prasantg

• Yang, Dongting; Liu, Hong li; Qin, Sheng li; Liu, Tie; Jiao, Wenyu & Garay, Guido [Vis alle 31 forfattere av denne artikkelen] (2026). Evolution of Starless Cores in Massive Clumps Seen by the ALMA ASHES and QUARKS Surveys. The Astrophysical Journal (ApJ). ISSN 0004-637X. 1006(2). doi: 10.3847/1538-4357/ae81ab. Fulltekst i vitenarkiv Vis sammendrag

  We present a systematic comparative analysis of 324 starless cores in early-phase infrared-dark clouds (IRDCs; ASHES survey) and evolved-phase infrared-bright clouds (IRBCs; QUARKS survey) using 1.3 mm continuum and line data by the Atacama Large Millimeter/submillimeter Array. Despite having comparable sizes (∼2500 au), starless cores in IRBCs exhibit systematically higher median mass (1.5 M⊙ versus 0.6 M⊙), number density, and surface density—enhancements of approximately a factor of 2 relative to starless cores in IRDCs. Starless cores in IRBCs also display relatively stronger nonthermal motions (σ ∼ 0.5 km s−1 versus 0.3 km s−1), higher total virial parameters (median αvir,tot ∼ 2.3 versus 1.0), and steeper density profiles, indicating more centrally concentrated structures in feedback-driven, turbulence-enhanced environments. These findings support a dual evolutionary origin: (i) new core formation in evolved IRBCs under altered initial conditions and (ii) subsequent dynamical mass growth via accretion from extended reservoirs. The prevalence of low-mass starless cores—even in late-stage IRBC environments—challenges models requiring massive prestellar cores and instead favors competitive-like dynamical mass accretion scenarios for high-mass star formation.

• Hoque, Ariful; Baug, Tapas; Guzman, Estrella; Lopez, Manuel Fernandez; Liu, Tie & Garay, Guido [Vis alle 28 forfattere av denne artikkelen] (2026). The ALMA-QUARKS Survey: Evidence of an Explosive Molecular Outflow in IRAS 15520-5234. The Astrophysical Journal (ApJ). ISSN 0004-637X. 1001(2). doi: 10.3847/1538-4357/ae5224. Fulltekst i vitenarkiv Vis sammendrag

  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 1048 erg. The protocluster contains 16 dense cores detected in the Atacama Large Millimeter/submillimeter Array (ALMA) band 6 continuum emission maps, having masses in the range from 0.2 to 11.0 M⊙. 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 1 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 yr. Additionally, we estimate the frequency of such explosive outflows in the Galaxy, which is one event every 83 yr. 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.

• Yang, Dongting; Liu, Hong-Li; Qin, Sheng-li; Liu, Tie; Tej, Anandmayee & Zhang, Siju [Vis alle 35 forfattere av denne artikkelen] (2025). The ALMA-QUARKS Survey: Evidence of a Candidate High-mass Prestellar Core Aside a Bright-rimmed Cloud IRAS 18290-0924. The Astrophysical Journal (ApJ). ISSN 0004-637X. 995(2). doi: 10.3847/1538-4357/ae2250. Fulltekst i vitenarkiv Vis sammendrag

  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 3 mm ATOMS and 1.3 mm 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 3 mm continuum data of the ATOMS survey (∼2 , ∼10,000 au at 5.3 kpc) has a mass ranging from 27 to 68 M ⊙ for temperatures 10–22 K within a radius of ∼2800 au. The highest-resolution (∼0 . 3, ∼1500 au) observations of this source presented to date from the QUARKS survey reveal no evidence of further fragmentation. Further analysis of a total ∼10 GHz bandwidth of molecular line survey does not find star formation activity (e.g., outflows and 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 vir ∼ 0.1−0.3) 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.

• Zou, Jiahang; Liu, Tie; Xu, Fengwei; Tang, Xindi; Meng, Dezhao & Zhang, Yan-Kun [Vis alle 22 forfattere av denne artikkelen] (2025). The ALMA-ATOMS-QUARKS Survey: Resolving a Chemically Rich Massive Protostellar Outflow. The Astrophysical Journal (ApJ). ISSN 0004-637X. 995(1). doi: 10.3847/1538-4357/ae1cad. Fulltekst i vitenarkiv Vis sammendrag

  We present a comprehensive study on the physical and chemical structures of a chemically rich bipolar outflow in a high-mass star-forming region IRAS 16272−4837 (SDC335), utilizing high-resolution spectral line data at 1.3 and 3 mm dual bands from the Atacama Large Millimeter/submillimeter Array, ATOMS, and QUARKS surveys. The high-velocity jet is enveloped by a lower-velocity outflow cavity, containing bright knots that show enhanced molecular intensities and elevated excitation temperatures. Along the outflow, we have identified 35 transitions from 22 molecular species. By analyzing the spatial distribution and kinematics of these molecular lines, we find that the molecular inventory in the outflow is regulated by three processes: (i) direct entrainment from the natal molecular core by the outflow; (ii) shock-induced release of molecules or atoms from dust grains; and (iii) thermal desorption and gas-phase reactions driven by shock heating. These results confirm that outflows are not only dynamical structures but also active chemical factories, where entrainment, shocks, and thermal processing jointly enrich the molecular content. Our findings confirmed that outflow chemistry has a multiorigin nature, and provide critical insights into chemical evolution during high-mass star formation.

• Gorai, P.; Saberi, M.; Khouri, T. & Danilovich, T. (2025). Probing sulphur chemistry in oxygen-rich asymptotic giant branch stars with ALMA. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 704. doi: 10.1051/0004-6361/202555994. Fulltekst i vitenarkiv Vis sammendrag

  Context. Sulphur and its isotopic ratios play a crucial role in our understanding of the physical properties of astrophysical environments; in particular, providing key insights into nucleosynthesis, interstellar medium processes, star formation, planetary system evolution, and galactic chemical evolution. Aims. We aim to investigate the distribution of sulphur species - SO 2 , 34 SO 2 , SO, and 34 SO - towards a sample of five oxygen-rich asymptotic giant branch (AGB) stars, along with measurements of excitation temperature, column density, and isotopic ratios. Methods. We used ALMA Band 6, 7, and 8 data of o Ceti, R Dor, W Hya, R Leo, and EP Aqr. SO 2 , 34 SO 2 , SO, and 34 SO were detected towards AGB stars using the CASSIS software. To estimate the gas temperature and column density of these species, we applied the rotational diagram method (when applicable) and the Markov chain Monte Carlo method, assuming local thermodynamic equilibrium (LTE). Finally, line imaging of different transitions was performed to infer the distributions of the detected sulphur-bearing species in our sample. Results. The measured excitation temperatures of SO 2 for our sample sources range from ∼200 to 600 K, with estimated column densities in the range of 1-7 × 10 16 cm −2 . The excitation temperatures estimated using 34 SO 2 are comparable or slightly lower, while the column densities are about an order of magnitude lower than those of SO 2 . Our measured 32 S/ 34 S ratios for R Dor and W Hya are close to the solar value; however, the measured value for o Ceti is slightly higher, and the measured values for EP Aqr and R Leo are lower. Finally, spatial analysis shows that most detected lines appear as centralized emissions. Moreover, the high excitation transitions of SO 2 show compact emission and probe hot gas of the inner region circumstellar envelopes (CSEs), whereas low-excitation transitions trace slightly extended structures. However, we find some differences in the emission of detected species across our sample. Conclusions. The excitation temperature of the observed regions of the CSE can be probed using the SO 2 molecule. The morphological correlation between SO and SO 2 emissions suggests that they are chemically linked. Differences in the emission distributions of the detected species across our sample of low mass-loss rate AGB stars such as (i) centralized emission towards o Ceti with irregular emission shapes, (ii) centralized emission with ordered circular features towards R Leo and W Hya, (iii) clumpy emission features in R Dor, and (iv) unresolved emission in Ep Aqr may arise from several factors, i.e. the physical conditions of the sources (e.g. density and temperature structures of the CSEs), source multiplicity, outflows, rotation, or other associated physical processes such as thermal and nonthermal desorption, the effects of UV photons and cosmic rays, and finally the resolution of our observations. Nonetheless, the predominantly centralized distributions of SO and SO 2 in our sample support previous findings for low mass-loss rate AGB stars. Our measured 32 S/ 34 S ratios for the two stars R Dor and W Hya agree well with solar values within uncertainties, indicating that these ratios likely reflect the isotopic composition of the stars’ natal clouds and deviate for three stars ( o Ceti, R Leo, and EP Aqr), which could be due to the metallicity and/or excitation conditions within various sources.

• Gorai, Prasanta; Taniguchi, Kotomi; Tan, Jonathan C.; Gómez-Garrido, Miguel; Rosero, Viviana & Jiménez-Serra, Izaskun [Vis alle 14 forfattere av denne artikkelen] (2025). The SOFIA Massive (SOMA) star formation Q-band follow-up: Hydrogen recombination lines towards high-mass protostars. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 702. doi: 10.1051/0004-6361/202556220. Fulltekst i vitenarkiv Vis sammendrag

  Context . Hydrogen recombination lines (HRLs) are valuable diagnostics of the physical conditions in ionized regions surrounding high-mass stars. Understanding these lines, including broadening mechanisms and intensity trends, can provide insights into HII region densities, temperatures, and kinematics. Aims . This study aims to investigate the physical properties of ionized gas around massive protostars by analysing the HRLs (H α and H β ) in the Q band. Methods . We carried out observations using the Yebes 40m radio telescope in the Q band (30.5–50 GHz) towards six high-mass protostars selected from the SOMA Survey (G45.12+0.13, G45.47+0.05, G28.20−0.05, G35.20−0.74, G19.08−0.29, and G31.28+0.06). The observed line profiles were analysed to assess broadening mechanisms, and electron densities and temperatures were derived. The results were compared with available Q-band data from the TianMa 65-m Radio Telescope (TMRT) that have been reported in the literature, and ALMA Band 1 (35–50 GHz) Science Verification observations towards Orion KL, analysed in this study. Results . A total of eight H α (n = 51 to 58) and ten H β (n = 64 to 73) lines were detected towards G45.12+0.13, G45.47+0.05, and G28.20−0.05; there were no detections in other sources. We derived electron densities of ~1−5 × 10 6 cm −3 and temperatures of 8000–10 000 K for the sources. However, for Orion KL, we obtained an electron density one order of magnitude lower, while its temperature was found to be more similar. Interestingly, G45.12 and G28.20 show an increasing intensity trend with frequency for both H α and H β transitions, contrary to the decreasing trend observed in Orion KL. Conclusions . The line widths of the detected HRLs indicate contributions from both thermal and dynamical broadening, suggesting the presence of high-temperature ionized gas that is likely kinematically broadened (e.g. due to turbulence, outflows, rapid rotation, or stellar winds). Pressure broadening caused by electron density may also have a minor effect. We discuss different scenarios to explain the measured line widths of the HRLs. The contrasting intensity trends between the sources may reflect variations in local physical conditions or radiative transfer effects, highlighting the need for further investigation through higher-resolution observations and detailed modelling.

• Mai, Xiaofeng; Liu, Tie; Liu, Xunchuan; Zhang, Bo; Goldsmith, Paul F. & Evans, Neal J. [Vis alle 45 forfattere av denne artikkelen] (2025). A misaligned protostellar disk fed by gas streamers in a barred spiral-like massive dense core. Science Advances. 11(38). doi: 10.1126/sciadv.ady6953. Fulltekst i vitenarkiv Vis sammendrag

  High-mass stars, born in massive dense cores (MDCs), profoundly affect 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 multiscale [40 to 2500 astronomical units (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 ~7500 au central bar, which channels gas to a ~2000 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. These multiscale 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 buildup of a massive disk.

• Yang, Dongting; Liu, Hong-Li; Liu, Tie; Liu, Xunchuan; Xu, Fengwei & Qin, Sheng-Li [Vis alle 46 forfattere av denne artikkelen] (2025). The ALMA-QUARKS Survey. III. Clump-to-core Fragmentation and Searches for High-mass Starless Cores. Astrophysical Journal Supplement Series. ISSN 0067-0049. 280(1). doi: 10.3847/1538-4365/adf847. Fulltekst i vitenarkiv Vis sammendrag

  The Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures (QUARKS) survey observed 139 infrared-bright (IR-bright) massive protoclusters at 1.3 mm wavelength with the Atacama Large Millimeter/submillimeter Array (ALMA). This study investigates clump-to-core fragmentation and searches for candidate high-mass starless cores within IR-bright clumps using combined ALMA 12 m (C-2) and Atacama Compact Array 7 m data, providing ∼1 (∼0.02 pc at 3.7 kpc) resolution and ∼0.6 mJy beam −1 continuum sensitivity (∼0.3 M ⊙ at 30 K). We identified 1562 compact cores from 1.3 mm continuum emission using getsf . Observed linear core separations ( λ obs ) are significantly less than the thermal Jeans length ( λ J ), with the λ obs / λ J ratios peaking at ∼0.2. This indicates that thermal Jeans fragmentation has taken place within the IR-bright protocluster clumps studied here. The observed low ratio of λ obs / λ J  ≪ 1 could be the result of evolving core separation or hierarchical fragmentation. Based on associated signatures of star formation (e.g., outflows and ionized gas), we classified cores into three categories: 127 starless, 971 warm, and 464 evolved cores. Two starless cores have masses exceeding 16 M ⊙ , and represent high-mass candidates. The scarcity of such candidates suggests that competitive accretion-type models could be more applicable than turbulent core accretion-type models in high-mass star formation within these IR-bright protocluster clumps.

• Hoque, Ariful; Baug, Tapas; Dewangan, Lokesh K.; Juvela, Mika; Tej, Anandmayee & Goldsmith, Paul F. [Vis alle 28 forfattere av denne artikkelen] (2025). The ALMA-ATOMS Survey: Exploring Protostellar Outflows in HC3N. The Astrophysical Journal (ApJ). ISSN 0004-637X. 987(2). doi: 10.3847/1538-4357/add928. Fulltekst i vitenarkiv Vis sammendrag

  We present the first systematic study of bipolar outflows using HC 3 N as a tracer in a sample of 146 massive star-forming regions from the Atacama Large Millimeter/submillimeter Array Three-millimeter Observations of Massive Star-forming Regions (ATOMS) survey. Protostellar outflows arise at the initial stage of star formation as a consequence of active accretion. In general, these outflows play a pivotal role in regulating the star formation processes by injecting energetic material in the parent molecular clouds. In this process, lower velocity components of outflows contain a significant portion of the energy. However, extraction of these components is difficult because the corresponding gas is often mixed with that of the ambient cloud. In our sample, we identified 44 bipolar outflows and one explosive outflow in HC 3 N ( J = 11–10). The host clumps of these outflows are found to be at different evolutionary stages, suggesting that outflows in HC 3 N are detectable in different stages of star formation. In addition, the noncorrelation of HC 3 N outflows with clump evolutionary stages suggests that HC 3 N is an unbiased tracer of outflows. Analyses revealed that HC 3 N performs slightly better in detecting low-velocity components of outflows than traditionally employed tracers such as SiO. The derived outflow parameters (i.e., outflow mass, momentum, and energy) show moderate correlations with clump mass and luminosity. Our analysis of outflow opening angles and position–velocity diagrams across the outflow lobes show that, HC 3 N is not only a good tracer of low-velocity outflows but can also detect high-velocity collimated outflows. Overall, this study indicates that HC 3 N can be used as a complementary outflow tracer along with the traditionally known outflow tracers, particularly in the detection of the low-velocity components of outflows.

• Telkamp, Zoie; Fedriani, Rubén; Tan, Jonathan C.; Law, Chi-Yan; Zhang, Yichen & Plunkett, Adele [Vis alle 19 forfattere av denne artikkelen] (2025). The SOFIA Massive (SOMA) Star Formation Survey. V. Clustered Protostars. The Astrophysical Journal (ApJ). ISSN 0004-637X. 986(1). doi: 10.3847/1538-4357/adcd79. Fulltekst i vitenarkiv Vis sammendrag

  We present ∼8–40 μ m SOFIA-FORCAST images of seven regions of “clustered” star formation as part of the SOFIA Massive Star Formation Survey. We identify a total of 34 protostar candidates and build their spectral energy distributions (SEDs). We fit these SEDs with a grid of radiative transfer models based on the turbulent core accretion (TCA) theory to derive key protostellar properties, including initial core mass, M c , clump environment mass surface density, Σ cl , and current protostellar mass, m * . We also carry out empirical graybody (GB) estimation of Σ cl , which allows a case of restricted SED fitting within the TCA model grid. We also release version 2.0 of the open-source Python package sedcreator , which is designed to automate the aperture photometry and SED building and fitting process for sources in clustered environments, where flux contamination from close neighbors typically complicates the process. Using these updated methods, SED fitting yields values of M c ∼ 30–200 M ⊙ , Σ cl,SED ∼ 0.1–3 g cm −2 , and m * ∼ 4–50 M ⊙ . The GB fitting yields smaller values of Σ cl,GB ≲ 1 g cm −2 . From these results, we do not find evidence for a critical Σ cl needed to form massive (≳8 M ⊙ ) stars. However, we do find tentative evidence for a dearth of the most massive ( m * ≳ 30 M ⊙ ) protostars in the clustered regions, suggesting a potential impact of environment on the stellar initial mass function.

• Li, Zi-Yang; Liu, Xunchuan; Liu, Tie; Qin, Sheng-Li; Goldsmith, Paul F. & García, Pablo [Vis alle 36 forfattere av denne artikkelen] (2025). The ALMA-ATOMS survey: A sample of weak hot core candidates identified through line stacking. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 697. doi: 10.1051/0004-6361/202452762. Fulltekst i vitenarkiv Vis sammendrag

  Context . Hot cores represent critical astrophysical environments for high-mass star formation, distinguished by their rich spectra of organic molecular emission lines. Nevertheless, comprehensive statistical analyses of extensive hot core samples remain relatively scarce in current astronomical research. Aims . We aim to utilize high-angular-resolution molecular line data from the Atacama Large Millimeter and Submillimeter Array (ALMA) to identify hot cores, with a particular focus on weak-emission candidates, and to provide one of the largest samples of hot core candidates to date. Methods . We propose to use spectral stacking and imaging techniques of complex organic molecules (COMs) in the ALMA-ATOMS survey, including line identification and weights, segmentation of line datacubes, resampling, stacking and normalization, moment 0 maps, and data analysis, to search for hot core candidates. The molecules involved include CH 3 OH, CH 3 OCHO, C 2 H 5 CN, C 2 H 5 OH, CH 3 OCH 3 , CH 3 COCH 3 , and CH 3 CHO. We classify cores with dense emission of CH 3 OH and at least one molecule from the other six molecules as hot core candidates. Results . In addition to the existing sample of 60 strong hot cores from the ALMA-ATOMS survey, we have detected 40 new weak candidates through stacking. All hot core candidates display compact emission from at least one of the other six COM species. For the strong sample, the stacking method provides molecular column density estimates that are consistent with previous fitting results. For the newly identified weak candidates, all species except CH 3 CHO show compact emission in the stacked image, which cannot be fully resolved spatially. These weak candidates exhibit column densities of COMs that are approximately one order of magnitude lower than the ones of the strong sample. The entire hot core sample, including the weak candidates, reveals tight correlations between the compact emission of CH 3 OH and other COM species, suggesting they may share a similar chemical environment for COMs, with CH 3 OH potentially acting as a precursor for other COMs. Among the 100 hot cores in total, 43 exhibit extended CH 3 CHO emission spatially correlated with SiO and H 13 CO + , suggesting that CH 3 CHO may form in widely distributed shock regions. Conclusions . The molecular line stacking technique is used to identify hot core candidates in this work, leading to the identification of 40 new hot core candidates. Compared to spectral line fitting methods, it is faster and more convenient, and enables weaker hot cores to be detected with greater sensitivity.

• Kou, Zhiping; Li, Xiaohu; Qin, Sheng-Li; Liu, Tie; Mannfors, E & Tang, Xindi [Vis alle 24 forfattere av denne artikkelen] (2025). ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions – XXI. A large-sample observational study of ethanol and dimethyl ether in hot cores. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 538(4), s. 2579–2645. doi: 10.1093/mnras/staf408. Fulltekst i vitenarkiv Vis sammendrag

  Hot cores, as a stage of massive star formation, exhibit abundant line emissions of complex organic molecules (COMs). We present a deep line survey of two isomers of C$_2$H$_6$O: ethanol (C$_2$H$_5$OH; EA), and dimethyl ether (CH$_3$OCH$_3$; DE) as well as their possible precursor CH$_3$OH towards 60 hot cores by using the Atacama Large Millimeter/submillimeter Array (ALMA) 3 mm line observations. EA is detected in 40 hot cores and DE is detected in 59 hot cores. Of these, EA and DE are simultaneously detected in 39 hot cores. We calculate rotation temperatures and column densities of EA and DE by using the eXtended CASA Line Analysis Software Suite (xclass) software. The average rotation temperature of EA is higher than that of DE, whereas the average column density of EA is lower than that of DE. Combined with previous studies of hot cores and hot corinos, we find strong column density correlations among EA and DE ($\rho$ = 0.92), EA and CH$_3$OH ($\rho$ = 0.82), as well as DE and CH$_3$OH ($\rho$ = 0.80). The column density ratios of EA/DE versus the column densities of CH$_3$OH remain nearly constant with values within ~1 order of magnitude. These strong correlations and the stable ratios, suggest that EA, DE, and CH$_3$OH could be chemically linked, with CH$_3$OH potentially serving as a precursor for EA and DE. Compared with chemical models, the three different warm-up time-scale models result in the systematic overproduction of EA and the systematic underproduction of DE. Therefore, our large sample observations can provide crucial constraints on chemical models.

• Bhat, Bratati; Das, Ankan; Gorai, Prasanta & Sahu, Dipen (2025). Radiative transfer modeling of the low-mass proto-binary system, IRAS 4A1 and 4A2. Life Sciences in Space Research. ISSN 2214-5524. 49, s. 48–60. doi: 10.1016/j.lssr.2025.11.002. Fulltekst i vitenarkiv Vis sammendrag

  NGC 1333 IRAS4A is a well-studied low-mass sun-like proto-binary system. It has two components, A1 and A2, which are diverse according to their physical and chemical properties. We modeled this hot corino using the RATRAN radiative transfer code and explained different spectral signatures observed towards A1 and A2, specifically for CH3OH and H2CO. Our main goal is to understand the kinematical and chemical differences between A1 and A2 and to classify their dust emission and absorption properties. We considered a simple 1D spherical infalling envelope consisting of collimated outflow in the source. Recent high-resolution interferometric observations of ALMA shed new light on why the same molecular transitions towards A1 and A2 show different spectral profiles. The significant difference between spectral profiles observed towards A1 and A2 is mainly due to the dust opacity effect. Dust continuum emission towards A1 is optically thick, causing the transitions observed in absorption. Meanwhile, A2 is optically thin, leading to the observed emission profiles, and an inverse P-Cygni profile suggests the presence of an infalling envelope. Using high-resolution observations from ALMA and VLA, we expanded our model from the millimeter wavelength range to the centimeter wavelength range. This expansion demonstrates the opacity effect, which is reduced in the centimeter wavelength range, causing us to observe the lines in emission. Using our model, we reproduced the population inversion causing maser emission of methanol 44 GHz and 95 GHz transitions.

• Zhang, C.; Liu, Tie; Jiao, Sihan; Zhu, Feng-Yao; Ren, Z.-Y. & Liu, H.-L. [Vis alle 19 forfattere av denne artikkelen] (2025). ATOMS: ALMA Three-millimeter Observations of massive Star-forming regions – XX. Probability distribution function of integrated intensity for dense molecular gas tracers. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 538(1), s. 1–10. doi: 10.1093/mnras/staf176. Fulltekst i vitenarkiv Vis sammendrag

  We report the observations of J = 1–0 of HCN, HCO+⁠, H13CO⁠, and H13CN, HCN (J = 11–10) emission towards 135 massive star-forming clumps, as part of the ALMA Three-millimeter Observations of Massive Star-forming regions Survey. We present the integrated intensity probability distribution function (I-PDF) for these molecular tracers, modelled as a combination of a lognormal distribution and a power-law tail. The molecular line luminosities for the power-law tail segment, Lmol(p)⁠, have been calculated. We have investigated the correlation between the bolometric luminosity, Lbol⁠, and the power-law part of the molecular line luminosity, Lmol(p)⁠. Our findings suggest that the scaling relationships between Lbol and Lmol(p) for HCN and HCO+ are sublinear, indicating that these molecules might not be the most effective tracers for the dense gas. In contrast, H13CN and HC3N exhibit a nearly linear relationship between Lbol and Lmol(p)⁠, indicating that they can well trace gravitationally bound dense gas. The ratios of Lbol-to-Lmol(p)⁠, serving as indicators of star formation efficiency (SFE) within massive star-forming clumps, exhibit a weak anticorrelation with the power-law index in the I-PDF. In addition, the SFE is also weakly anticorrelated with the exponent α of the corresponding equivalent density distribution. Our results implie that clumps with substantial gas accumulation may still display low star formation efficiencies.

• Chen, Li; Qin, Sheng-Li; Liu, Tie; Goldsmith, Paul F.; Liu, Xunchuan & Peng, Yaping [Vis alle 29 forfattere av denne artikkelen] (2025). The ALMA-ATOMS survey: Vibrationally excited HC3N lines in hot cores. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 694. doi: 10.1051/0004-6361/202452598. Fulltekst i vitenarkiv Vis sammendrag

  Context. Interstellar molecules are excellent tools for studying the physical and chemical environments of massive star-forming regions. In particular, the vibrationally excited HC3N (HC3N*) lines are the key tracers for probing hot cores environments. Aims. We present the Atacama Large Millimeter/submillimeter Array (ALMA) 3 mm observations of HC3N* lines in 60 hot cores and investigate how the physical conditions affect the excitation of HC3N* transitions. Methods. We used the XCLASS for line identification. Under the assumption of local thermodynamic equilibrium, we derived the rotation temperature and column density of HC3N* transitions in hot cores. Additionally, we calculated the H2 column density and number density, along with the abundance of HC3N* relative to H2, to enable a comparison of the physical properties of hot cores with different numbers of HC3N* states. Results. We have detected HC3N* lines in 52 hot cores, 29 of which show more than one vibrationally excited state. Hot cores with higher gas temperatures have more detections of these vibrationally excited lines. The excitation of HC3N* requires dense environments, and its spatial distribution is affected by the presence of UC HII regions. The observed column density of HC3N* contributes to the number of HC3N* states in hot-core environments. Conclusions. After analyzing the various factors influencing HC3N* excitation in hot cores, we conclude that the excitation of HC3N* is mainly driven by mid-IR pumping, while collisional excitation is ineffective.

• Cosentino, G.; Jiménez-Serra, I.; Barnes, A.T.; Tan, J.C.; Fontani, F. & Caselli, P. [Vis alle 14 forfattere av denne artikkelen] (2025). Interaction between the supernova remnant W44 and the infrared dark cloud G034.77-00.55: Shock induced star formation. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 693. doi: 10.1051/0004-6361/202452329. Fulltekst i vitenarkiv Vis sammendrag

  Context. We have studied the dense gas morphology and kinematics towards the infrared dark cloud (IRDC) G034.77-00.55, shock-interacting with the SNR W44, to identify evidence of early-stage star formation induced by the shock. Aims. We used high angular resolution N2H+(1−0) images across G034.77-00.55, obtained with the Atacama Large Millimeter/sub-Millimeter Array. N2H+ is a well-known tracer of dense and cold material, optimal for identifying gas that has the highest potential to harbour star formation. Methods. The N2H+ emission is distributed in two elongated structures, one towards the dense ridge at the edge of the source and one towards the inner cloud. Both elongations are spatially associated with well-defined mass-surface density features. The velocities of the gas in the two structures (i.e. 38–41 km s−1 and 41–43 km s−1) are consistent with the lowest velocities of the J- and C-type parts, respectively, of the SNR-driven shock. A third velocity component is present at 43–45.5 km s–1. The dense gas shows a fragmented morphology with core-like fragments at scales consistent with the Jeans lengths, masses of ~1–20 M⊙, densities of (n(H2)≥105 cm–3) sufficient to host star formation in free-fall timescales (a few 104 yr), and with virial parameters that suggest a possible collapse. Results. The W44 driven shock may have swept up the encountered material, which is now seen as a dense ridge, almost detached from the main cloud, and an elongation within the inner cloud, well constrained in both N2H+ emission and mass surface density. This shock compressed material may have then fragmented into cores that are either in a starless or pre-stellar stage. Additional observations are needed to confirm this scenario and the nature of the cores.

• Ghosh, Rana; Das, Ankan; Gorai, Prasanta; Mondal, Suman Kumar; Furuya, Kenji & Tanaka, Kei E. I. [Vis alle 7 forfattere av denne artikkelen] (2024). Understanding the various evolutionary stages of the low-mass star-formation process by SO and SO2. Frontiers in Astronomy and Space Sciences. 11. doi: 10.3389/fspas.2024.1427048. Fulltekst i vitenarkiv Vis sammendrag

  SO and SO2 are two potential candidates to trace the different evolutionary phases of the low-mass star-formation process. Here, we report observations of SO and SO2 along with their isotopologues, 34SO and 34SO2, respectively, in four distinct phases of the low-mass star-formation process (prestellar core, first hydrostatic core, Class 0, and Class I) with an unbiased survey carried out using the Institut de Radioastronomie Millimetrique (IRAM) 30 m telescope. Interestingly, the estimated abundances of SO and SO2 show an increasing trend from the prestellar phase to the Class 0 stage and then a decrease in the Class I phase. A similar trend is obtained for OCS and H2S. In contrast, the obtained SO/SO2 ratio decreases gradually from the prestellar core to the Class I stage. We have used the three-phase Rokko chemical code to explain our observations. The modeled abundances of SO and SO2 exhibit an increase within the inner region as the cold gas transforms into a hot gas. The modeled abundance ratio of SO to SO2 exhibits a notably high value in cold gas environments. This ratio decreases to less than 1 within the temperature range of 100–300 K and then increases to approximately 1 beyond 300 K. In the outer region, the simulated ratio consistently exceeds the value of 1. Our work is an observational testbed for modeling the chemistry of SO/SO2 during low-mass star formation. However, our findings may require more sample sources with higher resolution and a more robust model for validation.

• Ramachandran, R.; Sil, Milan; Gorai, Prasanta; Meka, J.K.; Sundararajan, Pavithraa & Lo, J.-I. [Vis alle 15 forfattere av denne artikkelen] (2024). Experimental and Computational Study of Ethanolamine Ices under Astrochemical Conditions. The Astrophysical Journal (ApJ). ISSN 0004-637X. 975(2). doi: 10.3847/1538-4357/ad77c5. Fulltekst i vitenarkiv Vis sammendrag

  Ethanolamine (NH2CH2CH2OH) has recently been identified in the molecular cloud G+0.693-0.027, situated in the SgrB2 complex in the Galactic center. However, its presence in other regions, and in particular in star-forming sites, is still elusive. Given its likely role as a precursor to simple amino acids, understanding its presence in the star-forming region is required. Here, we present the experimentally obtained temperature-dependent spectral features and morphological behavior of pure ethanolamine ices under astrochemical conditions in the 2–12 μm (MIR) and 120–230 nm (VUV) regions for the first time. These features would help in understanding its photochemical behavior. In addition, we present the first chemical models specifically dedicated to ethanolamine. These models include all the discussed chemical routes from the literature, along with the estimated binding energies and activation energies from quantum chemical calculations reported in this work. We have found that surface reactions CH2OH + NH2CH2 → NH2CH2CH2OH and NH2 + C2H4OH → NH2CH2CH2OH in warmer regions (60–90 K) could play a significant role in the formation of ethanolamine. Our modeled abundance of ethanolamine complements the upper limit of ethanolamine column density estimated in earlier observations in hot core/corino regions. Furthermore, we provide a theoretical estimation of the rotational and distortional constants for various species (such as HNCCO, NH2CHCO, and NH2CH2CO) related to ethanolamine that have not been studied in existing literature. This study could be valuable for identifying these species in the future.

• Sil, M.; Roy, A.; Gorai, Prasanta; Nakatani, N.; Shimonishi, T. & Furuya, K. [Vis alle 9 forfattere av denne artikkelen] (2024). Assessing realistic binding energies of some essential interstellar radicals with amorphous solid water: A fully quantum chemical approach. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 690. doi: 10.1051/0004-6361/202451642. Fulltekst i vitenarkiv Vis sammendrag

  In the absence of laboratory data, state-of-the-art quantum chemical approaches can provide estimates of the binding energy (BE) of interstellar species with grains. Without BE values, contemporary astrochemical models are compelled to utilize wild guesses, often delivering misleading information. Here, we employed a fully quantum chemical approach to estimate the BE of seven diatomic radicals – CH, NH, OH, SH, CN, NS, and NO – that play a crucial role in shaping the interstellar chemical composition, using a suitable amorphous solid water model as a substrate since water is the principal constituent of interstellar ice in dense and shielded regions. While the BEs are compatible with physisorption, the binding of CH in some sites shows chemisorption, in which a chemical bond to an oxygen atom of a water molecule is formed. While no structural change has been observed for the CN radical, it is believed that the formation of a hemibonded system between the outer layer of the water cluster and the radical is the reason for the unusually large BE in one of the binding sites considered in our study. A significantly lower BE for NO, consistent with recent calculations, is obtained, which helps explain the recently observed HONO/NH2OH and HONO/HNO ratios in the low-mass hot corino IRAS 16293–2422 B with chemical models.

• Yang, Dongting; Liu, Hong-Li; Liu, Tie; Tej, Anandmayee; Liu, Xunchuan & He, Jinhua [Vis alle 35 forfattere av denne artikkelen] (2024). The ALMA-QUARKS Survey: Fibers’ Role in Star Formation Unveiled in an Intermediate-mass Protocluster Region of the Vela D Cloud. The Astrophysical Journal (ApJ). ISSN 0004-637X. 976(2). doi: 10.3847/1538-4357/ad8919. Fulltekst i vitenarkiv Vis sammendrag

  In this paper, we present a detailed analysis of the IRS 17 filament within the intermediate-mass protocluster IRAS 08448-4343 (of ∼103L⊙), using ALMA data from the ATOMS 3 mm and QUARKS 1.3 mm surveys. The IRS 17 filament, which spans ∼54,000 au (0.26 pc) in length and ∼4000 au (0.02 pc) in width, exhibits a complex, multicomponent velocity field and harbors hierarchical substructures. These substructures include three bundles of seven velocity-coherent fibers and 29 dense (n ∼ 108 cm−3) condensations. The fibers have a median length of ∼4500 au and a median width of ∼1400 au. Among these fibers, four are identified as "fertile," each hosting at least three dense condensations, which are regarded as the "seeds" of star formation. While the detected cores are randomly spaced within the IRS 17 filament based on the 3 mm dust continuum image, periodic spacing (∼1600 au) of condensations is observed in the fertile fibers according to the 1.3 mm dust map, consistent with the predictions of linear isothermal cylinder fragmentation models. These findings underscore the crucial role of fibers in star formation and suggest a hierarchical fragmentation process that extends from the filament to the fibers and, ultimately, to the smallest-scale condensations.

• Taniguchi, Kotomi; Gorai, Prasanta; Tan, Jonathan C.; Gómez-Garrido, Miguel; Fedriani, Rubén & Yang, Yao-Lun [Vis alle 13 forfattere av denne artikkelen] (2024). The SOFIA Massive (SOMA) Star Formation Q-band follow-up: I. Carbon-chain chemistry of intermediate-mass protostars. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 692. doi: 10.1051/0004-6361/202451499. Fulltekst i vitenarkiv Vis sammendrag

  Context. Evidence that the chemical characteristics around low- and high-mass protostars are similar has been found: notably, a variety of carbon-chain species and complex organic molecules (COMs) form around both types. On the other hand, the chemical compositions around intermediate-mass (IM) protostars (2 M⊙ < m* < 8 M⊙) have not been studied with large samples. In particular, it is unclear the extent to which carbon-chain species form around them. Aims. We aim to obtain the chemical compositions of a sample of IM protostars, focusing particularly on carbon-chain species. We also aim to derive the rotational temperatures of HC5N to confirm whether carbon-chain species are formed in the warm gas around these stars. Methods. We conducted Q-band (31.5–50 GHz) line survey observations toward 11 mainly IM protostars with the Yebes 40 m radio telescope. The target protostars were selected from a subsample of the source list of the SOFIA Massive Star Formation project. Assuming local thermodynamic equilibrium, we derived the column densities of the detected molecules and the rotational temperatures of HC5N and CH3 OH. Results. Nine carbon-chain species (HC3N, HC5N, C3H, C4H linear-H2CCC, cyclic-C3H2, CCS, C3S, and CH3CCH), three COMs (CH3OH, CH3CHO, and CH3CN), H2CCO, HNCO, and four simple sulfur-bearing species (13CS, C34S, HCS+, and H2CS) are detected. The rotational temperatures of HC5N are derived to be ~20–30 K in three IM protostars (Cepheus E, HH288, and IRAS 20293+3952). The rotational temperatures of CH3OH are derived in five IM sources and found to be similar to those of HC5N. Conclusions. The rotational temperatures of HC5N around the three IM protostars are very similar to those around low- and high-mass protostars. These results indicate that carbon-chain molecules are formed in lukewarm gas (~20–30 K) around IM protostars via the warm carbon-chain chemistry process. Thus, carbon-chain formation occurs ubiquitously in the warm gas around protostars across a wide range of stellar masses. Carbon-chain molecules and COMs coexist around most of the target IM protostars, which is similar to the situation for low- and high-mass protostars. In summary, the chemical characteristics around protostars are the same in the low-, intermediate- and high-mass regimes.

• Taniguchi, Kotomi; Gorai, Prasanta & Tan, Jonathan C. (2024). Carbon-chain chemistry in the interstellar medium. Astrophysics and Space Science. ISSN 0004-640X. 369(4). doi: 10.1007/s10509-024-04292-9. Fulltekst i vitenarkiv Vis sammendrag

  The presence of carbon-chain molecules in the interstellar medium (ISM) has been known since the early 1970s and > 130 such species have been identified to date, making up ∼ 43% of the total of detected ISM molecules. They are prevalent not only in star-forming regions in our Galaxy but also in other galaxies. These molecules provide important information on physical conditions, gas dynamics, and evolutionary stages of star-forming regions. Larger species of polycyclic aromatic hydrocarbons (PAHs) and fullerenes (C60 and C70), which may be related to the formation of the carbon-chain molecules, have been detected in circumstellar envelopes around carbon-rich Asymptotic Giant Branch (AGB) stars and planetary nebulae, while PAHs are also known to be a widespread component of the ISM in most galaxies. Recently, two line survey projects toward Taurus Molecular Cloud-1 with large single-dish telescopes have detected many new carbon-chain species, including molecules containing benzene rings. These new findings raise fresh questions about carbon-bearing species in the Universe. This article reviews various aspects of carbon-chain molecules, including observational studies, chemical simulations, quantum calculations, and laboratory experiments, and discusses open questions and how future facilities may answer them.

Se alle arbeider i NVA