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Context. Star formation in the central molecular zone (CMZ) is suppressed with respect to that of the Galactic disk, and this is likely related to its high turbulent environment. This turbulence impedes the potential detection of prestellar cores. Aims. We present the temperature, density, and spatial structure of the CMZ molecular cloud G+0.693-0.027, which has been proposed to host a prestellar cluster in the Sgr B2 region. Methods. We analysed multiple HC3N rotational transitions that were observed with the IRAM 30m, APEX, Yebes 40m, and GBT radio telescopes, together with SMA+APEX spatially resolved maps. Results. The spectral shape of HC3N lines shows three distinct velocity components: a broad component with a line width of 23 km s−1 (C1), and two narrow components with line widths of 7.2 and 8.8 km s−1 (C2 and C3). This suggests that a fraction of the molecular gas in this cloud is undergoing turbulence dissipation. From an initial local thermodynamic equilibrium analysis, we found column densities of N = (6.54 ± 0.07) × 1014 cm−2, (9 ± 3) × 1014 cm−2, and (3.6 ± 0.7) × 1013 cm−2 for C1, C2, and C3, respectively. These values were used as input for a subsequent non-local thermodynamic equilibrium analysis, in which we found H2 densities of 2 × 104 cm−3, 5 × 104 cm−3, and 4 × 105 cm−3 and kinetic temperatures of 140 K, 30 K, and 80 K for C1, C2, and C3, respectively. The spatially resolved maps confirm that the colder and high-density condensations C2 and C3, which peak in the 70–85 km s−1 velocity range, have deconvolved sizes of 9″ (0.36 pc) and 7.6″ (0.3 pc), respectively, and are embedded in a more diffuse and warmer gas (C1). Conclusions. The larger-scale structure of the Sgr B2 region, consistently with previous works, shows a hole at 40–50 km s−1 that is likely due to a small cloud that shocked the Sgr B2 region and is spatially related with a massive cloud at 60–80 km s−1. We propose that the impacting small cloud sequentially triggered the formation of Sgr B2(M), (N), and (S) and the condensations in G+0.693-0.027 during its passage. The two condensations are in a post-shocked environment that has undergone internal fragmentation. Based on the analysis of their masses and the virial parameters, C2 might expand, while C3 might further fragment or collapse. [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]

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]

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 analyse 34 species for the first time plus 20 species analysed 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 pre-dominantly 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. [ABSTRACT FROM AUTHOR]

Context. The astrochemistry of the important biogenic element phosphorus (P) is still poorly understood, but observational evidence indicates that P-bearing molecules are likely associated with shocks. Aims. We study P-bearing molecules and some shock tracers towards one of the chemically richest hot molecular cores, G31.41+0.31, in the framework of the project "G31.41+0.31 Unbiased ALMA sPectral Observational Survey" (GUAPOS), which is being carried out with the Atacama Large Millimeter Array (ALMA). Methods. We observed the molecules PN, PO, SO, SO2, SiO, and SiS through their rotational lines in the spectral range 84.05– 115.91 GHz covered by the GUAPOS project. Results. PN is clearly detected, while PO is tentatively detected. The PN emission arises from two regions southwest of the hot core peak, named regions 1 and 2 here, and is undetected or tentatively detected towards the hot core peak. The PN and SiO lines are very similar both in spatial emission morphology and spectral shape. Region 1 is partly overlapping with the hot core and is warmer than region 2, which is well separated from the hot core and located along the outflows identified in previous studies. The SO, SO2, and SiS emissions are also detected towards the PN-emitting regions 1 and 2, but arise mostly from the hot core. Moreover, the column density ratio SiO/PN remains constant in regions 1 and 2, while SO/PN, SiS/PN, and SO2/PN decrease by about an order of magnitude from region 1 to region 2, indicating that SiO and PN have a common origin even in regions with different physical conditions. The PO/PN ratio in region 2, where PO is tentatively detected, is ~0.6–0.9, which is in line with the predictions of pure shock models. Conclusions. Our study provides robust confirmation of previous observational evidence that PN emission is tightly associated with SiO and is likely a product of shock chemistry, as the lack of a clear detection of PN towards the hot core allows us to rule out relevant formation pathways in hot gas. We propose the PN-emitting region 2 as a new astrophysical laboratory for shock-chemistry studies. [ABSTRACT FROM AUTHOR]

We present new observations of molecular anions with the Yebes 40 m and IRAM 30 m telescopes toward the cold, dense clouds TMC-1 CP, Lupus-1A, L1527, L483, L1495B, and L1544. We report the first detections of C3N− and C5N− in Lupus-1A as well as C4H− and C6H− in L483. In addition, we detected new lines of C6H− toward the six targeted sources, of C4H− toward TMC-1 CP, Lupus-1A, and L1527, and of C8H− and C3N− in TMC-1 CP. Excitation calculations using recently computed collision rate coefficients indicate that the lines of anions accessible to radiotelescopes run from subthermally excited to thermalized as the size of the anion increases, with the degree of departure from thermalization depending on the H2 volume density and the line frequency. We noticed that the collision rate coefficients available for the radical C6H are not sufficient to explain various observational facts, thereby calling for the collision data for this species to be revisited. The observations presented here, together with observational data from the literature, have been used to model the excitation of interstellar anions and to constrain their abundances. In general, the anion-to-neutral ratios derived here agree with the literature values, when available, within 50% (by a factor of two at most), except for the C4H−/C4H ratio, which shows higher differences due to a revision of the dipole moment of C4H. From the set of anion-to-neutral abundance ratios derived two conclusions can be drawn. First, the C6H−/C6H ratio shows a tentative trend whereby it increases with increasing H2 density, as we would expect on the basis of theoretical grounds. Second, the assertion that the higher the molecular size, the higher the anion-to-neutral ratio is incontestable; furthermore, this supports a formation mechanism based on radiative electron attachment. Nonetheless, the calculated rate coefficients for electron attachment to the medium size species C4H and C3N are probably too high and too low, respectively, by more than one order of magnitude. [ABSTRACT FROM AUTHOR]

The H2NC radical is the high-energy metastable isomer of H2CN radical, which has been recently detected for the first time in the interstellar medium towards a handful of cold galactic sources, besides a warm galaxy in front of the PKS 1830−211 quasar. These detections have shown that the H2CN/H2NC isomeric ratio, likewise the HCN/HNC ratio, might increase with the kinetic temperature (T kin), but the shortage of them in warm sources still prevents us from confirming this hypothesis and shedding light on their chemistry. In this work, we present the first detection of H2CN and H2NC towards a warm galactic source, the G+0.693−0.027 molecular cloud (with T kin > 70 K), using IRAM 30-m telescope observations. We have detected multiple hyperfine components of the |$N_{K_\text{a}K_\text{c}} =$| 101–000 and 202–101 transitions. We derived molecular abundances with respect to H2 of (6.8 ± 1.3) × 10−11 for H2CN and of (3.1 ± 0.7) × 10−11 for H2NC, and an H2CN/H2NC abundance ratio of 2.2 ± 0.5. These detections confirm that the H2CN/H2NC ratio is ≳2 for sources with T kin > 70 K, larger than the ∼1 ratios previously found in colder cores (T kin ∼ 10 K). This isomeric ratio dependence on temperature cannot be fully explained with the currently proposed gas-phase formation and destruction pathways. Grain surface reactions, including the H2NC → H2CN isomerization, deserve consideration to explain the higher isomeric ratios and H2CN abundances observed in warm sources, where the molecules can be desorbed into the gas phase through thermal and/or shock-induced mechanisms. [ABSTRACT FROM AUTHOR]

Recent observations of the pre-stellar core L1544 and the younger starless core L1498 have revealed that complex organic molecules (COMs) are enhanced in the gas phase towards their outer and intermediate-density shells. Our goal is to determine the level of chemical complexity towards the starless core L1517B, which seems younger than L1498, and compare it with the other two previously studied cores to see if there is a chemical evolution within the cores. We have carried out 3 mm high-sensitivity observations towards two positions in the L1517B starless core: the core's centre and the position where the methanol emission peaks (at a distance of ∼5000 au from the core's centre). Our observations reveal that a lower number of COMs and COM precursors are detected in L1517B with respect to L1498 and L1544, and also show lower abundances. Besides methanol, we only detected CH3O, H2CCO, CH3CHO, CH3CN, CH3NC, HCCCN, and HCCNC. Their measured abundances are ∼3 times larger towards the methanol peak than towards the core's centre, mimicking the behaviour found towards the more evolved cores L1544 and L1498. We propose that the differences in the chemical complexity observed between the three studied starless cores are a consequence of their evolution, with L1517B being the less evolved one, followed by L1498 and L1544. Chemical complexity in these cores seems to increase over time, with N-bearing molecules forming first and O-bearing COMs forming at a later stage as a result of the catastrophic depletion of CO. [ABSTRACT FROM AUTHOR]

We report here the first detection in the interstellar medium of the cyanomidyl radical (HNCN). Using the Yebes 40m and the IRAM 30m telescopes, we have targeted the doublets of the N  = 2–1, 4–3, 5–4, 6–5, and 7–6 transitions of HNCN towards the molecular cloud G+0.693-0.027. We have detected three unblended lines of HNCN, these are the N  = 6–5 doublet and one line of the N  = 4–3 transition. Additionally, we present one line of the N  = 5–4 transition partially blended with emission from other species. The local thermodynamic equilibrium best fit to the data gives a molecular abundance of (0.91 ± 0.05) × 10−10 with respect to H2. The relatively low abundance of this species in G+0.693-0.027 and its high reactivity suggest that HNCN is possibly produced by gas-phase chemistry. Our work shows that this highly reactive molecule is present in interstellar space, and thus it represents a plausible precursor of larger prebiotic molecules with the nitrogen–carbon–nitrogen backbone such as cyanamide (NH2CN), carbodiimide (HNCNH), and formamidine (NH2CHNH). [ABSTRACT FROM AUTHOR]

The 14N/15N ratio in molecules exhibits a large variation in star-forming regions, especially when measured from N2H+ isotopologues. However, there are only a few studies performed at high-angular resolution. We present the first interferometric survey of the 14N/15N ratio in N2H+ obtained with Atacama Large Millimeter Array observations towards four infrared-dark clouds harbouring 3 mm continuum cores associated with different physical properties. We detect N15NH+ (1–0) in |$\sim 20\!-\!40{{\ \rm per\ cent}}$| of the cores, depending on the host cloud. The 14N/15N values measured towards the millimetre continuum cores range from a minimum of ∼80 up to a maximum of ∼400. The spread of values is narrower than that found in any previous single-dish survey of high-mass star-forming regions and than that obtained using the total power data only. This suggests that the 14N/15N ratio is on average higher in the diffuse gaseous envelope of the cores and stresses the need for high-angular resolution maps to measure correctly the 14N/15N ratio in dense cores embedded in IRDCs. The average 14N/15N ratio of ∼210 is also lower than the interstellar value at the Galactocentric distance of the clouds (∼300–330), although the sensitivity of our observations does not allow us to unveil 14N/15N ratios higher than ∼400. No clear trend is found between the 14N/15N ratio and the core physical properties. We find only a tentative positive trend between 14N/15N and H2 column density. However, firmer conclusions can be drawn only with higher sensitivity measurements. [ABSTRACT FROM AUTHOR]

Infrared dark clouds (IRDCs) are very dense and highly extincted regions that host the initial conditions of star and stellar cluster formation. It is crucial to study the kinematics and molecular content of IRDCs to test their formation mechanism and ultimately characterize these initial conditions. We have obtained high-sensitivity Silicon Monoxide, SiO(2–1), emission maps towards the six IRDCs, G018.82–00.28, G019.27+00.07, G028.53–00.25, G028.67+00.13, G038.95–00.47, and G053.11+00.05 (cloud A, B, D, E, I, and J, respectively), using the 30-m antenna at the Instituto de Radioastronomía Millimétrica (IRAM30m). We have investigated the SiO spatial distribution and kinematic structure across the six clouds to look for signatures of cloud–cloud collision events that may have formed the IRDCs and triggered star formation within them. Towards clouds A, B, D, I, and J, we detect spatially compact SiO emission with broad-line profiles that are spatially coincident with massive cores. Towards the IRDCs A and I, we report an additional SiO component that shows narrow-line profiles and that is widespread across quiescent regions. Finally, we do not detect any significant SiO emission towards cloud E. We suggest that the broad and compact SiO emission detected towards the clouds is likely associated with ongoing star formation activity within the IRDCs. However, the additional narrow and widespread SiO emission detected towards cloud A and I may have originated from the collision between the IRDCs and flows of molecular gas pushed towards the clouds by nearby H  ii regions. [ABSTRACT FROM AUTHOR]

G+0.693-0.03 is a quiescent molecular cloud located within the Sagittarius B2 (Sgr B2) star-forming complex. Recent spectral surveys have shown that it represents one of the most prolific repositories of complex organic species in the Galaxy. The origin of such chemical complexity, along with the small-scale physical structure and properties of G+0.693-0.03, remains a mystery. In this paper, we report the study of multiple molecules with interferometric observations in combination with single-dish data in G+0.693-0.03. Despite the lack of detection of continuum source, we find small-scale (0.2 pc) structures within this cloud. The analysis of the molecular emission of typical shock tracers such as SiO, HNCO, and CH3OH unveiled two molecular components, peaking at velocities of 57 and 75 km s−1. They are found to be interconnected in both space and velocity. The position–velocity diagrams show features that match with the observational signatures of a cloud–cloud collision. Additionally, we detect three series of class I methanol masers known to appear in shocked gas, supporting the cloud–cloud collision scenario. From the maser emission we provide constraints on the gas kinetic temperatures (∼30–150 K) and H2 densities (104–105 cm−2). These properties are similar to those found for the starburst galaxy NGC 253 also using class I methanol masers, suggested to be associated with a cloud–cloud collision. We conclude that shocks driven by the possible cloud–cloud collision is likely the most important mechanism responsible for the high level of chemical complexity observed in G+0.693-0.03. [ABSTRACT FROM AUTHOR]

Aims. The Seeds Of Life In Space IRAM/NOEMA large program aims at studying a set of crucial complex organic molecules in a sample of sources with a well-known physical structure that covers the various phases of solar-type star formation. One representative object of the transition from the prestellar core to the protostar phases has been observed toward the very low luminosity object (VeLLO) L1521F. This type of source is important to study to link prestellar cores and Class 0 sources and also to constrain the chemical evolution during the process of star formation. Methods. Two frequency windows (81.6-82.6 GHz and 96.65-97.65 GHz) were used to observe the emission from several complex organics toward the L1521F VeLLO. These setups cover transitions of ketene (H2CCO), propyne (CH3CCH), formamide (NH2CHO), methoxy (CH3O), methanol (CH3OH), dimethyl ether (CH3OCH3), and methyl formate (HCOOCH3). Results. Only two transitions of methanol (A+, E2) have been detected in the narrow window centered at 96.7 GHz (with an upper limit on E1) in a very compact emission blob (~700 corresponding to ~1000 au) toward the northeast of the L1521F protostar. The CS 2-1 transition is also detected within theWideX bandwidth. Consistently with what has been found in prestellar cores, the methanol emission appears ~1000 au away from the dust peak. The location of the methanol blob coincides with one of the filaments that have previously been reported in the literature. The excitation temperature of the gas inferred from methanol is (10 ± 2) K, while the H2 gas density (estimated from the detected CS 2-1 emission and previous CS 5-4 ALMA observations) is a factor >25 higher than the density in the surrounding environment (n(H2) 107 cm-3). Conclusions. Based on its compactness, low excitation temperature, and high gas density, we suggest that the methanol emission detected with NOEMA is (i) either a cold and dense shock-induced blob that formed recently (≤ a few hundred years) by infalling gas or (ii) a cold and dense fragment that may just have been formed as a result of the intense gas dynamics within the L1521F VeLLO system. [ABSTRACT FROM AUTHOR]

GEMS is an IRAM 30 m Large Program whose aim is determining the elemental depletions and the ionization fraction in a set of prototypical star-forming regions. This paper presents the first results from the prototypical dark cloud Taurus molecular cloud (TMC) 1. Extensive millimeter observations have been carried out with the IRAM 30 m telescope (3 and 2 mm) and the 40 m Yebes telescope (1.3 cm and 7 mm) to determine the fractional abundances of CO, HCO+, HCN, CS, SO, HCS+, and N2H+ in three cuts which intersect the dense filament at the well-known positions TMC 1-CP, TMC 1-NH3, and TMC 1-C, covering a visual extinction range from AV ~ 3 to ~20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1−5 × 103 cm−3; and (ii) the dense phase, located at AV > 10 mag, with molecular hydrogen densities >104 cm−3. Observations and modeling show that the gas phase abundances of C and O progressively decrease along the C+/C/CO transition zone (AV ~ 3 mag) where C/H ~ 8 × 10−5 and C/O ~ 0.8−1, until the beginning of the dense phase at AV ~ 10 mag. This is consistent with the grain temperatures being below the CO evaporation temperature in this region. In the case of sulfur, a strong depletion should occur before the translucent phase where we estimate an S∕H ~ (0.4−2.2) × 10−6, an abundance ~7–40 times lower than the solar value. A second strong depletion must be present during the formation of the thick icy mantles to achieve the values of S/H measured in the dense cold cores (S∕H ~ 8 × 10−8). Based on our chemical modeling, we constrain the value of ζH2 $\zeta_{\textrm{H}_2}$ ζ H 2 to ~(0.5–1.8) × 10−16 s−1 in the translucent cloud. [ABSTRACT FROM AUTHOR]

Theories of a pre-RNA world suggest that glycolonitrile (HOCH2CN) is a key species in the process of ribonucleotide assembly, which is considered as a molecular precursor of nucleic acids. In this Letter, we report the first detection of this pre-biotic molecule in the interstellar medium by using ALMA data obtained at frequencies between 86.5 GHz and 266.5 GHz toward the Solar-type protostar IRAS16293–2422 B. A total of 15 unblended transitions of HOCH2CN were identified. Our analysis indicates the presence of a cold (T |$\rm _{ex}$|  = 24 ± 8 K) and a warm (T |$\rm _{ex}$|  = 158 ± 38 K) component meaning that this molecule is present in both the inner hot corino and the outer cold envelope of IRAS16293 B. The relative abundance with respect to H2 is (6.5 ± 0.6) × 10−11 and ≥(6 ± 2) × 10−10 for the warm and cold components, respectively. Our chemical modelling seems to underproduce the observed abundance for both the warm and cold component under various values of the cosmic ray ionization rate (ζ). Key gas phase routes for the formation of this molecule might be missing in our chemical network. [ABSTRACT FROM AUTHOR]

We report the first detection in the interstellar medium (ISM) of the Z-isomer of cyanomethanimine (HNCHCN), an HCN dimer proposed as precursor of adenine. We identified six transitions of Z-cyanomethanimine, along with five transitions of E-cyanomethanimine, using IRAM 30m observations towards the Galactic Centre quiescent molecular cloud G + 0.693. The Z-isomer has a column density of (2.0 ± 0.6) × 1014 cm−2 and an abundance of 1.5 × 10−9. The relative abundance ratio between the isomers is [Z/E]∼6. This value cannot be explained by the two chemical formation routes previously proposed (gas phase and grain surface), which predicts abundances ratios between 0.9 and 1.5. The observed [Z/E] ratio is in good agreement with thermodynamic equilibrium at the gas kinetic temperature (130−210 K). Since isomerization is not possible in the ISM, the two species may be formed at high temperature. New chemical models, including surface chemistry on dust grains and gas-phase reactions, should be explored to explain our findings. Whatever the formation mechanism, the high abundance of Z-HNCHCN shows that precursors of adenine are efficiently formed in the ISM. [ABSTRACT FROM AUTHOR]

We present an unbiased spectral line survey towards the Galactic Centre (GC) quiescent giant molecular cloud, G+0.693 using the GBT and IRAM 30  telescopes. Our study highlights an extremely rich organic inventory of abundant amount of nitrogen (N)-bearing species in a source without signatures of star formation. We report the detection of 17 N-bearing species in this source, of which eight are complex organic molecules. A comparison of the derived abundances relative to H2 is made across various Galactic and extragalactic environments. We conclude that the unique chemistry in this source is likely to be dominated by low-velocity shocks with X-rays/cosmic rays also playing an important role in the chemistry. Like previous findings obtained for O-bearing molecules, our results for N-bearing species suggest a more efficient hydrogenation of these species on dust grains in G+0.693 than in hot cores in the Galactic disc, as a consequence of the low-dust temperatures coupled with energetic processing by X-ray/cosmic ray radiation in the GC. [ABSTRACT FROM AUTHOR]

We present here a systematic search for cyanopolyynes in the shock region L1157-B1 and its associated protostar L1157-mm in the framework of the Large Program 'Astrochemical Surveys At IRAM' (ASAI), dedicated to chemical surveys of solar-type star-forming regions with the IRAM 30-m telescope. Observations of the millimeter windows between 72 and 272 GHz permitted the detection of HC3N and its 13C isotopologues, and HC5N (for the first time in a protostellar shock region). In the shock, the analysis of the line profiles shows that the emission arises from the outflow cavities associated with L1157-B1 and L1157-B2. Molecular abundances and excitation conditions were obtained from the analysis of the Spectral Line Energy Distributions under the assumption of Local Thermodynamical Equilibrium or using a radiative transfer code in the Large Velocity Gradient approximation. Towards L1157 mm, the HC3N emission arises from the cold envelope (Trot = 10 K) and a higher-excitation region (Trot = 31 K) of smaller extent around the protostar. We did not find any evidence of 13C or D fractionation enrichment towards L1157-B1. We obtain a relative abundance ratio HC3N/HC5N of 3.3 in the shocked gas. We find an increase by a factor of 30 of the HC3N abundance between the envelope of L1157-mm and the shock region itself. Altogether, these results are consistent with a scenario in which the bulk of HC3N was produced by means of gas phase reactions in the passage of the shock. This scenario is supported by the predictions of a parametric shock code coupled with the chemical model UCL_CHEM. [ABSTRACT FROM AUTHOR]

Infrared dark clouds (IRDCs) are thought to be potential hosts of the elusive early phases of high-mass star formation. Here, we conduct an in-depth kinematic analysis of one such IRDC, G034.43+00.24 (Cloud F), using high sensitivity and high spectral resolution IRAM-30m N2H+ (1-0) and C18O(1-0) observations. To disentangle the complex velocity structure within this cloud, we use Gaussian decomposition and hierarchical clustering algorithms. We find that four distinct coherent velocity components are present within Cloud F. The properties of these components are compared to those found in a similar IRDC, G035.39-00.33 (Cloud H). We find that the components in both clouds have high densities (inferred by their identification in N2H+), trans-to-supersonic non-thermal velocity dispersions with Mach numbers of ~1.5-4, a separation in velocity of ~3 kms-1, and a mean red-shift of ~0.3 kms-1 between the N2H+ (dense gas) and C18O emission (envelope gas). The latter of these could suggest that these clouds share a common formation scenario. We investigate the kinematics of the larger-scale Cloud F structures, using lower-density-tracing 13CO (1-0) observations. A good correspondence is found between the components identified in the IRAM-30m observations and the most prominent component in the 13CO data. We find that the IRDC Cloud F is only a small part of a much larger structure, which appears to be an inter-arm filament of the Milky Way. [ABSTRACT FROM AUTHOR]

The high sensitivity of the IRAM 30-m Astrochemical Surveys At IRAM (ASAI) unbiased spectral survey in the mm window allows us to detect NO emission towards both the Class I object SVS13-A and the protostellar outflow shock L1157-B1. We detect the hyperfine components of the 2Π1/2J = 3/2 → 1/2 (at 151 GHz) and the 2Π1/2J = 5/2 → 3/2 (at 250 GHz) spectral pattern. The two objects show different NO profiles: (i) SVS13-A emits through narrow (1.5 km s−1) lines at the systemic velocity, while (ii) L1157-B1 shows broad (∼5 km s−1) blueshifted emission. For SVS13-A, the analysis leads to Tex ≥ 4 K, N(NO) ≤ 3 × 1015 cm−2, and indicates the association of NO with the protostellar envelope. In L1157-B1, NO is tracing the extended outflow cavity: Tex ≃ 4–5 K, and N(NO) = 5.5 ± 1.5 × 1015 cm−2. Using C18O, 13C18O, C17O, and 13C17O ASAI observations, we derive an NO fractional abundance less than ∼10−7 for the SVS13-A envelope, in agreement with previous measurements towards extended photodissociation regions (PDRs) and prestellar objects. Conversely, a definite X(NO) enhancement is measured towards L1157-B1, ∼6 × 10−6, showing that the NO production increases in shocks. The public code uclchem was used to interpret the NO observations, confirming that the abundance observed in SVS13-A can be attained in an envelope with a gas density of 105 cm−3 and a kinetic temperature of 40 K. The NO abundance in L1157-B1 is reproduced with pre-shock densities of 105 cm−3 subjected to a ∼45 km s−1 shock. [ABSTRACT FROM AUTHOR]

Context. Modern versions of the Miller-Urey experiment claim that formamide (NH2CHO) could be the starting point for the formation of metabolic and genetic macromolecules. Intriguingly, formamide is indeed observed in regions forming solar-type stars and in external galaxies. Aims. How NH2CHO is formed has been a puzzle for decades: our goal is to contribute to the hotly debated question of whether formamide is mostly formed via gas-phase or grain surface chemistry. Methods. We used the NOrthern Extended Millimeter Array (NOEMA) interferometer to image NH2CHO towards the L1157-B1 blue-shifted shock, a well-known interstellar laboratory, to study how the components of dust mantles and cores released into the gas phase triggers the formation of formamide. Results. We report the first spatially resolved image (size ~9", ~2300 AU) of formamide emission in a shocked region around a Sun-like protostar: the line profiles are blueshifted and have a FWHM ≃ 5 km s-1. A column density of NNH2CHO = 8 × 1012 cm-1 and an abundance, with respect to H-nuclei, of 4 × 10-9 are derived. We show a spatial segregation of formamide with respect to other organic species. Our observations, coupled with a chemical modelling analysis, indicate that the formamide observed in L1157-B1 is formed by a gas-phase chemical process and not on grain surfaces as previously suggested. Conclusions. The Seeds of Life in Space (SOLIS) interferometric observations of formamide provide direct evidence that this potentially crucial brick of life is efficiently formed in the gas phase around Sun-like protostars. [ABSTRACT FROM AUTHOR]

Context. The formation of deuterated molecules is favoured at low temperatures and high densities. Therefore, the deuteration fraction (Dfrac) is expected to be enhanced in cold, dense prestellar cores and to decrease after protostellar birth. Previous studies have shown that the deuterated forms of species such as N2H+ (formed in the gas phase) and CH3OH (formed on grain surfaces) can be used as evolutionary indicators and to constrain their dominant formation processes and timescales. Aims. Formaldehyde (H2CO) and its deuterated forms can be produced both in the gas phase and on grain surfaces. However, the relative importance of these two chemical pathways is unclear. Comparison of the deuteration fraction of H2CO with respect to that of N2H+, NH3, and CH3OH can help us to understand its formation processes and timescales. Methods. With the new SEPIA Band 5 receiver on APEX, we have observed the J = 3 → 2 rotational lines of HDCO and D2CO at 193 GHz and 175 GHz toward three massive star-forming regions hosting objects at different evolutionary stages: two high-mass starless cores (HMSC), two high-mass protostellar objects (HMPOs), and one ultracompact HII region (UC HII). By using previously obtained H2CO J = 3 → 2 data, the deuteration fractions HDCO/H2CO and D2CO/HDCO are estimated. Results. Our observations show that singly deuterated H2CO is detected toward all sources and that the deuteration fraction of H2CO increases from the HMSC to the HMPO phase and then sharply decreases in the latest evolutionary stage (UCHII). The doubly deuterated form of H2CO is detected only in the earlier evolutionary stages, with D2CO/H2CO showing a pattern that is qualitatively consistent with the pattern of HDCO/H2CO, within current uncertainties. Conclusions. Our initial results show that H2CO may display a similar Dfrac pattern as that of CH3OH in massive young stellar objects. This finding suggests that solid-state reactions dominate its formation. [ABSTRACT FROM AUTHOR]

As part of the Large Program Astrochemical Surveys At IRAM, we have used the IRAM 30 m telescope to lead a systematic search for the emission of rotational transitions of P-bearing species between 80 and 350 GHz towards L1157-B1, a shock position in the solar-type star-forming region L1157. We report the detection of several transitions of PN and, for the first time, of pre-biotic molecule PO. None of these species are detected towards the driving protostar of the outflow L1157-mm. Analysis of the line profiles shows that PN arises from the outflow cavity, where SiO, a strong shock tracer, is produced. Radiative transfer analysis yields an abundance of 2.5 × 10−9 and 0.9 × 10−9 for PO and PN, respectively. These results imply a strong depletion (≈100) of phosphorus in the quiescent cloud gas. Shock modelling shows that atomic N plays a major role in the chemistry of PO and PN. The relative abundance of PO and PN brings constraints both on the duration of the pre-shock phase, which has to be ∼106 yr, and on the shock parameters. The maximum temperature in the shock has to be larger than 4000 K, which implies a shock velocity of 40 km s−1. [ABSTRACT FROM AUTHOR]

In a previous study of the L1157 B1 shocked cavity, a comparison between NH3(10-00) and H2O(110-101) transitions showed a striking difference in the profiles, with H2O emitting at definitely higher velocities. This behaviour was explained as a result of the high-temperature gas-phase chemistry occurring in the post-shock gas in the B1 cavity of this outflow. If the differences in behaviour between ammonia and water are indeed a consequence of the high gas temperatures reached during the passage of a shock, then one should find such differences to be ubiquitous among chemically rich outflows. In order to determine whether the difference in profiles observed between NH3 and H2O is unique to L1157 or a common characteristic of chemically rich outflows, we have performed Herschel-HIFI observations of the NH3(10-00) line at 572.5 GHz in a sample of eight bright low-mass outflow spots already observed in the H2O(110-101) line within the Water In Star-forming regions with Herschel Key Programme. We detected the ammonia emission at high velocities at most of the outflows positions. In all cases, the water emission reaches higher velocities than NH3, proving that this behaviour is not exclusive of the L1157-B1 position. Comparisons with a gas-grain chemical and shock model confirms, for this larger sample, that the behaviour of ammonia is determined principally by the temperature of the gas. [ABSTRACT FROM AUTHOR]

Infrared Dark Clouds (IRDCs) are cold, dense regions that are usually found within Giant Molecular Clouds. Ongoing star formation within IRDCs is typically still deeply embedded within the surrounding molecular gas. Characterizing the properties of relatively quiescent IRDCs may therefore help us to understand the earliest phases of the star formation process. Studies of local molecular clouds have revealed that deuterated species are enhanced in the earliest phases of star formation. In this paper, we test this towards IRDC G035.39-00.33.We present an 80 arcsec by 140 arcsec map of the J=2 →1 transition of N2D+, obtained with the Institut de Radioastronomie Millimétrique 30 m telescope telescope. We find that N2D+ is widespread throughout G035.39-00.33. Complementary observations of N2H+ (1 - 0) are used to estimate the deuterium fraction, DN2H+ frac ≡ N(N2D+)/N(N2H+). We report a mean DN2H+ frac = 0.04 ± 0.01, with a maximum of DN2H+ frac = 0.09 ± 0.02. The mean deuterium fraction is ~3 orders of magnitude greater than the interstellar [D]/[H] ratio. High angular resolution observations are required to exclude beam dilution effects of compact deuterated cores. Using chemical modelling, we find that the average observed values of DN2H+ frac are in agreement with an equilibrium deuterium fraction, given the general properties of the cloud. This implies that the IRDC is at least ~3 Myr old, which is ~8 times longer than the mean free-fall time of the observed deuterated region. [ABSTRACT FROM AUTHOR]

Infrared dark clouds (IRDCs) are dense, molecular structures in the interstellar medium that can harbour sites of high-mass star formation. IRDCs contain supersonic turbulence, which is expected to generate shocks that locally heat pockets of gas within the clouds. We present observations of the CO J = 8-7, 9-8, and 10-9 transitions, taken with the Herschel Space Observatory, towards four dense, starless clumps within IRDCs (C1 in G028.37+00.07, F1 and F2 in G034.43+0007, and G2 in G034.77-0.55). We detect the CO J = 8-7 and 9-8 transitions towards three of the clumps (C1, F1, and F2) at intensity levels greater than expected from photodissociation region (PDR) models. The average ratio of the 8-7 to 9-8 lines is also found to be between 1.6 and 2.6 in the three clumps with detections, significantly smaller than expected from PDR models. These low line ratios and large line intensities strongly suggest that the C1, F1, and F2 clumps contain a hot gas component not accounted for by standard PDR models. Such a hot gas component could be generated by turbulence dissipating in low velocity shocks. [ABSTRACT FROM AUTHOR]

Infrared dark clouds (IRDCs) host the initial conditions under which massive stars and stellar clusters form. It is therefore important to study the kinematics, as well as the physical and chemical properties of these regions. Their complex structure however posits challenges in the data interpretation. We have obtained high-sensitivity and high-spectral-resolution observations with the Instituto de Radioastronomía Milimétrica 30 m antenna, which allowed us to perform detailed analysis of the kinematics within one IRDC, G035.39−00.33. This cloud has been selected for its highly filamentary morphology and the presence of extended quiescent regions, characteristics of dynamical youth. We focus on the J = 1 → 0 and J = 3 → 2 transitions of N2H+, C18O (1–0), and make comparison with SiO (2–1) observations and extinction mapping. Three interacting filaments of gas are found. We report large-scale velocity coherence throughout the cloud, evidenced through small velocity gradients and relatively narrow line widths. This suggests that the merging of these filaments is somewhat ‘gentle’, possibly regulated by magnetic fields. This merging of filaments may be responsible for the production of weak, parsec-scale SiO emission, via grain mantle vaporization. A systematic velocity shift between the N2H+ (1–0) and C18O (1–0) gas throughout the cloud of 0.18 ± 0.04 km s−1 is also found, consistent with a scenario of collisions between filaments which is still ongoing. The N2H+ (1–0) is extended throughout the IRDC, in contrast to low-mass star forming regions, where N2H+ is known to trace only the dense cores. The average H2 number density across the IRDC is ≃5 × 104 cm−3, at least one order of magnitude larger than in nearby molecular clouds where low-mass stars are forming. A temperature gradient perpendicular to the filament is found. From our study, we conclude that G035.39−00.33 (clearly seen in the extinction map and in N2H+) has been formed via the collision between two relatively quiescent filaments with average densities of ≃5 × 103 cm−3, moving with relative velocities of ≃5 km s−1. The accumulation of material at the merging points started ≳ 1 Myr ago and it is still ongoing. [ABSTRACT FROM AUTHOR]

We present high-sensitivity arcmin2 maps of the J= 2→1 rotational lines of SiO, CO, 13CO and C18O, observed towards the filamentary infrared dark cloud (IRDC) G 00.33. Single-pointing spectra of the SiO J= 2→1 and J= 3→2 lines towards several regions in the filament are also reported. The SiO images reveal that SiO is widespread along the IRDC (size ≥2 pc), showing two different components: one bright and compact arising from three condensations (N, E and S) and the other weak and extended along the filament. While the first component shows broad lines (linewidths of ∼4–7 km s−1) in both SiO J= 2→1 and SiO J= 3→2, the second one is only detected in SiO J= 2→1 and has narrow lines (∼0.8 km s−1). The maps of CO and its isotopologues show that low-density filaments are intersecting the IRDC and appear to merge towards the densest portion of the cloud. This resembles the molecular structures predicted by flow-driven, shock-induced and magnetically-regulated cloud formation models. As in outflows associated with low-mass star formation, the excitation temperatures and fractional abundances of SiO towards N, E and S increase with velocity from ∼6 to 40 K and from ∼10−10 to , respectively, over a velocity range of ∼7 km s−1. Since 8 μm and 24 μm sources and/or extended m emission are detected in N, E and S, broad SiO is likely produced in outflows associated with high-mass protostars. The excitation temperatures and fractional abundances of the narrow SiO lines, however, are very low (∼9 K and ∼10−11, respectively), and consistent with the processing of interstellar grains by the passage of a shock with km s−1. This emission could be generated (i) by a large-scale shock, perhaps remnant of the IRDC formation process, (ii) by decelerated or recently processed gas in large-scale outflows driven by 8- and 24-μm sources or (iii) by an undetected and widespread population of lower mass protostars. High-angular-resolution observations are needed to disentangle between these three scenarios. [ABSTRACT FROM AUTHOR]