arXiv subjects

Paul F. Goldsmith

Publications and source records attributed to Paul F. Goldsmith.

At least 19 recordsLinked to original sources

arXiv2026

The ALMA-QUARKS Survey: Discovery of Superfine Dusty Fibrils inside Massive Star-forming Clumps

We report the discovery of more than 320 superfine dusty filamentary structures (fibrils) inside 121 massive star forming clumps that are located in widely different Galactic environments (Galactocentric distances of ~1.2 - 12.9 kpc). These fibrils are identified from the 1.3-mm continuum emission in the ALMA-QUARKS survey, which has a linear resolution of ~900 AU for a source at ~3 kpc. The typical width of these fibrils identified in clumps is found to be ~0.01 pc, which is about ten times narrower than that of dusty filaments in nearby clouds identified by the Herschel Space Observatory. The mass (M) versus length (l) relation for these fibrils follows M ~ l^2, similar to that of Galactic filaments identified in space (e.g., Herschel) and ground-based single-dish (e.g., APEX) surveys. However, these fibrils in the ALMA-QUARKS survey are significantly denser (N_{H_2} = 10^{23} - 10^{24} cm^{-2}) than the filaments found in previous Herschel surveys (N_{H_2} = 10^{20} - 10^{23} cm^{-2}). This work contributes a large sample of newly found superfine fibrils in massive clumps, following the identification of large 0.1 pc-wide filaments and associated internal velocity coherent molecular fibers in nearby molecular clouds, further emphasizing the crucial role played by filamentary structures in star formation at various physical scales.

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arXiv2026

The SIMPLIFI Survey: Polarization of Dense Filaments with SOFIA III. Relative orientations of antenna temperature gradients with the magnetic field in the DR21 molecular cloud

We investigate magnetohydrodynamic (MHD) turbulence in the DR21 molecular cloud using far infrared polarimetry from SOFIA HAWC+ and molecular spectroscopy from the Nobeyama 45~m telescope. The Velocity Channel Gradient (VChG) method is applied to thin velocity slices of the 12CO and 13CO J=1-0 emission to determine the antenna temperature gradients and their orientations in the plane of the sky. The relative orientations of the gradients with respect to the magnetic field position angles enable an evaluation of theoretically predicted alignment of elongated, turbulent eddies for Alfvenic, fast and slow modes and self-gravity. The projected Rayleigh statistic is calculated for both the full cloud and 6 regions of interest to provide a quantitative assessment of these alignments. Our analysis finds mostly parallel alignment of the gradient direction and the local magnetic field orientation in the Main Ridge of DR21 that comprises most of the cloud mass. While parallel alignment can result from fast MHD modes or cloud collapse, previous studies show spectroscopic evidence for the large scale collapse of the DR21 cloud, which supports self-gravity as the primary cause of the observed parallel alignment. One of the six sub-filaments that are connected to the Main Ridge exhibits mostly perpendicular alignment of the position angles of the gradient and magnetic field. These perpendicular relative orientations may be a product of Alfven and slow modes in a magnetized, sub-Alfvenic medium even if the sub-filament is accreting onto the Main Ridge.

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arXiv2026

The ALMA-QUARKS Survey. IV. Core Mass Function and Evolutionary Trends in Core Formation Efficiency and Chemistry

The ALMA-QUARKS (Querying Underlying Mechanisms of Massive Star Formation with ALMA-Resolved Gas Kinematics and Structures) survey targets 139 massive protoclusters selected from the ATOMS survey. The targets were observed at 1.3~mm wavelength with an angular resolution of $\sim0.3^{\prime\prime}$, corresponding to $\sim10^3$~au at the sample's median distance of $\sim3.8$~kpc. Using \texttt{getsf}, we identify 3374 dense cores and classify them as starless, protostellar, hot core, or H{\sc ii} region candidates based on spectral-line diagnostics (e.g., H30$α$, CH$_3$CN, and CH$_3$OH) and CO outflow associations. The resulting catalog provides core physical properties and enables statistical investigations of dense core populations in massive protocluster environments. The derived global core mass function (CMF) after excluding H{\sc ii} region candidates, which is biased by distance effects, has a relatively flat power-law slope at the high-mass end ($\mathrm{d}N/\mathrm{d}\log M \propto M^{-γ}$, with $γ=0.98\pm0.03$). In contrast, the measured high-mass slopes in individual distance bins are approximately Salpeter-like, while their fitted lower mass limits increase with distance. We further examine the core formation efficiency (CFE) across the full sample and find that it positively correlates with the luminosity-to-mass ratio of the parental clumps, consistent with an evolutionary increase in the fraction of mass concentrated into dense cores. We also investigate the detection rates of different molecular tracers and find systematic chemical variations with evolutionary stage. Compared with the ASHES survey, we find that the detection rates of deuterated species vary significantly even for cores at the same evolutionary stages, suggesting an important environmental influence on the chemical evolution of cores.

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arXiv2026

Discovery of a Compact Hub-Filament System in G286.21+0.17 with JWST and ALMA: Insights into Protocluster Formation and Competitive Accretion

We present a multi-wavelength study of the massive protocluster G286.21+0.17 (G286) using \emph{JWST} near-infrared (NIR) imaging and ALMA H$^{13}$CO$^{+}$(1--0) observations. The \emph{JWST} images uncover a compact ($\sim$0.5 pc) hub-filament system (HFS), comprising a dense central hub connected by at least four converging filaments seen in absorption, along with multiple H$_2$ protostellar jets/outflows. The hub hosts the dense core G286c1. H$^{13}$CO$^{+}$ emission confirms this HFS over [$-$19.2, $-$16.4]~km~s$^{-1}$, while the \emph{JWST} images also trace prominent photodissociation regions surrounding H\,{\sc ii}~region~A, powered by a B-type star. The identified H$^{13}$CO$^{+}$ skeletons closely trace the major \emph{JWST} absorption structures and show steep velocity gradients indicative of inflow. The radial distribution of ALMA 1.3 mm continuum cores (ALMAGAL and Cheng et al. 2020) exhibits power-law trends toward the hub center. The core number density, surface density, and core mass follow $Y \propto r^α$ with $α_ρ$ $\sim$$-$2.8 to $-$1.1, $α_Σ$ $\sim$$-$0.4 to $-$0.6, and $α_M$ $\sim$$-$0.7, whereas the core diameter remains nearly constant. Together with filament mass accretion rates of 7.6--11$\times10^{-5}$ M$_\odot$ yr$^{-1}$, these results are consistent with competitive accretion, highlighting preferential core growth toward the hub. Increasing filament linewidths toward the hub imply gravity-driven inflow, but misaligned local velocity gradient and gravitational force directions along filaments point to a dynamically evolved system. The HFS likely formed through large-scale gas-layer interactions aided by compression from the adjacent H\,{\sc ii} region. Overall, star formation in G286 appears to be regulated by filamentary accretion, competitive core growth in the hub, and stellar feedback.

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arXiv2026

The ALMA-QUARKS Survey: Properties of Hot Molecular Fragments in the Massive Protocluster IRAS 17233-3606

To investigate the physical mechanisms of fragmentation within the hot molecular core of the massive protocluster IRAS 17233-3606 (G351.78-0.54), we carried out a detailed analysis of continuum and lines, using the ALMA Band 3 data from the ATOMS survey and Band 6 data from the QUARKS survey. The low-resolution 3 mm data reveal a massive hot core MM1 with a mass of ~81.3 Msun, and a prominent ultracompact (UC) HII region MM2, while the high-resolution data resolve MM1 into 11 hot molecular fragments (HMFs). These HMFs exhibit hot (Trot = 100-310 K) CH3CN and CH3OH emission and high column densities (NH2 > 10^23 cm^-2), indicating their potential to form massive stars. Based on outflows, masers, HII regions, and f[CH3CN/CH3O] abundance ratios, the evolutionary sequences of the 11 HMFs are categorized as phases I to IV. The mean minimum-spanning tree (MST) separation (~1.8 x 10^3 au) of the HMFs is nearly half of the thermal Jeans length (~3.3 x 10^3 au). Together with the Q parameter Q = 0.77 and virial parameter alpha_vir = 0.84 of MM1, these results suggest an evolutionary scenario in which fragmentation is initially driven by thermal instability, followed by global gravitational contraction and growth through active accretion. Meanwhile, feedback from the B2-type zero-age main-sequence (ZAMS) star and the UC HII region significantly influence the morphology and chemical properties of MM1 and MM2. This heterogeneity highlights the role of diverse physical processes taking place in high-mass protoclusters.

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arXiv2026

Random gas motions inside sub-parsec scale supercritical filaments

Supercritical gas filaments in molecular clouds host the dense cores in which new stars form. The mechanisms governing their formation and subsequent gas accretion remain poorly understood. In this study, we conduct a statistical analysis of a large sample of sub-parsec supercritical filaments using H13COp J=1-0 data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) Survey. We identified velocity-coherent filaments in position-position-velocity (PPV) space and systematically examined velocity gradients both along and perpendicular to their skeletons. Our analysis uncovers a remarkable result: at scales of ~ 0.1-1 pc, the local velocity gradients within these supercritical filaments show no preferred alignment with the filament skeletons and exhibit no correlation with the local gravitational field. This random orientation suggests the presence of chaotic gas motions deep inside these dense structures. These findings may indicate that turbulence-rather than gravity-dominates gas dynamics and structural evolution at small scales, even in regions on the verge of star formation, challenging the paradigm of gravity-dominated structure formation within molecular clouds. This scenario should be further tested by more state-of-the-art simulations. This study offers key observational insights into the roles of turbulence and gravity in establishing the initial conditions for star formation.

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arXiv2026

PMO Polaris CO survey. I. A 100 deg$^2$ view of the Polaris Flare

Large-area CO surveys are essential for studying molecular cloud dynamics and evolution; however, most have focused on the Galactic plane, leaving high-latitude clouds less explored. We present the PMO Polaris CO Survey (PPCOS), which maps a 100~deg$^2$ region of the Polaris Flare in the $J=1-0$ transitions of $^{12}$CO, $^{13}$CO, and C$^{18}$O using the Delingha 13.7~m telescope. As the first large-area CO survey at high Galactic latitude ($|b| > 20^{\circ}$) with sub-arcminute resolution, PPCOS achieves sensitivities of $\sim$0.46~K for $^{12}$CO and $\sim$0.23~K for $^{13}$CO and C$^{18}$O at a spectral resolution of 0.16~km~s$^{-1}$ and an angular resolution of 50\arcsec. The $^{12}$CO emission reveals seven distinct complexes, where only $\sim$10\% of pixels display multiple velocity components, alongside a global velocity gradient of 0.18~km~s$^{-1}$~pc$^{-1}$. Typical line widths are $1.2 \pm 0.6$~\mbox{km~s$^{-1}$} for $^{12}$CO, while $^{13}$CO components are systematically narrower ($\lesssim 0.7\,ΔV_{\rm ^{12}CO}$). The $^{12}$CO/$^{13}$CO intensity ratios (5--25) indicate widespread $^{12}$CO optical thickness, resembling conditions found in giant molecular clouds (GMCs). Globally, the CO emission divides into two groups: a major group aligned with the velocity gradient and a secondary group elongated perpendicular to it, possibly regulated by large-scale coherent dynamics. We propose a three-layer hierarchy: a dynamically assembling and dispersing periphery traced by $^{12}$CO, a more stable intermediate kernel traced by $^{13}$CO, and gravitationally bound compact cores traced by C$^{18}$O. No young stellar objects are firmly associated with the molecular gas. PPCOS provides an ideal laboratory for studying turbulence, hierarchical structure, and early cloud evolution in a nearby, relatively simple molecular cloud.

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arXiv2026

The ALMA-QUARKS survey: Investigating Thermal Feedback of Massive Protostars in Hot Molecular Cores

We identify a sample of 83 spatially resolved hot molecular cores (HMCs) in the QUARKS survey, aiming at investigating thermal feedback from massive stars. Using CH$_3$CN\,(12--11) line emission together with 1.3\,mm continuum data we derive the radial temperature, volume density and \ch3cn{} abundance profiles for the 83 HMCs. Based on the envelope temperature and density profiles, we compute the luminosities of the embedded massive protostars with \radmc{} radiation transfer model. The derived luminosities are comparable (within $\sim1$ dex) to the bolometric luminosities of their natal clumps and show strong correlations with several core-scale properties, including the HMC mass ($Log[ M_\mathrm{env}] = 1.01\,Log [L_\star] - 4.80$), the inner core radius (the flat radius of Plummer-like volume density profile) ($Log[a] = 0.46\,Log[L_\star] + 0.52$) and the central density $ (Log[n_c] = -0.55 Log[L_\star] +10.47) $. These empirical relations provide useful observational constraints for physical models of protostellar objects. Importantly, we find a strong positive correlation between the massive protostellar luminosity and the local thermal Jeans mass. The derived Jeans masses, $M_\mathrm{Jeans}$, exceed the HMC masses $M_\mathrm{env}$, with the average $M_\mathrm{Jeans}$ being two times larger than the average $M_\mathrm{env}$. This provides observational evidence that thermal feedback from massive protostars can effectively suppress further fragmentation of HMCs, thereby promoting massive star formation. In addition, the positive correlation between massive protostellar luminosity and natal clump mass suggests that more massive clumps preferentially host more luminous protostars, leading to stronger thermal feedback.

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arXiv2026

SIMPLIFI -- Study of Interstellar Magnetic Polarization: a Legacy Investigation of Filaments. I. Magnetically-Guided Accretion onto the DR21 Ridge

We present first results from SIMPLIFI (Study of Interstellar Magnetic Polarization: a Legacy Investigation of Filaments), a SOFIA/HAWC+ $214~μ\rm{}m$ polarimetric survey of Galactic molecular cloud filaments. We trace magnetic field morphology from the DR21 Main Ridge into surrounding sub-filaments at $\sim{}0.1~\rm{}pc$ resolution, extending polarimetric detections for the first time beyond high-column-density regions probed by prior submillimeter observations. We compare the plane-of-sky orientations of the magnetic field $\hat{B}_{\rm{}pos}$, the projected gravitational acceleration $\vec{g}_{\rm{}pos}$, and the intensity gradient rotated by $90^{\circ}$. The relative orientation of $\hat{B}_{\rm{}pos}$ and the rotated gradient transitions from preferentially parallel in sub-filaments to perpendicular in the Main Ridge at $N({\rm{}H_2})\sim{}2\times{}10^{22}~\rm{}cm^{-2}$, consistent with thresholds seen with Planck. This is expected in clouds formed from strongly magnetized, sub-Alfvenic, magnetically sub-critical gas. We find region-to-region and pixel-to-pixel variations at fixed column density, indicating that column density alone is not sufficient to encode changes in magnetic field structure. Our central finding is that $\vec{g}_{\rm{}pos}$ and $\hat{B}_{\rm{}pos}$ remain aligned throughout the cloud regardless of column density or environment, unlike the environment-dependent behavior of either quantity vs. the intensity gradient. This persistent alignment is consistent with magnetically-guided accretion: sub-filaments channel material along field lines at several $10^{-3}\,M_{\odot}\,\rm{}yr^{-1}$, sufficient to assemble the Ridge within $\sim{}1~\rm{}Myr$ and sustain high-mass star formation. The framework also explains why observed radial velocities $\sim{}2~\rm{}km\,s^{-1}$ fall well below free-fall expectations $\sim{}8~\rm{}km\,s^{-1}$ due to projection effects.

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arXiv2026

ALMA-QUARKS view of W49N: Multipolar episodic outflow associated with the most energetic Galactic water maser

We present a detailed investigation of a multipolar episodic molecular outflow in the mini-starburst region W49N, which hosts the most luminous water maser in the Galaxy. Using high-resolution ($\sim$0.3 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the $\mathrm{^{12}CO}$ emission as part of the ALMA-QUARKS survey, we analyze the morphology and kinematics of the outflow. Our observations reveal four newly identified outflow lobes in addition to the previously known central bipolar jet. These lobes appear more jet-like rather than exhibiting wide opening angles. Based on the $\mathrm{^{12}CO}$ (2-1) and $\mathrm{^{13}CO}$ (2-1) emission, we provide a more reliable estimate of the outflow's physical parameters, confirming it as one of the most energetic outflows in the Galaxy. Notably, these newly discovered lobes exhibit chains of knots, a characteristic signature of episodic ejection. Furthermore, two of the lobes display prominent S-shaped wiggles, suggestive of a precessing jet. The discovery of these features -- commonly observed in outflows from low-mass protostars -- in such an extreme massive star-forming environment provides compelling evidence that some underlying physical mechanisms for launching outflows are conserved across a wide range of stellar masses.

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arXiv2026

The ALMA-QUARKS Survey: Evidence of an Explosive Molecular Outflow in IRAS 15520--5234

We present a study of the massive protocluster IRAS 15520$-$5234, which displays evidence of an explosive molecular outflow that unleashed a kinetic energy of at least 10$^{48}$ erg. The protocluster contains 16 dense cores detected in the ALMA band 6 continuum emission maps, having masses in the range from 0.2 to 11.0 M$_{\odot}$. Our analysis of CO $(2-1)$ emission reveals 28 well collimated outflow fingers, the majority of which follow a Hubble-Lemaître velocity law. The outflow fingers show no preferred orientation in the plane of sky and emerge from a common center of origin. We estimate the total mass, momentum, and kinetic energy of the outflow fingers and find that the values are at least one order of magnitude higher than the typical bipolar outflows associated with massive protostars. The morphology and kinematics of the outflow fingers suggest that the outflow associated with IRAS 15520$-$5234 is explosive in nature. We calculate the dynamical age of the explosive event to be approximately 6550 years. Additionally, we estimate the frequency of such explosive outflows in the Galaxy, which is one event every 83 years. Finally, we speculate that the rearrangement of masses within the massive protocluster and the dynamical interaction among the massive cores may result in the formation of such an energetic event.

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arXiv2026

Large scale mapping of [CI] and the [CI]-to-CO transition in $ρ$ Ophiuchus molecular cloud

Atomic carbon ([CI]) is a key species in the carbon chemistry of the interstellar medium (ISM). Using the Submillimeter Wave Astronomy Satellite (SWAS), we conducted a [CI]($^3$P$_1$--$^3$P$_0$) 492 GHz survey covering approximately 4 deg$^2$ of the L1688 and L1689 regions in the $ρ$ Oph molecular cloud, achieving a spatial resolution of 4.25$\hbox{$^{\prime}$}$. The derived [CI] column densities, N([CI]), range from 4.85 $\times$ 10$^{14}$ cm$^{-2}$ to 6.29 $\times$ 10$^{17}$ cm$^{-2}$, corresponding to an abundance ratio N([CI])/N($H_2$) of 2.24$\times$ 10$^{-7}$ to 2.39$\times$ 10$^{-4}$, with a median value of 1.8$\times$ 10$^{-5}$. Combining observations with photodissociation region (PDR) modeling, we find that [CI] abundance varies less than CO in regions with UV intensity G$_0$ $> 16$ and N(H$_2$) $<$ 4.6 $\times$ 10$^{21}$ cm$^{-2}$, suggesting [CI] is a more reliable tracer of molecular hydrogen in low-density, high-radiation environments where the [CI]-to-CO transition occurs. Utilizing [CI] as direct H$_2$ tracer, the CO-dark gas fraction is estimated to be 0.43 , meaning that 43% of the total cloud mass will be missed by conventional calculation based on CO observations but can be calibrated by [CI] emission. The [CI] line widths are systematically broader than those of $^{13}$CO, possibly due to contributions from atomic carbon. These findings provide key insights into Galactic [CI] emission and the carbon cycle evolution in the interstellar medium. Future high-sensitivity [CI] ($^3$P$_1$--$^3$P$_0$) surveys with the Chinese Survey Space Telescope (CSST) will significantly advance our understanding of the carbon cycle evolution.

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arXiv2025

ALMA-QUARKS: Few-Thousand-Year Hatching out of "Egg": The Supersonic Breakout of a Hypercompact H II Region from Its Parental Hot Core

The kinematic evolution of hypercompact H II (HC H II) regions around young high-mass stars remains poorly understood due to complex interactions with parental environs. We present ALMA QUARKS/ATOMS 1.3 mm/3 mm observations (the highest resolution $\sim0.01$ pc) of a deeply embedded HC H II region (diameter $\sim0.015$ pc, electron density $\sim2\times10^{5}$ cm$^{-3}$) exhibiting a striking $\gtrsim20$ km s$^{-1}$ global redshift seen in optically thin H30$α$/H40$α$ recombination lines relative to its parental hot molecular core within a hub-filament system. The 1.3 mm continuum data reveal a distinct 0.1-pc arc and a perpendicular 0.04-pc tail. We propose that this morphology arises from a dynamic champagne flow: the slow expansion of HC H II region into a pre-existing filament forms the arc and associated low-velocity (few km s$^{-1}$) SiO shocks. Meanwhile, in the opposite direction ionized gas escapes along a steep density gradient traced by the tail and high-velocity (20 km s$^{-1}$) SiO emission. We reject the bow shock scenario in which ionized gas co-moves with a runaway high-mass star because shocked gas in the arc aligns with the hub velocity, contradicting the bow shock prediction. Non-LTE radiative transfer modeling further rules out infall of ionized gas as the velocity shift origin. We conclude that this exceptional HC H II region is undergoing a few-thousand-year transition phase of "hatching out of the egg": the ionized gas of HC H II region has just broken out of its parental hot core and now is flowing outward supersonically. This work highlights how anisotropic density distributions induce supersonically anisotropic ionized flows that govern HC H II region evolution.

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arXiv2025

Discovery of a rich population of compact hub-filament systems in a single star-forming complex

We report the discovery of 45 compact hub-filament systems (HFSs; median size $\sim$2.4 pc) in infrared-dark clouds (IRDCs) in the W33 complex, located at the junction of the Scutum and Norma spiral arms. Using {\it Spitzer} 8 and 24 micron, and unWISE 12 $μ$m images, HFSs are identified as regions where three or more filaments converge onto a central hub, appearing as absorption features toward IRDCs. In each IRDC, HFSs mainly lie at the intersections of elongated substructures, associated with groups of protostars and lacking radio continuum emission. Minimum Spanning Tree (MST) analysis shows that protostars are closely associated with the HFSs, with protostellar core separations of $\leq$ 0.7 pc, indicating strong clustering within fragmented structures. The HFSs form two main groupings spanning 10--15 pc, with member separations of 1--3.3 pc. Around 65\% are tightly clustered ($<$ 2 pc), exhibiting rich small-scale structures and emphasizing the uniqueness of the complex. MST analysis of ALMAGAL 1.38 mm continuum cores -- predominantly low-mass and embedded in ten HFSs -- reveals a median core separation of $\sim$0.03 pc. The protostellar spacing ($\sim$0.7 pc) significantly exceeds the thermal Jeans length ($\sim$0.08 pc for temperature $\sim$18 K and density $\sim$10$^{5}$ cm$^{-3}$), whereas the core spacing is smaller than the Jeans length, suggesting that thermal fragmentation may influence core formation but alone cannot explain the larger-scale protostellar distribution. All these findings together support a picture in which fragments of clouds/filaments form clumps hosting compact HFSs that facilitate efficient and clustered star formation, often yielding massive stars.

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arXiv2025

The ALMA-QUARKS survey: Evidence of a candidate high-mass prestellar core aside a bright-rimmed cloud IRAS 18290-0924

Although frequently reported in observations, the definitive confirmation of high-mass prestellar cores has remained elusive, presenting a persistent challenge in star formation studies. Using two-band observational data from the 3mm ATOMS and 1.3mm QUARKS surveys, we report a high-mass prestellar core candidate, C2, located on the side of the bright-rimmed cloud IRAS 18290-0924. The C2 core identified from the 3mm continuum data of the ATOMS survey ($\sim$2 arcsecond, $\rm\sim 10000~au$ at 5.3 kpc) has a mass ranging from 27-68 $M_{\odot}$ for temperatures 10-22K within a radius of $\sim$2800 au. The highest-resolution ($\sim$0.3 arcsecond, $\rm\sim 1500 au$) observations of this source presented to date from the QUARKS survey reveal no evidence of further fragmentation. Further analysis of a total $\sim$10 GHz band width of molecular line survey does not find star-formation activity (e.g., outflows, ionized gas) associated with the core, with a few molecular lines of cold gas detected only. Additionally, virial analysis indicates the C2 core is gravitationally bound ($α_{\rm vir} \sim0.1-0.3$) and thus could be undergoing collapse toward star formation. These results strongly establish a candidate for a high-mass prestellar core, contributing to the very limited number of such sources known to date.

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arXiv2025

Unveiling the Chemical Complexity and C/O Ratio of the HD 163296 Protoplanetary Disk: Constraints from Multi-line ALMA Observations of Organics, Nitriles, Sulfur-bearing, and Deuterated Molecules

The physical and chemical conditions within a protoplanetary disk play a crucial role in determining its chemical composition, which is subsequently inherited by any forming planets. To probe these conditions, high-resolution molecular line observations, coupled with modelling, are essential. In this study, we investigate the chemistry of the nearby, massive, and relatively line-rich protoplanetary disk around HD 163296 using high-resolution observations from ALMA across Bands 3, 4, 6, and 7. We constrain the disk-averaged and radial distributions of column density and excitation temperature for the detected molecules using the new retrieval code DRive. The disk chemistry is modelled using the astrochemical code PEGASIS, with variations in the initial elemental C/O ratio. Our modelling, informed by molecular observations of HCO+, DCO+, HCN, DCN, CS, HC3N, H2CO, CH3OH, HNCO, and NH2CHO, allows us to place strong constraints on the C/O ratio, with a best-fit value of 1.1 that is broadly consistent with previous estimates. We present the highest-resolution DCO+ emission map of this disk to date, revealing triple-ringed chemical substructures that closely align with the dust continuum rings. Additionally, our results provide the first and most stringent upper limits on the column densities of NH2CHO and HNCO in this protoplanetary disk, measured at < 7e11 cm-2 and < 1e11 cm-2, respectively. Our chemical models suggest that NH2CHO and HNCO predominantly form on grain surfaces within the disk. However, physico-chemical desorption mechanisms are inefficient at releasing these species into detectable gas-phase abundances, yet they remain promising targets for future ALMA observations.

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arXiv2025

The ALMA-QUARKS survey: Hot Molecular Cores are a long-standing phenomenon in the evolution of massive protostars

We present an analysis of the QUARKS survey sample, focusing on protoclusters where Hot Molecular Cores (HMCs, traced by CH3CN(12--11)) and UC HII regions (traced by H30α/H40α) coexist. Using the high-resolution, high-sensitivity 1.3 mm data from the QUARKS survey, we identify 125 Hot Molecular Fragments (HMFs), which represent the substructures of HMCs at higher resolution. From line integrated intensity maps of CH3CN(12--11) and H30α, we resolve the spatial distribution of HMFs and UC HII regions. By combining with observations of CO outflows and 1.3 mm continuum, we classify HMFs into four types: HMFs associated with jet-like outflow, with wide-angle outflow, with non-detectable outflow, and shell-like HMFs near UC HII regions. This diversity possibly indicates that the hot core could be polymorphic and long-standing phenomenon in the evolution of massive protostars. The separation between HMFs and H30α/H40αemission suggests that sequential high-mass star formation within young protoclusters is not likely related to feedback mechanisms.

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arXiv2025

A misaligned protostellar disk fed by gas streamers in a barred spiral-like massive dense core

High-mass stars, born in massive dense cores (MDCs), profoundly impact the cosmic ecosystem through feedback processes and metal enrichment, yet little is known about how MDCs assemble and transfer mass across scales to form high-mass young stellar objects (HMYSOs). Using multi-scale (40-2500 au) observations of an MDC hosting an HMYSO, we identify a coherent dynamical structure analogous to barred spiral galaxies: three 20,000 au spiral arms feed a 7,500 au central bar, which channels gas to a 2,000 au pseudodisk. Further accretion proceeds through the inner structures, including a Keplerian disk and an inner disk (100 au), which are thought to be driving a collimated bipolar outflow. This is the first time that these multi-scale structures (spiral arms, bar, streamers, envelope, disk, and outflow) have been simultaneously observed as a physically coherent structure within an MDC. Our discovery suggests that well-organized hierarchical structures play a crucial role during the gas accretion and angular momentum build-up of a massive disk.

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