CO Line Research Articles

ALMA detection of CO rotational line emission in red supergiant stars of the massive young star cluster RSGC1

Context. The fate of stars largely depends on the amount of mass lost during the end stages of evolution. For single stars with an initial mass between ∼8–30 M⊙, most mass is lost during the red supergiant (RSG) phase, when stellar winds deplete the H-rich envelope. However, the RSG mass-loss rate (Ṁ) is poorly understood theoretically, and so stellar evolution models rely on empirically derived mass-loss rate prescriptions. However, it has been shown that these empirical relations differ largely, with differences up to 2 orders of magnitude. Aims. We aim to derive a new mass-loss rate prescription for RSGs that is not afflicted with some uncertainties inherent in preceding studies. Methods. We have observed CO rotational line emission towards a sample of RSGs in the open cluster RSGC1 that all are of a similar initial mass. The ALMA CO(2–1) line detections allowed us to retrieve the gas mass-loss rates (ṀCO). In contrast to mass-loss rates derived from the analysis of dust spectral features (ṀSED), the data allowed us a direct determination of the wind velocity and no uncertain dust-to-gas correction factor was needed. Results. Five RSGs in RSGC1 have been detected in CO(2–1). The retrieved ṀCO values are systematically lower than ṀSED. Although only five RSGs in RSGC1 have been detected, the data allow us to propose a new mass-loss rate relation for M-type red supergiants with effective temperatures between ∼3200 and 3800 K that is dependent on the luminosity and initial mass, and that is valid during the phase where nuclear burning determines the evolution along the RSG branch. The new mass-loss rate relation is based on the new ṀCO values for the RSGs in RSGC1 and on prior ṀSED values for RSGs in four clusters, including RSGC1. The new Ṁ-prescription yields a good prediction for the mass-loss rate of some well-known Galactic RSGs that are observed in multiple CO rotational lines, including α Ori, μ Cep and VX Sgr. Moreover, there are indications that a stronger, potentially eruptive, mass-loss process is occurring during some fraction of the RSG lifetime, suggesting that RSGs might experience a phase change in mass loss leading to the wind mass-loss rate dominating the RSG evolution at that stage. Conclusions. Implementing a lower mass-loss rate in evolution codes for massive stars has important consequences as to the nature of their end-state. A reduction of the RSG mass-loss rate implies that quiescent RSG mass loss is not enough to strip a single star’s hydrogen-rich envelope. Upon core collapse such single stars would explode as RSGs. Mass-loss rates of order ∼6 times higher would be needed to strip the H-rich envelope and produce a Wolf-Rayet star while evolving back to the blue side of the Hertzsprung–Russell diagram. Future observations of a larger sample of RSGs in open clusters should allow a more stringent determination of the ṀCO–luminosity relation and a sharper diagnostic as to when the phase change in mass loss is occurring.

The z-GAL survey

The z-GAL survey observed 137 bright Herschel-selected galaxies with the IRAM Northern Extended Millimeter Array (NOEMA) to measure their spectroscopic redshift. It detected several multiple sources and secured the spectroscopic redshift of a total of 165 individual galaxies over the range 0.8 < z < 6.5. The wealth of information provided by the NOEMA spectra allowed us to study the physical properties of these galaxies. By modelling their spectral energy distributions, we determined their dust mass, Mdust, temperature, Tdust, and emissivity index, βdust and found a significant anti-correlation between Tdust and βdust. Using the detected 12CO lines, we derived the molecular gas mass of the z-GAL sources. Combining the molecular lines and the dust continuum emission, we computed their gas depletion timescales, τdep: the z-GAL sample consists mainly of powerful starbursts with τdep in the range between 0.1 and 1.0 Gyr, while only ~ 25% belongs to the ‘main sequence’ of star forming galaxies.

CO and Atomic Line Emission from the Young Stellar Object V1331 Cygni

The infrared spectrum of the young disk star V1331 Cygni shows rare atomic emission lines from several species including C i, O i, Na i, Mg i, Al i, Si i, Ca i, Fe i, and probably S i. The presence of H i emission but the absence of N i recombination lines indicates excitation by a comparatively cool source unable to ionize nitrogen. Measurements of both the fundamental and first overtone emission of carbon monoxide indicate a hot (T ≈ 3000 K), optically thick (optical depth ≈100 in the strongest transitions of the fundamental) for the molecular gas.

Measurements and calculations of collisional line parameters for Raman lines of CO perturbed by H2

Close coupling calculations of line shape parameters have been performed for the first pure rotational Raman S0(j=0−3) lines of CO in an H2 bath. The pressure broadening coefficients obtained are in good agreement with the experimental values recently measured at 77, 180 and 298 K by some of us. The quantum dynamical calculations allow us to also determine line shift and Dicke parameters over a wide range of temperatures (20 to 400 K) for these lines. In addition, acquisitions of Raman spectra of the fundamental vibrational Q branch of CO in H2 have been performed allowing the determination of pressure broadening and line mixing coefficients for the first lines of the band at 77, 195 and 298 K. Based on our calculated pure rotational rate constants, we have also deduced pressure broadening and line mixing coefficients for these rovibrational lines. Theoretical values compare reasonably well with the set of experimental data.

Probing three-dimensional magnetic fields: II – an interpretable Convolutional Neural Network

ABSTRACT Observing 3D magnetic fields, including orientation and strength, within the interstellar medium is vital but notoriously difficult. However, recent advances in our understanding of anisotropic magnetohydrodynamic (MHD) turbulence demonstrate that MHD turbulence and 3D magnetic fields leave their imprints on the intensity features of spectroscopic observations. Leveraging these theoretical frameworks, we propose a novel Convolutional Neural Network (CNN) model to extract this embedded information, enabling the probe of 3D magnetic fields. This model examines the plane-of-the-sky magnetic field orientation (ϕ), the magnetic field’s inclination angle (γ) relative to the line-of-sight, and the total magnetization level (M$_{\rm A}^{-1}$) of the cloud. We train the model using synthetic emission lines of 13CO (J = 1–0) and C18O (J = 1–0), generated from 3D MHD simulations that span conditions from sub-Alfvénic to super-Alfvénic molecular clouds. Our tests confirm that the CNN model effectively reconstructs the 3D magnetic field topology and magnetization. The median uncertainties are under 5° for both ϕ and γ, and less than 0.2 for MA in sub-Alfvénic conditions (MA ≈ 0.5). In super-Alfvénic scenarios (MA ≈ 2.0), they are under 15° for ϕ and γ, and 1.5 for MA. We applied this trained CNN model to the L1478 molecular cloud. Results show a strong agreement between the CNN-predicted magnetic field orientation and that derived from Planck 353 GHz polarization. The CNN approach enabled us to construct the 3D magnetic field map for L1478, revealing a global inclination angle of ≈76° and a global MA of ≈1.07.

A Primordial Origin for the Gas-rich Debris Disks around Intermediate-mass Stars

While most debris disks consist of dust with little or no gas, a fraction have significant amounts of gas detected via emission lines of CO, ionized carbon, and/or atomic oxygen. Almost all such gaseous debris disks known are around A-type stars with ages up to 50 Myr. We show, using semianalytic disk evolution modeling, that this can be understood if the gaseous debris disks are remnant protoplanetary disks that have become depleted of small grains compared to the interstellar medium. Photoelectric heating by the A stars’ far-UV (FUV) radiation is then inefficient, while the stars’ extreme-UV (EUV) and X-ray emissions are weak owing to a lack of surface convective zones capable of driving magnetic activity. In this picture, it is relatively difficult for stars outside the range of spectral types from A through early B to have such long-lived gas disks. Less-massive stars have stronger magnetic activity in the chromosphere, transition region, and corona with resulting EUV and X-ray emission, while more-massive stars have photospheres hot enough to produce strong EUV radiation. In both cases, primordial disk gas is likely to photoevaporate well before 50 Myr. These results come from 0D disk evolution models where we incorporate internal accretion stresses, MHD winds, and photoevaporation by EUV and X-ray photons with luminosities that are functions of the stellar mass and age. A key issue this work leaves open is how some disks become depleted in small dust so that FUV photoevaporation slows. Candidates include the grains’ growth, settling, radial drift, radiation force, and incorporation into planetary systems.

Evidence for Low-power Radio Jet–ISM Interaction at 10 pc in the Dwarf AGN Host NGC 4395

Black-hole-driven outflows in galaxies hosting active galactic nuclei (AGN) may interact with their interstellar medium (ISM) affecting star formation (SF). Such feedback processes, reminiscent of those seen in massive galaxies, have been reported recently in some dwarf galaxies. However, such studies have usually been on kiloparsec and larger scales and our knowledge of the smallest spatial scales to which these feedback processes can operate is unclear. Here we demonstrate radio jet−ISM interaction on the scale of an asymmetric triple radio structure of ∼10 pc size in NGC 4395. This triple radio structure is seen in the 15 GHz continuum image and the two asymmetric jet-like structures are situated on either side of the radio core that coincides with the optical Gaia position. The high-resolution radio image and the extended [O iii]λ5007 emission, indicative of an outflow, are spatially coincident and are consistent with the interpretation of a low-power radio jet interacting with the ISM. Modelling of the spectral lines using MAPPINGS, and estimation of temperature using optical integral field spectroscopic data suggest shock ionization of the gas. The continuum emission at 237 GHz, though weak, was found to spatially coincide with the AGN. However, the CO(2−1) line emission was found to be displaced by around 20 pc northward of the AGN core. The spatial coincidence of molecular H2 λ2.4085 along the jet direction, the morphology of ionized [O iii]λ5007, and displacement of the CO(2−1) emission argues for conditions less favorable for SF in the central ∼10 pc region.

Observational chemical signatures of the past FU Ori outbursts

Abstract FU Ori-type stars are young stellar objects (YSOs) experiencing luminosity outbursts by a few orders of magnitude, which last for ∼102 years. A dozen of FUors are known up to date, but many more currently quiescent YSOs could have experienced such outbursts in the last ∼103 years. To find observational signatures of possible past outbursts, we utilise ANDES, RADMC-3D code as well as CASA ALMA simulator to model the impact of the outburst on the physical and chemical structure of typical FU Ori systems and how it translates to the molecular lines’ fluxes. We identify several combinations of molecular lines that may trace past FU Ori objects both with and without envelopes. The most promising outburst tracers from an observational perspective are the molecular flux combinations of the N2H+J = 3 − 2, C18O J = 2 − 1, H2CO $(J_{\rm K_a, K_c}) = 4_{04}-3_{03}$, and HCN J = 3 − 2 lines. We analyse the processes leading to molecular flux changes and show that they are linked with either thermal desorption or enhanced chemical reactions in the molecular layer. Using observed CO, HCN, N2H+ and H2CO line fluxes from the literature, we identify ten nearby disc systems that might have undergone FU Ori outbursts in the past ∼103 years: [MGM2012] 556, [MGM2012] 371 and [MGM2012] 907 YSOs in L1641, Class II protoplanetary discs around CI Tau, AS 209 and IM Lup and transitional discs DM Tau, GM Aur, LkCa 15 and J1640-2130.

The first ground-based detection of the 752 GHz water line in local ultra-luminous infrared galaxies using APEX-SEPIA

Abstract We report the first ground-based detection of the water line p-H2O (211–202) at 752.033 GHz in three z < 0.08 ultra-luminous infrared galaxies (ULIRGs): IRAS 06035-7102, IRAS 17207-0014 and IRAS 09022-3615. Using the Atacama Pathfinder EXperiment (APEX), with its Swedish-ESO PI Instrument for APEX (SEPIA) band-9 receiver, we detect this H2O line with overall signal-to-noise ratios of 8–10 in all three galaxies. Notably, this is the first detection of this line in IRAS 06035-7102. Our new APEX-measured fluxes, between 145 to 705 Jy km s−1, are compared with previous values taken from Herschel SPIRE FTS. We highlight the great capabilities of APEX for resolving the H2O line profiles with high spectral resolutions while also improving by a factor of two the significance of the detection within moderate integration times. While exploring the correlation between the p-H2O(211–202) and the total infrared luminosity, our galaxies are found to follow the trend at the bright end of the local ULIRG’s distribution. The p-H2O(211–202) line spectra are compared to the mid-J CO and HCN spectra, and dust continuum previously observed with ALMA. In the complex interacting system IRAS 09022-3615, the profile of the water emission line is offset in velocity with respect to the ALMA CO(J = 4 − 3) emission. For IRAS 17207-0014 and IRAS 06035-7102, the profiles between the water line and the CO lines are spectroscopically aligned. This pilot study demonstrates the feasibility of directly conducting ground-based high-frequency observations of this key water line, opening the possibility of detailed follow-up campaigns to tackle its nature.

Temperature-Dependent Line-Broadening Effects in CO2 Caused by Ar.

This computational study of line-broadening effects is based on an accurate, analytical representation of the intermonomer potential energy surface (PES) of the CO2 ⋅ Ar van der Waals (vdW) complex. The PES is employed to compute collisional broadening coefficients for rovibrational lines of CO2 perturbed by Ar. The semiclassical computations are performed using the modified Robert-Bonamy approach, including real and imaginary terms, and the exact trajectory model. The lines investigated are in the 10001←00011, 01101←00001, 00011←00001, and 00031←00001 vibrational bands and the computations are repeated at multiple temperatures. The computed results are in good agreement with the available experimental values, validating both the intermonomer PES developed and the methodology used. For lines in the 01101←00001 band of CO2 , temperature-dependent Ar-broadening coefficients are reported for the first time. The parameters presented should prove useful, among other applications, for the accurate experimental determination of CO2 and Ar abundances in planetary atmospheres.

Secondary Outflow Driven by the Protostar Ser-emb 15 in Serpens

We present the detection of a secondary outflow associated with a Class I source, Ser-emb 15, in the Serpens Molecular Cloud. We reveal two pairs of molecular outflows consisting of three lobes, that is, primary and secondary outflows, using Atacama Large Millimeter/submillimeter Array 12CO and SiO line observations at a resolution of ∼318 au. The secondary outflow is elongated approximately perpendicular to the axis of the primary outflow in the plane of the sky. We also identify two compact structures, Sources A and B, within an extended structure associated with Ser-emb 15 in the 1.3 mm continuum emission at a resolution of ∼40 au. The projected sizes of Sources A and B are 137 au and 60 au, respectively. Assuming a dust temperature of 20 K, we estimate the dust mass to be 2.4 × 10−3 M ⊙ for Source A and 3.3 × 10−4 M ⊙ for Source B. C18O line data imply rotational motion around the extended structure, but we cannot resolve rotational motion in Source A and/or B because the angular and frequency resolutions are insufficient. Therefore, we cannot conclude whether Ser-emb 15 is a single or binary system. Thus, either Source A or Source B could drive the secondary outflow. We discuss two scenarios that might explain the driving mechanism of the primary and secondary outflows: the Ser-emb 15 system is (1) a binary system composed of Sources A and B, or (2) a single-star system composed of Source A alone. In either case, the system could be a suitable target for investigating the disk and/or binary formation processes in complicated environments. Detecting these outflows should contribute to understanding complex star-forming environments, which may be common in the star formation processes.

SOFIA FEEDBACK Survey: The Pillars of Creation in [C ii] and Molecular Lines

We investigate the physical structure and conditions of photodissociation regions (PDRs) and molecular gas within the Pillars of Creation in the Eagle Nebula using SOFIA FEEDBACK observations of the [C ii] 158 μm line. These observations are velocity resolved to 0.5 km s−1 and are analyzed alongside a collection of complimentary data with similar spatial and spectral resolution: the [O i] 63 μm line, also observed with SOFIA, and rotational lines of CO, HCN, HCO+, CS, and N2H+. Using the superb spectral resolution of SOFIA, APEX, CARMA, and BIMA, we reveal the relationships between the warm PDR and cool molecular gas layers in context of the Pillars’ kinematic structure. We assemble a geometric picture of the Pillars and their surroundings informed by illumination patterns and kinematic relationships and derive physical conditions in the PDRs associated with the Pillars. We estimate an average molecular gas density cm−3 and an average atomic gas density n H ∼ 1.8 × 104 cm−3 and infer that the ionized, atomic, and molecular phases are in pressure equilibrium if the atomic gas is magnetically supported. We find pillar masses of 103, 78, 103, and 18 M ⊙ for P1a, P1b, P2, and P3, respectively, and evaporation times of ∼1–2 Myr. The dense clumps at the tops of the pillars are currently supported by the magnetic field. Our analysis suggests that ambipolar diffusion is rapid and these clumps are likely to collapse within their photoevaporation timescales.

Stored in the archives: Uncovering the CN/CO intensity ratio with ALMA in nearby U/LIRGs

ABSTRACT We present an archival Atacama Large Millimeter/submillimeter Array (ALMA) study of the cyanide radical (CN) N = 1 − 0/carbon monoxide (CO) J = 1 − 0 intensity ratio in nearby (z < 0.05) ultra-luminous and luminous infrared galaxies (U/LIRGs). We identify 16 U/LIRGs that have been observed in both CN and CO lines at ∼500 pc resolution based on 16 different ALMA projects. We measure the (CN bright)/CO and (CN bright)/(CN faint) intensity ratios at an ensemble of molecular clouds scales (CN bright = CN N = 1 − 0, J = 3/2 − 1/2; CN faint = CN N = 1 − 0, J = 1/2 − 1/2 hyperfine groupings). Our global measured (CN bright)/CO ratios range 0.02–0.15 in LIRGs and 0.08–0.17 in ULIRGs. We attribute the larger spread in LIRGs to the variety of galaxy environments included in our sample. Overall, we find that the (CN bright)/CO ratio is higher in nuclear regions, where the physical and excitation conditions favour increased CN emission relative to the disc regions. 10 out of 11 galaxies which contain well-documented active galactic nuclei show higher ratios in the nucleus compared with the disc. Finally, we measure the median resolved (CN bright)/(CN faint) ratio and use it to estimate the total integrated CN line optical depth in ULIRGs (τ ∼ 0.96) and LIRGs (τ ∼ 0.23). The optical depth difference is likely due to the higher molecular gas surface densities found in the more compact ULIRG systems.

Galactic ‘Snake’ IRDC G11.11−0.12: a site of multiple hub–filament systems and colliding filamentary clouds

ABSTRACT To probe star formation processes, we present a multiscale and multiwavelength investigation of the ‘Snake’ nebula/infrared dark cloud G11.11−0.12 (hereafter, G11; length ∼27 pc). Spitzer images hint at the presence of subfilaments (in absorption), and reveal four infrared-dark hub–filament system (HFS) candidates (extent < 6 pc) towards G11, where massive clumps (> 500 M⊙) and protostars are identified. The 13CO(2–1), C18O(2–1), and NH3(1,1) line data reveal a noticeable velocity oscillation towards G11, as well as its left part (or part-A) around Vlsr of 31.5 km s−1, and its right part (or part-B) around Vlsr of 29.5 km s−1. The common zone of these cloud components is investigated towards the centre of G11 housing one HFS. Each cloud component hosts two subfilaments. In comparison to part-A, more APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) clumps are observed towards part-B. The JWST near-infrared images discover one infrared-dark HFS candidate (extent ∼0.55 pc) around the massive protostar G11P1 (i.e. G11P1-HFS). Hence, the infrared observations reveal multiple infrared-dark HFS candidates at multiscale in G11. The Atacama Large Millimeter/submillimeter Array (ALMA) 1.16-mm continuum map shows multiple finger-like features (extent ∼3500–10 000 au) surrounding a dusty envelope-like feature (extent ∼18 000 au) towards the central hub of G11P1-HFS. Signatures of forming massive stars are found towards the centre of the envelope-like feature. The ALMA H13CO+ line data show two cloud components with a velocity separation of ∼2 km s−1 towards G11P1. Overall, the collision process, the ‘fray and fragment’ mechanism, and the ‘global non-isotropic collapse’ scenario seem to be operational in G11.

A Rotating Accretion Disk around MWC 297, a Young B1.5Ve Star

High-resolution spectra with iSHELL on IRTF in the K and M bands of the young, heavily accreting B1.5Ve star MWC 297 show numerous double-peaked CO lines. These CO lines originate in an inclined gaseous disk in Keplerian rotation. MWC 297 is the only early B star known to show a Keplerian disk in CO. Analysis of the spectra shows that 12CO 1–0 is optically thick for the low excitation lines. Even the 13CO 1–0 and 12CO 2–1 have somewhat optically thick lines at low J levels. We find that the CO emission in the disk can be fitted with CO being in a narrow ring at a radius of 12 au, with a temperature of 1500 K and a CO column density of 1.6 × 1018 cm−2. This model underestimates the line strength of high-J lines, indicating that they are excited by fluorescence. The CO overtone lines have a similar temperature. The 13CO lines are much brighter than expected from interstellar isotope ratios. The 13CO lines are wider than the 12CO ones, suggesting different excitation conditions. The same is true for 12CO 2–1. We see strong absorption in 12CO and 13CO 1–0 at low J levels, which is due to two cold foreground clouds. These clouds, one with a temperature of 8.3 K and a column density of 6.7 1017 cm−2 and the other one colder and with lower column density, can fully account for the observed extinction toward MWC 297.

Cygnus A obscuring torus: ionized, atomic, or molecular?

ABSTRACT The prototypical powerful FR II radio galaxy Cygnus A fits extremely well into the quasar/radio galaxy unified model: high polarization with an angle almost perpendicular to the radio jet and polarized flux showing broad permitted lines. It has been claimed that ionized gas in the torus reveals a very clear torus shape via Bremmstrahlung emission. We rule out the later with an energetic argument, and we constrain the molecular and atomic gas properties with existing observations. The atomic absorption against the core has been shown to match the X-ray column only if the spin temperature is an implausible Ts = 1 × 106 K. This points to a molecular medium for the X-ray column $\log (N_{\rm H} ~[\rm {cm^{-2}}]) \sim 23.5$. Yet not low-J CO absorption is detected to sensitive limits. The non-detection is surprising given that this powerful radio galaxy hosts a luminous, dust-obscured active nucleus and copious warm molecular hydrogen. These conditions suggest a detectable level of emission. Furthermore, the torus X-ray column density suggests detectable absorption. We explore various possibilities to explain the lack of a signature from warm CO (200–250 K). Specifically, that the radiative excitation by the radio core renders low-J CO absorption below current sensitivities, and that high-J levels are well populated and conducive to producing absorption. We test this hypothesis using archival Hershel/SPIRE FTS observations of Cygnus A of high-J CO lines (14 ≥ J ≥ 4 transitions). Still high-J CO lines are not detected. We suggest that ALMA observations near its high frequency limit can be critical to obtain the signature of molecular line of the torus of Cygnus A.

RedEye-1: a compact SWIR hyperspectral imager for observation of atmospheric methane and carbon dioxide

We present the development of our first prototype of a compact short-wavelength infrared (SWIR) hyperspectral imager, RedEye-1, designed to observe and measure the concentrations of methane (CH4) and carbon dioxide (CO2) in the atmosphere. It operates in the spectral range of 1588 nm to 1673 nm with a nominal spectral resolution of 0.5 nm and has a total weight of approximately 1.8 kg. We outline the optical design of the instrument, including its fore-optics (telescope), and evaluate its performance using the OpticStudio ZEMAX software. In addition, we explain the spectral and radiometric calibration procedures and present the results. Our preliminary data reduction and analysis revealed a high quality SWIR image and a single path measurement of an atmospheric profile displaying the absorption lines of CH4 and CO2.

ALMA Observations of Supernova Remnant N49 in the Large Magellanic Cloud. II. Non-LTE Analysis of Shock-heated Molecular Clouds

We present the first compelling evidence of shock-heated molecular clouds associated with the supernova remnant (SNR) N49 in the Large Magellanic Cloud (LMC). Using 12CO(J = 2–1, 3–2) and 13CO(J = 2–1) line emission data taken with the Atacama Large Millimeter/Submillimeter Array, we derived the H2 number density and kinetic temperature of eight 13CO-detected clouds using the large velocity gradient approximation at a resolution of 3.″5 (∼0.8 pc at the LMC distance). The physical properties of the clouds are divided into two categories: three of them near the shock front show the highest temperatures of ∼50 K with densities of ∼500–700 cm−3, while other clouds slightly distant from the SNR have moderate temperatures of ∼20 K with densities of ∼800–1300 cm−3. The former clouds were heated by supernova shocks, but the latter were dominantly affected by the cosmic-ray heating. These findings are consistent with the efficient production of X-ray recombining plasma in N49 due to thermal conduction between the cold clouds and hot plasma. We also find that the gas pressure is roughly constant except for the three shock-engulfed clouds inside or on the SNR shell, suggesting that almost no clouds have evaporated within the short SNR age of ∼4800 yr. This result is compatible with the shock-interaction model with dense and clumpy clouds inside a low-density wind bubble.

Observational Evidence of the Merging of Filaments and Hub Formation in G083.097+03.270

We uncover a hub–filament system correlated with massive young stellar associations in G083.097+03.270. Diagnosed with simultaneous 12CO, 13CO, and C18O line observations, the region is found to host two distinct and elongated filaments having separate velocity components, interacting spatially and kinematically, that appear to have seeded the formation of a dense hub at the intersection. A large velocity spread at the hub, in addition to a clear bridging feature connecting the filaments in velocity, indicate the merging of filaments. Along the filament axis, the velocity gradient reveals a global gas motion with an increasing velocity dispersion inward to the hub signifying turbulence. Altogether, the clustering of Class I sources, a high excitation temperature, a high column density, and the presence of a massive outflow at the central hub suggest enhanced star formation. We propose that the merging of large-scale filaments and velocity gradients along filaments are the driving factors in the mass accumulation process at the hub that have sequentially led to the massive star formation. With two giant filaments merging to coincide with a hub therein with ongoing star formation, this site serves as a benchmark for the “filaments to clusters” star-forming paradigm.

Dissecting the morphology of star forming complex S193

ABSTRACT We have studied a star-forming complex S193 using near-infrared (NIR) observations and other archival data covering optical to radio wavelengths. We identified stellar clusters in the complex using the NIR photometric data and estimated the membership and distance of the clusters. Using the mid-infrared (MIR) and far-infrared (FIR) images, the distribution of the dust emission around H ii regions is traced in the complex. The Herschel column density and temperature maps analysis reveal 16 cold dust clumps in the complex. The H α image and 1.4 GHz radio continuum emission map are employed to study the ionized gas distribution and infer the spectral type and the dynamical age of each H ii region/ionized clump in the complex. The 12CO(J = 3 − 2) and 13CO(J = 1 − 0) molecular line data hint at the presence of two velocity components around [−43, −46] and [−47, −50] km s−1, and their spatial distribution reveals two overlapping zones toward the complex. By investigating the immediate surroundings of the central cluster [BDS2003]57 and the pressure calculations, we suggest that the feedback from the massive stars seems responsible for the observed velocity gradient and might have triggered the formation of the central cluster [BDS2003]57.