Seeds Of Life In Space Research Articles

SOLIS

Context. The study of the early phases of star and planet formation is important to understand the physical and chemical history of stellar systems such as our own. In particular, protostars born in rich clusters are prototypes of the young Solar System. Aims. In the framework of the Seeds Of Life In Space (SOLIS) large observational project, the aim of the present work is to investigate the origin of the previously inferred high flux of energetic particles in the protocluster FIR4 of the Orion Molecular Cloud 2 (OMC-2), which appears asymmetric within the protocluster itself. Methods. Interferometric observations carried out with the IRAM NOEMA interferometer were used to map the silicon monoxide (SiO) emission around the FIR4 protocluster. Complementary archival data from the ALMA interferometer were also employed to help constrain excitation conditions. A physical-chemical model was implemented to characterise the particle acceleration along the protostellar jet candidate, along with a non-LTE analysis of the SiO emission along the jet. Results. The emission morphology of the SiO rotational transitions hints for the first time at the presence of a collimated jet originating very close to the brightest protostar in the cluster, HOPS-108. Conclusions. The NOEMA observations unveiled a possible jet in the OMC-2 FIR4 protocluster propagating towards a previously measured enhanced cosmic-ray ionisation rate. This suggests that energetic particle acceleration by the jet shock close to the protostar might be at the origin of the enhanced cosmic-ray ionisation rate, as confirmed by modelling the protostellar jet.

A train of shocks at 3000-au scale? Exploring the clash of an expanding bubble into the NGC 1333 IRAS 4 region. SOLIS XIV

ABSTRACT There is evidence that the star formation process is linked to the intricate net of filaments in molecular clouds, which may be also due to gas compression from external triggers. We studied the southern region of the Perseus NGC 1333 molecular cloud, known to be heavily shaped by similar external triggers, to shed light on the process that perturbed the filament where the Class 0 IRAS4 protostars lie. We use new IRAM-NOEMA observations of SiO and CH3OH, both known to trace violent events as shocks, towards IRAS 4A as part of the Large Program Seeds Of Life In Space (SOLIS). We detected three parallel elongated (>6000 au) structures, called fingers, with narrow-line profiles (∼1.5 km s−1) peaked at the cloud systemic velocity, tracing gas with high density ((5–20) × 105 cm−3) and high temperature (80–160 K). They are chemically different, with the northern finger traced by both SiO and CH3OH ([CH3OH]/[SiO] ∼ 160–300), while the other two only by SiO ([CH3OH]/[SiO] ≤ 40). Among various possibilities, a train of three shocks, distanced by ≥5000 yr, would be consistent with the observations if a substantial fraction of silicon, frozen on to the grain mantles, is released by the shocks. We suggest that the shock train is due to an expanding gas bubble, coming behind NGC 1333 from the south-west and clashing against the filament where IRAS 4A lies. Finally, we propose a solution to the two-decades-long debate on the nature and origin of the widespread narrow SiO emission observed in the south part of NGC 1333, namely that it is due to unresolved trains of shocks.

Interstellar complex organic molecules in the prototypical Class I protostar SVS13-A: From large scales to planet forming disks

We present a chemical systematic study of the Class I object SVS13- A obtained in the framework of two IRAM Large Programs: ASAI (Astrochemical Survey At IRAM-30m) with the 30m and SOLIS (Seeds Of Life In Space) with NOEMA. Thanks to the ASAI high-sensitivity unbiased spectral survey of the 3, 2 and 1.3mm bands, we detect and analyse several emission lines from deuterated species and interstellar complex organic molecules (iCOMs, e.g. molecules composed by 6 or more atoms and based on carbon). Within SOLIS, we obtain high-sensitivity and high-spatial resolution (∼ 180 au) maps of crucial iCOMs. As a follow up, thanks to ALMA we explore the chemistry in the planet forming region (∼ 50 au). We image emission lines from methanol (CH3OH), acetaldehyde (CH3CHO), formamide (NH2CHO) and dimethyl ether (CH3OCH3). The different spatial distributions suggest a chemical differentiation inside the binary system or a different continuum opacity in the two protostellar disks.

SOLIS

Context. Isotopic fractionation is an important tool for investigating the chemical history of our Solar System. In particular, the isotopic fraction of nitrogen (14N/15N) is lower in comets and other pristine Solar System bodies with respect to the value measured for the protosolar nebula, suggesting a local chemical enrichment of 15N during the formation of the Solar System. Therefore, interferometric studies of nitrogen fractionation in Solar System precursors are needed for us to obtain clues about our astrochemical origins. Aims. In this work we have investigated the variation in the 14N/15N ratio in one of the closest analogues of the environment in which the Solar System was born: the protocluster OMC-2 FIR4. We present the first comparison at high angular resolution between HCN and N2H+ using interferometric data. Methods. We analysed observations of the HCN isotopologues H13CN and HC15N in the OMC-2 FIR4 protocluster. Specifically, we observed the transitions H13CN (1−0) and HC15N (1−0) with the NOrthern Extended Millimeter Array (NOEMA) within the context of the IRAM Seeds Of Life In Space (SOLIS) Large Program. We combined our results with analysis of archival data obtained with the Atacama Large Millimeter Array of N2H+ and its 15N isotopologues. Results. Our results show a small regional variation in the 14N/15N ratio for HCN, from ~250 to 500. The ratios in the central regions of FIR4, where the candidate protostars are located, are largely consistent with one another and within that range (~300). They also show little variation from the part of the protocluster known to harbour a high cosmic-ray ionisation rate to the portion with a lower rate. We also found a small variation in the 14N/15N ratio of N2H+ across different regions, from ~200 to ~400. Conclusions. These results suggest that local changes in the physical parameters occurring on the small linear scales probed by our observations in the protocluster do not seem to affect the 14N/15N ratio in either HCN or N2H+ and hence that this is independent of the molecule used. Moreover, the high level of irradiation due to cosmic rays does not affect the N fractionation either.

SOLIS

Context. Recent results in astrochemistry have revealed that some molecules, such as interstellar complex organic species and deuterated species, can serve as valuable tools in the investigation of star-forming regions. Sulphuretted species can also be used to follow the chemical evolution of the early stages of a Sun-like star formation process. Aims. The goal is to obtain a census of S-bearing species using interferometric images towards SVS13-A, a Class I object associated with a hot corino that is rich in interstellar complex organic molecules. Methods. To this end, we used the NGC 1333 SVS13-A data at 3 mm and 1.4 mm obtained with the IRAM-NOEMA interferometer in the framework of the SOLIS (Seeds of Life in Space) Large Program. The line emission of S-bearing species was imaged and analyzed using local thermodynamic equilibrium (LTE) and large velocity gradient (LVG) approaches. Results. We imaged the spatial distribution on ≤300 au scale of the line emission of 32SO, 34SO, C32S, C34S, C33S, OCS, H2C32S, H2C34S, and NS. The low excitation (9 K) 32SO line traces: (i) the low-velocity SVS13-A outflow and (ii) the fast (up to 100 km s−1 away from the systemic velocity) collimated jet driven by the nearby SVS13-B Class 0 object. Conversely, the rest of the lines are confined in the inner SVS13-A region, where complex organics were previously imaged. More specifically, the non-LTE LVG analysis of SO, SO2, and H2CS indicates a hot corino origin (size in the 60–120 au range). Temperatures between 50 K and 300 K, as well as volume densities larger than 105 cm−3 have been derived. The abundances of the sulphuretted are in the following ranges: 0.3–6 × 10−6 (CS), 7 × 10−9–1 × 10−7 (SO), 1–10 × 10−7 (SO2), a few 10−10 (H2CS and OCS), and 10−10–10−9 (NS). The N(NS)/N(NS+) ratio is larger than 10, supporting the assessment that the NS+ ion is mainly formed in the extended envelope. Conclusions. The [H2CS]/[H2CO] ratio, once measured at high-spatial resolutions, increases with time (from Class 0 to Class II objects) by more than one order of magnitude (from ≤10−2 to a few 10−1). This suggests that [S]/[O] changes along the process of Sun-like star formation. Finally, the estimate of the [S]/[H] budget in SVS13-A is 2–17% of the Solar System value (1.8 × 10−5), which is consistent with what was previously measured towards Class 0 objects (1–8%). This finding supports the notion that the enrichment of the sulphuretted species with respect to dark clouds remains constant from the Class 0 to the Class I stages of low-mass star formation. The present findings stress the importance of investigating the chemistry of star-forming regions using large observational surveys as well as sampling regions on the scale of the Solar System.

Seeds of Life in Space (SOLIS)

Context. The isotopic ratio of nitrogen presents a wide range of values in the Solar System: from ~140 in meteorites and comets to 441 in the solar wind. In star-forming systems, we observe even a higher spread of ~150–1000. The origin of these differences is still unclear. Aims. Chemical reactions in the gas phase are one of the possible processes that could modify the 14N/15N ratio. We aim to investigate if and how the passage of a shock wave in the interstellar medium, which activates a rich chemistry, can affect the relative fraction of nitrogen isotopes. The ideal place for such a study is the chemically rich outflow powered by the L1157-mm protostar, where several shocked clumps are present. Methods. We present the first measurement of the 14N/15N ratio in the two shocked clumps, B1 and B0, of the protostellar outflow L1157. The measurement is derived from the interferometeric maps of the H13CN (1–0) and the HC15N (1–0) lines obtained with the NOrthern Extended Millimeter Array (NOEMA) interferometer as part of the Seeds of Life in Space (SOLIS) programme. Results. In B1, we find that the H13CN (1–0) and HC15N (1–0) emission traces the front of the clump, that is the apex of the shocked region, where the fast jet impacts the lower velocity medium with an averaged column density of N(H13CN) ~ 7 × 1012 cm−2 and N(HC15N) ~ 2 × 1012 cm−2. In this region, the ratio H13CN (1–0)/HC15N (1–0) is almost uniform with an average value of ~5 ± 1. The same average value is also measured in the smaller clump B0e. Assuming the standard 12C/13C = 68, we obtain 14N/15N = 340 ± 70. This ratio is similar to those usually found with the same species in prestellar cores and protostars. We analysed the prediction of a chemical shock model for several shock conditions and we found that the nitrogen and carbon fractionations do not vary much for the first period after the shock. The observed H13CN/HC15N can be reproduced by a non-dissociative, C-type shock with pre-shock density n(H) = 105 cm−3, shock velocity Vs between 20 and 40 km s−1, and cosmic-ray ionization rate of 3 × 10−16 s−1; this agrees with previous modelling of other chemical species in L1157-B1. Conclusions. Both observations and chemical models indicate that the rich chemistry activated by the shock propagation does not affect the nitrogen isotopic ratio, which remains similar to that measured in lower temperature gas in prestellar cores and protostellar envelopes.

Seeds of Life in Space (SOLIS)

Context. Contrary to what is expected from models of Galactic chemical evolution, the isotopic fractionation of silicon (Si) in the Galaxy has recently been found to be constant. This finding calls for new observations, also at core scales, to re-evaluate the fractionation of Si. Aims. L1157-B1 is one of the outflow-shocked regions along the blue-shifted outflow that is driven by the Class 0 protostar L1157-mm. It is an ideal laboratory for studying the material ejected from the grains on very short timescales because its chemical composition is representative of the composition of the grains. Methods. We imaged 28SiO, 29SiO, and 30SiO J = 2–1 emission towards L1157-B1 and B0 with the NOrthern Extended Millimeter Array (NOEMA) interferometer as part of the Seeds of Life in Space (SOLIS) large project. We present here a study of the isotopic fractionation of SiO towards L1157-B1. Furthermore, we used the high spectral resolution observations on the main isotopologue, 28SiO, to study the jet impact on the dense gas. We here also present single-dish observations obtained with the IRAM 30 m telescope and Herschel-HIFI. We carried out a non-local thermal equilibrium analysis using a large velocity gradient code to model the single-dish observations. Results. From our observations we can show that (i) the 2–1 transition of the main isotopologue is optically thick in L1157-B1 even at high velocities, and (ii) the [29SiO/30SiO] ratio is constant across the source, and consistent with the solar value of 1.5. Conclusions. We report the first isotopic fractionation maps of SiO in a shocked region and show the absence of a mass-dependent fractionation in 29Si and 30Si across L1157-B1. A high-velocity bullet in 28SiO has been identified, showing the signature of a jet impacting on the dense gas. With the dataset presented in this paper, both interferometric and single-dish, we were able to study the gas that is shocked at the B1a position and its surrounding gas in great detail.

Seeds of Life in Space (SOLIS)

Context.The interstellar complex organic molecules (iCOMs) are C-bearing molecules containing at least six atoms; two main proposals for their formation are suggested: a direct formation in the icy mantle of the dust grains and formation through the reaction in gas phase of released grain mantle species. The shocked gas along outflows driven by low-mass protostars is a unique environment to study how the iCOMs can be formed as the composition of the dust mantles is sputtered into the gas phase.Aims.The chemical richness in shocked material associated with low-mass protostellar outflows has been so far studied in the prototypical L1157 blue-shifted outflow to investigate the iCOM formation routes. To understand whether the case of L1157-B1 is unique, we imaged and studied the IRAS 4A outflows in the NGC 1333 star forming region.Methods.We used the NOrthern Extended Millimeter Array interferometer as part of the IRAM Seeds Of Life in Space (SOLIS) Large Program to image the large-scale bipolar outflows driven by the IRAS 4A system in the 3 mm band, and we compared the observation with the GRAINOBLE+ astrochemical model.Results.We report the first detection, in the IRAS 4A outflows, of several iCOMs: six lines of methanol (CH3OH), eight of acetaldehyde (CH3CHO), one of formamide (NH2CHO), and four of dimethyl ether (CH3OCH3), all sampling upper excitation energy up to ~30 K. We found a significant chemical differentiation between the southeast outflow driven by the IRAS 4A1 protostar, showing a richer molecular content, and the north–southwest one driven by the IRAS 4A2 hot corino. The CH3OH/CH3CHO abundance ratio is lower by a factor of ~4 in the former; furthermore, the ratio in the IRAS 4A outflows is lower by a factor of ~10 with respect to the values found in different hot corinos.Conclusions.After L1157-B1, the IRAS 4A outflow is now the second outflow to show an evident chemical complexity. Given that CH3OH is a grain surface species, the astrochemical gas-phase model run with GRAINOBLE+ reproduced our observation assuming that acetaldehyde is formed mainly through the gas-phase reaction of the ethyl radical (CH3CH2) and atomic oxygen. Furthermore, the chemical differentiation between the two outflows suggests that the IRAS 4A1 outflow is likely younger than that of the IRAS 4A2. Further investigation is needed to constrain the age of the outflow. In addition, observation of even younger shocks are necessary. In order to provide strong constraints on the CH3CHO formation mechanisms it would be interesting to observe CH3CH2, but given that its frequencies are not known, future spectroscopic studies on this species are needed.

Seeds of Life in Space (SOLIS). IX. Chemical Segregation of SO2 and SO toward the Low-mass Protostellar Shocked Region of L1157

Abstract We present observations of SO and SO2 lines toward the shocked regions along the L1157 chemically rich outflow, taken in the context of the Seeds of Life in Space IRAM Northern Extended Millimeter Array Large Program, and supported by data from the Submillimeter Array and IRAM-30 m telescope at 1.1–3.6 mm wavelengths. We simultaneously analyze, for the first time, all of the brightest shocks in the blueshifted lobe, namely, B0, B1, and B2. We found the following. (1) SO and SO2 may trace different gas, given that the large(-scale) velocity gradient analysis indicates for SO2 a volume density ( ) denser than that of the gas emitting in SO by a factor up to an order of magnitude. (2) Investigating the 0.1 pc scale field of view, we note a tentative gradient along the path of the precessing jet. More specifically, decreases from the B0–B1 shocks to the older B2. (3) At a linear resolution of 500–1400 au, a tentative spatial displacement between the two emitting molecules is detected, with the SO peak closer (with respect to SO2) to the position where the recent jet is impinging on the B1 cavity wall. Our astrochemical modeling shows that the SO and SO2 abundances evolve on timescales less than about 1000 years. Furthermore, the modeling requires high abundances (2 × 10−6) of both and S/H injected in the gas phase due to the shock occurrence, so prefrozen OCS only is not enough to reproduce our new observations.

Seeds of Life in Space (SOLIS)

Context. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC 1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO2 towards NGC 1333-IRAS4A in the 1.3, 2, and 3 mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by IRAS4A2 that is extended along the north east–south west direction. SO is detected at extremely high radial velocity up to + 25 km s−1 relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105 cm−3 and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is more enriched in species that have a gas phase origin, such as SO2.

Seeds of Life in Space (SOLIS)

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 (~7′′ corresponding to ~1000 au) toward the northeast of the L1521F protostar. The CS 2–1 transition is also detected within the WideX 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.

Seeds of Life in Space (SOLIS)

Context.It is nowadays clear that a rich organic chemistry takes place in protostellar regions. However, the processes responsible for it, that is, the dominant formation routes to interstellar complex organic molecules, are still a source of debate. Two paradigms have been evoked: the formation of these molecules on interstellar dust mantles and their formation in the gas phase from simpler species previously synthesised on the dust mantles.Aims.In the past, observations of protostellar shocks have been used to set constraints on the formation route of formamide (NH2CHO), exploiting its observed spatial distribution and comparison with astrochemical model predictions. In this work, we follow the same strategy to study the case of acetaldehyde (CH3CHO).Methods.To this end, we used the data obtained with the IRAM-NOEMA interferometer in the framework of the Large Program SOLIS to image the B0 and B1 shocks along the L1157 blueshifted outflow in methanol (CH3OH) and acetaldehyde line emission.Results.We imaged six CH3OH and eight CH3CHO lines which cover upper-level energies up to ~30 K. Both species trace the B0 molecular cavity as well as the northern B1 portion, that is, the regions where the youngest shocks (~1000 yr) occurred. The CH3OH and CH3CHO emission peaks towards the B1b clump, where we measured the following column densities and relative abundances: 1.3 × 1016cm−2and 6.5 × 10−6(methanol), and 7 × 1013cm−2and 3.5 × 10−8(acetaldehyde). We carried out a non-LTE (non-Local Thermodinamic Equilibrium) Large Velocity Gradient (LVG) analysis of the observed CH3OH line: the average kinetic temperature and density of the emitting gas areTkin~ 90 K andnH2~ 4 × 105cm−3, respectively. The CH3OH and CH3CHO abundance ratio towards B1b is 190, varying by less than a factor three throughout the whole B0–B1 structure.Conclusions.Comparison of astrochemical model predictions with the observed methanol and acetaldehyde spatial distribution does not allow us to distinguish whether acetaldehyde is formed on the grain mantles or in the gas phase, as its gas-phase formation, which is dominated by the reaction of ethyl radical (CH3CH2) with atomic oxygen, is very fast. Observations of acetaldehyde in younger shocks, for example those of ~102yr old, and/or of the ethyl radical, whose frequencies are not presently available, are necessary to settle the issue.

SOLIS IV. Hydrocarbons in the OMC-2 FIR4 Region, a Probe of Energetic Particle Irradiation of the Region∗

Abstract We report new interferometric images of cyclopropenylidene, c-C3H2, toward the young protocluster OMC-2 FIR 4. The observations were performed at 82 and 85 GHz with the NOrthern Extended Millimeter Array (NOEMA) as part of the project Seeds Of Life In Space (SOLIS). In addition, IRAM-30 m data observations were used to investigate the physical structure of OMC-2 FIR 4. We find that the c-C3H2 gas emits from the same region where previous SOLIS observations showed bright HC5N emission. From a non-LTE analysis of the IRAM-30 m data, the c-C3H2 gas has an average temperature of ∼40 K, a H2 density of ∼3 × 105 cm−3, and a c-C3H2 abundance relative to H2 of (7 ± 1) × 10−12. In addition, the NOEMA observations provide no sign of significant c-C3H2 excitation temperature gradients across the region (about 3–4 beams), with T ex in the range 8 ± 3 up to 16 ± 7 K. We thus infer that our observations are inconsistent with a physical interaction of the OMC-2 FIR 4 envelope with the outflow arising from OMC-2 FIR 3, as claimed by previous studies. The comparison of the measured c-C3H2 abundance with the predictions from an astrochemical PDR model indicates that OMC-2 FIR 4 is irradiated by an FUV field ∼1000 times larger than the interstellar one, and by a flux of ionizing particles ∼4000 times larger than the canonical value of 1 × 10−17 s−1 from the Galaxy cosmic rays, which is consistent with our previous HC5N observations. This provides an important and independent confirmation of other studies that one, or more, source inside the OMC-2 FIR 4 region emits energetic (≥10 MeV) particles.

Seeds of Life in Space (SOLIS). III. Zooming Into the Methanol Peak of the Prestellar Core L1544*

Abstract Toward the prestellar core L1544, the methanol (CH3OH) emission forms an asymmetric ring around the core center, where CH3OH is mostly in solid form, with a clear peak at 4000 au to the northeast of the dust continuum peak. As part of the NOEMA Large Project SOLIS (Seeds of Life in Space), the CH3OH peak has been spatially resolved to study its kinematics and physical structure and to investigate the cause behind the local enhancement. We find that methanol emission is distributed in a ridge parallel to the main axis of the dense core. The centroid velocity increases by about 0.2 km s−1 and the velocity dispersion increases from subsonic to transonic toward the central zone of the core, where the velocity field also shows complex structure. This could be an indication of gentle accretion of material onto the core or the interaction of two filaments, producing a slow shock. We measure the rotational temperature and show that methanol is in local thermodynamic equilibrium (LTE) only close to the dust peak, where it is significantly depleted. The CH3OH column density, N tot(CH3OH), profile has been derived with non-LTE radiative transfer modeling and compared with chemical models of a static core. The measured N tot(CH3OH) profile is consistent with model predictions, but the total column densities are one order of magnitude lower than those predicted by models, suggesting that the efficiency of reactive desorption or atomic hydrogen tunneling adopted in the model may be overestimated; or that an evolutionary model is needed to better reproduce methanol abundance.

Seeds Of Life In Space (SOLIS): The Organic Composition Diversity at 300–1000 au Scale in Solar-type Star-forming Regions*

Abstract Complex organic molecules have been observed for decades in the interstellar medium. Some of them might be considered as small bricks of the macromolecules at the base of terrestrial life. It is hence particularly important to understand organic chemistry in Solar-like star-forming regions. In this article, we present a new observational project: Seeds Of Life In Space (SOLIS). This is a Large Project using the IRAM-NOEMA interferometer, and its scope is to image the emission of several crucial organic molecules in a sample of Solar-like star-forming regions in different evolutionary stages and environments. Here we report the first SOLIS results, obtained from analyzing the spectra of different regions of the Class 0 source NGC 1333-IRAS4A, the protocluster OMC-2 FIR4, and the shock site L1157-B1. The different regions were identified based on the images of formamide (NH2CHO) and cyanodiacetylene (HC5N) lines. We discuss the observed large diversity in the molecular and organic content, both on large (3000–10,000 au) and relatively small (300–1000 au) scales. Finally, we derive upper limits to the methoxy fractional abundance in the three observed regions of the same order of magnitude of that measured in a few cold prestellar objects, namely –10−11 with respect to H2 molecules.

Seeds of Life in Space (SOLIS)

The interstellar delivery of carbon atoms locked into molecules might be one of the key ingredients for the emergence of life. Cyanopolyynes are carbon chains delimited at their two extremities by an atom of hydrogen and a cyano group, so that they might be excellent reservoirs of carbon. The simplest member, HC3N, is ubiquitous in the galactic interstellar medium and found also in external galaxies. Thus, understanding the growth of cyanopolyynes in regions forming stars similar to our Sun, and what affects it, is particularly relevant. In the framework of the IRAM/NOEMA Large Program SOLIS (Seeds Of Life In Space), we have obtained a map of two cyanopolyynes, HC3N and HC5N, in the protocluster OMC2-FIR4. Because our Sun is thought to be born in a rich cluster, OMC2-FIR4 is one of the closest and best known representatives of the environment in which the Sun may have been born. We find a HC3N/HC5N abundance ratio across the source in the range ~ 1 - 30, with the smallest values (< 10) in FIR5 and in the Eastern region of FIR4. The ratios < 10 can be reproduced by chemical models only if: (1) the cosmic-ray ionisation rate $\zeta$ is ~ $4 \times 10^{-14}$ s$^{-1}$; (2) the gaseous elemental ratio C/O is close to unity; (3) O and C are largely depleted. The large $\zeta$ is comparable to that measured in FIR4 by previous works and was interpreted as due to a flux of energetic (> 10 MeV) particles from embedded sources. We suggest that these sources could lie East of FIR4 and FIR5. A temperature gradient across FIR4, with T decreasing by about 10 K, could also explain the observed change in the HC3N/HC5N line ratio, without the need of a cosmic ray ionisation rate gradient. However, even in this case, a high constant cosmic-ray ionisation rate (of the order of $10^{-14}$ s$^{-1}$) is necessary to reproduce the observations.

Seeds of Life in Space (SOLIS)

Context: Modern versions of the Miller-Urey experiment claim that formamide (NH$_2$CHO) could be the starting point for the formation of metabolic and genetic macromolecules. Intriguingly, formamide is indeed observed in regions forming Solar-type stars as well as in external galaxies. Aims: How NH$_2$CHO 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 NOEMA interferometer to image NH$_2$CHO 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 $\sim$ 9", $\sim$ 2300 AU) of formamide emission in a shocked region around a Sun-like protostar: the line profiles are blueshifted and have a FWHM $\simeq$ 5 km s$^{-1}$. A column density of $N_{\rm NH_2CHO}$ = 8 $\times$ 10$^{12}$ cm$^{-1}$, and an abundance (with respect to H-nuclei) of 4 $\times$ 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 gas-phase chemical process, and not on grain surfaces as previously suggested. Conclusions: The 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.