Observational Evidence of the Merging of Filaments and Hub Formation in G083.097+03.270

We uncover a hub–filament system correlated with massive young stellar associations in G083.097+03.270. Diagnosed with simultaneous 12CO, 13CO, and C18O line observations, the region is found to host two distinct and elongated filaments having separate velocity components, interacting spatially and kinematically, that appear to have seeded the formation of a dense hub at the intersection. A large velocity spread at the hub, in addition to a clear bridging feature connecting the filaments in velocity, indicate the merging of filaments. Along the filament axis, the velocity gradient reveals a global gas motion with an increasing velocity dispersion inward to the hub signifying turbulence. Altogether, the clustering of Class I sources, a high excitation temperature, a high column density, and the presence of a massive outflow at the central hub suggest enhanced star formation. We propose that the merging of large-scale filaments and velocity gradients along filaments are the driving factors in the mass accumulation process at the hub that have sequentially led to the massive star formation. With two giant filaments merging to coincide with a hub therein with ongoing star formation, this site serves as a benchmark for the “filaments to clusters” star-forming paradigm.


Introduction
The filamentary structures are ubiquitous in the interstellar medium (André et al. 2010;Molinari et al. 2010).Enlightened by the Herschel Space Mission (Pilbratt et al. 2010) and the succeeding studies have revealed that the majority of the dense (A V > 7 mag) molecular gas involved in star formation is dispersed in filamentary formations (André et al. 2010;Arzoumanian et al. 2019;Hacar et al. 2023;Pineda et al. 2023).Those with higher column densities (N 10 H 22 2  cm −2 ) are preferred sites to initiate star formation when the densest filaments due to gravitational instability are subject to fragmentation into prestellar cores.Filaments exhibit a wide range of physical scales and kinematic properties (see the recent reviews by Hacar et al. 2023;Pineda et al. 2023), leading subsequently to different dynamical evolution.
Filaments are often found networked in complexity, where multiple units with sizes several parsecs radially merge into a central parsec-scale clump, referred to as hubs, which have low aspect ratios and high-column densities (Myers 2009).These hub-filament systems (HFSs) are considered the potential progenitors of massive young stellar associations, in which luminous (>10 4 L ☉ ) massive stars are formed (Kumar et al. 2020).
A comprehensive evolutionary sequence of the HFS has been forwarded by Kumar et al. (2020), in which the formation scenario of massive stars from molecular gas is categorized in snapshots of four consecutive stages.Briefly, in Stage I, dense filaments move toward each other and set up the initial conditions for HFS formation.The formation of HFS can be initiated by a variety of processes, manifest as flow-driven filaments, energetic stellar wind bubbles, expanding ionization fronts, supernova shocks, etc. (Kumar et al. 2020).In Stage II, the approaching filaments merge and form the hub with a small twist at the overlapping zone, thereby flattening the hub.In Stage III, the density in the hub amplifies due to the initial shock followed by self-gravity and hence drives longitudinal flows toward the hub leading to the formation of massive stars.Finally, in Stage IV, the radiation pressure and ionization feedback from the massive stars shape the remnant filaments as pillars, leaving a mass-segregated embedded cluster at the hub.It has been rapidly recognized that the HFS may play an important, if not dominant, role in massive star and cluster formation (Schneider et al. 2012;Baug et al. 2018;Montillaud et al. 2019;Kumar et al. 2022).
However, to date, direct observational evidence validating the causality of HFS with cluster formation has only emerged in a handful of studies in the literature.In addition to the results presented in Kumar et al. (2020Kumar et al. ( , 2022)), only a few cases have so far been reported, e.g., in the Mon OB1 star-forming region, Montillaud et al. (2019)  resembling Stage II/III of the "filaments to clusters" model (Kumar et al. 2020).
The target of our study is G083.097+03.270(hereafter G08; ℓ = 83°.0970; b = + 03°.2700), which is a part of the large-scale area previously studied by Panja et al. (2022) and therein referred to as Clump B. This complex, located in the Orion arm near the Cyg X system, was found by these authors associated with intense thermal dust emission (AKARI: 160 μm; Planck: 353 GHz), strong ionized gas emission (NVSS: 1.4 GHz), and dense molecular cloud (PMO: 12 CO, 13 CO, C 18 O).Moreover, the large-scale (∼2°.0)molecular gas is connected spatially and kinematically with a nearby nebulous H II complex Sh2-112, which has a distance of ∼2.1 kpc.Anderson et al. (2015) studied the radio recombination lines and referred to this H II region as G083.097+03.270,which is related to the molecular cloud 083.1+03.3(Dobashi et al. 1994).A massive young stellar object (VLA G083.0934 +03.2720;Urquhart et al. 2009) detected from the Very Large Array (VLA) radio continuum observations coincides with the central region, where a significant velocity dispersion has been reported.Panja et al. (2022) also presented ionized and molecular gas morphology and parameters and inferred the central region to likely host a group of ionizing stars.
An inspection of the molecular gas kinematics in G08 reveals spatially connected filaments having separate velocity components.This site therefore could be a potential HFS candidate that encompasses a dynamic range of substantial activities, from gas motions within filaments to young massive stellar cluster formation.Here we present a thorough investigation of the interaction of filaments and their dynamical evolution to clusters based on high spectral resolution (0.16-0.17 km s −1 ) observational data.We focus on the analysis of a relatively compact complex (0°.9 × 0°.9) with a narrow velocity range ([−6.0,+1.0] km s −1 ).
The paper is organized as follows.In Section 2, we present the observational data used in this work, followed by Section 3, which describes the spatial and kinematic morphology, and hence the possible interplay, of the filaments.In Section 4, we discuss the plausible formation history of the hub influenced by the merging of filaments and their observable outcomes.Finally, Section 5 contains a summary of the main results of this work.

Data
We have used the 12 CO, 13 CO, and C 18 O (J = 1-0) molecular line data obtained from the Milky Way Imaging Scroll Painting (MWISP; Su et al. 2019) survey carried out by the 13.7 m diameter millimeter-wavelength telescope of the Purple Mountain Observatory (PMO), China.For simultaneous observations of the three CO isotopologues, a multibeam sideband-separating Superconducting Spectroscopic Array Receiver system with an instantaneous bandwidth of 1 GHz is employed.The typical system temperatures are ∼250 K (rms noise ∼0.5 K) for 12 CO at the upper sideband and ∼140 K (rms noise ∼0.3 K) for 13 CO and C 18 O at the lower sideband.Finally, the raw data are resampled and mosaicked into FITS cubes for a spatial resolution of 30″ and a velocity resolution of 0.16-0.17km s −1 .We have reprocessed a part of the data already presented in Panja et al. (2022) in the velocity range [−6.0, +1.0] km s −1 .The observational techniques and reduction methodology are further detailed there.

Results
Here we have segregated the filament components based on spatial and spectral properties, using the observed CO isotopologues.We then diagnosed the pattern of the gas flow within filaments and the nature of possible interaction between them.

Hub-Filament Morphology in G08
The molecular gas spatial and kinematic structures are diagnosed using the CO isotopologues.The 12 CO emission is optically thick; therefore suitable to trace the spatial extents of the diffuse extended gas (density ∼10 2 cm −3 ).On the other hand, 13 CO and C 18 O trace comparatively dense (∼10 3 -10 4 cm −3 ) structures, except that C 18 O is optically even thinner than 13 CO, hence revealing denser regions than 13 CO does.Thus for this study, we have relied more on the 13 CO data to decipher the relatively dense hub and analogous filament structures.

Integrated Intensity
The 13 CO integrated intensity map for the velocity range [−6.0, +1.0] km s −1 toward G08 is shown in Figure 1(a), which clearly reveals two elongated filaments (hereafter Fi-N and Fi-S), aligned in a tilted Y-shaped distribution along the Galactic east-west direction.We recognize these structures as 'giant filaments' categorized in the filament families of Hacar et al. (2023).The two filaments interlace spatially, forming a hub, wherein we observe a notable enhancement in intensity.Toward the western part of Fi-N, we also see intensification in certain regions.

Velocity
The velocity distribution ( 13 CO) of the molecular gas, shown in Figure 1(b), reveals two separate components.The median velocities of Fi-N and Fi-S are found to be −3.98 km s −1 and −0.83 km s −1 considering their entire coverage area, estimated from the intensity-weighted respective 13 CO line width.A continuous velocity gradient is detected along Fi-N, suggesting inflow motions most likely toward the center of gravity, with bluer velocity along Galactic east (∼ − 4.31 km s −1 ) to relatively redder in the west (∼ − 2.41 km s −1 ).However we caution that the velocity ranges for the filaments mentioned above are to be considered as representative velocities and not as definite values, particularly for Fi-N, which displays a significant shift in peak velocity from east to west.

Velocity Dispersion
The velocity dispersion map ( 13 CO) is presented in Figure 1(c), which hints at a very turbulent gas motion around the hub.We mapped the median velocity dispersion around the junction as ∼3.0 km s −1 , a dispersion that could likely be caused by supersonic gas flows, which would inevitably create strong shock compression at the junction of filaments.From Figures 1(a) to (c), it is also distinctly evident that Fi-S has actually an extended arm to the north-eastern, whereas, at the intersection of two filaments, there is an X-shaped structure, also visible in Figure 9 of Panja et al. (2022).

H 2 Column Density
The H 2 column density map integrated for the mentioned velocity range and derived from 13 CO is depicted in Figure 1(d).The highest column density occurs at the hub, reaching ∼4.8 × 10 22 cm −2 , which surpasses the typical threshold of ∼1.0 × 10 22 cm −2 for massive star formation (Krumholz & McKee 2008).Additionally in this map, we have selected a few square regions, each of size ¢ 2. 5 (5 pixels), along the filament axis for the average spectra to investigate possible velocity entanglements, as will be discussed in the following section.The specific locations of the box are chosen along the filaments axis at those zones where we found relatively higher intensity ( 13 CO) visually.The H 2 column density derived from 13 CO for the molecular gas with an overplot of square regions each of size ¢ 2. 5 and numbered consequently, selected to study the variation of molecular properties along the filaments axis.Panels (a)-(c) are in linear scaling, whereas (d) is in square-root scaling.

Distance
The distance is an essential parameter to verify if the filaments are parts of the same physical system.In order to derive the distance of G08, we have utilized the BeSSeL (Reid et al. 2019) Survey, which computes the trigonometric parallaxes of massive star-forming regions by taking into account the spiral structure and kinematics of the Milky Way.Considering a median radial velocity of −3.98 km s −1 for Fi-N and −0.83 km s −1 for Fi-S, the model produced kinematic distances of ∼1.53 ± 0.12 kpc for Fi-N, and ∼1.51 ± 0.13 kpc for Fi-S, in the Local arm, placing the filaments at the same plane.To validate this distance measurement with another approach, we also made use of the Galactic three-dimensional dust distribution (Green et al. 2019), based on Gaia parallaxes, and stellar photometry from Pan-STARRS 1 and 2MASS.But unlikely, this model produced two ranges of distances (∼1.33 and ∼2.52 kpc) for the region, deviating from those of the kinematic values.Therefore we have relied on the Galactic rotation model and used an average distance of ∼1.52 ± 0.12 kpc for our subsequent analysis.We note that the kinematic distance measurements for nearby local clouds could be associated with a certain level of uncertainty.

Average Spectra
The average spectra along Fi-N and Fi-S for the square regions (mentioned in Section 3.1.4and marked in Figure 1(d)) for both 12 CO and 13 CO are shown in Figure 2.For region IDs 1-13 correspond to Fi-N (7 being the hub) and 14-18 to Fi-S.For ID up to 3, a single peak related to the ∼ − 3.98 km s −1 cloud dominates in both 12 CO and 13 CO.But from ID 4 to 7 both the peaks (∼ − 3.98 km s −1 and ∼ − 0.83 km s −1 ) are visible in 12 CO, while both are seen near the hub (ID 6 and 7) in 13 CO.For IDs 8 and 9, complex structures dominated by single peaks with large spread are prominent.Again from ID 10 to 13, both the peaks can be seen in 12 CO, but only for ID 11 in 13 CO.For IDs 14 and 15, both near the hub, the peaks are present, but for IDs 16-18, the −0.83 km s −1 peak prevails.To summarize, for regions adjacent to the hub (ID 6, 7, and 14), the eminent presence of the velocity components in both 12 CO and 13 CO stipulates the conjunction of molecular gas from two different velocity filaments.

Position-Velocity Diagrams
Another observational signature, if the filaments are indeed connected in velocity, is to probe the position-velocity diagram.As shown in the 13 CO longitude-velocity map, in Figure 3(a), the Fi-N and Fi-S comprise two distinct velocity components (∼ − 3.98 km s −1 and ∼ − 0.83 km s −1 ).The molecular gas in the two filaments is most prominently linked by the bridge feature (intermediate velocity) at the hub.We also witness a few additional locations of inter-filamentary interaction between the western part of Fi-N (segmented as Fi-NW, hereafter) and Fi-S, thus shifting the velocity in Fi-NW to an intermediate range.From now on we use the notation that Fi-N consists of two segments, one is the eastern part (hereafter Fi-NE) and another on the western part (Fi-NW), showing slightly different kinematics.In the 13 CO latitude-velocity map in Figure 3(b), Fi-N and Fi-S are clearly traced with separate velocities connected by the bridge feature.In this map, though there is a significant gas overlap between Fi-NE and Fi-NW kinematically, the velocity peaks differ marginally, probably due to the mutual interaction between Fi-NW and Fi-S.

Channel Maps and Interaction
The Fi-N as a whole (consisting of Fi-NE and Fi-NW) is a part of the same molecular structure, as is evinced in the channel maps for 12 CO and 13 CO (see Figure 5).Interestingly the 12 CO emission demonstrates vividly that the redshifted Fi-S is indeed a longer filament extending to the northeast, together in the 13 CO a comparatively less prominent feature can also be seen.The above offers a clear showcase of two filaments moving against each other and forming a hub, as expected in Stage II or III of the hub-filament paradigm (Kumar et al. 2020).Moreover, the interaction between Fi-NW and Fi-S could be the most plausible mechanism in reddening the velocity in Fi-NW (for details see Appendix A).Another possibility could be that Fi-NW is tilted farther away from our line of sight compared to that of Fi-NE.Nonetheless, this inter/ intra-filamentary interaction is the initial dominant factor that led to the formation of the intense and dense hub at the junction of filaments, until when gravity and turbulence kick in at a later stage.

Discussion
For more than a decade it has been shown that hubs are the preferred locations for the formation of most massive stars that can form within a filamentary network (Myers 2009;Baug et al. 2018;Montillaud et al. 2019;Kumar et al. 2022).However, the formation of such massive stars from molecular gas distributed in filamentary structures involves a dynamic range of activities that are still not fully understood or observationally demonstrated.Here we have identified massive young stars that spatially correlate with the HFS and therefore we interlink them with the dynamics of molecular gas within filaments and investigate their follow-up evolutionary activities.

Young Stellar Objects
The two color integrated intensity maps presented in Figure 4(a) for 12 CO and in Figure 4(b) for 13 CO demonstrate the elongated filamentary molecular structures for separate velocity ranges.The young stellar objects (Class I, Class II, and transition-disk) toward this region were previously identified (Panja et al. 2022) using the infrared color excess and are overplotted here in Figure 4(a).The young stars spatially correlate with Fi-N, with a high concentration of Class I and Class II sources populating the hub, indicating enhanced ongoing star formation.These results are consistent with the higher intensity at the hub, increased by ∼5 times (considering the median value for the 13 CO integrated intensity) compared to the filaments, caused because of the merging of filaments.Whereas Fi-N displays a strongly correlated arrangement of the proto-stellar objects along the entire filament (including Fi-NE and Fi-NW), Fi-S considerably lacks those, possibly due to the fact that Fi-S comprises lower column density (median ∼1.2 × 10 21 cm −2 from 13 CO) compared to Fi-NE (∼1.5 × 10 21 cm −2 ) or Fi-NW (∼2.1 × 10 21 cm −2 ).
Moreover, at the hub is located a massive (7.7 M ☉ , Maud et al. 2015) outflow (MSX6C G083.0936+03.2724)with a similar velocity (V lsr = − 3.0 km s −1 ).This outflow source spatially coincides with a Class I object (2MASS 20313550 +4505465) reported in Panja et al. (2022).Along the hub toward Fi-NW at certain locations (indicated as I1 and I2 in Figure 4(b)), we see density enhancements corresponding with the number of Class I sources.These results are suggestive of an active star formation scenario in G08, caused by the coalescence of molecular gas, thereby channeling material through the filaments and accumulating at the hub.

Evolutionary Scenarios
The filaments Fi-N and Fi-S have lengths of 20.7 and 10.4 pc, respectively, with an overlapping area (hub) of radius ∼0.9 pc.The width of the filaments varies between 0.7 pc and 2.2 pc, estimated with the 13 CO integrated intensity for the corresponding velocity range at the 3σ level.Several studies of nearby (<1 kpc) high-mass star-forming regions have recognized similar types of cluster-forming gas structures and hub morphology, e.g., the central integral shaped filament (ISF) in Orion, which is considered as a hub (radius ∼0.8 pc, Hacar et al. 2017) or the Mon R2 hub (radius ∼0.8 pc, Kumar et al. 2022), to which G08 reported here has a similar hub size (radius ∼0.9 pc).Moreover, in the Orion ISF there is evidence of the existence of a global velocity gradient (1.0 km s −1 pc −1 ) continuing along the entire filament (Hacar et al. 2017).There is increasing observational evidence that these longitudinal velocity gradients in filaments might be involved in driving accretion inflows that feed the central clumps and eventually lead to massive star formation (Kirk et al. 2013;Peretto et al. 2014;Hacar et al. 2017;Williams et al. 2018), as witnessed here in G08.
Near the hub of G08, in addition to the Class I grouping signifying ongoing star formation, there are also about half a dozen ionizing stars (early-B) with typical dynamical timescales of 0.2 Myr (Panja et al. 2022), based on radio continuum measurements.The hub of G08 produces moderately massive stars that are fairly comparable to Mon R2 (Kumar et al. 2022), which also contains a cluster of B-type stars but are significantly less massive than the Orion Trapezium Cluster (Berné et al. 2014).In that connection, we infer that the formation of high-mass stars is induced by the interaction of molecular gas at the hub, infalling from the largescale (∼10 pc) filaments with converging motions.The velocity gradient along Fi-N is on the order of ∼0.084 km s −1 pc −1 , which directly reflects the inflow of material into the central junction.Though a massive outflow is located at the hub, we further searched for fresh outflow wings, but given the moderate resolution of the data combined with a relatively larger distance to the region, we did not detect any.
We found a conspicuous rise both in the excitation temperature (median ∼20.4 K from 12 CO) and the molecular gas column density (median ∼2.0 × 10 22 cm −2 from 13 CO) predominantly in and around the hub (see Figures 7(a cm −2 from 13 CO, Berné et al. 2014) region, justifiable with the type of stars that are produced in each region.Hubs that are formed at the junctions of filaments (Myers 2009) essentially provide resources for enhanced star formation due to their density amplification properties (Kumar et al. 2020).This density amplification in the hub can produce a strong gravitational potential difference between the hub and the connected filaments, which in turn is responsible for driving longitudinal flows within the filaments directed inward to the hub (Peretto et al. 2014;Williams et al. 2018).So the observed HFS morphology in G08 is well consistent with the Stage II or III of the "filaments to clusters" model described by Kumar et al. (2020), where the two elongated filaments have merged, definitely forming a hub at the intersection and thereafter enhanced the star formation activity therein.
It is still a subject of discussion about what initiates the filaments to interact at the first instance, however an abundance of anisotropic agents could be liable (Hacar et al. 2023), and the most likely mechanism could be the filaments driven by flow (Kumar et al. 2020).Supplementary analyses are also required to compare the effects of gravity, turbulence, and magnetic fields and diagnose the dominating factors in driving the flows and forming the hub in G08.So this study presents direct observational evidence on filament merging and hub formation and the region has the potential to offer ample future avenues for further investigation and enhance our understanding of the dynamical evolution of HFSs.Here we reckon that, G08 is in the process of forming massive stars and clusters, with all the favorable circumstances being a reliable candidate for the Stage II or III of the "filaments to clusters" (Kumar et al. 2020) paradigm.With the aid of high-resolution interferometric (millimeter and submillimeter) and polarimetric (dust continuum and line emission) data, investigation of the central 2 pc hub area would probe deeper insight into the accretion and magnetic activities at such scales.

Summary and Conclusions
Our morpho-kinematic study of the filamentary structures in G08 using CO isotopologues reveals the conformity of an HFS that is sequentially inducted to the formation of massive young stars and clusters.The region harbors two elongated (length ∼10.4-20.7 pc) filaments with different velocity components (∼ − 3.98 and ∼ − 0.83 km s −1 ) interacting via a common hub, where we found large velocity spreads (up to ∼5.0 km s −1 ) with clear bridging features in both 12 CO and 13 CO.The significant enhancement in the velocity dispersion at the hub indicates a turbulent gas motion caused by the merging of filaments.The detection of a large-scale velocity gradient (∼0.084 km s −1 pc −1 ) along the filaments axis indicates a global motion of molecular gas directed inward to the hub and consequently feeding the central clumps.The observed molecular gas column density and corresponding star formation in terms of stellar mass in G08 are well comparable with Mon R2 and are reasonably much lower than Orion ISF.Together, the clusterings of Class I sources, higher excitation temperature (median ∼20.4 K), and higher H 2 column density (median ∼2.0 × 10 22 cm −2 for 13 CO) imply an HFS morphology in G08, where the star formation is similar to Stage II or III of the "filaments to clusters" model described by Kumar et al. (2020).These observational findings adhere to convincing evidence on the merging of two giant filaments, seeding the formation of a dense hub and subsequently leading to massive star formation.
Figure 5. 12 CO channel maps (background) with overlaid 13 CO contours (red) at the levels of 0.5, 1.0, 1.5, 2.0, and 2.5 K km s −1 integrated for the mentioned velocity ranges toward G08.In the first panel, the three black curves (labeled as ne, nw, and s) along the filaments axis and the two black lines (i1 and i2) along the additional interacting zones, each of width ¢ 2. 5 (5 pixels) with arrows, indicate the direction along which position-velocity diagrams are generated.

Appendix B Derivation of H 2 Column Density and H 2 Mass
Toward G08, we have computed the H 2 column density and the H 2 mass for both 13 CO and C 18 O for the velocity range of [−6.0, +1.0] km s −1 , using a similar methodology outlined in Sun et al. (2020) and the procedure is briefed below.Initially, the excitation temperature is derived from the peak brightness temperature of the optically thick 12 CO line and the resultant map is displayed in Figure 7(a).Following this, the optical depths for the corresponding isotopologues ( 13 CO and C 18 O) are derived (maps are not shown here) by assuming that they have the same excitation temperature.The obtained values are further used to compute the H 2 column density by assuming local thermodynamic equilibrium (LTE) approximation and abundance ratios of H 2 to 13 CO and C 18 O.The H 2 mass (for both 13 CO and C 18 O) is then obtained by integrating the column density maps and assuming the LTE method.The H 2 mass distribution for 13 CO is shown in Figure 7 demonstrated a pair of filaments approaching each other (Stage I), and recently as another example, in the massive protocluster G31.41+0.31,Beltrán et al. (2022) identified cloud structures that represent a transition phase between Stage III and Stage IV.In this work, we present an observational scenario of two giant molecular filaments crossing each other and at the intersection forming a hub along with the noticeable presence of a group of protostars, Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Figure 1 .
Figure1.(a) Intensity-weighted moment-0 map for 13 CO (J = 1-0), integrated in the velocity range [−6.0, +1.0] km s −1 toward G083.097+03.270(G08).Two filaments, Fi-N and Fi-S, are revealed and are found to be intersecting, forming a hub, i.e., with an enhanced gas density at the center.(b) The 13 CO moment-1 map shows the filaments to have two different velocity structures.(c) In the 13 CO moment-2 map, the large velocity dispersion is traced mostly in and around the junction of filaments.(d) The H 2 column density derived from 13 CO for the molecular gas with an overplot of square regions each of size ¢ 2. 5 and numbered consequently, selected to study the variation of molecular properties along the filaments axis.Panels (a)-(c) are in linear scaling, whereas (d) is in square-root scaling.

Figure 2 .
Figure2.Average spectra (blue: 12 CO; red: 13 CO) fitted with Gaussian (black dashed curves) for the square regions shown in Figure1(d), each labeled with an ID number.The vertical dashed lines mark velocities of −3.98 km s −1 and −0.83 km s −1 , respectively.For ID 7 and 12 CO, the T mb (K) is scaled down by a factor of 2.

Figure 4 .
Figure 4. Two color integrated intensity CO images, revealing the merging of filaments into a common junction as the hub.In (a) the young stellar objects (Class I: yellow circles; Class II: white triangles; transition-disk: green crosses) from Panja et al. (2022) are overlaid on the 12 CO distribution.A scale bar of 5 pc is shown considering a heliocentric distance of 1.52 kpc.In (b) the skeletons of the two filaments (Fi-N and Fi-S) are more clearly depicted by the 13 CO distribution.I1 and I2 indicate the subsidiary locations along which Fi-N (western part) and Fi-S are interacting (see Appendix A).At the hub, a massive outflow source MSX G083.0936 +03.2724 is marked by a black asterisk symbol.

Figure 7 .
Figure 7. (a) Excitation temperature map derived from 12 CO.The radio continuum emission from the NVSS 1.4 GHz is depicted in black contours at levels of 0.003, 0.006, 0.012, and 0.020 Jy beam −1 .A total of five emission peaks with integrated flux densities above the 3σ level are detected and are marked as P1-P5.(b) H 2 mass distribution derived from 13 CO in the velocity range [−6.0, +1.0] km s −1 .The C 18 O intensity map integrated for the same velocity range, as overlaid as white contours at levels of 0.199, 0.398, 0.597, and 0.796 K km s −1 .Six massive clumps labeled as C1-C6 are identified from the C 18 O data.