Shuting Lin

To investigate the initial conditions of high-mass star-forming regions, we use SiO (2–1) emission to trace early shock-related kinematics toward 16 70 μ m dark and massive clumps with luminosity-to-mass ratios ( L / M ) 2 km s ⁻¹ ) SiO (2–1) features not associated with outflows driven by clearly identified protostars. Lacking coincident 3 mm dust continuum cores, their origins may be young outflows from undetected low-mass protostars, dissipating shocks, cloud–cloud collisions, or projection effects when the outflows lie close to the plane of the sky. The detection of these shocks and outflows in such extremely young environments demonstrates that protostellar activity has already begun.

We present an investigation of the gas kinematics and an assessment of the evolutionary stages of dense cores embedded in four infrared dark clouds (IRDCs) using the NH_3(1,1) and NH_3(2,2) lines obtained from the VLA and GBT observations. There is no 1.3 cm continuum emission counterpart in 1.3 mm continuum emission revealed by the SMA toward these IRDCs. The low production rate of N_ ̊m uv ∼ 10^ 44 s -1 for the Lyman continuum photons indicates that the four IRDCs are in very early evolutionary stages, where free-free emission is still absent. We identified 61 dense cores at the size scale of ∼0.1 pc using the inner satellite groups of ) increases with an increasing radial distance from the center of dense core within the inner 0.1,pc toward eight dense cores, indicating that the turbulence is likely dissipated toward the center of these dense cores. In addition, two dense cores in AGAL 031.024+00.262 and one core in AGAL 024.314+00.086 exhibit nearly sonic motions on a small scale of 0.01 pc. The weakening of nonthermal support against gravity suggests that these dense cores are close to gravitational collapse or are already undergoing collapse. Conversely, there are seven dense cores in AGAL031.024+00.262 displaying a decrease in line. Among them, 38 dense cores exhibit a single velocity component, while 23 dense cores show multiple velocity components. We find that the nonthermal velocity dispersion (σ_ non non with increasing radial distance from the center. By comparing this trend with the outflow revealed by CO J=2-1 line, we find that these cores are likely associated with embedded star formation activities. Higher angular resolution observations on subparsec scales are essential to reveal the transition from thermal- to nonthermal-dominated regions, especially in dense cores associated with multiple velocity components.

Aims. We investigated the interplay between dense molecular gas, star formation, and active galactic nucleus (AGN) feedback in the luminous IR galaxy NGC 1068 at sub-kiloparsec scales. Methods. We present the HCN (4-3) and HCO ⁺ (4-3) maps of NGC 1068 obtained with JCMT as part of the Mapping the dense molecular gas in the strongest star-forming galaxies (MALATANG) project, and perform spatially resolved analyses of their correlations with IR luminosity and soft X-ray emission. Results. The spatially resolved relations between the luminosities of IR dust emission and dense molecular gas tracers ( L _IR − L ′ _dense ) are found to be nearly linear, without clear evidence of excess contributions from AGN activity. The spatially resolved X-ray emission ( L ^gas _{0.5−2 KeV} ) displays a radially dependent twofold correlation with the star formation rate (SFR), suggesting distinct gas-heating mechanisms are at play in areas between the galaxy center and the outer regions. A super-linear scaling is obtained in galactic center regions with SFR surface densities (Σ _SFR ) > 8.2 × 10 ⁻⁶ M _⊙ yr ⁻¹ kpc ⁻² : log( L ^gas _{0.5−2 KeV} /erg s ⁻¹ ) = 2.2 log(SFR/ M _⊙ yr ⁻¹ ) + 39.1. We further find a statistically significant super-linear correlation ( β = 1.34 ± 0.86) between L ^gas _{0.5−2 KeV} /SFR and the HCN(4–3)/CO(1–0) intensity ratio, whereas no such trend is seen for HCO ⁺ (4-3)/CO(1-0) or CO(3-2)/CO(1-0). These findings indicate that AGN feedback does not dominate star formation regulation on sub-kiloparsec scales, and that the excitation of dense gas traced by HCN (4-3) may be more directly influenced by high-energy feedback processes compared to HCO ⁺ (4-3) and CO (3-2).

The core mass function (CMF) of prestellar cores is essential for understanding the initial conditions of star and cluster formation. However, the universality of the CMF and its relationship to the initial mass function (IMF) remain unclear. We study the CMF in the earliest stage of high-mass star formation using 461 prestellar core candidates and 254 protostellar cores as a part of the ALMA Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES). We find that prestellar core candidates tend to have lower masses than protostellar cores. We also find that the lifetime of prestellar cores is several times longer than the freefall time, although it approaches the freefall time as the core mass increases. The CMF, including both protostellar and prestellar cores, has a power-law slope of −2.05 ± 0.04, shallower than Salpeter’s IMF slope of −2.35. Conversely, the CMF of gravitationally bound, prestellar cores has a steeper slope (−2.32 ± 0.30), indistinguishable from Salpeter’s slope. This finding is consistent with observations in both low-mass star-forming regions and high-mass protoclusters, implying a universal core formation mechanism. The protostellar CMF with a larger maximum core mass can be reproduced by the prestellar CMF when an external gas infall is considered. The inferred mass infall rate is higher than the Bondi–Hoyle–Lyttleton accretion rate and follows a shallower mass dependence (smaller power-law index), more consistent with the tidal-lobe accretion. This may contribute to the evolution of CMFs seen in later stages.

We report the discovery of a dense molecular ringlike structure in a dense (10⁵ cm⁻³), cold (parsec-scale CO depletion at a factor of 5), and young (10⁴ yr) star-forming region G34.74−0.12, revealed by C¹⁸O (2−1), HNC (1−0), and N₂H⁺ (1−0) observations with the Atacama Large Millimeter/submillimeter Array. The ringlike structure is redshifted with respect to the clump, spanning from V _sys,lsr + 0.9 to V _sys,lsr + 2.9 km s⁻¹, with a total mass of 109 M _⊙. It is spatially coincident with 1.3 and 3.0 mm dust continuum emission from the cores, and several protostellar outflows. However, no free–free emission or H ii region is detected in association with this structure. With a slow expansion speed indicated by the position–velocity diagram, this ring structure differs from rings previously identified in more evolved star-forming regions. Possible explanations for the ring-like structure include a relic windblown bubble produced by a deeply embedded young stellar object, a hollow cavity formed by cloud–cloud interactions, a gas ring resulting from a temperature gradient, or a line-of-sight superposition of multiple outflows or dense clouds. This discovery offers a rare observational glimpse into the earliest dynamical processes involved in massive star formation.

Outflows are key indicators of ongoing star formation. We report the discovery of an unanchored forked stream within the propagating path of an extremely young protostellar outflow in the 70 μ m-dark clump G34.74-0.12, based on Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations with an angular resolution of 1 . ″ 6 (∼5000 au). This outflow originates from a 9.7 M _⊙ core, exhibits a fork-shaped stream structure in its redshifted lobe, which is traced by CO (2–1), SiO (5–4), and H ₂ CO (3 _0,3 –2 _0,2 ). It has a momentum of 13 M _⊙ km s ⁻¹ , an energy of 107 M _⊙ km ² s ⁻² , and a dynamical timescale of ∼10 ⁴ yr. Significantly, the enhanced relative abundances of SiO, H ₂ CO, and CH ₃ OH with respect to CO, along with the increased temperature at the forked point, indicate a collisional origin. The forked point does not coincide with any dust continuum core >0.1 M _⊙ . Moreover, CO (2–1) emission also traces three other outflows in this region, characterized by their masses (0.40, 0.02, and 0.15 M _⊙ ) and momenta (5.2, 0.2, and 1.8 M _⊙ km s ⁻¹ ), as part of the ALMA Survey of 70 μ m dark High-mass clumps in Early Stages project. All the newly discovered morphological and kinematic features associated with these extremely young protostellar outflows (with timescales of 10 ³ –10 ⁴ yr) suggest that the initial stages of star formation are more complicated than previously understood.

Based on the newly acquired dense gas observations from the JCMT MALATANG survey and X-ray data from Chandra, we explore the correlation between hot gas and HCN J = 4 → 3 and HCO⁺ J = 4 → 3 emission for the first time at subkiloparsec scale of five nearby star-forming galaxies, namely M82, M83, IC 342, NGC 253, and NGC 6946. We find that both HCN J = 4 → 3 and HCO⁺ J = 4 → 3 line luminosity show a statistically significant correlation with the 0.5−2 keV X-ray emission of the diffuse hot gas ( L 0.5 − 2 keV gas ). The Bayesian regression analysis gives the best fit of log ( L 0.5 − 2 keV gas / erg s − 1 ) = 2.39 log ( L HCN ( 4 − 3 ) ′ /K km s⁻¹ pc²) + 24.83 and log ( L 0.5 − 2 keV gas / erg s − 1 ) = 2.48 log ( L HCO + ( 4 − 3 ) ′ /K km s⁻¹ pc²) + 23.84, with dispersion of ∼0.69 dex and 0.54 dex, respectively. At the subkiloparsec scale, we find that the power-law index of the L 0.5 − 2 keV gas −star formation rate (SFR) relation is log ( L 0.5 − 2 keV gas / erg s − 1 ) = 1.80 log ( SFR / M ⊙ yr − 1 ) + 39.16 , deviated from previous linear relations at the global scale. This implies that the global property of hot gas significantly differs from individual resolved regions, which is influenced by the local physical conditions close to the sites of star formation.