Massive Clumps Research Articles

Probing the initial conditions of high-mass star formation

Context. Fragmentation and feedback are two important processes during the early phases of star formation. Aims. Massive clumps tend to fragment into clusters of cores and condensations, some of which form high-mass stars. In this work, we study the structure of massive clumps at different scales, analyze the fragmentation process, and investigate the possibility that star formation is triggered by nearby H ii regions. Methods. We present a high angular resolution study of a sample of massive proto-cluster clumps G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71. Combining infrared data at 4.5, 8.0, 24, and 70 μm, we use a few arcsecond resolution, radiometer and millimeter inteferometric data taken at 1.3 cm, 3.5 mm, 1.3 mm, and 870 μm to study their fragmentation and evolution. Our sample is unique in the sense that all the clumps have neighboring H ii regions. Taking advantage of that, we tested triggered star formation using a novel method where we study the alignment of the center of mass traced by dust emission at multiple scales. Results. The eight massive clumps, identified based on single-dish observations, have masses ranging from 228 to 2279 M⊙ within an effective radius of Reff ~ 0.5 pc. We detect compact structures towards six out of the eight clumps. The brightest compact structures within infrared bright clumps are typically associated with embedded compact radio continuum sources. The smaller scale structures of Reff ~ 0.02 pc observed within each clump are mostly gravitationally bound and massive enough to form at least a B3-B0 type star. Many condensations have masses larger than 8 M⊙ at a small scale of Reff ~ 0.02 pc. We find that the two infrared quiet clumps with the lowest mass and lowest surface density with <300 M⊙ do not host any compact sources, calling into question their ability to form high-mass stars. Although the clumps are mostly infrared quiet, the dynamical movements are active at clump scale (~1 pc). Conclusions. We studied the spatial distribution of the gas conditions detected at different scales. For some sources we find hints of external triggering, whereas for others we find no significant pattern that indicates triggering is dynamically unimportant. This probably indicates that the different clumps go through different evolutionary paths. In this respect, studies with larger samples are highly desired.

Spatial Variation of the Chemical Properties of Massive Star-forming Clumps

Abstract We selected 90 massive star-forming clumps with strong N2H+(1−0), HCO+(1−0), HCN(1−0), and HNC(1−0) emission from the Millimetre Astronomy Legacy Team 90 GHz survey. We obtained Herschel data for all 90 sources and NRAO VLA Sky Survey data for 51 of them. We convolved and regridded all images to the same resolution and pixel size and derived the temperature, H2 column density, molecules’ abundances and abundance, and ratios of each pixel. Our analysis yields three main conclusions. First, the abundances of N2H+, HCO+, HCN, and HNC increase when the column density decreases and the temperature increases, with spatial variations in their abundances dominated by changes in the H2 column density. Second, the abundance ratios between N2H+, HCO+, HCN, and HNC also display systemic variations as a function of the column density due to the chemical properties of these molecules. Third, the sources associated with the 20 cm continuum emission can be classified into four types based on the behavior of the abundances of the four molecules considered here as a function of this emission. The variations of the first three types could also be attributed to the variation of the H2 column density.

Massive dust clumps in the envelope of the red supergiant VY Canis Majoris

The envelope of the red supergiant VY CMa has long been considered an extreme example of episodic mass loss that is possibly taking place in other cool and massive evolved stars. Recent (sub-)millimeter observations of the envelope revealed the presence of massive dusty clumps within 800 mas of the star and reinforce the picture of drastic mass-loss phenomena in VY CMa. We present new ALMA observations at an angular resolution of 0.1″ and at an unprecedented sensitivity that reveal further details about the dusty clumps. We resolve more discrete features and identify a submillimeter counterpart of a more distant Southwest (SW) Clump known from visual observations. The brightest clump, named C, is marginally resolved in the observations. Gas seen against the resolved continuum emission of clump C produces a molecular spectrum in absorption, in lines of mainly sulfur-bearing species. Except for SW Clump, no molecular emission is found to be associated with the dusty clumps and we propose that the dusty structures have an atypically low gas content. We attempt to reproduce the properties of the dusty clumps through 3D radiative transfer modeling. Although a clump configuration explaining the observations is found, it is not unique. A very high optical depth of all clumps to the stellar radiation makes the modeling very challenging, and requires an unrealistically high dust mass for one of the clumps. We suggest that the dusty features have substructures (e.g., porosity) that allow deeper penetration of stellar photons within the clumps than in a homogeneous configuration. A comparison of the estimated clump ages to variations in the stellar visual flux for over a century suggests that the mechanism responsible for their formation is not uniquely manifested by enhanced or strongly diminished visual light. The study demonstrates that the dusty mass-loss episodes of VY CMa are indeed unparalleled among all known non-explosive stars. The origin of these episodes remains an unsolved problem.

The effects of ionization feedback on star formation: a case study of the M 16 H II region

Aims. We aim to investigate the impact of the ionized radiation from the M 16 H II region on the surrounding molecular cloud and on its hosted star formation. Methods. To present comprehensive multi-wavelength observations towards the M 16 H II region, we used new CO data and existing infrared, optical, and submillimeter data. The 12CO J = 1−0, 13CO J = 1−0, and C18O J = 1−0 data were obtained with the Purple Mountain Observatory (PMO) 13.7 m radio telescope. To trace massive clumps and extract young stellar objects (YSOs) associated with the M 16 H II region, we used the ATLASGAL and GLIMPSE I catalogs, respectively. Results. From CO data, we discern a large-scale filament with three velocity components. Because these three components overlap with each other in both velocity and space, the filament may be made of three layers. The M 16 ionized gas interacts with the large-scale filament and has reshaped its structure. In the large-scale filament, we find 51 compact cores from the ATLASGAL catalog, 20 of them being quiescent. The mean excitation temperature of these cores is 22.5 K, while this is 22.2 K for the quiescent cores. This high temperature observed for the quiescent cores suggests that the cores may be heated by M 16 and do not experience internal heating from sources in the cores. Through the relationship between the mass and radius of these cores, we obtain that 45% of all the cores are massive enough to potentially form massive stars. Compared with the thermal motion, the turbulence created by the nonthermal motion is responsible for the core formation. For the pillars observed towards M 16, the H II region may give rise to the strong turbulence.

The possible hierarchical scales of observed clumps in high-redshift disc galaxies

ABSTRACTGiant clumps on ∼kpc scales and with masses of $10^8\rm {-}10^9 \, \mathrm{M_{\odot }}$ are ubiquitous in observed high-redshift disc galaxies. Recent simulations and observations with high spatial resolution indicate the existence of substructure within these clumps. We perform high-resolution simulations of a massive galaxy to study the substructure formation within the framework of gravitational disc instability. We focus on an isolated and pure gas disc with an isothermal equation of state with T = 104 K that allows capturing the effects of self-gravity and hydrodynamics robustly. The main mass of the galaxy resides in rotationally supported clumps which grow by merging to a maximum clump mass of $10^8 \, \mathrm{M_{\odot }}$ with diameter ∼120 pc for the dense gas. They group to clump clusters (CCs) within relatively short times ($\ll 50 \, \mathrm{Myr}$), which are present over the whole simulation time. We identify several mass and size scales on which the clusters appear as single objects at the corresponding observational resolution between ${\sim } 10^8 \,\rm{and}\, 10^9 \, \mathrm{M_{\odot }}$. Most of the clusters emerge as dense groups and for larger beams they are more likely to be open structures represented by a single object. In the high-resolution runs higher densities can be reached, and the initial structures can collapse further and fragment to many clumps smaller than the initial Toomre length. In our low-resolution runs, the clumps directly form on larger scales 0.3–1 kpc with $10^8\rm {-}10^9 \, \mathrm{M_{\odot }}$. Here, the artificial pressure floor which is typically used to prevent spurious fragmentation strongly influences the initial formation of clumps and their properties at very low densities.

ALMA Observations of a Massive and Dense Cold Clump: G305.137+0.069

Abstract We report observations, made with the Atacama Large Millimeter/submillimeter Array, of 3 mm dust continuum emission and molecular line emission in HCO+, CS, and N2H+, toward G305.137+0.069, a massive, dense, and cold clump, in order to characterize its small-scale (∼2000 au) structure. The dust continuum observations reveal the presence of twelve compact structures (cores) with masses ranging from 3.3 to 50.6 M ⊙, radii from 1800 to 5300 au, and densities from 3.1 × 106 to 3.1 × 107 cm−3. The line observations show that the molecular emission arises from a bright central region, with an angular size of ∼12″, and an extended, weaker envelope best seen in the HCO+ line. The N2H+ emission is best correlated with the continuum emission and hence with the cores. For cores with single line profiles, the line widths range from 1.9 to 3.1 km s−1 with an average value of 2.6 km s−1, indicating that they are dominated by nonthermal motions, either due to random turbulence or core-scale motions. The virial parameter of the three most massive cores are smaller than one, suggesting that they are undergoing collapse. We find that in the regime of masses probed by our observations (M > 3 M ⊙) the shape of the core-mass function is notably different from the initial mass function, showing an overpopulation of high-mass cores. We suggest that the formation and mass distribution of the dense cores within G305.137+0.069 can be explained as the result of hierarchical or turbulent fragmentation in a gravitationally collapsing clump.

Photoevaporation of Jeans-unstable molecular clumps

We study the photoevaporation of Jeans-unstable molecular clumps by isotropic FUV (6 eV $< {\rm h}\nu$ < 13.6 eV) radiation, through 3D radiative transfer hydrodynamical simulations implementing a non-equilibrium chemical network that includes the formation and dissociation of H$_2$. We run a set of simulations considering different clump masses ($M=10-200$ M$_\odot$) and impinging fluxes ($G_0=2\times 10^3-8\times 10^4$ in Habing units). In the initial phase, the radiation sweeps the clump as an R-type dissociation front, reducing the H$_2$ mass by a factor 40-90%. Then, a weak ($\mathcal{M}\simeq 2$) shock develops and travels towards the centre of the clump, which collapses while loosing mass from its surface. All considered clumps remain gravitationally unstable even if radiation rips off most of the clump mass, showing that external FUV radiation is not able to stop clump collapse. However, the FUV intensity regulates the final H$_2$ mass available for star formation: for example, for $G_0 < 10^4$ more than 10% of the initial clump mass survives. Finally, for massive clumps ($\sim 100$ M$_\odot$) the H$_2$ mass increases by 25-50% during the collapse, mostly because of the rapid density growth that implies a more efficient H$_2$ self-shielding.

DYNAMO: An upclose view of turbulent, clumpy galaxies

AbstractOver 2/3 of all star formation in the Universe occurs in gas-rich, super-high pressure clumpy galaxies in the epoch of redshift z ∼ 1 – 3. However, because these galaxies are so distant we are limited in the information available to study the properties of star formation and gas in these systems. I will present results using a sample of extremely rare, nearby galaxies (called DYNAMO) that are very well matched in gas fraction (fgas ∼ 20 – 80%), kinematics (rotating disks with velocity dispersions ranging 20 – 100 km/s), structure (exponential disks) and morphology (clumpy star formation) to high-z main-sequence galaxies. We therefore use DYNAMO galaxies as laboratories to study the processes inside galaxies in the dominate mode of star formation in the Universe. In this talk I will report on results from our programs with HST, ALMA, Keck, and NOEMA for DYNAMO galaxies that are aimed at testing models of star formation. We have discovered of an inverse relationship between gas velocity dispersion and molecular gas depletion time. This correlation is directly predicted by theories of feedback-regulated star formation; conversely, predictions of models in which turbulence is driven by gravity only are not consistent with our data. I will also show that feedback-regulated star formation can explain the redshift evolution of galaxy star formation efficiency. I will also present results from a recently acquired map of CO(2-1) in a clumpy galaxy with resolution less than 200 pc. With maps such as these we can begin to study these super giant star forming clumps at scales that are more comparable to local surveys. I will show results for the star formation efficiency of clumps, the boundedness of clumps of molecular gas, and discuss links between star formation efficiency and formation of clumps of stellar mass. The details of clumpy systems are a direct constraint of the results of simulations, especially on the nature of feedback in the high density environments of star formation that dominate the early Universe.

Molecular clouds in a Milky Way progenitor at z = 1

AbstractThanks to the remarkable ALMA capabilities and the unique configuration of the Cosmic Snake galaxy behind a massive galaxy cluster, we could resolve molecular clouds down to 30 pc linear physical scales in a typical Milky Way progenitor at z = 1.036, through CO(4–3) observations performed at the ∼ 0.2″ angular resolution. We identified 17 individual giant molecular clouds. These high-redshift molecular clouds are clearly different from their local analogues, with 10–100 times higher masses, densities, and internal turbulence. They are offset from the Larson scaling relations. We argue that the molecular cloud physical properties are dependent on the ambient interstellar conditions particular to the host galaxy. We find these high-redshift clouds in virial equilibrium, and derive, for the first time, the CO-to-H2 conversion factor from the kinematics of independent molecular clouds at z = 1. The measured large clouds gas masses demonstrate the existence of parent gas clouds with masses high enough to allow the in-situ formation of similarly massive stellar clumps seen in the Cosmic Snake galaxy in comparable numbers. Our results support the formation of molecular clouds by fragmentation of turbulent galactic gas disks, which then become the stellar clumps observed in distant galaxies.

A Tale of Two Clump Masses: A new way to study clump formation in simulations

We present a new method to study the characteristic scales of collapse and fragmentation in galactic disks. Clump formation is seeded in simulations via controlled perturbations with a specified wavelength and velocity. These are applied to otherwise quiet gas disks ranging from analogues of present day spirals to gas-rich, high-redshift galaxies. The results are compared to linear theory, turbulently perturbed disks and observations. The results reflect the expectations of linear, non-axisymmetric theory with a finite window for growth into a bound clump. We identify two new modes of clump formation: rotation-driven fission and fragmentation of tidal tails, though both are expected to rarely contribute to clump formation in observed disks. We find that bound clumps are generally much smaller than the so-called Toomre mass. The preferred scale for fragmentation increases with the disk gas mass but cannot produce bound objects larger than $\sim10^9$ M$_{\odot}$. The most likely bound clump mass increases from $3\times10^6$ in low mass disks up to $5\times10^8$ M$_{\odot}$. We conclude that observed massive stellar and gaseous clumps on 1 kpc scales at high redshift are most likely aggregates of many initially distinct bound clumps.

Magnetic Stability of Massive Star-forming Clumps in RCW 106

Abstract The RCW 106 molecular cloud complex is an active massive star-forming region where a ministarburst is taking place. We examined its magnetic structure by near-IR polarimetric observations with the imaging polarimeter SIRPOL on the IRSF 1.4 m telescope. The global magnetic field is nearly parallel to the direction of the Galactic plane and the cloud elongation. We derived the magnetic field strength of ∼100–1600 μG for 71 clumps with the Davis–Chandrasekhar–Fermi method. We also evaluated the magnetic stability of these clumps and found that massive star-forming clumps tend to be magnetically unstable and gravitationally unstable. Therefore, we propose a new criterion to search for massive star-forming clumps. These details suggest that the process enhancing the clump density without an increase of the magnetic flux is essential for the formation of massive stars and the necessity for accreting mass along the magnetic field lines.

Evolution of young protoclusters embedded in dense massive clumps. A new grid of population synthesis SED models and a new set of L/M evolutionary tracks

A grid of 20 millions 3-1100$\mu$m SED models is presented for synthetic young clusters embedded in dense clumps. The models depend on four primary parameters: the clump mass M$_{clump}$ and dust temperature T$_{dust}$, the fraction of mass f$_{core}$ locked in dense cores, and the age of the clump t$_{SF}$. We populate the YSO clusters using the IMF from Kroupa(2001) and the YSOs SED models grid of Robitaille et al. (2006). We conduct extensive testing of SED fitting using a simulated dataset and we find that M$_{clump}$ essentially depends on the submillimeter portion of the SED, while T$_{dust}$ is mostly determined from the shape of the SED in the 70-350$\mu$m range. Thanks to the large number of models computed we verify that the combined analysis of L/M, [8-24] and [24-70] colours removes much of the SEDs f$_{core}$-t$_{SF}$ degeneracy. The L/M values are particularly useful to diagnose f$_{core}$. L/M$\leq$1 identifies protoclusters with f$_{core}\leq$0.1 and t$_{SF} \leq 10^5$ years, while L/M$\geq$10 excludes f$_{core}\leq$0.1. We characterize lower limits of L/M where ZAMS stars are not found in models, and we also find models with L/M $\geq$10 and no ZAMS stars, in which [8-24]$\geq0.8\pm 0.1$ independently from M$_{clump}$, temperature and luminosity. This is the first set of synthesis SED models suited to model for embedded and unresolved clusters of YSOs. A set of new evolutionary tracks in the L/M diagram is also presented.

Numerical Analysis of a Catenary Mooring System Attached by Clump Masses for Improving the Wave-Resistance Ability of a Spar Buoy-Type Floating Offshore Wind Turbine

The International Energy Agency (IEA), under the auspices of their Offshore Code Comparison Collaboration (OC3) initiative, has completed high-level design OC-3 Hywind system. In this system the wind turbine is supported by a spar buoy platform, showing good wave-resistance performance. However, there are still large values in the motion of surge degree of freedom (DOF). Addition of clump masses on the mooring lines is an effective way of reducing the surge motion. However, the optimization of the locations where the clump masses are added is still not clear. In this study, therefore, an in-house developed code is verified by comparing the results of the original OC3 model with those by FAST. The improvement of the performance of this modified platform as a function of the location of the clump masses has been examined under three regular waves and three irregular waves. In the findings of these examination, it was apparent that attaching clump masses with only one-tenth of the mass of the total mooring-line effectively reduces the wave-induced response. Moreover, there is an obvious improvement as the depth of the location where the clump masses mounted is increased.

Sheets, filaments, and clumps – high-resolution simulations of how the thermal instability can form molecular clouds

This paper describes 3D simulations of the formation of collapsing cold clumps via thermal instability inside a larger cloud complex. The initial condition was a diffuse atomic, stationary, thermally unstable, 200pc diameter spherical cloud in pressure equilibrium with low density surroundings. This was seeded with 10% density perturbations at the finest initial grid level (0.29pc) around n_H = 1.1cm^{-3} and evolved with self-gravity included. No magnetic field was imposed. Resimulations at a higher resolution of a region extracted from this simulation (down to 0.039pc), show that the thermal instability forms sheets, then filaments and finally clumps. The width of the filaments increases over time, in one particular case from 0.26 to 0.56pc. Thereafter clumps with sizes of around 5pc grow at the intersections of filaments. 21 distinct clumps, with properties similar to those observed in molecular clouds, are found by using the FellWalker algorithm to find minima in the gravitational potential. Not all of these are gravitationally bound, but the convergent nature of the flow and increasing central density suggest they are likely to form stars. Further simulation of the most massive clump shows the gravitational collapse to a density >10^6 cm^{-3}. These results provide realistic initial conditions that can be used to study feedback in individual clumps, interacting clumps and the entire molecular cloud complex.

Spiral-arm instability – II. Magnetic destabilization

Fragmentation of spiral arms can drive the formation of giant clumps and induce intense star formation in disc galaxies. Based on the spiral-arm instability analysis of our Paper I, we present linear perturbation theory of dynamical instability of self-gravitating spiral arms of magnetised gas, focusing on the effect of toroidal magnetic fields. Spiral arms can be destabilised by the toroidal fields which cancel Coriolis force, i.e. magneto-Jeans instability. Our analysis can be applied to multi-component systems that consist of gas and stars. To test our analysis, we perform ideal magneto-hydrodynamics simulations of isolated disc galaxies and examine the simulation results. We find that our analysis can characterise dynamical instability leading arms to fragment and form clumps if magnetic fields are nearly toroidal. We propose that dimensionless growth rate of the most unstable perturbation, which is computed from our analysis, can be used to predict fragmentation of spiral arms within an orbital time-scale. Our analysis is applicable as long as magnetic fields are nearly toroidal. Using our analytic model, we estimate a typical mass of clumps forming from spiral-arm fragmentation to be consistent with observed giant clumps $\sim10^{7-8}~{\rm M_\odot}$. Furthermore, we find that, although the magnetic destabilisation can cause low-density spiral arms to fragment, the estimated mass of resultant clumps is almost independent from strength of magnetic fields since marginal instability occurs at long wavelengths which compensate the low densities of magnetically destabilised arms.

Why there is Symmetry between Shape and Orbit of Astronomical Bodies: a Little Deviation from Spherical Shape Allows Time to Flow in Forward Direction; Why Particles and Anti-particles Originate and Then, Recombine.

Sphere is an ideal shape in geometry. Whenever there is an enough mass clumps together to form an astronomical body, it tends to follow spherical shape. Irrespective of its material composition of any astronomical body, a diameter of few hundred kilometres is sufficient enough to create spherical form. But there is always little deviation from the spherical form of astronomical bodies to be elliptical to be precise. So, almost all big enough astronomical bodies have elliptical form of shape. There is definitely symmetry between the elliptical shape of an astronomical body and elliptical orbit where other astronomical bodies revolving around. In this paper, I will focus on the symmetry between shape and orbit of astronomical bodies. I will also focus how a little deviation from the spherical shape allows the physical time to flow in forward direction. At the end, I will discuss why particles and anti-particles originate and recombine together.

Initial phases of high-mass star formation: a multiwavelength study towards the extended green object G12.42+0.50

We present a multiwavelength study of the extended green object, G12.42+0.50 in this paper. The associated ionized, dust, and molecular components of this source are studied in detail employing various observations at near-, mid- and far-infrared, submillimeter and radio wavelengths. Radio continuum emission mapped at 610 and 1390 MHz, using the Giant Meterwave Radio Telescope, India, advocates for a scenario of coexistence of an UC H II region and an ionized thermal jet possibly powered by the massive young stellar object, IRAS 18079-1756 with an estimated spectral type of B1 - B0.5. Shock-excited lines of H2 and [FeII], as seen in the near-infrared spectra obtained with UKIRT-UIST, lend support to this picture. Cold dust emission shows a massive clump of mass 1375 M{\sun} enveloping G12.42+0.50. Study of the molecular gas kinematics using the MALT90 and JCMT archival data unravels the presence of both infall activity and large-scale outflow suggesting an early stage of massive star formation in G12.42+0.50. A network of filamentary features are also revealed merging with the massive clump mimicking a hub-filament layout. Velocity structure along these indicate bulk inflow motion.

External photoevaporation of protoplanetary discs in Cygnus OB2: linking discs to star formation dynamical history

Many stars form in regions of enhanced stellar density, wherein the influence of stellar neighbours can have a strong influence on a protoplanetary disc (PPD) population. In particular, far ultraviolet (FUV) flux from massive stars drives thermal winds from the outer edge of PPDs, accelerating disc destruction. In this work, we present a novel technique for constraining the dynamical history of a star forming environment using PPD properties in a strongly FUV irradiated environment. Applying recent models for FUV induced mass loss rates to the PPD population of Cygnus OB2, we constrain how long ago primordial gas was expelled from the region; $ 0.5$ Myr ago if the Shakura & Sunyaev $\alpha$-viscosity parameter is $\alpha = 10^{-2}$ (corresponding to a viscous timescale of $\tau_\mathrm{visc} \approx 0.5$ Myr for a disc of scale radius $40$ au around a $1\, M_\odot$ star). This value of $\alpha$ is effectively an upper limit, since it assumes efficient extinction of FUV photons throughout the embedded phase. With this gas expulsion timescale we are able to produce a full dynamical model that fits kinematic and morphological data as well as disc fractions. We suggest Cygnus OB2 was originally composed of distinct massive clumps or filaments, each with a stellar mass $\sim 10^4 \, M_\odot$. Finally we predict that in regions of efficient FUV induced mass loss, disc mass $M_\mathrm{disc}$ as a function of stellar host mass $m_\mathrm{star}$ follows a power law with $M_\mathrm{disc} \propto m_\mathrm{star}^\beta$, where $\beta \gtrsim 2.7$ (depending on disc initial conditions and FUV exposure). This is steeper than observed correlations in regions of moderate FUV flux ($1 < \beta <1.9$), and offers a promising diagnostic to establish the influence of external photoevaporation in a given region.

ATLASGAL-selected massive clumps in the inner Galaxy

Context. High-mass stars are formed within massive molecular clumps, where a large number of stars form close together. The evolution of the clumps with different masses and luminosities is mainly regulated by their high-mass stellar content and the formation of such objects is still not well understood. Aims. In this work, we characterise the mid-J CO emission in a statistical sample of 99 clumps (TOP100) selected from the ATLASGAL survey that are representative of the Galactic proto-cluster population. Methods. High-spatial resolution APEX-CHAMP+ maps of the CO (6–5) and CO (7–6) transitions were obtained and combined with additional single-pointing APEX-FLASH+ spectra of the CO (4–3) line. The data were convolved to a common angular resolution of 13.′′4. We analysed the line profiles by fitting the spectra with up to three Gaussian components, classified as narrow or broad, and computed CO line luminosities for each transition. Additionally, we defined a distance-limited sample of 72 sources within 5 kpc to check the robustness of our analysis against beam dilution effects. We have studied the correlations of the line luminosities and profiles for the three CO transitions with the clump properties and investigate if and how they change as a function of the evolution. Results. All sources were detected above 3-σ in all three CO transitions and most of the sources exhibit broad CO emission likely associated with molecular outflows. We find that the extension of the mid-J CO emission is correlated with the size of the dust emission traced by the Herschel-PACS 70 μm maps. The CO line luminosity (LCO) is correlated with the luminosity and mass of the clumps. However, it does not correlate with the luminosity-to-mass ratio. Conclusions. The dependency of the CO luminosity with the properties of the clumps is steeper for higher-J transitions. Our data seem to exclude that this trend is biased by self-absorption features in the CO emission, but rather suggest that different J transitions arise from different regions of the inner envelope. Moreover, high-mass clumps show similar trends in CO luminosity as lower mass clumps, but are systematically offset towards larger values, suggesting that higher column density and (or) temperature (of unresolved) CO emitters are found inside high-mass clumps.

A multiwavelength study of filamentary cloud G341.244-00.265

We present a multiwavelength study toward the filamentary molecular cloud G341.244-00.265, to investigate the physical and chemical properties, as well as star formation activities taking place therein. Our radio continuum and molecular line data were obtained from the Sydney University Molonglo Sky Survey (SUMSS), Atacama Pathfinder Experiment Telescope Large Area Survey of the Galaxy (ATLASGAL), Structure, excitation, and dynamics of the inner Galactic interstellar medium (SEDIGISM) and Millimeter Astronomy Legacy Team Survey at 90 GHz (MALT90). The infrared archival data come from Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE), Wide-field Infrared Survey Explorer (WISE), and Herschel InfraRed Galactic Plane Survey (Hi-GAL). G341.244-00.265 displays an elongated filamentary structure both in far-infrared and molecular line emissions; the “head” and “tail” of this molecular cloud are associated with known infrared bubbles S21, S22, and S24. We made H2 column density and dust temperature maps of this region by the spectral energy distribution (SED) method. G341.244-00.265 has a linear mass density of about 1654 M⊙ pc−1 and has a projected length of 11.1 pc. The cloud is prone to collapse based on the virial analysis. Even though the interactions between this filamentary cloud and its surrounding bubbles are evident, we found these bubbles are too young to trigger the next generation of star formation in G341.244-00.265. From the ATLASGAL catalog, we found eight dense massive clumps associated with this filamentary cloud. All of these clumps have sufficient mass to form massive stars. Using data from the GLIMPSE and WISE survey, we search the young stellar objects (YSOs) in G341.244-00.265. We found an age gradient of star formation in this filamentary cloud: most of the YSOs distributed in the center are Class I sources, while most Class II candidates are located in the head and tail of G341.244-00.265, indicating star formation at the two ends of this filament is prior to the center. The abundance ratio of N(N2H+)/N(C18O) is higher in the center than that in the two ends, also indicating that the gas in the center is less evolved. Taking into account the distributions of YSOs and the N(N2H+)/N(C18O) ratio map, our study is in agreement with the prediction of the so-called “end-dominated collapse” star formation scenario.