Molecular Clouds Research Articles

Turbulent fragmentation as the primary driver of core formation in Polaris Flare and Lupus I

Stars form from dense cores in turbulent molecular clouds. According to the standard scenario of star formation, dense cores are created by cloud fragmentation. However, the physical mechanisms driving this process are still not fully understood from an observational standpoint. Our goal is to investigate the process of cloud fragmentation using observational data from nearby clouds. Specifically, we aim to examine the role of self-gravity and turbulence, both of which are key to the dynamical evolution of clouds. We applied astrodendro to the Herschel H_2 column density maps to identify dense cores and determine their mass and separation in two nearby low-mass clouds: the Polaris Flare and Lupus I clouds. We then compared the observed core masses and separations with predictions from models of gravitational and turbulent fragmentation. In the gravitational fragmentation model, the characteristic length and mass are determined by the Jeans length and Jeans mass. For turbulent fragmentation, the key scales are the cloud’s sonic scale and its corresponding mass. The average core masses are estimated to be 0.242 M_⊙ for Lupus I and 0.276 M_⊙ for the Polaris Flare. The core separations peak at about $2-4 10^4$ au (≈ 0.1 -- 0.2 pc) in both clouds. These separations are significantly smaller than the Jeans length but agree well with the cloud sonic scale. Additionally, the density probability distribution functions of the dense cores follow log-normal distributions, which is consistent with the predictions of turbulent fragmentation. These findings suggest that the primary process driving core formation in the observed low-mass star-forming regions is not gravitational fragmentation but rather turbulent fragmentation. We found no evidence that filament fragmentation plays a significant role in the formation of dense cores.

Shock-induced HCNH+ abundance enhancement in the heart of the starburst galaxy NGC 253 unveiled by ALCHEMI

Understanding the chemistry of molecular clouds is pivotal to elucidate star formation and galaxy evolution. As one of the important molecular ions, HCNH^+ plays an important role in this chemistry. Yet, its behavior and significance under extreme conditions, such as in the central molecular zones (CMZs) of external galaxies, are still largely unexplored. We aim to reveal the physical and chemical properties of the CMZ in the starburst galaxy NGC 253 with multiple HCNH^+ transitions to shed light on the molecule's behavior under the extreme physical conditions of a starburst. We employed molecular line data including results for four rotational transitions of HCNH^+ from the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) large program to investigate underlying physical and chemical processes. Despite weak intensities, HCNH^+ emission is widespread throughout NGC 253's CMZ, which suggests that this molecular ion can effectively trace large-scale structures within molecular clouds. Using the quantum mechanical coupled states' approximation, we computed rate coefficients for collisions of HCNH^+ with para -H_2 and ortho -H_2 at kinetic temperatures up to 500 K. Using these coefficients in a non-local-thermodynamic-equilibrium (non-LTE) modeling framework and employing a Monte Carlo Markov chain analysis, we find that HCNH^+ emission originates from regions with H_2 number densities of ∼ 10^ cm^-3, establishing HCNH^+ as a tracer of low-density environments. Our analysis reveals that most of the HCNH^+ abundances in the CMZ of NGC 253 are higher than all values reported in the Milky Way. We perform static, photodissociation region (PDR), and shock modeling, and found that recurrent shocks could potentially account for the elevated HCNH^+ abundances observed in this CMZ. We propose that the unexpectedly high HCNH^+ abundances may result from chemical enhancement, primarily driven by the elevated gas temperatures and cosmic ray ionization rates of shocked, low-density gas in the nuclear starburst regions of NGC 253.

Isolated Black Holes as Potential PeVatrons and Ultrahigh-energy Gamma-Ray Sources

Abstract The origin of PeV cosmic rays (CRs) is a long-standing mystery, and ultrahigh-energy gamma-ray observations would play a crucial role in identifying it. Recently, LHAASO reported the discovery of “dark” gamma-ray sources that were detected above 100 TeV without any GeV–TeV gamma-ray counterparts. The origins of these dark gamma-ray sources are unknown. We propose isolated black holes (IBHs) wandering in molecular clouds as the origins of PeV CRs and LHAASO dark sources. An IBH accretes surrounding dense gas, which forms a magnetically arrested disk (MAD) around the IBH. Magnetic reconnection in the MAD can accelerate CR protons up to PeV energies. CR protons of GeV–TeV energies fall to the IBH, whereas CR protons at sub-PeV energies can escape from the MAD, providing PeV CRs into the interstellar medium. The sub-PeV CR protons interact with the surrounding molecular clouds, producing TeV–PeV gamma rays without emitting GeV–TeV gamma rays. This scenario can explain the dark sources detected by LHAASO. Taking into account the IBH and molecular cloud distributions in our Galaxy, we demonstrate that IBHs can provide a significant contribution to the PeV CRs observed on Earth. Future gamma-ray detectors in the southern sky and neutrino detectors would provide a concrete test to our scenario.

Correlated Molybdenum, Ruthenium, and Barium Isotope Anomalies in Presolar Silicon Carbide Grains

Abstract We have analyzed molybdenum, ruthenium, and barium isotopes simultaneously in 55 individual presolar silicon carbide (SiC) grains from the Murchison CM2 meteorite using the Chicago Instrument for Laser Ionization (or CHILI). Most grains show clear s-process signatures, which are strongly correlated for molybdenum and ruthenium. For all three elements, we provide estimates for s-process contributions from low-mass AGB stars with unprecedented precision. Variations in s-process production observed for some nuclides reflect a strong dependence on physical properties, neutron density, temperature, and timing, affecting various s-process branch points. Significant contamination can be excluded for a majority of grains. Instead, distributions along mixing lines in three-isotope diagrams reflect mixing between initial parent star material and matter synthesized in the star. The results suggest that the ratios between p- and r-process isotopes of molybdenum, ruthenium, and barium in presolar SiC from many parent stars are the same as the ones inferred for the solar system. This indicates that the products of these processes were well mixed by the time the molecular cloud collapsed to form the stars that eventually grew the SiC grains, and that this mixture did not change between formation of the precursor stars and formation of the Sun.

Galactic Structure Dependence of Cloud–Cloud-collision-driven Star Formation in the Barred Galaxy NGC 3627

Abstract While cloud–cloud collisions (CCCs) have been proposed as a mechanism for triggering massive star formation, it is suggested that higher collision velocities (v col) and lower giant molecular cloud (GMC) mass (M GMC) and/or density (ΣGMC) tend to suppress star formation. In this study, we choose the nearby barred galaxy NGC 3627 to examine the star formation rate and star formation efficiency (SFE) of a colliding GMC ( m CCC ⋆ and ϵ CCC) and explore the connections between m CCC ⋆ and ϵ CCC, M GMC(ΣGMC) and v col, and galactic structures (disk, bar, and bar end). Using Atacama Large Millimeter/submillimeter Array CO (2–1) data (60 pc resolution), we estimated v col within 500 pc apertures, based on line-of-sight GMC velocities, assuming random motion in a two-dimensional plane. We extracted apertures where at least 0.1 collisions occur per 1 Myr, identifying them as regions dominated by CCC-driven star formation, and then calculated m CCC ⋆ and ϵ CCC using attenuation-corrected Hα data from MUSE on the Very Large Telescope. We found that both m CCC ⋆ and ϵ CCC are lower in the bar (median values: 103.84 M ⊙ and 0.18%) and higher in the bar end (104.89 M ⊙ and 1.10%) compared to the disk (104.28 M ⊙ and 0.75%). Furthermore, we found that structural differences within the parameter space of v col and M GMC(ΣGMC), with higher M GMC(ΣGMC) in the bar end and higher v col in the bar compared to the disk, lead to higher star formation activity in the bar end and lower activity in the bar. Our results support the scenario in which variations in CCC properties across different galactic structures can explain the observed differences in SFE on a kiloparsec scale within a disk galaxy.

The Evolution of Molecular Clouds: Turbulence-regulated Global Radial Collapse

Abstract The star formation efficiency (SFE) measures the proportion of molecular gas converted into stars, while the star formation rate (SFR) indicates the rate at which gas is transformed into stars. Here we propose such a model in the framework of a turbulence-regulated global radial collapse in molecular clouds being in quasi-virial equilibrium, where the collapse velocity depends on the density profile and the initial mass-to-radius ratio of molecular clouds, with the collapse velocity accelerating during the collapse process. This simplified analytical model allows us to estimate a lifetime of giant molecular clouds of approximately 0.44−7.36 × 107 yr, and a star formation timescale of approximately 0.5–5.88 × 106 yr. Additionally, we can predict an SFE of approximately 1.59%, and an SFR of roughly 1.85 M ⊙ yr−1 for the Milky Way in agreement with observations.

Erosion of a dense molecular core by a strong outflow from a massive protostar

Molecular outflows from massive protostars can impact the interstellar medium in different ways, adding turbulence on different spatial scales, dragging material at supersonic velocities, producing shocks and heating, and physically impinging onto dense structures that may be harboring other protostars. We aim to quantify the impact of the outflow associated with the high-mass protostar GGD 27-MM2(E) on its parent envelope and how this outflow affects its environment. We present Atacama Large Millimeter/submillimeter Array Band 3 observations of N_2H^+ (1-0) and CH_3CN (5-4), as well as Band 7 observations of the H_2CO molecular line emissions from the protostellar system GGD 27-MM2(E). Through position--velocity diagrams along and across the outflow axis, we studied the kinematics and structure of the outflow. We also fit extracted spectra of the CH_3CN emission to obtain the physical conditions of the gas. We use the results to discuss the impact of the outflow on its surroundings. We find that N_2H^+ emission traces a dense molecular cloud surrounding GGD 27-MM2(E). We estimate that the mass of this cloud is ∼13.3--26.5 The molecular cloud contains an internal cavity aligned with the H_2CO-traced molecular outflow. The outflow, also traced by CN, shows evidence of a collision with a molecular core (MC), as indicated by the distinctive increases in the distinct physical properties of the gas such as the excitation temperature, column density, line width, and velocity. This collision results in an X-shaped structure in the northern part of the outflow around the position of the MC, which produces spray-shocked material downstream in the north of MC, as observed in position--velocity diagrams both along and across the outflow axis. The outflow has a mass of 1.7--2.1 a momentum of 7.8--10.1 a kinetic energy of 5.0--6.6times erg, and a mass-loss rate of 4.9--6.0 The molecular outflow from GGD 27-MM2(E) significantly perturbs and erodes its parent cloud, compressing the gas of sources such as the MC and ALMA 12. The feedback from this powerful protostellar outflow helps maintain the turbulence in the surrounding area.

Less-Dominant Resonance Configuration of Propargyl Radical Leads to a Growth Mechanism for Polycyclic Aromatic Hydrocarbons that Preserves the Cyclopenta Ring.

Understanding the growth of polycyclic aromatic hydrocarbons (PAHs) is essential for combustion, astrochemistry, and carbon-based nanomaterial synthesis. This study presents theory-guided experiments on radical-radical combination reactions of propargyl (•C3H3). The addition of •C3H3 to three cyclopenta-fused PAH radicals─1-indenyl (•1-C9H7), acenaphthenyl (•C12H9), and 4H-cyclopenta[def]phenanthrenyl (•C15H9)─revealed that the reaction between the dominant propyne-3-yl resonance configuration of •C3H3 and the three radicals consistently produces PAHs with all hexagonal rings, while the reaction between the less dominant allene-1-yl resonance configuration of •C3H3 and the three radicals selectively preserves the cyclopenta ring and forms a new hexagonal ring. Elusive intermediates and isomeric products were observed and identified by combining molecular beam-sampling synchrotron photoionization mass spectrometry with gas chromatography-mass spectrometry. The complementary results suggest a high selectivity of the allene-1-yl addition pathway, which is thermodynamically controlled. The findings presented here are based on a combination of experimental capabilities, and they provide new mechanisms and insights into the selective formation of bowl-shaped PAHs, serving as templates for fullerene and nanotube structures. The high selectivity of the allene-1-yl pathway provides a rational synthetic strategy for cyclopenta-fused PAHs, bearing barrierless and facile radical-radical reaction pathways in various environments, including high-temperature combustion, circumstellar envelopes, and cold molecular clouds.

Modelling methanol and hydride formation in the JWST Ice Age era

Recent JWST observations have measured the ice chemical composition towards two highly extinguished background stars, NIR38 and J110621, in the Chamaeleon I molecular cloud. The observed excess of extinction on the long-wavelength side of the H_2O ice band at 3$,$μm has been attributed to a mixture of CH_3OH with ammonia hydrates (NH_3⋅H_2O), which suggests that CH_3OH ice in this cloud could have formed in a water-rich environment with little CO depletion. Laboratory experiments and quantum chemical calculations suggest that CH_3OH could form via the grain surface reactions CH_3 + OH and/or C + H_2O in water-rich ices. However, no dedicated chemical modelling has been carried out thus far to test their efficiency. In addition, it remains unexplored how the efficiencies of the proposed mechanisms depend on the astrochemical code employed. We modelled the ice chemistry in the Chamaeleon I cloud to establish the dominant formation processes of CH_3OH, CO, CO_2, and of the hydrides CH_4 and NH_3 (in addition to H_2O). By using a set of state-of-the-art astrochemical codes (MAGICKAL, MONACO, Nautilus Uclchem and KMC simulations), we can test the effects of the different code architectures (rate equation vs. stochastic codes) and of the assumed ice chemistry (diffusive vs. non-diffusive). We consider a grid of models with different gas densities, dust temperatures, visual extinctions, and cloud-collapse length scales. In addition to the successive hydrogenation of CO, the codes' chemical networks have been augmented to include the alternative processes for CH_3OH ice formation in water-rich environments (i.e. the reactions CH_3 + OH → CH_3OH and C + H_2O → H_2CO). Our models show that the JWST ice observations are better reproduced for gas densities ≥10^5 cm^-3 and collapse timescales ≥10^5 yr. CH_3OH ice formation occurs predominantly ($>$99%) via CO hydrogenation. The contribution of reactions CH_3 + OH and C + H_2O is negligible. The CO_2 ice may form either via CO + OH or CO + O depending on the code. However, KMC simulations reveal that both mechanisms are efficient despite the low rate of the CO + O surface reaction. CH_4 is largely underproduced for all codes except for Uclchem for which a higher amount of atomic C is available during the translucent cloud phase of the models. Large differences in the predicted abundances are found at very low dust temperatures (T_ dust$<$12 K) between diffusive and non-diffusive chemistry codes. This is due to the fact that non-diffusive chemistry takes over diffusive chemistry at such low T_ dust. This could explain the rather constant ice chemical composition found in Chamaeleon I and other dense cores despite the different visual extinctions probed.

B-fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). III. Grain Alignment and Disruption Mechanisms in G34.43+0.24 Using Polarization Observations from JCMT/POL-2

<i>B</i>-fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). III. Grain Alignment and Disruption Mechanisms in G34.43+0.24 Using Polarization Observations from JCMT/POL-2

A new apparatus for gas-phase low temperature kinetics study: Kinetics measurement and product detection of the CH + propene reaction at 23 K.

We have developed a novel instrument to study reaction kinetics of astrochemical interest at low temperatures. This setup integrates laser-induced fluorescence (LIF) and vacuum ultraviolet (VUV) photoionization reflectron time-of-flight mass spectrometry (ReTOFMS) with a supersonic uniform low-temperature flow. A pulsed helium Laval nozzle with a Mach number of 6 was employed, achieving a temperature of 23 ± 3K and a density of (2.0 ± 0.4) × 1016moleculecm-3. The second-order rate coefficient for the reaction between the methylidyne radical (CH) and propene (C3H6) at 23(3) K was determined to be (3.4 ± 0.6) × 10-10cm3molecule-1s-1 using LIF kinetics measurements. VUV (118.27nm) photoionization ReTOFMS detected a dominant product channel, CH + C3H6 → C4H6 + H, without isomer identification. Another less intense mass peak at m/z 53 was also observed, which could either result from the dissociative ionization of the energized C4H6 primary products or indicate another product channel, C4H5 + H2. Given the presence of CH and C3H6 in cold molecular clouds (e.g., TMC-1, Lupus-1a, L1495B, L1521F, and Serpens South 1a), it is predicted that these products can exist in low-temperature interstellar environments.

Understanding Local Conformation in Cyclic and Linear Polymers Using Molecular Dynamics and Point Cloud Neural Network

Understanding Local Conformation in Cyclic and Linear Polymers Using Molecular Dynamics and Point Cloud Neural Network

Abundant water from primordial supernovae at cosmic dawn

Abstract Primordial (or population III) supernovae were the first nucleosynthetic engines in the Universe, and they forged the heavy elements required for the later formation of planets and life. Water, in particular, is thought to be crucial to the cosmic origins of life as we understand it, and recent models have shown that water can form in low-metallicity gas like that present at high redshifts. Here we present numerical simulations that show that the first water in the Universe formed in population III core-collapse and pair-instability supernovae at redshifts z ≈ 20. The primary sites of water production in these remnants are dense molecular cloud cores, which in some cases were enriched with primordial water to mass fractions that were only a factor of a few below those in the Solar System today. These dense, dusty cores are also probable candidates for protoplanetary disk formation. Besides revealing that a primary ingredient for life was already in place in the Universe 100–200 Myr after the Big Bang, our simulations show that water was probably a key constituent of the first galaxies.

Investigating ultraviolet and infrared radiation through the turbulent life of molecular clouds

Context. Molecular clouds (MCs) are the places where stars are formed and their feedback starts to take place, regulating the evolution of galaxies. Therefore, MCs represent the critical scale at which to study how ultraviolet (UV) photons emitted by young stars are reprocessed in the far-infrared (FIR) by interaction with dust grains, thereby determining the multiwavelength continuum emission of galaxies. Aims. Our goal is to analyze the UV and IR emission of a MC at different stages of its evolution and relate its absorption and emission properties with its morphology and star formation rate. Such a study is fundamental to determining how the properties of MCs shape the emission from entire galaxies. Methods. We considered a radiation-hydrodynamic simulation of a MC with self-consistent chemistry treatment. The MC has a mass of MMC = 105 M⊙, is resolved down to a scale of 0.06 pc, and evolves for ≃2.4 Myr after the onset of star formation. We post-processed the simulation via Monte Carlo radiative transfer calculations to compute the detailed UV-to-FIR emission of the MC. Such results were compared with data from physically motivated analytical models, other simulations, and observations. Results. We find that the simulated MC is globally UV-optically thick, but optically thin channels allow for photon escape (0.1–10%), a feature that is not well captured in analytical models. The dust temperature spans a wide range (Tdust ∼ 20–300 K) depending on the dust-to-stellar geometry, which is reproduced reasonably well by analytical models. However, the complexity of the dust temperature distribution is not captured in the analytical models, as is evidenced by the 10 K (20 K) difference in the mass (luminosity) average temperature. Indeed, the total IR luminosity is the same in all the models, but the IR emission peaks at shorter wavelengths in the analytical ones. Compared to a sample of Galactic clouds and other simulations, our spectral energy distribution (SED) is consistent with mid-IR data, but peaks at shorter wavelengths in the IR. This is due to a lack of cold dust, as a consequence of the high gas – and thus dust – consumption in our simulated MC. The attenuation properties of our MC change significantly with time, evolving from a Milky-Way-like relation to a flatter, featureless one. On the IRX-β plane, the MC position strongly depends on the observing direction and on its evolutionary stage. When the MC starts to disperse, the cloud settles at log(IRX) ∼ 1 and β ∼ −0.5, slightly below most of the local empirical relations. Conclusions. This work represents an important test for MC simulations and a first step toward the implementation of a physically informed, sub-grid model in large-scale numerical simulations to describe the emission from unresolved MC scales and its impact on the global galaxy SED.

Projection-angle effects when “observing” a turbulent magnetized collapsing molecular cloud

Context. Most of our knowledge regarding molecular clouds and the early stages of star formation stems from molecular spectral-line observations. However, the various chemical and radiative-transfer effects, in combination with projection effects, can lead to a distorted view of molecular clouds and complicate the interpretation of observations. Aims. Our objective is to simultaneously study all of these effects by creating synthetic spectral-line observations based on chemo- dynamical simulations of a collapsing molecular cloud. Methods. We performed a three-dimensional ideal magnetohydrodynamic simulation of a supercritical turbulent collapsing molecular cloud where the dynamical evolution was coupled to a nonequilibrium gas-grain chemical network consisting of 115 species, the evolution of which was governed by &gt;1600 chemical reactions. We post-processed this simulation with a multilevel nonlocal thermodynamic equilibrium radiative-transfer code to produce synthetic position-position-velocity data cubes of the CO, HCO+, HCN, and N2H+ (J = 1 → 0) transitions under various projection angles with respect to the mean component of the magnetic field. Synthetic polarization maps are presented in a companion paper. Results. We find that the chemical abundances of various species in our simulated cloud tend to be over-predicted in comparison to observationally derived abundances and attribute this discrepancy to the fact that the cloud collapses rapidly and therefore the various species do not have enough time to deplete onto dust grains. This suggests that our initial conditions may not correspond to the initial conditions of real molecular clouds and cores. We show that the projection angle has a notable effect on the moment maps of the species for which we produced synthetic observations. Specifically, the integrated emission and velocity dispersion of CO, HCO+ and HCN are higher when the cloud is observed “face on” compared to “edge on,” whereas column density maps exhibit an opposite trend. Finally, we show that only N2H+ is an accurate tracer of the column density of the cloud across all projection angles studied.

Formation of free-floating planetary mass objects via circumstellar disk encounters.

The origin of planetary mass objects (PMOs) wandering in young star clusters remains enigmatic, especially when they come in pairs. They could represent the lowest-mass object formed via molecular cloud collapse or high-mass planets ejected from their host stars. However, neither theory fully accounts for their abundance and multiplicity. Here, we show via hydrodynamic simulations that free-floating PMOs have a unique formation channel via the fragmentation of tidal bridges between encountering circumstellar disks. This process can be highly productive in dense clusters like Trapezium forming metal-poor PMOs with disks. Free-floating multiple PMOs also naturally emerge when neighboring PMOs are caught by their mutual gravity. PMOs may thus form a distinct population that is fundamentally different from stars and planets.

Survey of Orion Disks with ALMA (SODA). III: Disks in wide binary systems in L1641 and L1647

Observations of protoplanetary disks within multiple systems in nearby star-forming regions (SFRs) have shown that the presence of a neighboring object influences the evolution of dust in disks. However, the size of the available sample and the separation range covered are insufficient to fully understand the dust evolution in binary systems. The goal of this work, based on the Survey of Orion Disks with ALMA (SODA), is to comprehensively characterize the impact of stellar multiplicity on Class II disks in the L1641 and L1647 regions of Orion A (∼ 1-3 Myr). We characterized the protostellar multiplicity using the Atacama Large Millimeter/submillimeter Array (ALMA), the ESO-VISTA, and the Hubble Space Telescope. The resulting sample of 65 multiple systems is the largest catalog of wide binary systems to date (projected separation ≥ 1000 AU) and enables a more robust statistical characterization of the evolution and properties of protoplanetary disks. The disk population was observed in the continuum with ALMA at 225 GHz, with a median rms of 1.5 M_⊕. We combined these data (resolution of ∼1.1^'') with the ESO-VISTA near-infrared survey of the Orion A cloud (resolution of ∼0.7^''). From this dataset, multiple-star systems were selected using an iterative inside-out search in projected separation (≥1000 AU). We identify 61 binary systems, 3 triple systems, and 1 quadruple system. The separation range is between 1000 and 10^4 AU. The dust mass distributions inferred via the Kaplan-Meier estimator yield a median mass of 3.23^ M_⊕ for primary disks and 3.88^ M_⊕ for secondary disks. Combining our data with those available for the Lupus and Taurus disks, we identify a threshold separation of about 130 AU, beyond which the previously observed positive correlation between millimeter flux (and hence dust mass) and projected separation is lost. Recent theoretical models confirm that pre- and post-threshold systems are the result of different star formation processes, such as the fragmentation of gravitationally unstable circumstellar disks, the thermal fragmentation of infalling cores, or the turbulent fragmentation of molecular clouds. We can rule out the dependence on different SFRs: the cumulative mass distributions of multiples in SFRs of similar ages are statistically indistinguishable. This result strengthens the hypothesis that there is a universal initial mass distribution for disks.

Giant Molecular Clouds in RCW 106 (G333): Galactic Mini-starbursts and Massive Star Formation Induced by Supersonic Cloud–Cloud Collisions

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.

Large Molecular and Dust Reservoir of a Gravitationally Lensed Submillimeter Galaxy behind the Lupus I Molecular Cloud

Large Molecular and Dust Reservoir of a Gravitationally Lensed Submillimeter Galaxy behind the Lupus I Molecular Cloud

The GeV γ-Ray Emission from the Composite Supernova Remnant CTB 87

Abstract We report the GeV γ-ray emission around the composite supernova remnant (SNR) CTB 87 with more than 16 yr of PASS 8 data recorded by the Fermi Large Area Telescope. Two separate point sources with different GeV spectra are identified in this region: one has a soft γ-ray spectrum, likely due to interactions between the SNR shock and molecular clouds, and another source with a hard GeV γ-ray spectrum aligns with the TeV spectrum of VER J2016+371, suggesting it as the GeV counterpart. Considering the observations of CTB 87 in the radio and X-ray bands, VER J2016+371 is proposed to originate from the pulsar wind nebula (PWN) associated with PSR J2016+3711. A leptonic model with a broken power-law electron distribution could explain the multiwavelength data of VER J2016+371, with fitted parameters matching typical γ-ray PWNe. Deeper searching for the SNR shock of CTB 87 in other bands and the future TeV observations by LHAASO and Cherenkov Telescope Array are crucial to reveal the nature of CTB 87.