Context. During the early stages of star formation, accretion processes such as infall from the envelope and molecular streamers and ejection of matter through winds and jets take place simultaneously and distribute the angular momentum of the parent molecular cloud. The Class 0/I binary [BHB2007] 11 shows evidence for accretion and ejection at the scales of the circumbinary disk and the inner close binary. Recent observations of H2CO, however, have shown two elongated structures with indications of outflowing motion almost perpendicular to the main CO outflow, which is launched from the circumbinary disk. Aims. We study the kinematics of the molecular gas at intermediate scales of similar to 50-3000 au around [BHB2007] 11 to verify the nature of these elongated structures. Methods. We analyzed the line emission of (HCO+)-C-13, CCH, c-C3H2, and SiO observed with the Atacama Large Millimeter/submillimeter Array (ALMA) within the large program called Fifty AU STudy of the chemistry in the disc/envelope system of Solar-like protostars (FAUST). These molecules trace the material that moves at velocities close to that of the ambient cloud, which could not be probed in previous observations of the self-absorbed emission of CO. Results. The images of (HCO+)-C-13, CCH, and c-C3H2 show clear elongated structures similar to those previously detected in H2CO, whose gas kinematics are consistent with outflowing motions and with rotation in the opposite sense to the main CO outflow. The derived mass-loss rate from these large-scale structures is (1.7 +/- 0.5) x 10(-6) M-circle dot yr(-1), which agrees with the rates measured in outflows driven by Class 0/I protostars. The SiO image reveals compact emission close to the binary system, with a slight elongation that is aligned with the larger-scale structures. This suggests that SiO is released from the sputtering of dust grains in the shocked material at the base of the potential new outflow, with a relative abundance of >=(0.11-2.0) x 10(-9). However, higher angular and spectral resolution observations are needed to accurately estimate the outflow-launching radius and its powering source. Based on the location and the abundance of the SiO emission, we propose that the second outflow may be launched from inside the circumbinary disk, likely by the less massive companion that actively accretes material from its surroundings.

Context. In recent astrochemical studies it has become essential to study not only the most stable conformers, but also all the structures within the conformational panorama of the molecule, some of which are potentially detectable in the interstellar medium (ISM). In this context, the isomeric ratio can be used as a powerful tool to distinguish between different formation routes of molecules with increasing levels of complexity. Aims. While the most stable cis-conformer of methyl formate (CH3OCHO) is ubiquitous in the ISM, there is just one tentative detection of the higher-energy trans form (Delta E = 3000 K) toward the envelope of the star-forming region Sgr B2(N). For this work, our aim was to search for trans-methyl formate in additional sources and to perform new theoretical computations to better understand its conformational isomerism. Methods. We used an ultradeep molecular line survey of the Galactic Center molecular cloud G+0.693-0.027, carried out with the Yebes 40m and IRAM 30m telescopes, as well as publicly available data from the Large Program ASAI observed toward the prototypical protostellar shock L1157-B1. The observational results are compared with predictions based on new grain-surface theoretical computations, which are sensitive to the stereochemistry of the molecule. Results. We present the detections of trans-methyl formate in both astronomical regions, providing conclusive observational evidence of its presence in the ISM. Numerous unblended or slightly blended a-type K-a = 0, 1 transitions belonging to the A-substate of trans-methyl formate have been identified in both sources, many of which have been directly observed in radio astronomical data for the first time and remain unmeasured in the laboratory. We derive a molecular column density for trans-methyl formate of N = (8.2 +/- 0.4) x10(12) cm(-2) and N = (1.6 +/- 0.3) x10(12) cm(-2), respectively, for each source, yielding a molecular abundance with respect to H-2 of similar to 6 x10(-11) and similar to 8 x10(-10), respectively. Therefore, we obtain cis/trans isomeric ratios of similar to 72 and similar to 34 toward G+0.693 and L1157-B1, respectively, which are about seven and three times higher than that found in the Sgr B2(N) region. The results from our theoretical computations suggest that a stereospecific formation of trans-methyl formate via the CH3O + HCO route on grain surfaces can qualitatively explain the observed cis/trans abundance ratio. Nevertheless, we show that additional stereospecific gas-phase routes could also play a crucial role in maintaining the intricate balance between formation and destruction of trans-MF, ultimately leading to its detection.

Analyzing longitude–velocity diagrams (LVDs) in the CS (J = 2–1) and H$^{13}$CN (J = 1–0) molecular lines from the internal release data of the ALMA Central Molecular Zone (CMZ) Exploration Survey and in the $^{13}$CO (J = 1–0) line from the Nobeyama Galactic Center (GC) survey, we identify six GC arms as prominent straight LV ridges. In addition to the currently known Arms I to IV, we identify a new inner arm, Arm V, and further highlight the circumnuclear disk (CND) as Arm VI. Integrated intensity maps of the arms on the sky suggest that most of the arms compose ring-like structures inclined from the Galactic plane. We determine the radii (curvatures) of the arms using the velocity-gradient ($dv/dl$) method, assuming that the arms are rotating in circular orbits at a constant velocity of $\sim$150 km s$^{-1}$. We show that Arms I and II compose the main ring structure of the CMZ with radii $\sim$100–120 pc; Arm III is a dense arm 42 pc from the GC; Arm IV is a clear and narrow arm 20 pc from the GC; and Arm V is a faint, long arm of 8.2 pc radius. We show that the CND comprises the sixth arm, Arm VI, of radius $\sim$2.3 pc associated with bifurcated spiral fins. We also discuss the association of the 20 and 50 km s$^{-1}$ clouds with these arms. The radii of the arms fall on an empirical relation $R\sim 630 (2/5)^N$ for $N=1$ (Arm I) to 6 (VI), suggesting discrete rings or a logarithmic spiral with pitch angle ${\sim }22^{\circ }$. The vertical full extent of the arm increases with radius and is represented by $z\sim 0.7 (R/1 {\rm \ pc} )^{0.7}$ pc. The tilt angle of the arms from the Galactic plane, or the warping, increases rapidly toward the GC.

Utilizing the James Webb Space Telescope (JWST), the Atacama Large Millimeter/submillimeter Array (ALMA), and the Very Large Array (VLA), we present high angular resolution (0 . ″ 06–0 . ″ 42), multiwavelength (4 μ m–3 cm) observations of the VLA 1623-2417 protostellar system to characterize the origin, morphology and, properties of the continuum emission. JWST observations at 4.4 μ m reveal outflow cavities for VLA 1623 A and, for the first time, VLA 1623 B, as well as scattered light from the upper layers of the VLA 1623 W disk. We model the millimeter-centimeter spectral energy distributions to quantify the relative contributions of dust and ionized gas emission, calculate dust masses, and use spectral index maps to determine where optical depth hinders this analysis. In general, all objects appear to be optically thick down to ∼90 GHz, show evidence for significant amounts (tens to hundreds of M ⊕ ) of large (>1 mm) dust grains, and are dominated by ionized gas emission for frequencies ≲​​​​​​15 GHz. In addition, we find evidence of unsettled millimeter dust in the inclined disk of VLA 1623 B possibly attributed to instabilities within the circumstellar disk, adding to the growing catalog of unsettled Class 0/I disks. Our results represent some of the highest-resolution observations possible with current instrumentation, particularly in the case of the VLA. However, our interpretation is still limited at low frequencies (≲22 GHz) and thus motivates the need for next-generation interferometers operating at centimeter wavelengths.

Context. We have studied the dense gas morphology and kinematics towards the infrared dark cloud (IRDC) G034.77-00.55, shock-interacting with the SNR W44, to identify evidence of early-stage star formation induced by the shock. Aims. We used high angular resolution N2H+(1-0) images across G034.77-00.55, obtained with the Atacama Large Millimeter/sub-Millimeter Array. N2H+ is a well-known tracer of dense and cold material, optimal for identifying gas that has the highest potential to harbour star formation. Methods. The N2H+ emission is distributed in two elongated structures, one towards the dense ridge at the edge of the source and one towards the inner cloud. Both elongations are spatially associated with well-defined mass-surface density features. The velocities of the gas in the two structures (i.e. 38-41 km s(-1) and 41-43 km s(-1)) are consistent with the lowest velocities of the J- and C-type parts, respectively, of the SNR-driven shock. A third velocity component is present at 43-45.5 km s(-1). The dense gas shows a fragmented morphology with core-like fragments at scales consistent with the Jeans lengths, masses of similar to 1-20 M-circle dot, densities of (n(H-2)>= 10(5) cm(-3)) sufficient to host star formation in free-fall timescales (a few 10(4) yr), and with virial parameters that suggest a possible collapse. Results. The W44 driven shock may have swept up the encountered material, which is now seen as a dense ridge, almost detached from the main cloud, and an elongation within the inner cloud, well constrained in both N2H+ emission and mass surface density. This shock compressed material may have then fragmented into cores that are either in a starless or pre-stellar stage. Additional observations are needed to confirm this scenario and the nature of the cores.

Infrared Dark Clouds (IRDCs) are cold, dense structures representative of the initial conditions of star formation. Many studies of IRDCs employ CO to investigate cloud dynamics. However, CO can be highly depleted from the gas phase in IRDCs, impacting its fidelity as tracer. CO depletion is also of great interest in astrochemistry, since CO ice in dust grain mantles provides the raw material for forming complex organic molecules. We study CO depletion toward four IRDCs to investigate how it correlates with volume density and dust temperature, calculated from Herschel images. We use 13CO(1-0) and (2-1) maps to measure CO depletion factor, f_D, across IRDCs G23.46-00.53, G24.49-00.70, G24.94-00.15, and G25.16-00.28. We also consider a normalized CO depletion factor, f_D', which takes a value of unity, i.e., no depletion, in the outer, lower density, warmer regions. We then investigate the dependence of f_D and f_D' on gas density, n_H and dust temperature, T_dust. We find CO depletion rises as density increases, reaching maximum values of f_D'∼10 in regions with n_H>3×10^5 cm^-3, although with significant scatter at a given density. We find a tighter, less scattered relation of f_D' with temperature, rising rapidly for temperatures <18 K. We propose a functional form f_D^' = exp(T_0/[T_dust-T_1]) with T_0≃4K and T_1≃12K to reproduce this behaviour. We conclude that CO is heavily depleted from the gas phase in cold, dense regions of IRDCs. Thus CO depletion can lead to underestimation of total cloud masses based on CO line fluxes by factors up to 5. These results indicate a dominant role for thermal desorption in setting near equilibrium abundances of gas phase CO in IRDCs, providing important constraints for both astrochemical models and the chemodynamical history of gas during the early stages of star formation.

(Abridged) JWST observations have measured the ice composition toward two highly-extinguished field stars in the Chamaeleon I cloud. The observed extinction excess on the long-wavelength side of the H2O ice band at 3 micron has been attributed to a mixture of CH3OH with ammonia hydrates, which suggests that CH3OH ice could have formed in a water-rich environment with little CO depletion. Laboratory experiments and quantum chemical calculations suggest that CH3OH could form via the grain surface reactions CH3+OH and/or C+H2O in water-rich ices. However, no dedicated chemical modelling has been carried out thus far to test their efficiency and dependence on the astrochemical code employed. We model the ice chemistry in the Chamaeleon I cloud using a set of astrochemical codes (MAGICKAL, MONACO, Nautilus, UCLCHEM, and KMC simulations) to test the effects of the different code architectures and of the assumed ice chemistry. Our models show that the JWST ice observations are better reproduced for gas densities >1e5 cm-3 and collapse times >1e5 yr. CH3OH ice forms predominantly (>99 and C+H2O, is negligible. The CO2 ice may form either via CO+OH or CO+O depending on the code. However, KMC simulations reveal that both mechanisms are efficient despite the low rate constant of the CO+O surface reaction. CH4 is largely underproduced for all codes except for UCLCHEM, for which a higher amount of atomic C is available during the initial translucent cloud phase. Large differences in the ice abundances are found at Tdust<12 K between diffusive and non-diffusive chemistry codes. This is due to the fact that non-diffusive chemistry takes over diffusive chemistry at such low Tdust. This could explain the rather constant ice chemical composition found in Chamaeleon I and other dense cores despite the different visual extinctions probed.

Context.Isomerism in complex organic molecules provides key insights into the formation mechanisms and physical conditions of the interstellar medium (ISM). Among the C2H5NO isomers, only acetamide and trans-N-methylformamide (trans-NMF) have been detected in space. The recent detection of higher-energy isomers in other chemical families raises questions about the formation and abundance of less stable isomers. Aims. We aim to search for cis-N-methylformamide (cis-NMF), the next higher-energy conformer in the C2H5NO family, and investigate its possible formation pathways. Methods. We used ultra-sensitive wide-band spectral surveys obtained with the Yebes 40 m and IRAM 30 m telescopes to search for cis-NMF towards the Galactic centre molecular cloud, G+0.693-0.027. A spectroscopic catalogue was extrapolated from literature data to aid the search. Results. We present the first detection of cis-NMF in the ISM, with 55 unblended or slightly blended transitions, 44 of which were new transitions identified based on extrapolated spectroscopic data. Due to the lack of collisional rate coefficients, a quasi-non-LTE analysis, which separated the transitions into different K-a ladders, was used to determine the excitation conditions. The derived column density is (1.5 +/- 0.1) x 10(13) cm(-2), corresponding to a molecular abundance of (1.1 +/- 0.2) x 10(-10) relative to H-2. The resulting trans/cis-NMF isomeric ratio of 2.9 +/- 0.6 deviates significantly from thermodynamic expectations, suggesting that kinetic non-equilibrium processes and stereospecific chemical pathways are responsible for the formation of cis-NMF in this environment. Conclusions. The detection of cis-NMF expands the known inventory of interstellar C2H5NO isomers and challenges the assumption that isomer abundances strictly correlate with thermodynamic stability. Laboratory and theoretical studies propose formation via CH3NCO hydrogenation or spin-forbidden reactions involving CH2 and NH2CHO, though these may not reflect typical ISM conditions. This finding highlights the need for further investigation into isomerisation mechanisms and constrains astrochemical models of complex organic molecules.

Utilising JWST, ALMA and the VLA we present high angular resolution (0.06''- 0.42''), multi-wavelength (4 micron - 3cm) observations of the VLA 1623-2417 protostellar system to characterise the origin, morphology and, properties of the continuum emission. JWST observations at 4.4 micron reveal outflow cavities for VLA 1623 A and, for the first time, VLA 1623 B, as well as scattered light from the upper layers of the VLA 1623 W disk. We model the millimetre-centimetre spectral energy distributions to quantify the relative contributions of dust and ionised gas emission, calculate dust masses, and use spectral index maps to determine where optical depth hinders this analysis. In general, all objects appear to be optically thick down to ~90 GHz, show evidence for significant amounts (10's - 100's M_Earth) of large (>1 mm) dust grains, and are dominated by ionised gas emission for frequencies ~<15 GHz. In addition, we find evidence of unsettled millimetre dust in the inclined disk of VLA 1623 B possibly attributed to instabilities within the circumstellar disk, adding to the growing catalogue of unsettled Class 0/I disks. Our results represent some of the highest resolution observations possible with current instrumentation, particularly in the case of the VLA. However, our interpretation is still limited at low frequencies (~<22 GHz) and thus motivates the need for next-generation interferometers operating at centimetre wavelengths.

Context. Deuterium was primarily created during the Big Bang nucleosynthesis. This fact, alongside its fractionation reactions resulting in enhanced abundances of deuterated molecules, means that deuterium abundances can be used to better understand many processes within the interstellar medium as well as its history. Previously, observations of deuterated molecules have been limited to the Galaxy, the Magellanic Clouds, and (with respect to HD) to quasar absorption spectra. Aims. We present the first robust detection of a deuterated molecule in a starburst environment and, apart from HD, the first one detected outside the Local Group. As such, we could constrain the deuterium fractionation as observed by DCN. Methods. We observed the central molecular zone (CMZ) of the nearby starburst galaxy NGC 253 covering multiple giant molecular clouds (GMCs) with cloud scale observations (similar to 30 pc) using the Atacama Large Millimeter/submillimeter Array. Via the MADCUBA package, we were able to perform local thermodynamic equilibrium analysis in order to obtain deuterium fractionation estimates. Results. We detected DCN in the nuclear region of the starburst galaxy NGC 253 and estimated the deuterium fractionation (D/H ratio) of DCN within the GMCs of the CMZ of NGC 253. We found a range of 5x10(-4) to 10x10(-4), which is relatively similar to the values observed in warm galactic star-forming regions. We also determined an upper limit of D/H of 8x10(-5) from DCO+ within one region, closer to the cosmic value of D/H. Conclusions. Our observations of deuterated molecules within NGC 253 appear to be consistent with previous galactic studies of star-forming regions. This implies that warmer gas temperatures increase the abundance of DCN relative to other deuterated species. This study also further expands the regions, particularly in the extragalactic domain, in which deuterated species have been detected.

In the coldest regions of molecular clouds, carbon and oxygen are incorporated into icy dust grains. Despite its outsized role in star and planet formation, sequential formation of ice is poorly constrained. Infrared spectroscopy probes ice chemistry, but previous telescopes observed insufficient lines of sight to map a single cloud. Here we present cospatial maps of H2O, CO2 and CO ice over the central region of the Chamaeleon I molecular cloud, using 44 lines of sight observed with the James Webb Space Telescope. Correlations at column densities ten times larger than previous work suggest additional CO2 ice formation in CO ice for the densest lines of sight. This large statistical sampling within a single cloud represents a step change in ice mapping, eliminating averaging over clouds with different intrinsic chemical environments. Mapping opens the door to probing gas-grain exchanges, snow lines and chemical evolution in the densest regions and drawing conclusions on the impact of ice chemistry on wider astrophysics.

Following the discovery of dimethyl sulfide (DMS; CH 3 SCH 3 ) signatures in comet 67P/Churyumov–Gerasimenko, we report the first detection of this organosulfur species in the interstellar medium during the exploration of an ultradeep molecular line survey performed toward the Galactic center molecular cloud G+0.693-0.027 with the Yebes 40 m and IRAM 30 m telescopes. We derive a molecular column density of N = (2.6 ± 0.3) × 10 13 cm −2 , yielding a fractional abundance relative to H 2 of ∼1.9 × 10 −10 . This implies that DMS is a factor of ∼1.6 times less abundant than its structural isomer CH 3 CH 2 SH and ∼30 times less abundant than its O-analog dimethyl ether (CH 3 OCH 3 ) toward this cloud, in excellent agreement with previous results on various O/S pairs. Furthermore, we find a remarkable resemblance between the relative abundance of DMS/CH 3 OH in G+0.693-0.027 (∼1.7 × 10 −3 ) and in the comet (∼1.3 × 10 −3 ). Although the chemistry of DMS beyond Earth has yet to be fully disclosed, this discovery provides conclusive observational evidence on its efficient abiotic production in the interstellar medium, casting doubt on using DMS as a reliable biomarker in exoplanet science.

Context. Recent JWST observations have measured the ice chemical composition towards two highly extinguished background stars, NIR38 and J110621, in the Chamaeleon I molecular cloud. The observed excess of extinction on the long-wavelength side of the H2O ice band at 3 mu m has been attributed to a mixture of CH3OH with ammonia hydrates NH3H2O), which suggests that CH3OH ice in this cloud could have formed in a water-rich environment with little CO depletion. Laboratory experiments and quantum chemical calculations suggest that CH3OH could form via the grain surface reactions CH3 + OH and/or C + H2O in water-rich ices. However, no dedicated chemical modelling has been carried out thus far to test their efficiency. In addition, it remains unexplored how the efficiencies of the proposed mechanisms depend on the astrochemical code employed. Aims. We modelled the ice chemistry in the Chamaeleon I cloud to establish the dominant formation processes of CH3OH, CO, CO2, and of the hydrides CH4 and NH3 (in addition to H2O). By using a set of state-of-the-art astrochemical codes (MAGICKAL, MONACO, Nautilus, UCLCHEM, and KMC simulations), we can test the effects of the different code architectures (rate equation vs. stochastic codes) and of the assumed ice chemistry (diffusive vs. non-diffusive). Methods. We consider a grid of models with different gas densities, dust temperatures, visual extinctions, and cloud-collapse length scales. In addition to the successive hydrogenation of CO, the codes' chemical networks have been augmented to include the alternative processes for CH3OH ice formation in water-rich environments (i.e. the reactions CH3 + OH -> CH3OH and C + H2O -> H2CO). Results. Our models show that the JWST ice observations are better reproduced for gas densities >= 10(5) cm(-3) and collapse timescales >= 10(5) yr. CH3OH ice formation occurs predominantly (>99%) via CO hydrogenation. The contribution of reactions CH3 + OH and C + H2O is negligible. The CO2 ice may form either via CO + OH or CO + O depending on the code. However, KMC simulations reveal that both mechanisms are efficient despite the low rate of the CO + O surface reaction. CH4 is largely underproduced for all codes except for UCLCHEM, for which a higher amount of atomic C is available during the translucent cloud phase of the models. Large differences in the predicted abundances are found at very low dust temperatures (T-dust<12 K) between diffusive and non-diffusive chemistry codes. This is due to the fact that non-diffusive chemistry takes over diffusive chemistry at such low T-dust. This could explain the rather constant ice chemical composition found in Chamaeleon I and other dense cores despite the different visual extinctions probed.

Context. Planet formation around young stars requires the growth of interstellar dust grains from micron-sized (mu m-sized) particles to kilometre-sized (km-sized) planetesimals. Numerical simulations have shown that large (mm-sized) grains found in the inner envelope of young protostars could be lifted from the disc via winds. However, we are still lacking unambiguous evidence for large grains in protostellar winds and outflows. Aims. We investigated dust continuum emission in the envelope of the Class I binary L1551 IRS5 in the Taurus molecular cloud, aiming to identify observational signatures of grain growth, such as variations in the dust emissivity index (beta(mm)). Methods. In this context, we present new, high-angular resolution (50 au) observations of thermal dust continuum emission at 1.3 mm and 3 mm in the envelope (similar to 3000 au) of L1551 IRS5, obtained as part of the ALMA-FAUST Large Program. Results. We analysed dust emission along the cavity walls of the CO outflow, extended up to similar to 1800 au. We found an H-2 volume density > 2 x 10(5) cm(-3), a dust mass of similar to 58 M-circle plus, and beta(mm) less than or similar to 1, implying the presence of grains similar to 10(3) times larger than typical sizes for the interstellar medium (ISM). Conclusions. We present the first spatially resolved observational evidence of large grains within an outflow cavity wall. Our results suggest that these grains have been transported from the inner disc to the envelope by protostellar winds and may subsequently fall back into the outer disc by gravity and/or via accretion streamers. This cycle provides longer time for grains to grow, demonstrating their crucial role in the formation of planetesimals.

The study of the chemical composition of star-forming regions is key to understanding the chemical ingredients available during the formation of planetary systems. Because the chemical inventory of interstellar dust grains in the prestellar phases might be altered by protostellar warming, an alternative to inferring the chemical composition of the grains might be to observe regions that are affected by shocks associated with molecular outflows. These shocks are able to desorb the molecules and might produce less chemical processing because the timescales are shorter. We present a detailed study of the chemical reservoir of a shocked region located in the G31.41+0.31 protocluster using data from the G31.41+0.31 Unbiased ALMA sPectral Observational Survey (GUAPOS). We report the detection of 30 molecular species (plus 18 isotopologs) and derived the column densities. We compared the molecular ratios in the shocked region with those derived toward the hot core of G31.41+0.31. They are poorly correlated, with the exception of N-bearing species. Our results confirm observationally that a different level of chemical alteration is present in hot cores and in shocks. While the former likely alter the molecular ratios by thermal processing during longer timescales, the latter might represent freshly desorbed material that constitutes a better proxy of the composition of the ice mantle. The similarity of the molecular ratios of the N-bearing species in the G31.41+0.31 shock and the hot core suggests that these species are predominantly formed at early evolutionary stages. Interestingly, the abundances in the G31.41+0.31 shock are better correlated with other shock-dominated regions (two protostellar outflows and a molecular cloud in the Galactic center). This suggests that gas-phase chemistry after shock-induced ejection from grains is negligible and that the composition of the ice mantle is similar regardless of the Galactic environment.

Young low-mass protostars often possess hot corinos, which are compact, hot, and dense regions that are bright in interstellar complex organic molecules (iCOMs). In addition to their prebiotic role, iCOMs can be used as a powerful tool to characterize the chemical and physical properties of hot corinos. Using ALMA/FAUST data, our aim was to explore the iCOM emission at $<$ 50 au scale around the Class 0 prototypical hot corino IRAS 4A2. We imaged IRAS 4A2 in six abundant common iCOMs (CH_3OH, HCOOCH_3, CH_3CHO, CH_3CH_2OH, CH_2OHCHO, and NH_2CHO), and derived their emitting sizes. The column density and gas temperature for each species were derived at 1σ from a multi-line analysis by applying a non-LTE approach for CH_3OH, and LTE population or rotational diagram analysis for the other iCOMs. Thanks to the unique estimates of the absorption from foreground millimeter dust toward IRAS 4A2, we derived for the first time unbiased gas temperatures and column densities. We resolved the IRAS 4A2 hot corino, and found evidence for a chemical spatial distribution in the inner 50 au, with the outer emitting radius increasing from ∼ 22-23 au for NH_2CHO and CH_2OHCHO, followed by CH_3CH_2OH (∼ 27 au), CH_3CHO (∼ 28 au), HCOOCH_3 (∼ 36 au), and out to ∼ 40 au for CH_3OH. Combining our estimate of the gas temperature probed by each iCOM with their beam-deconvolved emission sizes, we inferred the gas temperature profile of the hot corino on scales of 20-50 au in radius, and found a power-law index q of approximately --1. We observed, for the first time, a chemical segregation in iCOMs of the IRAS 4A2 hot corino, and derived the gas temperature profile of its inner envelope. The derived profile is steeper than when considering a simple spherical collapsing and optically thin envelope, hinting at a partially optically thick envelope or a gravitationally unstable disk-like structure.

Low-velocity large-scale shocks impacting on the ISM may efficiently shape molecular clouds and trigger star formation within them. These shocks, both driven by galactic bubbles and/or cloud-cloud collisions, leave specific signatures in the gas morphology and kinematics. Observational studies of such signatures are crucial to investigate if and how shocks affect the clouds formation process and trigger their future star formation. We have analysed the shocked and dense gas tracers SiO(2-1) and H13CO+(1-0) emission toward the IRDC G035.39-00.33, using new, larger-scale maps obtained with the 30m telescope at the Instituto de Radioastronomìa Millimétrica. We find that the dense gas is organised into a northern and a southern filament having different velocities and tilted orientation with respect to each other. The two filaments are spatially separated yet connected by a faint bridge feature also seen in a position-velocity diagram extracted across the cloud. This bridge-feature, typical of cloud-cloud collisions, also coincides with a very spectrally narrow SiO-traced emission. The northern filament is suggested to be interacting with the nearby supernova remnant G035.6-0.4. Toward the southern filament, we also report the presence of a parsec-scale, spectrally narrow SiO emission likely driven by the interaction between this filament and a nearby expanding shell. The shell is visible in the 1.3 GHz and 610 MHz continuum images and our preliminary analysis suggests it may be the relic of a supernova remnant. We conclude that the two filaments represent the densest part of two colliding clouds, pushed toward each other by nearby Supernova Remnants. We speculate that this cloud-cloud collision driven by stellar feedback may have assembled the infrared dark cloud. We also evaluate the possibility that star formation may have been triggered within G035.39-00.33 by the collision.

Context. Protostars contain icy ingredients necessary for the formation of potential habitable worlds, therefore, it is crucial to understand their chemical and physical environments. This work is focused on the ice features towards the binary protostellar system Ced 110 IRS4A and IRS4B, separated by 250 au and observed with James Webb Space Telescope (JWST) as part of the Early Release Science (ERS) Ice Age collaboration. Aims. This study is aimed at exploring the JWST observations of the binary protostellar system Ced 110 IRS4A and IRS4B primarily to unveil and quantify the ice inventories towards these sources. Finally, we compare the ice abundances with those found for the same molecular cloud. Methods. We used data from multiple JWST instruments (NIRSpec, NIRCam, and MIRI) to identify and quantify ice species in the Ced 110 IRS4 system. The analysis was performed by fitting or comparing the laboratory infrared spectra of ices to the observations. Spectral fits are carried out with the ENIIGMA fitting tool that searches for the best fit out of a large number of solutions. The degeneracies of the fits are also addressed and the ice column densities are calculated. In cases where the full nature of the absorption features is not yet known, we explore different laboratory ice spectra to compare them with the observations. Results. We provide a list of securely and tentatively detected ice species towards the primary and the companion sources. For Ced 110 IRS4B, we detected the major ice species H2O, CO, CO2, and NH3. All species are found in a mixture except for CO and CO2, which have both mixed and pure ice components. In the case of Ced 110 IRS4A, we detected the same major species as in Ced 110 IRS4B, as well as the following minor species: CH4, SO2, CH3OH, OCN-, NH4+, and HCOOH. A tentative detection of N2O ice (7.75 mu m), forsterite dust (11.2 mu m), and CH3+ gas emission (7.18 mu m) in the primary source was also made. Compared with the two lines of sight towards background stars in the Chameleon I molecular cloud, the protostar exhibits similar ice abundances, except in the case of the ions that are higher in IRS4A. The most clear differences are the absence of the 7.2 and 7.4 mu m absorption features due to HCOO- and icy complex organic molecules in IRS4A. There is also evidence of thermal processing in both IRS4A and IRS4B, as probed by the CO2 ice features. Conclusions. We conclude that the binary protostellar system Ced 110 IRS4A and IRS4B has a large inventory of icy species. The similar ice abundances in comparison to the starless regions in the same molecular cloud suggests that the chemical conditions of the protostar were set at earlier stages in the molecular cloud. It is also possible that the source inclination and complex geometry cause a low column density along the line of sight, which hides the bands at 7.2 and 7.4 mu m. Finally, we highlight that a comprehensive analysis using radiative transfer modelling is needed to disentangle the spectral energy distributions of these sources.

The presence of molecular isomers in interstellar environments has become a topic of growing interest within the astrochemical community. Contrary to predictions based on thermodynamic equilibrium, recent observations reveal a diverse array of high-energy isomers and conformers. One of the most iconic molecular isomers detected in space, formic acid (HCOOH, FA), has been the focus of extensive theoretical research aimed at understanding its speciation into cis and trans conformers in dark clouds and photodissociation regions. In this work, we report the detection of c-FA, the higher-energy conformer, using ultrasensitive observations of TMC-1. This detection adds to previous findings in the Barnard-5 and L483 dark clouds. The derived trans-to-cis isomer ratio in TMC-1, 17.5, closely matches those observed in other sources, suggesting that the same chemical processes are at play across these environments. To investigate this, we conducted detailed astrochemical gas-grain models tailored to formic acid isomerism to explain the observed ratios. Our models successfully reproduce the observed trans/cis ratios and indicate that the presence of cis-formic acid can be attributed to the release of c-FA from grains, followed by isomerization driven by the excess energy released during the desorption process, a process that we name as isomerization upon desorption. The models also show that the isomerization of t-FA to c-FA in the gas phase is negligible at 10 K, meaning the observed ratios are a direct consequence of the formation pathways of both isomers on the surface of dust grains. However, at higher temperatures, quantum tunneling mediated direct isomerization in the gas becomes significant, and the ratios converge toward the thermodynamic equilibrium value.

Most stars, including the Sun, are born in rich stellar clusters containing massive stars. Therefore, the study of the chemical reservoir of massive star-forming regions is crucial to understand the basic chemical ingredients available at the dawn of planetary systems. We present a detailed study of the molecular inventory of the hot molecular core G31.41+0.31 from the project GUAPOS (G31.41+0.31 Unbiased ALMA sPectral Observational Survey). We analyze 34 species for the first time plus 20 species analyzed in previous GUAPOS works, including oxygen, nitrogen, sulfur, phosphorus, and chlorine species. We compare the abundances derived in G31.41+0.31 with those observed in other chemically-rich sources that represent the initial and last stages of the formation of stars and planets: the hot corino in the Solar-like protostar IRAS 16293-2422 B, and the comets 67P/Churyumov-Gerasimenko and 46P/Wirtanen. The comparative analysis reveals that the chemical feedstock of the two star-forming regions are similar. The abundances of oxygen- and nitrogen-bearing molecules exhibit a good correlation for all pair of sources, including the two comets, suggesting a chemical heritage of these species during the process of star formation, and hence an early phase formation of the molecules. However, sulfur- and phosphorus-bearing species present worse correlations, being more abundant in comets. This suggests that while sulfur- and phosphorus-bearing species are predominantly trapped on the surface of icy grains in the hot close surroundings of protostars, they could be more easily released into gas phase in comets, allowing their cosmic abundances to be almost recovered.