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The recent detection of CN-functionalized aromatics partly addresses the long-standing mystery of the apparent absence of five- and six-membered rings in interstellar environments. Nitrogen (N)-heterocycles, which are crucial as the fundamental structures of nucleobases, have been a focus of these aromatic searches due to their biological significance. Although N-heterocycles have not been conclusively detected in astrophysical environments, their presence in chondrites and meteorites signifies their interstellar and circumstellar connection. Precise spectral data identify the unique signatures of molecules, confirming their presence in space. In this light, this work reports an extensive computational investigation on interstellar 3-pyrroline, a five-membered ring N-heterocycle. This includes an alternative formation route in cold interstellar environments and highly accurate rotational and vibrational spectroscopy. The results indicate that 3-pyrroline can form on dust grain surfaces from vinyl cyanide, as its formation from pyrrole through double hydrogenation may lead to the formation of pyrrole itself via an H2-abstraction process. 3-Pyrroline's rotational transition at 52.3 GHz offers a potential tool for its detection in cold interstellar regions. Additionally, the strongest infrared (IR) features of 3-pyrroline at 16.09 and |$\sim$| 3.50 |$\mu$| m are observable with JWST. The provided data are crucial for laboratory identification and future interstellar observations of 3-pyrroline at both radio and IR wavelengths. [ABSTRACT FROM AUTHOR]

Cold (⁠|$\sim$| 10 K) and dense (⁠|$\sim 10^{5}$| cm |$^{-3}$|⁠) cores of gas and dust within molecular clouds, known as starless and dynamically evolved pre-stellar cores, are the birthplaces of low-mass (M |$\le$| few M |$_\odot$|⁠) stars. As detections of interstellar complex organic molecules, or COMs, in starless cores has increased, abundance comparisons suggest that some COMs might be seeded early in the star formation process and inherited to later stages (i.e. protostellar discs and eventually comets). To date observations of COMs in starless cores have been limited, with most detections reported solely in the Taurus molecular cloud. It is therefore still a question whether different environments affect abundances. We have surveyed 35 starless and pre-stellar cores in the Perseus molecular cloud with the Arizona Radio Observatory (ARO) 12 m telescope detecting both methanol, CH |$_3$| OH, and acetaldehyde, CH |$_3$| CHO, in 100 per cent and 49 per cent of the sample, respectively. In the sub-sample of 15 cores where CH |$_3$| CHO was detected at |$\gt 3\sigma$| (⁠|$\sim$| 18 mK) with the ARO 12 m, follow-up observations with the Yebes 40 m telescope were carried out. Detections of formic acid, t -HCOOH, ketene, H |$_2$| CCO, methyl cyanide, CH |$_3$| CN, vinyl cyanide, CH |$_2$| CHCN, methyl formate, HCOOCH |$_3$|⁠ , and dimethyl ether, CH |$_3$| OCH |$_3$|⁠ , are seen in at least 20 per cent of the cores. We discuss detection statistics, calculate column densities, and compare abundances across various stages of low-mass star formation. Our findings have more than doubled COM detection statistics in cold cores and show COMs are prevalent in the gas before star and planet formation in the Perseus molecular cloud. [ABSTRACT FROM AUTHOR]

Aminoacetonitrile (AAN), also known as glycinenitrile, has been suggested as a possible precursor of glycine and adenine in the interstellar medium. Here, we present the chemical modelling of AAN and its isomers in hot cores using the three-phase chemical model NAUTILUS with the addition of over 300 chemical reactions of the three AAN isomers and related species. Our models predicted a peak gas-phase abundance of AAN reaching the order of 10 |$^{-8}$|⁠ , which is consistent with observation towards Sgr B2(N). Regarding the reaction pathways of AAN and its isomers, we found that AAN is primarily formed via free radical reactions on grain surfaces during the early evolutionary stages. Subsequently, it is thermally desorbed into the gas phase as the temperature rises and is then destroyed by positive ions and radicals in gas phase. The isomers of AAN are formed through the hydrogenation reaction of CH |$_3$| NCN on the grain surface and via electron recombination reactions of ion C |$_2$| H |$_5$| N |$_2^+$| in gas phase. We speculate that there is a possibility for NCCN and AAN to react with each other, eventually leading to the formation of adenine in hot cores. However, further investigation is required to understand the efficiency of grain surfaces in adenine formation, through theoretical calculations or laboratory experiments in future research. [ABSTRACT FROM AUTHOR]

A theoretical line list for |$^{15}$| NH |$_3$| CoYuTe-15 is presented based on the empirical potential energy and ab initio dipole moments surfaces developed and used for the production of the ExoMol line list CoYuTe for |$^{14}$| NH |$_3$|⁠. The ro-vibrational energy levels and wavefunctions are computed using the variational program trove. The line list ranges up to 10 000 cm |$^{-1}$| (⁠|$\lambda \ge 1$| μ m) and contains 929 795 249 transitions between 1 269 961 states with |$J\le 30$|⁠. The line list should be applicable for temperatures up to |$\sim$| 1000 K. To improve the accuracy of the line positions, a set of experimentally derived energy levels of |$^{15}$| NH |$_3$| is produced using the marvel (Measured Active Rotation Vibration Energy Level) procedure. To this end, 37 experimental sources of the line positions of |$^{15}$| NH |$_3$| available in the literature are collected, combined, and systematized to produce a self-consistent spectroscopic network of 21 095 |$^{15}$| NH |$_3$| transitions covering 40 vibrational bands ranging up to 6818 cm |$^{-1}$| and resulting in 2777 energy term values. These marvel energies are then used to replace the theoretical values in the CoYuTe-15 line list and also complemented by pseudo- marvel energies obtained by an isotopologue extrapolation using the previously reported marvel energies of the |$^{14}$| NH |$_3$| parent isotopologue of ammonia. A list of 53 856 high-resolution transitions between marvel states and theoretical intensities is provided in the HITRAN format. Comparison with the recent experimental spectra of |$^{15}$| NH |$_3$| illustrate the potential of the line list for detections and as an efficient assistant in spectroscopic assignments. The line list is available from www.exomol.com. [ABSTRACT FROM AUTHOR]

A theoretical line list for |$^{15}$| NH |$_3$| CoYuTe-15 is presented based on the empirical potential energy and ab initio dipole moments surfaces developed and used for the production of the ExoMol line list CoYuTe for |$^{14}$| NH |$_3$|⁠. The ro-vibrational energy levels and wavefunctions are computed using the variational program trove. The line list ranges up to 10 000 cm |$^{-1}$| (⁠|$\lambda \ge 1$| μ m) and contains 929 795 249 transitions between 1 269 961 states with |$J\le 30$|⁠. The line list should be applicable for temperatures up to |$\sim$| 1000 K. To improve the accuracy of the line positions, a set of experimentally derived energy levels of |$^{15}$| NH |$_3$| is produced using the marvel (Measured Active Rotation Vibration Energy Level) procedure. To this end, 37 experimental sources of the line positions of |$^{15}$| NH |$_3$| available in the literature are collected, combined, and systematized to produce a self-consistent spectroscopic network of 21 095 |$^{15}$| NH |$_3$| transitions covering 40 vibrational bands ranging up to 6818 cm |$^{-1}$| and resulting in 2777 energy term values. These marvel energies are then used to replace the theoretical values in the CoYuTe-15 line list and also complemented by pseudo- marvel energies obtained by an isotopologue extrapolation using the previously reported marvel energies of the |$^{14}$| NH |$_3$| parent isotopologue of ammonia. A list of 53 856 high-resolution transitions between marvel states and theoretical intensities is provided in the HITRAN format. Comparison with the recent experimental spectra of |$^{15}$| NH |$_3$| illustrate the potential of the line list for detections and as an efficient assistant in spectroscopic assignments. The line list is available from www.exomol.com. [ABSTRACT FROM AUTHOR]

Forsterite is a primary constituent of interstellar dust and planetary systems. It is believed to originate from the outflows of oxygen-rich stars and undergo further processing within the interstellar medium through the action of cosmic rays and shocks. Under these harsh conditions, point defects may form, such as MgO Schottky vacancies. These vacancies can then undergo atom reconstruction as part of a chemical process to maintain the system's crystalline structure. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitously observed interstellar molecules and are thought to form through gas-phase reactions akin to sooting flames. However, their role and impact on dust stability remain unknown. In this study, we employ an atomistic artificial-intelligence-based method, surrogate machine learning trained directly by density functional theory. Specifically, we utilize gofee (global optimization with first-principles energy expressions) to predict possible reconstructions of MgO vacancies on a crystalline forsterite (010) surface as an important component of interstellar dust and planetary systems. We identify nine possible reconstructions involving the formation of unbound Si and O atoms. We investigate their energy stability and find that the reconstruction of Si–O atoms stabilizes the vacancy by about 0.54 eV. Additionally, if PAHs bind with the unbound O and Si atoms of the vacancy, the vacancy is stabilized by approximately 1.76 eV. We demonstrate that PAHs, along with the reconstruction of unbound atoms on the dust surface, affect the stability of the dust, which might open up avenues for diverse chemistry. [ABSTRACT FROM AUTHOR]

We present high-spatial resolution (0.7–1.0 arcsec) submillimeter observations of continuum and molecular lines of CH |$_{3}$| OCHO, CH |$_{3}$| OCH |$_{3}$|⁠ , and H |$_{2}$| CCO toward 11 high-mass star-forming regions using the Atacama large millimetre/submillimetre array (ALMA). A total of 19 separate cores from nine high-mass star-forming regions are found to be line-rich, including high-, intermediate-, and low-mass line-rich cores. The three molecules are detected in these line-rich cores. We map the emission of CH |$_{3}$| OCHO, CH |$_{3}$| OCH |$_{3}$|⁠ , and H |$_{2}$| CCO in nine high-mass star-forming regions. The spatial distribution of the three molecules is very similar and concentrated in the areas of intense continuum emission. We also calculate the rotation temperatures, column densities, and abundances of CH |$_{3}$| OCHO, CH |$_{3}$| OCH |$_{3}$|⁠ , and H |$_{2}$| CCO under the local thermodynamic equilibrium assumption. The abundances relative to H |$_{2}$| and CH |$_{3}$| OH, and line widths of the three molecules are significantly correlated. The abundances relative to H |$_{2}$|⁠ , temperatures, and line widths of the three molecules tend to be higher in cores with higher mass and outflows detected. The possible chemical links of the three molecules are discussed. [ABSTRACT FROM AUTHOR]

We studied the physical conditions in the local interstellar medium (ISM) and at high redshift by fitting observed column densities of CO and H2 rotational levels and C  i fine-structure levels using photodissociation models calculated with the Meudon PDR code. We analysed CO absorption systems in 28 sight lines in the local ISM and seven damped Lyman-α absorption systems at high redshift, covering |$N({\rm H_2})=10^{19}\!-\!10^{21.5}\,{\rm cm}^{-2}$| and |$N({\rm CO})=10^{13}\!-\!10^{18}\,{\rm cm}^{-2}$|⁠. We constructed a method to accurately calculate CO excitation, incorporating the effects of photon trapping. Our findings indicate that in the local ISM, CO excitation is primarily driven by collisions and excitation due to the CMB radiation. We demonstrated that an increase in CO excitation observed near |$N({\rm CO})\simeq 10^{15}~{\rm cm^{-2}}$|⁠ , is attributed to an increase in gas densities from |${\simeq}100\,{\rm cm}^{-3}$| to |${\simeq}300\!-\!1000\,{\rm cm}^{-3}$|⁠. CO absorption systems in the local ISM are characterized by a gas number density of about 10–1000 cm−3, a kinetic temperature of 10–100 K, and an intensity of external UV field ranging from 0.1 to 10 units of Mathis field. Compared to the average gas probed by C  i absorption, the gas detected in CO is denser and colder, while the external UV field remains nearly constant. We observed a negative correlation between the kinetic temperature and both N (CO) and N (H2), with power-law slopes of |$-0.21\pm 0.02$| and |$-0.65\pm 0.05$|⁠ , respectively. At the same time, the gas number density exhibits a positive correlation with N (CO) and N (H2) with slopes of |$0.38\pm 0.02$| and |$1.15\pm 0.05$|⁠ , respectively. [ABSTRACT FROM AUTHOR]

We present results on simultaneous observations of Class I methanol masers at 25, 36, and 44 GHz towards 22 Galactic targets carried out with the Effelsberg 100-m telescope. The study investigates relations between the hyperfine (HF) structure of the torsion–rotation transitions in CH |$_3$| OH and maser activity. By analysing the radial velocity shifts between different maser lines together with the patterns of the HF structure based on laboratory measurements and quantum-chemical calculations, we find that in any source only one specific HF transition forms the maser emission and that this transition changes from source to source. The physical conditions leading to this selective behaviour are still unclear. Using accurate laboratory rest frequencies for the 25 GHz transitions, we have refined the centre frequencies for the HF multiplets at 36, 44, and 95 GHz: |$f_{\scriptscriptstyle 36} = (36169.2488\pm 0.0002_{\scriptscriptstyle \rm stat} \pm 0.0004_{\scriptscriptstyle \rm sys})$|  MHz. |$f_{\scriptscriptstyle 44} = (44069.4176\pm 0.0002_{\scriptscriptstyle \rm stat} \pm 0.0004_{\scriptscriptstyle \rm sys})$|  MHz, and |$f_{\scriptscriptstyle 95} = (95169.4414\pm 0.0003_{\scriptscriptstyle \rm stat} \pm 0.0004_{\scriptscriptstyle \rm sys})$|  MHz. Comparison with previous observations of 44 GHz masers performed 6–10 yr ago with a Korean 21-m Korean Very Long Baseline Interferometry Network telescope towards the same targets confirms the kinematic stability of Class I maser line profiles during this time interval and reveals a systematic radial velocity shift of |$0.013\pm 0.005$|  km s |$^{-1}$| between the two telescopes. [ABSTRACT FROM AUTHOR]

We present deep, sub-arcsecond (⁠|$\sim$| 2000 au) resolution ALMA 0.82-mm observations of the former high-mass prestellar core candidate G11.92–0.61 MM2, recently shown to be an |$\sim$| 500 au-separation protobinary. Our observations show that G11.92–0.61 MM2, located in the G11.92–0.61 protocluster, lies on a filamentary structure traced by 0.82-mm continuum and N |$_2$| H |$^+$| (4-3) emission. The N |$_2$| H |$^+$| (4-3) spectra are multipeaked, indicative of multiple velocity components along the line of sight. To analyse the gas kinematics, we performed pixel-by-pixel Gaussian decomposition of the N |$_2$| H |$^+$| spectra using scousepy and hierarchical clustering of the extracted velocity components using acorns. Seventy velocity- and position-coherent clusters (called 'trees') are identified in the N |$_2$| H |$^+$| -emitting gas, with the eight largest trees accounting for |$\gt $| 60 per cent of the fitted velocity components. The primary tree, with |$\sim$| 20 per cent of the fitted velocity components, displays a roughly north–south velocity gradient along the filamentary structure traced by the 0.82-mm continuum. Analysing an |$\sim$| 0.17 pc-long substructure, we interpret its velocity gradient of |$\sim$| 10.5 km s |$^{-1}$|  pc |$^{-1}$| as tracing filamentary accretion towards MM2 and estimate a mass inflow rate of |$\sim 1.8\times 10^{-4}$| to 1.2 |$\times 10^{-3}$|  M |$_\odot$| yr |$^{-1}$|⁠. Based on the recent detection of a bipolar molecular outflow associated with MM2, accretion on to the protobinary is ongoing, likely fed by the larger scale filamentary accretion flows. If 50 per cent of the filamentary inflow reaches the protostars, each member of the protobinary would attain a mass of 8 M |$_\odot$| within |$\sim 1.6\times 10^5$| yr, comparable to the combined time-scale of the 70- μ m- and mid-infrared-weak phases derived for ATLASGAL-TOP100 massive clumps using chemical clocks. [ABSTRACT FROM AUTHOR]

In this study, we explore the impact of the galactic interaction/mergers on the central oxygen abundance. We analyse 234 star-forming galaxies included in the Calar Alto Legacy Integral Field Area survey with integrated molecular gas observations from the Atacama Pathfinder EXperiment millimeter telescope and the CARMA interferometer. This database has the most optical integral field spectroscopy data with CO data for yet, with integrated measurements within |$\sim 1~{R_{\rm{eff}}}$|⁠. Our sample includes 125 isolated galaxies (control sample) and 109 galaxies in different merging stages. We find that despite whether the merging galaxies show an increase or decrease in their molecular gas fraction, the oxygen abundance does not vary significantly, in comparison to our control sample. Therefore, the enhancement and suppression of oxygen abundance are similar in both isolated galaxies and interacting/merging galaxies. On the contrary, regardless of the merger stage (including isolated sample), galaxies that present an increase in their specific star formation rate present a metallicity dilution. We suggest that both internal and external events affect the chemical composition of merging galaxies. [ABSTRACT FROM AUTHOR]

We present the initial data for the |$(J = 3 \rightarrow 2)$| transition of |$^{13}\text{CO}$| obtained from the central molecular zone (CMZ) of the Milky Way as part of the CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). Covering |$359^{\circ } \le l \le 1^{\circ }$| and |$|b| \le 0.5^{\circ }$| with an angular resolution of 19 arcsec, velocity resolution of 1 km s |$^{-1}$|⁠ , and rms |$\Delta {T_{\rm A}^{*}} = 0.59\, \mathrm{K}$| at these resolutions, our observations unveil the complex structure of the CMZ molecular gas in improved detail. Complemented by the |$\rm {^{12}CO}$| CHIMPS2 data, we estimate a median optical depth of |$\tau _{13} = 0.087$|⁠. The preliminary analysis yields a median |$^{13}\text{CO}$| column-density range equal to |$N(^{13}{\rm CO}) = 2{\!-\!}5 \times 10^{18}\, \mathrm{cm}^{-2}$|⁠ , median H |$_{2}$| column density equal to |$N(\mathrm{H_{2}}) = 4 \times 10^{22}\, \mathrm{cm}^{-2}$| to |$1 \times 10^{23}\, \mathrm{cm}^{-2}$|⁠. We derive |$N({\rm H_{2}})$| -based total mass estimates of |$M({\rm H}_{2}) = 2{\!-\!}6 \times 10^{7}\, \mathrm{M}_{\odot }$|⁠ , in agreement with previous studies. We analyse the relationship between the integrated intensity of |$^{13}\text{CO}$| and the surface density of compact sources identified by Herschel Hi-GAL, and find that younger Hi-GAL sources detected at 500  |$\rm{\mu m}$| but not at 70  |$\rm{\mu m}$| follow the dense gas of the CMZ more closely than those that are bright at 70  |$\rm{\mu m}$|⁠. The latter, actively star-forming sources appear to be more associated with material in the foreground spiral arms. [ABSTRACT FROM AUTHOR]

The reservoir of sulphur accounting for sulphur depletion in the gas of dense clouds and circumstellar regions is still unclear. One possibility is the formation of sulphur chains, which would be difficult to detect by spectroscopic techniques. This work explores the formation of sulphur chains experimentally, both in pure H |$_2$| S ice samples and in H |$_2$| O:H |$_2$| S ice mixtures. An ultrahigh vacuum chamber, ISAC, eqquipped with FTIR and QMS, was used for the experiments. Our results show that the formation of H |$_2$| S |$_x$| species is efficient, not only in pure H |$_2$| S ice samples, but also in water-rich ice samples. Large sulphur chains are formed more efficiently at low temperatures (⁠|$\approx$| 10 K), while high temperatures (⁠|$\approx$| 50 K) favour the formation of short sulphur chains. Mass spectra of H |$_2$| S |$_x$|⁠ , x = 2–6, species are presented for the first time. Their analysis suggests that H |$_2$| S |$_x$| species are favoured in comparison with S |$_x$| chains. Nevertheless, the detection of several S |$_x^+$| fragments at high temperatures in H |$_2$| S:H |$_2$| O ice mixtures suggests the presence of S |$_8$| in the irradiated ice samples, which could sublimate from 260 K. ROSINA instrument data from the cometary Rosetta mission detected mass-to-charge ratios 96 and 128. Comparing these detections with our experiments, we propose two alternatives: (1) H |$_2$| S |$_4$| and H |$_2$| S |$_5$| to be responsible of those S |$_3^+$| and S |$_4^+$| cations, respectively, or (2) S |$_8$| species, sublimating and being fragmented in the mass spectrometer. If S |$_8$| is the parent molecule, then S |$_5^+$| and S |$_6^+$| cations could be also detected in future missions by broadening the mass spectrometer range. [ABSTRACT FROM AUTHOR]

In comets and in the cold phase of the interstellar medium (ISM), ammonium salts are key molecular species due to their role in the retention of volatile compounds on cold surfaces. In the case of sulphur, the H |$_2$| S/OCS ratio observed in protostars could be explained by the presence of ammonium hydrosulphide (NH |$_4$| SH) salts. However, laboratory data on the properties of NH4SH in ISM cold relevant conditions are rather scarce, as they usually focus on the atmosphere of Jupiter. We propose to consolidate the laboratory data regarding NH |$_4$| SH on grains, by performing temperature programmed desorption experiments and Fourier transform infrared reflection spectroscopy. The salt was also exposed to H atoms to mimic the ISM conditions. NH |$_4$| SH was found to form in situ at 10 K, from a mixture of ammonia (NH |$_3$|⁠) and hydrogen sulphide (H |$_2$| S). The NH |$_4^+$| infrared feature (1485 cm |$^{-1}$|⁠) is the most prominent one at 80 K. As pure species, H |$_2$| S and NH |$_3$| desorb at 76 and 90 K, respectively, whereas they are released into the gas phase at 153 K when adsorbed in the form of salt. The presence of water delays the desorption of the salt until the very end of the water desorption, but does not affect the desorption kinetics. During H-exposure, the salt is dissociated and no new product was detected. As a comparative study, salts have been included in the Nautilus gas–grain model. The results show a good correlation with the observations of IRAS 16293−2422B, as opposed to when NH |$_4$| SH is not included in the model. [ABSTRACT FROM AUTHOR]

Aims. We present a new sub-grid model, HYACINTH – HYdrogen And Carbon chemistry in the INTerstellar medium in Hydro simulations – for computing the non-equilibrium abundances of H2 and its carbon-based tracers, namely CO, C, and C+, in cosmological simulations of galaxy formation. Methods. The model accounts for the unresolved density structure in simulations using a variable probability distribution function of sub-grid densities and a temperature-density relation. Included is a simplified chemical network that has been tailored for hydrogen and carbon chemistry within molecular clouds and easily integrated into large-scale simulations with minimal computational overhead. As an example, we applied HYACINTH to a simulated galaxy at redshift z ~ 2.5 in post-processing and compared the resulting abundances with observations. Results. The chemical predictions from HYACINTH are in reasonable agreement with high-resolution molecular-cloud simulations at different metallicities. By post-processing a galaxy simulation with HYACINTH, we reproduced the H I − H2 transition as a function of the hydrogen column density NH for both Milky-Way-like and Large-Magellanic-Cloud-like conditions. We also matched the NCO versus NH2 relation inferred from absorption measurements towards Milky-Way molecular clouds, although most of our post-processed regions occupy the same region as (optically) dark molecular clouds in the NCO – NH2 plane. Column density maps reveal that CO is concentrated in the peaks of the H2 distribution, while atomic carbon more broadly traces the bulk of H2 in our post-processed galaxy. Based on both the column density maps and the surface density profiles oŕ the different gas species in the post-processed galaxy, we find that C+ maintains a substantially high surŕace density out to ~10 kpc as opposed to other components that exhibit a higher central concentration. This is similar to the extended [C II] emission ŕound in some recent observations at high redshifts. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) bubble structure of the Sgr-B molecular-cloud complex is derived by a kinematical analysis of CO-line archival cube data of the Galactic Centre (GC) observed with the Nobeyama 45-m telescope. The line-of-sight depth is estimated by applying the face-on transformation method of radial velocity to the projected distance on the Galactic plane considering the Galactic rotation of the central molecular zone (CMZ). The 3D complex exhibits a conical-horn structure with the Sgr-B2 cloud located in the farthest end on the line of sight at radial velocity |$v_{\rm lsr} \sim 70$|  km s |$^{-1}$|⁠ , and the entire complex composes a lopsided bubble opening toward the Sun at |$v_{\rm lsr}\sim 50$| to 30 km s |$^{-1}$|⁠. The line-of-sight extent of the complex is |$\sim 100$|  pc according to the large velocity extent for several tens of km s |$^{-1}$| from Sgr-B2 to the outskirts. The entire complex exhibits a flattened conical bubble with full sizes |$\sim 40 \ {\rm pc} \times 20 \ {\rm pc} \times 100 \ {\rm pc}$| in the l, b and line-of-sight directions, respectively. Based on the 3D analysis, we propose a formation scenario of the giant molecular bubble structure due to a galactic bow shock, and suggest that the star formation in Sgr-B2 was enhanced by dual-side compression (DSC) of the B2 cloud by the Galactic shock wave from up-stream and expanding H  ii region from the down-stream side of the GC Arm I in Galactic rotation. [ABSTRACT FROM AUTHOR]

The molecular phase of supernova-driven outflows originates from the cold, molecular gas in the disc of a star-forming galaxy, and may carry a substantial fraction of the wind mass flux in some galaxies, but it remains poorly understood. Observations of this phase come mostly from very nearby galaxies due its low-surface brightness and covering fraction, and simulations often lack the spatial resolution necessary to resolve it. Here, we analytically estimate the survivability of this phase in order to understand under what conditions a galactic wind can contain a significant molecular phase. We show that the molecular content of outflows is primarily determined by two dimensionless numbers: a generalized Eddington ratio describing the strength of the outflow and the dissociation parameter, an ionization parameter-like quantity describing the strength of the radiation field per baryon. We apply this model to a sample of galaxies and show that, while any molecules entrained in the winds of normal star-forming galaxies should be destroyed close to the galactic disc, the outflows of strong starburst should become increasingly dominated by molecules. [ABSTRACT FROM AUTHOR]

In this work, the gas-phase ion–atom collision reaction between large cationic carbon clusters and H-atoms is investigated. The carbon cluster cations (C |$_{48-2*n}$| |$^+$|⁠ , n = [0 |$-$| 8]) are produced from the photo-fragmentation processes of large PAH (dicoronylene, DC, C |$_{48}$| H |$_{20}$|⁠) cations. The hydrogenated carbon cluster cations are efficiently formed (e.g. C |$_{44/46}$| H |$_{9}$| |$^+$|⁠), and no even–odd hydrogenated mass patterns are observed. The hydrogenation behaviour and hydrogenation rate for these carbon cluster cations are the same. With theoretical calculations, the formation and bending processes of carbon cluster cations, the structure of these newly formed hydrogenated carbon cluster cations, and the bonding energies for the hydrogenation pathways are investigated. During the formation process of carbon clusters, the zigzagged edges gradually increase, and the planar configuration tends towards a bent and folded molecular configuration, i.e. from graphene to fullerene structures. The bending process with higher exothermic energies provides a reasonable explanation for the formation of the 'magic numbers' (e.g. C-atoms = 44) carbon clusters and their greater stability. The exothermic energy for each hydrogenation reaction pathway is relatively high; consequently, the forms and the hydrogenated states of carbon clusters are complex. The hydrogenation ability of edge carbon sites is higher than that of internal carbon sites; after bending and folding, the hydrogenation ability of these originally internal carbon sites becomes higher due to structural caged. As a result, under the co-evolution interstellar chemistry network, the (hydrogenation) states and forms of carbon compounds are complicated and diverse in the ISM. [ABSTRACT FROM AUTHOR]

In this paper, we provide a highly accurate value for the binding energy of benzene to proton-ordered crystalline water ice (XIh), as a model for interstellar ices. We compare our computed value to the latest experimental data available from temperature-programmed desorption experiments and find that our binding energy value agrees well with data obtained from binding to either crystalline or amorphous ice. Importantly, our new value is lower than that used in most astrochemical networks by about nearly half its value. We explore the impact of this revised binding energy value for both an asymptotic giant branch (AGB) outflow and a protoplanetary disc. We find that the lower value of the binding energy predicted here compared with values used in the literature (4050 K versus 7587 K) leads to less depletion of gas-phase benzene in an AGB outflow, and leads to a shift outwards in the benzene snowline in the mid-plane of a protoplanetary disc. Using this new value, the AGB model predicts lower abundances of benzene in the solid phase throughout the outflow. The disc model also predicts a larger reservoir of gas-phase benzene in the inner disc, which is consistent with the recent detections of benzene for the first time in protoplanetary discs with JWST. [ABSTRACT FROM AUTHOR]

For a better understanding of the physico-chemistry in the interstellar medium, collisional data are needed. In this work, we provide rate coefficients for the recently detected by Cabezas and collaborators in 2023 sodium cyanoacetylide molecule NaC |$_{3}$| N(⁠|$X^{1}\Sigma ^{+}$|⁠) induced by collisions with He. A new two-dimensional potential energy surface (2D-PES) is derived by adopting the high-level theory of the explicitly correlated coupled cluster with single, double, and perturbative triple excitations (CCSD(T)-F12) in conjunction with the aug-cc-pVTZ basis sets. Our 2D-PES presents two minima: the global one with a well depth of |$-86.58$|  cm |$^{-1}$| and the second well with a |$-47.01$|  cm |$^{-1}$| depth. This was expected by the Natural Bond Orbital analysis showing two electrophilic zones located on Na and N linked Carbon with respective atomic charges : |$+0.96575$| and |$+0.28910$|⁠. This PES was used to calculate inelastic cross-sections within the framework of the close-coupling theory for total energies |$\le 170$|  cm |$^{-1}$| and |$J\le 22$|⁠. Using the Maxwell–Boltzmann distribution of kinetic energies, these cross-sections were integrated to generate the collisional (de)-excitation rate coefficients for temperatures below 30 K. In order to estimate the impact of the computed collisional rates, a non-local thermodynamical equilibrium radiative transfer calculation was performed. The new collisional data can allow accurate NaC |$_{3}$| N abundance determination in the interstellar medium. [ABSTRACT FROM AUTHOR]

We investigate the chemical evolution of complex organic molecules (COMs) in turbulent discs using gas-ice chemical reaction network simulations. We trace trajectories of dust particles considering advection, turbulent diffusion, gas drag, and vertical settling, for 10 |$^6$| yr in a protoplanetary disc. Then, we solve a gas-ice chemical reaction network along the trajectories and obtain the temporal evolution of molecular abundances. We find that the COM abundances in particles can differ by more than two orders of magnitude even when the ultraviolet (UV) fluence (i.e. the time integral of UV flux) received by the particles are similar, suggesting that not only the UV fluence but also the time variation of the UV flux does matter for the evolution of COMs in discs. The impact of UV fluence on molecular abundances differs between oxygen-bearing and nitrogen-bearing COMs. While higher UV fluence results in oxygen being locked into CO |$_2$|⁠ , leading to reduced abundances of oxygen-bearing COMs such as CH |$_3$| OCH |$_3$|⁠ , mild UV exposure can promote their formation by supplying the precursor radicals. On the other hand, nitrogen is not locked up into specific molecules, allowing the formation of nitrogen-bearing COMs, particularly CH |$_3$| NH |$_2$|⁠ , even for the particle that receives the higher UV fluence. We also find that the final COM abundances are mostly determined by the inherited abundances from the protostellar core when the UV fluence received by dust particles is less than a critical value, while they are set by both the inherited abundances and the chemistry inside the disc at higher UV fluence. [ABSTRACT FROM AUTHOR]

We have investigated the behaviour of three strong near-infrared diffuse interstellar bands (DIBs) at λ13177 Å, λ14680 Å, and λ15272 Å, on a larger sample of sightlines and over a wider range of extinctions than previously studied, utilizing spectra from three observatories. We applied two telluric correction techniques to reduce atmospheric contamination and have used Gaussian fits to characterize the DIB profiles and measure equivalent widths. We confirmed strong and approximately linear correlations with reddening of the λ13177 Å, λ14680 Å, and λ15272 Å DIBs, extending them to higher reddening values and strengthening their link to interstellar matter. Modelling of the λ14680 Å DIB profiles revealed intrinsic variations, including line broadening, linked to their formation processes. This effect is particularly pronounced in the Galactic Centre (GC) environment, where multiple diffuse molecular clouds along the line of sight contribute to line broadening. We have detected one new DIB candidate at λ14795 Å on sightlines with high reddening. [ABSTRACT FROM AUTHOR]

Insufficient theoretical investigation is being conducted on the spectroscopic characteristics within the infrared wavelength range of SiP, an identified interstellar molecule. Using the ic-MRCI method, potential energy functions and dipole moment functions for the ground state (⁠|${X^2}\Pi $|⁠) and low excited states (⁠|${{\rm{A}}^2}{\Sigma ^ + }$|⁠) of the SiP molecule were calculated. Based on experimental spectroscopy data, least squares fitting was used for the potential energy functions of the |${X^2}\Pi $| and |${{\rm{A}}^2}{\Sigma ^ + }$| states. By combining these potential energy and dipole moment functions, the one-dimensional Schrödinger equation was solved to obtain the vibronic energy levels and Einstein A coefficients for the electronic states. Partition functions of the SiP molecule from 0.1 to 3000 K and the radiative properties of |${X^2}\Pi \leftrightarrow {X^2}\Pi $| and |${X^{\rm{2}}}\Pi \leftrightarrow {{\rm{A}}^2}{\Sigma ^ + }$| were derived. Infrared spectroscopy of the |${X^2}\Pi $| state and ultraviolet spectroscopy of the |${X^{\rm{2}}}\Pi \leftrightarrow {{\rm{A}}^2}{\Sigma ^ + }$| transition at 100 K, a temperature crucial for astronomical research, were calculated. Results indicate that the spectral-line intensity of the |${X^{\rm{2}}}\Pi \leftrightarrow {{\rm{A}}^2}{\Sigma ^ + }$| transition is greater, making it more suitable for astronomical observation. The obtained computational results in this paper yield spectroscopic parameters for the characterization of the interstellar molecule SiP, furnishing theoretical underpinnings for subsequent experimental observations. [ABSTRACT FROM AUTHOR]

Our ability to trace the star-forming molecular gas is important to our understanding of the Universe. We can trace this gas using CO emission, converting the observed CO intensity into the H |$_2$| gas mass of the region using the CO-to-H |$_2$| conversion factor (⁠|$X_{\rm{{\small CO}}}$|⁠). In this paper, we use simulations to study the conversion factor and the molecular gas within galaxies. We analysed a suite of simulations of isolated disc galaxies, ranging from dwarfs to Milky Way-mass galaxies, that were run using the fire-2 subgrid models coupled to the chimes non-equilibrium chemistry solver. We use the non-equilibrium abundances from the simulations, and we also compare to results using abundances assuming equilibrium, which we calculate from the simulation in post-processing. Our non-equilibrium simulations are able to reproduce the relation between CO and H |$_2$| column densities, and the relation between |$X_{\rm{{\small CO}}}$| and metallicity, seen within observations of the Milky Way. We also compare to the xCOLD GASS survey, and find agreement with their data to our predicted CO luminosities at fixed star formation rate. We also find the multivariate function used by xCOLD GASS overpredicts the H |$_2$| mass for our simulations, motivating us to suggest an alternative multivariate function of our fitting, though we caution that this fitting is uncertain due to the limited range of galaxy conditions covered by our simulations. We also find that the non-equilibrium chemistry has little effect on the conversion factor (<5 per cent) for our high-mass galaxies, though still affects the H |$_2$| mass and |$L_{\rm{{\small CO}}}$| by |$\approx$| 25  per cent. [ABSTRACT FROM AUTHOR]

We performed a |$^{12}$| CO- and |$^{13}$| CO-line study of the "Brick" (G0.253+0.016) in the Galactic Center (GC) by analyzing archival data obtained with the Nobeyama 45 m telescope. We present kinematics and molecular gas distributions in the longitude–velocity diagram, and suggest that the Brick is located along the GC Arm I in the central molecular zone (CMZ), which yields a distance from the Sun of 8 kpc and a Galactocentric distance of 0.2 kpc. The major- and minor-axis diameters of the Brick are |$D_x\times D_y=8.4 \times 4.1\, {\rm pc}$| at position angles of 40 and |$130^\circ$|⁠ , respectively, and the scale radius is |$r_{\rm Bri}=\sqrt{D_x D_y}=2.96\, {\rm pc}$|⁠. The molecular mass inferred from the |$^{12}$| CO-line integrated intensity is |$M_{\mathrm{Bri};X_\mathrm{CO}}\sim 5.1\times 10^4\, M_\odot$| for a conversion factor |$X_{\rm CO;GC}=1.0\times 10^{20}$| H |$_2$| cm |$^{-2}$| [K km s |$^{-1}]^{-1}$|⁠. On the other hand, the dynamical (virial) mass for the measured velocity dispersion of |$\sigma _v=10.0\, {\rm km\ s^{-1}}$| is calculated to be |$M_{\rm Bri;vir}\sim 6.8 \times 10^4\,M_\odot$|⁠ , which yields a new conversion factor of |$X_{\rm CO;Bri}=1.3\times 10^{20}$| H |$_2$| cm |$^{-2}$| [K km s |$^{-1}]^{-1}$|⁠. The Brick's center has a cavity surrounded by a spherical molecular bubble of radius |$r_{\rm bub}=1.85$| pc and mass |$\sim 1.7\times 10^4\,M_\odot$| expanding at |$v_{\rm exp}\simeq 10 \ {\rm km\ s^{-1}}$| with a kinetic energy of |$E_0\sim 1.7\times 10^{49}$| erg. If the bubble is approximated by an adiabatic spherical shock wave, the age is estimated to be |$t\sim 2/5 r_{\rm bub}/v_{\rm exp}\sim 7.2\times 10^4$| yr. Neither non-thermal radio structures nor thermal radio emission indicative of the H  ii region are found in the archival data from MeerKAT. We suggest that the molecular bubble is a dark supernova remnant buried in the Brick, which has therefore experienced past (⁠|${\sim}0.1$| Myr ago) massive star formation with a supernova explosion. [ABSTRACT FROM AUTHOR]

We performed correlation analyses between the 12CO and 13CO J = 1–0 line intensities in order to derive the variability of the CO-to-H2 conversion factor (X CO,iso) in the central molecular zone (CMZ) of our Galaxy. New high-resolution X CO,iso maps at a resolution of ∼30″ and a longitude–velocity diagram (LVD) at resolution |${\sim }{30^{\prime\prime}}\times 2$| km s−1 are presented using the 12CO and 13CO archival survey data obtained by the Nobeyama 45 m telescope. We revealed the variation of X CO,iso in the CMZ within the range of X CO,iso ∼ (0.2–1.3) × 1020 cm−2 (K km s−1)−1, if we assume a normalization value of 0.59 × 1020 cm−2 (K km s−1)−1. The mean value is obtained as X CO,iso = (0.48 ± 0.15) × 1020 cm−2 (K km s−1)−1 in the CMZ of our Galaxy. [ABSTRACT FROM AUTHOR]

Context. 3-Hydroxypropenal (HOCHCHCHO) is the lower energy tautomer of malonaldehyde which displays a complex rotation-tunneling spectrum. It was detected somewhat tentatively toward the solar-type protostellar system IRAS 16293-2422 with ALMA in the framework of the Protostellar Interferometric Line Survey (PILS). Several transitions, however, had large residuals, preventing not only their detection, but also the excitation temperature of the species from being determined unambiguously. Aims. We want to extend the existing rotational line list of 3-hydroxypropenal to shed more light on the recent observational results and to facilitate additional radio astronomical searches for this molecule. Methods. We recorded and analyzed the rotation-tunneling spectrum of 3-hydroxypropenal in the frequency regions between 150 and 330 GHz and between 400 and 660 GHz. Transitions were searched for in the PILS observations of IRAS 16293-2422. Local thermodynamic equilibrium (LTE) models were carried out and compared to the observations to constrain the excitation temperature. Additional transitions were searched for in other ALMA archival data of the same source to confirm the presence of 3-hydroxypropenal. Results. More than 7500 different spectral lines, corresponding to more than 11 500 transitions, were assigned in the course of our investigation with quantum numbers 2 ≤ J ≤ 100, Ka ≤ 59, and Kc ≤ 97, resulting in a greatly improved set of spectroscopic parameters. The comparison between the LTE models and the observations yields an excitation temperature of 125 K with a column density N = 1.0 × 1015 cm−2 for this species. We identified seven additional lines of 3-hydroxypropenal that show a good agreement with the model in the ALMA archive data. Conclusions. The calculated rotation-tunneling spectrum of 3-hydroxypropenal has sufficient accuracy for radio astronomical searches. With the solution of the excitation temperature conundrum and the detection of seven more lines, we consider the detection of 3-hydroxypropenal toward IRAS 16293-2422 as secure. [ABSTRACT FROM AUTHOR]

Episodic accretion in protostars leads to luminosity outbursts that end up heating their surroundings. This rise in temperature pushes the snow lines back, enabling the desorption of chemical species from dust grain surfaces, which may significantly alter the chemical history of the accreting envelope. However, a limited number of extensive chemical surveys of eruptive young stars have been performed thus far. In the present study, we carry out a large spectral survey of the binary Class I protostar L1551 IRS 5, known to be a FUor-like object, in the 3 mm and 2mm bands with the IRAM-30m telescope. As a result, we detected more than 400 molecular lines. The source displays a great chemical richness with the detection of 75 species, including isotopologues. Among these species, there are 13 hydrocarbons, 25 N-bearing species, 30 O-bearing species, 15 S-bearing species, 12 deuterated molecules, and a total of 10 complex organic molecules (l-C4H2, CH3CCH, CH2DCCH, CH3CHO, CH3CN, CH3OCH3, CH3OCHO, CH3OH, CH2DOH, and HC5N). With the help of local thermodynamic equilibrium (LTE) and non-LTE models, we determined the column densities of most molecules as well as excitation and kinetic temperatures. While most of those molecules trace the cold envelope (≲20 K), the OCS and CH3OH emission arise from the warm (>100 K) innermost (<2″) regions. We compared the chemical inventory of L1551 IRS 5 and its column density ratios, including isotopic ratios, with other protostellar sources. A broad chemical diversity is seen among Class I objects. More observations with both single-dish telescopes and interferometers are needed to characterize the diversity in a larger sample of protostars, while more astrochemical models would help explain this diversity, in addition to the impact of luminosity outbursts on the chemistry of protostellar envelopes. [ABSTRACT FROM AUTHOR]

Context. Cosmic rays are a key component of the interstellar medium because they regulate the dynamics and chemical processes in the densest and coldest regions of molecular clouds. Still, the cosmic-ray ionisation rate of H2 (ζH2ion) is one of the most debated parameters characterising molecular clouds because of the uncertainties in the adopted chemical networks and analysis techniques. Aims. This work aims to homogeneously estimate the ζH2ion at parsec scales towards the Orion Molecular Clouds OMC-2 and OMC-3. We explore the change in ζH2ion across a whole star-forming region by probing a range of column densities that has never been explored before. The significant increase in statistics obtained by studying an entire region allows us to place stronger constraints on the range of ζH2ion values and exploit its connection with the physical properties of the interstellar medium. Methods. The most recent ζH2ion estimates are based on o-H2D+, which is a direct product of the interaction between cosmic rays and H2 in cold clouds. Since observations of o-H2D+ are challenging, we proxy its abundance through CO depletion by employing C18O (2–1) observations towards OMC-2 and OMC-3, taking advantage of the existing correlation between the two parameters. Using additional observations of HCO+ (1–0) and DCO+ (3–2), we determine the deuteration fraction, and we finally derive the map of ζH2ion in these two regions. Results. The C18O depletion correlates with both the total column density of H2 and the N2H+ emission across OMC-2 and OMC-3. The obtained depletion factors and deuteration fractions are consistent with previous values obtained in low- and high-mass star-forming regions. These two parameters additionally show a positive correlation in the coldest fields of our maps. We derive cosmic-ray ionisation rates of ζH2ion ~ 5 × 10-18-10-16s-1. These values agree well with previous estimates based on o-H2D+ observations. The ζH2ion also shows a functional dependence on the column density of H2 across a full order of magnitude (~1022–1023 cm−2). The estimated values of ζH2ion decrease overall for increasing N(H2), as predicted by theoretical models. Conclusions. The results delivered by our approach are comparable with theoretical predictions and previous independent studies. This confirms the robustness of the analytical framework and promotes CO depletion as a viable proxy of o-H2D+. We also explore the main limitations of the method by varying the physical size of the gas crossed by the cosmic rays (i.e. the path length). By employing a path length obtained from low-resolution observations, we recover values of the ζH2ion that are well below any existing theoretical and observational prediction. This discrepancy highlights the need for interferometric observations in order to reliably constrain the ζH2ion at parsec scales as well. [ABSTRACT FROM AUTHOR]

We have started a measurement campaign of numerous methanol isotopologs in low-lying torsional states in order to provide extensive line lists for radio astronomical observations from an adequate spectroscopic model and to investigate how the intricate vibrationtorsion-rotation interactions manifest themselves in the spectra of different isotopic species. After CD3OH and CD3OD, we turn our focus to CH3OD, which is an important species for studying deuteration in prestellar cores and envelopes that enshroud protostars. Notably, deuteration is frequently viewed as a diagnostic tool for star formation. The measurements used in this study were obtained in two spectroscopic laboratories and cover large fractions of the 34 GHz-1.35 THz range. As done in previous studies, we employed a torsion-rotation Hamiltonian model for our analysis that is based on the rho-axis method. The resulting model describes the ground and first excited torsional states of CH3OD well up to quantum numbers J ⩽ 51 and Ka ⩽ 18. We derived a line list for radio astronomical observations from this model that is accurate up to at least 1.35 THz and should be sufficient for all types of radio astronomical searches for this methanol isotopolog in these two lowest torsional states. This line list was applied to a reinvestigation of CH3OD in data from the Protostellar Interferometric Line Survey of IRAS 16293–2422 obtained with the Atacama Large Millimeter/submillimeter Array. The new accurately determined value for the column density of CH3OD implies that the deuteration in methanol differs in its two functional groups by a factor of ~7.5. [ABSTRACT FROM AUTHOR]

Context. CF+ has been established as a valuable diagnostic tool for investigating photodissociation regions (PDRs) and fluorine abundances in the Milky Way. However, its role in extragalactic environments remains largely uncharted. Aims. Our objective is to explore the significance of CF+ in the Large Magellanic Cloud (LMC) and assess its utility as a probe for examining C+ and fluorine abundances in external galaxies. Methods. We performed pointed CF+ observations toward an active star-forming region, N113 in the LMC, using the Atacama Pathfinder EXperiment 12 m submillimeter telescope. Results. We report the first discovery of CF+ in the LMC through the successful detection of the CF+ (2→1) and (3→2) lines. The excitation models indicate that CF+ emission originates from dense PDRs characterized by an H2 number density of (0.5–7.9) × 104 cm−3 in N113. Our observations provide the first constraint on the fluorine abundance in molecular clouds in the LMC, ≲1.7 × 10−9. This value is about an order of magnitude lower than those previously measured toward red giants in the LMC, indicative of fluorine deficiency in the molecular gas. The estimated column density ratio between C+ and CF+ appears to be lower than the anticipated equilibrium ratio derived from the fluorine abundance in red giants. Both phenomena can be explained by the deficiency of CF+ caused by the freeze-out of its primary chemical precursor, HF, onto dust grains. Conclusions. The deficiency of CF+ within molecular clouds suggests that the measurements presented in this work serve exclusively as conservative estimates, establishing lower bounds for both the fluorine abundance and C+ column densities in external galaxies. [ABSTRACT FROM AUTHOR]

Context. The presence of grains is key to the synthesis of molecules in the interstellar medium that cannot form in the gas phase due to its low density and temperature conditions. In these reactions, the role of the grains is to enhance the encounter rate of the reactive species on their surfaces and to dissipate the energy excess of largely exothermic reactions, but less is known about their role as chemical catalysts; namely, bodies that provide low activation energy pathways with enhanced reaction rates. Different refractory materials with catalytic properties, such as those containing space-abundant d-block transition metals like iron (Fe), are present in astrophysical environments. Aims. Here, we report for first time mechanistic insights into the Fischer-Tropsch-type (FTT) synthesis of ethanol (CH3CH2OH), through ketene (CH2CO) and acetaldehyde (CH3CHO) intermediates, and methane (CH4) via a chain growing mechanism using a single-Fe atom supported on silica (SiO2) surfaces as a heterogeneous astrocatalyst. Methods. Quantum chemical simulations based on extended periodic surfaces were carried out to characterize the potential energy surfaces of the FTT chain growing mechanism. Calculations of the binding energies of reaction intermediates and products and Rice–Ramsperger–Kassel–Marcus kinetic calculations were performed to evaluate catalytic efficiencies and determine the feasibility of the reactions in different astrophysical environments. Results. Mechanistic studies demonstrate that the FTT chain growing mechanism enters into direct competition with FTT methanol formation, since formation of the CH2 chain growth initiator is feasible. The coupling of the CH2 with CO (forming ketene) and subsequent H2 additions yield acetaldehyde and finally ethanol, while direct H2 addition to CH2 produces methane. Thermodynamically, both processes are largely exergonic, but they present energy barriers that require external energy inputs to be overcome. Kinetic calculations demonstrate the strong temperature dependency of the FTT processes as tunneling does not dominate. Conclusions. The results could explain the presence of CH3CH2OH and CH4 in diverse astrophysical regions where current models fail to reproduce their observational quantities. The evidence that the chain growing mechanism is operating opens a new reactivity paradigm toward the formation of complex organic molecules, which is constrained by the temperature-dependent behaviour of the FTT reactions and by making their energy features a crucial aspect. [ABSTRACT FROM AUTHOR]

The kinetic temperature structure of the massive filament DR21 within the Cygnus X molecular cloud complex has been mapped using the IRAM 30 m telescope. This mapping employed the para-H2CO triplet (JKaKc = 303−202, 322−221, and 321–220) on a scale of ~0.1 pc. By modeling the averaged line ratios of para-H2CO 322–221/303–202 and 321–220/303 –202 with RADEX under non local thermodynamic equilibrium (LTE) assumptions, the kinetic temperature of the dense gas was derived, which ranges from 24 to 114 K, with an average temperature of 48.3 ± 0.5 K at a density of n(H2)= 105 cm−3. In comparison to temperature measurements using NH3 (1, 1)/(2,2) and far-infrared (FIR) wavelengths, the para-H2CO(3–2) lines reveal significantly higher temperatures. The dense clumps in various regions appear to correlate with the notable kinetic temperature (Tkin ≳ 50 K) of the dense gas traced by H2CO. Conversely, the outskirts of the DR21 filament display lower temperature distributions (Tkin < 50 K). Among the four dense cores (N44, N46, N48, and N54), temperature gradients are observed on a scale of ~0.1–0.3 pc. This suggests that the warm dense gas traced by H2CO is influenced by internal star formation activity. With the exception of the dense core N54, the temperature profiles of these cores were fitted with power-law indices ranging from −0.3 to −0.5, with a mean value of approximately −0.4. This indicates that the warm dense gas probed by H2CO is heated by radiation emitted from internally embedded protostar(s) and/or clusters. While there is no direct evidence supporting the idea that the dense gas is heated by shocks resulting from a past explosive event in the DR21 region on a scale of ~0.1 pc, our measurements of H2CO toward the DR21W1 region provide compelling evidence that the dense gas in this specific area is indeed heated by shocks originating from the western DR21 flow. Higher temperatures as traced by H2CO appear to be associated with turbulence on a scale of ~0.1 pc. The physical parameters of the dense gas as determined from H2CO lines in the DR21 filament exhibit aremarkable similarity to the results obtained in OMC-1 and N113, albeit on a scale of approximately 0.1–0.4 pc. This may imply that the physical mechanisms governing the dynamics and thermodynamics of dense gas traced by H2CO in diverse star formation regions may be dominated by common underlying principles despite variations in specific environmental conditions. [ABSTRACT FROM AUTHOR]

Context. Mid-infrared emission features are important probes of the properties of ionized gas and hot or warm molecular gas, which are difficult to probe at other wavelengths. The Orion Bar photodissociation region (PDR) is a bright, nearby, and frequently studied target containing large amounts of gas under these conditions. Under the "PDRs4All" Early Release Science Program for JWST, a part of the Orion Bar was observed with MIRI integral field unit (IFU) spectroscopy, and these high-sensitivity IR spectroscopic images of very high angular resolution (0.2″) provide a rich observational inventory of the mid-infrared (MIR) emission lines, while resolving the H II region, the ionization front, and multiple dissociation fronts. Aims. We list, identify, and measure the most prominent gas emission lines in the Orion Bar using the new MIRI IFU data. An initial analysis summarizes the physical conditions of the gas and demonstrates the potential of these new data and future IFU observations with JWST. Methods. The MIRI IFU mosaic spatially resolves the substructure of the PDR, its footprint cutting perpendicularly across the ionization front and three dissociation fronts. We performed an up-to-date data reduction, and extracted five spectra that represent the ionized, atomic, and molecular gas layers. We identified the observed lines through a comparison with theoretical line lists derived from atomic data and simulated PDR models. The identified species and transitions are summarized in the main table of this work, with measurements of the line intensities and central wavelengths. Results. We identified around 100 lines and report an additional 18 lines that remain unidentified. The majority consists of H I recombination lines arising from the ionized gas layer bordering the PDR. The H I line ratios are well matched by emissivity coefficients from H recombination theory, but deviate by up to 10% because of contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni. We show how the Ne III/Ne II, S IV/S III, and Ar III/Ar II ratios trace the conditions in the ionized layer bordering the PDR, while Fe III/Fe II and Ni III/Ni II exhibit a different behavior, as there are significant contributions to Fe II and Ni II from the neutral PDR gas. We observe the pure-rotational H2 lines in the vibrational ground state from 0–0 S(1) to 0–0 S (8), and in the first vibrationally excited state from 1–1 S (5) to 1–1 S(9). We derive H2 excitation diagrams, and for the three observed dissociation fronts, the rotational excitation can be approximated with one thermal (~700 K) component representative of an average gas temperature, and one nonthermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model of the Orion Bar PDR, and find that the predicted excitation matches the data qualitatively, while adjustments to the parameters of the PDR model are required to reproduce the intensity of the 0–0 S (6) to S (8) lines. [ABSTRACT FROM AUTHOR]

Aims. We aim to identify and characterize cores in the high-mass protocluster W49A, determine their evolutionary stages, and measure the associated lifetimes. Methods. We built a catalog of 129 cores extracted from an ALMA 1.3 mm continuum image at 0.26″ (2900 au) angular resolution. The association between cores and hypercompact or ultracompact HII (H/UC HII) regions was established from the analysis of VLA 3.3 cm continuum and H30α line observations. We also looked for emission of hot molecular cores (HMCs) using the methyl formate doublet at 218.29 GHz. Results. We identified 40 cores associated with an H/UC HII region and 19 HMCs over the ALMA mosaic. The 52 cores with an H/UC HII region and/or an HMC are assumed to be high-mass protostellar cores, while the rest of the core population likely consists of prestellar cores and low-mass protostellar cores. We found a good agreement between the two tracers of ionized gas, with 23 common detections and only four cores detected at 3.3 cm and not in H30α. The spectral indexes from 3.3 cm to 1.3 mm range from 1, for the youngest cores with partially optically thick free-free emission, to about −0.1, which is for the optically thin free-free emission obtained for cores that are likely more evolved. Conclusions. Using the H/UC HII regions as a reference, we found the statistical lifetimes of the HMC and massive protostellar phases in W49N to be about 6 × 104 yr and 1.4 × 105 yr, respectively. We also showed that HMCs can coexist with H/UC HII regions during a short fraction of the core lifetime, about 2 × 104 yr. This indicates a rapid dispersal of the inner molecule envelope once the HC HII is formed. [ABSTRACT FROM AUTHOR]

Context. The James Webb Space Telescope (JWST) has captured the sharpest infrared images ever taken of the Horsehead nebula, a prototypical moderately irradiated photon-dominated region (PDR) that is fully representative of most of the UV-illuminated molecular gas in the Milky Way and star-forming galaxies. Aims. We investigate the impact of far-ultraviolet (FUV) radiation emitted by a massive star on the edge of a molecular cloud in terms of photoevaporation, ionization, dissociation, H2 excitation, and dust heating. We also aim to constrain the structure of the edge of the PDR and its illumination conditions. Methods. We used NIRCam and MIRI to obtain 17 broadband and 6 narrowband maps of the illuminated edge of the Horsehead across a wide spectral range from 0.7 to 28 µm. We mapped the dust emission, including the aromatic and aliphatic infrared (IR) bands, scattered light, and several gas phase lines (e.g., Paa, Brα, H2 1-0 S(1) at 2.12 µm). For our analysis, we also associated two HST-WFC3 maps at 1.1 and 1.6 µm, along with HST-STIS spectroscopic observations of the Ha line. Results. We probed the structure of the edge of the Horsehead and resolved its spatial complexity with an angular resolution of 0.1 to 1″ (equivalent to 2 × 10−4 to 2 × 10−3 pc or 40 to 400 au at the distance of 400 pc). We detected a network of faint striated features extending perpendicularly to the PDR front into the HII region in NIRCam and MIRI filters sensitive to nano-grain emission, as well as in the HST filter at 1.1 µm, which traces light scattered by larger grains. This may indeed figure as the first detection of the entrainment of dust particles in the evaporative flow. The filamentary structure of the 1-0 S(1) line of H2 at the illuminated edge of the PDR presents numerous sharp sub-structures on scales as small as 1.5″. An excess of H2 emission compared to dust emission is found all along the edge, in a narrow layer (width around 1″, corresponding to 2 × 10−3 pc or 400 au) directly illuminated by σ-Orionis. The ionization front and the dissociation front appear at distances 1–2″ behind the external edge of the PDR and seem to spatially coincide, indicating a very small thickness of the neutral atomic layer (below 100 au). All broadband maps present strong color variations between the illuminated edge and the internal regions. This can be explained by dust attenuation in a scenario where the illuminating star σ-Orionis is slightly inclined compared to the plane of the sky, so that the Horsehead is illuminated from behind at an oblique angle. The deviations from predictions of the measured emissions in the Hα, Paα, and Brα lines also indicate dust attenuation. With a very simple model, we used the data to derive the main spectral features of the extinction curve. A small excess of extinction at 3 µm may be attributed to icy H2O mantles onto grains formed in dense regions. We also derived attenuation profiles from 0.7 to 25 µm across the PDR. In all lines of sight crossing the inner regions of the Horsehead, especially around the IR peak position, it appears that dust attenuation is non-negligible over the entire spectral range of the JWST. [ABSTRACT FROM AUTHOR]

Aims. Astrophysical ices on dust grain mantles in the interstellar medium (ISM) and dense circumstellar envelopes (CSEs) are continuously exposed to galactic cosmic rays (GCRs). In a laboratory setting, we studied the physical and chemical modifications of ice layers induced by energetic heavy ions as GCR analogues. The ice layers used have a molecular composition similar to that of icy grain mantles. Methods. Mixtures of H2O:CO:CH3OH molecules (percentages 73:24:3, 68:30:3, and 58:38:3) were condensed on a substrate at 15 K and irradiated with 40 MeV 58Ni11+ ion beams. Irradiation-induced modifications were followed using the mid-infrared absorption spectroscopy technique. Results. We observed the evolution of infrared bands of CO2, HCO, HCOOH, CH4, H2CO,H2O2, and more complex synthesised molecules. From the molecular column densities, cross-sections and sputtering yields were determined and compared to published results of water and carbon monoxide. Analysis of the chemical modifications reveals that the precursors are easily destroyed when they are in a molecular mixture, while others are desorbed. Conclusions. The main radiolitic modifications induced by GCR irradiations are molecular decomposition and sputtering. Extrapolation to astrophysical radiation conditions shows a strong dependence on the intensity of the GCR distributions at low energies, which allows the analysis of the ice evolution at timescales comparable to those of the ISM and CSE. [ABSTRACT FROM AUTHOR]

Context. Nearby extended protoplanetary disks are commonly marked by prominent rings in dust emission, possibly carved by forming planets. High-resolution observations show that both the dust and the gas are structured. These molecular structures may be related to radial and azimuthal density variations in the disk and/or the disk chemistry. Aims. The aim of this work is to identify the expected location and intensity of rings seen in molecular line emission in gapped disks while exploring a range of physical conditions across the gap. In particular, we aim to model the molecular rings that are, in contrast with most other gapped disks, co-spatial with the dust rings at ~20 and ~200 au in the HD 100546 disk using the thermochemical code DALI. Methods. We modelled observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of CO isotopologues, [C I], HCN, CN, C2H, NO, and HCO+ in the HD 100546 disk. An axisymmetric 3D thermochemical model reproducing the radial profiles of the CO isotopologue observations and the double ring seen in continuum emission was used to make predictions for various emission lines. The effect of the amount of gas in the dust gap, the C/O ratio, an attenuated background UV radiation field, and the flaring index on the radial distribution of different molecules were investigated. Results. The fiducial model of a gapped disk with a gas cavity at 0–15 au, a dust cavity at 0–20 au, and a gas and dust gap at 40–175 au provides a good fit to the continuum and the CO isotopologues in the HD 100546 disk. In particular, the CO isotopologue emission is consistent with a shallow gas gap with no more than a factor of approximately ten drop in gas density at 40–175 au. Similar to the CO isotopologues, the HCN and HCO+ model predictions reproduce the data within a factor of a few in most disk regions. However, the predictions for the other atom and molecules, [C I], CN, C2H, and NO, neither match the intensity nor the morphology of the observations. An exploration of the parameter space shows that, in general, the molecular emission rings are only co-spatial with the dust rings if the gas gap between the dust rings is depleted by at least four orders of magnitude in gas or if the C/O ratio of the gas varies as a function of radius. For shallower gaps the decrease in the UV field roughly balances the effect of a higher gas density for UV tracers such as CN, C2H, and NO. Therefore, the CN, C2H, and NO radicals are not good tracers of the gas gap depth. In the outer regions of the disk around 300 au, these UV tracers are also sensitive to the background UV field incident on the disk. Reducing the background UV field by a factor of ten removes the extended emission and outer ring seen in CN and C2H, respectively, and reduces the ring seen in NO at 300 au. The C/O ratio primarily effects the intensity of the lines without changing the morphology much. The [C I], HCN, CN, and C2H emission all increase with increasing C/O, whereas the NO emission shows a more complex dependence on the C/O ratio depending on the disk radius. Conclusions. CO isotopologues and HCO+ emission trace gas gaps and gas gap depths in disks. The molecular rings in HCN, CN, C2H, and NO predicted by thermochemical models do not naturally coincide with those seen in the dust, contrary to what is observed in the HD 100546 disk. This could be indicative of a radially varying C/O ratio in the HD 100546 disk with a C/O above one in a narrow region across the dust rings, together with a shallow gas gap that is depleted by a factor of approximately ten in gas, and a reduced background UV field. The increase in the C/O ratio to approximately greater than one could point to the destruction of some of the CO, the liberation of carbon from ice and grains, or, in the case of the outer ring, it could point to second generation gas originating from the icy dust grains. [ABSTRACT FROM AUTHOR]

Context. The solid-state C2H2 chemistry in interstellar H2O-rich ice has been proposed to explain astronomically observed complex organic molecules (COMs), including ketene (CH2CO), acetaldehyde (CH3CHO), and ethanol (CH3CH2OH), toward early star-forming regions. This formation mechanism is supported by recent laboratory studies and theoretical calculations for the reactions of C2H2+OH/H. However, the analog reaction of C2H2+NH2 forming N-bearing species has been suggested to have a relatively low rate constant that is orders of magnitude lower than the value of C2H2+OH. Aims. This work extends our previous laboratory studies on O-bearing COM formation to investigate the interactions between C2H2 and NH3 ice triggered by cosmic ray-induced secondary UV photons under molecular cloud conditions. Methods. Experiments were performed in an ultra-high vacuum chamber to investigate the UV photolysis of the C2H2:NH3 ice mixture at 10 K. The ongoing chemistry was monitored in situ by Fourier-transform infrared spectroscopy as a function of photon fluence. The IR spectral identification of the newly formed N-bearing products was further secured by a quadrupole mass spectrometer during the temperature-programmed desorption experiment. Results. The studied ice chemistry of C2 H2 with NH2 radicals and H atoms resulting from the UV photodissociation of NH3 leads to the formation of several N-bearing COMs, including vinylamine (CH2CHNH2), acetaldimine (CH3CHNH), acetonitrile (CH3CN), ketenimine (CH2CNH), and tentatively ethylamine (CH3CH2NH2). The experimental results show an immediate and abundant CH2CHNH2 yield as the first-generation product, which is further converted into other chemical derivatives. The effective destruction and formation cross-section values of parent species and COMs were derived, and we discuss the chemical links among these molecules and their astronomical relevance. [ABSTRACT FROM AUTHOR]

Context. The Small Magellanic Cloud (SMC) is an ideal laboratory for studying the properties of star-forming regions thanks to its low metallicity, which has an impact on the molecular gas abundance. However, a small number of molecular gas surveys of the entire galaxy have been carried out in the last few years, limiting the measurements of interstellar medium (ISM) properties in a homogeneous manner. Aims. We present the CO(3-2) APEX survey at a 6 pc resolution of the bar of the SMC, observed with the SuperCAM receiver attached to the APEX telescope. This high-resolution survey has allowed us to study certain properties of the ISM and to identify CO clouds in the innermost parts of the H2 envelopes. Methods. We adopted the CO analysis in the SMC bar comparing the CO(3–2) survey with that of the CO(2–1) of a similar resolution. We studied the CO(3–2)-to-CO(2–1) ratio (R32), which is very sensitive to the environment properties (e.g., star-forming regions). We analyzed the correlation of this ratio with observational quantities that trace the star formation such as the local CO emission, the Spitzer color [70/160], and the total IR surface brightness measured from the Spitzer and Herschel bands. For the identification of the CO(3–2) clouds, we used the CPROPS algorithm, which allowed us to measure the physical properties of the clouds. We analyzed the scaling relationships of such physical properties. Results. We obtained R32 = 0.65 ± 0.02 for the SW bar and a slightly higher ratio, R32 = 0.7 ± 0.1, for N66 in the SMC. We found that R32 varies from region to region, depending on the star formation activity. In regions dominated by HII and photo-dissociated regions (e.g., N22, N66) R32 tends to be higher than the median values. Meanwhile, lower values were found toward quiescent clouds. We also found that R32 is correlated with the IR color [70/160] and the total IR surface brightness. This finding indicates that R32 increases with environmental properties, such as the dust temperature, total gas density, and radiation field. We identified 225 molecular clouds with sizes of R > 1.5 pc and signal-to-noise ratios (S/N) of >3, of which only 17 are well resolved CO(3–2) clouds with S/N ≳ 5. These 17 clouds follow consistent scaling relationships to the inner Milky Way clouds but with some departures. For instance, CO(3–2) tends to be less turbulent and less luminous than the inner Milky Way clouds of similar sizes. Finally, we estimated a median virial-based CO(3–2)-to-H2 conversion factor of 12.6−7+10M⊙ (K km s−1 pc2)−1 for the total sample. [ABSTRACT FROM AUTHOR]

Context. The star formation process leads to an increased chemical complexity in the interstellar medium. Sites associated with high-mass star and cluster formation exhibit a so-called hot core phase, characterized by high temperatures and column densities of complex organic molecules. Aims. We aim to systematically search for and identify a sample of hot cores toward the 15 Galactic protoclusters of the ALMA-IMF Large Program and investigate their statistical properties. Methods. We built a comprehensive census of hot core candidates toward the ALMA-IMF protoclusters based on the detection of two CH3OCHO emission lines at 216.1 GHz. We used the source extraction algorithm GExt2D to identify peaks of methyl formate (CH3OCHO) emission, a complex species commonly observed toward sites of star formation. We performed a cross-matching with the catalog of thermal dust continuum sources from the ALMA-IMF 1.3 mm continuum data to infer their physical properties. Results. We built a catalog of 76 hot core candidates with masses ranging from ~0.2 M⊙ to ~80 M⊙, of which 56 are new detections. A large majority of these objects, identified from methyl formate emission, are compact and rather circular, with deconvolved full width at half maximum (FWHM) sizes of ~2300 au on average. The central sources of two target fields show more extended, but still rather circular, methyl formate emission with deconvolved FWHM sizes of ~6700 au and 13 400 au. About 30% of our sample of methyl formate sources have core masses above 8 M⊙ and range in size from ~1000 au to 13 400 au, which is in line with measurements of archetypical hot cores. The origin of the CH3OCHO emission toward the lower-mass cores may be explained as a mixture of contributions from shocks or may correspond to objects in a more evolved state (i.e., beyond the hot core stage). We find that the fraction of hot core candidates increases with the core mass, suggesting that the brightest dust cores are all in the hot core phase. Conclusions. Our results suggest that most of these compact methyl formate sources are readily explained by simple symmetric models, while collective effects from radiative heating and shocks from compact protoclusters are needed to explain the observed extended CH3OCHO emission. The large fraction of hot core candidates toward the most massive cores suggests that they rapidly enter the hot core phase and that feedback effects from the forming protostar(s) impact their environment on short timescales. [ABSTRACT FROM AUTHOR]

Context. Complex organic molecules have been observed toward many protostars. Their column density ratios are generally constant across protostellar systems, with some low-level scatter. However, the scatter in the column density ratio of formamide (NH2CHO) to methanol (CH3OH), NNH2CHO/NCH3OH, is one of the highest compared to other ratios. The larger scatter for NNH2CHO/NCH3OH (or weak correlation of these two molecules) is sometimes interpreted as evidence of gas-phase formation of NH2CHO. Aims. In this work, we propose an alternative interpretation in which this scatter is produced by differences in the snowline locations related to differences in binding energies of these species (formamide typically has a ≳2000 K larger binding energy than methanol) and the small-scale structure of the envelope and the disk system. Therefore, we do not include chemistry in our models in order to isolate the effect of physical factors. We also include CH3CN in our work as a control molecule, as it has a similar binding energy to CH3OH. Methods. We used radiative transfer models to calculate the emission from NH2CHO, CH3OH, and CH3CN in protostellar systems with and without disks. The abundances of these species were parameterized in our models, and we fit the calculated emission lines to find the column densities and excitation temperatures of these species, as done in real observations. Results. Given the difference in binding energies of NH2CHO and CH3OH, we find the gas-phase NNH2CHO/NCH3OH needs to be multiplied by a correction factor of approximately ten in order to give the true abundance ratio of these two species in the ices. This factor is much smaller (i.e., ~2) for NCH3CN/NCH3OH (the control molecule). We find that models with different disk sizes, luminosities, and envelope masses produce a scatter in this correction factor, and hence in NNH2CHO/NCH3OH comparable with that of observations. The scatter in NNH2CHO/NCH3OH is larger than that of NCH3CN/NCH3OH in models consistent with the observations. However, the scatter in the models for NCH3CN/NCH3OH is smaller than observations by a factor of around two, as expected from the similar binding energies of CH3OH and CH3CN pointing to the need for some chemical effects in the gas or ice to explain the observed ratios. We show that the scatter in NNH2CHO/NCH3OH will be lower than previously measured if we correct for the difference in sublimation temperatures of these two species in observations of ~40 protostellar systems with ALMA. Conclusions. The scatter in NNH2CHO/NCH3OH (or the ratio of any two molecules with a large binding energy difference) can be partially explained by the difference in their binding energies. Correction for this bias makes the scatter in this ratio similar to that in ratios of other complex organics in the observations, making NH2CHO a "normal" molecule. Therefore, we conclude that gas-phase chemistry routes for NH2CHO are not necessary to explain the larger scatter of NNH2CHO/NCH3OH compared with other ratios. [ABSTRACT FROM AUTHOR]

Phosphorus plays an essential role in prebiotic chemistry. The origin of P-bearing molecules in the protostellar gas remains highly uncertain. Only PO and PN have been detected towards low-mass star-forming regions and their emission is mainly associated with outflow shocks. In order to make progress in the characterisation of P-chemistry, we present NOEMA observations of PO and PN at 3″−4″ resolution towards the outflow shock region L1157-B1. Our resolved observations confirm the association of both P species with the apex of the bow shock. High-velocity emission is detected in the compact region where the jet impacts the shock. Analysis of the spatial distributions of PO and PN indicates that these molecules are not sputtered from the icy mantles of dust grains; they are the gas-phase products of a P-mother species released in the shock. PO appears to form first in the gas phase, followed by PN, which remains longer in the shock, when PO is no longer detected. Variations of the PO/PN abundance ratio in the range 1–5 are detected over the apex and confirm the short time variability of P-chemistry, which typically lasts a few hundred years. These results are consistent with the previous modelling of P-chemistry in L1157-B1. Complementary observations of N-bearing species at high angular resolution are needed to better understand the formation pathways of PO and PN. [ABSTRACT FROM AUTHOR]

Nucleobases are essential molecules for life, forming integral parts of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in all terrestrial life forms. Despite evidence of their abiotic synthesis in meteorites and laboratory simulations of interstellar medium (ISM) conditions, nucleobases have not been detected in the ISM. This study investigates the infrared spectra of uracil, cytosine, and thymine – pyrimidine nucleobases – embedded in an ice mixture simulating common volatiles found in protostellar discs. Our objective was to explore the feasibility of identifying unique infrared bands of pyrimidines in the ISM, despite significant overlapping absorption features from simpler, more abundant interstellar species such as H2O, CO, CH3OH, and NH3. Laboratory results revealed that although two common bands (1240 and 760 cm−1 in uracil; 1236 and 763 cm−1 in cytosine; and 1249 and 760 cm−1 in thymine) were identified, the detection of these bands in space is challenged by overlapping absorption features. Recent observations with the JWST have shown that interstellar organic species exhibit infrared signals within similar ranges, making it impossible to distinguish pyrimidine bands from these organics. Thus, detecting pyrimidines with current telescopes is infeasible, not due to sensitivity limitations or the need for more powerful instrumentation, but because of the intrinsic overlap in spectral features. This study complements previous research on purines by examining pyrimidines and including the impact of common ISM volatiles in the ice composition. The results highlight the significant challenges in detecting complex molecules in the ISM, underscoring the importance of understanding the spectral complexities and interactions to interpret astronomical observations accurately. [ABSTRACT FROM AUTHOR]

We present synthetic line observations of a simulated molecular cloud, utilizing a self-consistent treatment of the dynamics and time-dependent chemical evolution. We investigate line emission from the three most common CO isotopologues (12CO, 13CO, C18O) and six supposed tracers of dense gas (NH3, HCN, N2H+, HCO+, CS, HNC). Our simulation produces a range of line intensities consistent with that observed in real molecular clouds. The HCN-to-CO intensity ratio is relatively invariant with column density, making HCN (and chemically similar species such as CS) a poor tracer of high-density material in the cloud. The ratio of N2H+ to HCN or CO, on the other hand, is highly selective of regions with densities above |$10^{22} \, {\rm cm}^{-2}$|⁠ , and the N2H+ line is a very good tracer of the dynamics of high volume density (⁠|$\gt 10^4 \, {\rm cm}^{-3}$|⁠) material. Focusing on cores formed within the simulated cloud, we find good agreement with the line intensities of an observational sample of prestellar cores, including reproducing observed CS line intensities with an undepleted elemental abundance of sulphur. However, agreement between cores formed in the simulation, and models of isolated cores which have otherwise-comparable properties, is poor. The formation from and interaction with the large-scale environment has a significant impact on the line emission properties of the cores, making isolated models unsuitable for interpreting observational data. [ABSTRACT FROM AUTHOR]

Astrochemical models are important tools to interpret observations of molecular and atomic species in different environments. However, these models are time-consuming, precluding a thorough exploration of the parameter space, leading to uncertainties and biased results. Using neural networks to simulate the behaviour of astrochemical models is a way to circumvent this problem, providing fast calculations that are based on real astrochemical models. In this paper, we present a fast neural emulator of the astrochemical code Nautilus based on conditional neural fields. The resulting model produces the abundance of 192 species for arbitrary times between 1 and 107 yr. Uncertainties well below 0.2 dex are found for all species, while the computing time is of the order of 104 smaller than Nautilus. This will open up the possibility of performing much more complex forward models to better understand the physical properties of the interstellar medium. As an example of the power of these models, we ran a feature importance analysis on the electron abundance predicted by Nautilus. We found that the electron density is coupled to the initial sulphur abundance in a low-density gas. Increasing the initial sulphur abundance from a depleted scenario to the cosmic abundance leads to an enhancement of an order of magnitude of the electron density. This enhancement can potentially influence the dynamics of the gas in star formation sites. [ABSTRACT FROM AUTHOR]

This paper presents maps of the J=2-1 transition of CO towards the Draco nebula intermediate-velocity cloud (IVC). The maps cover 8500 square arcmin with a velocity resolution of 0.33 km s |$^{-1}$| and angular resolution of 38 |${\rm arcsec}$|⁠ , or 0.11 pc at the cloud distance of 600 pc. The mapped area includes all the emission detected by the Herschel satellite with 250 |$\mu$| m intensity >5 MJy sr−1. Previously published observations of the far-infrared (far-IR) emission and the 21 cm line of HI are used to derive the column density distribution of H |$_2$| and the abundance ratio CO/H |$_2$|⁠ , as well as the distribution of the molecular fraction of hydrogen, which approaches 90 per cent over much of the brighter parts of the nebula. The CO emission is highly clumpy and closely resembles the structures seen in far-IR images. The kinematics of the CO show supersonic motions between clumps but near-thermal to trans-sonic motions within clumps, consistent with model predictions that the scale length for dissipation of supersonic turbulence should be |$\sim 0.1$| pc, mediated by kinematic viscosity and/or ambipolar diffusion. Different parts of the nebula show evidence for a spread of molecular formation time-scales of a few 10 |$^5$| yr, comparable with the dynamical time-scale of the infalling gas. The IVC will likely merge with the Galactic interstellar medium in |$\sim 10^7$| yr, and the densest clumps may form an unbound cluster of low-mass stars. [ABSTRACT FROM AUTHOR]

Imidogen (NH) is a reactive molecule whose presence in astrochemical environments is of interest due to its role in the formation of nitrogen-containing molecules and as a potential probe of nitrogen abundance. Spectroscopic NH monitoring is useful for Earth-based combustion and photolysis processes of ammonia and other nitrogen-containing species. NH is also relevant to ultracold molecular physics and plasma studies. To enable these diverse applications, high-quality molecular spectroscopic data are required. Here, a new line list with significant advantages over existing data is presented. Most notably, this line list models isotopologue spectroscopy and forbidden transitions (important for NH visible absorption), alongside some overall improvements to accuracy and completeness. This approach takes advantage of existing experimental data (from a previous MARVEL compilation) and perturbative line lists together with new MRCI ab initio electronic data. These are used to produce a novel variational spectroscopic model and trihybrid line list for the main 14N1H isotopologue, as well as isotopologue-extrapolated hybrid line lists for the 14N2H, 15N1H, and 15N2H isotopologues. The new 14N1H ExoMol-style trihybrid line list, kNigHt , comprises 4076 energy levels (1078 experimental) and 327 014 transitions up to 47 500 cm−1 (211 nm) between five low-lying electronic states (X 3Σ−, a 1Δ, b 1Σ+, A 3Π, and c 1Π). For most anticipated applications aside from far-infrared studies, this line list will be of sufficient quality; any improvements should focus on the b 1Σ+ energies, and the a 1Δ – A 3Π and b 1Σ+ – A 3Π spin–orbit couplings. [ABSTRACT FROM AUTHOR]

The presence in the interstellar medium of several imines suggests that other molecules of the same family could be present as well. The propargylimine molecule (HCCCHNH), which arises from CCH substitution on the C atom of methanimine (H2CNH), the simplest imine, has been recently detected in space. Therefore, the analogous CCH derivative substituted on the N atom, known as N-ethynylmethanimine (H2CNCCH), is a good candidate to be observed as well. To allow for its astronomical detection we have investigated its laboratory rotational spectra. The species has been produced by an electric discharge of acetonitrile (CH3CN) and acetylene (HCCH) in argon, and its rotational spectrum between 9 and 40 GHz has been characterized using a Balle–Flygare narrow band-type Fourier-transform microwave spectrometer. The spectral analysis allowed us to derive accurate spectroscopic parameters to obtain reliable frequency predictions for astronomical searches in different sources. We searched for H2CNCCH in several molecular clouds, G+0.693−0.027, L483, and TMC-1, but did not detect it. The upper limits to its abundance derived are consistent with a preference of the CCH substitution of H2CNH on the C atom rather than on the N atom, in line with quantum chemical calculations on the reaction between CCH and H2CNH. [ABSTRACT FROM AUTHOR]

Given the complex nature of galaxies' interstellar medium (ISM), multiwavelength data are required to probe the interplay among gas, dust, and stellar populations. Spiral galaxies are ideal laboratories for such a goal as they are rich in gas and dust. Using carbon monoxide (CO) along with GALEX far-ultraviolet (FUV) and Spitzer near-infrared (NIR) data we probe the correlations amongst the properties of stellar populations, gas, and dust over the disc of the spiral galaxy NGC 1055 at multiple angular resolutions, that is, 2, 4, and 17 arcsec corresponding to a linear size of 144, 288, and 1.2 kpc, respectively. Our results indicate an asymmetry in the physical conditions along the galaxy's disc, that is, the gas is slightly more extended and brighter, and molecular gas mass is higher on the disc's eastern side than the western side. All physical properties (i.e. molecular gas mass, CO line ratios, stellar mass, and NIR emission) decrease from the centre going outwards in the disc with some exceptions (i.e. the extinction, FUV radiation, and the [3.6]−[4.5] colour). Our analysis indicates that the colour gets bluer (metallicity increases) halfway through the disc, then redder (metallicity decreases) going outwards further in the disc. [ABSTRACT FROM AUTHOR]