Molecular Cloud Complex Research Articles

The molecular cloud complex G34 is located at a distance of $2.12 ± 0.38$ kpc and contains two giant filaments, F1 and F2. It is considered a good example of colliding filaments. We mapped these two filaments using the and ̧o ( lines that were observed with the 13.7m millimeter-wavelength telescope of the Purple Mountain Observatory. The fraction of high-column density gas (N_ in F1 and F2 is 4.16% and 8.33%, respectively, which is lower than the typical value of 10% for giant molecular filaments. Moreover, only one of the 13 dense clumps identified in F1 and F2 correlates with the infrared dust cores traced by the NASA Wide-field Infrared Survey Explorer (WISE) 22 μm emission. This suggests that F1 and F2 may be in early stages of their evolution and might be forming low-mass stars. We also observe large-scale velocity gradients in F1 and F2. Along the spine of F1, the velocity and line mass increase from the ends toward the center, while in F2, they increase from the northwest to the southeast. These parameters are inversely correlated with the gravitational potential, which may indicate a transformation between kinetic energy and gravitational potential energy between F1 and F2. Furthermore, no H sc,ii regions correlate with F1 and F2 in the WISE data of galactic H sc,ii regions, which indicates that the gas distribution within F1, as well as the V-shaped structure of F1, is unaffected by feedback from H sc,ii regions, but is instead caused by gravitational effects. The material in F1 and F2 is not concentrated at the ends of the filaments, but rather in the middle of F1 and at one end of F2 and therefore does not lead to the edge-collapse effect. The collapse and merging timescales thus do not compete. Finally, we calculated the merging time of F1 and F2. When the angle between the line-of-sight velocity and the direction of the relative velocity between F1 and F2 is $45^̧irc$, the average relative velocity between F1 and F2 is 1.39̨ms. The resulting merging timescale is approximately 4.62,±,1.12 Myr. This process might be influenced by additional stellar feedback from ongoing star formation within the filaments.

We decomposed the G333 complex and the G331 giant molecular cloud into multi-scale hub-filament systems (HFs) using the highresolution 13CO (3-2) data from LAsMA observations. We employed the filfinder algorithm to identify and characterize filaments within HFs. Compared with non-HFs, HFs have a significantly higher density contrast, higher masses, and lower virial ratios. Velocity gradient measurements around intensity peaks provide evidence of gas inflow within these structures. There may be an evolutionary sequence from non-HFs to HFs. There is currently no distinct gravitational focusing process for non-HFs that would result in a significant density contrast. The density contrast can effectively measure the extent of gravitational collapse and the strength of the gravitational center of the structure, which definitively shape the hub-filament morphology. Based on the results from this study and the kinematic evidence from our previous studies, we suggest that molecular clouds are network structures formed by the gravitational coupling of multi-scale hub-filament structures. The knots in the networks are the hubs: they are the local gravitational centers and the main star-forming sites. Clumps in molecular clouds are equivalent to the hubs. The network structure of molecular clouds can naturally explain why feedback from protoclusters does not significantly change the kinematic properties of the surrounding embedded dense gas structures, as concluded in our previous studies.

Context. Identifying members of star-forming regions is an initial step to analyse the properties of a molecular cloud complex. In such a membership analysis, the sensitivity of a dataset plays a significant role in detecting stellar mass up to a specific limit, which is crucial for understanding various stellar properties, such as disc evolution and planet formation across different environments. Aims. IC 1396 is a nearby classical H II region dominated by feedback-driven star formation activity. In this work, we aim to identify the low-mass member populations of the complex using deep optical multi-band imaging with Subaru-Hyper Suprime Cam (HSC) over ∼7.1 deg2 in r2, i2, and Y bands. The optical dataset is complemented by UKIDSS near-infrared data in the J, H, and K bands. Through this work, we evaluate the strengths and limitations of machine learning techniques when applied to such astronomical datasets. Methods. To identify member populations of IC 1396, we employed the random forest (RF) classifier of machine learning technique. The RF classifier is an ensemble of individual decision trees suitable for large, high-dimensional datasets. The training set used in this work is derived from previous Gaia-based studies, in which the member stars are younger than ∼10 Myr. However, its sensitivity is limited to ∼20 mag in the r2 band, making it challenging to identify candidates at the fainter end. In this analysis, in addition to magnitudes and colours, we incorporated several derived parameters from the magnitude and colour of the sources to identify candidate members of the star-forming complex. By employing this method, we were able to identify promising candidate member populations of the star-forming complex. We discuss the associated limitations and caveats in the method and improvements for future studies. Results. In this analysis, we identify 2425 high-probability low-mass stars distributed within the entire star-forming complex, of which 1331 are new detections. A comparison of these identified member populations shows a high retrieval rate with Gaia-based literature sources, as well as sources detected through methods based on optical spectroscopy, Spitzer, Hα/X – ray emissions, optical photometry, and 2MASS photometry. The mean age of the member populations is ∼2–4 Myr, consistent with findings from previous studies. Considering the identified member populations, we present preliminary results by exploring the presence of sub-clusters within IC 1396, assessing the possible mass limit of the member populations, and providing a brief discussion on the star formation history of the complex. Conclusions. The primary aim of this work is to develop a method of identifying candidate member populations from a deep, sensitive dataset such as Subaru-HSC by employing machine learning techniques. Although we overcome some limitations in this study, the method requires further improvements to address the caveats associated with such a membership analysis.

Star formation takes place in the coldest parts of molecular clouds, beginning in the densest, collapsing regions of filaments. As pre-main sequence stars are luminous X-ray emitters, X-ray point sources can serve as effective tracers of YSOs. In our study, we examined the distribution of X-ray point sources in two nearby molecular clouds: Heiles Cloud 2 (HCL 2), a ring-like molecular cloud complex in the Taurus region, and Heiles Cloud 1 (LDN 1251), a cometary-shaped dark molecular cloud. By incorporating the latest YSO catalogue from Gaia DR3, we analysed how YSO positions compare to the structure of the interstellar medium (ISM) and found that the sources are primarily aligned just outside the densest regions. Additionally, we compared the positions with the magnetic field structure and found no clear correlation at the given resolution.

Abstract To reveal the origin of the mini-starbursts in the Milky Way, we carried out large-scale CO observations toward the RCW 106 giant molecular cloud (GMC) complex using the NANTEN2 4 m radio telescope operated by Nagoya University. We also analyzed the Mopra Southern Galactic Plane CO survey and Herschel infrared continuum archival data. The RCW 106 GMC complex contains the radial velocity components of −68 km s−1 and −50 km s−1 reported by H. Nguyen et al. (2015). Focusing on the RCW 106 East and West region with the massive star formation having the bright infrared dust emission, we found that these regions have three different velocity components with ∼10 km s−1 differences. The two out of three velocity components show morphological correspondence with the infrared cold dust emission and connect with the bridge feature on a position–velocity diagram. Therefore, two molecular clouds with ∼10 km s−1 differences are likely to be physically associated with massive star-forming regions in the GMC complex. Based on these observational results, we argue that mini-starbursts and massive star/cluster formation in the RCW 106 GMC complex are induced by supersonic cloud–cloud collisions in an agglomerate of molecular gas on the Scutum–Centaurus arm.

ABSTRACT The external environments surrounding molecular clouds vary widely across galaxies such as the Milky Way, and statistical samples of clouds are required to understand them. We present the Perseus Arm Molecular Survey (PAMS), a James Clerk Maxwell Telescope (JCMT) survey combining new and archival data of molecular-cloud complexes in the outer Perseus spiral arm in $^{12}$CO, $^{13}$CO, and C$^{18}$O (J = 3–2). With a survey area of $\sim$8 deg$^2$, PAMS covers well-known complexes such as W3, W5, and NGC 7538 with two fields at $\ell \approx 110^{\circ }$ and $\ell \approx 135^{\circ }$. PAMS has an effective resolution of 17 arcsec, and rms sensitivity of $T_\mathrm{mb}= 0.7$–1.0 K in 0.3 km s$^{-1}$ channels. Here we present a first look at the data, and compare the PAMS regions in the Outer Galaxy with Inner Galaxy regions from the CO Heterodyne Inner Milky Way Plane Survey (CHIMPS). By comparing the various CO data with maps of H$_2$ column density from Herschel, we calculate representative values for the CO-to-H$_2$ column-density X-factors, which are $X_\mathrm{^{12}CO\, (3-2)}$$\, =4.0\times 10^{20}$ and $X_\mathrm{^{13}CO\, (3-2)}$$\, =4.0\times 10^{21}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$ with a factor of 1.5 uncertainty. We find that the emission profiles, size–linewidth, and mass–radius relationships of $^{13}$CO-traced structures are similar between the Inner and Outer Galaxy. Although PAMS sources are slightly more massive than their Inner Galaxy counterparts for a given size scale, the discrepancy can be accounted for by the Galactic gradient in gas-to-dust mass ratio, uncertainties in the X-factors, and selection biases. We have made the PAMS data publicly available, complementing other CO surveys targeting different regions of the Galaxy in different isotopologues and transitions.

Context. The giant molecular cloud complex Sagittarius B2 (Sgr B2) in the central molecular zone of our Galaxy hosts several high-mass star formation sites, with Sgr B2(M) and Sgr B2(N) being the main centers of activity. This analysis aims to comprehensively model each core spectrum, considering molecular lines, dust attenuation, and free-free emission interactions. We describe the molecular content analysis of each hot core and identify the chemical composition of detected sources. Aims. Using ALMA’s high sensitivity, we aim to characterize the hot core population in Sgr B2(M) and N, gaining a better understanding of the different evolutionary phases of star formation processes in this complex. Methods. We conducted an unbiased ALMA spectral line survey of 47 sources in band 6 (211-275 GHz). Chemical composition and column densities were derived using XCLASS, assuming local thermodynamic equilibrium. Quantitative descriptions for each molecule were determined, considering all emission and absorption features across the spectral range. Temperature and velocity distributions were analyzed, and derived abundances were compared with other spectral line surveys. Results. We identified 65 isotopologs from 41 different molecules, ranging from light molecules to complex organic compounds, originating from various environments. Most sources in the Sgr B2 complex were assigned different evolutionary phases of high-mass star formation. Conclusions. Sgr B2(N) hot cores show more complex molecules such as CH3OH, CH3OCHO, and CH3OCH3, while M cores contain lighter molecules such as SO2, SO, and NO. Some sulfur-bearing molecules are more abundant in N than in M. The derived molecular abundances can be used for comparison and to constrain astrochemical models. Inner sources in both regions were generally more developed than outer sources, with some exceptions.

Context. The supernova remnant (SNR) W44 and its surroundings are a prime target for studying the acceleration of cosmic rays (CRs). Several previous studies established an extended gamma-ray emission that is set apart from the radio shell of W44. This emission is thought to originate from escaped high-energy CRs that interact with a surrounding dense molecular cloud complex. Aims. We present a detailed analysis of Fermi-LAT data with an emphasis on the spatial and spectral properties of W44 and its surroundings. We also report the results of the observations performed with the MAGIC telescopes of the northwestern region of W44. Finally, we present an interpretation model to explain the gamma-ray emission of the SNR and its surroundings. Methods. We first performed a detailed spatial analysis of 12 years of Fermi-LAT data at energies above 1 GeV, in order to exploit the better angular resolution, while we set a threshold of 100 MeV for the spectral analysis. We performed a likelihood analysis of 174 hours of MAGIC data above 130 GeV using the spatial information obtained with Fermi-LAT. Results. The combined spectra of Fermi-LAT and MAGIC, extending from 100 MeV to several TeV, were used to derive constraints on the escape of CRs. Using a time-dependent model to describe the particle acceleration and escape from the SNR, we show that the maximum energy of the accelerated particles has to be ≃40 GeV. However, our gamma-ray data suggest that a small number of lower-energy particles also needs to escape. We propose a novel model, the broken-shock scenario, to account for this effect and explain the gamma-ray emission.

We present a computational investigation into the fragmentation pathways of ethanolamine (C2H7NO, EtA), propanol (C3H8O, PrO), butanenitrile (C4H7N, BuN), and glycolamide (C2H5NO2, GlA)-saturated organic molecules detected in the interstellar medium (ISM), particularly in the molecular cloud complex Sagittarius B2 (Sgr B2) and its molecular cloud G+0.693-0.027. Using electron-impact ionization data and Born-Oppenheimer molecular dynamics simulations, we investigate how cosmic rays, cosmic-ray-induced UV fields, and shock-induced heating can induce the fragmentation of these molecules, resulting in the formation of unsaturated species with extended π-bond networks. Despite the attenuation of external UV radiation in G+0.693-0.027, these energetic processes are capable of driving partial transformations of saturated into unsaturated molecules, supporting the coexistence of species like EtA and GlA alongside unsaturated nitriles such as cyanoacetylene (HC3N), cyanopropyne (CH3C3N), and cyanoallene (CH2CCHCN). Our findings underscore the significance of high-energy mechanisms in enhancing chemical complexity within molecular clouds and offer insights into the pathways that govern the evolution of organic molecules in the ISM.

NGC 6334 is a giant molecular cloud (GMC) complex that exhibits elongated filamentary structure and harbours numerous OB-stars, H II regions, and star-forming clumps. To study the emission morphology and velocity structure of the gas in the extended NGC 6334 region using high-resolution molecular line data, we made observations of the 12CO and 13CO J = 3 → 2 lines with the LAsMA instrument at the APEX telescope. The LAsMA data provided a spatial resolution of 20″ (~0.16 pc) and sensitivity of 0.4 K at a spectral resolution of 0.25 km s−1. Our observations revealed that gas in the extended NGC 6334 region exhibits connected velocity coherent structure over ~80 pc parallel to the Galactic plane. The NGC 6334 complex has its main velocity component at approximately −3.9 km s−1 with two connected velocity structures at velocities approximately −9.2 km s−1 (the ‘bridge’ features) and −20 km s−1 (the northern filament, NGC 6334-NF). We observed local velocity fluctuations at smaller spatial scales along the filament that are likely tracing local density enhancement and infall, while the broader V-shaped velocity fluctuations observed towards the NGC 6334 central ridge and G352.1 region located in the eastern filament EF1 indicate globally collapsing gas onto the filament. We investigated the 13CO emission and velocity structure around 42 WISE H II regions located in the extended NGC 6334 region and found that most H II regions show signs of molecular gas dispersal from the centre (36 of 42) and intensity enhancement at their outer radii (34 of 42). Furthermore most H II regions (26 of 42) are associated with least one ATLASGAL clump within or just outside of their radii, the formation of which may have been triggered by H II bubble expansion. Typically towards larger H II regions we found visually clear signatures of bubble shells emanating from the filamentary structure. Overall the NGC 6334 filamentary complex exhibits sequential star formation from west to east. Located in the west, the GM-24 region exhibits bubbles within bubbles and is at a relatively evolved stage of star formation. The NGC 6334 central ridge is undergoing global gas infall and exhibits two gas bridge features possibly connected to the cloud-cloud collision scenario of the NGC 6334-NF and the NGC 6334 main gas component. The relatively quiescent eastern filament (EF1 - G352.1) is a hub-filament in formation, which shows the kinematic signature of global gas infall onto the filament. Our observations highlight the important role of H II regions in shaping the molecular gas emission and velocity structure as well as the overall evolution of the molecular filaments in the NGC 6334 complex.

Context. The Orion Molecular Cloud complex, one of the nearest (D = 406 pc) and most extensively studied massive star-forming regions, is ideal for constraining the physics of stellar feedback, but its ~12 deg diameter on the sky requires a dedicated approach to mapping ionized gas structures within and around the nebula. Aims. The Sloan Digital Sky Survey (SDSS-V) Local Volume Mapper (LVM) is a new optical integral field unit (IFU) that will map the ionized gas within the Milky Way and Local Group galaxies, covering 4300 deg2 of the sky with the new LVM Instrument (LMV-I). Methods. We showcase optical emission line maps from LVM covering 12 deg2 inside of the Orion belt region, with 195 000 individual spectra combined to produce images at 0.07 pc (35.3″) resolution. This is the largest IFU map made (to date) of the Milky Way, and contains well-known nebulae (the Horsehead Nebula, Flame Nebula, IC 434, and IC 432), as well as ionized interfaces with the neighboring dense Orion B molecular cloud. Results. We resolve the ionization structure of each nebula, and map the increase in both the [S II]/Hα and [N II]/Hα line ratios at the outskirts of nebulae and along the ionization front with Orion B. [O III] line emission is only spatially resolved within the center of the Flame Nebula and IC 434, and our ~0.1 pc scale line ratio diagrams show how variations in these diagnostics are lost as we move from the resolved to the integrated view of each nebula. We detect ionized gas emission associated with the dusty bow wave driven ahead of the star σ Orionis, where the stellar wind interacts with the ambient interstellar medium. The Horsehead Nebula is seen as a dark occlusion of the bright surrounding photo-disassociation region. This small glimpse into Orion only hints at the rich science that will be enabled by the LVM.

ABSTRACT Three-dimensional (3D) bubble structure of the Sgr-B molecular-cloud complex is derived by a kinematical analysis of CO-line archival cube data of the Galactic Centre (GC) observed with the Nobeyama 45-m telescope. The line-of-sight depth is estimated by applying the face-on transformation method of radial velocity to the projected distance on the Galactic plane considering the Galactic rotation of the central molecular zone (CMZ). The 3D complex exhibits a conical-horn structure with the Sgr-B2 cloud located in the farthest end on the line of sight at radial velocity $v_{\rm lsr} \sim 70$ km s$^{-1}$, and the entire complex composes a lopsided bubble opening toward the Sun at $v_{\rm lsr}\sim 50$ to 30 km s$^{-1}$. The line-of-sight extent of the complex is $\sim 100$ pc according to the large velocity extent for several tens of km s$^{-1}$ from Sgr-B2 to the outskirts. The entire complex exhibits a flattened conical bubble with full sizes $\sim 40 \ {\rm pc} \times 20 \ {\rm pc} \times 100 \ {\rm pc}$ in the l, b and line-of-sight directions, respectively. Based on the 3D analysis, we propose a formation scenario of the giant molecular bubble structure due to a galactic bow shock, and suggest that the star formation in Sgr-B2 was enhanced by dual-side compression (DSC) of the B2 cloud by the Galactic shock wave from up-stream and expanding H ii region from the down-stream side of the GC Arm I in Galactic rotation.

Deuterated molecules and their molecular D/H-ratios ($R_D$(D)) are important diagnostic tools with which to study the physical conditions of star-forming regions. The degree of deuteration, $R_D$(D), can be significantly enhanced over the elemental D/H-ratio depending on physical parameters such as temperature, density, and the ionization fraction. Within the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE), we aim to explore the large-scale distribution of deuterated molecules in the nearby ($d 1.5$ kpc) Cygnus-X region, a giant molecular cloud complex that hosts multiple sites of high-mass star formation. We focus on the analysis of large-scale structures of deuterated molecules in the filamentary region hosting the prominent region DR21 and DR21(OH), a molecular hot core that is in an earlier evolutionary state. The DR21 filament has been imaged using the IRAM 30-m telescope in a variety of deuterated molecules and transitions. Here we discuss the HCO+ HNC, and HCN molecules and their deuterated isotopologs DCO+ DNC, and DCN, and their observed line emissions at 3.6, 2, and 1.3 mm. The spatial distributions of integrated line emissions from DCO+ DNC, and DCN reveal morphological differences. Notably DCO+ displays the most extended emission, characterized by several prominent peaks. Likewise, DNC exhibits multiple peaks, although its emission appears less extended compared to DCO+ . In contrast to the extended emission of DCO+ and DNC, DCN appears the least extended, with distinct peaks. Focusing only on the regions where all three molecules are observed, the mean deuteration ratios for each species, $R_D$, are 0.01 for both DNC and DCN, and $=0.005$ for DCO+ respectively. Anticorrelations are found with deuterated molecules and dust temperature or $N$( H2 The strongest anticorrelation is found with $R_D$( DCO+ ) and $N$( H2 ), with a Pearson correlation coefficient of $ -0.74$. We analyzed the SiO emission as a tracer for shocks and the $N$(HCO)/$N$( H^13CO+ ) as a tracer for increased photodissociation by ultraviolet radiation. It is suggested that the anticorrelation of $R_D$( DCO+ ) and $N$( H2 ) is a result of a combination of an increased photodissociation degree and shocks. A strong positive correlation between the ratio of integrated intensities of DCN and DNC with their 13C-isotopologs is found in high-column-density regions. The positive relationship between the ratios implies that the D-isotopolog of the isomers could potentially serve as a tracer for the kinetic gas temperature.

The kinetic temperature structure of the massive filament DR21 within the Cygnus X molecular cloud complex has been mapped using the IRAM 30 m telescope. This mapping employed the para-H2CO triplet (JKaKc = 303−202, 322−221, and 321–220) on a scale of ~0.1 pc. By modeling the averaged line ratios of para-H2CO 322–221/303–202 and 321–220/303 –202 with RADEX under non local thermodynamic equilibrium (LTE) assumptions, the kinetic temperature of the dense gas was derived, which ranges from 24 to 114 K, with an average temperature of 48.3 ± 0.5 K at a density of n(H2)= 105 cm−3. In comparison to temperature measurements using NH3 (1, 1)/(2,2) and far-infrared (FIR) wavelengths, the para-H2CO(3–2) lines reveal significantly higher temperatures. The dense clumps in various regions appear to correlate with the notable kinetic temperature (Tkin ≳ 50 K) of the dense gas traced by H2CO. Conversely, the outskirts of the DR21 filament display lower temperature distributions (Tkin < 50 K). Among the four dense cores (N44, N46, N48, and N54), temperature gradients are observed on a scale of ~0.1–0.3 pc. This suggests that the warm dense gas traced by H2CO is influenced by internal star formation activity. With the exception of the dense core N54, the temperature profiles of these cores were fitted with power-law indices ranging from −0.3 to −0.5, with a mean value of approximately −0.4. This indicates that the warm dense gas probed by H2CO is heated by radiation emitted from internally embedded protostar(s) and/or clusters. While there is no direct evidence supporting the idea that the dense gas is heated by shocks resulting from a past explosive event in the DR21 region on a scale of ~0.1 pc, our measurements of H2CO toward the DR21W1 region provide compelling evidence that the dense gas in this specific area is indeed heated by shocks originating from the western DR21 flow. Higher temperatures as traced by H2CO appear to be associated with turbulence on a scale of ~0.1 pc. The physical parameters of the dense gas as determined from H2CO lines in the DR21 filament exhibit aremarkable similarity to the results obtained in OMC-1 and N113, albeit on a scale of approximately 0.1–0.4 pc. This may imply that the physical mechanisms governing the dynamics and thermodynamics of dense gas traced by H2CO in diverse star formation regions may be dominated by common underlying principles despite variations in specific environmental conditions.

The origins and mergers of supermassive black holes (SMBHs) remain a mystery. We describe a scenario from a novel multiphysics simulation featuring rapid (≲1 Myr) hyper-Eddington gas capture by a ∼1000 M ⊙ “seed” black hole (BH) up to supermassive (≳106 M ⊙) masses in a massive, dense molecular cloud complex typical of high-redshift starbursts. Due to the high cloud density, stellar feedback is inefficient, and most of the gas turns into stars in star clusters that rapidly merge hierarchically, creating deep potential wells. Relatively low-mass BH seeds at random positions can be “captured” by merging subclusters and migrate to the center in ∼1 freefall time (vastly faster than dynamical friction). This also efficiently produces a paired BH binary with ∼0.1 pc separation. The centrally concentrated stellar density profile (akin to a “protobulge”) allows the cluster as a whole to capture and retain gas and build up a large (parsec-scale) circumbinary accretion disk with gas coherently funneled to the central BH (even when the BH radius of influence is small). The disk is “hypermagnetized” and “flux-frozen”: dominated by a toroidal magnetic field with plasma β ∼ 10−3, with the fields amplified by flux-freezing. This drives hyper-Eddington inflow rates ≳1 M ⊙ yr−1, which also drive the two BHs to nearly equal masses. The late-stage system appears remarkably similar to recently observed high-redshift “little red dots.” This scenario can provide an explanation for rapid SMBH formation, growth, and mergers in high-redshift galaxies.

We perform a comprehensive CO study toward the Monoceros OB1 (Mon OB1) region based on the Milky Way Imaging Scroll Painting survey at an angular resolution of about 50″. The high-sensitivity data, together with the high dynamic range, show that molecular gas in the 8° × 4° region displays complicated hierarchical structures and various morphology (e.g., filamentary, cavity-like, shell-like, and other irregular structures). Based on Gaussian decomposition and clustering for 13CO data, a total of 263 13CO structures are identified in the whole region, and 88% of raw data flux is recovered. The dense gas with relatively high column density from the integrated CO emission is mainly concentrated in the region where multiple 13CO structures are overlapped. Combining the results of 32 large 13CO structures with distances from Gaia DR3, we estimate an average distance of 729−45+45pc for the giant molecular cloud (GMC) complex. The total mass of the GMC complex traced by 12CO, 13CO, and C18O is 1.1 × 105 M ⊙, 4.3 × 104 M ⊙, and 8.4 × 103 M ⊙, respectively. The dense gas fraction shows a clear difference between Mon OB1 GMC East (12.4%) and Mon OB1 GMC West (3.3%). Our results show that the dense gas environment is closely linked to the nearby star-forming regions. On the other hand, star-forming activities have a great influence on the physical properties of the surrounding molecular gas (larger velocity dispersion, higher temperatures, more complex velocity structures, etc.). We also discuss the distribution/kinematics of molecular gas associated with nearby star-forming activities.

ABSTRACT Jets and outflows are the early signposts of stellar birth. Using the UKIRT Wide Field Infrared Survey for H2 (UWISH2) at 2.12 μm, 127 outflows are identified in molecular cloud complexes Vulpecula OB1 and IRDC G53.2 covering 12 square degrees of the Galactic plane. Using multiwavelength data sets, from 1.2 to 70 μm, 79 young stellar objects (YSOs) are proposed as potential driving sources, where ∼79 per cent are likely Class 0/I protostars, 17 per cent are Class II YSOs, and the remaining 4 per cent are Class III YSOs. The outflows are characterized in terms of their length, flux, luminosity, and knot-spacing. The identified outflows have a median lobe length of 0.22 and 0.17 pc for outflows in Vulpecula OB1 and IRDC G53.2, respectively. Our analysis, from the knot spacing, reveals a typical ejection frequency of ∼1.2 kyr suggesting an intermediate type between the FU-Ori and EX-Ori type of eruptions in both cloud complexes. Furthermore, the physical parameters of the driving sources are obtained by performing radiative transfer modelling to the observed spectral energy distributions, which suggest that the outflows are driven by intermediate mass stars. Various observed trends between the outflow properties and the corresponding driving sources, and various interesting outflows and star forming sites, including sites of triggered star formation and protocluster forming clump with clusters of jets, are discussed. The obtained results and the identified jet-bearing protostellar sample will pave the way to understand many aspects of outflows with future high-resolution observations.

Organic compounds are a major component of dust in molecular clouds, alongside silicates and water ice, due to the high abundances of elements that make up these compounds in the Galaxy. The initial molecular inventory of the Solar System, inherited from the molecular cloud, was modified and new complex molecules were formed in the protoplanetary disk and planetesimals. Because astronomical observations mainly target gas, while cosmochemical evidence deals with solid phases, it is crucial to link discrepant knowledge on organic species through state-of-the-art modeling. This chapter reviews the latest understanding of surface reactions on inter-stellar dusts, gas–dust reactions in the protoplanetary disk, and alteration processes on planetesimals in the early Solar System.

Context. Feedback from young massive stars has an important impact on the star formation potential of their parental molecular clouds. Aims. We investigate the physical properties of gas structures under feedback in the G333 complex using data of the 13CO J = 3–2 line observed with the LAsMA heterodyne camera on the APEX telescope. Methods. We used the Dendrogram algorithm to identify molecular gas structures based on the integrated intensity map of the 13CO (3–2) emission, and extracted the average spectra of all structures to investigate their velocity components and gas kinematics. Results. We derive the column density ratios between different transitions of the 13CO emission pixel by pixel, and find the peak values N2−1/N1−0 ≈ 0.5, N3−2/N1−0 ≈ 0.3, and N3−2/N2−1 ≈ 0.5. These ratios can also be roughly predicted by the nonlocal thermodynamic equilibrium (NLTE) molecular radiative transfer code RADEX for an average H2 volume density of ~4.2 × 103 cm−3. A classical virial analysis does not reflect the true physical state of the identified structures, and we find that external pressure from the ambient cloud plays an important role in confining the observed gas structures. For high-column-density structures, velocity dispersion and density show a clear correlation that is not seen for low-column-density structures, indicating the contribution of gravitational collapse to the velocity dispersion. Branch structures show a more significant correlation between 8 μm surface brightness and velocity dispersion than leaf structures, implying that feedback has a greater impact on large-scale structures. For both leaf and branch structures, σ − N * R always has a stronger correlation compared to σ − N and σ − R. The scaling relations are stronger, and have steeper slopes when considering only self-gravitating structures, which are the structures most closely associated with the Heyer relation. Conclusions. Although the feedback disrupting the molecular clouds will break up the original cloud complex, the substructures of the original complex can be reorganized into new gravitationally governed configurations around new gravitational centers. This process is accompanied by structural destruction and generation, and changes in gravitational centers, but gravitational collapse is always ongoing.

ABSTRACT A massive molecular cloud complex represents local gravitational potential that can constrain the vertical distribution of surrounding stars and gas. This pinching effect results in the local corrugation of the scale height of stars and gas which is in addition to the global corrugation of the mid-plane of the disc. For the first time, we report observational evidence for this pinching on the H i vertical structures in the Galactic region (20° < l < 40°), also called W41–W44 region. The H i vertical distribution is modelled by a double Gaussian profile that physically represents a narrow dense gas distribution confined to the mid-plane embedded in a wider diffuse H i. We find that the estimate of the H i scale height distribution of wider components shows corrugated structures at the locations of molecular complexes, as theoretically predicted in literature. While the narrow component is less affected by the pinching, we found a hint of the disc being disrupted by the active dynamics in the local environment of the complex, for example, supernova explosions. Molecular complexes of mass of several $10^6 \rm M_{\odot } $, associated with the mini-starburst region W43 and the supernova remnant W41 show the strongest evidence for the pinching; here a broad trough, with an average width of ∼400 pc and height ∼300 pc, in the disc thickness of the wider component is prominently visible. Searching for similar effect on the stars as well as in the location of other complexes in the Milky Way and other galaxies will be useful to establish this phenomenon more firmly.