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Massive star-forming regions (MSFRs) are commonly associated with hub-filament systems (HFSs) and sites of cloud–cloud collision (CCC). Recent observational studies of some MSFRs suggest a possible connection between CCC and the formation of HFSs. To understand this connection, we analyzed the magnetohydrodynamic simulation data from Inoue et al. This simulation involves the collision of a spherical turbulent molecular cloud with a plane-parallel sea of dense molecular gas at a relative velocity of about 10 km s ^−1 . Following the collision, the turbulent and nonuniform cloud undergoes shock compression, rapidly developing filamentary structures within the compressed layer. We found that CCC can lead to the formation of HFSs, which is the combined effect of turbulence, shock compression, magnetic field, and gravity. The collision between the cloud components shapes the filaments into a cone and drives inward flows among them. These inward flows merge at the vertex of the cone, rapidly accumulating high-density gas, which can lead to the formation of massive star(s). The cone acts as a mass-collecting machine, involving a nongravitational early process of filament formation, followed by gravitational gas attraction to finalize the HFS. The gas distribution in the position–velocity (PV) and position–position spaces highlights the challenges in detecting two cloud components and confirming their complementary distribution if the colliding clouds have a large size difference. However, such CCC events can be confirmed by the PV diagrams presenting gas flow toward the vertex of the cone, which hosts gravitationally collapsing high-density objects, and by the magnetic field morphology curved toward the direction of the collision.

We report the discovery of intertwined/entangled substructures toward the bubble wall of NGC 3324 below a physical scale of 4500 au, which is the sharp edge/ionization front/elongated structure traced at the interface between the H ii region and the molecular cloud. The sharp edge appears wavy in the Spitzer 3.6–8.0 μ m images (resolution ∼2″). Star formation signatures have mostly been traced on one side of the ionization front, which lies on the molecular cloud’s boundary. The James Webb Space Telescope’s (JWST) near- and mid-infrared images (resolution ∼0.″07—0.″7) are employed to resolve the sharp edge, which has a curvature facing the exciting O-type stars. The elongated structures are associated with the 3.3 μ m polycyclic aromatic hydrocarbon (PAH) emission, the 4.05 μ m ionized emission, and the 4.693 μ m H _2 emission. However, the PAH-emitting structures are depicted between the other two. The H _2 emission reveals numerous intertwined substructures that are not prominently traced in the 3.3 μ m PAH emission. The separation between two substructures in the H _2 emission is ∼1.″1 or 2420 au. The intertwined substructures are traced in the spatial areas associated with the neutral to H _2 transition zone, suggesting the origin of these structures by “thin-shell” instability. Furthermore, an arc-like feature traced in the Spitzer 3.6–8.0 μ m images is investigated as a bipolar H ii region (extent ∼0.35 pc) at T _d ∼25–28 K using the JWST images. A massive-star candidate VPHAS-OB1 #03518 seems to be responsible for the bipolar H ii region.

We present a near-infrared H- band polarimetric study toward the S235 e2s3 protostar, obtained using the POLICAN instrument on the 2.1 m OAGH telescope. The images reveal a bipolar outflow with a total length of about 0.5 pc. The outflow nebulosity presents a high degree of linear polarization (∼80%) and reveals a centrosymmetric pattern with the polarization position angles. The polarization characteristics suggest their origin to be single scattering associated with dust in the outflow. Using multiwavelength archival data, we performed spectral energy distribution (SED) fitting based on radiative transfer models of turbulent core accretion theory. The best-fit SED model indicated that the protostar has a mass of 6.8 ± 1.2 M _⊙ , with a disk accretion rate of 3.6 ± 1.2 × 10 ^−4 M _⊙ yr ^−1 and a total bolometric luminosity of 9.63 ± 2.1 × 10 ^3 L _⊙ . Narrowband H _2 (2.12 μ m) observations show shocked emission along the bipolar lobes tracing the jet’s interaction with the surrounding medium. The estimated H _2 luminosity of the outflow is ${2.3}_{-1.3}^{+3.5}\,{L}_{\odot }$ , which matched the known power-law correlation with the source bolometric luminosity, similar to other high-mass outflows. The orientation of the bipolar outflow was found to be parallel to the local magnetic field direction. The overall results assert the fact that the S235 e2s3 source is a massive young star driving a highly collimated bipolar outflow through disk accretion.

The paper presents an analysis of multiwavelength data of a nearby star-forming site, the IC 5146 dark streamer ( d ∼ 600 pc), which has been treated as a single and long filament, fl . Two hub-filament systems (HFSs) are known to exist toward the eastern and the western ends of fl . Earlier published results favor simultaneous evidence of HFSs and end-dominated collapse (EDC) in fl . A Herschel column density map (resolution ∼13.″5) reveals two intertwined sub-filaments (i.e., fl-A and fl-B ) toward fl , displaying a nearly double helix-like structure. This picture is also supported by the C ^18 O(3–2) emission. The fray and fragment scenario may explain the origin of intertwined sub-filaments. In the direction of fl , two cloud components around 2 and 4 km s ^−1 are depicted using ^13 CO(1–0) and C ^18 O(1–0) emission and are connected in velocity space. The HFSs are spatially found at the overlapping areas of these cloud components and can be explained by the cloud–cloud collision scenario. Nonthermal gas motion in fl with a larger Mach number is found. The magnetic field position angle measured from the filament’s long axis shows a linear trend along the filament. This signature is confirmed in the other nearby EDC filaments, presenting a more quantitative confirmation of the EDC scenario. Based on our observational outcomes, we witness multiple processes operational in the IC 5146 streamer. Overall, the streamer can be recognized as the first reliable candidate for edge collapse, HFSs, and intertwined sub-filaments.

We investigate the influence of Wolf–Rayet (W-R) stars on their surrounding star-forming molecular clouds. We study five regions containing W-R stars in the inner Galactic plane (l ∼ [14°–52°]), using multiwavelength data from near-infrared to radio wavelengths. Analysis of 13CO line data reveals that these W-R stars have developed gas-deficient cavities in addition to molecular shells with expansion velocities of a few kilometers per second. The pressure owing to stellar winds primarily drives these expanding shells and sweeps up the surrounding matter to distances of a few parsecs. The column densities of shells are enhanced by a minimum of 14% for one region to a maximum of 88% for another region with respect to the column densities within their central cavities. No active star formation—including molecular condensations, protostars, or ionized gas—is found inside the cavities, whereas such features are observed around the molecular shells. Although the expansion of ionized gas is considered an effective mechanism to trigger star formation, the dynamical ages of the H ii regions in our sample are generally not sufficiently long to do so efficiently. Overall, our results hint at the possible importance of negative W-R wind-driven feedback on the gas-deficient cavities, where star formation is quenched as a consequence. In addition, the presence of active star formation around the molecular shells indicates that W-R stars may also assist in accumulating molecular gas, and that they could initiate star formation around those shells. [ABSTRACT FROM AUTHOR]

We observationally investigate star formation process occurring in AFGL 5157 (area ∼13.5 pc × 13.5 pc) using a multi-wavelength approach. Embedded filaments are seen in the Herschel column density map, and one of them is identified as an elongated filamentary feature (FF) (length ∼8.3 pc; mass ∼1170 M⊙). Five Herschel clumps (Mclump ∼45–300 M⊙) are traced in the central part of the FF, where an extended temperature structure (Td ∼13.5–26.5 K) is observed. In the direction of the central part of the FF, the warmer region at Td ∼20–26.5 K spatially coincides with a mid-infrared shell surrounding a previously known evolved infrared cluster. Diffuse Hα emission is traced inside the infrared shell, suggesting the presence of massive stars in the evolved cluster. Based on the surface density analysis of young stellar objects (YSOs), embedded clusters of YSOs are traced toward the central part of the FF, and are distributed around the infrared shell. Previously detected H2O masers, H2 knots, massive protostar candidates, and an H ii region are also seen toward the embedded clusters. Using the 12CO and 13CO line data, the central part of the FF is observed at the overlapping zones of two filamentary molecular clouds (length ∼12.5 pc) around −20 and −17 km s−1, which are also connected in velocity. Our observational results suggest that the formation of massive stars appears to be triggered by a collision of two filamentary molecular clouds, which might have also influenced the birth of YSOs in AFGL 5157. [ABSTRACT FROM AUTHOR]

Most recent numerical simulations suggest that bipolar H ii regions, powered by O-type stars, can be formed at the interface of two colliding clouds. To observationally understand the birth of O-type stars, we present a detailed multiwavelength analysis of an area of 1° × 1° hosting G8.14+0.23 H ii region associated with an infrared bipolar nebula (BPN). Based on the radio continuum map, the H ii region is excited by at least an O-type star, which is located toward the waist of the BPN. The NANTEN2 13CO line data reveal the existence of two extended clouds at [9, 14.3] and [15.3, 23.3] km s−1 toward the site G8.14+0.23, which are connected in the position–velocity space through a broad-bridge feature at the intermediate velocity range. A “cavity/intensity-depression” feature is evident in the blueshifted cloud, and is spatially matched by the “elongated redshifted cloud.” The spatial and velocity connections of the clouds suggest their interaction in the site G8.14+0.23. The analysis of deep near-infrared photometric data reveals the presence of clusters of infrared-excess sources, illustrating ongoing star formation activities in both the clouds. The O-type star is part of the embedded cluster seen in the waist of the BPN, which is observed toward the spatial matching zone of the cavity and the redshifted cloud. The observational results appear to be in reasonable agreement with the numerical simulations of cloud–cloud collision (CCC), suggesting that the CCC process seems to be responsible for the birth of the O-type star in G8.14+0.23. [ABSTRACT FROM AUTHOR]

To probe the ongoing physical mechanism, we studied a wide-scale environment around AFGL 5142 (area ∼25 pc × 20 pc) using a multiwavelength approach. The Herschel column density (N(H2)) map reveals a massive inverted Y-like structure (mass ∼6280 M⊙), which hosts a pair of elongated filaments (lengths >10 pc). The Herschel temperature map depicts the filaments in a temperature range of ∼12.5–13.5 K. These elongated filaments overlap each other at several places, where N(H2) > 4.5 × 1021 cm−2. The 12CO and 13CO line data also show two elongated cloud components (around −1.5 and −4.5 km s−1) toward the inverted Y-like structure, which are connected in the velocity space. First moment maps of CO confirm the presence of two intertwined filamentary clouds along the line of sight. These results explain the morphology of the inverted Y-like structure through a combination of two different filamentary clouds, which are also supported by the distribution of the cold H i gas. Based on the distribution of young stellar objects (YSOs), star formation (SF) activities are investigated toward the inverted Y-like structure. The northern end of the structure hosts AFGL 5142 and tracers of massive SF, where high surface density of YSOs (i.e., 5–240 YSOs pc−2) reveals strong SF activity. Furthermore, noticeable YSOs are found toward the overlapping zones of the clouds. All this observational evidence supports a scenario of collision/interaction of two elongated filamentary clouds/flows, which appears to explain SF history in the site AFGL 5142. [ABSTRACT FROM AUTHOR]

We present a multiwavelength observational study of IRAS 17008-4040 and IRAS 17009-4042 to probe the star formation (SF) mechanisms operational in both the sites. Each IRAS site is embedded within a massive ATLASGAL 870 μm clump (∼2430–2900 M⊙), and several parsec-scale filaments at 160 μm are radially directed toward these clumps (at Td ∼ 25–32 K). The analysis of the Spitzer and VVV photometric data depicts a group of infrared-excess sources toward both the clumps, suggesting the ongoing SF activities. In each IRAS site, high-resolution GMRT radio maps at 0.61 and 1.28 GHz confirm the presence of H ii regions, which are powered by B-type stars. In the site IRAS 17008-4040, a previously known O-star candidate without an H ii region is identified as an infrared counterpart of the 6.7 GHz methanol maser emission (i.e., IRcmme). Based on the Very Large Telescope/NAOS-CONICA adaptive-optics L′ image (resolution ∼0.″1), the source IRcmme is resolved into two objects (i.e., IRcmme1 and IRcmme2) within a scale of 900 au that are found to be associated with the Atacama Large Millimeter/submillimeter Array core G345.50M. IRcmme1 is characterized as the main accreting high mass protostellar object candidate before the onset of an ultracompact H ii region. In the site IRAS 17009-4042, the 1.28 GHz map has resolved two radio sources that were previously reported as a single radio peak. Altogether, in each IRAS site, the junction of the filaments (i.e., massive clump) is investigated with the cluster of infrared-excess sources and the ongoing massive SF. This evidence is consistent with the “hub-filament” systems as proposed by Myers. [ABSTRACT FROM AUTHOR]

To probe the star formation process, we present a thorough multiwavelength investigation of several H ii regions located toward l = 24.°8, b = 0.°1. A system of at least five H ii regions, including the mid-infrared bubble N36 (hereafter system N36; extension ∼35 pc), is observationally investigated and is located at a distance of 6.0 kpc. With this distance, the system N36 is found to be situated at the interface of the Galactic bar and the Norma Galactic arm in our Galaxy, where one may expect the collisions of molecular clouds due to the bar potential. Each H ii region (dynamical age ∼0.4–1.3 Myr) in the system is powered by an O-type star. The system contains 27 ATLASGAL dust clumps at 870 μm. Several clumps are massive (>103M⊙) and have high bolometric luminosity (>103L⊙). Using the GRS 13CO line data, in the direction of the system N36, two velocity components are found around 109 and 113 km s−1 and are linked in the velocity space. The morphological analysis of 13CO favors the presence of interacting molecular clouds in the system. Four H ii regions and two 6.7 GHz masers are spatially observed at the common areas of the two clouds. The analysis of the Spitzer photometric data also traces the noticeable star formation activity in the system. Considering the observational outcomes, the formation of O-type stars (including ongoing star formation) in the system appears to be triggered by the collisions of molecular clouds at the bar–arm interface. [ABSTRACT FROM AUTHOR]

To investigate ongoing physical processes, we present the results of observations of the sites S234, V582, and IRAS 05231+3512 situated toward l = 171.°7–174.°1. Based on the CO line data, we find that these sites are not physically connected, and contain at least one filament (with length >7 pc). The observed line masses (Mline,obs) of the filaments associated with V582 and IRAS 05231+3512 are ∼37 and ∼28 M⊙ pc−1, respectively. These filaments are characterized as thermally supercritical, and harbor several clumps. Groups of infrared-excess sources and massive B-type stars are observed toward the filament containing V582, while very little star formation (SF) activity is found around IRAS 05231+3512. Our results favor a radial collapse scenario in the filaments harboring V582 and IRAS 05231+3512. In the site S234, two filaments (i.e., ns1 (Mline,obs ∼ 130 M⊙ pc−1) and ns2 (Mline,obs ∼ 45 M⊙ pc−1)) are identified as thermally supercritical. An extended temperature structure at 27–30 K surrounds the relatively cold (∼19 K) ∼8.9 pc long filament ns1. At least four condensations (Mclump ∼ 70–300 M⊙) are seen in ns1, and are devoid of 610 MHz radio emission as observed by the Giant Metrewave Radio Telescope. The filament ns2 hosting clumps is devoid of ongoing SF, and could be at an early stage of fragmentation. Intense SF activity, with an SF efficiency ∼3.3% and SF rate ∼40–20 M⊙ Myr−1 (for tsf ∼ 1–2 Myr), is observed in ns1. The feedback of massive stars in S234 seems to explain the observed SF in the filament ns1. [ABSTRACT FROM AUTHOR]

In the direction of l = 17.°6–19°, the star-forming sites Sh 2-53 and IRAS 18223-1243 are prominently observed, and seem to be physically detached from each other. Sh 2-53 has been investigated at the junction of the molecular filaments, while a larger-scale environment of IRAS 18223-1243 remains unexplored. The goal of this paper is to investigate the star formation processes in the IRAS site (area ∼0.°4 × 0.°4). Based on the GRS 13CO line data, two molecular clouds, peaking at velocities of 45 and 51 km s−1, are found. In the position–velocity plots, a relatively weak 13CO emission is detected at intermediate velocities (i.e., 47.5–49.5 km s−1) between these two clouds, illustrating a link between two parallel elongated velocity structures. These clouds are physically connected in both space and velocity. The MAGPIS data at 20 cm trace free–free continuum emission toward the IRAS 18223-1243 source. Using the Spitzer and UKIDSS photometric data, we have identified infrared-excess young stellar objects (YSOs), and have observed their groups toward the intersection zones of the clouds. IRAS 18223-1243 is also spatially seen at an interface of the clouds. Considering these observational findings, we propose the onset of the collision of two clouds in the IRAS site about 1 Myr ago, which triggered the birth of massive star(s) and the YSO groups. A nonuniform distribution of the GPIPS H-band starlight mean polarization angles is also observed toward the colliding interfaces, indicating the impact of the collision on the magnetic field morphology. [ABSTRACT FROM AUTHOR]

We present a multiwavelength study to probe the star formation (SF) process in the molecular cloud linked with the G35.673-00.847 site (hereafter MCG35.6), which is traced in a velocity range of 53–62 km s−1. Multiwavelength images reveal a semi-ring-like feature (associated with ionized gas emission) and an embedded face-on ring-like feature (without the NVSS 1.4 GHz radio emission, where 1σ ∼ 0.45 mJy beam−1) in MCG35.6. The semi-ring-like feature is originated by the ionizing feedback from a star with spectral type B0.5V–B0V. The central region of the ring-like feature does not contain detectable ionized gas emission, indicating that the ring-like feature is unlikely to be produced by the ionizing feedback from a massive star. Several embedded Herschel clumps and young stellar objects (YSOs) are identified in MCG35.6, tracing the ongoing SF activities within the cloud. The polarization information from the Planck and GPIPS data trace the plane-of-sky magnetic field, which is oriented parallel to the major axis of the ring-like feature. At least five clumps (having Mclump ∼ 740–1420 M⊙) seem to be distributed in an almost regularly spaced manner along the ring-like feature and contain noticeable YSOs. Based on the analysis of the polarization and molecular line data, three subregions containing the clumps are found to be magnetically supercritical in the ring-like feature. Altogether, the existence of the ring-like feature and the SF activities on its edges can be explained by the magnetic field mediated process as simulated by Li & Nakamura. [ABSTRACT FROM AUTHOR]

We present a multiwavelength analysis of a ∼30′ × 30′ area around the Sh 2-53 region (hereafter S53 complex), which is associated with at least three H ii regions, two mid-infrared bubbles (N21 and N22), and infrared dark clouds. The 13CO line data trace the molecular content of the S53 complex in a velocity range of 36–60 km s−1 and show the presence of at least three molecular components within the selected area along this direction. Using the observed radio continuum flux of the H ii regions, the derived spectral types of the ionizing sources agree well with the previously reported results. The S53 complex harbors clusters of young stellar objects (YSOs) that are identified using the photometric 2–24 μm magnitudes. It also hosts several massive condensations () that are traced in the Herschel column density map. The complex is found at the junction of at least five molecular filaments, and the flow of gas toward the junction is evident in the velocity space of the 13CO data. Together, the S53 complex is embedded in a very similar “hub–filament” system to those reported in Myers, and the active star formation is evident toward the central “hub” inferred by the presence of the clustering of YSOs. [ABSTRACT FROM AUTHOR]

We investigate the star formation processes operating in a mid-infrared bubble N49 site that harbors an O-type star in its interior, an ultracompact H ii region, and a 6.7 GHz methanol maser at its edges. The 13CO line data reveal two velocity components (at velocity peaks ∼88 and ∼95 km s−1) in the direction of the bubble. An elongated filamentary feature (length >15 pc) is investigated in each molecular cloud component, and the bubble is found at the interface of these two filamentary molecular clouds. The Herschel temperature map traces all these structures in a temperature range of ∼16–24 K. In the velocity space of 13CO, the two molecular clouds are separated by ∼7 km s−1, and are interconnected by a lower-intensity intermediate velocity emission (i.e., a broad bridge feature). A possible complementary molecular pair at [87, 88] km s−1 and [95, 96] km s−1 is also observed in the velocity channel maps. These observational signatures are in agreement with the outcomes of simulations of the cloud–cloud collision process. There are also noticeable embedded protostars and Herschel clumps distributed toward the filamentary features including the intersection zone of the two molecular clouds. In the bubble site, different early evolutionary stages of massive star formation are also present. Together, these observational results suggest that in the bubble N49 site, the collision of the filamentary molecular clouds appears to be operated about 0.7 Myr ago, and may have triggered the formation of embedded protostars and massive stars. [ABSTRACT FROM AUTHOR]

We present a multi-wavelength data analysis of the extended star-forming region S235 (hereafter E-S235), where two molecular clouds are present. In E-S235, using the 12CO (1–0) and 13CO (1–0) line data, a molecular cloud linked with the site “S235main” is traced in a velocity range [−24, −18] km s−1, while the other one containing the sites S235A, S235B, and S235C (hereafter “S235ABC”) is depicted in a velocity range [−18, −13] km s−1. In the velocity space, these two clouds are separated by ∼4 km s−1, and are interconnected by a lower-intensity intermediate velocity emission, tracing a broad bridge feature. In the velocity channel maps, a possible complementary molecular pair at [−21, −20] km s−1 and [−16, −15] km s−1 is also evident. The sites, “S235ABC,” east 1, and south–west, are spatially seen in the interface of two clouds. Together, these observed features are consistent with the predictions of numerical models of the cloud–cloud collision (CCC) process, favoring the onset of the CCC in E-S235 about 0.5 Myr ago. Deep UKIDSS near-infrared photometric analysis of point-like sources reveals significant clustering of young stellar populations toward the sites located at the junction, and the “S235main.” The sites “S235ABC” harbor young compact H ii regions with dynamical ages of ∼0.06–0.22 Myr, and these sites (including south–west and east 1) also contain dust clumps (having Mclump ∼ 40 to ). Our observational findings suggest that the star formation activities (including massive stars) appear to be influenced by the CCC mechanism at the junction. [ABSTRACT FROM AUTHOR]

We present a multiwavelength data analysis of IRAS 05463+2652 (hereafter I05463+2652) to study star formation mechanisms. A shell-like structure around I05463+2652 is evident in the Herschel column density map, which is not associated with any ionized emission. Based on the Herschel submillimeter images, several parsec-scale filaments (including two elongated filaments, “s-fl” and “nw-fl” having lengths of ∼6.4 and ∼8.8 pc, respectively) are investigated in the I05463+2652 site. The Herschel temperature map depicts all these features in a temperature range of ∼11–13 K. 39 clumps are identified and have masses between . The majority of clumps (having ) are distributed toward the shell-like structure. 175 young stellar objects (YSOs) are selected using the photometric 1–5 μm data and a majority of these YSOs are distributed toward the four areas of high column density ( cm−2; AV ∼ 5.3 mag) in the shell-like structure, where massive clumps and a spatial association with filament(s) are also observed. The knowledge of observed masses per unit length of elongated filaments and critical mass length reveals that they are supercritical. The filament “nw-fl” is fragmented into five clumps (having ) and contains noticeable YSOs, while the other filament “s-fl” is fragmented into two clumps (having ) without YSOs. Together, these observational results favor the role of filaments in the star formation process in I05480+2545. This study also reveals the filament “s-fl,” containing two starless clumps, at an early stage of fragmentation. [ABSTRACT FROM AUTHOR]

We present a multi-wavelength study to probe the star-formation (SF) processes on a larger scale () around the S242 site. The S242 molecular cloud is depicted in a velocity range from −3.25 to 4.55 km s−1 and has a spatially elongated appearance. Based on the virial analysis, the cloud is prone to gravitational collapse. The cloud harbors an elongated filamentary structure (EFS; length ∼25 pc), which is evident in the Herschel column density map, and the EFS has an observed mass per unit length of ∼200 pc−1, exceeding the critical value of ∼16 pc−1 (at T = 10 K). The EFS contains a chain of Herschel clumps (Mclump ∼ 150–1020 ), revealing the evidence of fragmentation along its length. The most massive clumps are observed at both the EFS ends, while the S242 H ii region is located at one EFS end. Based on the radio continuum maps at 1.28 and 1.4 GHz, the S242 H ii region is ionized by a B0.5V–B0V type star and has a dynamical age of ∼0.5 Myr. The photometric 1–5 μm data analysis of point-like sources traces young stellar objects (YSOs) toward the EFS and the clusters of YSOs are exclusively found at both the EFS ends, revealing the SF activities. Considering the spatial presence of massive clumps and YSO clusters at both the EFS ends, the observed results are consistent with the prediction of an SF scenario of the end-dominated collapse driven by the higher acceleration of gas. [ABSTRACT FROM AUTHOR]

To probe the star formation (SF) process, we present a multi-wavelength study of IRAS 05480+2545 (hereafter I05480+2545). Analysis of Herschel data reveals a massive clump (Mclump ∼ 1875 peak N(H2) ∼ 4.8 × 1022 cm−2; AV ∼ 51 mag) containing the 6.7 GHz methanol maser and I05480+2545, which is also depicted in a temperature range of 18–26 K. Several noticeable parsec-scale filaments are detected in the Herschel 250 μm image and seem to be radially directed to the massive clump. It resembles more of a “hub-filament” system. Deeply embedded young stellar objects (YSOs) have been identified using the 1–5 μm photometric data, and a significant fraction of YSOs and their clustering are spatially found toward the massive clump, revealing the intense SF activities. An infrared counterpart (IRc) of the maser is investigated in the Spitzer 3.6–4.5 μm images. The IRc does not appear as a point-like source and is most likely associated with the molecular outflow. Based on the 1.4 GHz and Hα continuum images, the ionized emission is absent toward the IRc, indicating that the massive clump harbors an early phase of a massive protostar before the onset of an ultracompact H ii region. Together, the I05480+2545 is embedded in a very similar “hub-filament” system to those seen in the Rosette Molecular Cloud. The outcome of the present work indicates the role of filaments in the formation of the massive star-forming clump and cluster of YSOs, which might help channel material to the central hub configuration and the clump/core. [ABSTRACT FROM AUTHOR]

To probe star formation (SF) processes, we present results of an analysis of the molecular cloud G35.20−0.74 (hereafter MCG35.2) using multi-frequency observations. The MCG35.2 is depicted in a velocity range of 30–40 km s−1. An almost horseshoe-like structure embedded within the MCG35.2 is evident in the infrared and millimeter images and harbors the previously known sites, ultra-compact/hyper-compact G35.20−0.74N H ii region, Ap2-1, and Mercer 14 at its base. The site, Ap2-1, is found to be excited by a radio spectral type of B0.5V star where the distribution of 20 cm and Hα emission is surrounded by the extended molecular hydrogen emission. Using the Herschel 160–500 μm and photometric 1–24 μm data analysis, several embedded clumps and clusters of young stellar objects (YSOs) are investigated within the MCG35.2, revealing the SF activities. A majority of the YSOs clusters and massive clumps (500–4250 ) are seen toward the horseshoe-like structure. The position–velocity analysis of 13CO emission shows a blueshifted peak (at 33 km s−1) and a redshifted peak (at 37 km s−1) interconnected by lower intensity intermediate velocity emission, tracing a broad bridge feature. The presence of such a broad bridge feature suggests the onset of a collision between molecular components in the MCG35.2. A noticeable change in the H-band starlight mean polarization angles has also been observed in the MCG35.2, probably tracing the interaction between molecular components. Taken together, it seems that the cloud–cloud collision process has influenced the birth of massive stars and YSOs clusters in the MCG35.2. [ABSTRACT FROM AUTHOR]

We present a detailed multiwavelength study of observations from X-ray, near-infrared, and centimeter wavelengths to probe the star formation processes in the S237 region. Multiwavelength images trace an almost sphere-like shell morphology of the region, which is filled with the 0.5–2 keV X-ray emission. The region contains two distinct environments—a bell-shaped cavity-like structure containing the peak of 1.4 GHz emission at center, and elongated filamentary features without any radio detection at edges of the sphere-like shell—where Herschel clumps are detected. Using the 1.4 GHz continuum and 12CO line data, the S237 region is found to be excited by a radio spectral type of B0.5V star and is associated with an expanding H ii region. The photoionized gas appears to be responsible for the origin of the bell-shaped structure. The majority of molecular gas is distributed toward a massive Herschel clump (Mclump ∼ 260 ), which contains the filamentary features and has a noticeable velocity gradient. The photometric analysis traces the clusters of young stellar objects (YSOs) mainly toward the bell-shaped structure and the filamentary features. Considering the lower dynamical age of the H ii region (i.e., 0.2–0.8 Myr), these clusters are unlikely to be formed by the expansion of the H ii region. Our results also show the existence of a cluster of YSOs and a massive clump at the intersection of filamentary features, indicating that the collisions of these features may have triggered cluster formation, similar to those found in the Serpens South region. [ABSTRACT FROM AUTHOR]

We present a multiscale and multiwavelength study to investigate the star formation process around IRAS 17599–2148, which is part of an elongated filamentary structure (EFS) (extension ∼21 pc) seen in the Herschel maps. Using the Herschel data analysis, at least six massive clumps (Mclump ∼ 777–7024 M⊙) are found in the EFS with a range of temperature and column density of ∼16–39 K and ∼(0.6–11) × 1022 cm−2 (AV ∼ 7–117 mag), respectively. The EFS hosts cold gas regions (i.e., infrared dark cloud) without any radio detection and a bipolar nebula (BN) linked with the H ii region IRAS 17599–2148, tracing two distinct environments inferred through the temperature distribution and ionized emission. Based on virial analysis and higher values of self-gravitating pressure, the clumps are found unstable against gravitational collapse. We find 474 young stellar objects (YSOs) in the selected region, and ∼72% of these YSOs are found in the clusters distributed mainly toward the clumps in the EFS. These YSOs might have spontaneously formed due to processes not related to the expanding H ii region. At the edges of BN, four additional clumps are also associated with YSO clusters, which appear to be influenced by the expanding H ii region. The most massive clump in the EFS contains two compact radio sources traced in the Giant Metre-wave Radio Telescope 1.28 GHz map and a massive protostar candidate, IRS 1, prior to an ultracompact H ii phase. Using the Very Large Telescope/NACO near-infrared images, IRS 1 is resolved with a jet-like feature within a 4200 au scale. [ABSTRACT FROM AUTHOR]

We have performed a multi-wavelength analysis of a mid-infrared (MIR) bubble N37 and its surrounding environment. The selected 15′ × 15′ area around the bubble contains two molecular clouds (N37 cloud; 37–43 km s−1, and C25.29+0.31; 43–48 km s−1) along the line of sight. A total of seven OB stars are identified toward the bubble N37 using photometric criteria, and two of them are spectroscopically confirmed as O9V and B0V stars. The spectro-photometric distances of these two sources confirm their physical association with the bubble. The O9V star appears to be the primary ionizing source of the region, which is also in agreement with the desired Lyman continuum flux analysis estimated from the 20 cm data. The presence of the expanding H ii region is revealed in the N37 cloud, which could be responsible for the MIR bubble. Using the 13CO line data and photometric data, several cold molecular condensations as well as clusters of young stellar objects (YSOs) are identified in the N37 cloud, revealing ongoing star formation (SF) activities. However, the analysis of ages of YSOs and the dynamical age of the H ii region do not support the origin of SF due to the influence of OB stars. The position–velocity analysis of 13CO data reveals that two molecular clouds are interconnected by a bridge-like structure, favoring the onset of a cloud–cloud collision process. The SF activities (i.e., the formation of YSO clusters and OB stars) in the N37 cloud are possibly influenced by the cloud–cloud collision. [ABSTRACT FROM AUTHOR]

In order to investigate star-formation (SF) processes in extreme environments, we have carried out a multi-wavelength analysis of the mid-infrared bubble N46, which hosts a WN7 Wolf–Rayet (W–R) star. We have used 13CO line data to trace an expanding shell surrounding the W–R star containing about five condensations within the molecular cloud associated with the bubble. The W–R star is associated with a powerful stellar wind having a mechanical luminosity of ∼4 × 1037 erg s−1. A deviation of the H-band starlight mean polarization angles around the bubble has also been traced, indicating the impact of stellar wind on the surroundings. The Herschel temperature map shows a temperature range of ∼18–24 K toward the five molecular condensations. The photometric analysis reveals that these condensations are associated with the identified clusters of young stellar objects, revealing ongoing SF process. The densest among these five condensations (peak N(H2) ∼9.2 × 1022 cm−2 and AV ∼ 98 mag) is associated with a 6.7 GHz methanol maser, an infrared dark cloud, and the CO outflow, tracing active massive SF within it. At least five compact radio sources (CRSs) are physically linked with the edges of the bubble, and each of them is consistent with the radio spectral class of a B0V–B0.5V-type star. The ages of the individual infrared counterparts of three CRSs (∼1–2 Myr) and a typical age of WN7 W–R star (∼4 Myr) indicate that the SF activities around the bubble are influenced by the feedback of the W–R star. [ABSTRACT FROM AUTHOR]

We have carried out an extensive multi-wavelength study to investigate the star formation process in the S235 complex. The S235 complex has a spherelike shell appearance at wavelengths longer than 2 μm and harbors an O9.5V type star approximately at its center. A near-infrared extinction map of the complex traces eight subregions (having AV > 8 mag), and five of them appear to be distributed in an almost regularly spaced manner along the spherelike shell surrounding the ionized emission. This picture is also supported by the integrated 12CO and 13CO intensity maps and by Bolocam 1.1 mm continuum emission. The position–velocity analysis of CO reveals an almost semi-ringlike structure, suggesting an expanding H ii region. We find that the Bolocam clump masses increase as we move away from the location of the ionizing star. This correlation is seen only for those clumps that are distributed near the edges of the shell. Photometric analysis reveals 435 young stellar objects (YSOs), 59% of which are found in clusters. Six subregions (including five located near the edges of the shell) are very well correlated with the dust clumps, CO gas, and YSOs. The average values of Mach numbers derived using NH3 data for three (East 1, East 2, and Central E) out of these six subregions are 2.9, 2.3, and 2.9, indicating these subregions are supersonic. The molecular outflows are detected in these three subregions, further confirming the ongoing star formation activity. Together, all these results are interpreted as observational evidence of positive feedback of a massive star. [ABSTRACT FROM AUTHOR]

We present an analysis of multi-wavelength observations from various data sets and Galactic plane surveys to study the star-formation process in the W42 complex. A bipolar appearance of the W42 complex is evident due to the ionizing feedback from the O5–O6 type star in a medium that is highly inhomogeneous. The Very Large Telescope/NACO adaptive-optics K and L′ images (resolutions ∼0.″2–0.″1) resolved this ionizing source into multiple point-like sources below ∼5000 AU scale. The position angle ∼15° of the W42 molecular cloud is consistent with the H-band starlight mean polarization angle, which in turn is close to the Galactic magnetic field, suggesting the influence of the Galactic field on the evolution of the W42 molecular cloud. Herschel sub-millimeter data analysis reveals three clumps located along the waist axis of the bipolar nebula, with the peak column densities of ∼(3–5) × 1022 cm−2 corresponding to visual extinctions of AV ∼ 32–53.5 mag. The Herschel temperature map traces a temperature gradient in W42, revealing regions of 20 K, 25 K, and 30–36 K. Herschel maps reveal embedded filaments (length ∼1–3 pc) that appear to be radially pointed to the denser clump associated with the O5–O6 star, forming a hub-filament system. A total of 512 candidate young stellar objects (YSOs) are identified in the complex, ∼40% of which are present in clusters distributed mainly within the molecular cloud, including the Herschel filaments. Our data sets suggest that the YSO clusters, including the massive stars, are located at the junction of the filaments, similar to those seen in the Rosette Molecular Cloud. [ABSTRACT FROM AUTHOR]

We report on the discovery of an infrared jet from a deeply embedded infrared counterpart of the 6.7 GHz methanol maser emission (MME) in W42 (i.e., W42-MME). We show that W42-MME drives a parsec-scale H2 outflow, with the detection of a bow shock feature at ∼0.52 pc to the north. The inner ∼0.4 pc part of the H2 outflow has a position angle of ∼18° and the position angle of ∼40° is found farther away on either side of the outflow from W42-MME. W42-MME is detected at wavelengths longer than 2.2 μm and is a massive young stellar object with an estimated stellar mass of 19 ± 4 . We map the inner circumstellar environment of W42-MME using Very Large Telescope (VLT)/NACO adaptive optics Ks and L′ observations at resolutions of ∼0.″ 2 and ∼0.″1, respectively. We discover a collimated jet in the inner 4500 AU using the L′ band, which contains prominent Brα line emission. The jet is located inside an envelope/cavity (extent ∼10,640 AU) that is tapered at both ends and is oriented along the north–south direction. Such observed morphology of the outflow cavity around the massive star is scarcely known and is very crucial for understanding the jet-outflow formation process in massive star formation. Along the flow axis, which is parallel to the previously known magnetic field, two blobs are found in both the NACO images at distances of ∼11800 AU, located symmetrically from W42-MME. The observed W42-MME jet-outflow configuration can be used to constrain the jet launching and jet collimation models in massive star formation. [ABSTRACT FROM AUTHOR]