^{\prime\prime}$ | 1.00 | SiO 7–6 | 11.4 $\pm$ 5.3 | 39.52 | 11.8 | 0.56 $\pm$ 0.28
|  |  |  | SO 8(7)–7(6) | 20.5 $\pm$ 4.1 | 38.73 | 15.0 |
N7a | $17^{h}45^{m}40.88^{s}$ | $-29^{\circ}00^{\prime}12.23^{\prime\prime}$ | 10.65 | SiO 7–6 | 4.31 $\pm$ 0.47 | 41.23 | 13.9 | 0.56 $\pm$ 0.07
|  |  |  | SO 8(7)–7(6) | 7.66 $\pm$ 0.40 | 40.1649 | 16.2 |
N7b | $17^{h}45^{m}41.04^{s}$ | $-29^{\circ}00^{\prime}13.24^{\prime\prime}$ | 19.59 | SiO 7–6 | 3.7 $\pm$ 0.22 | 39.33 | 13.9 | 0.67 $\pm$ 0.05
|  |  |  | SO 8(7)–7(6) | 5.53 $\pm$ 0.20 | 41.1081 | 15.5 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 2.43 $\pm$ 0.36 | 37.68 | 8.68 |
C1 | $17^{h}45^{m}41.35^{s}$ | $-29^{\circ}00^{\prime}43.23^{\prime\prime}$ | 33.03 | SiO 7–6 | 8.13 $\pm$ 0.35 | -42.7327 | 24.8 | 0.48 $\pm$ 0.03
|  |  |  | SO 8(7)–7(6) | 17.0 $\pm$ 0.47 | -42.5732 | 18.6 |
G1 | $17^{h}45^{m}43.92^{s}$ | $-29^{\circ}00^{\prime}28.07^{\prime\prime}$ | 14.8 | SiO 7–6 | 5.84 $\pm$ 0.42 | 67.47 | 35.4 | 0.88 $\pm$ 0.08
|  |  |  | SO 8(7)–7(6) | 7.77 $\pm$ 0.5 | 64.58 | 30.3 |
|  |  |  | CH3OH 2(1,1)-2(0,2) | 4.49 $\pm$ 0.47 | 59.29 | 31.7 |
G2 | $17^{h}45^{m}43.77^{s}$ | $-29^{\circ}00^{\prime}16.19^{\prime\prime}$ | 73.6 | SiO 7–6 | 9.53 $\pm$ 0.10 | 56.84 | 19.7 | 0.75 $\pm$ -0.01
|  |  |  | SO 8(7)–7(6) | 16.7 $\pm$ 0.13 | 55.64 | -15.0 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 9.57 $\pm$ 0.12 | 56.14 | 15.6 |
|  |  |  | H2CS 9(1,9)–8(1,8) | 6.6 $\pm$ 0.19 | 54.66 | 9.99 |
|  |  |  | OCS 25–24 | 1.72 $\pm$ 0.16 | 54.34 | 12.5 |
G3a | $17^{h}45^{m}43.82^{s}$ | $-29^{\circ}00^{\prime}25.43^{\prime\prime}$ | 1.59 | SiO 7–6 | 32.2 $\pm$ 3.8 | 53.65 | 9.86 | 0.92 $\pm$ 0.15
|  |  |  | SO 8(7)–7(6) | 39.2 $\pm$ 4.3 | 52.77 | 8.82 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 29.1 $\pm$ 3.9 | 54.01 | 9.7 |
|  |  |  | H2CS 9(1,9)–8(1,8) | 21.2 $\pm$ 4.4 | 53.24 | 8.42 |
G3b | $17^{h}45^{m}43.87^{s}$ | $-29^{\circ}00^{\prime}26.05^{\prime\prime}$ | 2.24 | SiO 7–6 | 35.1 $\pm$ 3.5 | 56.66 | 10.6 | 0.68 $\pm$ 0.08
|  |  |  | SO 8(7)–7(6) | 48.6 $\pm$ 3.3 | 56.98 | 11.2 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 22.5 $\pm$ 3.0 | 57.15 | 12.2 |
|  |  |  | H2CS 9(1,9)–8(1,8) | 16.4 $\pm$ 3.7 | 55.51 | 10.1 |
Table 4:  Source | $\alpha$ | $\delta$ | Extent | Emission | Flux density | v | $\Delta v$ | $\mathrm{I}_{\mathrm{SiO}}/\mathrm{I}_{\mathrm{SO}}$
---|---|---|---|---|---|---|---|---
| (J2000) | (J2000) | (beam) | Line | (mJy/beam) | (km s-1) | (km s-1) |
G4 | $17^{h}45^{m}43.41^{s}$ | $-29^{\circ}00^{\prime}24.51^{\prime\prime}$ | 2.85 | SiO 7–6 | 20.3 $\pm$ 3.1 | 52.59 | 11.2 | 0.72 $\pm$ 0.13
|  |  |  | SO 8(7)–7(6) | 25.7 $\pm$ 2.8 | 53.18 | 12.3 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 14.5 $\pm$ 2.7 | 52.37 | 13.0 |
G5 | $17^{h}45^{m}42.32^{s}$ | $-29^{\circ}00^{\prime}8.55^{\prime\prime}$ | 11.6 | SiO 7–6 | 39.0 $\pm$ 4.7 | 55.18 | 15.5 | 0.93 $\pm$ 0.15
|  |  |  | SO 8(7)–7(6) | 36.1 $\pm$ 4.0 | 56.19 | 18.1 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 39.9 $\pm$ 4.9 | 54.99 | 14.9 |
|  |  |  | H2CS 9(1,9)–8(1,8) | 17.6 $\pm$ 5.3 | 55.48 | 13.8 |
D1 | $17^{h}45^{m}42.28^{s}$ | $-28^{\circ}59^{\prime}47.11^{\prime\prime}$ | 3.69 | SiO 7–6 | 14.5 $\pm$ 1.4 | 107.1 | 19.6 | 0.7 $\pm$ 0.08
|  |  |  | SO 8(7)–7(6) | 33.2 $\pm$ 2.2 | 107.5 | 12.2 |
D2 | $17^{h}45^{m}41.90^{s}$ | $-28^{\circ}59^{\prime}47.76^{\prime\prime}$ | 5.52 | SiO 7–6 | 14.4 $\pm$ 0.7 | 106.3 | 17.3 | 0.65 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 25.4 $\pm$ 0.8 | 106.0 | 15.1 |
D3c1 | $17^{h}45^{m}41.94^{s}$ | $-28^{\circ}59^{\prime}49.41^{\prime\prime}$ | 4.2 | SiO 7–6 | 4.61 $\pm$ 0.58 | 109.8 | 21.3 | 0.55 $\pm$ 0.0.08
|  |  |  |  | 4.51 $\pm$ 0.6 | 75.89 | 20.5 | 0.46 $\pm$ 0.07
|  |  |  | SO 8(7)–7(6) | 11.2 $\pm$ 0.77 | 108.0 | 15.8 |
|  |  |  |  | 9.55 $\pm$ 0.59 | 76.10 | 21.1 |
D4 | $17^{h}45^{m}41.80^{s}$ | $-28^{\circ}59^{\prime}47.44^{\prime\prime}$ | 3.3 | SiO 7–6 | 16.3 $\pm$ 1.3 | 107.31 | 11.7 | 0.62 $\pm$ 0.06
|  |  |  | SO 8(7)–7(6) | 23.3 $\pm$ 1.2 | 106.34 | 13.2 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 6.53 $\pm$ 1.4 | 107.233 | 11.0 & |
D5 | $17^{h}45^{m}41.88^{s}$ | $-28^{\circ}59^{\prime}51.00^{\prime\prime}$ | 4.04 | SiO 7–6 | 4.75 $\pm$ 0.74 | 77.92 | 18.8 | 0.33 $\pm$ 0.05
|  |  |  | SO 8(7)–7(6) | 12.1 $\pm$ 0.63 | 76.81 | 22.1 |
D6 | $17^{h}45^{m}41.72^{s}$ | $-28^{\circ}59^{\prime}48.78^{\prime\prime}$ | 1.63 | SiO 7–6 | 15.5 $\pm$ 3.1 | -12.20 | 9.44 | 0.71 $\pm$ 0.17
|  |  |  | SO 8(7)–7(6) | 12.9 $\pm$ 1.8 | -14.01 | 15.9 |
D7 | $17^{h}45^{m}41.77^{s}$ | $-28^{\circ}59^{\prime}44.10^{\prime\prime}$ | 1.65 | SiO 7–6 | 10.9 $\pm$ 2.2 | 93.44 | 13.3 | 0.67 $\pm$ 0.16
|  |  |  | SO 8(7)–7(6) | 19.5 $\pm$ 2.6 | 93.69 | 11.1 |
H1a | $17^{h}45^{m}39.38^{s}$ | $-28^{\circ}59^{\prime}51.18^{\prime\prime}$ | 3.1 | SiO 7–6 | 18.4 $\pm$ 1.1 | 35.10 | 14.7 | 0.83 $\pm$ 0.07
|  |  |  | SO 8(7)–7(6) | 25.6 $\pm$ 1.3 | 34.95 | 12.7 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 4.96 $\pm$ 0.88 | 35.74 | 19.3 |
H1b | $17^{h}45^{m}39.39^{s}$ | $-28^{\circ}59^{\prime}50.36^{\prime\prime}$ | 2.3 | SiO 7–6 | 22.3 $\pm$ 1.1 | 30.53 | 21.7 | 1.24 $\pm$ 0.1
|  |  |  | SO 8(7)–7(6) | 18.2 $\pm$ 1.1 | 30.61 | 21.4 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 6.49 $\pm$ 1.3 | 28.36 | 17.2 |
H2 | $17^{h}45^{m}39.60^{s}$ | $-28^{\circ}59^{\prime}51.33^{\prime\prime}$ | 2.6 | SiO 7–6 | 17.5 $\pm$ 1.7 | 37.15 | 15.6 | 1.85 $\pm$ 0.37
|  |  |  | SO 8(7)–7(6) | 12.6 $\pm$ 2.2 | 36.92 | 11.7 |
H3 | $17^{h}45^{m}39.70^{s}$ | $-28^{\circ}59^{\prime}51.26^{\prime\prime}$ | 1.1 | SiO 7–6 | 14.2 $\pm$ 1.7 | 53.01 | 28.2 | 1.78 $\pm$ 0.43
|  |  |  | SO 8(7)–7(6) | 10.3 $\pm$ 2.2 | 48.21 | 21.9 |
H4 | $17^{h}45^{m}39.76^{s}$ | $-28^{\circ}59^{\prime}46.03^{\prime\prime}$ | 2.11 | SiO 7–6 | 13.5 $\pm$ 0.97 | 73.59 | 32.9 | 2.04 $\pm$ 0.34
|  |  |  | SO 8(7)–7(6) | 7.24 $\pm$ 1.1 | 70.22 | 30.1 |
J1 | $17^{h}45^{m}38.14^{s}$ | $-29^{\circ}00^{\prime}1.65^{\prime\prime}$ | 1.3 | SiO 7–6 | 14.3 $\pm$ 2.9 | 62.28 | 11.3 | 0.95 $\pm$ 0.27
|  |  |  | SO 8(7)–7(6) | 18.5 $\pm$ 3.6 | 60.90 | 9.23 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 8.42 $\pm$ 2.4 | 60.49 | 13.7 |
|  |  |  | H2CS 9(1,9)–8(1,8) | 6.57 $\pm$ 1.9 | 60.76 | 17.5 |
Table 5:  Source | $\alpha$ | $\delta$ | Extent | Emission | Flux density | v | $\Delta v$ | $\mathrm{I}_{\mathrm{SiO}}/\mathrm{I}_{\mathrm{SO}}$
---|---|---|---|---|---|---|---|---
| (J2000) | (J2000) | (beam) | Line | (mJy/beam) | (km s-1) | (km s-1) |
J2 | $17^{h}45^{m}38.15^{s}$ | $-29^{\circ}00^{\prime}0.01^{\prime\prime}$ | 2.2 | SiO 7–6 | 46.9 $\pm$ 1.0 | 67.16 | 27.5 | 2.26 $\pm$ 0.12
|  |  |  | SO 8(7)–7(6) | 25.0 $\pm$ 1.2 | 65.70 | 22.8 |
J3 | $17^{h}45^{m}38.10^{s}$ | $-29^{\circ}00^{\prime}2.82^{\prime\prime}$ | 5.2 | SiO 7–6 | 14.6 $\pm$ 0.81 | 75.19 | 14.3 | 0.67 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 25.5 $\pm$ 0.94 | 74.50 | 12.3 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 10.2 $\pm$ 0.87 | 73.31 | 13.3 |
|  |  |  | H2CS 9(1,9)–8(1,8) | 6.13 $\pm$ 1.6 | 75.00 | 7.43 |
J4 | $17^{h}45^{m}38.25^{s}$ | $-28^{\circ}59^{\prime}59.44^{\prime\prime}$ | 2.06 | SiO 7–6 | 10.3 $\pm$ 2.2 | 68.63 | 12.7 | 0.88 $\pm$ 0.25
|  |  |  | SO 8(7)–7(6) | 14.6 $\pm$ 2.8 | 68.91 | 10.2 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 10.8 $\pm$ 4.4 | 67.94 | 6.46 |
K1 | $17^{h}45^{m}38.34^{s}$ | $-29^{\circ}00^{\prime}38.38^{\prime\prime}$ | 2.61 | SiO 7–6 | 16.6 $\pm$ 1.8 | -5.85 | 12.6 | 0.67 $\pm$ 0.09
|  |  |  | SO 8(7)–7(6) | 21.6 $\pm$ 1.6 | -6.27 | 14.4 |
K2 | $17^{h}45^{m}38.23^{s}$ | $-29^{\circ}00^{\prime}40.30^{\prime\prime}$ | 3.03 | SiO 7–6 | 17.5 $\pm$ 2.1 | -9.06 | 10.3 | 0.71 $\pm$ 0.1
|  |  |  | SO 8(7)–7(6) | 21.4 $\pm$ 1.8 | -7.60 | 11.9 |
K3 | $17^{h}45^{m}38.26^{s}$ | $-29^{\circ}00^{\prime}41.39^{\prime\prime}$ | 1.83 | SiO 7–6 | 11.4 $\pm$ 1.8 | 4.86 | 14.9 | 0.55 $\pm$ 0.1
|  |  |  | SO 8(7)–7(6) | 18.7 $\pm$ 1.7 | 2.45 | 16.5 |
K4 | $17^{h}45^{m}38.40^{s}$ | $-29^{\circ}00^{\prime}42.32^{\prime\prime}$ | 3.35 | SiO 7–6 | 14.6 $\pm$ 1.2 | -17.53 | 13.9 | 0.65 $\pm$ 0.06
|  |  |  | SO 8(7)–7(6) | 22.7 $\pm$ 1.2 | -18.35 | 13.7 |
K5a | $17^{h}45^{m}38.23^{s}$ | $-29^{\circ}00^{\prime}42.06^{\prime\prime}$ | 3.35 | SiO 7–6 | 9.71 $\pm$ 1.5 | -15.30 | 11.7 | 0.41 $\pm$ 0.07
|  |  |  | SO 8(7)–7(6) | 13.7 $\pm$ 0.89 | -10.31 | 20.0 |
K5b | $17^{h}45^{m}38.31^{s}$ | $-29^{\circ}00^{\prime}42.90^{\prime\prime}$ | 2.94 | SiO 7–6 | 8.55 $\pm$ 1.3 | -20.32 | 14.8 | 0.59 $\pm$ 0.11
|  |  |  | SO 8(7)–7(6) | 16.3 $\pm$ 1.5 | -20.30 | 13.1 |
K5c | $17^{h}45^{m}38.22^{s}$ | $-29^{\circ}00^{\prime}42.80^{\prime\prime}$ | 2.11 | SiO 7–6 | 8.55 $\pm$ 1.3 | -20.32 | 14.8 | 0.59 $\pm$ 0.11
|  |  |  | SO 8(7)–7(6) | 16.3 $\pm$ 1.5 | -20.30 | 13.1 |
K6a | $17^{h}45^{m}38.09^{s}$ | $-29^{\circ}00^{\prime}42.12^{\prime\prime}$ | 3.63 | SiO 7–6 | 11.6 $\pm$ 1.1 | -1.67 | 20.7 | 0.62 $\pm$ 0.07
|  |  |  | SO 8(7)–7(6) | 19.4 $\pm$ 1.1 | -3.04 | 20.1 |
K6b | $17^{h}45^{m}38.01^{s}$ | $-29^{\circ}00^{\prime}42.17^{\prime\prime}$ | 2.44 | SiO 7–6 | 10.3 $\pm$ 1.6 | -13.41 | 19.8 | 0.58 $\pm$ 0.1
|  |  |  | SO 8(7)–7(6) | 19.0 $\pm$ 1.7 | -12.71 | 18.6 |
K7a | $17^{h}45^{m}38.12^{s}$ | $-29^{\circ}00^{\prime}44.66^{\prime\prime}$ | 7.20 | SiO 7–6 | 21.4 $\pm$ 1.1 | -42.07 | 13.7 | 0.61 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 35.5 $\pm$ 1.1 | -41.93 | 13.5 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 4.99 $\pm$ 0.94 | -39.19 | 15.4 |
K7b | $17^{h}45^{m}38.09^{s}$ | $-29^{\circ}00^{\prime}45.52^{\prime\prime}$ | 2.50 | SiO 7–6 | 12.3 $\pm$ 3.0 | -50.34 | 15.3 | 0.7 $\pm$ 0.21
|  |  |  | SO 8(7)–7(6) | 18.3 $\pm$ 3.2 | -45.76 | 14.7 |
K8a | $17^{h}45^{m}37.98^{s}$ | $-29^{\circ}00^{\prime}47.01^{\prime\prime}$ | 5.00 | SiO 7–6 | 25.6 $\pm$ 1.5 | -43.72 | 25.9 | 0.69 $\pm$ 0.05
|  |  |  | SO 8(7)–7(6) | 41.9 $\pm$ 1.7 | -44.99 | 23.0 |
K8b | $17^{h}45^{m}38.02^{s}$ | $-29^{\circ}00^{\prime}47.97^{\prime\prime}$ | 6.10 | SiO 7–6 | 23.9 $\pm$ 1.7 | -40.48 | 21.9 | 1.90 $\pm$ 0.33
|  |  |  |  | 13.1 $\pm$ 2.1 | -10.80 | 17.8 | 0.61 $\pm$ 0.11
|  |  |  | SO 8(7)–7(6) | 13.1 $\pm$ 2.1 | -41.07 | 21.0 |
|  |  |  |  | 23.7 $\pm$ 2.3 | -9.99 | 16.2 |
K9 | $17^{h}45^{m}38.41^{s}$ | $-29^{\circ}00^{\prime}45.39^{\prime\prime}$ | 1.83 | SiO 7–6 | 12.4 $\pm$ 1.6 | -3.19 | 26.6 | 0.55 $\pm$ 0.08
|  |  |  | SO 8(7)–7(6) | 24.6 $\pm$ 1.7 | -5.23 | 24.4 |

Table 6:  Source | $\alpha$ | $\delta$ | Extent | Emission | Flux density | v | $\Delta v$ | $\mathrm{I}_{\mathrm{SiO}}/\mathrm{I}_{\mathrm{SO}}$
---|---|---|---|---|---|---|---|---
| (J2000) | (J2000) | (beam) | Line | (mJy/beam) | (km s-1) | (km s-1) |
K10 | $17^{h}45^{m}38.48^{s}$ | $-29^{\circ}00^{\prime}46.14^{\prime\prime}$ | 2.94 | SiO 7–6 | 13.0 $\pm$ 1.6 | -24.71 | 21.0 | 0.8 $\pm$ 0.13
|  |  |  | SO 8(7)–7(6) | 18.5 $\pm$ 1.8 | -23.93 | 18.4 |
K11 | $17^{h}45^{m}38.51^{s}$ | $-29^{\circ}00^{\prime}47.07^{\prime\prime}$ | 1.13 | SiO 7–6 | 11.8 $\pm$ 3.7 | -16.19 | 22.7 | 0.59 $\pm$ 0.22
|  |  |  | SO 8(7)–7(6) | 23.8 $\pm$ 4.4 | -20.11 | 19.0 |
K12 | $17^{h}45^{m}38.56^{s}$ | $-29^{\circ}00^{\prime}47.52^{\prime\prime}$ | 1.58 | SiO 7–6 | 13.5 $\pm$ 5.2 | -28.22 | 15.4 | 0.48 $\pm$ 0.2
|  |  |  | SO 8(7)–7(6) | 29.1 $\pm$ 5.3 | -28.69 | 15.0 |
K13a | $17^{h}45^{m}38.60^{s}$ | $-29^{\circ}00^{\prime}48.68^{\prime\prime}$ | 5.85 | SiO 7–6 | 16.3 $\pm$ 2.7 | -92.39 | 14.5 | 0.50 $\pm$ 0.18
|  |  |  | SO 8(7)–7(6) | 32.37 $\pm$ 2.5 | -95.18 | 14.3 |
|  |  |  | OCS 25–24 | 11.1 $\pm$ 5.5 | -92.99 | 7.15 |
K13b | $17^{h}45^{m}38.58^{s}$ | $-29^{\circ}00^{\prime}49.50^{\prime\prime}$ | 2.09 | SiO 7–6 | 18.0 $\pm$ 7.4 | -83.93 | 16.4 | 0.51 $\pm$ 0.23
|  |  |  | SO 8(7)–7(6) | 41.4 $\pm$ 8.6 | -83.68 | 14.0 |
K14 | $17^{h}45^{m}38.42^{s}$ | $-29^{\circ}00^{\prime}46.46^{\prime\prime}$ | 1.81 | SiO 7–6 | 13.9 $\pm$ 3.8 | -26.31 | 14.1 | 0.73 $\pm$ 0.25
|  |  |  | SO 8(7)–7(6) | 17.5 $\pm$ 3.5 | -23.83 | 15.3 |
K15a | $17^{h}45^{m}38.29^{s}$ | $-29^{\circ}00^{\prime}46.18^{\prime\prime}$ | 4.50 | SiO 7–6 | 19.5 $\pm$ 2.3 | -9.54 | 9.75 | 1.01 $\pm$ 0.17
|  |  |  | SO 8(7)–7(6) | 17.7 $\pm$ 2.1 | -8.82 | 10.6 |
K15b | $17^{h}45^{m}38.30^{s}$ | $-29^{\circ}00^{\prime}47.27^{\prime\prime}$ | 2.85 | SiO 7–6 | 15.7 $\pm$ 3.3 | 2.05 | 13.7 | 0.71 $\pm$ 0.18
|  |  |  | SO 8(7)–7(6) | 22.7 $\pm$ 3.4 | 1.17 | 13.3 |
K16 | $17^{h}45^{m}38.26^{s}$ | $-29^{\circ}00^{\prime}49.87^{\prime\prime}$ | 4.15 | SiO 7–6 | 18.3 $\pm$ 5.4 | -36.22 | 10.5 | 0.5 $\pm$ 0.17
|  |  |  | SO 8(7)–7(6) | 31.5 $\pm$ 4.7 | -35.98 | 12.2 |
K17 | $17^{h}45^{m}37.95^{s}$ | $-29^{\circ}00^{\prime}50.36^{\prime\prime}$ | 2.94 | SiO 7–6 | 29.2 $\pm$ 8.3 | -36.32 | 16.2 | 1.05 $\pm$ 0.43
|  |  |  | SO 8(7)–7(6) | 26.9 $\pm$ 8.0 | -37.58 | 16.8 |
K18 | $17^{h}45^{m}38.81^{s}$ | $-29^{\circ}00^{\prime}40.52^{\prime\prime}$ | 7.51 | SiO 7–6 | 6.05 $\pm$ 1.1 | -14.92 | 14.7 | 0.6 $\pm$ 0.13
|  |  |  | SO 8(7)–7(6) | 9.54 $\pm$ 1.0 | -16.35 | 15.6 |
K19 | $17^{h}45^{m}38.70^{s}$ | $-29^{\circ}00^{\prime}38.51^{\prime\prime}$ | 4.37 | SiO 7–6 | 7.46 $\pm$ 0.73 | -29.25 | 29.4 | 0.91 $\pm$ 0.12
|  |  |  | SO 8(7)–7(6) | 8.54 $\pm$ 0.76 | -27.55 | 28.2 |
K20 | $17^{h}45^{m}38.58^{s}$ | $-29^{\circ}00^{\prime}31.29^{\prime\prime}$ | 9.93 | SiO 7–6 | 10.3 $\pm$ 1.3 | -2.82 | 19.7 | 0.53 $\pm$ 0.08
|  |  |  | SO 8(7)–7(6) | 16.0 $\pm$ 1.1 | -5.92 | 24.0 |
K21a | $17^{h}45^{m}38.15^{s}$ | $-29^{\circ}00^{\prime}32.82^{\prime\prime}$ | 2.03 | SiO 7–6 | 17.5 $\pm$ 2.3 | 32.31 | 27.1 | 0.74 $\pm$ 0.12
|  |  |  | SO 8(7)–7(6) | 25.1 $\pm$ 2.4 | 31.28 | 25.4 |
K21b | $17^{h}45^{m}38.13^{s}$ | $-29^{\circ}00^{\prime}32.09^{\prime\prime}$ | 2.33 | SiO 7–6 | 18.4 $\pm$ 4.2 | 22.53 | 13.1 | 0.69 $\pm$ 0.19
|  |  |  | SO 8(7)–7(6) | 28.6 $\pm$ 4.4 | 21.08 | 12.3 |
K22 | $17^{h}45^{m}37.85^{s}$ | $-29^{\circ}00^{\prime}31.02^{\prime\prime}$ | 3.83 | SiO 7–6 | 13.4 $\pm$ 5.7 | -8.65 | 14.5 | 0.66 $\pm$ 0.34
|  |  |  | SO 8(7)–7(6) | 18.7 $\pm$ 5.3 | -9.83 | 15.7 |
K23 | $17^{h}45^{m}37.99^{s}$ | $-29^{\circ}00^{\prime}35.57^{\prime\prime}$ | 5.45 | SiO 7–6 | 6.86 $\pm$ 1.8 | 51.19 | 10.4 | 0.47 $\pm$ 0.14
|  |  |  | SO 8(7)–7(6) | 15.0 $\pm$ 1.8 | 51.66 | 10.1 |
K24 | $17^{h}45^{m}37.97^{s}$ | $-29^{\circ}00^{\prime}36.19^{\prime\prime}$ | 2.49 | SiO 7–6 | 9.11 $\pm$ 2.2 | -17.10 | 15.2 | 0.79 $\pm$ 0.24
|  |  |  | SO 8(7)–7(6) | 12.6 $\pm$ 2.4 | -16.90 | 13.9 |
L1 | $17^{h}45^{m}39.60^{s}$ | $-29^{\circ}01^{\prime}04.29^{\prime\prime}$ | 3.67 | SiO 7–6 | 16.1 $\pm$ 1.1 | -58.68 | 20.8 | 0.81 $\pm$ 0.07
|  |  |  | SO 8(7)–7(6) | 29.1 $\pm$ 1.6 | -58.91 | 14.2 |
L2 | $17^{h}45^{m}39.74^{s}$ | $-29^{\circ}01^{\prime}05.41^{\prime\prime}$ | 2.25 | SiO 7–6 | 17.2 $\pm$ 2.0 | -35.33 | 16.8 | 0.58 $\pm$ 0.08
|  |  |  | SO 8(7)–7(6) | 31.7 $\pm$ 2.2 | -35.60 | 15.8 |
Table 7:  Source | $\alpha$ | $\delta$ | Extent | Emission | Flux density | v | $\Delta v$ | $\mathrm{I}_{\mathrm{SiO}}/\mathrm{I}_{\mathrm{SO}}$
---|---|---|---|---|---|---|---|---
| (J2000) | (J2000) | (beam) | Line | (mJy/beam) | (km s-1) | (km s-1) |
L3 | $17^{h}45^{m}39.79^{s}$ | $-29^{\circ}01^{\prime}5.57^{\prime\prime}$ | 1.02 | SiO 7–6 | 7.95 $\pm$ 3.3 | -62.66 | 15.6 | 0.37 $\pm$ 0.16
|  |  |  | SO 8(7)–7(6) | 22.4 $\pm$ 3.4 | -61.95 | 15.1 |
L4 | $17^{h}45^{m}38.80^{s}$ | $-29^{\circ}01^{\prime}06.84^{\prime\prime}$ | 2.18 | SiO 7–6 | 10.3 $\pm$ 1.2 | -48.40 | 23.1 | 0.47 $\pm$ 0.06
|  |  |  | SO 8(7)–7(6) | 28.2 $\pm$ 1.6 | -51.13 | 18.0 |
L5 | $17^{h}45^{m}39.66^{s}$ | $-29^{\circ}01^{\prime}06.15^{\prime\prime}$ | 1.99 | SiO 7–6 | 16.7 $\pm$ 2.1 | -49.29 | 17.2 | 0.53 $\pm$ 0.08
|  |  |  | SO 8(7)–7(6) | 22.4 $\pm$ 1.5 | -51.23 | 24.0 |
L6 | $17^{h}45^{m}39.70^{s}$ | $-29^{\circ}01^{\prime}07.10^{\prime\prime}$ | 5.11 | SiO 7–6 | 13.0 $\pm$ 0.71 | -55.02 | 24.5 | 0.6 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 26.6 $\pm$ 0.87 | -54.88 | 20.0 |
L7 | $17^{h}45^{m}39.75^{s}$ | $-29^{\circ}01^{\prime}07.79^{\prime\prime}$ | 3.20 | SiO 7–6 | 18.9 $\pm$ 1.7 | -61.44 | 17.9 | 0.43 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 51.2 $\pm$ 1.9 | -62.67 | 15.5 |
L8 | $17^{h}45^{m}39.68^{s}$ | $-29^{\circ}01^{\prime}07.93^{\prime\prime}$ | 6.58 | SiO 7–6 | 10.1 $\pm$ 0.99 | -63.48 | 17.4 | 0.4 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 34.2 $\pm$ 1.3 | -64.93 | 13.0 |
L9 | $17^{h}45^{m}39.81^{s}$ | $-29^{\circ}01^{\prime}7.82^{\prime\prime}$ | 2.25 | SiO 7–6 | 6.18 $\pm$ 1.6 | -57.91 | 17.5 | 0.25 $\pm$ 0.07
|  |  |  | SO 8(7)–7(6) | 28.4 $\pm$ 1.8 | -60.78 | 15.3 |
L10a | $17^{h}45^{m}39.81^{s}$ | $-29^{\circ}01^{\prime}8.68^{\prime\prime}$ | 2.20 | SiO 7–6 | 12.1 $\pm$ 2.4 | -60.44 | 15.2 | 0.34 $\pm$ 0.07
|  |  |  | SO 8(7)–7(6) | 28.9 $\pm$ 1.9 | -59.95 | 18.6 |
L10b | $17^{h}45^{m}39.78^{s}$ | $-29^{\circ}01^{\prime}08.75^{\prime\prime}$ | 2.80 | SiO 7–6 | 14.6 $\pm$ 1.6 | -64.80 | 21.1 | 0.46 $\pm$ 0.06
|  |  |  | SO 8(7)–7(6) | 39.1 $\pm$ 2.0 | -64.58 | 17.2 |
L11 | $17^{h}45^{m}30.80^{s}$ | $-29^{\circ}01^{\prime}09.66^{\prime\prime}$ | 3.50 | SiO 7–6 | 8.47 $\pm$ 3.8 | -64.30 | 7.15 | 0.2 $\pm$ 0.09
|  |  |  | SO 8(7)–7(6) | 17.3 $\pm$ 1.5 | -69.77 | 17.7 |
L12 | $17^{h}45^{m}39.88^{s}$ | $-29^{\circ}01^{\prime}9.93^{\prime\prime}$ | 1.78 | SiO 7–6 | 7.32 $\pm$ 2.3 | -34.75 | 19.8 | 0.59 $\pm$ 0.22
|  |  |  | SO 8(7)–7(6) | 15.0 $\pm$ 2.8 | -35.23 | 16.3 |
L13 | $17^{h}45^{m}39.88^{s}$ | $-29^{\circ}01^{\prime}4.67^{\prime\prime}$ | 5.74 | SiO 7–6 | 7.62 $\pm$ 0.31 | -46.78 | 36.6 | 0.51 $\pm$ 0.02
|  |  |  | SO 8(7)–7(6) | 18.1 $\pm$ 0.38 | -46.09 | 30.0 |
L14 | $17^{h}45^{m}39.91^{s}$ | $-29^{\circ}01^{\prime}4.06^{\prime\prime}$ | 4.39 | SiO 7–6 | 10.1 $\pm$ 0.59 | -58.36 | 24.2 | 0.62 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 15.5 $\pm$ 0.55 | -55.07 | 25.6 |
L15 | $17^{h}45^{m}39.96^{s}$ | $-29^{\circ}01^{\prime}3.62^{\prime\prime}$ | 1.78 | SiO 7–6 | 18.2 $\pm$ 2.3 | -59.76 | 14.5 | 0.48 $\pm$ 0.07
|  |  |  | SO 8(7)–7(6) | 30.8 $\pm$ 1.9 | -58.14 | 17.7 |
L16 | $17^{h}45^{m}40.00^{s}$ | $-29^{\circ}01^{\prime}3.38^{\prime\prime}$ | 1.70 | SiO 7–6 | 10.3 $\pm$ 1.4 | -52.46 | 22.9 | 0.5 $\pm$ 0.08
|  |  |  | SO 8(7)–7(6) | 26.9 $\pm$ 1.8 | -51.29 | 17.5 |
L17 | $17^{h}45^{m}40.05^{s}$ | $-29^{\circ}01^{\prime}2.33^{\prime\prime}$ | 4.53 | SiO 7–6 | 30.9 $\pm$ 0.99 | -65.43 | 18.2 | 0.74 $\pm$ 0.03
|  |  |  | SO 8(7)–7(6) | 35.1 $\pm$ 0.83 | -64.85 | 21.6 |
L18 | $17^{h}45^{m}40.09^{s}$ | $-29^{\circ}01^{\prime}2.60^{\prime\prime}$ | 2.97 | SiO 7–6 | 14.1 $\pm$ 0.86 | -49.59 | 23.6 | 0.59 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 25.9 $\pm$ 0.92 | -49.22 | 21.9 |
L19 | $17^{h}45^{m}40.12^{s}$ | $-29^{\circ}01^{\prime}1.78^{\prime\prime}$ | 4.07 | SiO 7–6 | 9.37 $\pm$ 1.3 | -45.00 | 13.8 | 0.47 $\pm$ 0.07
|  |  |  |  | 28.3 $\pm$ 0.92 | -69.00 | 20.2 | 0.80 $\pm$ 0.03
|  |  |  | SO 8(7)–7(6) | 18.0 $\pm$ 1.2 | -46.16 | 15.2 |
|  |  |  |  | 35.8 $\pm$ 0.92 | -68.97 | 20.0 |
Table 8:  Source | $\alpha$ | $\delta$ | Extent | Emission | Flux density | v | $\Delta v$ | $\mathrm{I}_{\mathrm{SiO}}/\mathrm{I}_{\mathrm{SO}}$
---|---|---|---|---|---|---|---|---
| (J2000) | (J2000) | (beam) | Line | (mJy/beam) | (km s-1) | (km s-1) |
L20 | $17^{h}45^{m}40.14^{s}$ | $-29^{\circ}01^{\prime}1.13^{\prime\prime}$ | 2.73 | SiO 7–6 | 24.5 $\pm$ 1.3 | -48.49 | 20.2 | 0.65 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 48.4 $\pm$ 1.7 | -48.64 | 15.8 |
L21 | $17^{h}45^{m}40.15^{s}$ | $-29^{\circ}01^{\prime}00.44^{\prime\prime}$ | 3.22 | SiO 7–6 | 16.9 $\pm$ 1.2 | -51.05 | 17.8 | 0.47 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 31.4 $\pm$ 1.1 | -52.57 | 20.4 |
L22 | $17^{h}45^{m}40.181^{s}$ | $-29^{\circ}01^{\prime}00.89^{\prime\prime}$ | 2.52 | SiO 7–6 | 26.4 $\pm$ 1.4 | -47.16 | 19.5 | 0.54 $\pm$ 0.03
|  |  |  | SO 8(7)–7(6) | 44.5 $\pm$ 1.3 | -47.60 | 21.3 |
L23 | $17^{h}45^{m}40.19^{s}$ | $-29^{\circ}01^{\prime}1.47^{\prime\prime}$ | 2.88 | SiO 7–6 | 15.2 $\pm$ 0.94 | -48.15 | 29.4 | 0.52 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 32.6 $\pm$ 1.1 | -48.62 | 26.2 |
L24 | $17^{h}45^{m}40.25^{s}$ | $-29^{\circ}01^{\prime}00.94^{\prime\prime}$ | 4.02 | SiO 7–6 | 17.1 $\pm$ 1.1 | -62.84 | 22.1 | 0.46 $\pm$ 0.03
|  |  |  | SO 8(7)–7(6) | 37.1 $\pm$ 1.1 | -62.44 | 22.0 |
L25 | $17^{h}45^{m}40.20^{s}$ | $-29^{\circ}01^{\prime}00.14^{\prime\prime}$ | 2.94 | SiO 7–6 | 17.5 $\pm$ 0.92 | -61.57 | 29.6 | 0.66 $\pm$ 0.04
|  |  |  | SO 8(7)–7(6) | 28.7 $\pm$ 1.0 | -58.58 | 27.2 |
L26 | $17^{h}45^{m}40.27^{s}$ | $-29^{\circ}00^{\prime}59.59^{\prime\prime}$ | 3.35 | SiO 7–6 | 12.4 $\pm$ 1.2 | -52.84 | 22.7 | 0.53 $\pm$ 0.06
|  |  |  | SO 8(7)–7(6) | 22.6 $\pm$ 1.2 | -51.51 | 23.3 |
L27 | $17^{h}45^{m}40.28^{s}$ | $-29^{\circ}00^{\prime}58.81^{\prime\prime}$ | 1.69 | SiO 7–6 | 17.7 $\pm$ 2.8 | -30.47 | 18.8 | 0.56 $\pm$ 0.1
|  |  |  | SO 8(7)–7(6) | 26.5 $\pm$ 2.3 | -29.15 | 22.6 |
L28 | $17^{h}45^{m}40.46^{s}$ | $-29^{\circ}00^{\prime}59.67^{\prime\prime}$ | 89.40 | SiO 7–6 | 12.7 $\pm$ 0.84 | -60.86 | 19.5 | 0.62 $\pm$ 0.05
|  |  |  | SO 8(7)–7(6) | 18.7 $\pm$ 0.77 | -59.57 | 21.2 |
L29 | $17^{h}45^{m}40.19^{s}$ | $-29^{\circ}01^{\prime}3.83^{\prime\prime}$ | 3.09 | SiO 7–6 | 7.54 $\pm$ 0.99 | -49.50 | 21.6 | 0.55 $\pm$ 0.08
|  |  |  | SO 8(7)–7(6) | 12.2 $\pm$ 0.88 | -53.33 | 24.2 |
L30 | $17^{h}45^{m}40.47^{s}$ | $-29^{\circ}01^{\prime}8.10^{\prime\prime}$ | 3.52 | SiO 7–6 | 14.0 $\pm$ 3.1 | -26.48 | 14.9 | 0.89 $\pm$ 0.21
|  |  |  |  | 6.18 $\pm$ 4.2 | -52.43 | 10.9 | 13.46 $\pm$ 9.69
|  |  |  | SO 8(7)–7(6) | 21.6 $\pm$ 2.0 | -30.01 | 10.9 |
|  |  |  |  | 12.7 $\pm$ 2.7 | -63.94 | 0.394 |
M1 | $17^{h}45^{m}41.31^{s}$ | $-29^{\circ}00^{\prime}58.84^{\prime\prime}$ | 4.50 | SiO 7–6 | 8.67 $\pm$ 1.0 | -45.25 | 14.4 | 0.65 $\pm$ 0.09
|  |  |  | SO 8(7)–7(6) | 13.8 $\pm$ 1.1 | -44.42 | 14.0 |
M2 | $17^{h}45^{m}41.41^{s}$ | $-29^{\circ}00^{\prime}59.93^{\prime\prime}$ | 1.00 | SiO 7–6 | 2.98 $\pm$ 0.63 | -50.17 | 18.2 | 0.38 $\pm$ 0.09
|  |  |  | SO 8(7)–7(6) | 8.22 $\pm$ 0.66 | -54.28 | 17.2 |
M3 | $17^{h}45^{m}41.38^{s}$ | $-29^{\circ}00^{\prime}58.16^{\prime\prime}$ | 2.02 | SiO 7–6 | 6.39 $\pm$ 1.9 | -42.64 | 15.4 | 0.43 $\pm$ 0.14
|  |  |  | SO 8(7)–7(6) | 9.23 $\pm$ 1.2 | -44.63 | 24.8 |
M4 | $17^{h}45^{m}41.23^{s}$ | $-29^{\circ}00^{\prime}57.77^{\prime\prime}$ | 2.27 | SO 8(7)–7(6) | 10.8 $\pm$ 3.2 | 23.10 | 8.21 |
|  |  |  | CH3OH 2(1,1)–2(0,2) | 8.19 $\pm$ 2.2 | 21.39 | 12.0 |

##  Appendix C Inferred conditions

Table 9: The points of highest posterior density (HPD) of the physical conditions towards each observational source. Sources with parameter entries marked with – represent an unconstrained value in that dimension.  Source | $\mathrm{T_{kin}}$ | $\log{\mathrm{n_{H}}}$ | $\log{\mathrm{N_{SiO}}}$ | $\log{\mathrm{N_{SO}}}$
---|---|---|---|---
| [$\mathrm{K}$] | [${\mathrm{cm}}^{-3}$] | [${\mathrm{cm}}^{-2}$] | [${\mathrm{cm}}^{-2}$]
N8 | – | – | $13.30^{+0.85}_{-0.68}$ | $14.65^{+0.56}_{-0.23}$
N7a | – | $6.73^{+0.26}_{-1.70}$ | $12.92^{+0.61}_{-0.13}$ | $14.202^{+0.421}_{-0.071}$
N7b | – | $5.70^{+0.80}_{-0.72}$ | $12.830^{+0.378}_{-0.073}$ | $14.027^{+0.258}_{-0.049}$
C1 | $440^{+300}_{-240}$ | $5.74^{+0.62}_{-0.31}$ | $13.416^{+0.142}_{-0.053}$ | $14.593^{+0.144}_{-0.051}$
G1 | $310^{+490}_{-110}$ | $5.69^{+0.65}_{-0.51}$ | $13.45^{+0.22}_{-0.12}$ | $14.489^{+0.161}_{-0.100}$
G2 | $610^{+140}_{-180}$ | $5.88^{+0.16}_{-0.18}$ | $13.392^{+0.058}_{-0.064}$ | $14.500^{+0.075}_{-0.058}$
G3a | $81^{+159}_{-18}$ | $6.56\pm 0.29$ | $13.648^{+0.106}_{-0.095}$ | $14.717^{+0.115}_{-0.080}$
G3b | $108^{+182}_{-45}$ | $6.42^{+0.45}_{-0.27}$ | $13.710^{+0.114}_{-0.087}$ | $14.905^{+0.126}_{-0.062}$
G4 | – | $6.21^{+0.56}_{-0.31}$ | $13.50^{+0.20}_{-0.13}$ | $14.639^{+0.199}_{-0.081}$
G5 | $63^{+22}_{-0}$ | $6.99^{+0.00}_{-0.31}$ | $13.981\pm 0.090$ | $14.985^{+0.055}_{-0.058}$
D1 | – | – | $13.59^{+0.40}_{-0.12}$ | $14.725^{+0.275}_{-0.069}$
D2 | $300^{+450}_{-100}$ | $5.76^{+0.49}_{-0.44}$ | $13.53^{+0.19}_{-0.11}$ | $14.704^{+0.115}_{-0.090}$
D3c1 | – | $5.99^{+0.61}_{-0.75}$ | $13.13^{+0.31}_{-0.13}$ | $14.37^{+0.22}_{-0.10}$
D3c2 | $520^{+320}_{-310}$ | $5.81^{+0.57}_{-0.60}$ | $13.11^{+0.24}_{-0.14}$ | $14.417^{+0.178}_{-0.096}$
D4 | $297^{+509}_{-98}$ | $5.72^{+0.56}_{-0.52}$ | $13.408^{+0.199}_{-0.083}$ | $14.594^{+0.131}_{-0.057}$
D5 | $340^{+410}_{-210}$ | $5.78^{+0.67}_{-0.63}$ | $13.10^{+0.31}_{-0.15}$ | $14.55^{+0.19}_{-0.10}$
D6 | – | $5.83^{+1.16}_{-0.76}$ | $13.33^{+0.56}_{-0.20}$ | $14.45^{+0.39}_{-0.16}$
D7 | – | $6.40^{+0.59}_{-1.26}$ | $13.32^{+0.55}_{-0.21}$ | $14.47^{+0.37}_{-0.12}$
H1a | – | $5.74^{+0.69}_{-0.50}$ | $13.558^{+0.225}_{-0.076}$ | $14.635^{+0.152}_{-0.089}$
H1b | – | $5.90^{+0.65}_{-0.51}$ | $13.809^{+0.180}_{-0.069}$ | $14.713^{+0.154}_{-0.094}$
H2 | – | $5.95^{+0.90}_{-1.34}$ | $13.57^{+0.74}_{-0.13}$ | $14.31^{+0.49}_{-0.20}$
H3 | – | $6.84^{+0.15}_{-1.83}$ | $13.75^{+0.62}_{-0.13}$ | $14.52^{+0.43}_{-0.23}$
H4 | – | $6.63^{+0.36}_{-1.48}$ | $13.774^{+0.556}_{-0.095}$ | $14.47^{+0.37}_{-0.12}$
J1 | – | $5.67^{+1.05}_{-0.27}$ | $13.36^{+0.30}_{-0.17}$ | $14.38^{+0.21}_{-0.16}$
J2 | – | – | $14.239^{+0.316}_{-0.052}$ | $14.859^{+0.276}_{-0.051}$
J3 | – | $5.69^{+0.85}_{-0.14}$ | $13.448^{+0.187}_{-0.088}$ | $14.593^{+0.175}_{-0.046}$
J4 | – | – | $13.29^{+0.45}_{-0.22}$ | $14.33^{+0.29}_{-0.18}$
K1 | $480^{+380}_{-240}$ | $5.93^{+0.68}_{-0.56}$ | $13.46^{+0.23}_{-0.12}$ | $14.61^{+0.19}_{-0.10}$
K2 | $450^{+370}_{-260}$ | – | $13.39^{+0.42}_{-0.13}$ | $14.532^{+0.280}_{-0.099}$
K3 | – | $5.67^{+1.32}_{-0.43}$ | $13.37^{+0.48}_{-0.16}$ | $14.614^{+0.321}_{-0.095}$
K4 | $460^{+290}_{-310}$ | $5.84^{+0.46}_{-0.68}$ | $13.45^{+0.24}_{-0.11}$ | $14.63^{+0.15}_{-0.10}$
K5a | – | $5.61^{+1.16}_{-0.29}$ | $13.20^{+0.34}_{-0.16}$ | $14.57^{+0.25}_{-0.11}$
K5b | – | $5.87^{+1.12}_{-0.56}$ | $13.24^{+0.41}_{-0.15}$ | $14.446^{+0.303}_{-0.081}$
K5c | – | $5.87^{+0.85}_{-0.60}$ | $13.25^{+0.34}_{-0.17}$ | $14.47^{+0.24}_{-0.12}$
K6a | $360^{+400}_{-200}$ | $5.73^{+0.76}_{-0.47}$ | $13.51^{+0.27}_{-0.12}$ | $14.72^{+0.18}_{-0.10}$
K6b | – | $5.82^{+0.99}_{-0.79}$ | $13.46^{+0.47}_{-0.14}$ | $14.668^{+0.294}_{-0.089}$
K7a | – | $5.65^{+0.85}_{-0.32}$ | $13.594^{+0.188}_{-0.072}$ | $14.784^{+0.151}_{-0.042}$
K7b | – | $5.9\pm 1.0$ | $13.44^{+0.61}_{-0.24}$ | $14.58^{+0.44}_{-0.20}$
K8a | $590^{+210}_{-340}$ | $5.78^{+0.46}_{-0.45}$ | $13.97^{+0.17}_{-0.11}$ | $15.108^{+0.127}_{-0.097}$
K8bc1 | – | $6.20^{+0.79}_{-1.20}$ | $13.848^{+0.595}_{-0.097}$ | $14.58^{+0.39}_{-0.15}$
K8bc2 | $--$ | $5.84^{+1.15}_{-0.46}$ | $13.52^{+0.34}_{-0.16}$ | $14.703^{+0.254}_{-0.086}$
Source | $\mathrm{T_{kin}}$ | $\log{\mathrm{n_{H}}}$ | $\log{\mathrm{N_{SiO}}}$ | $\log{\mathrm{N_{SO}}}$
---|---|---|---|---
| [$\mathrm{K}$] | [${\mathrm{cm}}^{-3}$] | [${\mathrm{cm}}^{-2}$] | [${\mathrm{cm}}^{-2}$]
K9 | – | $6.09^{+0.53}_{-0.77}$ | $13.65^{+0.30}_{-0.12}$ | $14.907^{+0.215}_{-0.097}$
K10 | – | $5.93^{+1.06}_{-0.63}$ | $13.58^{+0.44}_{-0.13}$ | $14.654^{+0.301}_{-0.088}$
K11 | – | $5.77^{+1.22}_{-0.77}$ | $13.61^{+0.62}_{-0.32}$ | $14.83^{+0.38}_{-0.20}$
K12 | – | – | $13.49^{+0.73}_{-0.47}$ | $14.81^{+0.42}_{-0.21}$
K13a | – | $6.01^{+0.82}_{-0.86}$ | $13.53^{+0.36}_{-0.18}$ | $14.787^{+0.263}_{-0.072}$
K13b | – | – | $13.68^{+0.73}_{-0.51}$ | $14.95^{+0.43}_{-0.22}$
K14 | $580^{+360}_{-290}$ | – | $13.48^{+0.68}_{-0.31}$ | $14.59^{+0.50}_{-0.24}$
K15a | $470^{+400}_{-240}$ | $5.85^{+1.14}_{-0.65}$ | $13.43^{+0.44}_{-0.14}$ | $14.41^{+0.31}_{-0.14}$
K15b | $720^{+280}_{-360}$ | $6.16^{+0.83}_{-1.05}$ | $13.50^{+0.51}_{-0.21}$ | $14.63^{+0.35}_{-0.15}$
K16 | – | $5.66^{+1.33}_{-0.60}$ | $13.47^{+0.57}_{-0.30}$ | $14.73^{+0.36}_{-0.14}$
K17 | – | – | $13.87^{+0.79}_{-0.31}$ | $14.84^{+0.63}_{-0.35}$
K18 | – | $6.32^{+0.68}_{-1.11}$ | $13.11^{+0.48}_{-0.19}$ | $14.30^{+0.33}_{-0.10}$
K19 | – | $5.81^{+1.17}_{-0.55}$ | $13.47^{+0.41}_{-0.11}$ | $14.494^{+0.286}_{-0.084}$
K20 | – | $5.43^{+0.98}_{-0.45}$ | $13.46^{+0.37}_{-0.14}$ | $14.71^{+0.23}_{-0.12}$
K21a | – | $5.82^{+1.17}_{-0.47}$ | $13.82^{+0.38}_{-0.13}$ | $14.931^{+0.263}_{-0.086}$
K21b | $610^{+270}_{-380}$ | $6.04^{+0.92}_{-1.08}$ | $13.54^{+0.59}_{-0.22}$ | $14.70^{+0.39}_{-0.17}$
K22 | – | – | $13.50^{+0.86}_{-0.58}$ | $14.65^{+0.63}_{-0.33}$
K23 | – | $5.88^{+1.07}_{-0.66}$ | $13.01^{+0.51}_{-0.25}$ | $14.31^{+0.35}_{-0.13}$
K24 | $917^{+81}_{-574}$ | $5.74^{+1.25}_{-0.93}$ | $13.31^{+0.75}_{-0.25}$ | $14.40^{+0.53}_{-0.24}$
L1 | $610^{+190}_{-420}$ | $5.65^{+0.67}_{-0.45}$ | $13.66^{+0.25}_{-0.11}$ | $14.739^{+0.160}_{-0.096}$
L2 | – | $5.75^{+0.63}_{-0.52}$ | $13.61^{+0.25}_{-0.14}$ | $14.84^{+0.16}_{-0.12}$
L3 | $480^{+360}_{-320}$ | $5.85^{+1.00}_{-0.91}$ | $13.29^{+0.67}_{-0.52}$ | $14.68^{+0.41}_{-0.17}$
L4 | $580^{+230}_{-410}$ | $5.68^{+0.80}_{-0.47}$ | $13.52^{+0.26}_{-0.13}$ | $14.828^{+0.189}_{-0.095}$
L5 | – | – | $13.60^{+0.37}_{-0.12}$ | $14.843^{+0.271}_{-0.063}$
L6 | $560^{+220}_{-330}$ | $5.77^{+0.58}_{-0.31}$ | $13.631^{+0.156}_{-0.093}$ | $14.85^{+0.13}_{-0.10}$
L7 | – | $5.69^{+0.63}_{-0.53}$ | $13.68^{+0.24}_{-0.13}$ | $15.029^{+0.160}_{-0.095}$
L8 | – | $5.76^{+0.66}_{-0.42}$ | $13.38^{+0.20}_{-0.12}$ | $14.78^{+0.15}_{-0.11}$
L9 | – | $5.63^{+1.08}_{-0.42}$ | $13.20^{+0.38}_{-0.24}$ | $14.78^{+0.25}_{-0.12}$
L10a | $580^{+310}_{-340}$ | $5.46^{+1.07}_{-0.41}$ | $13.41^{+0.35}_{-0.18}$ | $14.86^{+0.24}_{-0.10}$
L10b | – | $5.78^{+0.58}_{-0.59}$ | $13.64^{+0.25}_{-0.13}$ | $14.96^{+0.16}_{-0.10}$
L11 | – | – | $12.97^{+0.54}_{-0.51}$ | $14.604^{+0.324}_{-0.076}$
L12 | – | $6.20^{+0.79}_{-1.26}$ | $13.35^{+0.64}_{-0.35}$ | $14.55^{+0.44}_{-0.21}$
L13 | $510^{+260}_{-270}$ | $5.72^{+0.50}_{-0.37}$ | $13.58^{+0.17}_{-0.10}$ | $14.847^{+0.112}_{-0.085}$
L14 | $420^{+340}_{-240}$ | $5.79^{+0.65}_{-0.42}$ | $13.513^{+0.200}_{-0.090}$ | $14.721^{+0.148}_{-0.095}$
L15 | $350^{+410}_{-190}$ | $5.71^{+0.78}_{-0.52}$ | $13.56^{+0.27}_{-0.14}$ | $14.863^{+0.195}_{-0.096}$
L16 | $480^{+390}_{-240}$ | $5.79^{+0.93}_{-0.39}$ | $13.51^{+0.28}_{-0.13}$ | $14.81^{+0.21}_{-0.11}$
L17 | $500^{+300}_{-230}$ | $5.78^{+0.50}_{-0.33}$ | $13.876^{+0.135}_{-0.075}$ | $14.998^{+0.113}_{-0.083}$
L18 | – | $5.83^{+0.52}_{-0.46}$ | $13.66^{+0.17}_{-0.10}$ | $14.869^{+0.144}_{-0.092}$
L19c1 | $680^{+320}_{-290}$ | $5.81^{+0.62}_{-0.77}$ | $13.26^{+0.31}_{-0.16}$ | $14.559^{+0.230}_{-0.097}$
L19c2 | – | $5.88^{+0.47}_{-0.41}$ | $13.886^{+0.146}_{-0.082}$ | $14.979^{+0.118}_{-0.088}$
L20 | $500^{+290}_{-260}$ | $5.88^{+0.46}_{-0.44}$ | $13.828^{+0.147}_{-0.094}$ | $15.002^{+0.137}_{-0.083}$
L21 | $560^{+190}_{-410}$ | $5.80^{+0.55}_{-0.53}$ | $13.61^{+0.21}_{-0.10}$ | $14.928^{+0.145}_{-0.086}$
L22 | – | $5.75^{+0.62}_{-0.32}$ | $13.845^{+0.172}_{-0.093}$ | $15.095^{+0.137}_{-0.083}$
L23 | – | $5.77^{+0.61}_{-0.38}$ | $13.781^{+0.162}_{-0.090}$ | $15.052^{+0.134}_{-0.089}$
L24 | $590^{+140}_{-370}$ | $5.82^{+0.47}_{-0.43}$ | $13.706^{+0.180}_{-0.098}$ | $15.040^{+0.119}_{-0.099}$
Source | $\mathrm{T_{kin}}$ | $\log{\mathrm{n_{H}}}$ | $\log{\mathrm{N_{SiO}}}$ | $\log{\mathrm{N_{SO}}}$
---|---|---|---|---
| [$\mathrm{K}$] | [${\mathrm{cm}}^{-3}$] | [${\mathrm{cm}}^{-2}$] | [${\mathrm{cm}}^{-2}$]
L25 | $300^{+420}_{-130}$ | $5.74^{+0.45}_{-0.51}$ | $13.85^{+0.23}_{-0.11}$ | $15.016^{+0.122}_{-0.094}$
L26 | $580^{+260}_{-350}$ | $5.86^{+0.67}_{-0.56}$ | $13.58^{+0.24}_{-0.11}$ | $14.85^{+0.18}_{-0.11}$
L27 | $360^{+430}_{-210}$ | $5.82^{+0.68}_{-0.57}$ | $13.67^{+0.28}_{-0.17}$ | $14.92^{+0.18}_{-0.13}$
L28 | $350^{+460}_{-150}$ | $5.89^{+0.55}_{-0.54}$ | $13.54^{+0.19}_{-0.11}$ | $14.719^{+0.152}_{-0.097}$
L29 | – | $5.79^{+0.72}_{-0.55}$ | $13.35^{+0.26}_{-0.15}$ | $14.59^{+0.20}_{-0.11}$
L30c1 | $490^{+410}_{-240}$ | $5.99^{+0.89}_{-0.68}$ | $13.48^{+0.43}_{-0.21}$ | $14.50^{+0.30}_{-0.11}$
L30c2 | $450^{+410}_{-270}$ | – | $13.02^{+0.62}_{-1.01}$ |
M1 | $400^{+460}_{-170}$ | $5.65^{+0.87}_{-0.58}$ | $13.23^{+0.36}_{-0.14}$ | $14.42^{+0.23}_{-0.12}$
M2 | $510^{+370}_{-290}$ | – | $12.89^{+0.39}_{-0.19}$ | $14.27^{+0.28}_{-0.10}$
M3 | – | $6.78^{+0.17}_{-1.49}$ | $13.17^{+0.51}_{-0.27}$ | $14.50^{+0.35}_{-0.13}$