Cluster Formation Triggered by Filament Collisions in Serpens South
Fumitaka Nakamura1,2,3,4 , Koji Sugitani5 , Tomohiro Tanaka6 , Hiroyuki Nishitani2 , Kazuhito
Dobashi7 , Tomomi Shimoikura7 , Yoshito Shimajiri8 , Ryohei Kawabe1 Yoshinori Yonekura9 , Izumi
Mizuno2,11 , Kimihiko Kimura6 , Kazuki Tokuda6 , Minato Kozu6 , Nozomi Okada6 , Yutaka
Hasegawa6 , Hideo Ogawa6 , Seiji Kameno12 , Hiroko Shinnaga1 , Munetake Momose13 , Taku
Nakajima14 , Toshikazu Onishi6 , Hiroyuki Maezawa6 , Tomoya Hirota1 , Shuro Takano2,3 , Daisuke
Iono1 , Nario Kuno2,3,15 , Satoshi Yamamoto16
ABSTRACTThe Serpens South infrared dark cloud consists of several ﬁlamentary ridges, someof which fragment into dense clumps. On the basis of CCS (JN = 43 − 32 ), HC3 N(J = 5 − 4), N2 H+ (J = 1 − 0), and SiO (J = 2 − 1, v = 0) observations, we investigatedthe kinematics and chemical evolution of these ﬁlamentary ridges. We ﬁnd that CCS
is extremely abundant along the main ﬁlament in the protocluster clump. We emphasize that Serpens South is the ﬁrst cluster-forming region where extremely-strong CCS
1National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan; fumitaka.nakamura@nao.ac.jp

2

Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1305, Japan

3

The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan

4

Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106-4030

5Graduate School of Natural Sciences, Nagoya City University, Mizuho-ku, Nagoya 467-8501, Japan

6

Department of Physical Science, Osaka Prefecture University, Gakuen 1-1, Sakai, Osaka 599-8531, Japan

7

Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan

8

Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, IRFU/Service d’Astrophysique, CEA Saclay, F91191 Gif-sur-Yvette, France
9

Center for Astronomy, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan10

Institute of Astrophysics and Planetary Sciences, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512, Japan

11

Department of Physics, Faculty of Science, Kagoshima University, 1-21-35 Korimoto, Kagoshima, Kagoshima
890-0065, Japan
12

Joint ALMA Observatory, Alonso de Crdova 3107 Vitacura, Santiago, Chile

13

Institute of Astrophysics and Planetary Sciences, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512, Japan

14

Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601,
Japan
15

Department of Physics, Graduate School of Pure and Applied Sciences, The University of Tsukuba, 1-1-1 Tennodai, Tsukuba Ibaraki 305-8577, Japan
16

Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan

–2–emission is detected. The CCS-to-N2 H+ abundance ratio is estimated to be about 0.5
toward the protocluster clump, whereas it is about 3 in the other parts of the main ﬁlament. We identify six dense ridges with diﬀerent VLSR . These ridges appear to converge
toward the protocluster clump, suggesting that the collisions of these ridges may havetriggered cluster formation. The collisions presumably happened within a few × 105 yr
because CCS is abundant only in such a short time. The short lifetime agrees with thefact that the number fraction of Class I objects, whose typical lifetime is 0.4 × 105 yr,
is extremely high as about 70 percent in the protocluster clump. In the northern part,two ridges appear to have partially collided, forming a V-shape clump. In addition, we
detected strong bipolar SiO emission that is due to the molecular outﬂow blowing outof the protostellar clump, as well as extended weak SiO emission that may originate
from the ﬁlament collisions.
Subject headings: ISM: structure — ISM: clouds — ISM: kinematics and dynamics —stars: formation

1.

Introduction

Over the last few decades, considerable progress has been made in the understanding of starcluster formation (e.g., Lada & Lada 2003). For example, radio and infrared observations haverevealed that star clusters form in parsec-scale dense molecular clumps with masses of order of
102 − 103 M⊙ (Lada & Lada 2003; Ridge et al. 2003; Battersby et al. 2010). In the cluster-forming
clumps, stellar feedback plays a crucial role in the structure formation of the clumps (Sandell &Knee 2001). The clumps tend to keep quasi-virial equilibrium states at least for several free-falltimes, by sustaining supersonic turbulence supplied by stellar feedback (e.g., Tan et al. 2006; Li& Nakamura 2006; Matzner 2007; Nakamura & Li 2014).
In contrast, the initial conditions of cluster formation remain to be elucidated because of thelack of the observational characterization. This is because once active star formation is initiated,stellar feedback such as protostellar outﬂows and radiation rapidly shapes their surroundings, making it diﬃcult to track back the physical conditions of the clumps prior to active cluster formation,i.e., pre-protocluster clumps (or, precluster clumps, in short). According to recent numerical simulations, the initial conditions such as density proﬁle, magnetic ﬁeld distribution, and turbulent
Mach number determine some properties of forming clusters (Girichidis et al. 2012; Li et al. 2010)
because these factors control the fragmentation process. Therefore, it is important to search formolecular clouds where active cluster formation have just been initiated or is just about to be
initiated.
Recently, Tanaka et al. (2013) found that the Serpens South infrared dark cloud (IRDC,
d ∼ 415 pc) is the region that contains both extremely-young protocluster and precluster clumps.
The Serpens South IRDC is a ﬁlamentary molecular cloud that contains several ﬁlamentary ridges

–3–(Gutermuth et al. 2008; André et al. 2010; Maury et al. 2011; Kirk et al. 2013; Arzoumanian et al.
2013). The central clump is associated with a very young (. 0.5 Myr) cluster of low-mass protostars(Gutermuth et al. 2008) and is most massive with about 230 M⊙ (Tanaka et al. 2013). A northernclump shows no sign of active star formation, although its mass (∼ 200 M⊙ ) and size are comparable
to those of the central protocluster clump, i.e., this northern clump is the precluster clump. Both
protocluster and precluster clumps have virial ratios as small as 0.2, indicating that the internal
turbulent motions cannot support the whole clumps against gravity. In spite of the small virial
ratios, the clumps do not exhibit rapid infall motions, and therefore their global contraction is likely
to be delayed by the moderately-strong magnetic ﬁelds that are perpendicular to the ﬁlament axis.
From the Chandrasekhar-Fermi method, the ﬁeld strength is estimated to be a few × 102 µG, close
to the critical value above which the cloud can be supported against collapse (Sugitani et al. 2011).
In the present paper, we aim to unveil how cluster formation has been initiated in Serpens
South, by investigating the kinematics of ﬁlamentary ridges on the basis of CCS and N2 H+ observations. CCS and N2 H+ are known to be abundant in early and late phases of prestellar evolution,
respectively, and therefore are appropriate to inspect the evolutionary stages of young star-forming
regions (e.g., Hirota et al. 2009).

2.

Observations and Data

We carried out CCS JN = 43 − 32 (45.379033 GHz) and HC3 N J = 5 − 4 (45.490316 GHz)
mapping observations toward Serpens South in 2013 May with the Nobeyama 45-m telescope. We
use a new 45 GHz band, dual-polarization receiver, Z45 (Tokuda et al. 2013). The main beameﬃciency and Half Power Beam Width (HPBW) were ηZ45 ≃ 0.7 and Θ ≃ 37′′ , respectively. At
the back end, we used the 4 sets of 4096 channel SAM45 spectrometer whose frequency resolution
was set to 3.81 kHz (≈ 0.025 km s−1 at 45 GHz), The intensity calibration was made by observing
the cyanopolyyne peak of TMC-1 using the S40 receiver + AOS system.
We also carried out SiO J = 2 − 1 (86.847010 GHz) observations in 2013 May using the TZ +SAM45 receiver system of the 45-m telescope. The main beam eﬃciency and HPBW were ηTZ ≃0.36 and 19′′ at 86 GHz, respectively (Nakajima et al. 2013).
The typical system temperatures during the observations were 150 K and 120 K for Z45 andTZ, respectively. The telescope pointing was checked every 1 hour by observing a SiO maser source,
IRC+00363, and the typical pointing oﬀset was better than 3′′ during the whole observing period.
By applying a convolution scheme with a spheroidal function, the ﬁnal maps were obtained by
combining x-scan and y-scan OTF data into single maps with grid sizes of 15′′ and 7.5′′ for the Z45
and TZ observations, respectively. The resultant eﬀective resolutions of the maps were about 49′′
and 25′′ for Z45 and TZ, respectively. In the following, the intensities are shown in the main beam
brightness temperature units, Tmb = TA∗ /ηZ45 or TA∗ /ηTZ , where TA∗ is the antenna temperaturecorrected for the atmospheric attenuation. The rms noise levels are 0.32 K and 0.24 K at the

–4–velocity resolution of 0.05 km s−1 for Z45 and TZ, respectively.
For the N2 H+ data, we used the data presented in Tanaka et al. (2013).

3.

Global Gas Distribution and Kinematics

In Serpens South, several less-dense ﬁlamentary ridges appear to converge toward the protocluster clump (see also Myers 2009). In Figure 1(a), we show the positions of nine representativeﬁlamentary ridges that are overlaid on the H2 column density map obtained by Herschel data with36′′ .3 eﬀective resolution (see Tanaka et al. 2013). The positions of the ridges are determined byeye from the Herschel map. The identiﬁed ridges are named as F1, F2, · · ·, F9 in Figure 1(a).
F2 and F8 trace the main ﬁlamentary cloud. F2 and F3 appear to be connected with eachother at their southern tips, creating the V-shape precluster clump. F1 is located between F2 andF3. F2, F3, and F8 are essentially the same as those identiﬁed by Kirk et al. (2013) who found thelarge velocity gradient of 2.2 ± 0.3 km s−1 pc−1 along F8, where we adopted the distance of 415
pc. F7 is extended toward the eastward direction and can also be recognized in the Spitzer IRAC
image (see Figure 1 of Gutermuth et al. 2008).
The CCS, HC3 N, and N2 H+ integrated intensity maps show that their emission traces reasonably well the dense parts of the cloud (Figures. 1(b) though 1(d)). F1, F2, F3, F7, F8, and F9
are detected in N2 H+ , HC3 N, and/or CCS, and thus contain dense gas with densities of 104 − 105
cm−3 . Other ridges, F4, F5, and F6, are not clearly detected in CCS, HC3 N, and N2 H+ . The
CCS emission tends to be strong along the main ﬁlamentary cloud F2+F8. In particular, the CCS
emission is extremely strong along F2, whereas it is weak in the protocluster clump where theN2 H+ emission is strongest. The CCS column density is estimated to be about ∼ 1 × 1014 cm−2
toward the precluster clump. Such an extremely high column density of CCS is typical of the
Carbon-Chain Producing Regions suggested by Hirota et al. (2009).
The CCS fractional abundances are estimated to be about 1 × 10−9 , 1 × 10−10 , and 1 × 10−9
toward the dense part of F8, protocluster clump, and precluster clump, respectively, where we
adopted the excitation temperature of 5 K and LTE approximation (e.g., Wolkovitch et al. 1997;
Lai & Crutcher 2000). We note that a change in excitation temperature of 1K causes a change incolumn density and abundance of 30 %. The CCS fractional abundance in the protocluster clump
is of the order of magnitude smaller than the other parts of the main ﬁlament. The [CCS]/[N2 H+ ]abundance ratio are also estimated to be 3.0, 0.4, and 2.5, for F8, protocluster clump, and precluster
clump, respectively, where N2 H+ abundances are adopted from Tanaka et al. (2013). In other words,
the distribution of CCS tends to be anti-correlated with that of N2 H+ . According to the chemical
evolution (e.g., Suzuki et al. 1992; Marka et al. 2012), CCS is abundant only in the early phase ofprestellar evolution (. a few × 105 yr), whereas N2 H+ becomes abundant in the late phase. Thus,
CCS and N2 H+ can often been used as an age indicator of dense cores (e.g., de Gregorio-Monsalvo
et al. 2006; Sakai et al. 2007; Hirota et al. 2009; Devine et al. 2011). The CCS-rich F2 and F8

–5–
ridges are likely to be chemically and dynamically young. HC3 N distribution is roughly similar tothat of CCS.
To see the global kinematic motions of the ﬁlamentary ridges, we show in Figures 2 (a) and 2(b) the centroid velocity maps of N2 H+ and CCS, respectively, which are overlaid on the HerschelH2 column density contour map. The CCS and N2 H+ centroid velocity maps are in good agreementwith each other, except at the central clump. The maps show that the main ﬁlamentary ridge, F8,
is blueshifted from the systemic velocity of the central protocluster clump (Vsys ≃ 7 km s−1 ).
On the other hand, other ridges, F2, F3, F7, and F9, are redshifted from Vsys (Figures. 2(a) and 2 (b).) The velocity structures in the northern part are somewhat complicated. The
typical diﬀerence in VLSR is around 0.5 − 0.7 km s−1 in the northern part. The dynamical timeof the ﬁlament suggests that the ﬁlaments are formed with short spacing of 0.4 − 0.5 pc (≈0.5 Myr × (0.5 − 0.7) km s−1 / cos 45◦ ), where we assume that the collision velocity is equal to thevelocity diﬀerence and this region has an inclination of 45◦ . Here we adopt the dynamical timeof about 0.5 Myr, which is the lifetime of Serpens South protocluster. This suggests that theﬁlaments do not form by gravitational fragmentation, instead by external events such as turbulent
compression, and the densities become as high as 104 cm−3 within a few × 105 Myr.
In fact, the CCS line proﬁles shown in Figures 2 (c) through 2 (f) consist of a couple ofcomponents with diﬀerent velocities in several positions around the V-shape clump. The CCS line
width of each component is typically 0.6 − 0.8 km s−1 , which is about 1.5 − 2 times larger than
the typical CCS line widths (0.3 − 0.6 km s−1 ) of more quiescent clouds such as Taurus (Suzuki etal. 1992).
The main ridge F8 has a signiﬁcant velocity gradient that can be interpreted as an infall motion
toward the protocluster clump (Kirk et al. 2013), although the northern part of the ﬁlament does
not show similar velocity gradients. On the other hand, CCS is weak along F7 and F9. It is worth
noting that Serpens South is a really unique cluster-forming region in terms of the extremely-highfractional abundance of CCS and other carbon-chain molecules such as HC7 N (Friesen et al. 2013).
The CCS line widths are also wider than those of nearby CCS-rich dark clouds such as Taurus.

4.

A Scenario of Triggered Cluster Formation in Serpens South

From these characteristics, we propose the following scenario of cluster formation in Serpens
South, as in Figure 3.
In Serpens South, the magnetic ﬁeld is relatively strong and plays an important role in clouddynamics (Sugitani et al. 2011). In the parent cloud, multiple ﬁlamentary ridges were created due
to internal MHD turbulence and/or large-scale ﬂows. These ﬁlamentary ridges were preferentiallyperpendicular to the global magnetic ﬁeld lines and moved along the magnetic ﬁeld lines. The
ﬁlaments also fragmented into several subclumps. Since the ﬁlaments were likely to be magnetically–6–
supported (Sugitani et al. 2011), the fragmentation was presumably triggered by ambipolar diﬀusion
accelerated in a turbulent environment (Nakamura & Li 2008; Tanaka et al. 2013). The collisions
tend to make the eﬀective magnetic support reduced and inject additional turbulence in the denseparts. Consequently, cluster formation was initiated in the central clump.
It is diﬃcult to identify which ridges are paired with which because the velocity structure iscomplicated particularly in the northern part. But, we suggest that F2 and F8 were from the sameﬁlament because CCS is abundant along these ridges. This identiﬁcation agrees with the structure
identiﬁed by Kirk et al. (2013). Kirk et al. (2013) also suggested that F3 is paired with F9. If thisis the case, F1 and F7 might be from the same ﬁlament. But, there is a possibility that F1 and F3
may be paired with F9 and F7, respectively.
In any of these cases, at least three ﬁlamentary ridges may have collided at the position of the
protocluster clump. The collision may have happened within a few × 105 yr because most of the
protostars in the dense clump are the Class I objects whose typical lifetime is around 0.4 Myr (Evanset al. 2009). This timescale is in good agreement with that inferred from the chemical evolutionof CCS. Two subclumps formed along the diﬀerent ridges F2 and F3 have just collided with eachother to form the V-shape clump, which may be on the verge of future cluster formation. Such
dynamical event may have caused the CCS line widths to be wider than those in more quiescentdark clouds.
To search for further evidence of the ﬁlament collisions, we carried out SiO (J = 2 − 1, v = 0)
observations. The SiO emission is sometimes used as a shock tracer of the cloud-cloud collision(e.g., Jimenez-Serra et al. 2010). Figure 2 (j) shows the SiO integrated intensity map. We detected
emission from both the central protocluster and northern precluster clumps. We note that Kirk etal. (2013) reported no detection of SiO emission on the basis of Mopra 22-m observations. Thisapparent discrepancy comes from the fact that the sensitivity of our map is much better thanthat of Kirk et al. (2013). The emission associated with the central clump is likely to be due
to a protostellar outﬂow, because the emission shows a well-deﬁned bipolar feature. In addition,
we detected weak emission lines at several positions as presented in Figures 2 (g) through 2 (d).
These weak SiO lines might contain contribution of compressional heating by the ongoing ﬁlamentcollision at around VLSR ∼ 7 km s−1 . However, the higher velocity component (VLSR & 10 km s−1 )near the southern tip of the northern clump presumably originates from the interaction between
the northern clump and the redshifted CO lobe identiﬁed by Nakamura et al. (2011) as R2, because
the SiO emission overlaps well with the northern part of the redshifted CO lobe whose velocity
range is VLSR ∼ 10 − 30 km s−1 . Further justiﬁcation is needed to conﬁrm the origin of the weak
SiO emission.
Position-velocity diagrams presented in Figures. 4 (a) though 4 (c) show two components with
diﬀerent VLSR in the northern part. These two appear to converge at the precluster clump whereline width becomes wider (Figure. 4 (c)). Such structure is reminiscent of the kinetic structure
generated by ﬁlament collision (Duarte-Cabral et al. 2011). At the protocluster clump, there also

–7–
appear two components with diﬀerent VLSR : 6.5 km s−1 and 7.5 km s−1 . The latter is weak andvaguely recognized in the position-velocity diagrams. This component might be a remnant of F9due to ﬁlament collision. A large velocity gradient along F8 appears inconsistent with an accretion
ﬂow model (Kirk et al. 2013) because the accretion ﬂow model predicts that the velocity gradientnear the clump should be largest because the ﬂow is accelerated by self-gravity and at both sidesof the clump, infall motions should be observed (Figure 5d of Nakamura et al. (1991)). Thus, weconclude that our collision scenario appears more consistent with kinetic structure of Serpens Souththan an accretion model.
Recently, the cloud-cloud collision has paid attention as a promising mechanism for triggering
cluster formation (e.g., Tasker & Tan 2009; Higuchi et al. 2010; Shimoikura et al. 2013; Fukui et al.
2014; Jimenez-Serra et al. 2014). Serpens South is the nearest IRDC that contains both protocluster
and precluster clumps. Therefore, it is an interesting region to investigate how the cloud-cloud collision triggers individual star formation by using high-angular resolution interferometric observations
such as ALMA.
This work is supported in part by a Grant-in-Aid for Scientiﬁc Research of Japan (24244017)
and the National Science Foundation under Grant (NSF PHY11-25915). We are grateful to the
staﬀs at the Nobeyama Radio Observatory for both operating the 45-m and helping us with thedata reduction. NRO is a branch of the National Astronomical Observatory, National Institutes of
Natural Sciences, Japan.

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– 10 –
50 ′0 ″

N H2 ( ×10 cm -3 )23(a) H 2 column densityCCS(b) (b)2.0(d) N2H+(c) HC3Nc

F2

55 ′0 ″F1

DEC (J2000)

F3
F4

1.5

d
e
f

-2 °0 ′0 ″1.0F5

-2 °5 ′0 ″ F7

F6

g

0.5

h
i

F8

F9

30m20s 30m10s 30m0s 18h29m50s

30m20s 30m10s 30m0s 18h29m50s

30m20s 30m10s 30m0s18h29m50s

RA (J2000)

RA (J2000)

RA (J2000)

30m20s30m10s30m0s

18h29m50s

0.0

RA (J2000)

Fig. 1.— (a) The H2 column density map (see Tanaka et al. 2013 for detail.) The positions ofnine ridges are indicated with the dashed curves. The contours start at 0.12 × 1023 cm−2 with alogarithmic interval of log[∆NH2 /(1.2 × 1023 cm−2 )] = 0.2. (b) CCS (JN = 43 − 32 ) integrated
intensity contour map in the velocity range from VLSR = 5.5 to 9.0 km s−1 . The image is overlaid
on the H2 column density map. The contour level starts from 0.33 K km s−1 with an interval of
0.33 K km s−1 , corresponding to the 3 σ noise level. (c) HC3 N (J = 5 − 4) integrated intensity
contour map in the velocity range from VLSR = 5.5 to 9.0 km s−1 . The image is overlaid on the H2column density map. The contour level starts from 0.3 K km s−1 with an interval of 0.4 K km s−1 .
(d) N2 H+ (J = 1 − 0) integrated intensity contour map overlaid on the H2 column density map.
The contour level starts from 2 K km s−1 with an interval of 2 K km s−1 .

– 11 –

7.0

7.2

7.4

7.6

(a) N2H+

Vc (km/s)

6.6

6.8

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Tmb (K)(b) CCS1d

F4-2 °0 ′0 ″0(d) CCS
20

Tmb (K)F930m20s 30m10s 30m0s18h29m50s

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i

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3

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c

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2

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56

7
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9-2°4 ′
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18h29m50s

Fig. 2.— (a) Centroid velocity map for N2 H+ (J = 1−0) across Serpens South. The N2 H+ centroid
velocity map was obtained by ﬁtting the seven hyperﬁne lines with Gaussian proﬁles (Tanaka et
al. 2013). (b) same as panel (a) but for CCS (JN = 43 − 32 ). For panels (a) and (b), the contours
are the same as those in Fig. 1 (a). (c) through (f) CCS line proﬁles at four positions that aredesignated in Fig. 2b with circles. (g) SiO (J = 2 − 1, v = 0) line proﬁle at the position g in panel(j). (h) Same as panel (g) but for the position h. (i) Same as panel (g) but for the position i. (j)SiO (J = 2 − 1) integrated intensity contour map overlaid on the H2 column density map. The
black and gray contours show the blueshifted and redshifted components integrated over −10 ∼ 7
km s−1 and 8 ∼ 20 km s−1 , respectively. The contour level starts from 1 K km s−1 with an intervalof 1 K km s−1 , corresponding to the 3.5 σ and 2.5 σ noise levels for the blueshifted and redshiftedcomponents, respectively. The color image is the same as that shown in Figure 1.

– 12 –

(a) filament-filament interaction(b) triggered cluster formation
F1
F2

precluster clump (CCS rich)
F3

collision point?

magnetic field lines
CCS poor

protocluster clump

F7
F8

CCS poor
CCS rich

F9

CCS rich

Fig. 3.— Possible scenario of cluster formation triggerd by ﬁlament collisions in Serpens South.
(a) at least three ﬁlamentary ﬂows are on the verge of the collisions along the global magnetic
ﬁeld lines. The ﬁlaments fragment into several subclumps due to turbulence-accelerated ambipolar
diﬀusion. Several stars may have formed in the subclumps before the collisions, and these stars
are now observed as Class II sources. (b) They collided and crossed at the center where cluster
formation was triggered. For the northern clump, the collision has just happened at its southerntip.

– 13 –

0

VLSR (km/s)

6

0.5

1.0

1.5

2 Tmb (K)(a) along F2
precluster clump

7
8

a remnant of F8?

9

F1

6
7
8
9

(b)

6
7
8
9

(c)

6
7
8
9

(d) precluster clump

6
7
8
9

(e) protocluster clump

6
7
8
9
6
7
8
9

F2

a remnant of F9?

(f)

(g)
F8
-5’

F9
0

5’

Fig. 4.— Position-velocity diagram of CCS. The positions of these cuts in the map are shown aswhite dashed lines in