Giant Molecular Cloud Complex Research Articles

High-resolution observations of 12CO and 13CO J = 3 2 towards the NGC 6334 extended filament. I. Emission morphology and velocity structure

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" (sim 0.16 pc) and sensitivity of 0.4 K at a spectral resolution of 0.25 km $. Our observations revealed that gas in the extended NGC 6334 region exhibits connected velocity coherent structure over sim 80 pc parallel to the Galactic plane. The NGC 6334 complex has its main velocity component at $ -3.9$ km $ with two connected velocity structures at velocities $ -9.2$ km $ (the `bridge' features) and $ km $ (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.

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE. III. The large scale distribution of DCO+, DNC, and DCN in the DR21 filament

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.

Distribution and Properties of Molecular Gas toward the Monoceros OB1 Region

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.

High-resolution APEX/LAsMA 12CO and 13CO (3–2) observation of the G333 giant molecular cloud complex

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.

The physical and chemical structure of Sagittarius B2

Context. Sagittarius B2 (Sgr B2) is a giant molecular cloud complex in the central molecular zone of our Galaxy hosting several sites of high-mass star formation. The two main centers of activity are Sgr B2(M) and Sgr B2(N), which contain 27 and 20 continuum sources, respectively. Our analysis aims to be a comprehensive modeling of each core spectrum, where we take the complex interaction between molecular lines, dust attenuation, and free-free emission arising from H II regions into account. In this work, which is the first of two papers on the complete analysis, we determine the dust and, if H II regions are contained, the parameters of the free-free thermal emission of the ionized gas for each core, and derive a self-consistent description of the continuum levels of each core. Aims. Using the high sensitivity of ALMA, we characterize the physical and chemical structure of these continuum sources and gain better insight into the star formation process within the cores. Methods. We used ALMA to perform an unbiased spectral line survey of all 47 sources in ALMA band 6 with a frequency coverage from 211 to 275 GHz. In order to model the free-free continuum contribution of a specific core, we fit the contained recombination lines to obtain the electron temperatures and the emission measures, where we use an extended XCLASS program to describe recombination lines and free-free continuum simultaneously. In contrast to previous analyses, we derived the corresponding parameters here not only for each core, but also for their local surrounding envelope, and determined their physical properties. Results. The distribution of recombination lines we found in the core spectra closely fits the distribution of H II regions described in previous analyses. In Sgr B2(M), the three inner sources are the most massive, whereas in Sgr B2(N) the innermost core A01 dominates all other sources in mass and size. For the cores we determine average dust temperatures of around 236 K (Sgr B2(M)) and 225 K (Sgr B2(N)), while the electronic temperatures are located in a range between 3800 and 23 800 K. Conclusions. The self-consistent description of the continuum levels and the quantitative description of the dust and free-free contributions form the basis for the further analysis of the chemical composition of the individual sources, which is continued in the next paper. This detailed modeling will give us a more complete picture of the star formation process in this exciting environment.

High-resolution APEX/LAsMA 12CO and 13CO (3–2) observation of the G333 giant molecular cloud complex

Context. Hub-filament systems are suggested to be the birth cradles of high-mass stars and clusters. Aims. We investigate the gas kinematics of hub-filament structures in the G333 giant molecular cloud complex using 13CO (3–2) observed with the APEX/LAsMA heterodyne camera. Methods. We applied the FILFINDER algorithm to the integrated intensity maps of the 13CO J = 3–2 line to identify filaments in the G333 complex, and we extracted the velocity and intensity along the filament skeleton from moment maps. Clear velocity and density fluctuations are seen along the filaments, allowing us to fit velocity gradients around the intensity peaks. Results. The velocity gradients we fit to the LAsMA and ALMA data agree with each other over the scales covered by ALMA observations in the ATOMS survey (<5 pc). Changes in velocity gradient with scale indicate a funnel structure of the velocity field in position-position-velocity (PPV) space. This is indicative of a smooth, continuously increasing velocity gradient from large to small scales, and thus is consistent with gravitational acceleration. The typical velocity gradient corresponding to a 1 pc scale is ~1.6 km s−1 pc−1. Assuming freefall, we estimate a kinematic mass within 1 pc of ~1190 M⊙, which is consistent with typical masses of clumps in the ATLASGAL survey of massive clumps in the inner Galaxy. We find direct evidence for gravitational acceleration from a comparison of the observed accelerations to those predicted by freefall onto dense hubs with masses from millimeter continuum observations. On large scales, we find that the inflow may be driven by the larger-scale structure, consistent with the hierarchical structure in the molecular cloud and gas inflow from large to small scales. The hub-filament structures at different scales may be organized into a hierarchical system extending up to the largest scales probed through the coupling of gravitational centers at different scales. Conclusions. We argue that the funnel structure in PPV space can be an effective probe for the gravitational collapse motions in molecular clouds. The large-scale gas inflow is driven by gravity, implying that the molecular clouds in the G333 complex may be in a state of global gravitational collapse.

Possible Implications of Relatively High Levels of Initial 60Fe in Iron Meteorites for the Noncarbonaceous–Carbonaceous Meteorite Dichotomy and Solar Nebula Formation

Cook et al. found that iron meteorites have an initial abundance ratio of the short-lived isotope 60Fe to the stable isotope 56Fe of 60Fe/56Fe ∼ (6.4 ± 2.0) × 10−7. This appears to require the injection of live 60Fe from a Type II supernova (SN II) into the presolar molecular cloud core, as the observed ratio is over a factor of 10 times higher than would be expected to be found in the ambient interstellar medium (ISM) as a result of galactic chemical evolution. The supernova triggering and injection scenario offers a ready explanation for an elevated initial 60Fe level, and in addition provides a physical mechanism for explaining the noncarbonaceous–carbonaceous (NC–CC) dichotomy of meteorites. The NC–CC scenario hypothesizes the solar nebula first accreted material that was enriched in supernova-derived nuclides, and then later accreted material depleted in supernova-derived nuclides. While the NC–CC dichotomy refers to stable nuclides, not short-lived isotopes like 60Fe, the SN II triggering hypothesis provides an explanation for the otherwise unexplained change in nuclides being accreted by the solar nebula. Three-dimensional hydrodynamical models of SN II shock-triggered collapse show that after triggering collapse of the presolar cloud core, the shock front sweeps away the local ISM while accelerating the resulting protostar/disk to a speed of several kilometers per second, sufficient for the protostar/disk system to encounter within ∼1 Myr the more distant regions of a giant molecular cloud complex that might be expected to have a depleted inventory of supernova-derived nuclides.

High resolution LAsMA 12CO and 13CO observation of the G305 giant molecular cloud complex

Context. Understanding the effect of feedback from young massive stars on the star-forming ability of their parental molecular clouds is of central importance for studies of the interstellar medium and star formation. Aims. We observed the G305 star-forming complex in the J = 3−2 lines of 12CO and 13CO to investigate whether feedback from the central OB stars was triggering star formation in G305 or actually disrupting this process. Methods. The region was decomposed into clumps using dendrogram analysis. A catalog of the clump properties such as their positions, luminosities, masses, radii, velocity dispersions, volume densities, and surface mass densities was created. The surface mass densities of the clumps were plotted as a function of the incident 8 μm flux. A mask of the region with 8 μm flux > 100 MJy sr−1 was created and clumps were categorized into three classes based on their extent of overlap with the mask, namely mostly inside (>67% overlap), partly inside (>10 and <67% overlap), and outside (<10% overlap). The surface mass density distribution of each of these populations was separately plotted. This was followed by comparing the G305 clumps with the Galactic average taken from a distance-limited sample of ATLASGAL and CHIMPS clumps. Finally, the cumulative distribution functions (CDFs) of the clump masses in G305 and their L∕M ratios were compared to that of the Galactic sample to determine which mechanism of feedback was dominant in G305. Results. The surface mass densities of clumps showed a positive correlation with the incident 8 μm flux. The data did not have sufficient velocity resolution to discern the effects of feedback on the linewidths of the clumps. The subsample of clumps labeled mostly inside had the highest median surface mass densities followed by the partly inside and outside subsamples. The difference between the surface mass density distribution of the three subsamples were shown to be statistically significant using the Kolmogorov–Smirnov test. The mostly inside sample also showed the highest level of fragmentation compared to the other two subsamples. These prove that the clumps inside the G305 region are triggered. The G305 clump population is also statistically different from the Galactic average population, the latter approximating that of a quiescent population of clumps. This provided further evidence that redistribution was not a likely consequence of feedback on the giant molecular cloud. The CDFs of clump masses and their L∕M ratios are both flatter than that of the Galactic average, indicating that clumps are heavier and more efficient at forming stars in G305 compared to the Galactic average. Conclusions. Feedback in G305 has triggered star formation. The collect and collapse method is the dominant mechanism at play in G305.

Anatomy of Orion Molecular Clouds—The Astrochemistry Perspective/Approach

The Orion molecular cloud (OMC) complex is the nearest and perhaps the best-studied giant molecular cloud complex within which low-mass and massive star formation occur. A variety of molecular species, from diatomic molecules to complex organic molecules (COMs), have been observed in the OMC regions. Different chemical species are found at different scales—from giant molecular clouds at parsec scales to cloud cores around young stellar objects at hundreds of au scales, and they act as tracers of different physical and chemical conditions of the sources. The OMC, therefore, is an ideal laboratory for studying astrochemistry over a broad spectrum of molecular cloud structures and masses. In this review, we discuss the usage of astrochemistry/molecular tracers and (sub) millimeter observations to understand the physical and chemical conditions of large-scale molecular clouds, filaments, and clumps down to cores and protostars in the OMC complex as a demonstration case.

Core Mass Function of a Single Giant Molecular Cloud Complex with ∼10,000 Cores

Abstract Similarity in shape between the initial mass function (IMF) and the core mass functions (CMFs) in star-forming regions prompts the idea that the IMF originates from the CMF through a self-similar core-to-star mass mapping process. To accurately determine the shape of the CMF, we create a sample of 8431 cores with the dust continuum maps of the Cygnus X giant molecular cloud complex, and design a procedure for deriving the CMF considering the mass uncertainty, binning uncertainty, sample incompleteness, and the statistical errors. The resultant CMF coincides well with the IMF for core masses from a few M ⊙ to the highest masses of 1300 M ⊙ with a power-law of dN / dM ∝ M − 2.30 ± 0.04 , but does not present an obvious flattened turnover in the low-mass range as the IMF does. More detailed inspection reveals that the slope of the CMF steepens with increasing mass. Given the numerous high-mass star-forming activities of Cygnus X, this is in stark contrast with the existing top-heavy CMFs found in high-mass star-forming clumps. We also find that the similarity between the IMF and the mass function of cloud structures is not unique at core scales, but can be seen for cloud structures of up to several parsec scales. Finally, our SMA observations toward a subset of the cores do not present evidence for the self-similar mapping. The latter two results indicate that the shape of the IMF may not be directly inherited from the CMF.

Herschel observations of extraordinary sources: Full Herschel/HIFI molecular line survey of Sagittarius B2(M)

Context. We present a full analysis of a broadband spectral line survey of Sagittarius B2 (Main), one of the most chemically rich regions in the Galaxy located within the giant molecular cloud complex Sgr B2 in the central molecular zone. Aims. Our goal is to derive the molecular abundances and temperatures of the high-mass star-forming region Sgr B2(M) and thus its physical and astrochemical conditions. Methods. Sgr B2(M) was observed using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory in a spectral line survey from 480 to 1907 GHz at a spectral resolution of 1.1 MHz, which provides one of the largest spectral coverages ever obtained toward this high-mass star-forming region in the submillimeter with high spectral resolution and includes frequencies >1 THz that are unobservable from the ground. We modeled the molecular emission from the submillimeter to the far-infrared using the XCLASS program, which assumes local thermodynamic equilibrium. For each molecule, a quantitative description was determined taking all emission and absorption features of that species across the entire spectral range into account. Because of the wide frequency coverage, our models are constrained by transitions over an unprecedented range in excitation energy. Additionally, we derived velocity resolved ortho/para ratios for those molecules for which ortho and para resolved molecular parameters are available. Finally, the temperature and velocity distributions are analyzed and the derived abundances are compared with those obtained for Sgr B2(N) from a similar HIFI survey. Results. A total of 92 isotopologues were identified, arising from 49 different molecules, ranging from free ions to complex organic compounds and originating from a variety of environments from the cold envelope to hot and dense gas within the cores. Sulfur dioxide, methanol, and water are the dominant contributors. Vibrationally excited HCN (v2 = 1) and HNC (v2 = 1) are detected as well. For the ortho/para ratios, we find deviations from the high temperature values between 37 and 180%. In total 14% of all lines remain unidentified. Conclusions. Compared to Sgr B2(N), we found less complex molecules such as CH3OCH3, CH3NH2, or NH2CHO, but more simple molecules such as CN, CCH, SO, and SO2. However some sulfur bearing molecules such as H2CS, CS, NS, and OCS are more abundant in N than in M. The derived molecular abundances can be used for comparison to other sources and for providing further constraints for astrochemical models.

Hunting for the elusive methylene radical

Context. The NKaKc = 404−313 transitions of ortho-CH2 between 68 and 71 GHz were first detected toward the Orion-KL and W51 Main star-forming regions. Given their high upper level energies (225 K) above the ground state, they were naturally thought to arise in dense, hot molecular cores near newly formed stars. However, this has not been confirmed by further observations of these lines and their origin has remained unclear. Generally, there is a scarcity of observational data for CH2 and, while it is an important compound in the astrochemical context, its actual occurrence in astronomical sources is poorly constrained. Aims. In this work, we aim to investigate the nature of the elusive CH2 emission, address its association with hot cores, and examine alternative possibilities for its origin. Owing to its importance in carbon chemistry, we also extend the search for CH2 lines by observing an assortment of regions, guided by the hypothesis that the observed CH2 emission is likely to arise from the hot gas environment of photodissociation regions (PDRs). Methods. We carried out our observations first using the Kitt Peak 12 m telescope to verify the original detection of CH2 toward different positions in the central region of the Orion Molecular Cloud 1. These were followed-up by deep integrations using the higher angular resolution of the Onsala 20 m telescope. We also searched for the NKaKc = 212−303 transitions of para-CH2 between 440–445 GHz toward the Orion giant molecular cloud complex using the APEX 12 m telescope. We also obtained auxiliary data for carbon recombination lines with the Effelsberg 100 m telescope and employing archival far infrared data. Results. The present study, along with other recent observations of the Orion region reported here, rule out the possibility of an association with gas that is both hot and dense. We find that the distribution of the CH2 emission closely follows that of the [CII] 158 μm emission, while CH2 is undetected toward the hot core itself. The observations suggest, rather, that its extended emission arises from hot but dilute layers of PDRs and not from the denser parts of such regions as in the case of the Orion Bar. This hypothesis was corroborated by comparisons of the observed CH2 line profiles with those of carbon radio recombination lines (CRRLs), which are well-known PDR tracers. In addition, we report the detection of the 70 GHz fine- and hyperfine structure components of ortho-CH2 toward the W51 E, W51 M, W51 N, W49 N, W43, W75 N, DR21, and S140 star-forming regions, and three of the NKaKc = 404−313 fine- and hyperfine structure transitions between 68–71 GHz toward W3 IRS5. While we have no information on the spatial distribution of CH2 in these regions, aside from that in W51, we again see a correspondence between the profiles of CH2 lines and those of CRRLs. We see a stronger CH2 emission toward the extended HII region W51 M rather than toward the much more massive and denser W51 E and N regions, which strongly supports the origin of CH2 in extended dilute gas. We also report the non-detection of the 212−303 transitions of para-CH2 toward Orion. Furthermore, using a non-LTE radiative transfer analysis, we can constrain the gas temperatures and H2 density to (163 ± 26) K and (3.4 ± 0.3) × 103 cm−3, respectively, for the 68–71 GHz ortho-CH2 transitions toward W3 IRS5, for which we have a data set of the highest quality. This analysis confirms our hypothesis that CH2 originates inwarm and dilute PDR layers. Our analysis suggests that for the excitation conditions under the physical conditions that prevail in such an environment, these lines are masering, with weak level inversion. The resulting amplification of the lines’ spontaneousemission greatly aids in their detection.

FOREST unbiased Galactic plane imaging survey with the Nobeyama 45 m telescope (FUGIN). VI. Dense gas and mini-starbursts in the W 43 giant molecular cloud complex

Abstract We performed new large-scale 12CO, 13CO, and C18O J = 1–0 observations of the W 43 giant molecular cloud complex in the tangential direction of the Scutum arm (l ∼30°) as a part of the FUGIN project. The low-density gas traced by 12CO is distributed over 150 pc × 100 pc (l × b), and has a large velocity dispersion (20–30 km s−1). However, the dense gas traced by C18O is localized in the W 43 Main, G30.5, and W 43 South (G29.96−0.02) high-mass star-forming regions in the W 43 giant molecular cloud (GMC) complex, which have clumpy structures. We found at least two clouds with a velocity difference of ∼10–20 km s−1, both of which are likely to be physically associated with these high-mass star-forming regions based on the results of high 13CO J = 3–2 to J = 1–0 intensity ratio and morphological correspondence with the infrared dust emission. The velocity separation of these clouds in W 43 Main, G30.5, and W 43 South is too large for each cloud to be gravitationally bound. We also revealed that the dense gas in the W 43 GMC has a high local column density, while “the current SFE” (star formation efficiency) of the entire GMC is low ($\sim\!\! 4\%$) compared with the W 51 and M 17 GMC. We argue that the supersonic cloud–cloud collision hypothesis can explain the origin of the local mini-starbursts and dense gas formation in the W 43 GMC complex.

Local Molecular Gas toward the Aquila Rift Region

Abstract We present the results of a ∼250 square degrees CO mapping (+26° ≲ l ≲ +50° and −5° ≲ b ≲ +5°) toward the Aquila Rift region at a spatial resolution of ∼50″ and a grid spacing of 30″. The high dynamic range CO maps with a spectral resolution of ∼0.2 km s−1 display highly structured molecular cloud (MC) morphologies with valuable velocity information, revealing complex spatial and dynamical features of the local molecular gas. In combination with the MWISP CO data and the Gaia DR2, distances of the main MC structures in the local ISM are well determined toward the Aquila Rift region. We find that the total MC mass within 1 kpc is about ≳4.1 × 105 in the whole region. In fact, the mass of the molecular gas is dominated by the W40 giant molecular cloud (GMC) at ∼474 pc (∼1.4 × 105 ) and the GMC complex G036.0+01.0 at ∼560–670 pc (∼2.0 × 105 ), while the MCs at ∼220–260 pc have gas masses of ∼102–103 . Interestingly, an ∼80 pc long filamentary MC G044.0–02.5 at a distance of ∼404 pc shows a systematic velocity gradient along and perpendicular to the major axis of the filament. The H i gas with enhanced emission has similar spatial morphologies and velocity features compared to the corresponding CO structure, indicating that large-scale converging H i flows are probably responsible for the formation of the MC. Meanwhile, the long filamentary MC consists of many sub-filaments with lengths ranging from ∼0.5 pc to several pc, as well as prevalent networks of filaments in other large-scale local MCs.

Cloud fragmentation cascades and feedback: on reconciling an unfettered inertial range with a low star formation rate

ABSTRACT Molecular cloud complexes exhibit both (i) an unfettered Larson-type spectrum over much of their dynamic range, whilst (ii) still producing a much lower star formation rate than were this cascade to remain unfettered all the way down to star-forming scales. Here we explain the compatibility of these attributes with minimalist considerations of a mass-conserving fragmentation cascade, combined with estimates of stellar feedback. Of importance is that the amount of feedback needed to abate fragmentation and truncate the complex decreases with decreasing scale. The scale at which the feedback momentum matches the free-fall momentum marks a transition scale below most of the cascade is truncated and the molecular cloud complex dissipated. For a 106 M⊙ giant molecular cloud (GMC) complex starting with radius of ∼50 pc, the combined feedback from young stellar objects, supernovae, radiation, and stellar winds for a GMC cloud complex can truncate the cascade within an outer free-fall time but only after the cascade reaches parsec scales.

Dense cores and star formation in the giant molecular cloud Vela C

Context. The Vela Molecular Ridge is one of the nearest (700 pc) giant molecular cloud (GMC) complexes hosting intermediate-mass (up to early B, late O stars) star formation, and is located in the outer Galaxy, inside the Galactic plane. Vela C is one of the GMCs making up the Vela Molecular Ridge, and exhibits both sub-regions of robust and sub-regions of more quiescent star formation activity, with both low- and intermediate(high)-mass star formation in progress. Aims. We aim to study the individual and global properties of dense dust cores in Vela C, and aim to search for spatial variations in these properties which could be related to different environmental properties and/or evolutionary stages in the various sub-regions of Vela C. Methods. We mapped the submillimetre (345 GHz) emission from vela C with LABOCA (beam size ~19′′2, spatial resolution ~0.07 pc at 700 pc) at the APEX telescope. We used the clump-finding algorithm CuTEx to identify the compact submillimetre sources. We also used SIMBA (250 GHz) observations, and Herschel and WISE ancillary data. The association with WISE red sources allowed the protostellar and starless cores to be separated, whereas the Herschel dataset allowed the dust temperature to be derived for a fraction of cores. The protostellar and starless core mass functions (CMFs) were constructed following two different approaches, achieving a mass completeness limit of 3.7 M⊙. Results. We retrieved 549 submillimetre cores, 316 of which are starless and mostly gravitationally bound (therefore prestellar in nature). Both the protostellar and the starless CMFs are consistent with the shape of a Salpeter initial mass function in the high-mass part of the distribution. Clustering of cores at scales of 1–6 pc is also found, hinting at fractionation of magnetised, turbulent gas.

The physical and chemical structure of Sagittarius B2

Context.Sagittarius B2 (north) is a chemically rich, high-mass star-forming region located within the giant molecular cloud complex Sgr B2 in the central molecular zone of our Galaxy. Dust continuum emission at 242 GHz, obtained at high angular resolution with the Atacama Large Millimeter Array (ALMA), reveals that it has a filamentary structure on scales of 0.1 pc.Aims.We aim to characterize the filamentary structure of Sgr B2(N) and its kinematic properties using multiple molecular dense gas tracers.Methods.We have used an unbiased, spectral line-survey that covers the frequency range from 211 to 275 GHz and obtained with ALMA (angular resolution of 0.′′4, or 3300 au) to study the small-scale structure of the dense gas in Sgr B2(N). In order to derive the kinematic properties of the gas in a chemically line-rich source like Sgr B2(N), we have developed a python-based tool that stacks all the detected line transitions of any molecular species. This allows us to increase the signal-to-noise ratio (S/N) of our observations and average out line blending effects, which are common in line-rich regions.Results.A filamentary network is visible in Sgr B2(N) in the emission maps of the molecular species CH3OCHO, CH3OCH3, CH3OH and H2CS. In total, eight filaments are found that converge to the central hub (with a mass of 2000M⊙, assuming a temperature of 250 K) and extending for about 0.1 pc (up to 0.5 pc). The spatial structure, together with the presence of the massive central region, suggest that these filaments may be associated with accretion processes, transporting material from the outer regions to the central dense hub. We derive velocity gradients along the filaments of about 20–100 km s−1pc−1, which are 10–100 times larger than those typically found on larger scales (~1 pc) in other star-forming regions. The mass accretion rates of individual filaments are ≾0.05M⊙yr−1, which result in a total accretion rate of 0.16M⊙yr−1. Some filaments harbor dense cores that are likely forming stars and stellar clusters. We determine an empirical relation between the luminosity and stellar mass of the clusters. The stellar content of these dense cores is on the order of 50% of the total mass. The timescales required for the dense cores to collapse and form stars, exhausting their gas content, are compared with the timescale of their accretion process onto the central hub. We conclude that the cores may merge in the center when already forming stellar clusters but still containing a significant amount of gas, resulting in a “damp” merger.Conclusions.The high density and mass of the central region, combined with the presence of converging filaments with high mass, high accretion rates and embedded dense cores already forming stars, suggest that Sgr B2(N) may have the potential to evolve into a super stellar cluster.

Near-IR imaging polarimetry of the RCW 106 cloud complex

AbstractWe have carried out near-IR imaging polarimetry toward RCW 106 with the JHKs-simultaneous imaging polarimeter SIRPOL mounted on the IRSF 1.4m telescope at SAAO, in March and May, 2017 and January, 2018. We have observed 29 fields and covered mostly the southern part of the giant molecular cloud complex associated with the ${{\rm{H}}_\mathbb{I}}$ region RCW 106, which is located at a distance of 3.5 kpc (Moises etal 2011) and is elongated approximately in the north-south direction with a size of ∼70×15 pc. Our preliminary analysis indicates that the magnetic field seems to globally run along the complex elongation, unlike many other elongated clouds that are often reported to have their global elongations perpendicular to the magnetic fields. The RCW 106 complex consists of many small filaments or clumps. Some of such filaments seem to parallel to the magnetic fields, but some others perpendicular. Around the central part of the ${{\rm{H}}_\mathbb{I}}$ region RCW 106, the magnetic field appears to be influenced by the expansion of this ${{\rm{H}}_\mathbb{I}}$ region. Here, we present our preliminary results by comparing with the archival molecular line and far- to mid-IR data.

Molecular Cloud Structures and Massive Star Formation in N159

Abstract The N159 star-forming region is one of the most massive giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC). We show the 12CO, 13CO, CS molecular gas lines observed with ALMA in N159 west (N159W) and N159 east (N159E). We relate the structure of the gas clumps to the properties of 24 massive young stellar objects (YSOs) that include 10 newly identified YSOs based on our search. We use dendrogram analysis to identify properties of the molecular clumps, such as flux, mass, linewidth, size, and virial parameter. We relate the YSO properties to the molecular gas properties. We find that the CS gas clumps have a steeper size–linewidth relation than the 12CO or 13CO gas clumps. This larger slope could potentially occur if the CS gas is tracing shocks. The virial parameters of the 13CO gas clumps in N159W and N159E are low (<1). The threshold for massive star formation in N159W is 501 M ⊙ pc−2, and the threshold for massive star formation in N159E is 794 M ⊙ pc−2. We find that 13CO is more photodissociated in N159E than N159W. The most massive YSO in N159E has cleared out a molecular gas hole in its vicinity. All the massive YSO candidates in N159E have a more evolved spectral energy distribution type in comparison to the YSO candidates in N159W. These differences lead us to conclude that the giant molecular cloud complex in N159E is more evolved than the giant molecular cloud complex in N159W.

Diffuse X-ray sky in the Galactic center

Abstract The Galactic diffuse X-ray emission (GDXE) in the Milky Way Galaxy is spatially and spectrally decomposed into the Galactic center X-ray emission (GCXE), the Galactic ridge X-ray emission (GRXE), and the Galactic bulge X-ray emission (GBXE). The X-ray spectra of the GDXE are characterized by the strong K-shell lines of the highly ionized atoms, and the brightest lines are the K-shell transition (principal quantum number transition of n = 2 → 1) of neutral iron (Fe i-Kα), He-like iron (Fe xxv-Heα), and He-like sulfur (S xv-Heα). Accordingly, the GDXE is composed of a high-temperature plasma of ∼7 keV (HTP) and a low-temperature plasma of ∼1 keV, which emit the Fe xxv-Heα and S xv-Heα lines, respectively. The Fe i-Kα line is emitted from nearly neutral irons, and hence the third component of the GDXE is a cool gas (CG). The Fe i-Kα distribution in the GCXE region is clumpy (Fe i-Kα clump), associated with giant molecular cloud (MC) complexes (Sagittarius A, B, C, D, and E) in the central molecular zone. The origin of the Fe i-Kα clumps is the fluorescence and Thomson scattering from the MCs irradiated by past big flares of the supermassive black hole Sagittarius A*. The scale heights and equivalent widths of the Fe i-Kα, Fe xxv-Heα, and Fe xxvi-Lyα (n = 2 → 1 transition of H-like iron) lines are different among the GCXE, GBXE, and GRXE. Therefore, their structures and origins are separately examined. This paper gives an overview of the research history and the present understandings of the GDXE, while in particular focusing on the origin of the HTP and CG in the GCXE.